Copyright is owned by the Author of the thesis.  Permission is given for 
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the permission of the Author. 
 
GAS EXCHANGE CHARACTERISTICS 
AND QUALITY OF APPLES 
A thesis presented in parti al fulfi l me nt 
of the requi re m ents fo r the deg ree of 
Doctor of Philosophy 
in Plant Science 
at 
Massey Unive rsity 
N ew Zealand 
Benjamin Kwesi Dadzie 
1992 
Massey University Library 
Thesis Copyright Form 
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15 
i i  
ABSTRACT 
Atmospheric modification can exten d  the storage l ife of harvested fruits 
a n d  v e g et a b les beyo n d  that wh ich can be a ch ie ve d  w i t h  ref r i g e ra te d  a i r  
storage a lone. Apples are particularly wel l  suited t o  modif ied atmosphe re (MA) 
storage and yet the recommended atm ospheres for different cu ltivars of a pples 
vary w i d e l y  a n d  re s p o n s e s  of in d i v i d u a l  populat i o n s  of a pples t o  a g iven 
t re a t m e n t  c a n  be v a ri a b l e .  P a rt of th i s  v a r i a t i o n  m ay be re l ate d to the 
variabi l ity in the internal atmosphe re composition of individual fruit. Thi s  thesis 
explores the rel ationships between internal atmosphere composition of apples 
and factors s u ch as skin res i stance to gas d iffusion (R) ,  respi ration , external 
oxygen concentration ([02]ext) ,  temperature and artif icial barriers, all of which 
can influence the outcome of a g iven MA t reatment. 
Skin resistance to gas diff u s ion (R) values of fresh l y  harvested ap p les of 
eight cultivars g rown in New Zealan d ,  we re obta ined u s i n g  n on - stea d y  state 
and ste ady state methods at 20±1 cC. R was cultivar dependent, with f resh l y  
ha rvested B raeburn app les h aving t h e  h i g hest mean R a n d  Royal G a la the 
lowest. S k i n  res i st a nce to et h a n e  d iff u s io n  (RC2 H 6 ) was l inearl y  related to 
s k i n  re s i st a n ce t o  eth y l e n e  d iffu s i o n  (RC2 H 4 ) for i n d ividual a p p l e s  w i t h i n  
cu ltivars. Although the re was a large deg ree of variation i n  between pa i rs of R 
va lues obtai ned on d ifferent apples wit h i n  each cultivar, individual R values 
with i n  these p a i r s  we re very s i m i l a r  to each other. The c l ose r e l a t i o n ship 
between the two independent estimates of R confirmed that th is was rea l  fruit 
to fruit variation rather than m eas u rement e rror. I n  contrast, estim ates of skin 
re s i sta n ce to ca rbo n d ioxide d iff u s i o n  (RC02) were con s i stently h i gher than 
va l ues f o r  R C2 H 4 . There was a cu rv i l i n ea r  re lationsh i p  between RC02 and 
RC2 H 6 in a c o m bined data set for a l l  cu ltivars, i ndicat i n g  that CO2 m ay d iffuse 
th rough additional routes to those available for 02 , C2 H4 a n d  ethane (C2 H 6) .  
i i i  
Fre s h l y  h a rvested C ox's O ra n ge P i p p in a p p l e s  were respi ring nearly 
twice as f a s t  as S plendou r ,  G ranny Smith or B rae bu r n  a p p les and a t h i rd 
h ig h e r  t h an Ga la, Royal Gala and G olden Del icious a p ples. Resp iration rate 
appea red to be independent of RC2 H6 both within i n dividua l  cultivars and in a 
combined d a ta set for a l l  cultiva rs. On the other hand, there was a deClining 
exponenti a l  relationship between [02]i and RC2 H6 for individua l apples and a n  
increasin g  re lationship between [C02] i and RC2 H 6 . Thus , t h e  magn itude of R 
affects internal atmosphere composition for a g iven exte rnal atmosphere. 
The respiratory and C2 H4 p roduction responses of C ox's O range P ippin 
and G ranny Smith apples to reduced 02 concentrations were characterised by 
studying the variation i n  the magnitude of 02 , C02 and C2 H 4 concentration 
differences between the internal and external atmospheres (�[02] ' �[C02 ] and 
� [ C 2 H 4 ] )  of individu a l  a p p les maintai ned i n  d iffe rent 02 a tmosph e re s  at 
20± 1  cC. �[02] decreased at low 02 levels, reflect ing the decreased rate of 02 
uptake in low 02 concentrations. Oxygen uptake relative to that in air ( ReI02) 
approximatel y  fol lowed Michaelis-Menten kinetics ,  with a h a l f-maximal rate of 
2 . 5 %  02 f o r  [02 ]i a n d  7 . 5 %  f o r  [02 ] ext . A mat h em a tic a l  equation w a s  
deve l o ped t o  describe the t w o  physi o l o g ic a l  p roce s ses (ie. a n aero b ic and 
aerobic res p i ration ) i nvolved in the re lation s h i p  between re lative rate of C 02 
p roduct ion ( Re/C 02 ) o r  internal C O2 conce n t rat ion ( [C 02 ] i ) and [02]ext or 
[02] i . The equati o n  had two components, e ach d e sc rib ing one of the t wo 
physiologica l processes. 
The relationship between relative rate of C2 H4 production ( ReIC2 H 4 ) or 
inter n a l  C2 H4 concentration ([C2 H4] i) and [02] i was m ore c losely described by 
an e x p o ne n t i a l  r a t h e r  t h a n  a M i c h ae l is- M e n ten t y pe h y pe rb o l ic cu r ve. 
Neve r t h e l e s s, t h e o ve r a l l  s h ape o f  t h e  re l at i o n s h i p  c on f o rm e d  t o  t h e 
expectation that sma l l  changes in 02 concentration wou ld h ave much g reater 
effect at low [02] i than they do at high [02] i . In contrast, the p resence of the 
- , 
iv 
skin as a d i ffus i o n  b a r r i e r  (R) resulted in d eve l o pm e nt of an a p p a re nt 'Iag 
phase' i n  the relati onshi p  between ReC2H4 o r  [C2 H4] i and [02]ext such that it 
was no l onger described by an expone nti al type curve a n d-became ess e ntial l y  
sigmoidal. These d i ff e rences are att ri butable to g radie nts i n  g as co m positio n  
betwee n  i nternal a n d  external atmospheres. 
Washing of G ra n n y Smith a p p l e s  i n  Twe e n  2 0 s o l ut i o n s  i nh i bited 
d ev e l o pment o f  g re asiness. This effect was associated with i n c re as e d  R, 
d e p ressed [02] i ' l ow e r  respi ration a n d  i nc reased [ C 02] i a nd [C2 H 4] i in the 
w a shed fruit c o m pa re d  to contro l s. The d e p ress i o n  o f  [ 02] i i n  T w e e n  2 0 
t re ated fruit was g re ater t h an the elevation of C02' suggesting that the Twee n 
20 t re atment may have affected C02 p ro duct i o n  and 02 uptake to d i ffe rent 
e x t e n ts or a l t e rn at i v e l y  t h e  Tw e e n  2 0 d e p o s it on the f ru i t  s u rf a c e  w as 
d i ffe rent i a l l y  pe rme a b l e  to these t w o  g as e s .  Washed fruit a l s o  remai ned 
g re e n e r  and f i rm e r t h an c o n t ro l s .  P re-t r e a t m ent b y  w i ping without u s i n g  
Twee n  2 0 s o lut i o n  h ad none o f  t h ese effects but d i d  s timu l at e  w e i ght loss . 
,� N o ne of t h e  t re atments induced i nt e r n a l  b rowni ng which is often asso c i ated 
with the development of g reasiness in G ranny Smith apples. 
Th e re l at i o n sh i p  between t e m pe r a tu re and R, i nt e rn a l  atmo s phere 
compost i o n ,  res pi rat i on and rate of C 2 H 4 p roduct i o n  of e i ght cu l t i v a rs of 
apples was ascertained after eq u i l i b rating fruit at temperatures rang ing from 0 -
3 0°C for 72h. R appe ared to be independe nt of tempe ratu re. [02] i d e c re ased, 
whi le [C02] i increase d ,  in response to increasing te m peratures and v a ried with 
cultivar. Braebu rn apples consistently had l ower [02] i and higher [C02] i than 
t h e  other cult iva rs wh i l e  t h e  conve rse applied for Sple n d ou r  appl es. I nt e rnal 
C2 H 4 concent rati ons ([C 2 H 4] i ) and rate of C2 H4 p roduction increased with 
i n c r e a s i n g  t e m p e ratu res to a m a x i m u m at 2 5 ° C , a b ove w h i ch i nt e r n a l  
concent rations a nd rates of p ro duct i on d e c l ined. T h e  m a gnitude o f  d ecl ine 
was cult ivar de pendent . Compared to t h e  other cultiv a rs ,  Splendour apples 
had the l e ast c a p a c i t y  t o  acc u m u l at e  and p r o d u ce C 2 H 4. The re w as a 
v 
p ro g re s s ive increase i n  fru it resp i rat i o n  rate with i n c re a s i n g  tempe r a t u re s ,  
which v a r i e d  with cultivar. Over a l l  t h e  temperature reg imes ,  Sple n d ou r  had 
the lowest average respi ration rate while Cox's O ra n ge P ippin apples h a d  the 
h i ghest. The pote n t i a l  for varia b i l ity i n  these gas exc h a n ge variables bei n g  
associated with overall storage l ife a n d  response t o  MAs i s  d iscussed. 
S m a l l  g a s  c on c e n t ra t i o n  d i ffe re nces were me a su red between the 
equato r and calyx end, and between the equator and calyx end shoulde r with i n  
individua l  fruit i n  Golden De l icious , Red Del iciousJ Gra n n y  Smith a n d  S p le ndou r 
apples at 20±1 ° C .  I n  contrast, large 02 a n d  C02 co ncent ration differences 
betwee n the same positio n s  were found in G a l a ,  R oya l Gala, B raebur n  and 
Cox's O ran ge P ippin apples. The d ifferences were much g reater than those 
measu red between the core cavity and the fruit su rface. S im ilarly, t i s sues i n  
the calyx reg i o n  o f  B raeburn and G ranny Smith apples consistently h a d  l ower 
02 but h i gher C 02 and C2 H 4 concent rations than any othe r position o n  the 
fruit surface, wh i lst tissues at the equator had higher 02 a n d  lower C 02 and 
C2 H4 concentrations than oth e r  pa rts of the fruit. These data falsify the n otion 
that the i n te r n a l  atmosphere of i n dividua l app les can be regarded a s  be i n g  
homogeneous. The heterogeneous distribution of g ases with i n  ind ividua l  fruit 
would p resumably affect the tendency of individual t issues t o  develop low-02 
o r  h i gh C 0 2 d i s o rde r s ,  pa rt icu l a r l y  f o r  f ru i t  s t o re d  i n  MAs at e le vated 
temperatures. 
A conceptu a l  mode l is presented w h ich summ a ries the re lat i o n sh ips 
betwe e n  f ru i t  [ 02 ] i and [02] ext , R ,  re s p i rat i o n ,  tem pe ratu re a n d  a rt if i c i a l  
barriers. The [02] i of apples a re a lways lowe r  than the [02 ]ext use d  during 
MA storage, to an extent which is determined by the respi ratory 02 upt a ke by 
t he t i ssues coupled with R .  With eve ryth i n g  e lse be i n g  m a i n t a i ne d  e q u a l ,  
i n c reased R o r  increased res p i ration rate therefore depresses [02] i wh ich i n  
turn mod i f ies the extent o f  res p o n s e  o f  t h e  c r o p  t o  a g i ven M A  t re atme n t .  
These variab les a re therefore all important in determ i n i n g  the fruit's res p o nse 
t o  atmospheric modificat ion. 
vi 
ACKNOWLEDGEMENTS 
I am particular1y indebted to my chief supervisor Dr. N.  H. Banks and 
co-supervisors Prof. E .  W. Hewett and Dr. D. J. 'Cleland for their guidance and 
e ncouragement. 
Special thanks to the New Zealand Government for awarding me  the 
scholarship to study at Massey University, which was made  possible through 
the personal efforts of Prof. D.  J. Chalmers, former Head of Department of 
Horticultural Science and the Mi nistry of Fi nance and Economic Pla n ni ng ,  
Ghana. I am extremely grateful to Prof. D .  J. Chalmers for his u nsti nting  
support, encouragement and keen interest in  my academic and personal well 
being. He would always be remembered for the rest of my l ife. 
I wish to acknowledge the friendship, assistance and encouragement 
g iven by Mr. J .  Dixon ,  C. Tod and B. Christie during this Ph.D.  programme .  
My  g ratitude i s  also extended to al l  the postgraduate students and 
members of staff of the Department of Plant Science, Massey University. My 
sincere thanks to Dr. E .  Pesis (Volcanic Research I nstitute,  Israel) ,  Prof. A.  C.  
Cameron (Michigan State University, USA), Or .  N .  C .  Rajapakse (Clemson 
University, South Carolina), Miss. B. Cregoe (DSIR, Auckland), Mr. C.  Pugmire 
(DSIR,  Lower Hutt) , Prof. K. Mi lne ,  D r. D .  Chadee, Dr. H .  Behboudian, Ms. 
Pam Howel l ,  Mrs. C. Hanlon, Mrs. J .  Thompson,  Mrs. L. J. Mather, M rs. P. J .  
Barker, Ms .  S .  Bautista and Mr .  H .  Caspari (Massey U n iversity) for their 
assistance and encouragement. 
My deep appreciation goes to the entire members of my family, Dr. and 
Mrs. Hemeng and Dr. D. C. Asante-Kwatia of the University of Science and 
Technology, Ghana. This achievement, l ike many others is a resu lt of the 
confidence imposed in me, their unstinting support and encouragement. 
vii 
I am very grateful to all my numerous friends· both in New Zealand and 
abroad for their encouragement. A special thank you to Mr. and M rs. Kitchin, 
Mr. T. Adson ,  Mrs. M. Dunne and B. Wil l iams of the Computer Centre, Massey 
University, for their support and friendship during my stay i n  New Zealand. 
Fi nal ly ,  I g ive special thanks to my Lord Jesus Christ who i n  many 
diverse ways has helped me to this day. 
vii i 
CONTENTS 
CHAPTER PAGE 
ABSTRACT i i  
ACKNOWLEDGEMENTS vi 
TABLE OF CONTENTS vii i 
LIST OF FIGURES xvi 
LIST OF TABLES xxvi 
LIST OF ABBREVIATIONS xxvii 
CHAPTER 1 .  GENERAL INTRODUCTION 1 
CHAPTER 2. LITERATURE REVIEW 4 
2. 1  I nternal atmosphere of fruits 4 
2 . 1 . 1 Factors affecting internal atmosphere composit ion 4 
2. 1 . 1 . 1  Temperature 5 
2. 1 . 1 .2 Composition of the external atmosphere 6 
2. 1 . 1 .3 Skin resistance to gas diffusion 7 
2. 1 . 1 .4 Artificial barrier  7 
2. 1 . 1 .5 Stage of maturity 1 0  
2. 1 .2 Methods of sampling internal atmosphere 1 1  
2. 1 .2. 1  Di rect sampl ing method 1 1  
2. 1 .2.2 Artificial internal cavity extraction method 1 3  
2. 1 .2.3 External cavity extraction method 1 4 
2. 1 .2.4 Vacuum extraction method 1 6  
2. 1 .2.5 Heat extraction method 1 8  
2 . 1 .2.6 Digestion method 1 9  
2.2 Respiration metabolism 1 9  
2.2. 1  Aerobic respi ration 21 
2.2.2 Anaerobic respiration 23 
ix 
2.2.3 Extinction Point (EP) or  Anaerobic Compensation 
Poi nt (ACP) 24 
2.2.4 Respiration quotient (RQ) 26 
2.2.5 Respi ration patterns of fruits 28 
2.2.6 Methods of estimating respiration rate 32 
2.2.6.1 Flow through system 33 
2.2 .6.2 Closed system 34 
2.2.6.3 Tissue disc respi ration 34 
2.3 Gas exchange in fruits 35 
2.3.1 Laws of gas diffusion 37 
2.3.2 Skin resistance to gas diffusion  38 
2.3.3 Avenues to gas exchange 40 
2.3.4 Methods of estimating skin resistance to gas 
diffusion 42 
2.3.4.1 Non Steady-state approach 42 
2 .3.4.2 Steady-state approach 44 
CHAPTER 3. GENERAL MATERIALS AND METHODS 47 
3.1 Fruit supply 47 
3.2 Measurement of surface area 47 
3.3 Measurement of gases 48 
3.3.1 Analysis of Carbon dioxide and Oxygen 48 
3.3.2 Analysis of Ethylene and Ethane ", . .  ,: 48 
( . 
3.3.3 Analysis of Acetaldehyde and Ethanol 48 
3.3.4 Measurement of internal atmosphere concentrat ions 49 
3.3.4.1 Di rect sampling method 49 
3.3.4.2 External chamber method 50 
3.3.5 Measurement of skin resistance 50 
3.3.5.1 Ethane efflux method 50 
3.3.5.2 Steady state method 51 
x 
3 .3.6 Gas mixing and measurement 52 
3 .3.7 Calculation of gas concentrations from 
chromatOgrJR ic data 52 
3.3.7. 1 Oxygen, carbon dioxide and ethylene concentrations 52 
3.3.7.2 Oxygen concentration usi ng oxygen electrode 53 
3 .3.7.3 Calculation of the rate of 02 uptake and CO2 
and C2H4 production 53 
3 .3.8 Measurement of qual ity parameters 54 
3.3.8. 1 Firmness 54 
3.3.8.2 Soluble solids 55 
3 .3.8.3 Fruit skin colour 55 
3 .3 .9 Data analysis 55 
CHAPTER 4. ESTIMATING SKIN RESISTANCE TO GAS D IFFUSION IN  
APPLES. 56 
4. 1  ABSTRACT 56 
4.2 INTRODUCTION 57 
4 .3 MATERIALS AND METHODS 59 
4.3 . 1  Fruit supply 59 
4.3.2 Estimation of skin resistance using ethane 
efflux method 59 
4.3.3 Estimation of skin resistance using steady-state 
method 60 
4.3.4 Fruit quality assessment 60 
4.3.5 Experimental design and analysis 60 
4.4 RESULTS 6 1  
4.4. 1  Skin resistance to gas diffusion 6 1  
4 .4.2 Fruit respiration rate 68 
4.4.3  I nternal 02 and C02 concentrations 68 
4.4.4 I nternal C2H4 and C2H4 evolution 74 
4.4.5 Quality i ndices 
4.5 D ISCUSSION 
4.6 LITERATURE C ITED 
CHAPTER 5. RELATIONSHIP BETWEEN APPLE RESPIRATION AND 
OXYGEN CONCENTRATION IN THE INTERNAL AND 
5.1 
5.2 
5 .3 
5.4 
5.4.1 
5.4.2 
5 .4 .3 
5.5 
5.5.1 
5 .5.2 
5.5.3 
5.5.4 
5.5.5 
5.5.6 
5.6 
5.7 
EXTERNAL ATMOSPHERES. 
ABSTRACT 
INTRODUCTION 
Theoretical background 
MATERIALS AND METHODS 
Fruit supply 
Gas measurement and analysis 
Experimental design and analysis 
RESULTS 
[02]i as a function of [02]ext 
RelO2 as a function of [02]ext or [02]i 
ReIC02 as a function of [02]ext or  [02]i 
Re/RQ versus [021ext or [021i 
[AAlse or [ETOHlse versus [02]ext or [02
] i 
ReIC2H4 or [C2H41i as a function of [021ext 
or [021i 
D ISCUSSION 
LITERATURE C ITED 
xi 
79 
79 
89 
94 
94 
95 
97 
1 00 
1 00 
1 01 
1 03 
1 03 
1 03 
1 04 
1 08 
1 1 2  
1 1 2  
1 1 9  
1 24 
1 35 
CHAPTER 6. GAS DIFFUSION AND QUALITY OF APPLES INFLUENCED 
6 . 1  
6.2 
BY SURFACTANT. 
ABSTRACT 
INTRODUCTION 
1 42 
1 42 
1 43 
xii 
6.3 MATERIALS AND METHODS 146 
6.3.1 Fruit supply 146 
6.3.2 Treatment 1 46 
6.3.2.1 Experiment 1 146 
6.3.2.2 Experiment 2 147 
6.3.3 Assessment of g reasiness 1 47 
6.3.4 Estimation of gas exchange variables 147 
6.3.5 Fruit quality assessment 1 48 
6.3.6 Experimental design and analysis 1 48 
6.3.6.1 Experiment 1 1 48 
6.3.6.2 Experiment 2 1 48 
6.4 RESULTS 1 49 
6.4.1 Greasiness and internal browning 1 49 
6.4.1 .1 Experiment 1 1 49 
6.4.1 .2 Experiment 2 1 49 
6.4.2 Skin resistance to gas diffusion 1 53 
6.4.3 Respiration rate and ethylene production 1 53 
6.4.4 I nternal gas concentrations 1 57 
6.4.4.1 Experiment 1 1 57 
6.4.4.2 Experiment 2 1 57 
6.4.5 Percentage weight loss 1 62 
6.4.5.1 Experiment 1 1 62 
6.4.5.2 Experiment 2 1 65 
6.4.6 Qual ity indices 1 65 
6.4.6.1 Experiment 1 1 65 
6.4.6.2 Experiment 2 1 65 
6.5 D ISCUSSION 1 74 
6.6 LITERATURE CITED 1 79 
xii i 
CHAPTER 7. TEMPERATURE EFFECTS ON INTERNAL ATMOSPHERE 
COMPOSITION, RESPIRATION, ETHYLENE  PRODUCTION 
AND SKIN RESISTANCE TO GAS DIFFUSION OF 
APPLES. 
7.1 ABSTRACT 
7.2 INTRODUCTION 
7.3 MATERIALS AND METHODS 
7.3.1 Materials 
7.3.2 Methods 
7.3.2.1 Estimation of gas exchange variables 
7.3.2.2 Fruit quality assessment 
7.3.2.3 Experimental design and analysis 
7.4 RESULTS 
7.4.1 Internal 02 concentration 
7.4.2 I nternal C02 concentration 
7.4.3 Fruit respiration rate 
7.4.4 Internal C2H4 concentration 
7.4.5 C2H4 production 
7.4.6 Skin resistance to gas diffusion 
7.4.7 Quality indices 
7.5 D ISCUSSION 
7.6 LITERATURE C ITED 
CHAPTER 8. VARIATION IN INTERNAL ATMOSPHERE 
COMPOSITION WITHIN SINGLE APPLES. 
8.1 
8.2 
8.3 
8.3.1 
ABSTRACT 
INTRODUCTION 
MATERIALS AND METHODS 
Fruit supply 
1 84 
184 
1 85 
1 87 
1 87 
1 88 
1 88 
1 88 
1 88 
1 89 
1 89 
1 94 
1 94 
201 
205 
205 
21 3 
21 8 
224 
230 
230 
231 
234 
234 
xiv 
8.3.2 Methods 234 
8.3.2.1 Experiment 1 234 
8.3.2.1.1 Estimation of 02 and C02 concentration g radients 234 
8.3.2.2 Experiment 2 237 
8.3.2.2.1 Determination of d istribution of i nternal 
atmosphere composition 237 
8.3.2.2.2 Fruit qual ity assessment 237 
8.3.2.3 Experimental design and analysis 240 
8.3.2.3.1 Experiment 1 240 
8.3.2.3.2 Experiment 2 240 
8.4 RESULTS 240 
8.4.1 Experiment 1 240 
8.4.1.1 02 and C02 concentration differences between 
the equator and calyx end 240 
8.4.1.2 02 and C02 concentration differences between 
the  equator and calyx shoulder 242 
8.4.1.3 02 and CO2 concentration differences between 
the  equator and core cavity 244 
8.4.2 Experiment 2 244 
8.4.2.1 Distribution of gas concentrations at the stem 
end, equator and calyx end 244 
8.4.2.1.1 02 concentrations 244 
8.4.2.1.2 C02 concentrations 250 
8.4.2.1.3 C2H4 concentrations 250 
8.4.2.2 Qual ity indices 256 
8.4.2.3 Distribution of gas concentrations at five 
positions on the fruit surface 261 
8.4.2.3.1 02 concentrations 261 
8.4.2.3.2 CO2 concentrations 265 
8.4.2.3.3 C2H4 concentrations 265 
8.4.2.4 Quality indices 271 
8.5 
8.6 
D ISCUSSION 
L ITERATURE C ITED 
CHAPTER 9. GENERAL DISCUSSION 
9. 1 
9 . 1 . 1 
9 . 1 .2 
9 . 1 .2. 1  
9 . 1 .2.2 
9 . 1 .3 
9.2 
9.3 
9 .4 
9.5 
Relationship between [021ext and [021i . 
respiration and C2H4 concentration 
Relationship between [021ext and [021i 
Relationship between respi ration and 02 
concentration 
Rate of 02 uptake 
Rate of C02 production 
Relationship between [021ext and C2H4 
Effects of washi ng or coating on gas 
exchange 
A model describing the form of relationships 
between [021i . R and respiration 
Recommendations for further research 
CONCLUSION 
LITERATURE CITED 
APPENDIX 
Appendix 1 Change in glass vial 02 concentrations with t ime 
Appendix 2 Effects of handl ing by touching on  [021i and [C021i 
of g reasy G ranny Smith apples stored for 1 7  days 
at 20°C 
Appendix 3 < Photog raph show� browning around the core cavity 
. . .... .... -- ---------
of Granny Smith apple 
Appendix 4 Variation i n  internal atmosphere composit ion 
with in  single apples 
xv 
276 
280 
283 
288 
288 
290 
290 
295 
298 
301 
305 
307 
31 0 
31 1 
336 
337 
338 
339 
"< 
,. 
i' 
xvi 
LIST OF FIGURES 
FIGURES PAGE 
2- 1  Principal pathways responsible for the respiration of 
carbohydrate (ap Rees, 1 980) .  21 
2-2 Pathways of aerobic metabolism (Montgomery et al., 1990) 22 
2-3 Pathways of anaerobic metabolism (Wil ls et al., 1 98 1 )  23 
2-4 A schematic representation of the effects of 02 
concentration of the external atmosphere on aerobic 
and anaerobic respi rat ion. The arrow indicates the 
EP (Redrawn from Kader, 1 987) 24 
2-5 Phases of the climacteric period (Redrawn from 
Watada, 1 984) 29 
2-6 Stages in fruit development and maturation and 
respi ratory trends un ique to the climacteric and 
non-cl imacteric fruits. (Redrawn from Biale, 1 964) 31 
4-1  Comparison of RC2H S and RC2H4 of individual (a)=Cox's 
Orange Pippin and (b)=Braeburn apples estimated by the 
ethane efflux and steady state methods respectively 62 
4-2 Comparison of RC2H6 and RC2H4 of i ndividual (a)=Splendour  
and (b)=Granny Smith apples estimated by the ethane 
eff lux and steady state methods respectively 63 
4-3 Comparison of RC2H6 and RC2H4 of individual (a)=Royal Gala 
and (b)=Red Del icious apples estimated by the ethane 
efflux and steady state methods respectively 64 
4-4 Skin resistance to C02 and C2H4 diffusion of freshly 
harvested apples, est imated by the steady state 
method at 20°C 65 
4-5 Relationship between RC02 and RC2H S of individual apples 
4-6 
4-7 
4-8 
4-9 
4-1 0 
4-1 1 
4- 1 2 
4-1 3 
4-1 4 
4-1 5 
4-1 6 
4-1 7 
5-1 
5-2 
5-3 
5-4 
5-5 
with in cultivar estimated by the steady state method 
and ethane efflux methods respectively 
s 
Respi ration rates of freshly harvested appl� at 20°C 
Relationship between respi ration and RC2H6 of 
individual apples within cultivar 
I nternal 02 and C02 concentrations of freshly harvested 
apples at 20°C 
Relationship between [02]i and RC2H6 of i ndividual 
apples within cultivar 
Relationship betwe"en [C02] i and RC2H6 of individual 
apples within cultivar 
Relationship between [02]i and respiration rate of 
individual apples within cultivar 
Relationship between [C02] i and respi ration rate of 
individual apples within cultivar 
I nternal C2H4 concentrations of freshly harvested apples 
at 20°C 
Ethylene production of freshly harvested apples at 20°C 
Firmness of freshly harvested apples at 20°C 
Soluble sol ids content of freshly harvested apples at 20°C 
Hue angle values of freshly harvested apples at 20°C 
Arrangement of glass sampling chamber on the surface 
of an apple fruit 
Relationship between [02] i and [02]ext of apples kept 
at 20°C 
Relationship between Rel02 and [02]ext of apples kept 
at 20°C 
Relationship between Rel02 and [02]i of apples kept 
at 20°C 
Relationship between RelC02 and [02]ext of apples kept 
at 20°C 
xvii 
66 
69 
70 
71 
72 
73 
75 
76 
77 
78 
80 
8 1  
82 
1 02 
1 04 
1 06 
1 09 
1 1 0 
5-6 
5-7 
5-8 
5-9 
5-1 0 
5-1 1 
5- 1 2 
5-1 3  
5-1 4 
5-1 5 
5-1 6 
5- 1 7  
5- 1 8  
6-1 
6-2 
Relationship between [C02]i and [02]ext of apples kept 
at 20°C 
Relationship between RelC02 and [02]i of apples kept 
at 20°C 
Relationship between [C02]i and [02]i of apples kept 
at 20°C 
Relationship between RelRO and [02]ext of apples kept 
at 20°C 
Relationship between RelRO and [02]i of apples kept 
at 20°C 
Relationship between [AA]se and [02]ext of apples kept 
at 20°C 
Relationship between [AA]se and [02]i of apples kept 
at 20°C 
Relationship between [ETOH]se and [02]ext of apples kept 
at 20°C 
Relationship between [ETOH]se and [02]i of apples kept 
at 20°C 
Relationship between RelC2H4 and [02]ext of apples kept 
at 20°C 
Relationship between [C2H4]i and [02]ext of apples kept 
at 20°C 
Relationship between RelC2H4 and [02] i of apples kept 
at 20°C 
Relationship between [C2H4]i and [02] i of apples kept 
at 20°C 
Grease weight of Granny Smith apples after wiping or  
washing in Tween 20 solution and storage for 22 days 
at 20°C 
Grease score of Granny Smith apples after wiping or 
washing in Tween 20 solution and storage for 22 days 
xvii i  
1 1 1  
1 1 3 
1 1 4 
1 1 5 
1 1 6 
1 1 7 
1 1 8 
1 20 
1 2 1 
1 22 
1 23 
1 25 
1 26 
1 50 
xix 
at 20°C 1 5 1 
6-3 G rease weight of Granny S m ith apples after wash i ng i n  
different co n ce ntrations of Twee n  2 0  so luti o n ,  stored 
(fo r (a)::::O ,  (b):::: 8, (c):::: 1 6, (d)::::24 weeks) at ooe and 
subseq uent t ransfer to 20°C (for 0 ,  1 ,  8 and 1 5  days) 1 52 
6-4 RC02 and Re2H4 of G ra n n y  S mith apples after wipi ng o r  
was h i n g  i n  Tween 20 s o l u t i o n  and storage fo r 2 2  days 
at 20°C 1 54 
6-5 Respi ration rate of G ra n n y  S m it h  apples after wiping 
o r  was h i n g  i n  Tween 20 solution and storage for 22 days 
at 20°C 1 55 
6-6 e2 H4 produ ction of G ran n y  S m ith apples afte r wiping or 
was h i ng in Tween 20 solution and storage for 22 days 
at 20°C 1 56 
6-7 [02]i and [C02] i of G ra n n y  S mith apples after wiping or 
was h i n g  in Tween 20 sol utio n and storage for 22 days 
at 20°C 1 58 
6-8 [C2 H4] i of Gra n ny Smith appl es aft e r  wi p i n g  o r  wash i n g  i n  
Tween 2 0  s o l ution and storage fo r 22 days at 20°C 1 59 
� 
6-9 I nt e rnal 02 concentrations of Gran ny S m ith apples after 
was h i n g  in diffe rent co ncentrations of Tween 20 soluti o n ,  
sto red (fo r (a)::::O, (b):::: 8, (c):::: 1 6 , (d}::::24 weeks) a t  ooe and 
subsequent transfer to 20°C (fo r 0, 1 ,  8 and 1 5  days) 1 60 
6 - 1 0 I nt e rnal C02 concentrati o ns of Gra n ny S m ith apples after 
was h i n g  i n  different co ncentrati ons of Tween 20 soluti o n ,  
sto red (fo r (a)::::O, (b):::: 8, (c):::: 1 6 , (d)::::24 weeks) at ooe and 
subsequent t ransfer to 20°C (for 0, 1 ,  8 and 1 5  days) 1 6 1 
6 - 1 1 I nt e rnal e2 H4 conce ntrations of G ra n ny S m ith apples after 
was h i n g  in diffe rent co nce ntrations of Tween 2 0  so luti o n ,  
stored (fo r (a)::::O, ( b ):::: 8, (c):::: 1 6 , (d)::::24 weeks) a t  ooe 
and s ubsequent transfer to 20°C (fo r 0, 1 ,  8 and 1 5  days ) 1 6 3 
xx 
6-1 2 Percentage weight loss of Granny Smith apples after wiping 
or washing in Tween 20 solution and storage for 22 days 
at 200e 1 64 
6-1 3  Percentage weight loss of Granny Smith apples after 
washing in different concentrations of Tween 20 solution, 
stored (for (a)=O, (b)=8, (c)=1 6, (d)=24 weeks) at ooe 
and subsequent transfer to 200e (for 0 ,  1 ,  8 and 1 5  days) 1 66 
6- 1 4 <Pllo(Qgrap�_�h_o.��g)Granny Smith apples after wiping .\ 
or washing in Tween 20 solution and storage for 
22 days at 200e 1 67 
6-1 5  Hue angle of G ranny Smith apples after wiping or  washing 
in Tween 20 solution and storage for 22 days at 200e 1 68 
6-1 6 Firmness of Granny Smith apples after wiping or washing 
in Tween 20 solution and storage for 22 days at 20°C 1 69 
6-1 7 Percentage decrease in hue angle of G ranny Smith 
apples after  washing in different concentrations of 
Tween 20 solution, stored (for (a)=O, (b)=8, 
(c)= 1 6, (d)=24 weeks) at O°C and subsequent transfer 
to 200e (for 0, 1 ,  8 and 1 5  days) 1 71 
6-1 8 Firmness of G ranny Smith apples after washing in 
different concentrations of Tween 20 solution , stored 
(for (a)=O, (b)=8, (c)=1 6, (d)=24 weeks) at O°C and 
subsequent transfer to 20°C (for 0, 1 ,  8 and 15  days) 1 72 
6-1 9 Soluble sol ids contents of Granny Smith apples after 
washing i n  different concentrations of Tween 20 solution,  
stored (for (a)=O, (b)=8, (c)=1 6, (d)=24 weeks) at O°C 
and subsequent transfer to 20°C (for 0, 1, 8 and 1 5  days) 1 73 
7-1 Relationship between temperature and [02]i of 
(a)=Cox's Orange Pippin (b)=Braebu rn (c)=Splendour 
(d)=Granny Smith apples 1 90 
7-2 Relationship between temperature and [02]i of 
xxi 
(a)=Gala (b)=Royal Gala (c)=Golden Del icious (d )=Red 
Delicious apples 1 91 
7-3 Relationship between temperature and [C02] i of 
(a)=Cox's Orange Pippin (b)=Braeburn (c)=Splendour  
(d)=G ranny Smith apples 1 95 
7-4 Relationship between temperature and [C02] i of 
(a)=Gala (b)=Royal Gala (c)=Golden Delicious 
(d)=Red Del icious apples 1 96 
7-5 Relationship between temperature and respiration rate 
of (a)=Cox's Orange Pippin (b)=Braeburn (c) =Splendour 
(d)=Granny Smith apples 1 99 
7-6 Relationship between temperature and respiration rate 
of (a)=Gala (b)=Royal Gala (c)=Golden Delicious 
(d)=Red Delicious apples 200 
7-7 Temperature effects on [C2H4]i of (a)=Cox's Orange 
Pippin (b)=Braeburn (c)=Splendour (d)=Granny Smith 
apples 203 
7-8 Temperature effects on [C2H4]i of (a)=Gala (b}=Royal 
Gala (c}=Golden Delicious (d}=Red Del icious apples. 204 
7-9 Temperatu re effects on C2H4 production of (a)=Cox's 
Orange Pippin (b}=Braeburn (c}=Splendour (d}=G ranny 
Smith  apples 207 
7-1 0 Temperature effects on C2H4 production of (a} =Gala 
(b)=Royal Gala (c)=Golden Delicious (d}=Red 
Del icious apples 208 
7-1 1 Temperature effects on RC02 of (a}=Cox's Orange Pippi n 
(b)=Braeburn (c}=Splendour  (d}=Granny Smith apples 209 
7-1 2 Temperature effects on RC02 of (a}=Gala (b}=Royal Gala 
(c}=Golden Del icious (d}=Red Delicious apples 21 0  
7-1 3 Temperature effects on RC2H4 of (a}=Cox's Orange Pippi n 
(b}=Braeburn (c}=Splendour (d}=Granny Smith apples 2 1 1  
xxii 
7 -1 4 Temperature effects on RC2H4 of (a)=Gala (b)=Royal Gala 
(c)=Golden Delicious (d)=Red Delicious apples 21 2 
7-1 5  Relationship between temperature and firmness 
of (a)=Cox's Orange Pippin (b)=Braeburn (c)=Splendour 
(d)=Granny Smith apples 21 4 
7-1 6  Relationship between temperature and firmness 
of (a)=Gala (b)=Royal Gala (c)=Golden Delicious 
(d)=Red Delicious apples 21 5  
7-1 7  Temperature effects on soluble sol ids contents 
of (a)=Cox's Orange Pippin (b)=Braeburn (c)=Splendour 
(d)=Granny Smith apples 21 6  
7-1 8 Temperature effects on soluble sol ids contents 
of (a)=Gala (b)=Royal Gala (c)=Golden Delicious 
(d )=Red Del icious apples 21 7  
8- 1 Arrangement of glass sampling chambers on the surface 
of an apple fruit (equator and calyx end) 235 
8-2 Arrangement of glass sampl ing chambers on the surface 
of an apple fru it (equator and calyx end shoulder) 236 
8-3 Arrangement of glass sampling chambers on the surface 
of an apple fruit (stem end .  equator and calyx end)  238 
8-4 Arrangement of glass sampling chambers on the su rface 
of an apple fruit (five positions) 239 
8-5 Oxygen and carbon dioxide concentration gradients 
between the equator and calyx end of freshly 
harvested apples at 20°C 241 
8-6 Oxygen and carbon dioxide concentration gradients 
between the equator and calyx end shoulder of freshly 
harvested apples at 20°C 243 
8-7 Oxygen and carbon dioxide concentration gradients 
between the equator and core cavity of freshly 
harvested apples at 20°C 245 
xxii i 
8-8 Oxygen concentrations in the stem end, equator and 
calyx end of Braeburn apples stored (for (a)=O ,  
(b)=4, (c)=8, (d)=1 2 weeks) at ooe and subsequent 
transfer to 20°C (for 3, 1 0, and 1 7  days) 246 
8-9 Oxygen concentrations in the stem end, equator and 
calyx end of Granny Smith apples stored (for (a)=O ,  
(b)=4, (c)=8, (d)=1 2 weeks) at ooe and subsequent 
transfer to 20°C (for 3, 1 a, and 1 7  days) 247 
8-1 0 Core cavity 02 concentrations of Braeburn and 
Granny Smith apples stored at O°C for 0, 4, 8 and 1 2 
weeks and subsequent storage at 20°C for 1 7  days 249 
8-1 1 Carbon dioxide concentrations at the stem end, 
equator and calyx end of Braeburn apples stored (for 
(a)=O, (b)=4, (c)=8, (d)=1 2 weeks) at O°C and 
subsequent transfer to 20°C (for 3, 1 0 , and 1 7  days) 251  
8- 1 2 Carbon dioxide concentrations at the stem end, 
equator and calyx end of Granny Smith apples stored 
(for (a)=O, (b)=4, (c)=8, (d )=1 2 weeks) at O°C and 
subsequent transfer to 20°C (for 3, 1 0 , and 1 7  days) 252 
8-1 3  Core cavity C02 concentrations of Braeburn and 
Granny Smith apples stored at O°C for 0, 4 , 8  and 1 2 
weeks and subsequent storage at 20°C for 1 7  days 253 
8- 1 4 Ethylene concentrations at the stem end, equator and 
calyx end of Braeburn apples stored (for (a)=O , 
(b)=4, (c) =8,  (d)=1 2 weeks) at ooe and subsequent 
transfer to 20°C (for 3, 1 0, and 1 7  days) 254 
8-1 5 Ethylene concentrations at the stem end, equator and 
calyx end of Granny Smith apples stored (for (a)=O , 
(b)=4, (c)=8,  (d )=1 2 weeks) at ooe and subsequent 
transfer to 20°C (for 3 ,  1 0, and 1 7  days) 255 
8-1 6 Core cavity C2H4 concentrations of Braeburn and 
xxiv 
Granny Smith apples stored at ooe for 0 , 4, 8  and 1 2 
weeks and subsequent storage at 200e for 1 7  days 257 
8-1 7  Firmness of Braeburn and Granny Smith apples stored 
at ooe for 0, 4, 8 and 1 2 weeks and subsequent 
storage at 20°C for 1 7  days 258 
8-1 8 Soluble solids content of B raeburn and Granny Smith 
apples stored at O°C for 0, 4, 8 and 1 2 weeks and 
subsequent storage at 20°C for 1 7  days 259 
8-1 9 Hue angle of Braeburn and Granny Smith apples 
stored at ooe for 0, 4, 8 and 1 2 weeks and 
subsequent storage at 20°C for 1 7  days 260 
8-20 Distribution of 02 concentrations at five positions 
in the sub-epidermis of Braeburn apples stored (for 
(a)=O, (b)=4, (c)=8, (d)=1 2 weeks) at Doe and 
subsequent transfer to 20°C (for 3, 1 0, and 1 7  days) 262 
8-21 Distribution of 02 concentrations at five positions 
in the sub-epidermis of Granny Smith apples stored 
\or (a)=O,  (b)=4, (c)=8, (d )=1 2 weeks) at O°C and X 
subsequent transfer to 20°C (for 3, 1 0, and 1 7  days) 263 
8-22 Core cavity 02 concentrations of Braeburn and G ranny 
Smith apples stored at Doe for 0, 4, 8 and 1 2 weeks 
and subsequent storage at 20°C for 1 7  days 264 
8-23 Distribution of C02 concentrations at five positions 
in the sub-epidermis of Braeburn apples stored (for 
(a)=O, (b)=4, (c)=8, (d)=1 2 weeks) at Doe and 
subsequent t ransfer to 20°C (for 3, 1 0, and 1 7  days) 266 
8-24 Distribution of C02 concentrations at five positions 
in the sub-epidermis of Granny Smith apples stored 
(for a=O,  b=4, c=8, d=1 2 weeks) at O°C and 
subsequent transfer to 20°C (for 3, 1 0, and 1 7  days) 267 
8-25 eore cavity e02 concentrations of Braeburn and 
8-26 
8-27 
8-28 
8-29 
8-30 
8-31 
9-1 
9-2 
9-3 
Granny Smith apples stored at ooe for 0 ,  4, 8 and 1 2 
weeks and subsequent storage at 20°C for 1 7  days 
Distribution of e2H4 concentrations at five 
positions in the sub-epidermis of Braeburn apples stored 
(for (a)=O, (b)=4, (c)=8, (d)=1 2 weeks) at ooe and 
subsequent transfer to 20°C (for 3, 1 0, and 1 7  days) 
Distribution of e2H4 concentrations at five 
positions in the sub-epidermis of Granny Smith apples 
stored (for (a)=O, (b)=4, (c)=8, (d)=1 2 weeks) at ooe and 
subsequent transfer to 20°C (for 3, 1 0, and 1 7  days) 
Core cavity e2H4 concentrations of Braeburn and 
Granny Smith apples stored at ooe for 0, 4, 8 and 1 2 
weeks and subsequent sto rage at 20°C for 1 7  days 
Firmness of Braeburn and Granny Smith apples stored 
at ooe for 0, 4, 8 and 1 2 weeks and subsequent 
storage at 20°C for 1 7  days 
Soluble sol ids content of B raeburn and Granny Smith 
apples stored at ooe for 0 , 4 , 8  and 1 2 weeks and 
subsequent storage at 20°C for 1 7  days 
Hue angle of Braeburn and Granny Smith apples 
stored at ooe for 0, 4, 8 and 1 2 weeks and 
subsequent storage at 20°C for 1 7  days 
Schematic model i l lustrati ng the relationships between 
[021ext, [021i , F or  respiration rate and R 
Schematic representation of the effects of washing or 
CQating with Tween 20 solution on R, [021i , [C021i , 
F or respiration rate and 02 uptake of apples 
-Tentat ive model describing the form of relationships 
between [02] i , skin resistance to gas diffusion (R)  
and temperature. 
xxv 
268 
269 
270 
272 
273 
274 
275 
285 'f..-
-. 
, / /". --!;i) , �. � • . # 
302 
306 
TABLE 
4-1 
4-2 
5-1 
5-2 
7-1 
7-2 
7-3 
7-4 
7-5 
7-6 
LIST OF TABLES 
Coefficients of variation in different apple cultivars 
Approximate storage l ife of various apple cultivars in  
refrigerated a i r  storage together with ranking from 
1 to 8 of cultivars based on mean respiration rates 
Apparent Km and Fmax values calculated using equation 
[5.4] for [02] i of Cox's Orange Pippin and Granny Smith 
apples as a function of [02]ext 
rKm and rFmax of equation [5.6] for RelO2 as a function 
of [02]ext or [02]i fitted with non-l inear reg ression 
for Cox's Orange Pippi n and Granny Smith 
Comparison of significant differences between the 
intercepts of the regression l i nes relati ng [02] i 
of apples to temperatu re 
Comparison of significant differences between the 
slopes of the reg ression li nes relat ing [02] i of 
apples to temperature 
Comparison of significant differences between the 
intercepts of the regression l i nes relating [C02]i 
of apples to temperatu re 
Comparison of significant differences between the 
slopes of the regression l i nes relating [C02]i of 
apples to temperature 
Relationship between [C2H4]i and temperature of apples 
Relationship between C2H4 production and temperatu re 
of apples 
xxvi 
PAGE 
67 
86 
1 05 
1 07 
1 92 
1 93 
1 97 
1 98 
202 
206 
xxvi i  
LIST OF ABBREVIATIONS. 
A = Fruit surface area (cm2) 
AA = Acetaldehyde 
[AAlse = Subepidermal acetaldehyde concentration (J.Ll r
1 ) 
ACP = Anaerobic compensation point (% 02) 
[ACP]ext = Anaerobic compensation point for external oxygen 
(% °2) 
[ACP]i = Anaerobic compensation point for internal oxygen 
(% °2) 
CA = Controlled atmosphere 
CO2 = Carbon dioxide 
[C02]i = Internal carbon dioxide concentration (%) 
[C02] initial = In itial carbon dioxide concentration in  jar (%) 
[C02]final = Final carbon dioxide concentration in jar (%) 
C2H4 = Ethylene 
[C2H41i = I nternal ethylene concentration (,..d r 1 ) 
[C2H41 in itial = Initial ethylene concentration in  jar (Ill r 1 ) 
[C2H41tinal = Final ethylene concentration in jar (Ill r 
1 ) 
C2H6 = Ethane 
!!lCCA = Difference in gaseous concentration ( ie.  !!l[02] .  !!l[C02] ,  
!!l[C2H4] etc.)  between the external and i nternal 
atmospheres of a fruit in  CA (%) 
!!lCair = Difference in gaseous concentration ( ie. !!l[02] .  !!l[C02] .  
!!l[C2H41 etc. ) between the external and i nternal 
atmospheres of a fruit in ai r (%) 
ETOH = Ethanol 
[ETOH]se = Subepidermal ethanol concentration (Ill r 1 ) 
xxviii 
F = Flux or  respi ration rate (cm3 s-1 ) 
Fmax = Maximum rate of exchange when 02 
is saturating (cm3 02 s- 1 ) 
Fai r = Flux of gases (ie. 02' C02 .' C2H4 etc) i n  air (cm
3 s-1 ) 
FCA = Flux of gases (ie. 02, C02, C2H4 etc) in  CA (cm
3 s-1 ) 
F02 = Rate of oxygen uptake (cm3 kg- 1  h- 1 ) 
FC02 = Rate of carbon dioxide production (cm3 kg- 1  h-1 ) 
FC2H4 = Rate of ethylene production (Ill kg- 1  h-1 ) 
h = Hour 
k'f = a fruit constant (AIR) (cm
3 s- 1 ) 
Km = Michaelis-Menten constant (% 02) 
MA = Modified atmosphere 
N = Newtons 
°2 = Oxygen 
[02] i = I nternal oxygen concentration (%) 
[02]ext = External oxygen concentration (%) 
[02]in itial = I nitial oxygen concentration in  jar (%) 
[02ltinal = Final oxygen concentration in  jar (%) 
R = Skin resistance to gas diffusion (s cm- 1 ) 
RC02 = Skin resistance to carbon dioxide diffusion (s cm-1 ) 
RC2H4 = Skin resistance to ethylene d iffusion (s cm-1 ) 
RC2H S = Skin resistance to ethane diffusion (s cm-1 ) 
RelE = Relative rate of exchange 
RelO2 = Relative rate of oxygen uptake 
ReIC02 = Relative rate of carbon dioxide product ion 
ReIC2H4 = Relative rate of ethylene production 
Re/RQ = Relative respi ratory quotient 
RQ = Respi ratory quotient 
rFmax = Maximum relative rate of exchange when [02] i 
is saturating (cm3 02 s-1 ) 
xxix 
rKm = Michaelis-Menten constant for the relative 
rate (% 02) 
s = Seconds 
n = 3.1 41 6  
Vfruit = Fruit volume (cm
3) 
\+jar = Jar volume (cm3) 
Wfruit = Fruit weight (kg) 
T = Time· 
1 
CHAPTER 1 
GENERAL INTRODUCTION 
Innumerable physiological processes are accelerated (or in it iated) in 
apples at the t ime of harvest. On removal from the parent plant, the fruit are 
deprived of the i r  no rmal  supp ly  of water, m inera ls and s imple o rg anic 
molecules (eg .  sugars, hormones) which normal ly would be translocated to 
them from other parts of the plant. However, harvested apples are sti l l  l iving 
as they cont inue to perform metabol ic reactions i ncluding those involved in 
resp i rati o n  a nd ma intai n the p hys io log ical system ,  wh i l e  be i n g  so le l y  
�. ..... 
dependent on their own reserves and moisture content (Biale, 1 975; Pai and 
Sastry, 1 990) . 
During normal respiration, oxygen (02) diffuses i nwards via the skin and 
flesh of the fruit from the external atmosphere to the sites of reaction i nside the 
ce l ls .  Uti l isati on of 02 at the react ion centres resu lts in a concentration 
d i ffe re nce ( g rad i e nt )  betwee n the s ites of react i on  and  the e xt e rna l  
, 
atmosphere, causing more 02 to diffuse towards the sites of uti l isation (Burton,  
1 982 ). 
Carbon dioxide (C02) and ethylene (C2H4) produced by respi ratory 
metabo l i sm  occu r w i th i n  t he  ce l l  sap  and  cause l oca l  i nc reases  i n  
co ncent rat i o ns .  Th is  i nduces d i ffus i on  outwards  to reg i ons o f  l ower  
concentrations through the openings. on the surface of the fruit to the external 
v"- .;-'.' atmosphere (Burton, 1 982 ; Wolfe ,  1 980). The pattern of the g radient that is 
established for � diffusion is the reverse of that for CO2 and C2H4 (Burton, 
1 982 ; Kader et al., 1 989). The f lux of gases to and from a fruit is related to the 
2 
magnitude of the resistance of its skin and of its flesh to gas diffusion ,  the 
respiration rate and the magnitude of the gas concentration difference between 
� 
the i nternal and external atmosphere (8urg and Burg, 1 965; 8urton, 1 982) .  
The problem of gas exchange in harvested apples can be appreciated 
considering the fact that they lack the blood Circulatory system which functions 
./ 
i n  animals (Rahn et a/. , 1 979) to provide gas exchange.  Sti l l ,  fruit tissues are 
usual ly  considered to be adequately venti lated. There is continuous gas 
exchange between the internal and external atmosphere of the fruit (Ben­
Yehosua and C/meron, 1 988; 8urton,  ((82) .  Adequate ventilation of the fruit 
re l i es o n  propert ies of the  gas phase p resent wit h i n  fru it  t issues . The  
parenchymatous tissue of a fruit is i nterlaced with intercel lu lar spaces which i n  
some cases may occupy one  fourth of the total volume (Biale, 1 960a).  The 
gas phase i n  the  i nterce l lu lar  spaces acts as a continuum which extends 
throughout the fruit (Burton , 1 982 ; 8en-Yehoshua, 1 969 ;  Burg and Bu rg ,  
ell 
1 965; Devaux, 1 891 ; Marcell in, 1 974). Any action that results in the clogging 
1\ 
of these spaces can impede gas exchange which can lead to fermentation 
(8en-Yehoshua et a/. , 1 963; Sacher, 1 973). Most cells of a fruit are in d i rect 
contact with the gaseous phase in  adjacent i nterce l lu lar  spaces commonly 
referred to as internal atmosphere. This internal atmosphere is  general ly quite 
'- ./ 
different in  composition frorl"! .that outside the fruit (8urton, 1 98
2 ; 8en-Yehosua 
and Cameron,  1 988tPhan, 1 987} The internal atmosphere of the commodity 
is affected by factors such as respi ration rate, skin resistance to gas d iffusion .... 
(R)  temperatu re, artificial barriers and stage of physiological maturitjfBurton,  
1 982 ; Cameron  Y'and Reid, 1 982; S harples and Johnson ,  1 9�.?; Zagory and 
Kader, 1 988). 
Oxygen concentrations between 1 an�5% have generally been used in  
controlled atmosphere (CA) of apples (Meheriuk, 1 990). These concentrations 
are measured in the atmosphere su rrounding the fruit a nd it is important to 
know the concentrations inside the fruit since it is the internal atmosphere that 
1" -' • � ,  
3 
b rings about the  reduced rate of dete rio rat ion seen in CA stored apples. 
Furthermore ,  knowledge of the internal atmosphere composition may also help 
develop physiological explanations of the mode of action of low-02 sto rage. 
The development of some post harvest physiological d isorders in apples such 
as i nternal b rowning o r  core flush and brown-heart has been related to the 
: fruit internal atmosphere composition (Hewett and Thompson, 
1 989). However, d i rect sampling of gas concentrations in fruit under l ow-02 
atmospheres and even under normal atmospheric condit ions is SUbjeC� 
many problems and reported results often seem' , to be e rroneous (Knee, 
1 973 ; pekm� , 1 97 1 ). Consequently, there is a dearth of information  on 
factors affect ing the internal atmosphere composit ion of apples presumably 
because of the difficulties in obtaining internal gas samples from fruits. 
Most i nvest igators have looked at the impact of the e xternal  02 
([02]ext ) rather  than the internal 02 concentration ([02] i ) on fruit respi ration 
(and C2H4 production). However, it is the 02 inside the fruit that is the most 
d i rect cause of depressed respi rat ion (and C2H4 p roduction )  rather than 
[02]ext on which [02]i is dependent. The present i nvestigation focused on 
[02] i (and [C02] i and [C2H4]i ) by studying the relationships between i nternal 
atmosphere composition of apples and factors such as skin resistance to gas 
d iffus ion (R ) ,  respi rat ion, [02]ext, artif icial barriers and tempe ratu re .  An 
attempt was a lso made to deve lop conceptual models i l l ust rati ng t hese 
re lationsh ips.  From these studies, it is hoped that fu rther  insight may be 
provided into the way in which these factors affect the inte rnal atmosphere 
composition of apples and hence regulate the rate of deterioration of the fruit. 
Pertinent l iterature re lated to the internal atmosphere <?omposit ion as 
wel l  as respiration and gas exchange in fruits includi ng apples ate. reviewed in  
the next chapter. As far as possib le ,  th is  was constructed from results of  
expe riments carr ied out on  app les by other  invest igators .  Howeve r, a 
considerable proportion of the l iterature relevant to this work comprise results 
obtained with a variety of other fruits. 
CHAPTER 2 
LITERATURE REVIEW 
2.1 Internal atmosphere of fruits 
4 
Gases  a re p resent i ns ide fru its e i the r  i n  g aseous phase  i n  t he  
i ntercellular air spaces, hereafter called the 'internal atmosphere', o r  they are 
d issolved i n  the aqueous phase of the t issue, i nclud ing the cel l  contents. 
Those present in the latter phase are most directly related to the levels of each 
gas present at the sites of metabolic activity within the cells. The intracellu lar 
concentration of a gas is determined by: 
1 .  i ts  conce n t rat i o n  i n  t he  gaseous  phase i n  the  su rro u nd i n g  
i ntercellular spaces i .e .  the internal atmosphere i n  that part of the fruit ; 
2 . t h e  so l u b i l i ty of  t he  gas i n  t he  cytop lasm at the  p reva i l i n g  
temperature and pressure ;  
3 .  its rate of  uti l isation or production withi n the cells ; 
4. the resistance to movement between the intercel lular gas phase and 
the intracel lu lar solut ion (e.g . ,  that afforded by the cell membrane and  cell 
wal l ), which is affected by the solubi l ity and diffusivity of the gas i n  water 
./ 
(Banks�-·l 981 ). 
/ 
2.1 .1 Factors affecting internal atmosphere composition 
Extensive research has been conducted by various  i nvestig ato rs to 
dete rmine how the i nternal concentrations of gases in  fruits includi ng  apples 
a re affected by facto rs such as temperatu re , composit ion of the external 
5 
atmosphere, skin resistance to gas diffusion,  artificial barriers and stage of 
maturity. The results of these studies are reviewed briefly i n  the fo l lowing 
sections. However there is sti l l  a dearth of i nformation on the importance of 
these factors on the internal atmosphere composition of apples. 
2.1 .1 .1 Temperature 
Temperature is one of the most important single environmental factors 
affecting the intemal atmosphere composition of fruits and other plant o rgans 
(Kader, 1 987) . Decline in internal 02 concentration and increase in i nternal 
C02 concentration within bu lky plant organs in response to an increase in 
temperatu re has been demonstrated for d ifferent commodit ies i nc l ud ing  
.../' ./ 
apples ( Kader et al. 1 989; Kidd and West, 1 925), potatoes (Burton ,  1 950; 
Q / � ,.-Deav,px, 1 891 b), oranges (Eaks and Ludi, 1 960) papaya and banana (Leonard ,..-
and Ward law, 1 94 1 ) , peaches and apricots (Maxie and Mitche l l ,  1 974) .  
I 
Claypool ( 1 938) reported that in apples, peaches, nectaries and plums internal 
J 
C02 increased proportionally to increases in temperature. Trout et al. ( 1 942) 
showed that Granny Smith apples in air had an internal 02 content of 1 7% at 
7°C and only 2% at 29°C. The corresponding C02 percentages were 2 and 1 7  
,/" 
at these two temperatures. Anzueto and Rizvi ( 1 985) reported that apples 
stored at low temperatures (0, SOC) had lower internal C02 and h igher internal 
02 than their counterparts at h igher temperatures (20, 2S0C). Ladeinde and 
H icks ( 1 988) observed that at 0.3% external 02 temperature did not inf luence J 
the internal 02 level of onions.  but at h igher external 02 levels an i ncrease in 
temperature lowered internal 02 levels. However. when onions were sto red at 
30°C with external 02 levels of less than 1 0%, the internal 02 level in the  bulb 
was close to zero. I nformation on the effects of a range of temperatures on  the 
in terna l  atm osphere com posi t ion of f ru its is l im i ted .  I n  N ew Zea land  
quantitative data on  the effects of different temperature regimes on  the internal 
atmosphere composit ion of various cu ltivars of apples are unavai lable. 
6 
2.1 .1 .2 Composition of the external atmosphere 
The internal atmosphere composit ion of fru its and other  bu lky p lant 
organs is closely related to the external atmosphere. Thus a change in the 
e xternal atmosphere sign ificant ly  in fl uences the fruit internal atmosphere 
(HulmE( 1 951 ; Lalagu�a and Thome, 1 982; Lidste;:1 982; Knee, 1� 19'80, . 
1990; Wi l l iams and Patterson ,  1 962) .  Leonard11 947) reported that when 
bananas we re  p laced at d iffe rent 02 l eve ls at 1 2 °C ,  t h e  i n te rna l  02 
concentrat ion was l inearly related to the external 02 concentration. Simi lar 
observations wererde by Wardlaw andieonard (1 936) for pawpaw and 
Leonard and Ward law ( 1941 )  for banana. 
Wardlaw ( 1 936) found that there was a close relation between the 
composition of the internal atmosphere of bananas and pawpaws and that of 
the atmosphere in which the fruit is stored. The lower l imit to wh ich 02 can be 
reduced i n  the  external atmosphe re without subsequent inj u ry has been 
� . 
empirically determined for large number of fruits and vegetables (Kader, 1 980). 
According to Weichrrlann (1 987) vegetable crops react ing posit ively to CA 
conditions usually require a minimum external 02 content of 1 - 3%. At such 
concentrations it is possible that the 02 level inside the t issue is just 0.2% 
(Kader, ((86). I senber'9(1 979) observed that at external 02 levels below 2% 
most vegetables react with a sudden increase in internal CO2, I nformation on 
the effect of external atmosphere composition on the internal atmosphere of 
fru it including apples is l imited presumably because direct analysis of internal 
gas concentration in fruits under low 02 or h igh C02 atmospheres is subject to 
many problems (such as contamination of gas samples with air or water during 
sampling) and often g ives results which are obviously in error (Knee,v1�73). 
7 
2.1 .1 .3 Skin resistance to gas diffusion 
The skin of a fru it p resents signifi cant barrie r  to g as exchange and 
hence infl,,"ce the i nternal atmosphere cOr1)position (Burg and �J:g;' 1 965;  
Burton ,;-950; Cameron, J,.962; Hardy, � Monter�7 ;  Solom�1-985; 
Soudain an
/
d Phan tpue, 1 979 ; Ulrich andJkcfrcel l in ,  1 968). For i nstance , 
Burg �urg (1 965) observed that internal C02 and C2H4 concentrations i n  
apples decl ined considerably when the fruit skin was peeled off. Trout e t  al. 
( 1  ��orted that on removal of the skin of stored apples containing low 
internal 02, there was an increase in internal 02 concentration and a decrease 
in i nternal C02' Variation i n  skin resistance to gas diffusion between fru it 
cultivars could result in variation in internal atmosphere composition  (§lJrton, 
1 982) .  In  New Zealand information on the effects of skin resistance to gas 
diffus ion o n  the i nternal gas composit io n  of various l ocal ly  g rown appl e  
cultivars is unavailable. 
2.1 .1 .4 Artificial barrier 
Artificial barriers such as coatings, waxes or plastic fi lms or polyl iners 
have been used extensively in commercial and postharvest research (Banks,  
19�a:) 1 - 1 985)l, J;'" 5�; Ben-Yehoshua, 1 �,�
- 1 9��- Hardenb�71  ; Kader, 
1 9�-1- Rizvi ,�81 ; Smith etpt;- 1 987). The presence of an artificial barrier to 
diffus ion around fru it may result in reduced internal 02 and i ncrease C02 
concentrations, altered water vapour and C2H4 concentrations (SmitQ�al. , 
1 987). The degree to which these factors are altered for a given commodity 
will depend on species, cultivar, mass :surface area ratio and respi ration rate 
(Banks, 1 9�, �,� 1 9�5a; Kader, 1Jl86 ; Smittlyral. , 1 987). 
Trout et a/u.t942} recognised that coating apples reduced internal 02 
and i ncreased internal C02 concentrations to leve ls that cou ld  resu lt i n  
anaerobiosis and off-flavours. Wax applications have been shown to increase 
8 
internal C02 concentrations (Claypool...l938; Wardlaw, 1 936) and to decrease 
i nternal 02 concentrations (Hulme,flS1 ;  Eaks a�udi ,  1 960). I n  some 
instances the increase in C02 has been noted to exceed the decrease in  02' 
but usually the reverse is true. The difference would be due to whether or not 
the i nternal 02 was below the anaerobic compensation  point (Be n:;:.'tehOsh ua, 
1 969;  Hall et al.�). Ladeinde aB!J:I icks (1 988) observed that paraffin wax 
applied to the root plate of onions caused a dramatic reduction in i nternal 02 
and elevation of i nternal C02 concentration. Burg and �1 965) reported 
that when  the pedicels of tomatoes and peppers were blocked with l anol in  
paste, the i nternal C02 doubled within 6h as a result of i ncreased resistance to 
d i f fus i on  o f  C02 from the fru i t ,  s howi ng  that the  main pathway to gas 
movement was in the stem scar. Cohen et al. �) reported that postharvest 
waxing  of 'Murcott ' tangeri ne with Britex or  Zivdar, resulted i n  i ncreased 
internal C02, ethanol and consequently off-flavour. 
Coating with TAL Pro-long modified internal concentrations of 02, C02 
and C2H4 and delayed ripen ing of bananas (Banks, 1 983, 1 984a ,  b )  and 
apples (Banks, 1 9¥B). Banks (1 9eAa, }b) observed that the depression of 02 
levels i nside coated fruit was greater than the elevation of C02' suggesting 
that coat ing may have affected C02 evolut ion and 02 uptake to d ifferent 
extents or that the coati ng deposit on  the fruit surface was diffe rent ial ly  
permeable to  these gases. 
Us ing another coat ing agent (Nutri-save ), E lson  eJ -a/. ( 1 985)  and 
Meheriuk a�-Lau ( 1 988) obtained similar results for Golden Delicious apples 
and 'd'Anjou pears.  Studies by Banks (��a), indicated that sucrose ester 
coat i n g  app l ied to bananas had no si g n if icant effect on i nternal  C2H4 
concentration.  Ben-Yehoshua.)r967) coated oranges, avocados and bananas 
with a formulation called Tag, and observed slightly higher C02 and markedly 
lower  02 co ncentrat i ons i n  t he i r  i nternal  atmosphere as wel l  as l ower 
9 
respi ration rates .  Other commercial wax emulsions were found to h ave a 
similar effect on internal atmosphere composition (Ben-Yehospua, 1 967; D�is--·· -­
and Hardi ng , 1 960). 
Earl y  work s howi ng t h at i nte rnal atmosphe re mod i fi cat i o n  was 
dependent on cu ltivar, coating type and th ickness and h olding temperature 
(Trout et al., ,�;.��) was confirmed in work on apples (Banks, VlB5a; SJllith-and 
Stow, 1 984j. Accord ing  to Smith et al.p987 ), relat ive concentrat ions of 
i nternal 02 and C02 which develop i nside coated fruit depends on coating 
type and cultivar. For i nstance some cultivars such as Bramley's seedling 
have relatively high concentrations of natural surface wax which may p revent 
wetti ng of the surface by the coating. Consequently the internal gases would 
be relatively different from another cultivar ego Spartan which has less natural 
surface wax (Smith et �1987) .  Ben-Yehos�( 1 967) suggested that the 
effects of skin coating such as Tag (a polyethylene-wax emulsion) and several 
other commercial waxes (Zivdar, Britex, Flavorseal) on oranges depended on 
the type of coating and its thickness; Ben-YehOS� 967) suggested that the 
opt imal coat ing  should maximal ly reduce weight loss without creat ing an 
i nj u ri ous  atmosphere i ns ide the fru i t .  He recogn i sed t hat the  i nternal  
atmosphere should be within  the range in  which there is neither a deficiency of 
02 nor an excess of C02 during storage l ife at the range of temperatures to 
which the fruit would be exposed. 
Fi lms are generally extruded plastic o r  polymeric materials that are 
used to surround the produe-9 as shrink or stretch wraps, o r  as sealed loose 
covers (Sm it h  et al.�7). The use of po lymer ic  f i lms  to extend t he  
postharvest l ife o f  fru its and other plant organs th rough modificatio n  of  the 
internal atmosphere of the commodity has increased greatly duri ng the last two 
decades (Kawada« �82). This is due mainly to the rapid development of new 
fi lms and packaging technology, together with changes i n  produce marketing  
systems (Kawada,
,
) 982). Films have been employed to  restrict water loss i n  
1 0  
storage for many years but their use Jp modified atmosphere packs has been 
re l at i ve l y  l i m i t�d ( Eave�.  Gerh a� -95 1 ;  H a rdenb.e'f9.
, 
1 97.1 ;  
Mannapperu�et al . •  1 989; Scott an(�J�oberts. 1 966; Tomkins. J.962. 1� 
Watkins  � 1 989) .  Early attempts resulted i n  on ly partially modif ied or  
anaerobic conditions. presumably because the fi lms used had either excessive 
or inadequate permeabi l ity to 02 (Al ien a�tEjn. 1 960 ; Scott and�. V 
1 947). The i nternal atmosphere of the commodity i n  a plastic package i s  
known to  be  i nfluenced by the atmosphere inside the package (Ka� al . •  
1 989 ; Hudson et �989). However. quantitative data of  the concentration of 
gases inside the produce within packages is l imited. Usually when fruits and 
vegetables are enclosed in a polymeric fi lm. the internal atmosphere becomes 
modified - depleted in and enriched in C02 (Gees��>1 988). On the other 
. ( 1 988) claimed that the use of a rig id fi lm package  for 
Delicious apples significantly reduced internal C02 and C2H4 content of fruit. 
2.1 .1 .5 Stage of maturity 
The stage of matu rity of a fru it appears to affect the i nte rnal gas 
composit ion. As plant organs advance towards senescence. the i ntercel lu lar 
spaces become clogged with cel lular sap consequently reducing the d iffusivity 
of gases and causing a decrease in internal 02 and increase in i nternal C02 
(Burton. �; Kader et a/�89 Trout et�1942) .  Early work by Kidd and 
West. ( 1�i ndicated that the i nternal atmosphere of apples was infl uenced 
by thei r physiolog ical stage .  For instance i n  climacte ric fru it (eg . banana). 
during the preclimacteric stage. i nternal 02 levels are high whi le internal C02 
levels a re low. At the peak of the cl imacteric. internal 02 decreases while 
i nternal CO2 (and respirat ion rate ie .  CO2 production )  i ncreases. �s 
(1 937) also reported that the C02 in  the internal atmosphere of tomatoes 
increased with an increase in  maturity from the mature g reen to the pi nk  stage. 
Re id  et a�3 )  report ed t hat the i nte rnal  concent rat i o n  of C02 i n  
precl imacteric Cox's Orange Pippin apples was 2% while the internal C2H4 
content was about 0.02ppm (at 1 2°C). 
1 1  
Mart in  and ptliper  (1 970) observed that as fruit matu re, the cuticle 
th icke ns, t h u s  affecti ng the d i ffu s iv ity of  g as and hence i nternal gas 
composit ion .  Some apple cUltivars notably G ranny Smith , develop a natural 
coating or become greasy after a period of storage (Huelin and Gallop, .J95fs, ,-
/-t(Lea�t at, 1 989a; Lil l et af.',
' 1 989; Martin and Ju'2!J>8f,' 1 970; Trout et al. , 
1 9� This is l ikely to increase the resistance of the skin to gaseous d iffusion  
and thus affect the internal gas concentrations. 
2.1 .2 Methods of sampling Internal atmosphere 
The gas concentration g radient of a g iven species is an estimate of the 
chemical potential or driving force of gas diffusion. It is usually estimated from 
accurate measurement of the internal and external gas concentrations using a 
method which does not alter the composition (Ben-YehOSh��eron, 
1 988). Accurate measurement of the internal gas composition is essential for 
the est imation of skin resistance to gas diffusion and also in estimat ing t he 
phys io logical stage of matu rity of a fru it (especial ly apples and fru its with 
internal cavities) .  
Several different approaches have been util ised to  obtain internal gas 
samples from fruits and other bulky plant organs and none of t hese methods is 
entirely satisfactory. Some of these approaches are summarised briefly i n  the 
fol lowing sections: 
2.1 .2.1 Direct sampling method 
The d i rect sampl ing method is easy, quick and stra ightforward for 
obtain ing samples from the internal atmospheres of bu lky o rgans such as 
musk-melon (Lyons et al. , 1 962) and apple (Blanpied,  1 968, . Dadzie et 
al. , 1 990a, b ;  Smith ,  1 947 ;  Lyons and Pratt, 1 964 ; Rajapkse e t  al. , 
, . 1 2  
1 989a�/�, A 99�{ �fakiotakis and Di l ley, �. Saltveit" . 1 982; Wil l iams and 
Patterson:- 1� It consists of inserting a long hol low hypode rmic needle 
through t";; ski n i nto the tissue or core cavity and slowly ext ract ing gas 
samples by pul l i ng back the plunger on  an attached syringe. The resulting 
partial vacuum causes gas to flow from the tissue into the syringe (Ben­
Yehoshua an�970; Burg and Burg, 1962;"1965; 
.
�Ianpied, 1%8;- 'LY� 
and Pratt , 1 964: Sfakiotakis and DiI I�973; William� and patterso�62; 
Forsyth e�973; Lyons e���;., 1 962; Maxie e;,Jk; 1 965). 
Contamination of the sample with air from outside the tissue may result 
if the sample is taken while holding the commodity in the air. This can be 
prevented either by taki ng samples from produce submerged an aqueous 
//" .'  . -
solution (Ben-Yeh�1969; Hulmet . ..l·9S-1 ;  Ly?ns et al.J,962 ; Max
,
i e  � 
1 974; Sfakiotakis and Dil le�3 ;  Smith, � Williams and Pa�6n, 1 962) 
or by seal ing around the needle with wax or Vasel ine (Smitly-1'947; Hul�' 
1 951 ) or cement (Wil l iams and Patte�962). The needles of hypo�mic 
syringes are frequently blocked by fruit tissue when the internal atmosphere of 
fruits are sampled. This problem can be avoided by taking samples from  just 
beneath the skin of fruit (Burg and B;.u:Q." 1 962) or a wire filament may be used 
to prevent blockage of the needle during insertion (Raj�t. al. , 1 989a, 
�Sfakiotakis a�:-1 973; Reid et ;!�A·973; Smith,� or by using 
a blunted or side-del ivery needle (Wi l l iams and �on, 1 962). Blockage 
can sti l l  occur during sampl ing of fru it with any of these techniques. In the 
current work, this problem was overcome �sing a modification of the 'di rect 
removal' method described by Banks �3) in which a pin ' head is fitted into 
the mouth of a canula which is also fitted to a disposable syringe. 
It should be mentioned that most 1 ml disposable syringes have 0 . 1  m l  
or more dead space at the tip and in the needle. This is  not much of  a problem 
if large samples are taken. However if only very smal l samples are taken the 
dead space can cause severe dilution problems. Purging with nitrogen or salt 
1 3  
solution prior to sampling does not solve the problem completely. When only 
very smal l  volumes of gas are avai lable for sampl ing, g lass syri nges with 
minimal dead space volume should be used for best possible accuracy (Ben­
Yehoshua and Camero"ry,/1"988). 
I' 
J -!�/ ' • t."" "", ,:,,'ft 7 I .. 
Direct measurement of internal Qas concentrationJ is usually difficult or  G<",J , 
i nconven ient and reported resu lts ,�particularly for 02' often seem to be 
erroneous (Knee, 1 991 a, b). Fidler and North ( 1 967) also found the direct 
sampling method to be unreliable. However in this research reliable results 
were easily obtained using a modification of this techn ique. Similarly various 
research workers including Banks ( 1 981 , 1 984a, b, 1 986), Banks and Kays 
( 1 988), Cameron ( 1 982), Dadzie et al. (1 990a, b), Rajapkse et al. (1 989a, b, 
1 990), Hewett et al. ( 1 989) have also obtained reliable results using the di rect .' 
sampl ing method. , ' 
2.1 .2.2 Artificial Internal cavity extraction method 
Devaux ( 1 8'91b) while attempting to take gas samples from the i nternal 
atmospheres of potatoes, appears to have been the fi rst to have created an 
artificial i nternal cavity from which repeated gas samples could be taken. In 
this technique, which was rediscovered by Wardlaw (1 936"), a cork borer is /' 
used to remove a cylinder of tissue from the plant organ. One end of a short 
piece of glass tubing is inserted mid way into the cavity created and the other 
end is sealed with a septum. Samples are withdrawn after the air i n  the tube 
equil ibrates with the atmosphere inside the organ .  Trout et aYf9
'
42) critically 
examined this approach and concluded that equil ibrium was establ ished within 
24 hour after each sampl ing .  Ben-Yehoshua et al. (1 963) also used this 
method for avocado, after showing that the injury involved in establishing the 
cavity did not affect respiration and gas exchange during the sampling period. 
1 4  
An appraach was used by Wardlaw ( 1 9�.sJ�· Kidd and West J1.949) and 
Ekambaram (�n which a small section of skin was rern'oved and the tube 
attached to the outside of the plant organ. Wardlaw and Leonard (�a, b). 
sampled the i nternal atmosphere of banana fruit by placing a volume of ai r'(5.o 
m' 
ml) in contact with the pulp of the fruit via insertion and leaving it to equi l ibrate 1\ 
with the contents of the intercel lu lar spaces. Samples were withdrawn at 
regular intervals for analysis. 
Hulme (1 �Sfakiotakis and �t973), Smith ( � .�47) and V
"E!
J)drall . 
( 1 970) used an alternative approach which involved a combination of the direct 
sampl ing and artificial cavity methods. A sl ightly larger syringe needle was 
inserted i nto the organ rather than a piece of glass tubing and covered with a 
septum before sampl i ng. This method permitted repeated gas samples to be 
taken from a given depth beneath the skin. 
The g reatest drawback of the internal cavity methods described is the 
u nmeasured effect of wounding ,  as wounding wi l l  no rmally increase f ruit 
respiration rate, rate of ethylene production and the degree of water soaking in 
the tissue (Burton)-.914 ;  Kahyf974) any one of which can change diffusion 
behaviour markedly. In addition, these methods have the disadvantage that 
they involve considerable muti lation of the tissue of the fruit. Further, they do 
not take into account the existence of gaseous diffusion gradients between 
different parts of the tissue (Smith, 1 947). 
2.1 .2.3 External cavity extraction method 
The method has been used to study the internal atmosphere of potatoes 
(Banks and Kays,;,t 988 ;  Devaux, 1 J�91 b), apples (Cameran ,) 982 ;  Dadzie et 
./ 
al. , 1 990a, b ;  Ekambaram, 1 922, Rajapkse et al. , 1 989a, b, 1 990, Solomos, 
1 9�nd other bu lky organs such as banana (Banks ,  1 983) nectari nes, 
(Rajapkse et al. , 1 990) and tomatoes (Cameran, J 982). In this method , using 
,. 
1 5  
gelatin or soft wax (Devaux, 1 89 1 b) or vaseline (Cameron ,  1 982 ) or PVA glue 
(Oadzie et al. , 1 990a, b; Rajapkse et al. ,  1 989a, b; 1 990) a small chamber is 
attached to the surface of a fru it o r  vegetable and al lowed to equ i l ib rate.  
Came ro n  ( 1 982 ) modif ied the techn ique  by sea l i n g  a �:;,./ chamber  
to  the surface of the fruit using a small amount of 
vasel ine; both the fru it and chamber were held in place by a ring stand and 
clamps. Samples were taken through the septum.  As the p lunge r  of the 
syringe is moved back and forth , the water in the arm of the chamber is drawn 
up and down. The method ensures a tight seal, prevents a sign ificant d rop in 
cham ber p ressu re (wh ich cou ld ca use mass f l ow from the f r u i t ), and 
equ il ibrates the gas in the syringe with that in  the chamber. After the sample is 
withdrawn, the water level remains elevated in the arm, drawing a very sl ig ht 
vacuum on the skin of the fruit exposed to the chamber. 
For fru its w ith lentice ls o r  other ' ho les' ,  th is  s l ight vacuum  s lowly 
dissipates by net movement of gas from the tissue to the chamber. For fru its 
such as tomato, wh ich contain no lenticels, a quantity of gas equal to that 
removed can be injected into the chamber after sampling. Cameron ( 1 982 ) 
found that sampling could be in itiated about 8 hour after attaching the chamber 
onto apples and every 2 hour thereafter. A much simpler method developed 
by Banks and Kays ( 1 988) based on the pr inciples described by Cameron 
( 1 982 ) invo lves attaching one more sampl ing chambers to the fruit su rface 
(Dadzie et al. , 1 990a, b; Rajapkse et al. ,  1 989a, b ,  1 990). Contents of the 
chambe r  o n  app les  have been  found  to equ i l i b rate w ith  t he  i nterna l  
atmosphere of the organ after 40 to 90h equil ibration (Dadzie et  al. ,  1 990a, b; 
Rajapkse et al. ,  1 989a, b) and repeated samples can be taken. 
Since this method measures the concentration immediately beneath the 
skin ,  it is ideal for estimating skin resistance even for organs with substantial 
flesh resistance (Cameron , 1 982 , Dadzie et al. ,  1 990a; Rajapkse et al. , 1 989a, 
1 990). In addition, wounding of the p lant organ is avoided. 
1 6  
Banks (1 983) found that this technique may modify the atmosphere 
under the skin considerably. He found that chambers (7 .0 mm d iameter) 
attached to the surface of green banana fruit, after ripening for 4 days at 20°C, 
the skin of the fruit was yellow except for that covered by the chamber, which 
remained g reen .  This problem has not been found i n  apples in wh ich this 
method is used on a routine basis (Cameron, 1 982 ; Dadzie et al. , 1 990a, b; 
Rajapkse et al., 1 989a, b, 1 990). I n  fact in this study rel iable data were easily 
obtained using this technique. 
2.1 .2.4 Vacuum extraction method 
Several workers have used vacuum extraction to obtain samples of 
gases from i nside fruits and vegetables. Magnes� 920) appears to have 
been the fi rst to report the use of this method to extract gases from tissue 
segments of plant organs. He removed tissue segments from the o rgan of 
i nterest with a cork borer and transferred them di rectly i nto the extraction 
chamber, keeping the tissue segments submerged under mercury. Using a 
series of tubes, valves and a bott le of mercury, the pressure was dropped, 
causing the internal gases to expand and escape into the mercury where they 
were eventually col lected and analysed. 
Many modifications of the apparatus have been developed for tissue 
segments (Burton and Spragg, )948; Christensen et �/. , 1 939; CulR�pper et 
,/ 
al. , 1 936 ; Gerhardt and Ezel l , 1 934 ; Harley and Fistlf#(, 1 930 ; Whit�man and 
� r 
;. Schomer, 1 945) and for enti re organs (Brookyt9"38; Maxie et ii/:."- 1 965). A 
partial vacuum can be appl ied to tissue in  air (Blanpied, 1 971 ; Hulme, 1 951 ; 
Poapst et al. , 1 974 ; Smith, 1 947) ,  to tissue submerged in an aqueous solution 
(Denny, 1 946; Maxie et al. , 1 965; Staby and De Hertogh ,  1 970) , o r  to tissue " 
"'.,� l) it!.l,\" 
submerged in mercury (Brooks, 1 938 ; Culpepper et al. , 1 936 ; Magness" 
1 924). 
1 7  
Beye r and Morgan ( 1 970) used a satu rated sol ution of ammonium 
sulphate instead of mercury because it absorbed ethylene relatively slowly and 
saturated salt solutions are often used in place of the toxic mercury, since they 
have a relatively low solubi l ity coefficient for gases (Bussel and Maxie, 1 966; 
Denny, 1 946 ; Maxie et al. , 1 965). Bussel and Maxie (1 966) and Beyer and 
Morgan ( 1 970) developed a more convenient system for vacuum extraction for 
fruit and for vegetative tissues. The organ or tissue segment was placed in a 
pressure cooker or desiccator jar half fi l led with saturated salt solution .  An 
i nverted fun ne l  with a septum i nserted into the tip was then placed over the 
tissue and all ai r from the surface of the tissue and the interior of the funnel 
was removed. The apparatus was then covered and a vacuum applied. As 
the pressure was reduced, i nternal gases expanded and there was a mass 
flow of gases out of the fruit through the lenticels, stomata, pores, and other 
regions of low resistance to accumulate in the neck of the inverted funnel .  The 
vacuum was released after a short t ime and gas samples taken di rectly 
through the septum with a hypodermic needle for gas analysis. A s imi lar 
method was used by Blanpied (1 971 ) ,  Fidler and North (1 971 ) and Staby and 
De Hertogh ( 1 970). 
Gorter and Nadort ( 1 941 ) ,  usi ng Magness's technique demonstrated 
that the volume of gas extracted from potato tubers was greater than the 
volume of i nte rcel lular spaces. Solomos ( 1 987) reported that the vacuum 
extraction method introduces the uncertainty that some of the gases extracted 
may i nclude not only those present i n  the i ntercel lu lar spaces but also those 
that are dissolved in the cel l sap. Beyer and Morgan ( 1 970) reckoned that a 
vacuum below 1 00 mm Hg can i nduce the release of bou nd and dissolved 
gases, particularly ethylene, from plant tissue. These gases may alte r the 
concentration of gases normal ly with in the ai r spaces of t issues due to the 
differing solubi l ities of the gases under investigation . The resu lting samples 
from the vacuum extraction method are therefore not representative of the 
1 8  
gaseous atmosphere normally present i n  the i ntercel lu lar spaces. Higher 
estimates of i nternal ethylene of 'Winesap' apples and cantaloupes have been 
obtained when comparing vacuum with syringe sampli ng (Seyer and Morgan, 
1 970) and at best, estimates of i ntemal gaseous concentrations obtained using 
this method may only be relative. Thus it is generally suggested that a small 
. vacuum be used for as short a time as possible to avoid extraction of dissolved 
gases (Ben-Yehoshua and Aloni , 1 974; Beyer and Morgan, 1 970; Gorter and 
Nadort, 1 941 ) .  However Cameron ( 1 982), using a modification of the vacuum 
extraction method presented by Beyer and Morgan ( 1 970) and Busse l  and 
Maxie ( 1 966) on Golden Delicious apples, obtained internal gas concentrations 
comparabl e  with the di rect samp l i ng and external chamber met hod he 
developed. 
2.1 .2.5 Heat extraction method 
Some workers developed a number of methods to extract internal gases 
by boi l ing segments of plant organs in alcohol (Burton, 1 950; Denny, 1 946 ; 
Eaks and Ludi, 1 960 ; Willamen and Beaumont, 1 928), salt solution (Claypool ,  
1 938), buffer solution (U l rich and Thaler, 1 952) or water (Gerhardt, 1 942 ; 
Poapst et al. , 1 974). The gases evolved were entrained in  a flow of inert gas 
and trapped in  alkal i .  However Fidler and North ( 1 971 ) reported that using 
these methods they obtained inconsistent results. In a similar method , Jerie et 
al. ( 1 979) removed previously loaded rad ioactive ethylene fro m  t issue 
segments by ho ld i ng the tissue in a closed chamber over boi l i n g  wate r. 
Cameron ( 1 982) i n  a series of experiments to test the applicabi l ity of the 
method by Jerie et al. (1 979) to sampling endogenous C2H4' found that the 
amount of ethylene driven from the tissue increased with t ime of exposure to 
the boi l ing water for up to 30 minutes. Cameron ( 1 982) found the method 
unsatisfacto ry except for fru its such as apples which contain exceptio nal ly 
large amounts of i nte rnal ethylene .  For other  tissues tested , s i gnif icantly 
greater amounts of ethylene were found to be released than were extracted by 
the vacuum extraction or direct sampling methods. 
1 9  
Most authors who have used th is method have recogn ised that the 
amount of gas l iberated from the tissue is far i n  excess of that o rig i nal ly 
contained in the intercellu lar space as determined by other methods (Burton, 
1 950 ; Denny, 1 947) . Although attempts have been made to calcu late the 
original concentration of gases in the i ntercellular spaces (Burton, 1 950), heat 
extract ion methods a re not des i rable for the  est imat ion  of i nterna l  g as 
composition and skin resistance to gas diffusion  (Cameron, 1 982). 
2.1 .2.6 Digestion method 
I n  the estimation of the i nternal atmosphere ,  Denny (1 947) and Eaks 
and Ludi ,  ( 1 960) attempted to digest tissue segments in strong alkali solution. 
The severity and i naccuracy of this method as well as the problems associated 
with gas solubi l ity and calcu lation of orig inal gas concentration i n  the plant 
o rgan make this method unacceptable for the estimat ion  of i nternal  gas 
composition and resistance coefficients (Cameron, 1 982). 
2.2 Respiration metabolism 
Resp i rat i o n  i s  t he  metabo l i c  process def i ned  as t he  ox i dat ive 
breakdown of complex materials such as starch,  sugars and organic acids, to 
simpler molecules such as C02 and H20, with the concurrent production of 
energy and other molecules wh ich can be used by the ce l l  for synthetic 
reactions (Hardenburg et al. , 1 986; Forcier et11 987 ; Wills et al. , 1 981 ). 
Such metabol ic  react ions are essent ia l  fo r maintenance of biochemical 
p rocesses,  ce l l u la r  organ isat ion and membrane i nteg rity of l iv i n g  ce l ls .  
Maintain ing the supply of adenosine triphosphate (ATP) is the primary purpose 
of respiration (Kader, 1 987). 
Respiration takes place in the cells (cytoplasm, �itochondria) of tissues 
both in l ight and in the dark (Berrie et al. , 1 987; Debney �\ al. , 1 980). 
'. \ 
20 
The rate of respirat ion of pro duce is  an excel l ent i nd icator  o f  t he  
metabolic activity of the tissue and thus i s  a useful guide to the potential 
storage l ife of the produce (Fidler and North, 1 97 1 ; Wills et al. , 1 981 ) .  Kader et 
al. ( 1 985) contended that the rate of deterioration or perishability of harvested 
commodities is generally proportional to their respi ration rate. The respi ration 
rate of a given commodity differs with plant part, cultivar, area of production, 
g rowing conditions and growing season (Hardenburg et al. , 1 986). According 
to Oebney et al. ( 1 980), i f  different types of produce are classified by  their  
botanical structure ,  there is a close relationship between structural type and 
respi ration rate . H igh respiration rates are typical of young tissues such as 
growing points, (eg. asparagus) ,  partly developed flower buds (broccol i ,  globe 
artichoke) ,  developing seeds (green peas, g reen beans) and immature fruits 
(sweet corn) .  l-ow respiration rates are typical of storage organs such as roots 
(carrots, sweet potatoes), underground stems (potatoes) ,  bulbs (onions) and 
mature fruits (apples) .  Intermediate respiration rates occur in un ripe fruits 
(cucumbers, zucchin i )  and most leafy vegetables (Oebney et al. , 1 980) .  
Respi rat ion  rate of  a commod ity is dependent upon various facto rs 
related to the produce, which include type of commodity and genotype, stage 
of development at harvest, weight of commodity, and chemical composition .  It 
is also dependent on environmental factors such as temperature , l ight ,  stress, 
02' C02, carbon monoxide and C2H4 concentrations, and other hydrocarbons 
such as propylene ,  acetylene (Oebney et al., 1 980 ; Hardenburg et al. , 1 986 ; 
Kader et al., 1 989). Respiration is also one of the important factors affecting 
the i nterna l  atmosphere composit i on  of fruits, however t he re is l im ited 
i nformation on  the relationship between ,respi ration and internal atmosphere 
", a s  
composition of apples. This relationship � been investigated i n  the current 
study. 
21 
Respiration can occur in the presence (aerobic respiration) o r  absence 
of 02 (anaerobic respi ration ,  sometimes called fermentation) (Biale , 1 960a; 
Montgomery et al. , 1 990; Forward, 1 965; Wil ls et al. , 1 981 ). 
2.2.1 Aerobic respiration 
Most of the e nergy required by fruits and vegetables is suppl ied by 
aerobic respiration. Aerobic respiration i nvolves a series of reactions, each of 
which is catalysed by a specific enzyme and involves oxidative breakdown of 
complex molecules (certain organic substances such as carbohydrates stored 
i n  the tissue) to s impler molecules (Biale ,  1 960a; ap Rees, 1 980 ; Forward, 
1 965). Figure 2- 1 taken from ap Rees ( 1 980) shows the principal pathways 
responsible for the respiration of carbohydrate. 
Socro� � Starch 
� � G'uck-1- p  HeJOSe l � Glucose-6 ·P-+6·Phosphoguc�te 
FrUC!".6.�P RSa:-P 
Fructose-l.6-diP 
Tr�e - P  
l 3-F'hosphOglycerote 
l CDz ______ -- Phosphoenolpyruvate .- I 
Oxoloocetote . r> .. 
I \ ryruvote 
AsporlOte Molote � CDl 
Acetyl-CoA 
..... 
OxoIooC;;le --... Cilrate 
I' \. .  
Malate Aconltole 
f 1 Fumarote Iso(: It role 
\ 1' . � C02 Succinate .. -Ketoglutarate 
�SUCCinyl-CoA � C� 
Fig .  2- 1 . P ri n cipal pathways respo nsi b le for  t he  resp i rati o n  of 
carbohydrate (ap Rees, 1 980) . 
22 
It i nvolves the fol lowing three metabolic pathways: 
1 .  Glycolysis, which takes place i n  the cytoplasm, is the degradative 
pathway i nvolvi ng a series of react ions, each of which is catalysed by a 
specific enzyme, i n  which glucose, g lucose-1 -phosphate or fructose released 
by hyd rolysis of starch or  other reserve polysaccharides is converted to 
pyruvate (fi g .  2-2 ; Montgomery et ·al. , 1)90 ; SOUI�85) . Glycolysis is 
accompanied by the formation of ATP, although this is only about a quarter of 
the ATP that can be derived from the complete oxidation of g lucose to C02 
and water. Glycolysis can proceed either under aerobic or anaerobic (hypoxic) 
conditions (Montgomery et al. , 1 990). 
aerobic decarboxylated Krebs 
Glucose -----+) 2 pyruvate -----+) 2 Acetyl CoA ----t) 6C02 + 6H20 
glycolysis + + cycle + 
8 ATP 6 ATP 24 ATP 
Fig . 2-2. Pathways of aerobic metabol ism (Montgomery et al. , 1 990). 
2. Krebs (Citric or Tricarboxylic acid) cycle ,  is the second major phase 
i n  respirat ion which occurs in  the mitochondria. The pyruvate formed by 
g lycolysis is decarboxylated to acetyl CoA, which enters the Krebs cycle by 
condensation with oxaloacetate, where it is oxidised to C02 and water (fig . 2-
2) .  No 02 is absorbed in any part of the cycle (Kader, 1 987; Montgomery et 
al. , 1 990; Soule, 1 985) . 
3. Electron transport system, the last major phase of respi ration ,  where 
low-energy nicoti namide adenine dinucleotide (NAD) is reduced to the high­
energy form NADH. Electrons are transferred by a series of inte rmediate 
23 
compounds (Le. several cytochromes, a qu inone, and a riboflavin-containing 
prote i n )  u l t imate ly to combine with 02 to form H20 and produce ATP 
(Montgomery et al. , 1 990 ; Soule, 1 985). 
2.2.2 Anaerobic respiration 
The normal atmosphere is rich in 02 (20.95%), thus 02 is avai lable in 
the plant organ. However, under various storage conditions (such as under 
low 02 o r  h i g h  C02 en ri chment condit i ons )  the  amount of 02 i n  the 
atmosphere may be l imiting and insufficient to  maintain ful l  aerobic metabolism 
(Wil ls et al. , 1 981 ) .  U nder these condit ions the tissue can initiate anaerobic 
respiration, in which glucose is converted to pyruvate through the process of 
glycolysis, but the pyruvate produced (rather than going into the Krebs cycle) is 
metabolised into either lactate ( in animals) or acetaldehyde (AA) and ethanol 
(ETOH)( in plants) (see fig. 2-3) (Wills et al. , 1 98 1 ) .  Conversion of pyruvate to 
AA and C02 is catalysed by the enzyme carboxylase and the cofactor thiamin 
pyrophosphate. Acetaldehyde is converted i nto ETOH by the act ion of the 
enzyme alcohol dehydrogenase. Two moles of ATP and 21 k calories of heat 
energy are produced i n  anaerobic respi rat ion per mole of glucose (Kader, 
1 987). Anaerobic respi ration produces much less energy per mole of g lucose 
than does aerobic respi ration ,  but it does al low some energy  to be  made 
avai lable to the tissue under adverse conditions (Wills et al. , 1 981 ) .  
Pyruvate 
C02 Acetaldehyde 
y 
� Lactate 
-----+) Ethanol 
Fig. 2-3. Pathways of anaerobic metabolism (Wills et al. , 1 981 ). 
24 
2.2.3 Extinction Point (EP) or Anaerobic Compensation Point (ACP) 
The external 02 concentration at which a shift from aerobic to anaerobic 
resp i rat ion  occurs is known as the 'Ext i nction  Poi nt' (EP) or anaerobic 
compensation point (ACP). Figure 2-4 taken from Kader ( 1 987) shows the 
effects of 02 concentration on aerobic and anaerobic respi ration .  The 02 
concentrat ion at EP  depends on several factors such as species, cu ltivar, 
physiolog ical stage of maturity and temperatu re (Biale, 1 960a; Fidler, 1 951 ; 
Kader, 1 987; Wills et al. , 1 981 ) .  
c: 
0 / 
'+=i / (.) % :J "C 
e 
a. 
N 
0 
u 
-
0 
Cl) ... � 
Cl) 
> ';:i ca 
Q; 
a: 
0 
0 -
'< 
a: 
/t' / , 
10 20 
/ 
/ 
ESP\RA'f\ON 'r AEROB\C R 
30 
% °2 
Fig. 2-4. A schematic representation of the effects of 02 concentration 
of the external atmosphere on aerobic and anaerobic respiration. The arrow 
indicates the EP (Redrawn from Kader, 1 987) .  
-
10 0 
25 
The t ransitio n  zone between aerobic and anaerobic respi rat io n  was 
examined by ear1y workers (Blackman, 1 928;  Fidler, 1 9�1 957Thomas and 
Fidler, 1 933) who reasoned that the salient feature of th is transition was the 
EP. Blackman (1 928) working with Bramley's Seedl ing apples, defined the EP  
as t he  t h reshold 02 concent rat ion wh ich  just ext i nguishes a l l  aerobic 
resp i rati o n .  Thomas and F id le r ( 1� ) approached t he  concept more 
empirical ly by defin ing  the EP as that concentration of 02 at which alcohol 
p roduction  ceased. Kidd and West ( 1 937) reported that the t h resh old 02 
concentration for alcohol formation was different for different stages of maturity 
of apples. They did not detect alcohol in immature fruits even at 0 .5% 02' 
while ripe and yel low apples produced appreciable quantities of alcohol even in 
air. Singh  (1 937) found the critical 02 concentration for mangoes to be 9 .2%. 
I 
Platenius ( 1 9� determined the critical 02 concentration to be 1 % for s pinach 
and snap beans, 2 .5% for asparagus and 4% for peas and carrots when held 
for several days at 20°C. 
/ 
Boersig et al. ( 1  �8) re-examined the aerobic - anaerobic respi ratory 
transition i n  pear fruit .lnd cultured pear fruit cells. They argued that the use of 
alcohol p roduction by ear1y workers as an indicator of the shift from aerobic to 
anaerobic respi ration was unacceptable, since ethanol is now known to be a 
normal constituent of many fruits held under aerobic conditions. In addition the 
methods of analysis for alcohol used at that time were less sensitive than the 
more recent chromatographic techniques. Consequently the EP defined by 
(.VI 
early research workers was"untenable concept based on archaic analytical 
methods. Boersig et al. ( 1 988) therefore suggested the use of C02 evolution 
rather than alcohol  p roduction as an i ndicator of the sh ift from aerobic to 
anaerobic respi ration .  Based on that concept, these authors proposed an 
alternative terminology, the 'Anaerobic Compensation Poi nt' (ACP),  which they 
defi ned as the exte rnal 02 concent rat ion at which C02 p roduct i o n  was 
minimum. The EP defined by early workers is probably erroneous as aerobic 
26 
respiration would continue at some reduced level even below the EP as shown 
� 
i n  Kader's diag ram (fig. 2-4) .  This makes the ACP"more sensible term from a 
physiological point of view. 
The ACP shifted to lower 02 concentrations after extended exposure of 
the cells to lower 02 atmospheres and it shifts to higher 02 concentrat ions as 
fruits matured physiological ly or as the diffusion coefficient of cel l  suspensions 
decreased (Boersig et al. , 1 988; Fidler, 1 951 ; Thomas and Fidler, 1 933) .  
2.2.4 Respiration quotient (RQ) 
Respiration quotient (Ra) is the volume or molecular ratio of the volume 
of C02 produced to 02 simultaneously consumed during respiration (O�Ynn 
and Witham, 1 983 ; Berrie et al. , 1 987) .  // 
The Ra usually gives an indication of the type of respiratory substrate 
being metabol ised as the main source of respiration (Burton ,  1 982 ; Sal isbury 
and Ross, 1 985;  Wil ls et al. ,  1 98t) :  However a precise identificat ion of the 
,. 
type of substrate being respired-by a tissue through Ra values is impossible .  
If d i fferent subst rates ar.&· 'be in g  respi red s imu ltaneously, t he  RQ value  
obtained is on ly  an average o f  the Ra values of each ind ividual substrate 
(Oevl i n  and Witham, 1 983) .  The Ra has the greatest advantage of being a 
})t
fie' -;
'
;�
-'
i nde��ndent of the amount of respi ri ng material .  Accord ing to 
/' Hackney (1 944) ,  alcohol analyses are not necessarily a true i ndex of anaerobic 
\ 
f�spi ratLon.- 'Only determination of the RQ can be regarded as a true i ndex of 
""--- . ..' . 
the nature of respi ration. 
Metl itski i  et al. ( 1 972) reported that the RQ general ly  i ncreases with 
ripen ing and senescence of most fruits and vegetables. An i ncrease in  Ra 
indicates an i ncreased use of organic acids rather than carbohydrates or fatty 
acids as the major substrate for respi ration.  Since organic acids have more 
27 
02 per carbon atom than sugars or fatty acids, they therefore require less 02 
consumption for the production of C02 (Wills et al. , 1 981 ) .  Neal and Hulme 
(1 958) reported that addition of organic acids to the tissues of post-cl imacteric 
apple fruit i nduced a large increase in- C02 output and l i tt le change  in  02 
uptake, thus i ncreasing the Ra values. However this phenomenon was not 
observed i n  precl imacteric fruit , suggesting  that the abil ity to utilise o rganic 
acids in fruit i ncreased with senescence. Kidd and West ( 1 938) observed that 
the Ra of Bramley's seedl ing apples, ripened i n  ai r at 22.5°C, rose during the 
climacteric from 1 .02 to 1 .25. Apples have a high content of malic acid which 
is uti lised by the fruit in the cl imacteric stage (Burton,  1 982) .  Simi lar f indings 
have been reported by other investigators (Burton, 1 982; Hulme and Rhodes, 
1 971 ; Neal and Hulme, 1 958) . 
The increase in  Ra of apples duri ng and after the cl imacteric, according 
to Hartmann ( 1 962) is not a un iversal phenomenon in  fru its which exhibit a 
climacteric phase, but only in those, such as apples and pears i n  which an acid 
is respired during the climacteric. For instance, Kidd and West ( 1 925) reported 
that preclimacteric apples have an RQ of about 1 .04, a value consistent with 
carbohydrate as the main respi ratory substrate. This Ra rises to about 1 .4 
during the respiratory climacteric, a finding consistent with an increased use of 
organic acids (mainly malic acid, in addition to sugar) as respiratory substrates. 
Conversely, precl imacteric banana fruit have an Ra of about 1 ; this d rops to 
about 0.76 during the climacteric rise but is again equal to 1 at the peak of the 
respi ratory cl imacteric (Palmer, 1 971 ) .  The value of 0.76 could imply util ization 
of fat for a short period befo re carbohydrates once aga in  becomes the 
dominant substrate (Tucker and Grierson ,  1 987) .  
Modified atmosphere (MA) conditions can alter the RQ which in turn wi l l  
affect the atmosphere created by the respiration of the commodity with in  the 
package (Kade r  et al. , 1 989 ; Tomki ns ,  1 965) .  Ra in apples decreased 
markedly in gas mixtures containing high C02 and low 02 or high C02 alone 
28 
compared to that i n  ai r storage (Metlitskii et al. , 1 972 ; Fidler and North,  1 967; 
Fidler, 1 950) .  Accord ing to James ( 1 953) when respiration has settled to a 
steady state , the RQ is usual ly determined by the chemical nature of the 
substrate being consumed. At low 02 concentrations the results are complex, 
because anaerobic processes release additional CO2 ; but above 5-1 0% 02 
complete ox idatio n  of the respi ratory subst rate is l i ke ly to dom i nate. A 
reduction i n  RQ value by CA also indicates a retardation of the ripening and 
senescence of fruit and a reduced catabolism of organic acids, resu lt ing in 
higher acid retention  under CA conditions (Kader, 1 986). Very high RQ values 
usually i ndicate anaerobic respiration (Kader, 1 987).  
2.2.5 Respiration patterns of fruits 
The pioneeri ng work of Kidd and West , ( 1 922 , 1 930) made t he  fi rst 
major contribution to the study of patterns of respiration i n  fleshy fru its. They 
showed that the onset of visible ripeni ng changes of detached unri pe apples 
was marked by an upsurge in the rate of respi ration.  Kidd and West coined 
the term 'respiration climacteric' to describe what they saw as a critical phase 
in the life of the fruit. The climacteric was seen as a period of reorganisation 
that was a necessary prelude to ripening. 
Fruit have been classified as 'climacteric' and 'non-cl imacte ric' on the 
basis of respi ration and C2H4 product ion patte rns duri ng maturat ion and 
ripening (Biale and Young, 1 981 ; Biale 1 960a, 1 964 ; McMurchie et al. , 1 972).  
Climacteric fruits, such as apple, banana, mango, pawpaw and avocado, which 
are harvested ful ly developed but unripe, exhibit a decl ine in their respiration 
rate to a min imum (precl imacteric min imum) before rising  (cl imacteric rise) at 
the time of onset of ripening to a peak (cl imacteric peak) after which it declines 
(post c l imacte ric) .  F igure 2-5 shows the phases of the cl imacteric period 
(Watada et al. , 1 984) .  According to Rhodes ( 1 970, 1 980a, b) the sign ificance 
.,// 
29 
of the cl i macteric phase is t hat i t  marks the t ransit ion from g rowth and 
maturation phases in  the l ife of  the fruit to  the onset of senescence. It i s  the 
'beg inning of the end' as Biale ( 1 960b) puts it. 
z 
o 
t­
u 
:> 
o 
o 
0:: 
,0.. 
' v 
J: 
N 
U 
0:: 
o 
N 
o 
u 
� 
0 , 
W 
t­
<X 
a: 
Cl imact er ic peak  
� 
Pastc l imacter ic 
� l imacter ic 
Prec l imccter ic  
J 
� Precl imacteric m ir.'imum 
TIM E 
Fig . 2-5.  Phases of the cl imacte ric pe ri od (Redrawn from Watada, 
1 984). 
30 
Known factors that i nfl uence onset of the cl i macteric i n  f ru its  are 
temperatu re ( lowe ri ng  the t empe ratu re gene ral ly  de lays o nset o f  t he  
cl i macteric; Kidd and West, 1 930), 02 and C02 concentration,  �nerallY 02 y 
mixtures richer than ai r tend to hasten the climacteric, those poorer than air to 
de lay it, a nd  someti mes to depress it 's i ntensity (Rhodes ,  1 970) .  The 
climacteric, according to Forward (1 965) is an aerobic phenomenon and fails 
to appear in the absence of 02. High C02 concentrations (5% or 1 0%) tend to 
delay and depress the cl imacteric in apples and pears (and a combination of 
low 02 and high C02 elimrnates it in banana), and the onset of the cl imacteric 
is hastened by traces of ethylene (Melford and Prakash, 1 986; Peacock, 1 972 ; 
Pratt and Goeschl, 1 969). 
An upsurge in respiration occurs in cl imacteric fruits allowed to ripen 
while sti l l  attached to the plant (except avocado) and in fruits detached after 
maturity has been reached (Biale, 1 964).  
In  non-climacteric fruits, such as strawberry, citrus fruits and pineapple, 
respi ration and C2H4 production continue to decl ine steadi ly after harvest 
(Biale , 1 964 ; B iale and Young ,  1 981 ; Rhodes, 1 970, 1 980a, b). Figure 2-6 
taken from Biale ( 1 964) shows the stages in fruit development and maturation 
and respi ratory trends which characterise climacteric and non-cl imacteric fruits. 
G) 
C) 
C 
to 
.c 
o 
G) 
> 
� 
.!S! G) 
CC 
31 
Fru it �owth 
Respiration 
non-climacteric 
o ________ .-__ �-------===�-----� 
---Maturation---..If , J---G)-
I-�+Cel l  enlargement-l I en :  g .; i r-c:-I G) 
._ I I .- I 0 
_ .� I I 
c: I en 
_ � I I Q) 
I G) 
G) I a. I C 
U - '
 G) 
cc Cl) 
Fig . 2-6. Stages in  fruit development, maturation and respiratory t rends 
which characterise climacteric and non-cl imacteric fruits (Biale, 1 964) .  
32 
C l imacter ic fru it at the end of g rowth undergo a large i nc rease i n  
resp i rat ion accompan ied by  marked changes i n  composition and texture, 
whereas non-c l imacteric fru it show no change in respi ration that can be 
associated with d istinct changes in composition. Ripening in climacteric fruit is 
associated with large i ncrease in C2H4 product ion  ( B iale, 1 960b) .  The 
increase in  respiration and C2H4 production can be induced prematurely in 
climacteric fruit by treating them with a suitable concentration of C2H4 or its 
analogues (such as propylene, acetylene). The ripen ing process is irreversible 
once endogenous (autocatalytic) C2H4 production increases to a certain level 
(McG lasson ,  1 985) . I n  contrast, an unnatural c l imacteric- like resp i ratory 
increase can be induced in nonclimacteric fruit by treating them with C2H4 o r  
its analogues (Biale and Young, 1 962, 1 981 ) .  Yet this increased respiration is 
not accompanied by an increase in endogenous C2H4 production ,  and the 
respiration rate usually subsides fairly rapidly upon removal of the exogenous 
C2H4 . H owever ,  C2H 4 t reatment  does acce le rate senescence i n  
nonclimacteric fruit. Ethylene treatment of climacteric fruit does not change the 
climacteric patterns and magn itude of respi ration and C2H4 production, thus 
response of respi ration and C2H4 biosynthesis to C2H4 are concentration 
i ndependent .  I n  contrast i n  n onc l imacteric f ru i t ,  the magn itude of the 
respiratory response increases as a function of C2H4 concentration,  but this 
increase in respiratory activity is not accompanied by C2H4 production .  The 
internal C2H4 levels in climacteric fruit can range f rom low to h ig h ,  but i n  
noncl imacteric fruit levels are low (Burg and Burg ,  1 962 ; McMurch ie et  al. ,  
1 972 ; Reid and Pratt , 1 970; Yang ,  1 985, 1 987) .  
2.2.6 Methods of  estimating respiration rate 
Accurate estimation of respi rat ion rate of fruits ( including apples) and 
other plant organs is important in determining the rate of metabolic activity i n  
the p lant organ. I t  i s  also important i n  the estimation of skin resistance to gas 
d iffusion. Various methods of estimating respiration rate or rate of flux of bulky 
33 
plant organs have been reported but none of them is enti re ly satisfactory. 
These methods are either based on di rect measurements of C02 and/or 02, 
o r  on  i ndi rect dete rminat ion by mon itori ng pressure or  vol ume variations 
resu lt ing from C02 evolution and 02 uptake (Forcier et al. , 1 987). Some of 
the methods that have been used are briefly reviewed i n  the following sections. 
2.2.6.1 Flow through system 
A flow through system i nvolves incubati ng the plant organ i n  a sealed 
contai ner throug h  which is passed a known flow of gas. The exit stream is 
passed through a column containing a suitable C02 absorber, such as sodium 
hydroxide , wh ich absorbs the respi red C02' The amount of C02 production 
during a specific duration is determined by subsequent titrimetric or g ravimetric 
analysis of the absorbed material .  Alternatively, C02 and/or 02 concentration 
differences between the i nlet and outlet of the container can be determined 
using a gas chromatograh (TCO) or an infra red gas analyser ( IRGA) and the 
respiration rate calculated on the basis of commodity weight,  flow rate, and 
change i n  C02 o r  change i n  02 concentrat i on  ( Bu rg and  B u rg ,  1 965 ;  
Cameron, 1 982; Kader, 1 987; Reid et a/., 1 973; Solomos, 1 989). 
Accord ing  to Ben-Yehoshua and Cameron  ( 1 988) the flow through 
system is  especial ly suited for the measurement of C02 and C2H4 flux since 
these gases can be scrubbed from the i ncoming gas flow so that on ly  the 
amounts produced by the organ are present in the effluent stream of ai r. It can 
also be used fo r measuri ng water f lux if the vapour  pressu re or dew point is 
measured in  both inlet and outlet streams. 
It is extremely difficult to measure 02 accurately using th is  approach, 
since it  is necessary to measu re accurately the difference between the i nlet 
and outlet streams, fol lowing the relatively small amount of 02 uptake by the 
34 
product. It may be necessary to uS,e very slow flow rates or even a closed 
system for a g iven time i nterval to monitor 02 flux  i nto the o rgan  (Ben­
Yehoshua and Cameron, 1 988). 
2.2.6.2 Closed system 
In this method, samples are sealed in a container and the accumulation 
of C02, and/or depletion of 02 in the atmosphere of the sealed container are 
measured after a specific duration usual ly one or two hours. For a known 
weight of ·commodity in a known volume of free space, respi ration rate (cm3 
C02 o r  02 kg- 1 h- 1 ) can be calculated (Banks,  1 984a, b ;  Burg and Burg ,  
1 965; Rajapkse et al., 1 989a, b, 1 990). 
The p rincipal l imitat ion of this method is that it is a non equi l ibrium 
system, and the depletion of  02 and accumulation of  C02 or other  g ases 
(especially C2H4) may affect the tissue and its respiration rate (Kader, 1 987) . 
However these problems can be overcome by keeping the incubation period to 
the min imum possible and/or by plac ing C02 and C2H4 absorbers in  the 
sealed container to absorb these gases if desired . Re l iable est imate of 
respiration using this method have been reported by various authors i ncluding 
Banks (1 984a, b), Burg and Burg (1 965) ; Cameron (1 982) and Rajapkse et al. , 
1 989a, b, 1 990) . In the current study, estimates of respiration rates of apples 
were obtained using the closed system. Conscious of the l imitation posed by 
t h i s  tech n i que ,  i ncubat i on  per iod was kept to the m i n imum poss ib le  
(approximately one hour) .  
2.2.6.3 Tissue disc respiration 
Studies with tissue discs have faci l itated experiments on the effects of 
exogenous substances on tissue physiolo�y, respiration, metabolic pathways 
and react i on  mechanisms (par/f987 ; ap Ree\ 1 966 ; Pa lme r  and 
35 
McGlasson ,  1 969; Gude and van der .l?las, 1 985; Lee et al. , 1 970 ; Atta-Aly et 
.. 
al. , 1 987}. I n  this method whole/ i ntact fruit a re sanitised or steri l ised by 
washing with 80% ethanol (Atta-Aly et al. , 1 987) or soaked for a few minutes i n  
a solution of 20% commercial bleach (Parkin,  1 987; Saltveit and Mencarell i ,  
1 988). A steri l ised cork borer is used to take discs of tissue usually from the 
equatori al region of the fruit. Fru i t  discs are resteri l ised by immers ing  i n  
ethano l .  The cut t issue s l ices are usual ly suspended i n  a buffered iso­
osmoticum of sucrose, mann itol or other carbohydrate (Parkin ,  1 987; Pesis 
and Ben-Arie ,  1 986). Disc respi rat ion is then determined i n  a i r-saturated 
mannitol and potassium phosphate. According to Parkin ( 1 987) t he rates of 
02 uptake of discs suspended in ai r-saturated, buffered mann itol are s imilar to 
the rates of C02 evolution for discs i ncubated in an air-tight flask as measured 
by head space gas analysis using gas chromatography. This method requires 
that all procedures are performed under steri l ised conditio ns (Edwards et al. , 
1 983; Gross and Saltveit, 1 982) .  
The primary l imitation of  this method is  due to the susceptibil ity of  the 
cut tissue to m icrobial contamination and decay, which renders it unsuitable for 
lengthy study (Parki n,  1 987; ap Rees, 1 966). In the absence of suspending 
medium ,  t issue sl ices are p rone to desiccate or re-di rect thei r physiology 
toward callus formation (Lee et al. , 1 970) ,  a metabolic activity that may not be 
representative of the i ntact tissue during certain periods of its life cycle or be 
the focus of intended study (Parkin,  1 987). Wounding of the tissue is known to 
i ncrease respiration (Burton,  1 974; Kahl ,  1 974). In v iew of these l imitations, 
whole fruit were used in this study. 
2.3 Gas exchange In fruits 
Gas exchange in fru its and othe r bulky p lant o rgans is by passive 
process of diffusion : the tendency for a h igh concentrat ion of one type of 
mo lecu le  to move down a concentrat ion g rad ien t  to a n  a rea  of l owe r 
36 
concentration .  Diffusion takes place because of the  kinetic energy of  gas 
molecules and does not require the direct expenditure of metabolic energy by 
the fruit tissue (Rahn et al. , 1 979). The lower concentration of 02 i nside the 
f ru it bri ngs new 02 molecules from the  external atmosphere ,  whe re t he  
concentration is usually h igher. Conversely, the concentration of C02 inside 
the f ru it causes those molecules to d i ffuse toward the outside,  whe re the 
concentrat ion  is very low [0 .03%] (Burton ,  1 982 ). I n  simple terms gases 
diffuse according to concentration gradients from regions of high concentration 
to regions of low concentration (Kader et al. , 1 989). 
Ideal ly,  when there is no pressure-driven mass flow, each g as i n  a 
mixture behaves independently of al l  other gases, diffusing in  a di rection 
dete rmined by its own g radient in  concentration. The rate at which a gas 
moves depends on the properties of the gas molecule, the magnitude of the 
concentrat ion  d i fference ,  and the physical p ropert ies of any i nterven ing  
barriers, such as thickness, su rface a rea, density and molecu lar structure 
(Barrer, 1 951 ) .  
In  fru its and other  bu lky p lant o rgans ,  rates of gas d iffusio n  are 
determined largely by the respiration rate, stage of maturity, physiological age ,  
commodity mass and volume, pathways and barriers for diffusion , properties of 
the gas molecu le, concentration of the gases in the atmosphere surrounding 
the commodity, magnitude of gas concentration difference across barriers and 
temperature (Burton, 1 982 ; Banks, 1 984a, b; Smith and Stow, 1 984).  
The p roperties of a barrier  can sign ificantly i nfluence the rate of gas 
movement. For instance, 02 moves about 1 0,000 times more slowly i n  water 
than in  air for a g iven concentration difference (Himmelblau, 1 965). Movement 
of a gas directly through a solid (eg . plastic) or l iquid film involves adsorption 
o nto the fi l m  surface, d iffusion across the fi lm  and  evaporation from the 
opposite surface. Thus, both solubil ity and diffusivity are important for diffusion 
across films (Stannett 1 968, 1 978). 
2.3.1 Laws of gas diffusion 
37 
Many of the diffusion processes of relevance to this thesis are governed 
by Fick's First Law of diffusion, which applies to all gases and has often been 
used to study gas exchange in fruits and other bulky plant organs (Ben­
Yehoshua et al. , 1 963 ; Burg and Burg, 1 965; Burton,  1 974, 1 978 ; Cameron,  
1 982 ; Cameron and Reid, 1 982 ; Cameron and Yang, 1 982; Marcel l in ,  1 963, 
1 974 ; Sastry et al. , 1 978; Trout et al. , 1 942) and in  leaves (Nobel ,  1 974, 1 983) .  
Within l imits, Fick's first law of diffusion states that the movement or  flux 
of a gas in or out of a plant tissue depends on the concentration drop across 
the barrier involved, the surface area of the barrier, and the resistance of the 
barrier to diffusion (Burg and Burg ,  1 965). A simpl ified version of Fick's Law 
can be written as follows: 
[2. 1  ] 
where the total flux of species j ( ie. 02' C02' C2H4' water vapour, etc) per unit 
t ime (1j i n  cm3 s- 1 ) is moving across a barrier which has surface a rea (A) 
(cm2) and resistance to diffusion of species j of Rj (s cm-1 ) .  The drivi ng force 
for the movement depends on the concentration difference across the barrier 
(��). 
Some researchers (Brooks, 1 937; Burg and Burg ,  1 965 ; Burton ,  1 950, 
1 974 ; Cameron, 1 982 ; Cameron  and Reid, 1 982 ; Cameron and Yang , 1 982) ,  
contended that the use of the simpl ified form of Fick's law to the study of gas 
exchange of bulky plant o rgans is only valid as long as the resistance of the 
tissue is i nsig n if icant re lative to the resistance of the  ski n ,  and t hat the 
thickness of  the skin is  an insign ificant part of  the fruit d iameter. I f  resistance 
38 
with i n  the  fru it becomes sig n if icant, for example when a fruit softens or  
becomes water soaked, the equation ceases to be valid, si nce concentration 
gradients wil l  then be established between the skin and the fruit centre. 
2.3.2 Skin resistance to gas diffusion 
Most studies on gas exchange i n  fruits and other bulky plant o rgans 
indicate that the skin represents the primary significant barrier to gas exchange 
between the commodity and the atmosphere surrounding it (Burg and Burg ,  
1 965; Burton, 1 950 ; Cameron, 1 982 ; Hardy, 1 949;  Montero, 1 987; Solomos, 
1 985; Soudain and Phan Phuc, 1 979 ; Ulrich and Marcell in ,  1 968). Hal l  et al. 
( 1 954)  also contended that the most important cause of resistance to gas 
diffusion was the skin.  Many other workers have reached similar conclusions. 
According to Burg and Burg ( 1 965), Burton ( 1 982),  Soudain and Phan Phuc 
(1 979) and Ulrich and Marcell in ( 1 968) resistance of apple skin to gas diffusion 
is higher than that of the flesh. Solomos ( 1 987) observed that depending on 
cultivar, the resistance of the skin of apples is 10 to 20 fold higher than that of 
the pulp. On the contrary, Ben-Yehoshua et al. (1 963) observed that the site 
of resistance in avocado fruit changed during ripening. Thei r results i ndicate 
that before and during the climacteric, the major barrier to gas exchange  was 
in the peel, but the pulp became an important barrier  to gas exchange i n  post­
cl imacteric avocados. The increase pulp resistance probably arose because of 
the clogg ing of the ai r space with cel lu lar sap (Ben-Yehoshua et al. , 1 963; 
Sacher, 1 973).  
Resistance of fruits to gas diffusion has been shown to increase during 
maturation and ripening. As plant o rgans advance in the senescence stage, 
cel l  walls and membranes begin to breakdown and cell contents fi l l  some of 
the air spaces. Consequently the resistance of the flesh to gas diffusion may 
become significant resulting in decrease in internal 02 and i ncrease in i nternal 
C02 (Kader et al. , 1 989; Trout et al. , 1 942).  Resistance to diffusion of C02 
39 
out of f ru its and vegetables increases during the maturation period ( Ben­
Yehoshua, 1 969; Kidd and West, 1 949). The period of least resistance to gas 
diffusion appears to be when the fruit is sti l l  immature (Marcel l in ,  1 974) , and 
general ly there is a marked i ncrease in  resistance to 02 and C02 diffusion 
shortly after harvest (Burton ,  1 965;  Trout et al. , 1 942) .  Resistance to gas 
diffusion continues to increase duri ng ripening (Ben-Yehoshua, 1 987) and in  
some fruits there is evidence that, duri ng  the i r  postcl imacteric stage,  the 
res istance to respi ratory gases i ncreases substantia l ly  (Marcel l i n ,  1 974 ; 
Leonard and Wardlaw, 1 941 ;  Williams and Patterson, 1 962) .  
Changes in water vapour d iffusion during  maturatio n  of bulky o rgans 
have been  characterised. Generally rates of water vapour diffusion decline 
during maturation and ripening, reaching a minimum, in  fruits, about the time of 
the climacteric and i ncreasing thereafter (Pieniazek, 1 943 ;  Sastry et al. , 1 978) . 
A n umber of workers (Leonard and Ward law, 1 94 1 ;  Markley and Sando, 
1 93 1  a, b ;  Smith ,  1 931 , 1 933) reported that transpi ration rates of bulky o rgans 
decli ne sharply in the period immediately after harvest. The peel of some  fruit 
shrivels after prolonged exposures to low vapour concentrations, and there is 
evidence that this leads to an increase in resistance to diffusion (Ben-Yehosua 
1 969 ; Smith, 1 931 , 1 954; Wilkinson ,  1 965) . 
Ski n resistance to water vapour diffusion has been  shown to be much 
lowe r than  resistance to 02' C02 ' or C2H4 diffus ion  (Cameron ,  1 982 ) .  
Waxes, and not cut ins ,  seem t o  be  the primary barrie rs t o  water vapour 
diffus io n t h rough  the ski n in leaves and bulky o rgans  ( Horrocks , 1 964 ; 
Schonherr, 1 976 ;  Sol iday et al. , 1 979 ) .  Wi lk i nson ( 1 9 65) attempted to 
determine the effects of re lative h umidity on the res istance to g aseous 
d iffus ion of apples. He found that apples tested under humid condit ions 
showed a two or threefold i ncrease in  permeabi l ity to gases over a 6 month 
period. Apples in  dry envi ronments, decreased steadi ly in  permeabi lity over 
the same period, and also shrivel led gradual ly. However, no immediate or 
sudden effects were noted. 
40 
2.3.3 Avenues to gas exchange 
Theoret ical ly,  gases diffuse th rough the pathways that offer  least 
resistance (Kader et al. , 1 989) ,  i .e . , channels fi l led with air (Burton,  1 982 ; 
1 974; Burg and Burg ,  1 965; Solomos, 1 987). In  leaves, by control of stomatal 
aperture, the resistance of the epidermal layer to gas diffusion can be altered 
so that water vapour movement from the tissue can be m i nim ised when 
adequate C02 is present in the tissue. However, in  fruits and other bulky plant 
organs, evidence of the presence of functional stomata or other active control 
mechanisms of gas exchange is lacki ng (Clements, 1 935;  Adams, 1 975).  
These organs have a much lower surface-to-volume ratio t han leaves ;  the 
distance over which gases diffuse in the tissues is very large, and respiration, 
not photosynthesis, accounts for the major metabolic source of C02 and s ink 
for 02 (Kader et al. , 1 989).  
Several investigators have attempted to identify the principal avenue of 
gas exchange i n  bulky plant organs and many conflicting reports have been 
presented. For instance, Hall et al. ( 1 954) contended that lenticels on the skin 
of apples play no role in  gas exchange. They stated that i n  mature G ranny 
Smith apples, gas exchange took place by diffusion through the skin and none 
occurred through the calyx and the lentice ls. In  contrast the majority of gas 
diffusion i n  bul ky o rgans has been shown by other  workers i n  subsequent 
studies to occur th rough the lenticels (Burg and Burg ,  1 965; Burton, 1 965; 
Burton and Wigginton,  1 970 ; Haberlandt, 1 91 4 ; Wigginton, 1 973). The role of 
l e nt i ce l s  i n  wate r  vapo ur  loss was noted  by P i e n i azek  ( 1 944 ) who  
demonstrated that when every lenticel of apples was blocked with Vasel ine, 
water vapour flux dropped by 8-20% compared to untreated fruit. In  Burton's 
view ( 1 982) ,  lenticels and stomata have only minor importance i n  water loss 
because of their sparse distribution in  fruit. 
41 
In oranges. however. the relative contribution of stomata or lenticels to 
gas exchange is unclear. Moreshet and Green ( 1 980) studied the functioning 
of stomata in  o range fruit on and off the tree. Thei r data i ndicated that the 
stomata sti l l  open and close in response to l ight and are highly effective in 
conducting water and CO2 before harvest in spite of being occluded by n atural 
wax (Albrigo .  1 972) .  However the i r  data i ndicated that the stomata stop 
functioning after harvest. 8en-Yehoshua et al. ( 1 983 . 1 985) using  sca nning 
e lectron microscope photomicrographs showed that i n  Haml in  o ranges and 
Duncan grapefruits. although most stomata were closed. some stomatal pores 
may be seen as dark open slits between the two guard cel ls on fruit stored in  
the  dark. Thus it appears that the stomata of harvested oranges are partial ly 
open and allow some gas exchange. 
In fu l ly matu red harvested banana fruit Johnson and B ru n  ( 1 966) 
reported that the stomata open in high relative humidity and l ight and close 
with low relative humidity and in darkness. 
The calyx open ing of apples has been shown to contribute to gas 
exchange (Cameron and Reid. 1 982 ; Marcel l i n .  1 974 ; Markley and Sando. 
1 931  a. b). For i nstance. Cameron ( 1 982) observed that the contribution of the 
calyx to the passage of different gases varied in different fru its. In Golden 
Delicious apples. the calyx provided for the diffusion of 42% of the C2H4. 24% 
of the C02' and only 2% of the water. I n  tomatoes. the percentages were 94. 
8 1 . and 67 respectively. 
Many researchers i ncluding Burg and Burg ( 1 965) .  Cameron ( 1 982) 
Cameron and Reid ( 1 982) .  Cameron and Yang ( 1 982) .  Clendenning ( 1 941 ) . 
have i nvest igated the contribut ion of the stem scar as an avenue for gas 
exchange in tomatoes. For example. Burg and Burg ( 1 965) found that sealing 
the stem scars of g reen peppers and tomatoes reduced C02 emanation by 
60%; with cantaloupes and grapefruits a 1 0% decl ine was noted. In o ranges. 
42 
the exchange of C02 and C2H4 through the stem scar is only twice that of the 
peel (Barmore and Biggs, 1 972).  Cameron and Yang (1 982) showed that the 
peel of tomato had 1 227 -fold more resistance to ethane than the stem scar per 
unit surface area. Brooks ( 1 937), working  with tomatoes noted that the skin of 
harvested tomato is practically impermeable to gases and any gas exchange is 
ent i rely through the stem scar. 
2.3.4 Methods of estimating skin resistance to gas diffusion 
Several approaches have been  uti l ised by researchers to determine of 
the numerical value of the resistance of the skin of fruit and other bulky plant 
organs to gas diffusion ,  none of which are entirely free of criticisms. Basically 
there are two main approaches used; these are as follows. 
2.3.4.1 Non steady-state approach 
Based on the observed net movement of gases moving i n  opposite 
directions across the fruit skin, Marcell in ( 1 963, 1 974) developed a non steady 
state approach to measu re the resistance of app le  fruit to 02 and C02 
d iffus io n .  I n  o ne system ,  hydrogen was i nt roduced i nto t he  ex te rna l  
atmosphere surround ing the apple fru it and he monitored the i ncrease in  
i nternal gas volume using a movi ng l iquid index in  a glass tube wh ich  was 
confluent with the central locule. This approach is based on the principle that 
hydrogen moves much more rapidly through both gaseous and solid phases 
than 02 or nitrogen.  Thus, the hydrogen was observed to move i nto the fruit 
much faster than 02 and nitrogen (assumed to be the primary components of 
the i nternal atmosphere) moved out. The moving liquid index ensured that the 
i nternal pressu re remained near one atmosphere. The measured rate of 
volume i ncrease combined with the known diffusivity of hydrogen in ai r was 
used to estimate the resistance coefficients of 02' Marcell i n ,  then replaced the 
hydrogen with pure C02 and estimated the resistance to C02 by comparison 
with the results obtai ned with hydrogen. 
43 
I n  a nother  approach , Cameron  and Yang ( 1 982) conscious  of the  
inherent p roblems associated with using the steady-state method. developed a 
s im ple  alte rnative approach for  the  quant itat ive measurement of skin 
resistance based on  a kinetic analysis of the efflux of preloaded gases from 
plant o rgans which did not require flux to be at steady-state. In essence, the 
method i nvolves i ncubati ng a f ruit in an atmosphere contain ing a known 
concentration of ethane, and measurement of the i ncrease in concentration of 
this gas after transferring the fruit to an ethane free container. It is apparent 
that if there is a h igh resistance to ethane movement, the measured rate of 
ethane increase in  the jar will be slow and vice versa. 
Cameron  and  Yang ( 1 982) chose ethane because it  h as s im i la r  
molecular weight to  n itrogen and 02 and has diffusional p roperties s imilar to 
those of C2H4 and 02' Besides it is neither p roduced nor  metabolised to a 
significant degree by the tissue under normal conditions. 
Cameron and Yang's ( 1 982) method is time consuming since it requires 
equil ibrat ion for several hours during the load ing and u nloading phases, and 
several ch romatog raphic analyses are performed in o rder  to establ ish  the 
effl ux ki netics. Banks ( 1 985b) usi ng some of the p ri nciples employed by 
Cameron and Yang ( 1 982) ,  developed a more rapid method, involving several 
measurements in the first two minutes of efflux, but equil ibration during loading 
was sti l l  requ i red . Both of these approaches are certai n ly time consuming. 
Based on the same principles, Knee ( 1 991 a) devised a much more rapid 
method for measu ring  the resistance to gaseous diffus ion of bu lky plant 
o rgans, such as apple fruit. I n  his method, an apple fru it is incubated in a 
sealed contai ner i n  the presence of a measured ethane concentration for a 
certain time, usually 20 minutes. The fruit is then transferred to another s imilar 
container. The ethane concentration which diffuses i nto the new container is 
measured after an equal t ime usual ly 20 minutes. This method requi res an 
estimate of the internal volume of the fruit, accessible to ethane. 
44 
The non steady-state approach to measurement of ski n resistance to 
gas diffusion overcomes some of the d rawbacks associated with the steady 
state method : the system need not be at equi l ibrium ;  the diffusion  of gases 
which are not produced in significant amounts (such as C2H4 in preclimacteric 
fruits or in vegetative tissues) can be studied; and the techniques can be 
designed such that the internal atmosphere need not be sampled. Ethane can 
be  measu red qu ickl y a nd accu rate l y  at l ow  conce n t rat i ons  by  gas 
c h romatog raphy  (Cameron and Yang , 1 982 ; Banks,  1 985b) .  Accu rate 
estimation of fruit surface area is essential for the estimation of skin resistance 
to gas diffusion using the approach. 
Despite these advantages, the primary l imitation of the efflux  approach 
in the determination of skin resistance for other physiologically important gases 
is that suitable analogs are difficult to fi nd. In addition,  the use of hydrocarbon 
gases i n  tissues with high fat content is not feasible because of the i r  h igh  
solubil ity in  l ipids. For example, avocado give unrealistically h igh  i ntercellular 
volume when ethane is used for measurement (Solomos, 1 987) .  Under certain 
ci rcumstances because of l imited amount of a i r  space with in  tissues much 
g reater flesh resistance to gas diffusion could occur and this could affect the 
measured values using the efflux method (Cameron,  1 982) .  
2.3.4.2 Steady-state approach 
Resistance of plant tissues and organs to diffusion of 02' C02 ' and 
C2H4 has been i nvestigated usi ng a steady-state approach (Burg and Burg ,  
1 962 , 1 965 ; Burton ,  1 974, 1 978 ; Cameran, 1 982 ; Cameran  and Reid, 1 982 ; 
Forsyth et al. , 1 973 ; Kidd and West, 1 949).  
The steady-state approach is  g reat l y  depende nt on accu rate 
measurement of the surface area (cm2) of the commodity, the production or 
45 
consumption rate ( ie.  respiration rate ; cm3 s- 1 ) of the gas of interest by the 
o rgan  and  t h e  conce nt rati o n  of t h e  g as i n  t he  i nt e rna l  and e xte rnal  
atmospheres (% by volume/1 00) (Ben-Yehoshua and Cameron, 1 988). 
The skin resistance to gas diffusion  (R ;  s cm- 1 ) is then calculated as 
fol lows: 
concentration g radient * surface area 
R == --------------------------------------------- [2 .2] 
, production (or consumption) rate 
The steady state approach relies on the assumption that both i nternal 
atmosphere and respi ratory rates are at equ i l ibrium,  a condition wh ich is 
difficult to ensu re .  Furthermore, i n  some bulky plant o rgans (e.g .  avocado, 
potato) rel iable est imates of the i nternal atmosphere compositio n  may be 
difficult to obtain (Banks, 1 985b) because of the compactness of the tissues. 
In addition, by definition the syst�m must be in a steady state having a 
constant fl ux of gas th rough o rgan 's ski n .  Th is is a l im it i ng  factor if the 
resistance of the fruit to 02 is being measured at a developmental stage when 
fluxes are most l ikely not to be at steady-state such as duri ng the cl i macte ric 
when there are marked changes in  the rate of production of CO2 and C2H4 
and uti l isation of 02 (Banks, 1 985b; Cameron and Reid, 1 982) .  
This approach also requ i res that the t issue must p roduce s ign ificant 
levels of the gas of interest. For example , both production rates and i nternal 
concentrations of C2H4 are often extremely difficult to detect i n  precl imacteric 
fruits or in vegetative tissues. Accurate measurement of internal concentration 
of gases can be difficult. Although i nternal samples are easily withdrawn from 
fru its with internal cavities such as apples, cantaloupes, extraction methods 
46 
used to determine the internal atmosphere of bulky organs such as avocado or 
potato can often yield inconsistent or mis leading results (Cameron and Reid, 
1 982) .  
Another drawback may result i f  wounding or oth er perturbations occur 
wh ich i nvar iab ly cause non-steady state f l uxes (Cameron ,  1 982 ) .  For 
instance, wounding has the potential to increase rate of  respirat ion,  rate of 
C2H4 production and degree of water soaking (Kahl, 1 974) any one of which 
can change diffusion behaviour markedly. 
I n  spite of these l im itat ions the steady state method can be  u sed to 
obtain usefu l information on a wide variety of gases and tissues ( Bu rg and 
Burg, 1 965; Cameron,  1 982; Cameron and Reid, 1 982) .  I n  the current study, 
reliable data were obtained using both the steady state and non steady state 
methods. 
The foregoing review clearly demonstrates that there is a d earth of 
information on factors affecting the internal atmosphere composition of fru its 
(including apples) as wel l  as the relationships between these factors and the 
atmosphere inside the fruit. There is a clear need for further research in this 
area. 
In the ensuing chapters the relationships between skin resistance to gas 
�"Jl­
diffusion ,  respiration and internal atmosphere composition of apples-flas been 
exam ined .  I n  add i t ion the re lation sh ip  between resp i rat ion and i nternal 
atmosphere composition of apples under vary ing 02 atmospheres has been 
ascerta i ned .  The effects of temperatu re and coat ing t reatments o n  gas 
exchange  character i st ics as we l l  as va r iat ion  in i n te rna l  atmo s p here 
� 
compos it i o n  w it h i n  s i ng l e  app les  wi th  t ime  i n  storag e  fl.a.& a l s o  been 
investigated . 
47 
CHAPTER 3 
GENERAL MATERIALS AND METHODS 
This chapter describes the techn iques, materials and experimental 
conditions used in this study. 
. ../', . :; � . 
3.1 Fruit supply 
• , � \v; : (' 
\ j'" - :. ·:tf1 ' ,� " ; • 
• \..,. I I  , \  I ' �. (.t .- 1'" r-." . ..... - (,-Cll. 
! J 
Freshly harvested apple,  (Malus domestlca Borkh . )  cultivars ,  Cox's 
� 
Pippin Orange, Gala, Royal Gala, Golden Delicious, Red Delicious, Sple ndour, 
Braeburn and G ranny Smith apples, count 1 25 were obtained from the New 
Zealand Apple and Pear Marketing Board in Hastings. 
3.2 Measurement of surface area 
Fruit surface area (A) was estimated (assuming that the fruit geometry 
approximated a sphere)  from an average measu rement of the t h ree axial 
diameters using digital calipers. Using the standard formula for calculating the 
radius (r) of a sphere,  the surface area (cm2) was obtained as fol lows: 
A = 4 . n . r2 [3 . 1 ] 
where n = 3. 1 41 6  
48 
3.3 Measurement of gases 
3.3.1 Analysis of Carbon d ioxide and Oxygen 
The 02 and C02 in gas samples were analysed respectively using an 
02 electrode (City Technology Ltd. London) ;  (Bar1f<s, 1 986) in series with an 
i nfra-red C02 analyser (Binos- 1 -2, Leybold-Heraeus). The 02 electrode was 
insens it ive to argon ,  an i mportant advantage ove r the use of a thermal 
conductivity detecto r fo r samples with low 02 content. Using a gas-tight 
monoject tubercul in syringe,  each gas sample was injected manually i nto the 
apparatus in a stream of n it rogen (flow rate of 25 cm3 m in- 1 ) carrie r gas 
flowing through both pieces of equipment and the response to sample injection 
measured as peak heights using a Hewlett Packard 3393A i ntegrator. 
3.3.2 Analysis of Ethylene and Ethane 
Ethylene (C2H4) and ethane (C2H6) concentrat ions (Ill 1- 1 ) i n  gas 
samples were estimated using either  a Varian 3400 or  Pye Unicam Series 1 04 
gas ch romatograph (GC) f itted with f lame ion isat ion detector (F ID )  and a 
stai nless steel activated alumina column (80- 1 00 mesh,  1 .8m long and 0.32cm 
diameter). Temperatures of the column,  injector and detector were 1 00°C, 
1 00°C and 1 50°C respectively. Nitrogen was used as carrie r  gas with a flow 
rate of 30 cm3 min-1 and hydrogen and ai r for the detector (flow rates 30 cm3 
min- 1 and 300 cm3 min-1 respectively). Samples were injected manually into 
the GC using a gas-tight or monoject tuberculin disposal syringe. 
3.3.3 Analysis of Acetaldehyde and Ethanol 
Acetaldehyde (AA) and ethanol (ETOH) (Ill r 1 ) in gas samples were 
estimated using a Pye Unicam Series GCD gas chromatograph fitted with an 
FID and a 1 0% Carbowax 20 m column (80/1 00 chromosorb WAW, 1 .8m long 
49 
and 0.32cm in diamete r) .  Temperatures of the column,  injector and detector 
were 80°C, 1 1  O°C and 1 50°C respectively. Nitrogen was used as carrie r  gas : 
with a flow rate of 30 cm3 min- 1 and hydrogen and air for the detector (flow 
rates 30  cm3 m in- 1  and 300 cm3 min - 1  respect ive ly) . Standards were 
prepared by adding 5�1 acteldehyde to 5�1 , 95% ethanol in  an empty 2 .5 litre 
bott le with a magnetic sti rrer. The bott le was placed on a magnetic sti rer to 
m ix  the contents . A concentrat ion of 799 and 729�1 1 - 1 of AA and ETOH 
(respectively) was obtained. 
3.3.4 Measurement of Internal atmosphere concentrations 
The internal atmosphere concentrations of fruit were measured using 
the fol lowing methods: 
3.3.4.1 Direct sampling method 
Direct sampl ing of internal atmospheres was carried out by the method 
desc ri bed by Banks ( 1 983) .  F ru it were submerg ed i n  wate r, a 1 . 0 m l  
disposable hypodermic syringe was fitted with a stain less steel canu la  (1 6 
g auge ,  38 mm  long , luer-fitt i ng ) .  The dead ai r space was replaced with 
satu rated sod ium ch loride solut io n  (NaCI) .  The mouth of the canu la  was 
occluded by a pin head to prevent blockage with tissue during i nsertion i nto the 
fruit. The canula was inserted into the core cavity through the calyx end of the 
fruit and withdrawn sl ightly so that the pin head remained at t he base of the 
bore-hole,  leavi ng the canula's mouth open .  The i nternal atmosphere was 
obtained by withdrawing the plunger s lowly. If l iquid from the tissue e ntered 
the syringe, the sample was discarded. Sampl ing was completed i n  less than 
25 seconds (s) to avoid any change in  respiration and C2H4 production due to 
wounding.  
After sample withdrawal, the canula was detached from the syringe and 
a septum cap was fitted to the syri nge t ip.  A gas-tight syringe,  i n  which the 
50 
dead space had been replaced with saturated NaCI solution ,  was used to take 
90J,11 gas samples by piercing through the septum cap fitted to the 1 .0ml  
hypodermic syringe. 
3.3.4.2 External chamber method 
A non-destructive method was used for repeated sampling of i nternal 
atmospheres (Banks and Kays, 1 988). 
A 2 ml glass vial from which the bottom had been removed and the top 
fitted with a 0 .4 ml p lastic tube was stuck, using polyvinyl acetate adhesive 
(PVA) , o nto the fruit su rface.  Chambers were sealed after a l lowi ng  the  
adhesive to dry for 24 hours (h), by inserting a rubber septum into the  p lastic 
tube fitted onto each chamber. The wel l  so formed i n  the plastic tube after 
seali ng the chamber was f i l led with water to prevent gas leaks through the 
septum and atmospheric contamination of gas samples during sampl ing. 
3.3.5 Measurement of skin resistance 
3.3.5.1 Ethane efflux method 
The ethane eff lux method described by Banks (1 9 85b) was used to 
determine skin resistance to gas diffusion. Each fruit was individually p laced 
in a 1 000 cm3 glass 'Le Parfait' storage container (fitted with brass coupl ings 
sealed with sil icone rubber septa) and injected with 1 rnl of pure ethane using 
an hypodermic syringe. After overnight equil ibration, samples of the container 
atmospheres were analysed for ethane content (Ci (O) . J,11 r1 ) .  A stopwatch 
was started as a single fruit was removed from its jar outside the l aboratory 
(t=O). held in front of a fan for 2-3s. then quickly rushed into the laboratory and 
sealed in a 1 000 cm3 glass jar (t=1 4- 1 6s) th rough which the contents were 
rapidly being circulated using a diaphragm pump. Samples were taken at 1 O� 
intervals for 50s. Samples of the atmosphere inside the jar were analysed for 
their ethane contents by GC with flame ionisation detector (see 3.3.2) .  
\ 
51 
Ski n resistance to gas diffus ion was calculated using the fol lowing 
formula (Banks 1 985b) : 
Ci (O) * A 
FI == ------------------
Ve * (dCeldt) 
[3.2] 
where FI was the resistance of the fruit surface to gas d iffusion (s cm-1 ) and 
Ci(O) in (1.L1 r1 ) was the internal concentration of ethane at time t == 0, A was the 
f ru it surface area (cm2) ,  Ve (cm3) the external volume,  equal to container 
v o l ume  m i nus  f r u i t  vo l ume ,  and  (dCe/dt) was t h e  rate of c hange of  
concentration of  ethane in the container bLl r1 ) .  
3.3.5.2 Steady state method 
Fruit were weighed and surface area determined as described in 3.2 . 
Fru it respiration (C02 evolution) and C2H4 production were determined by 
seal i ng  s ing le  fru it i n  580cm3 g lass sto rage jars fo r 60min  at 20 °C  and 
measuring  the diffe rence in the i n it ial and f inal gaseous contents of each 
container. Jars were usually submerged in a water bath at 20°C during the run 
to ensure both constant temperature and that no gas leakage occurred. 
Core cavity 02, C02 and C2H4 concentrations were determined by the 
direct sampling method described in 3.3.4. 1 . 
Skin resistance to gas (ie. CO2 or C2H4) diffusion  was calculated from 
the following equation  assuming that composition of the internal atmosphere 
was uniform throughout the fru it and that the fruit geometry approximated a 
sphere (Burg and Burg ,  1 965). For example skin resistance to C02 diffusion 
was calculated as : 
where. 
RC02 
A 
[C02]core 
[C02]ext 
FC02 
= skin resistance to gas diffusion (s cm-1 ) 
= fruit surface area (cm2) 
= core cavity carbon dioxide concentration (%) 
= external carbon dioxide concentration (%) 
= flux at steady state or  respiration rate (cm3 s- 1 ) 
3.3.6 Gas mixing and measurement 
52 
[3.3] 
Fru it were i ndividual ly placed in  contai ners under  continuous flow of  
humidified air o r  gas at known flow rates. Precision needle valves were used 
to mix air and n itrogen to produce the required atmospheres. The composit ion 
of the atmospheres were verified daily by taking 1 ml gas samples which were 
analysed as previously described (section 3.3). 
3.3.7 Calculation of gas concentrations from chromatograhic data 
Peak height data were used to calcu late the concentrat ions of C02 ' 
C2H4 and 02 as fol lows:  
3.3.7.1 Oxygen, carbon dioxide and ethylene concentrations 
A Hewlett Packard 3393A integrator was used to determine the peak he ight of 
eluent peaks of 02' C02 and C2H4 on the gas chromatograh (section 3.3. 1 ) . 
Sample concentrations were estimated from these areas as outli ned below: 
53 
3.3.7.2 Oxygen concentration using Oxygen electrode: 
Oxygen concentration was calculated as fol lows: 
Sample peak height '* 20.95 
:: 
----------------------------------
Mean standard peak height 
[3.4] 
3.3 .7 .3  Cal c u lat i on of the  rate of  02 u ptake and  C02 and  C2H4 
production 
The rates of 02 uptake, C02 and C2H4 production were calcu lated as 
fol lows: 
[02] in itial - [02]final 1 000 60 
F02 = -
---
-
---
-
-
--.
--
-
-
---
-
'* ( \'jar - Vfruit) '* '* [3.5] 
1 00 Wfruit T 
[C02]final - [C02]initial 1 000 60 
FC02 = ---
--
---
-
----
---
-----
--
-
-
'* ( \'jar - Vfruit) 
'* '* ---- [3.6] 
1 00 Wfruit T 
1 000 60 
'* ( \'jar - Vfruit) '* 
'* --- [3.7] 
1 000 wtruit T 
where :  
F02 
FC02 
FC2H4 
[021initial 
[02hinal 
[C021initial 
[C02ltinal 
[C2H41in itial 
[C2H41initial 
l1ar 
Vfruit 
K'fruit 
T 
= rate of oxygen uptake (cm3 kg-1 hr-1 ) 
= rate of carbon dioxide production (cm3 kg-1 hr-1 ) 
= rate of ethylene production (J.11 kg-1 hr-1 ) 
= i nitial oxygen concentration (%) 
= final oxygen concentration (%) 
= in itial carbon dioxide concentration (%) 
= final carbon dioxide concentration (%) 
= in itial ethylene concentration (J.1I r 1 ) 
= final ethylene concentration (J.11 r 1 ) 
= jar volume (cm3) 
= fruit volume (cm3) 
= fruit weight (kg) 
= time (h) 
3.3.8 Measurement of qual ity parameters 
The following methods were used to assess fruit qual ity: 
3.3.8.1 Firmness 
54 
Using  a potato peeler, 1 mm of apple sk in  was removed from two 
opposite areas on the equatorial surface of the fru it. Fruit f irmness (the force 
requi red to penetrate the cortical tissue in kg) was measured on both areas 
using a hand-held Effegi penetrometer fitted with an 1 1 . 1 mm diameter probe. 
Fruit firmness was obtained as the mean of the two measurements taken and 
converted to newtons (N) by multiplying by 9.807 (Soule, 1 985). 
55 
3.3.B.2 Soluble solids 
Un less described otherwise soluble solids concentration (%) of juice 
exp ressed f rom  two opposite s ides of the  f ru i t  equato rial su rface was 
estimated using a hand-held Atago N-20 refractometer (Model N,  McCormick 
Fruit Tech., brix range from 0 - 20% at 20°C). The refractometer was zeroed 
using d isti l led water. The prism surface and the l ight plate were tho roughly 
washed and dried with a clean soft tissue paper between each reading. The 
two readings taken on each fruit were averaged prior to data analysis. 
3.3.B.3 Fruit skin colour 
Fruit skin background colou r was measured at any two green parts on  
the  equatorial surface using a Minolta chromameter (CR-1 00) . Skin colour 
was expressed as hue ang le . Hue angle values decrease as skin colou r 
changes from green to ye l low (Litt le ,  1 975) . Thus h igh  hue ang le values 
indicate an intense green colou r. The two readings taken on each fruit were 
averaged prior to data analysis. 
3.3.9 Data analysis 
Unless stated otherwise, Statistical Analysis System (SAS) prog rammes 
(SAS/STAT Use r's Guide , 1 988)  were used to ana lyse data f rom  e ach  
experiment for Analysis of variance (ANOVA) , means, standard deviations, 
and standard errors. Mean comparisons were also carried out by Duncan's 
Mult iple range test at 5% and 1 % level of significance (Duncan, 1 955). Unless 
stated othe rwise, l i near and non l i near reg ression and correlat ion analysis 
were also carried out as described by Steel and Torrie ( 1 980) .  
\ 
\. 56 
CHAPTER 4 
ESTIMATING SKIN .RESIST ANCE TO GAS DIFFUSION IN APPLES. 
4.1 ABSTRACT 
Skin resistance to gas diffus ion (R)  values of freshly harvested apple 
cu lt ivars , Cox's Orange P ipp in ,  Ga la, Royal Gala, Golden Delic ious ,  Red 
Delicious, Splendour, Braeburn and Granny Smith were obta ined us ing n on­
steady state (ethane efflux) and steady state methods at 20±1 °C. 
R was cu lt ivar dependent w ith fresh ly harvested B raebu rn app les  
having the h ighest mean R and Royal Gala the lowest. There was a l inear 
relationship between skin resistance to ethane diffusion (RC2H6) and ethylene 
diffus ion (RC2H4) of individual  apples with in cu ltivars. Th is  suggests that 
RC2H6 and RC2H4 are i ndeed very s im i lar .  Although the re was a large 
degree of variation in R values of individual apples within  each cu ltivar, the 
close relationsh ip between the two independent estimates of R confirmed that 
this was real fru it to fru it variat ion rather than measurement error. I n  contrast, 
estimates of skin resistance to C02 diffusion (RC02) and RC2H4 estimated 
concurrent ly by the steady state method were different and the mean RC02 
was h igher  than RC2H4' The relationsh ip between RC02 and RC2H6 in  
combined data set for all cu ltivars was hyperbo l ic, ind icating that C02 may 
diffuse through additional routes to those available for 02 ' C2H4 and ethane e 
(C2H6)' 
,/ 
Respirat ion rate of Cox's Orange Pippin apples were nearly twice as 
fast as Splendour, Granny Sm ith or Braeburn apples and a th ird h igher  than 
Gala, Royal Gala and Golden Del icious apples. I n  fresh l y  harvested fru it, 
57 
respi ration rate appeared to be independent of RC2HS (both within  i ndividual 
cultivars and in a combined data set for all cultivars). 
In spite of their intermediate respiration rate, Braeburn apples had lower 
interna l  02 concentration ( [02] i ) than the other cultivars and t h is c ould be 
related to their high R and low intercellular space volume. The mean [02]i in 
freshly harvested Splendour, Golden Delicious, Gala and Royal Gala apples 
were about a fifth greater than in Cox's Orange Pippin and half as m uch  again 
as in  Bra eburn app les .  O n  t he  other  hand  t he  average i nterna l  C02 
concentration ([C02] i) in Braeburn and Cox's Orange Pippin were nearly three 
fold h igher than in Splendour and twice h igher than in Gala, Royal Gala and 
Golden Del icious apples. There was a decreasing exponential  relationship 
between [02]i and RC2HS but an increasing relationship between [C02] i and 
RC2HS of individual apples for all cu ltivars. Thus, the magnitude of R affects 
internal atmosphere composition for a given external atmosphere composition . 
The rate of C2H4 evolution, internal C2H4 concentration ([C2H4]i) and 
quality indices of freshly harvested fruits d iffered between cultivars . Freshly 
harvested Braeburn apples had the highest mean f irmness and t he  lowest 
soluble solids content compared to the other cultivars, whi lst Splendou r  apples 
had the h ighest soluble sol ids content and Granny  Smith apples were the 
greenest fruit. 
4.2 INTRODUCTION 
"f,t1e skin of apples presents a much greater barrier to gas diffus ion than 
the 6fBurton , 1 978}. It therefore plays an important role n ot o n ly as a 
mechan ical protection for the tissues beneath but also as a partial regu lator of 
the  i n te rn a l  a tmosphere compos i t ion and consequent ly  p h ys i o l og ica l  
processes occurring in the fru it (Cameron and Yang, 1 982; see chapter 2 for a 
review of R as a factor affecting the internal atmosphere composit ion of fruit). 
58 
Magness and Diehl ( 1 924) contended that the storage quality of apples was 
.... Cl! 
closely associated with skin condition and it l&- important in  determin ing the 
resistance of the fruit to decay and wilting. 
-I n  apples, the large degree of variat ion in R of i ndividual frui t  is well 
known .  Kidd and  West ( 1 938, 1 949) recognised that th is ,  togethe r  with 
variation in the respiratory rates between fruit, caused major differences in the 
composit ion of the i nternal atmospheres of fruit. Burton (1 974) emphasised 
the s ign if icance of natural variat ion i n  R of f ruits when  setti ng l im its  for 
control l ing the composition of the atmosphere within CA stores. Since that 
t ime ,  the  concept of skin diffusive resistance and flesh resistance to gas 
diffusion and thei r physiological significance in  postharvest technology have 
been further  i nvestigated (Banks, 1 984, 1 985a; Cameron and Reid ,  1 982 ; 
Solomos, 1 982, 1 987 ; Soudain and Phan Phuc, 1 979) . Whi le the m ean R 
values of small samples of populations have been reported, the significance of 
the variation around the mean values and the effects that this variation may 
have on the physiological response to externally imposed atmospheric regimes 
have been largely ig nored, despite the fact that he re i n  may l i e  a major  
component of  the  cause of variabil ity in  qual ity of  fruits stored under  such 
conditions. 
Only l imited information is available on cultivar variation in  R (Banks, 
1 985a;  Came ron ,  1 982 ; Knee ,  1 991 ) though such i nfo rmation  cou ld  be 
important in explaining observed cultivar differences in sensitivity to MA or CA 
condit ions .  Furthe rmore ,  on ly  l im ited research has been  conducted to 
measure seasonal changes in R of fru its even though it is  wel l known that 
there are seasonal variations in sensitivity to low 02 (Marcell in ,  1 974). 
Knowledge of R may also provide some valuable information on some 
of the physiological disorders that develop in some apple cultivars during CA 
storage .  Furthermore ,  knowledge of R is needed for studying the nature of 
59 
ox idases that may be involved i n  fruit respi rat ion and also for p redict ing 
minimum gas levels that can be safely used in CA storage (Solomos, 1 987). 
Information on R (as well as internal atmosphere composition and respi ration 
rates) of  different apple cultivars grown in New Zealand is  meagre. 
The foregoing clearly demonstrate that research is requi red to quantify 
apple R ,  s ince i t  may he lp  i n  u nderstanding some of the phys io log ical 
behaviour of fruit during storage. Therefore, the current research was in itiated 
to estimate R of freshly harvested apples of e ight cultivars grown in  New 
Zealand, using both the ethane e ff lux ( non-steady state) and steady-state 
methods (see chapter 2 for a comprehensive review of the two methods). 
4.3 MATERIALS AND METHODS 
4.3.1 Fruit supply 
Freshly harvested apples (Mslus domestics Borkh . ;  count 1 25 ;  av. 
weight 1 48 g) of eight export cultivars (Cox's Orange Pippin ,  Gala, Royal Gala, 
Golden Delicious,  Red Del icious, Splendour, B raeburn and G ranny Smith) 
were obtained by courier within 48h of commercial mid-season harvest of each 
. 
; . .  �---'''- ' -�" . ', ' ,  . .  -
cu lt ivar f�6m s im i lar source as p reviously described i n  3. 1 ,) Experiments 
- .  - ---- " _. 
-- "
'-.-.. -. . " 
. .  - -_.' ,- .. -- -.� .. . .  -.-. . _ ,  . . _._ . ..  ---- ....",-. 
commenced on the day of receiving the fruit. Even-size, b lemish-free f ru it 
-..... . ' .',_ .. - . ... ,-, '- ', .. , .. . ... �-. '-'-
.' --" 
..
... _
 ,-, ... ,.. ,-... - "t_ ..
. '�_"' '';:' _ . ....,,-____ .. 
were selected. All measurements were done at 20±1 °C. 
4.3.2 Estimation of skin resistance using ethane efflux method 
I n  a se ri es of experiments , the ethane efflux  method descri bed by 
Banks (1 985a) was used to estimate R (see 3.3.5. 1 ) . 
60 
4.3.3 Estimation of skin resistance using steady-state method 
After estimating R using the ethane efflux method, the same fruit were 
allowed to equi librate at 20±1 °C for 6h before measuring the rate of respiration 
(C02 production) and C2H4 production in fruit kept in the dark as previously 
described in 3.3.5.2. 
Core cavity 02' C02 and C2H4 concentrations were measured by the 
direct sampling method (see 3.3.4. 1 )  and gas samples analysed as described 
in 3.3. 1 .  and 3.3.2 . 
RC02 and RC2H4 were then calculated (see 3.3.5.2) .  
4.3.4 Fruit quality assessment 
Fru it f i rmness, so lub le sol ids content and backg round colour  were 
measured as described in 3.3.8. 1 ,  3.3.8.2 and 3.3.8.3, respectively. 
4.3.5 Experimental design and analysis 
Sixteen s ingle fruit replicates from each apple cu ltivar were used in a 
completely randomised design.  Data were analysed as previously described in 
section 3.3.9. Mean comparisons were carried out by Duncan's multiple range  
test at 1 % levels o f  s ign if icance (Duncan,  1 955 ;  Petersen,  1 977) , to test 
cu ltivar differences. Linear and non l inear regression analyses (Mead and 
Curnow, 1 983; Steel and Torrie, 1 980) were performed using SAS and in some 
cases CGLE graph ics and statistical package (version 3.2, 1 99 1 ) .  
4.4 RESULTS 
4.4.1 Skin resistance to gas diffusion 
6 1 
Skin resistance to gas diffusion of apples varied with cultivart> < 0 .0 1 ) . 'r 
Regression analysis of the raw data from each cult ivar revea led that p lots of 
the estimates of RC2H4 as a function of RC2H6 estimated respectively by the 
steady state and ethane eff lux methods were l inear (figs. 4- 1 ,  4-2 and 4-3) .  
Est imates of RC2H4 and RC2H6 using both methods corresponded c losely 
(with coefficient of variation from the regression analyses for Braeburn, Cox's 
Orange P ippin, G ranny Sm ith, Red Del icious, Royal Gala and Splendour  
apples being 6 .4, 9 .3 ,  7 .7 ,  8.6 , 1 1 .4 and 1 1 .4% respectively) . I n  con t rast, 
comparison of RC02 and RC2H4 of each cu lt ivar estimated concurrent ly by 
steady state method indicated that mean est imates of RC02 were different 
and h igher than estimates of RC2H4 (fig . 4-4) .  A plot of RC02 as a function of 
RC2H6 of individual apples for al l  cultivars ( in a combine set of data) indicated 
that the relationsh ip was curv i l inea r (f ig. 4-5) and was reasonably c losely 
described by an exponential equation of the form: 
RC02 = a * [ 1 .0 - exp(-(b * RC2H6)) ]  + c 
where a, b and c are parameters of the equation .  
[4 . 1  ] 
With the exception of Braeburn apples, fruit of the other cu ltivars which 
had RC02 in the range of approximately 5,000 and 20,000 s cm- 1  a lso had 
RC2H6 between about 5,000 and 1 5,000 s cm- 1 . 
There was large a degree of variation of R va lues of ind ividual apples 
within each cu ltivar, as shown by the coefficient of variation presented in Table 
4- 1 .  Despite these variat ions, R of Braeburn apples was greater than the othe r  
cu ltivars. The mean R of Braeburn apples was approximately three t imes 
h igher than Royal Gala apples wh ich had the lowest R. 
-. -, 
E 
(,) 
CZI 
§ -
� '-' 
� 
::t: 
N U � 
1 5  
12 
9 
6 
50 
40 
30 
20 
Y=2047.0+0.84x 
2 R =0.86 
• 
• 
6 8 
Y=989.7+1 .00x 
R2=O.97 
o 
(a) 
• 
• 
10  12 14  16  1 8  
(b) 
0 
10 �--�--�--�----�--�--�----�--� 
10 20 30 40 
- 1  RC2H6 (X 1000 s cm ) 
50 
62 
Fig. 4- 1 .  Comparison of RC2H6 and RC2H4 of individual (a) Cox 's 
Orange Pippin and (b) Braebum apples estimated by the ethane efflux 
and steady state methods respectively with fitted regression. 
-. -
I 
E u 
en 
8 
0 
-
>< -.-
� 
:t N U � 
12 �--�--�--�----�--�---.----�--� 
10 
8 
6 
4 
4 
1 8  
1 5  
12  
9 
Y=2456.8+0.74x 
R2=O.67 
... 
.... 
6 
Y = 1360.9+0. 90x 
R2=O.90 
(a) 
8 10  1 2  
(b) 
6 �--�----�--�--��--�----�--�--� 
6 9 12  15  
- 1  RC2H6 (X  1 000 s cm ) 
1 8  
63 
Fig. 4-2. Comparison of RC2H6 and RC2H4 of individual (a) 
Splendour and (b) Granny Smith apples estimated by the ethane 
efflux and steady state methods respectively with fitted regression .  
-. -. 
E 
C) 
Cl) 
8 
0 
-
>< --
...,. 
::t N U � 
10��------�------�----�------.-------. 
B 
6 
4 
2 
20 
1 5  
1 0  
5 
Y=-1352.B+ 1 .3x  
R2=O.B3 
3 
Y=40B.3+1 .03x 
R2=O.94 
<a) 
• 
• 
• 
• 
5 7 
(b) 
0 
O�--�----�--�----�--�----�--�--� 
o 5 10 1 5  
- 1  RC2H6 ( x  1000 s cm ) 
20 
64 
Fig. 4-3 . Comparison of RC2H6 and RC2H4 of individual (a) Royal 
Gala and (b) Red Delicious apples estimated by the ethane efflux and 
steady state methods respectively with fitted regression. 
30 
-
E u 25 
.......... 
en 
g 20 
o 
.... 
x '-'" 
q­
I 
N 
1 5  
� 1 0  
"0 c: 
o 
N 5 o u Cl::: 
COX'S 
ORANGE 
PIPPIN 
GA L A  ROYA L 
GALA 
GOLDEN 
D E L ICIOUS 
a III RC0 2 
• RC2H4 
RED BRAEBURN SPLENDOUR 
D E L ICIOUS 
GRANNY 
SMITH 
F ig .  4 - 4 . Sk in  res istance to C02 and C2H4 d i ffus ion of fresh ly harvested app les,  
est imated by the steady state method at 2 0·C. * indicate no detectab l e  C2H4 at the 
t ime of experiment . Letters in  common for each gas not s ign ificant ly  d ifferent at the 
1 % l eve l .  Mean separat ion . by Duncan's mu l t ip le  range test. 
30 
10 
2 Y=352 1 O*( 1 .0-exp(-(5. 1 9 1 36e-05x)))+(- 1 87.242) ;  R =0.96 
66 
o �--�--�--�--�--��--�--�--�--�--� 
o 10 20 30 40 50 
- 1  RC2H6 (X 1000 s cm ) 
KEY: 
• Cox's Orange Pippin 
• Gala 
* Royal Gala 
• Golden Delicious 
o Red Delicious 
£. Braebum 
o Splendour 
6. Granny Smith 
Fig. 4-5 . Relationship between RC02 and RC2H6 of individual 
apples within cultivar estimated by the steady state and ethane 
efflux methods respectively. Solid line was fitted by nonlinear 
regression using equation [4. 1 ] .  
67 
Table 4-1 . Coefficients of variation (ie. standard error as a percentage of the 
mean) for RC2H6' RC2H4 and RC02 [s cm-1 ] in different apple cultivars. 
Cultivar 
Cox's Orange Pippin 
Gala  
Royal Gala 
Golden Delicious 
Red Delicious 
Braeburn 
Splendour 
Granny Smith 
Coefficient of variation {%} 
RC2H6 RC2H4 
28. 1  23.8 
21 .2 .. 
1 9.7 26.4 
21 .5 .. 
35.0 34.6 
34.5 33.8 
22 .9 1 9. 1  
25.2 23.2 
RC02 
1 5.4 
1 4.8 
1 7.2 
1 8.6 
38.3 
1 4.6 
25 . 1  
1 8.8 
.. indicate no detectable C2H4 at the time of experimentation ,  hence no values 
for the coefficient of variation .  
" �,. : . ,,; 
".,�.� 
," , I .. '. 
. . ' .-i . ' :. 
,,� ' �. 
68 
4.4.2 Fruit respiration rate 
Fruit respiration rate (C02 evolution) differed between cu lt iva rs (P < 
0.0 1 ; f ig. 4-6) .  Cox's Orange Pippin apples were respir ing nearly twice as 
rapidly as Splendour, Granny Smith or Braeburn apples and a third as rapidly 
again as Gala, Royal Gala and Golden Delicious apples (fig. 4-S) .  An attempt 
was made to fit an exponent ial model to describe the apparent decl in ing 
relat ionship between respiration rate and RC2HS of individual apples within 
cult ivars (fig .  4-7). The fitted parameters were not significantly different from 
zero and the visual fit to the data was poor which was attributed to the effects 
of the wide spread of respi ration rates between cultivars with RC2HS between 
3 ,000 and 1 2 ,000 s cm-1 (fig .  4-7) .  With the exception of Braeburn apples 
wh ich had intermediate respiration rate and high RC2HS' most of the fru it of 
the other cultivars which had respiration rates in  the range of about 7.5 and 20 
cm3 C02 kg-1 h- 1 had RC2HS between approximately 3 ,000 and 1 2 ,000  s 
cm-1 . 
4.4.3 Internal 02 and C02 concentrations 
I nternal 02 and C02 concentrat ions d iffered s ign if icantly between 
cu ltivars (P < 0.0 1 ; fig. 4-8) .  The mean [02] i in freshly harvested Splendour, 
Golden Delicious) Gala and Royal Gala apples were about a fifth g reater  than 
in Cox's Orange Pippin and nearly half as high again as in  Braeburn apples. 
On the other hand, the average [C02]i in Braeburn and Cox's Orange  P ippin 
_. 
were nearly three�fold as high as in Splendour and twice as h igh as i n  Gala, f-.' 
Royal Gala and Golden Delicious apples. 
A plot of [02]i or [C02]i as a function of RC2HS of individual apples for 
all cultivars using equation [4. 1 ]  indicated a declin ing exponential relat ionship 
between [02] i and RC2HS (fig. 4-9) and an increasing relationship between 
[C02]i and RC2HS (fig. 4-1 0) .  Apart from Braeburn apples, wh ich had 
" , ' 
1 8 
_ 1 6  
.c 
......... 
C'I 1 4  
� 
......... 
N 1 2  
0 u ,.., 1 0  
E 
u ........ 
Q) +J 
e 
c 
o 
+J 
8 
6 
e 4 
a. 11) 
& 2 
o 
a 
COX'S 
ORANGE 
PIPPIN 
GA L A  ROYAL 
GALA 
GOL D EN 
D E L ICIOUS 
REO 
D E LICIOUS 
BRAEBURN SPLENDOUR GRANNY 
SMITH 
F ig .  4- 6. Respirat ion rates of fresh ly  harvested app les at 2 0 · C .  L etters in common 
not s i gn i f icant ly d i fferent at the 1 % l eve l .  Mean separat ion by D uncan's mu l t i p l e  
range test .  
70 
22.5 
-. 20.0 -
'.c 
-, 
.: 17 .5 
� 0 U 
�E 15 .0 C,) --
� 
12.5 .... � .... 
r:: 
0 .-.... � 10.0 . == 
0.. c;n 
� 
� 7.5 
5.0 
0 
I I I 
• 
• 
• 
• 
• 
. � 0 0 • 
o * o� 
:* � . • 0 • 
�� 
• • 
•• • • '*014· • • 
6b� � • • 
0 06 6 
I I 1 
10 20 30 
- 1  RC2H6 (X  1000 s cm ) 
KEY: 
• Cox's Orange Pippin 
• Gala 
* Royal Gala 
• Golden Delicious 
o Red Delicious 
• Braeburn 
o Splendour 
6 Granny Smith 
I 
• • 
• 
1 
40 
Fig. 4-7 .  Relationship between respiration and RC2H6 of 
individual apples within cultivar. 
50 
20 
--. 1 5  
� 
1'"""'\ 
N 
o 3 1 0  
"'0 c: o 
1'"""'\ 
N 
2. 5 
o 
(I [02] i 
• [C02] i 
COX'S GALA ROYA L GOLDEN RED BRAEBURN SPLENDO� GRANNY 
ORANGE GA L A  DEL ICIOUS D E L ICIOUS SMITH 
P IPPIN 
F i g . 4-8. I nterna l  02 and C02 concentrat ions of freshly harvested app l es at 20·C. 
Letters in  common for each gas not s ign i ficant ly  d i fferent at the 1 % l eve l .  Mean 
separat ion by Duncan's mu l t i p l e  range test. 
72 
22 
20 
1 8  
-. 16  
� '-" 
N 14 0 � 
1 2  
1 0  
8 
0 
2 Y=- 1 2.8639*(1 .0-exp(-(3.81 6 1 1 e-05x» )+20.7823, R =0.9 1 
��. 
• 
•• 
• 
• 
• 
o 
• 
10 
KEY: 
20 30 
-1 RC2H6 (X 1000 s cm ) 
• Cox's Orange Pippin 
• Gala 
* Royal Gala 
• Golden Delicious 
o Red Delicious 
£ Braebum 
o Splendour 
6 Granny Smith 
40 
Fig.  4-9. Relationship between [02] i  and RC2H6 of individual 
apples within cultivar. Solid line was fitted by nonlinear 
regression using equation [4. 1 ] .  
50  
8 
6 -.. 
� "-" 
,...-, N 
0 4 U '--' 
2 
o 
o 
73 
2 Y=8.07088* ( l .0-exp( -(8.80246e-05x» )+( -0.408908), R =D.88 
0 
• .& .& 
• • .& .& 
• . 0  .. •• • 
. ,-
. CtJ o � 
o 
10 20 30 
· 1  RC2H6 (X 1000 s cm ) 
KEY: 
• Cox's Orange Pippin 
• Gala 
* Royal Gala 
• Golden Delicious 
o Red Delicious 
.& Braebum 
o Splendour 
6 Granny Smith 
40 50 
Fig. 4- 10. Relationship between [C02]i and RC2H6 of individual 
apples within cultivar. Solid line was fitted by nonlinear 
regression using equation [4. 1 ]  
74 
comparatively low [021i, h igh [C021i and high RC2H6 ' the majority of the fruit 
of the other seven cultivars which had [021i in the range of approximately 1 2 
and 21 %  and [C021i between 1 and 8% had RC2H6 between approximately 
3,000 and 1 2,000 s cm-1 . 
There were no  sign ificant relationsh ips between [021 i or [C021 i and 
respiration rate in a combined data set for al l  cu ltivars (f ig. 4- 1 1  and 4- 1 2) .  
With the exception of Cox's Orange Pippin apples, most of the fru it of t he  other 
cu ltivars wh ich had respiration rates between about 8 and 1 4 cm3 C02 kg- 1 h-
1 had [021i in the range of approximate ly 1 2 and 2 1 % and [C021i between 
approximately 1 and 8%. 
A multiple regression relating [02]i or [C02]i to RC2H6 and respiration 
rate was h igh l y  s ign ificant (P < 0.000 1 ) , so a stepwise reg ress ion was 
performed. In the case of [021i , when the first variable ( ie .  RC2H6) was added 
to the stepwise regression model, an R2 of 0 .55 was obtained but when the 
second variab le ( ie.  respi rat ion rate) was added to the model the R2 was 
improved from 0.55 to 0.62. S imi larly, in the case of [C021 i, addition of the 
second variable to the regression model improved R2 from 0.44 to 0.69. 
Internal C2H4 concentrat ion and rate of C2H4 evolution were cu ltivar 
dependent (P < 0.01 ; figs. 4- 1 3 and 4- 1 4) .  With the exception of Red Del icious 
and Cox's Orange Pippin apples, most of the cultivars were e ither in the pre­
c l imacte r ic stage or just en tering the cl imacteric stage  of deve lopment, 
consequently, their [C2H4] i as wel l  as production rates were rather low. In the 
case of Gala and Golden Delicious apples, there was no  detectable C2H4 at 
the t ime of experimentation. 
20 
1 8  
� 14 o '--' 
12  
10 
8 
5.0 
1 
7.5 
o 
• 
• 
• • 
• 
• o 
: 
1 1 1 I 
• 
10.0 12 .5 15 .0 1 7 .5 
• 
Respiration rate (cm3 CO2 kg- l h-l) 
KEY: 
• Cox's Orange Pippin 
• Gala 
* Royal Gala 
• Golden Delicious 
o Red Delicious 
• Braeburn 
o Splendour 
/:). Granny Smith 
75 
• 
I 
20.0 22.5 
Fig .  4- 1 1 .  Relationship between [02] i  and respiration rate of 
individual apples within cultivar. 
76 
10 r-�-
-�I--��Ir--r--T,--��,r--r--�,--�--r-,�--� 
8 
6 
,........, 
N 
0 4 U 
........ 
2 
o 
5.0 
o • 
I I I 
• 
� . • • • 
• • • 
o 
I 
• 
• 
I 
• 
• 
I 
7.5 10.0 12.5 1 5 .0 1 7.5 20.0 
Respiration rate (cm3 CO2 kg- 1 h-1 ) 
KEY: 
• Cox 's Orange Pippin 
• Gala 
* Royal Gala 
• Golden Delicious 
o Red Delicious 
... Braeburn 
o Splendour 
6 Granny Smith 
Fig. 4- 12 .  Relationship between [C07J i and respiration rate of 
individual apples within cultivar. 
22.5 
4 
3.6 
3.2 
-
.......... 2.8 
� 2.4 
,...... 2 � 
I 
N 
� 1 .6 
0 
.... g' ' .2 
...J 
0.8 
0.4 
0 
b 
* 
----- � -- - -
.... 
c .v-i 
* 
a 
COX'S GALA ROYA L GOLDEN REO 8RAE8URN SPLENDOUR GRANNY 
ORANGE GALA D E L ICIOUS D E L ICIOUS SMITH 
P IPPIN 
F ig .  4- 1 3 . I nterna l C2H4 concentrat ions of fresh ly harvested app l es at 20·C. * ind icate 
no detectab le  C2H4 at the t ime of experiment . Letters in common not s ign i ficant ly 
different at the 1 % l eve l .  Mean separat ion by Duncan's mu l t ip l e  range test. 
25 
-
.c 20 
" 
C7' 
� 
" 
:L 1 5 "-" 
c: 
0 
+J 
U 1 0 ::J 
"0 
0 \.. 
a. 
� 
I 
N 5 
U 
o 
a 
* 
. " . .. .. . , )  ..
b 
* 
a 
b b b 
COX'S GALA ROYA L GOLDEN RED BRAEBURN SPLENDOUR GRANNY 
ORANGE GALA DE L ICIOUS D E L ICIOUS SMITH 
PIPPIN 
F ig .  4- 1 4 . Ethy l ene product ion of fresh ly harvested app l es at 20·C. * ind icate no 
detectab l e C2H4  at the t i m e  of e xperiment. L etters in common not s i gn ificant l y  
di fferent at the 1 % l eve l . Mean separat ion b y  Duncan's mul t ip le  range test. 
79 
4.4.5 Quality indices 
s 
Fruit fi rmness and soluble sol ids content differed between cu ltivar" (P  < 
0.01 ; figs. 4- 1 5  and 4-1 6  respectively). Braeburn apples had the h ig hest mean 
firmness and the lowest soluble solids content compared to the other  cu lt ivars 
(P < 0.0 1 ) ,  whi le Splendour apples had the h ighest soluble sol ids content. 
Background colour (hue angle) measurements were h igh ly cultivar specific (P 
< 0 .0 1 ; f ig .  4- 1 7) .  As expected , Granny Sm ith apples were s ign if icantly 
greener than the other cu ltivars (P < 0.01 ) .  
4.5 DISCUSSION 
The study clearly demonstrates that both the ethane efflux and steady 
state methods provide similar estimates of resistance of the apple's skin to gas 
d iffusion .  The close agreement between RC2H6 and RC2H4 determ i ned 
respectively by each method suggest strongly that RG2HS and RC2H4 are 
indeed very s imi lar. These f indings are consistent w ith those reported by 
Cameron ( 1 982) .  These resu lts further support the assert ion of Cameron 
(1 982) that the efflux method using C2H6 al lows direct estimation of RC2H4 of 
plant organs. It has been util ised to examine the resistance characterist ics of 
gas d iffusion in fru its including apples and tomatoes (Cameron ,  1 982) .  
The res istance of  t issues and organs to C02 and C2H4 gases has 
normal ly been investigated using the steady state approach (Burg and Burg, 
1 962 , 1 965 ;  Burton ,  1 974 , 1 978 ;  Cameron ,  1 982 ; Kidd and West, 1 949) . 
Comparison of the mean RC02 and RC2H4 of apples estimated by the steady 
state method (fig .  4-4) indicated that RC02 was h igher  than RC2H4 . The 
difference could be due to differences in their molecular weight (44 and 28 for 
C02 and C2H4 respectively) which would affect the ir relative diffusivity in air 
by a factor of about 20%, similar to the differences observed in this study. It is 
apparent that C02 would be expected to have h igher resistance values than 
90 
85 
- 80 z '-' 
If) If) Q.) c: 75 
E 
� 70 
65 
60 
COX'S 
ORANGE 
PIPPIN 
GALA ROYAL 
GA LA 
GOLDEN 
D E L ICIOUS 
RED 
D E L ICIOUS 
a 
BRAEBURN SPLENDO� GRANNY 
SMITH 
F ig .  4- 1 5 . F irmness of fresh ly harvested app l es at 2 0·C . L etters in common not 
s ign if icant ly  d i fferent at the 1 %. Mean separat ion by D uncan ' s  mu l t i p l e  ran ge t e s t .  
co o 
-
� ......... 
o+J c: 
Q.) o+J C 
o 
u 
1 4  
1 3  
en 1 2  
"0 
o en 
Q.) 
..0 
::3 
o 
Vl 1 1  
1 0  
a 
COX'S GALA ROYAL GOLDEN REO BRAEBURN SPLENDO� GRANNY 
ORANGE GALA D E LICIOUS D E LICIOUS SMITH 
PIPPIN 
F i g .  4- 1 6. So l ub l e  so l ids content of fresh ly  harvested app l es .  Letters in common not 
s ign i f icant ly  d i fferent at the 1 % l eve l .  Mean separat ion by Duncan's mu l t ip l e  range test.  
-
• ......., 
Cl.) 
0'1 
c: 
0 
Cl.) :l 
I 
1 50 
1 20 
90 
60 
30 
o 
COX'S 
ORANGE 
P IPPIN 
GA LA ROYA L 
GA LA 
GOLDEN 
DELICIOUS 
REO 
DEL ICIOUS 
BRAEBURN SPLENDOUR GRANNY 
SMITH 
F ig .  4- 1 7 . Hue ang le  va l ues of fresh ly harvested app les at 20·C. L etters in common 
not s i gn i ficant ly  d i fferent at the 1 % l eve l .  Mean separat ion by D un c a n ' s  mu l t ip l e  range 
test.  
co N 
83 
C2H4' si nce it shou ld move more s lowly i n  the  gas phase. I n  contrast, 
although the data presented by Cameron ( 1 982) i ndicated that the mean 
RC02 and RC2H4 of Golden De l ic ious was 8 , 00 0  and 1 1 , 500 s cm-1 
respectively, whi lst i n  Yellow Newton apples it was 9,500 and 1 3,500 s cm-1 
respectively he concluded that RC02 and RC2H4 determined by the steady 
state method were quantitatively simi lar. 
The exponential relationship between  RC02 and RC2HS (obtained in  
th is  study) supports the concept that C02 may diffuse through add itional 
routes to t hose avai lable for 02, C2H4 and ethane (C2HS )  d i ff us i o n  as 
suggested by other researchers including Banks (1 984 ) ,  Burton (1 974) and 
Marcel l in (1 974). If it is assumed that C02 diffuses through the epidermal cells 
and cuticle as wel l  as the pores and C2HS only through pores, then reducing 
the area of pores avai lable for diffusion wou ld have differential effects on  the 
movement of the two gases. As avai lable pore area declined towards zero ,  so 
would RC2HS increase towards infin ity. I n  contrast, RC02 would i ncrease 
towards an asymptotic value representative of the resistance of the e pidermal 
cells and cuticular route. 
Although there was a large variation in R values of individual apples 
with in  each variety, the close relat ionsh ip between  the  two i ndep e ndent 
estimates of R that this was real fruit to fruit variation rather than measurement 
error. R largely depends on skin characteristics such as thickness of the  peel ,  
number and distribution of open lenticels, su rface cracks and wax deposits. 
The skin characteristi'cs are affected by both environmental and genetic factors 
(Padfie ld ,  1 9S9 ;  Pratt, 1 988) . Diffe rences in these characterist ics among 
cultivars may have contributed to the large variation in R values of individual 
apples within each cultivar. Variation in R of apples, coupled with variation in  
respiratory rates , wi l l  lead to variat ion in  the fru i t 's 1 nte rnal atmosphe re 
composition which in turn will lead to variabi l ity in physiological response .  The 
physiological significance of such variabil ity in apples has been emphas ised in 
84 
relat ion  to the effects of CA/MA and coating t reatments (Banks, 1 985b, c ;  
B u rton ,  1 982 ; Cameron and  Re id ,  1 982) .  I n he rent d i ffe re nces i n  the  
resistance of both the skin and internal tissues to gas diffusion may affect the 
re l at ive  effects of CA/MA and coat i ng t reatme nts o n  02-dependent 
physio logical processes (such as, respi ration ,  C2H4 production etc. ; Burton,  
1 982 ) . Anatomical differences responsible for differing diffusion resistance, 
rather than biochemical differences among different fruits and vegetables, may 
be largely responsible for differences in tolerance to low-02 and high C02 in  
CA/MA storage (Burton, 1 974). The findings of  the current study concu r� with 
a more l imited study report by Kidd and West ( 1 949) which was based o n  data 
obtained with the steady state method. 
R was found to differ between cultivars (figs. 4- 1 , 4-2 ,  4-3 and 4-4) .  
Braeburn apples had the h ighest mean R compared t o  the othe r  cult ivars. 
Cu lt ivar diffe rences in R cou ld be due to anatomical differences such as 
differences in size of i ntercellular spaces near the fruit surface ; size, number 
and distribut ion of functional lenticels on the fruit surface and thickness and 
natu re of wax deposits of the cuticle etc. As a result of the differences in R 
between  apple cultivars, it would be expected that d ifferent cultivars wou ld 
respond differently to CA/MA treatment. These findings are in l ine with simi lar 
f indi ngs reported by other  researchers i nc lud ing Cameron ( 1 982) ,  Knee  
(1 991 ) ,  Padfield, (1 969), Rajapakse et al. ( 1 990).  
Cox's Orange Pipp in apples had the h ig hest mean respi rat i on  rate 
compared to the other cultivars, while Splendour apples had the lowest mean 
respiration rate. Rajapakse et al. ( 1 990) working with two cultivars of apples, 
showed that the respi ration of Cox's Orange Pippin was higher than Braeburn 
apples .  S imi lar  fi ndings have also been reported by othe r  i nvest igators 
including Fidler and North ( 1 967, 1 971 ) .  
85 
Respi ration rate of a fruit is often regarded as an i ndex of its rate of 
deterioration and hence storage potential (Blanke, 1 99 1 ; Johnson and Ertan, 
1 983). W ith in  a g iven fruit species,  a h ig h  respi rat ion  rate is common ly 
associated with a short storage l ife. On this basis, it would be expected that a 
cultivar such as Cox's Orange Pippin apples with h igh respiration rate wou ld 
have a h igher rate of deterioration and shorter shelf- l ife than those cu ltivars 
such as Sp lendou r wi th l ow respirat ion  rate o r  t hose with inte rmed iate 
respiration rates. 
Approximate storage l ife of fruit of different cultivars of apples i n  air  
storage (Table 4-2 ; Persona l communication , McLeod (1 992); New Zealand 
Apple and Pear Marketing Board) broad ly reflects the respiration rates of the 
var ious cu lt ivars ( f ig .  4-6 ). I t  is  s ign i f icant to ment ion that in addit ion  to 
respiration, other factors such as resistance to bruising damage, gas exchange 
characteristics, stage of maturity at harvest as wel l  as adequate preharvest 
and postharvest handl ing techn iques also affect the storage potent ia l  of a 
cultivar. 
r 
The h igh respiration rate coupled with the h igh [C02]i and intermediate \ �/ � :I�. 
RC02 of freshly harvested Cox's Orange Pippin apples may account for the 
cu ltivar's low storage potential ,  h igh  susceptibi l ity to C02 injury and h igh  
i ncidence o f  postharvests disorders such as core flush or internal b rowning. 
As a result of the h igh  [C02Ji and h igh respiration rate of Cox's Orange Pippin 
apples, it would be expected that exposure to a h igh CO2 atmosphere could 
predispose th is cult ivar to C02 injury .  The degree of injury however would 
depend upon temperature and physiological stage of maturity of the fru it. 
I nternal ' atmosphere composit ion of fresh ly harvested apples d iffered 
among cultivars. The difference in [02J i , [C02J i and [C2H4Ji of the various 
cultivars was related to the differences in R and fruit respirat ion rate. Stepwise 
regression analysis indicated that although both R and respiration contributed 
86 
Table 4-2. Approximate storage l i fe of f ru it of various apple cu lt ivars in 
ref ri g e rated ai r sto rage (McLeod,  1 992 ;  Personal communication ,  New 
Zealand Apple and Pear Marketi ng Board) together  with ranking from 1 to 8 
(ie. high to low) of cultivars based on mean respi ration rates (see fig.  4-6). 
Cultivar Storage l ife In weeks Ranked respiration  rates 
Cox's Orange Pippin 1 2  1 
Red Delicious 1 8-26 2 
Golden Delicious 1 8  3 
Royal Gala 1 6  4 
Gala 1 6  5 
Braeburn 1 8-26 6 
Granny Smith 26 7 
Splendour 26 8 
87 
to the variation in internal atmosphere composition ,  R contributed more to the 
variabil ity than respiration.  High R affects gas movement across the fruit skin 
and results in lower [02] i and h igher  [C02] i and/o r [C2H4]i for a g iven 
resp i rati on  rate and external  atmosphe re composit io n .  Differences in 
i nterce l lu lar  space volume  could contribute to the differences in i nternal 
atmosphere composition of the various cultivars. Furthermore,  the presence or 
absence of open calyx could also provide explanation for the differences in 
internal atmosphere composition between cultivars. Variation in  the diffusive 
properties of the fruit could resu lt in different [02]i and [C02]i within fruit under 
the same external conditions (Knee and Farman, 1 989). 
In spite of their intermediate respiration rate , freshly harvested B raebu rn 
apples contained higher [C02]i (sim i lar in  Cox's Orange Pippin) and lower 
[02]i than the other cultivars and this could be associated with their h igh R and 
low intercel lu lar space volume.  Exposing apple cUltivars with high R and/or 
high respi ration rate , high [C02]i and low [02]i to low-02 or  h igh C02 regimes 
or elevated temperatures could predispose the cultivar to various postharvest 
disorders such as internal browning, C02 toxicity or low 02 injury. Splendour 
apples on the other hand contained higher [02]i and lower [C02]i compared to 
the other cultivars. This could presumably be due in  part to the fact that f ruit of 
th is  cu lt ivar often have an open calyx. The poss ib i l ity that open  calyx 
contributed to this effect was supported by the observation that during internal 
atmosphere sampl ing, no resistance to penetration of the syringe into the core 
cavity (via the calyx) was felt in any of the Splendour apples used in th is study. 
The high [02]i and low [C02]i of Splendour apples could also be l inked to their 
relatively thin skin,  numerous visible lenticels, high intercel lu lar space volume 
and hence easier gas d iffus ion into and out of the fruit . These variables 
together  with the low respi rat ion  rate of Splendour apples provide some 
explanation for the high storage potential of this cultivar� However it shou ld be 
mentioned that one important disadvantage of this cultivar is that it is  h ighly 
susceptible to bruising damage. 
88 
There were no  significant relat ionships between [02]i o r  [C02]i and 
resp i rati on  rate (in a combined data set for all cultivars), suggesti ng that 
variation i n  fruit respiration rate at this one temperature ( ie. 20°C) was not an 
overriding factor i n  determining [02]i and/or [C02]i of freshly harvested apples 
and v ice versa. Fo r instance Cox's Orange P i pp in  and Braeburn apples 
compared to the other six cultivars had higher [C02]i and lower [02]i (fig. 4-8) 
but then,  although Cox's Orange Pippin apples had high rate of respi ration  
(C02 production) that was not the case in  Braeburn apples. The disparity 
could be due to anatomical differences as well as differences in R. 
Internal C2H4 concentration is a good index of climacteric fruit maturity 
(Pratt et al. , 1 977; Saltveit, 1 982 ; Su et al. , 1 984; Zagory and Kade r, 1 988) . 
Based on thei r [C2H41i ' most of the cultivars used in this study were either i n  
the p recl imacteric phase or just entering the climacteric stage of maturation, 
consequently they had not commenced rapid softening. Braeburn apples had 
the highest mean fi rmness compared to the other cultivars, while Cox's Orange 
P ipp i n  had the  lowest mean f i rmness.  This may be re lated to the low 
intercel lu lar space volume of B raeburn apples (approxi mately 1 4. 1  %; Cox's 
Orange Pippi n 1 7.4%;  Rajapakse et al. , 1 990). Blanpied et al. ( 1 978) showed 
that n it rogen fert i l isation of apple trees decreased the fi rmness of apples at 
harvest and after four  months storage.  These authors also showed that the 
position of the fruit on the tree affects the fi rmness. Apples g rown in exposed 
posit ions that receive much sun l ight are generally f i rmer than wel l -shaded 
apples grown on the same tree . Splendour apples were also found to contain 
more soluble solids than the other cultivars whilst, Granny Smith apples were 
greener. Background colour (hue angle) measurements were highly cultivar 
dependent reflecting the differing distribution of the different coloured pigments 
on the greenest part of the fruit as wel l  as providing some measure of with in 
cultivar variation in maturity. 
89 
I n  concl us ion estimates of RC2H6 and RC2H4 of i ndividual apples 
using the ethane efflux  and steady state methods respectively corresponded 
closely and provided consistent estimates of RC2H6 and RC2H4' However 
the former approach i n  comparison to the latter was easier to use and d id not 
requ i re t hat the  system be  at equ i l i b ri um . The e ffl u x  method e nabled 
estimation of RC2H4 even in  cultivars which were in  the preclimacteric stage of 
maturity and not producing detectable quantities of C2H4' Estimates of RC02 
and RC2H4 of apples estimated concurrently by the steady state method were 
different and the mean RC02 was consistently higher than RC2H4' There was 
large degree of variation in  R values of individual apples within each cultivar. 
Cu lt ivar  d iffe re nces i n  resistance to gas d i ffusio n  may be important i n  
dete rm i n i ng  sensit iv ity to CA l im its . Knowledge o f  R might be u sed i n  
conjunction with other physiological data to predict optimum storage conditions 
for apples. However, when consideri ng opt imum CA sto rage conditions for 
apples, the combined influence of both the rates of flu xes and the resistance 
coefficients on internal atmosphere composition must be taken into account. 
4.6 LITERATURE CITED 
Banks, N .  H .  1 984. Studies of the banana fruit surface in relation to the effects 
of Tal Pro-long coating on gaseous exchange. Scientia Hort . 24:279-
286. 
Banks, N. H. 1 985a. Estimating skin resistance to gas diffusion in apples and 
potatoes. J. Expt. Bot. 36 : 1 842- 1 850. 
Banks ,  N .  H .  1 985b. Internal atmosphere modificat ion i n  PrO- long coated 
apples. Acta Hort. 1 57:1 05- 1 1 2 . 
Banks, N .  H .  1 985c. Coating and modified atmosphere effects on g reening in 
potatoes. J. Agric. Sci. 1 05 :59-62. 
Blanke, M .  M. 1 99 1 . Respi ration of apple and avocado fruits. Postharvest 
News and Information 2(6) :429-436. 
90 
Blanpied, G. D. ,  Bramlage, W. J . ,  Dewey, D. H . ,  Labelle ,  R. L. , Massey, L. M. 
J R . ,  Mattus ,  G. E . ,  St i l es ,  W.  C. and Watada,  A .  E. 1 978. A 
standardised method for collecting apple pressure test data. N .V. Food 
Ufe Sci . Bul l .  Pomology No. 1 .  
Burg, S. P.  and Burg, E .  A. 1 962. The physiology of ethylene formation.  Ann. 
Rev. Plant Physiol. 1 3 :265-302. 
Burg ,  S .  P.  and Burg ,  E.  A. 1 965. Gas exchange in  fru its. Physio l .  Plant. 
1 8:870-884. 
Burton ,  W. G.  1 974 . Some biophysical principles underlying the control led 
atmosphere storage of plant material . Ann. Appl . BioI . 78:1 49-1 68. 
Bu rton ,  W. G. 1 978 .  Biochemical and physio logical  effects of modified 
atmospheres and their role in qual ity maintenance. In 'Postharvest 
biology and biotechnology' . (Hu ltin ,  H .  O. and Mi l ner, M. eds.) ,  Food 
and Nutrition Press, Westport, Conn.  pp. 97-1 1 0. 
Burton, W. G.  1 982. Postharvest physiology of food crops. Longman Scientific 
and Technical , Harlow, U.K. 339 pp. 
Cameron ,  A. C. 1 982. Gas diffusion in bu lky p lant organs.  P h .D .  thesis, 
University of California, Davis. 1 1 7 pp. 
Cameron ,  A. C. and Reid, M .  S. 1 982. Diffusion resistance : importance and 
measu re ments in co ntro l l ed atmosphe re sto rage .  I n :  Cont ro l l ed 
atmosphe res fo r sto rage and t ransport of perishable ag ricultu ral 
commodities. (D. G. Richardson and M. Meheriuk. eds . )  Oregon State 
University School of Ag ricu lture, Symposium Series No. 1 ,  Timber Press, 
Beaverton ,  Oregon. pp. 1 71 - 1 80. 
Cameron,  A. C .  and Vang, S. F. 1 982. A simple method for the determination 
of resistance to gas diffusion in plant organs. Plant Physio l .  70 :21 -23 .  
Duncan, D .  B .  1 955. Multiple range and mu ltiple F test. Biometrics 1 1  : 1 -42 . 
Fid ler, J .  C .  and North ,  C. J. 1 967. The effect of conditions of storage on the 
respiratio n of apples. 1 .  The effects of temperature and concentration 
of carbon dioxide on the production of carbon d ioxide and uptake of 
oxygen. J. Hort. Sci . 42:1 89-206. 
91 
Fidler, J .  C.  and North, C .  J .  1 971 . The effect of  storage conditions on the 
respiration of apples. V. The relationship between temperature, rate of 
respi ration and composition of the internal atmosphere of the fruit. J. 
Hort. Sci .  46 :229-235. 
Johnson, O .  S .  and Ertan , U .  1 983. I nteraction of temperature and oxygen 
levels on the respiration rate and quality of Idared apples. J. Hort. Sci . 
58 :527-533. 
Kidd, F. and West, C. 1 938. Individual variation in apples. Great Brit. Oept. 
Sci . & Ind. Res. Rep. Food Invest. Bd. for 1 937, pp. 1 1 4- 1 1 5. 
Kidd , F. and West, C.  1 949 .  Resistance of the sk in  of the apple fruit to 
gaseous exchange. Rep. Food Invest. Bd. ,  Lond. ( 1 949), pp. 57-64. 
Knee, M. 1 99 1 . Rapid measurement of diffusive resistance to gases in apple 
fruits. HortSci . 26 :885-887. ",,' 
Knee, M .  and Farman, D .  1 989. Sou rces of variat ion i n  the qual ity of CA 
stored apples. I n :  Fifth proceedings of the i nternational control led ./ 
atmosphere research conference. vol .  1 - Pome  fru its. June 1 4- 1 6 ,  
1 989. Wenatchee, Washington, USA. pp. 255-26 1 . 
McLeod, S .  1 992. Personal communication .  New Zealand Apple and Pear 
Marketi ng Board. 
Mag,ness, J .  R. and Diehl , H. C. 1 924. Physiological studies on apples i n  
storage. J .  Agric. Res. 27:1 -38. 
Marce l l i n ,  P. 1 974 . Co nd i t i o ns phys iqu es de l a  c i rcu lat ion  des g az 
respiratoi res a travers la masses des fru its et maturation.  I n  Col loques 
internationaux C.N.R.S. No 238 : Facteu rs et reg ulation de la maturation 
des fruits. pp. 241 -251 . 
Mead, R .  and Cu rnow, R .  N .  1 983. Statistical methods i n  ag ricultu re and 
experimental biology. Chapman and Hal l .  London,  New York. 335 pp. 
Padfield, C.  A. S. 1 969. Storage of apples and pears .  N. Z.  Oept. Sci . Ind. 
Bul l .  1 1 1 .  1 1 6 pp. 
Petersen ,  R. G. 1 977. Use and misuse of mu ltiple comparison procedures. 
Agron. J. 69 :205-208. 
j 
92 
Pratt, C. 1 988. Apple flower and fruit : morphology and anatomy. Hort .  Rev.  
1 0 :273-308. 
Pratt , H .  K . , Goesch l , J. D. and Mart i n ,  F. W. 1 977.  Fruit g rowth and  
deve lopment ,  ri pen i n g .  The ro le  o f  ethy lene i n  t he  honey  dew 
muskmelon. J .  Amer. Soc. Hort. Sci . 1 02 :203-21 0. 
Rajapakse,  N .  C . ,  Banks, N .  H . ,  Hewett, E .  W. and C le land, D.  J .  1 990.  
Development of oxygen concentration g radients i n  flesh tissues of  bu lky 
plant organs. J. Amer. Soc. Hort. Sci . 1 1 5:793-797. 
Saltveit, M. E. 1 982. Procedures for extracting and analyzi ng internal g as 
samples from plant tissue by gas chromatography. HortSci . 1 7 :878-
881 . 
Solomos, T. 1 982. Effects of low oxygen concentration on respi ration :  N ature 
of respi ratory diminution .  I n  Controlled atmospheres fo r storage  and 
transport of perishable agricultural commodities. (D. G. Richardson and 
M. Meher iuk .  eds . )  Oregon State U n iversity School  of Ag ricu lt u re ,  
Symposium Series No. 1 , Timber Press, Beaverton,  Oregon. pp .  1 61 -
1 70. 
Solomos, T. 1 987. Principles of gas exchange in bulky plant tissues. HortSci. 
22 :766-771 . 
Soudain ,  P. and Phan Phuc, A. 1 979 . La diffusion des gaz dans les t issus 
vegetaux  en rapport avec la structu re des o rganes mass i fs . I n :  
Perspectives nouvel les dans la conservation des fruits et legumes frais .  
Semi naire I nternational organise par l e  Cent re de Recherches  e n  
Sciences Appl iquees a l 'Alimentation, Universite du Quebec, Montreal , 
1 4- 1 5 April 1 978. pp. 67-86. 
Steel ,  R. G. D. and Torrie, J. H. 1 980. Principles and procedures of statistics, 
a biometrical approach. McGraw-Hil l  Book Co. ,  New York, NY, 2nd  ed. 
633 pp. 
Su , L . ,  McKeon ,  T . ,  G rierson ,  D . ,  Cantwel l ,  M .  and Yang , S .  F .  1 984 . 
Development of 1 -aminocyclopropane-1 -carboxylic acid synthase and 
po lygalactu ronase activit ies du ri ng the maturat ion  and ripe n i n g  of 
tomato fruit. HortSci . 1 9 :576-578. 
.,/ 
93 
Zagory, D .  and Kader, A. A. 1 988. Modified atmosphere packaging of fresh 
produce. Food Technol. 42:70-77. 
94 
CHAPTER 5 
RELATIONSH IP  BETWEEN  APPLE  R ESP IRAT ION  AND  OXYGEN  
CONCENTRATION IN THE INTERNAL AND EXTERNAL ATMOSPHERES. 
5.1 ABSTRACT 
Oxygen uptake , C02 and C2H4 output by Cox's Orange Pippin and 
G rann y  Sm i th  app les  were cha racte r ised by s t udying var i at i on in t he  
magn it ude o f  02' C02 and C2H4 concentrat ion d ifferences between the 
internal  and external atmospheres (L\[02] .  L\[C02] and L\[C2H4]) of  ind ividual 
apples maintained in different 02 atmospheres at 20±1  QC. 
L\[02] was conf irmed to decrease at low 02 leve l s ,  ref lect i ng  the  
decreased rate of 02 uptake in low 02 concentrations.  Two approaches to 
analysing these data yielded similar relationships between respiration rate and 
[02] i ' Oxygen uptake relat ive to that in air (Re102) fol lowed approximately 
Michaelis-Menten kinetics, with a half-maximal rate at 2 .5% 02 for internal 02 
([02] i) and 7.5% 02 for external 02 concentrat ion ( [02]ext) .  The d ifference 
between the figures derives from the impact of L\[02] on the availabi l i ty of 02 
to fru it t issues. Th is underl ines the importance of considering factors affecting 
the size of A[02] when setting lim its for CNMA storage. 
A ma t h emat i ca l  eq uat i on was  deve loped  to d esc r i be  t h e  two  
physiological processes (ie. anaerobic and aerobic respirat ion)  involved in the 
relationship between relative rate of CO2 production (Re1C02) or internal CO2 
concen t ra t i on ( [C02 ] i ) and [02 ]ext or [02] i ' T h e  equat i on h a d  two 
components, each describing one of  the two physiolog ical processes. 
95 
Fru it contained sim i lar amounts of acetaldehyde (AA) irrespect ive of 
[02]ext. On the other hand, ethanol (ETOH) was only detectable when [02]ext 
was kept at zero. 
The relationship between relative rate of C2H4 production (Re,c2H4) or 
in ternal  C2H4 concentrat ion ([C2H4] i ) and [02]e xt was s igmo idal .  Th i s  
contrasted with the i r  relat ionsh ip  with [02] i which lacked t he  apparent ' Iag 
phase' seen  in p lots against [02]ext and were described by an exponential 
hyperbola. These observat ions were used as a bas is for discussion of the 
relative aff inities of the oxidases involved in C2H4 production and respiration . 
5.2 INTRODUCTION 
Depression of respiration rate induced by low-02 concentrations is one 
of the fundamental effects thought to l i nk reduction of 02 avai labil ity to the 
s lowing of  a fru it 's physio log ical deter iorat ion ach ieved by  CA sto rage. 
Identifying the relationsh ip between respirat ion rate and 02 concentration has 
therefore been a critical area of research in postharvest physiology since the 
p ionee r i ng  work on MAs by K idd and West (Knee ,  1 99 1 ) .  S uccessfu l  
characte risat ion of th is relationsh ip would g reat ly faci l itate model l ing work 
a imed at opt im is ing  MA  packages pub l ished recent ly (Cameron , 1 985;  
Cameron et al. ,  1 989; Emond et al. ,  1 991 ; Lakin, 1 987; Wade and G raham, 
1 987) because it would permit prediction of modified rates of uptake u nder a 
changing atmospheric regime. 
The 02 concentration to wh ich the tissues respond most directly is that 
in the cell sap ( [02]cs) .  wh ich is in equi l ibrium with the 02 concentration in the 
fruit's internal atmosphere ([02] i) '  Measuring [02]cs is d ifficult and prone to 
art i facts ( B u rton , 1 974, 1 982 ; Ben-Yehoshua and Cameron ,  1 988)  but 
respiration (review of fru it respiration is presented in chapter 2) can be studied 
as a function of e ither [02]ext or [02 ] i ' Studies with [02]e xt are simpler to 
96 
undertake and are most readily applicable to the empi rical design of packages. 
U nfortunately, fruit responses to lowered [02]ext can vary widely, depending 
on crop type and physiological condition as shown for avocados (Tucker and 
Laties, 1 985) and for freshly harvested versus coolstored pears (Boers ig et al. , 
1 988). This may be caused by variabi lity of individual fruit skin resistance to 
gas diffusion (R ,  s cm-1 ; Bu rton ,  1 982) .  It is th is variabil ity, coupled with 
respiration rate, which determines the d ifference between the i nte rnal and 
external atmospheres of the fruit (.1[02]) and which therefore determ ines the 
[02] i for a given [02]ext· 
This suggests that if the variation in  R could be el iminated by exam ining 
the respi ratory response of the tissues to [021i , rather than [02]ext then some 
of the variab i l i ty in p lots of resp i rat ion  versus 02 m ight be ove rcome.  
However, characterisation of the relationship between respiration versus [02]i 
i n  i ntact fruit has to date only been attempted i ndi rectly v ia mathematical 
models (Andrich et al. , 1 989 , 1 99 1 ; Banks et al. , 1 989;  Chevi l lotte , 1 973 ; 
Solomos, 1 985 , 1 988;  Tucker and Laties, 1 985) presumably because of the 
experimental d i fficulties (such as contamination of gas samples with air or 
b lockage of syri nge du ri ng i nternal atmosphere sampl i ng )  i nvo lved with 
concurrent monitori ng of internal atmosphere and respi ration rate i n  d ifferent 
[021ext . Usi ng  a combi nat ion of a non- i nvasive techn ique for mon itoring 
i nternal atmospheres and the use of  f ruit immersion ( in  water) to  p revent 
co ntam i nat i on  of d i rect removal samp les ,  t he  cu rre nt resea rc h has 
characterised the respi ratory and C2H4 production responses of  two apple 
c u l t i va rs (Cox 's O ra n g e  P i p p i n a n d  G ranny  S m i t h )  to red u c ed  02 
concentrations. Th is i nvolved studying the variation i n  the magnitude of 02 
and C02 (and C2H4) concentrat ion d i fferences between the i nternal and 
exte rna l  atmosphe res of i nd iv idual  appl es  ma in ta ined i n  d i ffe re nt  02 
atmospheres at 20±1 QC. 
97 
5.3 Theoretical background 
If it is assumed that the concentrations of the respi ratory gases, 02 and 
C02 , i ns ide  any f ru it are at equ i l i b r i um  and t hat t hey  are effect ive ly  
homogeneous throughout the fruit (And rich et al. , 1 989, 1 99 1 ), then their rates 
of flux between the i nternal and external atmospheres are governed by Fick's 
Law of diffusion (Burg and Burg ,  1 965). A simpl ified version of this is: 
where 
F = flux at steady state or  respiration rate (cm3 s- 1 ) 
A = fruit surface area (cm2) 
R = skin resistance to gas diffusion (s cm-1  ) 
[02]ext = external oxygen concentration (%) 
[02] i = i nternal oxygen concentration (%) 
If F is related to [02]ext or [02] i by the Michael is-Menten equation ie. 
where 
F == ---------------
Fmax = maximum rate of exchange when 02 
is saturating (cm3 02 s- 1 ) 
Km = Michaelis-Menten constant for 02 (%) 
[5. 1  ] 
[5.2] 
98 
then it is possible to express [02] i as a function of [02)ext by rearrang i ng  and 
solving  the fol lowing equation, obtai ned by substituti ng  equation [5.2 ] i nto 
equation [5. 1 ) : 
* [5.3) 
As [02) i cannot be a negat ive num ber ,  o n l y  t he  fo l l owi ng  so l u t i o n  i s  
acceptable :  
[5 .4] 
Whi lst R has been shown to change during ripening under certain conditions 
(Wilkinson ,  1 965) ,  the ratio of AIR is l ikely to remain approximately constant 
over short periods of time. Thus, for any given fruit studied for a short period, 
equation [5. 1 )  may be rewritten as : 
where 
F 
k'f = a fruit constant (=AlR) (cm3 s- 1 ) 
[5.5] 
flC = difference in gaseous concentration between the 
external and i nternal atmospheres (%) 
99 
Thus, a relative measure of the effects of different CA mixtures on  the gas 
exchange of a fruit can be obtained simply by studying variation in Il.C in these 
mixtures.  For each fruit, i t  is possible to quantify the rate of exchange for a 
particular gas under CA relative to its rate of exchange in  air as a ratio of the 
two: 
where 
RelE 
FCA 
Fair 
Il.CCA 
= relative rate of exchange 
= flux in CA at steady state (cm3 s-1 ) 
= flux in air at steady state (cm3 s-1 ) 
= difference in gaseous concentration between the 
external and i nternal atmospheres of a fruit in CA 
(%) 
= difference in gaseous concentration between the 
external and i nternal atmospheres of a fruit in  
a i r  (%) 
[5.6] 
Since th is is a relative rather than an absolute measure of the process, an 
alternative notat ion fo r constants i nvolved ( ie .  rKm = relative Michael is­
Menten constant and rFmax = maximum relative respiration rate) can be used : 
RelE = 
------.--------
[5.7] 
where 
rFmax = maximum relative rate of exchange when [02] i 
is saturating (cm3 02 s- 1 ) 
rKm = Michaelis-Menten constant for [02] i (%) for 
the relative rate 
100  
The relat ionsh ip between Re/C02 and [021ext or [02 1 i . i n vo lves  two 
physiological processes, anaerobic and aerobic respiration. A mathematical 
equation was deve loped to describe the overa l l  rate of C02 product ion in 
different 02 atmospheres: 
1r ------------------ [5.8] 
The first part of the equation describes a curve wh ich declines with increasing 
02 concentrat ion ([02]) at a rate determ ined by the values of a and b. two 
parameters of the equation. This describes the anaerobic contribution to total 
C02 production. The second part describes the aerobic contribution to C02 
production using a Michaelis-Menten equation . 
5.4 MATERIALS AND METHODS 
5.4.1 Fruit supply 
Freshly harvested apples (Ma/us domestica Borkh. )  of two cu ltivars, 
Cox's Orange Pippin and Granny Smith (count 1 25; av. weight 1 48 g) were 
1 01 
obtained as previously described in 3. 1 .  Fru it were stored in air at oQe unti l  
needed. Fruit were removed from storage and held at room temperature for at 
least 24h before experimentation to ensure complete temperature equ i l ibrium .  
5.4.2 Gas measurement and analysis 
A 2 m l  (9mm diamete r) g lass vial , from wh ich the bottom had been 
removed was stuck, us ing polyvinyl  acetate adhes ive, onto the equatorial 
surface (see fig. 5- 1 )  of thirty-six fru it of each cultivar. Sub-epidermal internal 
gas concentrat ions were estimated to be the same as the equi l ibrated gas 
concentrat ions in  the g lass chambers after 40 to 90h (see appendix 1 )  at 
20±1 QC in air (Banks and Kays, 1 988). Each fruit was individually p laced on a 
tray ( in the dark) wh ich was connected to a flow through system (flow rate of 
approximately 80 m l. m in- 1 ) which gave various 02 concentrat ions rang ing 
from 0 to 20%. Precision needle valves were used to m ix  air and n itrogen to 
the required atmospheres, wh ich were bubbled through water to g ive a relative 
hum idity of approximately 98%. The required gas concentrations were verified 
at least three times daily by analysis of gas samples as previously described in  
sect ion  3 . 3 .  Afte'r 40 to 90h of equ i l i b rat ion  (see append i x  1 )  of  t he  
atmosphere i n  the  g lass v i a l  w i th t he  fru i t  s u b-e p idermal  i n te rna l  gas 
concentrat ions at  20±1 QC,  a gas t ight  syringe was used to take 9011 1 gas 
samples from each g lass vial  as we l l  as from the t ray's headspace and 
ana lysed for 02 and C02 (see 3 . 3 . 1 ) , C2H4 (see 3 .3 .2) ,  AA and ETOH 
concentrat ions (see 3.3.3) .  
Immediately after sampl ing, each tray was submerged in water and fruit 
core cavity gas samples were taken by the d i rect samp l ing  method (see 
3 .3 .4 . 1 )  and ana lysed for 02 ' CO2 , C2H4, AA and ETOH as p revio us ly  
described (see 3.3 . ) . As the difference between sub-epidermal and core 
cavity sample composition within each apple was smal l, internal 02' CO2 and 
C2H4 concentrations ([021i , [e021 i and [C2H41i) were estimated as the 
---, , , 
I " 
: A ; \ , , , 
'" .I - -' 
c 
F i g .  5- 1 . ARRANGEMENT OF GLASS SAMPL I NG CHAMBER 
ON THE SURFACE OF AN APPLE FRU IT  
A .  Core cavi ty 
B .  Fru i t  surface 
C .  Gl ass  chamber 
D .  Septum c ap 
E .  S i l i cone tube wi th water 
1 .  Equator 
1 02 
1 03 
average of t h e  s u b-epide r m a l  a n d  core cavity gas s a m ples. AA a n d  ETOH 
w e re n o t d e t e c t e d in t h e  c o r e  c a v i t y  of f r u i t  h e n c e ,  s u b - e p i d e r m a l  
concentrations ([AA]se and [ETOH]se) a re reported. 
Re102 ' ReIC02 and ReIC2 H 4 were estim ated from e q u at i o n  [ 5 . 6] a n d  r e lative 
respiratory q u otient ( ReIRQ) was estim ated as the rati o  o f  ReIC02 t o  Re102' 
5.4.3 Experimental design and analysis 
T h i rt y - s i x s i n g l e f r u it r e p l i c a t e s  o f  e a c h  c u l t i v a r  w e r e  u s e d  in a 
completely random ised design. E x p e r i m e n t s  were re p e ated at l e a st o nc e .  
Data w e re a n a l ysed as p revi o u s l y  desc r i bed ( 3 . 3 . 9 ) .  N o n l inear reg r essions 
, . 
(Steel a n d  Torrie, 1 980) were performed u s ing CGLE g raph ics a n d  s t a t i stical 
package (version 3.2 , 1 99 1 )  and, i n  some cases, SAS. 
5.5 RESULTS 
5.5.1 [02] i as a function of [021e xt 
Ass u m ing a fru it skin re sistance of 9 , 000 and 1 0 ,2 00 s cm - 1  f o r  C ox's 
Orange P i p p i n  a n d  G ra n n y  S m i th a p p les respect i ve l y  ( s e e  c h a p t e r  4 ) ,  t h e  
e s t i m at e s  of [02 ] i a s  a f u n ct i on o f  [0 2] e xt o bta i n e d  u s i n g  e q u a t i o n  [ 5 . 4 ] 
indicated that there was a non l inear relationship between t h e  two var i a b l es (fig. 
5-2 ) .  The r e g ression accou nted for between 99.0% and 99.5 % o f  t h e  total 
variation in [02] i in both cu ltivars. ,There was essential ly a l i n ea r  red uction i n  ,1\  
[02] i a s  [02]e xt decl ined from th at"air (20 . 95%) to about 6 %  [02]ext. B elow 
t h i s ,  t h e  s lo p e  of the rel a t i on s h i p decrea sed p rogre s s i v e l y  a s  [ 02 ] e xt was 
re d u c e d  t ow a rds ze r o .  The f i t t e d  l i n e  i n d icated t h a t  a t  1 8 % [ 0 2 ] ext the 
difference� between t h e  [02 ] ext and [02 ]i was about 5 . 0% f o r  Cox's Orange 
Pippin and 3 . 7% for G ranny Sm ith apples. At 2% [02]ext t h ese d iffe ren ces 
104 
16  
Ca) 
14 • 
1 2  
10  
8 
6 
4 
2 
0 
-. 
� 
"":. -2 ,........, 
C"I 
Q 16  
Cb) 
o 
14  
12  
10  
8 
6 
4 
2 
0 
-2 
0 2 4 6 8 10 1 2  
[02]exl (%) 
14 1 6  1 8  
Fig . 5-2. Relationship between [02]i and [02]exl of individual (a) 
Cox's Orange Pippin (R
2
=O.99) and (b) Granny Smith (R
2
=O.995) 
apples kept at 20°C.  Solid lines were fitted by nonlinear regression 
using equation [5 .4] . 
2C 
1 05 
had decreased to  approx imate ly 1 .6%  and 1 . 0% for t he  two cu lt ivars, 
respectively. Although the apparent Km estimated for Granny Smith (obtained 
using equation [5.4] ;  Table 5-1 ) was almost twice that for Cox's Orange Pippin 
apples the standard error of the Granny Smith value was high and the two did 
not d iffer significantly (at P = 0.05) . Simi larly there was no difference in the 
Fmax of these cultivars. 
Table 5-1 . Apparent Km and Fmax values calculated using equation [5.4] for 
[02] i of Cox's Orange P ipp in and Granny Smith apples as a functio n  of  
[02]ext· 
Cultivar 
Cox's Orange Pippin 
Granny Smith 
Km 
(%) 
2.2 ± 0.82 
4.2 ± 1 .68 
5.5.2 RelO2 as a function of [02]ext or [02]i 
Fmax 
(cm3 s- 1  fruit- 1  x 1 0-4) 
1 0.9 ± 1 .05 
7.5 ± 1 .00 
Fruit relative rate of 02 uptake (ReI02) estimated from equat ion [5.6] 
was significantly (P < 0.000 1 ) influenced by [02]ext i n  both cultivars. RelO2 
i ncreased f rom ze ro ( i n  an  anaerob ic  atmosphe re )  towards a va l u e  
approach ing  approxi mately one i n  air  (f ig 5-3 ) .  T h e  data we re c lose ly  
described by Michaelis-Menten curves (R2 = 0.98 and 0 .94 , respectively) .  
Cox's Orange Pippin had higher rFmax values than G ranny Smith apples (P < 
0 .05 ,  Table 5-2 ) but the rKm val ues for the two cu lt ivars d id  not  d i ffer 
significantly (overall mean = 7.55 for rKm and 1 .37 for rFmax). 
N 0 
-
� � 
1 .2 
0.8 
0.4 
0.0 
1 .2 
0.8 
0.4 
0.0 
Y=C l .4 1 695x)/(7.34459+x) 
R2=O.98 
Y=( 1 .3 1 733x)/(7.8 1 335+x) 
R2=O.94 
o 2 4 6 
� 
o 
8 10 1 2  
[02]ext (%) 
0 
1 4  1 6  
1 06 
Ca) 
• 
(b) 
0 
1 8  
Fig .  5-3 . Relationship between Rel02 and [02]ext of individual (a) 
Cox's  Orange Pippin and Cb) Granny Smith apples kept at 20°C .  
Solid lines were fitted by nonlinear regression using equation [5 .7 ] .  
20 
1 07 
Table 5-2 . rKm and rFmax of equation [5.6] for RelO2 as a funct ion of 
[02]ext or  [021i fitted by nonl inear regression fo r Cox's Orange Pippin and 
Granny Smith apples. 
Cox's Orange Pippin 
Granny Smith 
7.3 ± 1 .44 
2. 1  ± 0.59 
7.8 ± 1 .32 
2 .9 ± 0.80 
rFmax 
1 .42 ± 0. 1 1 6  
1 . 1 3 ± 0 .088 
rFmax 
1 .32 ± 0 . 1 50 
1 .06 ± 0 .09 1 
1 08 
The relationships between RelO2 and [02]i followed a similar general 
form to those with [02]ext (fig. 5-4), although the slopes were steeper at low 
02 levels, as reflected in the lower rKm values (Table 5-2) .  rKm and rFmax 
values were simi lar for [02] i i n  both cultivars (overall mean = 2.5  and 1 . 1 0, 
respectively) . 
Average 02 gradients across the flesh (ie. between the sub-epidermal 
and core cavity) were significant (0.306 ± 0 .052 and 0 .462 ± 0 .064 for Cox's 
O range  P i pp i n  and  G ranny Smith apples respective l y ) .  However  the  
relationsh ips between these g radients and [02] i were poorly defi ned (R
2 
= 
0.1 1 ,  P < 0 .05 and R2 = 0.37, P < 0.001 for l inear regression respectively) for 
Cox's Orange Pippin and Granny Smith apples (data not shown). 
The relationships between relative rate of C02 production (ReC02) or 
internal C02 concentration ([C02]i ) and [02]ext (figs. 5-5 and 5-6) were well 
described by fitted cu rves obtained by nonl inear reg ression using equation 
[5.8] . However, with the spread of data poi nts around the fitted l ine,  coupled 
with the complexity of the equation ( ie. with 4 parameters ) ,  the parameter 
values cannot be claimed to have been accurately estimated in  this study. 
At zero percent [02]ext, ReC02 or [C02]i of both Cox's Orange Pippin 
and G ranny Smith  apples i ncreased markedly  i nd icat i ng  that fru it were 
respiri ng anaerobical ly. Between 2% and 1 8% [02] ext , Re/C02 of Cox's 
Orange Pippin  apples increased from approximately 0 .5 to a maximum value 
of one, whi le [C02]i increased from about 3 to 7% over the same range of 02 
concentrations. I n  contrast in  G ranny Smith apples ReIC02 increased from 
approximately 0.4 at [02]ext of approximately 3% to a maximum value of about 
0.9 ,  whi le [C02]i i ncreased from about 1 .5 to 3.5%. 
1 09 
cS 0.0 � �-r�--;--+--+--r--r-��--�-+--+--r--�-r--�� =: 
1 .2 
0.8 
0.4 
0.0 
Y=( 1 .06358x)/(2.887 14+x) 
R2=O.95 
o 2 4 
0 0 
6 8 
[02]i (%) 
o 
(b) 
00 
o 
o o 
o 
o 
-10 12  1 4  
Fig .  5-4. Relationship between Rel02 and [02] i  of individual (a) 
Cox's Orange Pippin and (b) Granny Smith apples kept at 20°C.  
Solid lines were fitted by nonlinear regression using equation [5 .7] .  
I t  
1 .6 
1 .2 
0.8 
0.4 
1 .2 
Y= lI« x+ 1 .04)5)+( 1 . 1 825x)/(2.9 1 1 3+x) 
R2=0.97 
• •  . .  - . 
6 y= l /« x+ 1 .08) )+C 1 .0644x)/(6 .0245+x) 
R2=0.98 
o 2 4 6 8 10 1 2 · 14 
[02]ext (%) 
1 10 
Ca) 
• 
(b) 
o 0 
1 6  1 8 
Fig . 5-5. Relationship between RelC02 and [02]ext of individual (a) 
Cox's Orange Pippin and (b) Granny Smith apples kept at 20oe. 
Dotted lines represent individual anaerobic and aerobic components 
of the relationship. Solid lines describing the composite function 
were fitted by nonlinear regression using equation [5 .8] . 
20 
8 
2 
5 
4 
3 
2 
y= 1 I« x+O.7272)9)+(7 .44 16x)/(3.4744+x) 
R2=O.97 
7 Y= 1I« x+O.8083) )+(3.74 1 6x)/(3 .4744+x) 
R2=O.97 
o 2 4 6 
0 
0 
8 10 1 2  
[02]ext (%) 
1 1 1  
(a) 
(b) 
0 0 
0 0 0 
0 
0 
14 1 6  1 8  
Fig . 5-6. Relationship between [C02]j and [02]ext of individual (a) 
Cox's Orange Pippin and (b) Granny Smith apples kept at 20°C .  
Dotted l ines represent individual anaerobic and aerobic components 
of the relationship. Solid lines describing the composite function 
were fitted by nonlinear regression using equation [5 . 8] . 
2( 
1 1 2 
The relationship between ReIC02 o r  [C02]i and [02 ]i fol lowed a s i m i l a r  
general trend t o  t h ose with [02]ext (figs. 5 - 7  a n d  5-8). However t h e  s h a pe o f  
t h e  a e r o b i c  p h a s e  of the c u rves re l a t i n g  Re/C02 a n d  [02] i was steeper ( at 
lower 02 levels) than with [02]ext· 
5.5.4 RelRO versus [021ext or [021 i 
T h e  re l a t i o n s h i p  between r e l a t i ve respi rato ry q u otient ( Re /R O )  a n d  
[02]ext (fig. 5-9) was described by a n  exponential equation of t h e  form : 
Re/RO = a /[ 1 + b * exp(-(c * [02]ext + d * [02]ext * * 2 ))] 
wh ere a ,  b, c and d a re constants of the equation .  
[ 5 . 9] 
Re/ROs of G ranny Sm ith apples were approxim ately con stant between 
1 8% and approx i m ately 6% [02]ext. Below approxim ately 6% [02] ext, Re/RO 
i n c re a s e d  i n  G ra n n y  S m i t h : In c o n t ra s t ,  Re/ROs of Cox's O ra n g e  P i p p i n  
a pp l e s  i n c reased cont i n u a l l y  from 1 8% [02]e xt down w a r d s ,  with t h e  s lope 
increasing towards the lower 02 leve ls. 
The relat ionsh i p  between Re/RO a nd [02 ] i f o l l owed a s i m i la r  general 
form to t h ose with [02 ]ext (fig. 5- 1 0 ) a n d  was described by eq u a t i o n  [5 . 9 ] .  
Generally Re/ROs i n  Cox's O range Pippin were h igher than i n  G ra n n y  S m ith 
apples. 
5.5.5 [AA1se or [ ETOHlse versus [ 021 ext or [02] i 
I n  both Cox's Orange Pippin a nd G ranny Sm ith app les n e ither [ 02]ext 
(fig . 5- 1 1 )  n o r  [02] i ( f i g .  5- 1 2 ) h ad a s i g n ificant (P = 0 . 05) influence on sub­
epidermal acetaldehyde ( [AA]se) .  On t h e  other hand there was no detect a b le 
1 .6 
1 .2 
0.8 
0.4 
N 
5 Y= lI« x+ 1 .04) )+( 1 .0899x)/( 1 . 1 924+x) 
2 R =0.98 
. . 
. . " 
• • • 
• 
1 13 
(a) 
8 0.0�4-�-+--�+-�-+��+-�-+�--+-�-+--��� 
-
� er::: 
1 .2 
0.8 
0.4 
6 Y = l I«x + 1 .08) )+(0.9348x)/(2.6574+x) 
2 R =0.98 
o 
.,. ;. 
2 4 6 8 10  
[02]j (%) 
Cb) 
0 0 
o 
1 2  1 4  1 6  
Fig. 5-7. Relationship between RelC02 and [02] j of individual (a) 
Cox's Orange Pippin and (b) Granny Smith apples kept at 20°C .  
Dotted lines represent individual anaerobic and aerobic components 
of the relationship. Solid lines describing the composite function 
were fitted by nonlinear regression using equation [5 .8] .  
8 
6 
4 
2 
9 Y= 1 I((x+0.7272) )+(7.04 1 6x)/( 1 .4744+x) 
2 R =0.98 
. . . . 
• 
1 14 
(a) 
• 
• 
� 0 ���--+--+--��--���--+--+--+--r--��--�� o U '--' 
5 
7 Y= 1 I((x+0 . 8083) )+(3 .6822x)/( 1 .79 1 9+x) 
2 R =0.98 
o 2 4 6 8 
[02]j (%) 
(b) 
- 1 0  1 2  14 
Fig.  5-8 .  Relationship between [C02] j  and [02] j of individual (a) 
Cox's Orange Pippin and (b) Granny Smith apples kept at 20°C . 
Dotted lines represent individual anaerobic and aerobic components 
of the relationship. Solid lines describing the composite function 
were fitted by nonlinear regression using equation [5 .8] . 
1 6  
y=( 1 . 1 48/( 1 +( -O.6702)*exp( -(O.2292x+324.554x * * 2)))) 
2.4 R2=O.84 
• 
2.0 
1 .6 
• 
1 .2 
• 
• 
• • 
1 15 
(a) 
, 
• 
, 
Cl � 0 .8 -
QJ 
� 
2.0 
1 .6 
1 .2 
0.8 
Y=O.7845/( 1 +(- 1 .2246)*exp(-(0.4 1 1 7x+997 .957x* *2))) 
R2=O.80 
o· 
0 0 
00 
0 
0 
0 
0 
0 2 4 6 8 10 12  14  
[02]ext (%) 
(b) 
0 0 
0 
00 0 
0 
0 
1 6  1 8  
Fig. 5-9. Relationship between ReIRQ and [02]ext of individual (a) 
Cox's Orange Pippin and (lP) Granny Smith apples kept at 20oe. Solid 
lines were fitted by nonlinear regression using equation [5 .9] . 
2( 
2. 8 Y=( 1 . 1 806/( 1 +C-OA02)*expC-(0.38 1 4x+30.334x**2)))) 
2.4 
2.0 
1 .6 
1 .2 
2.0 
1 .6 
1 .2 
0.8 
2 R =0.85 
• 
• 
• 
• 
• • 
• • 
• • • • • • 
• 
• • 
Y=(0.7325/( 1 +( -OA852) *exp( -(0. 1 87x+299 .6 1 2x * * 2))) 
2 R =0.8 1 
0 
0 0 
� 
0 
0 
00 
0 
0 0 0  
0 0 
0 2 4 6 8 10  12  
[02] j (%) 
1 16 
Ca) 
• 
Cb) 
0 0 
1 4  
Fig. 5- 10. Relationship between RelRQ and [02] j of individual (a) 
Cox 's Orange Pippin and (b) Granny Smith apples kept at 20°C. 
Solid lines were fitted by nonlinear regression using equation [5 .9] . 
1 6  
1 17 
I I I I I I I I I I 
140 - (a) -
120 
• ... • 
• 
• 
100 
• • l- • • • 
• 
I- • 
• 
80 •• • 
• 
• 
• 
60 l- • • • 
-. • - • . - • • • 
� 40 - • • 
• 
'-'" • 
U I I I I I I I I I I '" ,......... I I I I I I I I I I < < (b) � 
140 -
120 - 0 
0 
100 .... 
00 0 
0 0 
80 I-
0 0 
0 0 0 0 0 
60 ... 0 0 0 0 8 0 0 0 0 0 
40 r- 0 0 0 0 
20 '= ? I 
0 I I I I I L � 1 
0 2 4 6 8 10 1 2  14  1 6  1 8  
[02]exl (%) 
Fig. 5- 1 1 .  Relationship between [AA]se and [02]exl of individual (a) 
Cox 's Orange Pippin and (b) Granny Smith apples kept at 20°C. 
-
-
-
-
-
-
-
. 
-
-
-
-
-� 
20 
1 18 
160 I I I I I I I I 
(a) 
140 f- -
1 20 f- • -• 
• 
• 
100 f- •• • -• 
• 
• 
80 - • • • •• -• 
• 
• • 
60 - • -• • 
•• 
,,-.... • • • 
"":' 40 - • • • -- • -
::t --
� 20 I I I I I I I I < I I I I I I I I < (b) '--' 
140 f- -
1 20 f- 0 -
0 
100 f- -
00 0 
0 0 
80 f- -
0 0 
0 @ 0 
0 
60 f- 0 0 -0 0 00 0 0 0 0 0 
40 f- 0 0 0 0-
20 « 0 I I I I I I I 
0 2 4 6 8 10 1 2  14  16 
[02]j (%) 
Fig.  5- 1 2. Relationship between [AA]se and [02] j  of individual (a) 
Cox's Orange Pippin and (b) Granny Smith apples kept at 20°C.  
1 1 9  
sub-epidermal ethanol ([ETO H ]se) except in fruit kept i n  a zero % [02]e xt (fi g .  
5-1 3) .  A p lot o f  [ETOH]se versus [02]i (fig. 5-1 4) showed similar rel a t i o n s h i p  
to t h o s e  with [02]ext. Surprisingly, n either AA n o r  ETOH was detect a b l e  i n  the ' 
c o r e  c a v i t y  of f r u i t of C o x ' s  O ra n g e  P i p p i n  a n d  G ra n n y  S m i t h  a p p l e s · 
irrespective of the levels of [02 ]ext or [02]i ' 
F r u it relat ive rates of C2 H 4 p ro d uction ( ReIC2 H 4) and inte r n a l  C2 H 4 
concentration ([C2 H 4]i) were sign ificantly ( P  < 0.0001 ) i nfl uenced by t h e  lev�1 
of 02 c o n ce n t r a t i o n  and d i ffered betwee n the two c u ltivars. A p lo t  of t h e  
re l a t i o n s h i p  betwe e n  ReIC2 H 4 o r  [C2 H 4] i and [02]ext (figs. 5- 1 5  a n d  5- 1 6) 
was wel l  descr i bed by a logist ic type equation of the form : 
[5. 1 0] 
where a ,  b, and c are constants of the equat ion . 
At zero p e rcent [02]e xt, ReIC2 H 4 and [ C2 H 4] i of both C ox' s  Orange 
Pippin and G ranny Sm ith apples was zero. H owever ,  as [02] ext rose f r o m  0 t o  
a b o u t  2% there w a s  a 'Iag phase' d u ri ng wh ich t h e re w a s  l itt le res p o n se of 
RelC 2 H 4 o r  [C2 H 4] i of Cox's O ra n g e  P i ppi n a n d  G ra n ny S m it h  a p p l e s  t o  
[02]ext. However between approximately 2% and 6 o r  8 %  [02]ext the r e  was a 
p h a s e  of r a p i d  i n c re a se in Re/C2 H 4 o r  [C2 H 4] i i n  response to i n c r e a s i n g  
[02] ext . Above approximat e ly 8 %  [02 ]ext , ReIC2 H4 o r  [C2 H 4] i rea c h ed a n  
asym ptote. 
The [02]ext value at which ReIC2 H 4 was half of the u ppe r a s y m ptote 
(of t h e  fitted l i n e )  was approximately 4 . 2 and 3 . 1 %  for C ox's Orange P ippin 
and G ranny Sm ith apples respectively. 
1 20 
800 
700 
(a) 
600 
• 
500 
400 • 
• 
300 • • 
200 
---
'- 100 • -::t • '-" 
'I> '" 0 � ::t 
� 
t:! 240 
(b) 
200 0 
1 60 
1 20 
80 
40 
0 
0 2 4 6 8 10 1 2  14  1 6  
[02]ext (%) 
1 8  20 
Fig . 5- 13 .  Relationship between [ETOH]se and [02]ext of individual 
(a) Cox's Orange Pippin and (b) Granny Smith apples kept at 20°C.  
121  
800 
700 
(a) 
600 
• 
500 
400 • 
• 
300 • • 
200 
-. -
'- 100 • 
::t • '-" 
11> '" 0 � ::c 
� 
� 240 
(b) 
200 0 
160 
120 
80 
40 
0 
0 2 4 6 8 10 1 2  14 
[02] j (%) 
Fig. 5- 14. Relationship between [ETOH]se and [02]j of individual (a) 
Cox's Orange Pippin and (b) Granny Smith apples kept at 20°C .  
16 
3 .0 
2.5 
2.0 
1 .5 
1 .0 
0.5 
..,. 
::z:: 
Y=2. 1 1 37/( 1 .0+48.7 1 87*exp(-0.8872x)) 
2 R =0.94 
• 
• 
• 
• • 
• 
• 
• 
1 22 
Ca) 
• 
cJ 0.0 I---.--+--+---+--+-I--+---+--+--+---+--t-+---+--+--+---+-I--+--_+_----I 
-� 
Cl:: 
1 .4 
1 .2 
1 .0 
0.8 
0.6 
0.4 
0.2 
Y= 1 . 1 286/( l .0+ 74.6896*expC - 1 . 2722x)) 
R2=0.94 0 o 
o 
Cb) 
0 0  
__ --��------------o 
o 
o 2 4 6 
o 
o 
8 10 1 2  
[02]ext (%) 
o 0 
o 
o 
o 
1 4  1 6  1 8  
Fig . 5- 1 5 .  Relationship between RelC2H4 and [02]ext of individual (a) 
Cox's Orange Pippin and (b) Granny Smith apples kept at 20°C .  
Solid lines were fitted by nonlinear regression using equation [5 . 10] . 
21 
600 
500 
400 
300 
200 
Y =520.693/( 1 .0+83.5735 *exp( -0.965547x)) 
2 R =0.96 
• 
• 
• • 
• 
• 
1 23 
(a) 
• 
-. 100 
-
. 
-
300 
250 
200 
1 50 
100 
50 
Y=273 .993/( 1 .0+32.3 809*exp( - 1 .0 1 655x)) 
R2=O.95 
o 2 4 6 
o 0 
o 8 
8 10 1 2  1 4  
[02]ext (%) 
(b) 
o 
o 
o 
1 6  1 8  
Fig .  5- 1 6. Relationship between [C2H4] j and [02]ext of individual (a) 
Cox's Orange Pippin and (b) Granny Smith apples kept at 20°C.  
Solid lines were fitted by nonlinear regression using equation [5 . 10] .  
20 
1 24 
In contrast, the relationship between  RelC2H4 o r  [C2H4] i and [02]i 
(figs.  5- 1 7  and 5-1 8) was wel l  described by an exponential type equation 
(rather than the Michaelis-Menten equation (equation [5.7] )) of the form : 
[5. 1 1 ] 
where a and b are constants of the equation . 
Between 0% and approximately 6% [02] i there was a phase of rapid 
i ncrease in ReIC2H4 or [C2H4] i of Cox's Orange Pippin and Granny Smith 
apples in  response to increasing [02] i '  Above about 6% [02]i . ReC2H4 or  
[C2H4] i reached a plateau . General ly, Cox's Orange Pippi n had h igher  
ReC2H4 and [C2H4]j than Granny Smith apples. 
The [02] i value at which Re/C2H4 was approx imately half the upper 
asymptote (of the fitted line) was approximately 1 .6 and 1 .4% for Cox's O range 
Pippin and Granny Smith apples respectively. 
5.6 DISCUSSION 
I nte rnal 02 concentrat ion ([02] i ) i n  i ndividual apple fruit ( ie .  Cox's 
Orange P ippi n and Granny Smith apples) closely mirro rs [02]ext, with the 
slope of the re lat ionship approach ing the theoretical maximum of 1 as 02 
avai labi l ity becomes increasingly non-l imit ing at high [021ext . At low [021ext. 
the reduced [021 i decreased the rate of resp i rat ion  and decreased the 
difference between the internal and external atmosphere composition .  Whi lst 
the nonl inear regression (equation [5.4]) accounted for a large proportion of the 
overal l variation in [02] i . variab i l ity in the estimates of the 02 contents of the 
two atmospheres (ie. in air and in CA) l imited the accuracy of this approach for 
characteris ing the re lationsh ip  between respi ration and [02] i ' An increased 
density of points in the lower quadrant of the graph cou ld clearly have assisted 
in this regard. 
3.0 
2.5 
2.0 
1 .5 
1 .0 
0.5 
'<t 
::I: 
2 Y=2. 14673*( 1 .0-exp(-0.550529x)), R =0.93 
2 Y=(2.45396x)/( 1 .3 1 026+x), R =0.9 1 
• 
• 
• 
• • • • 
• 
• . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. 
125 
(a) 
• 
cJ 0.0 1--........ ----tf---+--+--+---t--t---t----t--t----t---+---t--t----+-�t----1 
-
� 
� 
1 .4 
1 .2 
1 .0 
0.8 
0.6 
0.4 
0.2 
2 Y= 1 . 1 4895*( 1 .0-exp(-0.44876 1 x)), R =0.93 
Y=( 1 .35986x)/( 1 .99502+x), R2=0.9 1 
00 
o 
o 0 
(b) 
.. . . .. .. .. .. . 
o 
o 
. . . .. . . 
� __ �����---
--o 
. . · · · · · · · · ·
· 0 
o 2 4 
o 
6 8 
[02]i (%) 
o 
1 0  
o 
o 
12 
o 
14  
Fig.  5- 17 .  Relationship between RelC2H4 and [02]i of  individual (a) 
Cox's Orange Pippin and (b) Granny Smith apples kept at 20°C. 
Solid lines were fitted by nonlinear regression using an exponential 
model (equation [5 . 1 1 ] ). Dashed lines were fitted using the 
Michaelis-Menten model (equation [5 .7] ) .  
16  
1 26 
800 
2 (a) Y=550.494*( 1 .0-exp(-0.437 1 84x)), R =0.96 
700 2 Y =(65 8.292x)/( 1 .95708+x), R =0.95 
600 , • • • • . . . . . . . .. . .. . . . . . . . . .. . . . . . . . • . . . . • 
500 • 
400 
300 
200 
_-- lOO 
I --
:::i. '-'" 0 ,........, 
v ::c 2 N (b) Y=279.769*( 1 .0-exp(-0.42476x)), R =0.93 U 350 2 0 .......... Y =(330.52 1 x)/(2.06536+x), R =0.9 1 
0 0 300 0 0 0 0 . . . .. .. . .. .. . . .. . . . .  
250 0 0 0 
0 
200 0 
150 
0 
100 
50 
0 
0 2 4 6 8 10  12  14  
[02l (%) 
Fig. 5- 1 8 . Relationship between [C2H4]i and [02]i of individual (a) 
Cox's Orange Pippin and (b) Granny Smith apples kept at 20°C. 
Solid lines were fitted by nonlinear regression using an exponential 
model (equation [5. 1 1 ] ). Dashed lines were fitted using the 
Michaelis-Menten model (equation [5.7]) .  
1 6  
1 27 
The alternative approach out l i ned i n  equat ion [5 . 6] h as permitted 
confi rmation that the relationship between RelO2 and 02 conforms at least 
approximately to the hyperbolic Michael is-Menten kinetics as suggested by 
previous investigations on apples (And rich et al. , 1 99 1 ; Solomos, 1 982, 1 985), 
and avocados (Tucker and Laties, 1 985). This contrasts with the linear pattern 
of respiratory 02 uptake versus [02]i reported for apples in a sealed system i n  
which [02]ext levels were i n  continuous decl ine by Banks et al. ( 1 989) .  Their 
data also contrast with those of Tucker and Laties (1 985) obtained on a similar, 
dynamic system, although i n  the latter case C02 was allowed to accumulate 
with in  the system and its contri bution  to the shape of the curve obtained 
cannot be ru led out.  However, the s imilar curves obtained by Leshuk  and 
Saltveit ( 1 990) for disks of carrot tissue indicate that the effects of C02 with in  
Tucker and Laties' system were probably quite smal l .  
. Val ues for  rKm were about th ree times as h igh  fo r plots of RelO2 
versus [02]ext as they were for Re02 as a function  of [02]i ' The difference 
was due to the 02 concentrat ion g radient between i nte rnal and e xte rnal 
atmospheres (�[02]) '  Clearly, this difference would itself depend greatly upon 
the magnitude of this 02 concentration gradient. This means that �[02] would 
be affected by both fruit respi rat ion rate (which is itself a function of  both 
developmental stage and temperatu re) and of R, which has been shown to 
vary between apples of different cult ivars and, to a lesser extent, between 
indiv idual fruit  with i n  a cu ltivar (this subject has been addressed i n  t he  
preceding chapter). This clearly i l lustrates the advantages of consideri ng fruit 
physiological responses to CNMAs as a function of their i nternal atmosphere 
composition rather than the external atmosphere to which they are exposed. 
Although model l ing can be used quite satisfactori ly to develop our  knowledge 
in this area (Andrich et al. 1 991 ; Banks et al. , 1 989 ; Tucker and Laties, 1 985) 
the responses of individual fru it can only be identified if  i ndividual data are 
gathered (as util ised in this .study). 
1 28 
Whilst the scatter in  the data makes it difficult to be definitive about the 
exact shape of the curve relating RelO2 and [02]i (fig .  5-4),  nevertheless it is 
clear that rKm for th is relat ionship is much h igher than that reported for 
cytochrome oxidase (is < 0.1 % 02 in  the gas phase; Burton, 1 978; Butt, 1 991 ; 
Knee , 1 99 1 ) . This is supported by the simi lar values for apparent Km for 
respi ration  derived by describ ing [02] i as a function of [02]ext (fig .  5-2) .  
Simi lar conclusio ns have been reported by other researchers (Knee , 1 973; 
Solomos, 1 985, 1 988; Theologis and Laties, 1 978). 
Chevil lotte ( 1 973) attributed the deviation of this relationship from what 
might be expected for cytochrome uptake, to the development of zones of 
anaerobiosis . with in i ndividual" fruit cel ls. If the effect was solely med iated by 
i n hi bition of the efficiency of uptake by a te rminal oxidase then we would 
predict that any depression of respirat ion rate would be accompani ed by 
ethanol accumulation ,  which was not observed in th is study. I n  contrast, 
Tucker and Laties ( 1 985) proposed a mechanism which i nvolved at least two 
steps: a rapid response which involved i nh ibition of 02 uptake by a terminal 
oxidase (thought to be cytochrome oxidase) followed only later by a response 
which i nvolved in hibition of glycolytic flux. The apparent Km02 for the latter 
was much higher than for di rect inhibition of uptake by cytochrome oxidase 
and accounted for the different responses of their avocados in rapid and slow 
02 depletion experiments . This mechanism m ight also accou nt fo r  the 
delayed response of  apples to a reduced 02 atmosphere reported by Knee 
( 1 980). 
Interestingly, rFmax values were also higher for [02]ext than for [02Ji . 
Since rFmax theoretically must be the same in both approaches this d i fference 
presumably represents the relative accuracy with which the Michael is-Menten 
curve fits the two sets of data. 
1 29 
The difference between sub-epidermal 02 ([02]se) and core cavity 02 
concentration ([02]core) would itself be predicted to be affected by [02]i as, 
l ike re lative rate of exchange (Re/E) it shou ld be d i rectly proportional to 
respi ration rate. The weak relationships between the g radients (across the 
flesh) and [02]i identified in Cox's Orange Pippin and in Granny Smith apples 
were presumably a reflection of the l imitations in accuracy of this approach 
g iven the othe r factors involved (eg .  flesh porosity, in it ial respiration rate, 
measurement error). 
The difference in estimate of the Michaelis-Menten constants obtained 
when consideri ng  [02] i or [02]ext confi rm the importance of considering 
factors affecting the size of this difference (such as R and respi ration rate) 
when sett ing l i mits for MA sto rage.  The magn itude of this concentration 
difference would be substantial ly affected by natu ral or imposed variation in R 
(such as development of g reasi ness , wax ing ,  coat ing and packaging )  and 
part icularly by variat ion in respirati on rate ach ieved by exposi ng  f ru it to 
different temperatures (see chapter 7 for details on this subject) or i nherent in  
fruit of  different cultivars, production regimes or developmental stages. 
One of the measurable effects of reduced [02]ext in  'an atmosphere is 
on C02 evolution ,  which gives an indication of the rate of metabolic activity 
(8en-Yehoshua et al. , 1 963; Isenberg , 1 986 ; Wo"in et al. , 1 985). ReIC02 and 
[C02]i of Cox's Orange Pippin or Granny Smith apples declined in  response to 
diminishing [02]ext and [02li - However under anoxic conditions, ReIC02 and 
[C02] i i ncreased , suggesting that anaerobic respirat ion was predominant. 
Carbon dioxide was produced by the fru it even in the absence of 02 . These 
findings are consistent with those report by other i nvestigators including ap 
Rees ( 1 980, 1 985) . 81ackman ( 1 954), Kader (1 986) and Isenberg ( 1 986) who 
i ndicated that the re lative re lease of C02 decreased as the avai lable 02 
decreased from the amount in air (ie. 20.95%) to approximately 3% (depending 
on the commodity) . I n  this range of 02 concentrations, the Krebs cycle is the 
1 30 
predominant energy-generating system funct ion i n g  in the organ and t h e  b u l k  of 
the C 02 is evolved from this system ( Isenbe rg, 1 986) .  Anae robic C 02 r e l e ase 
f rom pyruvate and acc o m p a n yi n g  aceta ldehyd e  and eth a n ol rele a s e  i n  t h is 
range of 02 concen t ration a re insign ificant d u e  t o  indirect i n h i b ition effects of 
02 on g lycoysis. When 02 becomes more severely l im iting somewhe r e  below 
approxi m at e l y  3% t h e re i s  a rapid rise in C02 evo l u ti o n .  At t h i s  p o i n t ,  t h e  
g lyco l ytic system i s  n o  l o n g e r  i n h i b ited b y  02 , a n d  takes o v e r  t h e  e n e rgy 
s upplying fu nction i n  pl ace of the Krebs cycle (ap Rees, 1 980, 1 985 ) .  I n  t h i s  
reg ion (ie. below 3%) ,  t h e  02 concentration is l o w  enough t o  a l low s i g n ificant 
a n ae robic C 02 release from pyruvate and acco m panyi n g  ethanol p ro d u ct ion 
(ap Rees, 1 985; Kader, 1 987; I senberg, 1 986; Lam be rs, 1 98 5 ) .  
Th e re l at i o n s h i p  between Re/C02 o r  [ C 02] i and [ 02]ext o r  [ 02 ] i was 
described m athem at ic a l l y  a s  the com posite of its two com ponent p ro cesses 
(anaerobic and aerobic respi ration) as suggested by p revi o u s  investi g a t i o n s  on 
a p p l e s  ( B i a l e  a n d  Y o u n g ,  1 9 6 2 ; B l a c k m a n ,  1 9 5 4 ; B o e rs i g  et a l. 1 9 8 8 ;  
Cameron, 1 985; Kader, 1 987; Leshuk a n d  Saltveit, 1 990; S olomos, 1 98 8 ,  Wil ls 
et al. ,  1 98 1 ) .  An attempt was m ade to estim ate the anae robic com p e n sation 
point (ACP) for both [02]ext ([ACP]ext) and [02] i ([ACP]i) ;  (ACP def i n e d  a s  the 
[02] ext concentration at which CO2 prod uct i o n  wa s m in im u m ;  Boe rs i g  et al. 
1 988). Whilst the scatter in the data m akes it d ifficult to be defi n itive a b o u t  the 
estim ate of the AC P, neve rtheless the fitted c u rve i ndicated that [AC P ]ext (for 
[02]ext) was about 0.5% and [ACP] i (for [02]i ) was approxim ately 0 . 3% i n  both 
Cox's Orange Pippin apples a nd Gra n ny Smith apples. T h e  m in i m u m  [ C 02] i 
coinci des with t h e  [ACP]e xt ; below t h i s ,  fe rmentation o r  off-flavo u r  w i l l  occ u r  
a n d  the fruit w i l l  be u n sa leable. Blackm a n ,  ( 1 954 ) ,  Boersi g  et al. ,  ( 1 988 )  a n d  
F i d l e r ,  ( 1 9 5 1 )  i n d i c ated t h a t  ACP s h ifts i n  r e l a t i o n  t o  d u rat i o n  o f  l o w  02 
t re a t m e n t ,  p h y s i o l o g i c a l a g e of t h e  f r u i t ,  t e m pe ra t u r e  a n d  0 2 d i ff u s i o n  
coefficient o f  the fru it. 
1 31 
Re/ROs in  Cox's Orange Pippin were general ly greater than unity whi le 
i n  Granny Smith apples Re/ROs were mostly lower than one except i n  fruit 
kept in 02 levels lower than approximately 4%. The disparity was presumably 
related to real differences in the rates of 02 uptake and C02 output as cultivar 
differences in differential skin resistance to the two gases would cancel in the 
way that Re/RO was calculated. Similar variations in respi ratory quotient (RO) 
have been reported by other investigators including Fidler and North ( 1 971 ) , 
and Forcier et al. ( 1 987) . Cameron ( 1 985) also reported RO's g reater than 
unity for tomato and cherry fruit sealed in packages. Simi larly, Hudson et al. 
(1 991 ) also obtained Ra's higher than one for tomatoes in  MA packages. An 
i ncrease i n  Ra ind icates an i ncreased use of o rganic acids rather  t han 
carbohydrates or  fatty acids as the major substrate for respi ration (ap Rees, 
1 980, 1 985) . Organic acids have more 02 per carbon atom than sugars or  
fatty acids, therefore requiri ng less 02 consumption for the production of  a 
g iven amount of C02' It has also been observed that RO generally increases 
with ripening and senescence of most fruits and vegetables (Metl itskii et al. , 
1 972 ) . Othe r  t reatments can also i nduce i ncreases i n  Ra, such as the 
acetaldehyde treatment of grapes reported by Pesis and Marinansky ( 1 992) .  
Respi ratory quoti ent i n  apples decreased markedly  i n  gas m i xt u res 
containing high C02 and low 02 or high C02 alone compared to that in  the air 
storage (Metlitskii et al. , 1 972; Fidler and North, 1 967; Fidler, 1 950). This was 
attributed to an increase in the fixation  of C02 into organic acids i n  fruit. A 
reduction in Ra values by CA according to Wang ( 1 990) indicates retardation 
of the ripening and senescence of fruit and a reduced catabolism of o rganic 
acids, resulting in higher acid retention under CA conditions. 
Aceta ldehyde (AA) was measu red i n  f ru i t sub -epide rmal l aye r 
i rrespective of the level of [02]ext or [021i - On the othe
"r hand there was no 
detectable ETOH until [02]ext or [02] i dropped to zero. It was observed that 
at zero percent [02]ext fruit were producing large quantities of ETOH. This is 
1 32 
consistent with what might be expected of these fruit becoming anaerobic : 
pyruvic acid produced by the process of glycolysis is no longer oxidised but is  
decarboxylated to form AA, C02 and u ltimately, ETOH (ap Rees, 1 980; Kader, 
1 987 ;  Montgomery et al. , 1 990 ;  Pesis a nd  Mari nansky,  1 992) .  The  
accumulation o f  the products o f  anaerobic metabol ism can lead to  cel lu lar 
breakdown, typically accompanied by i nternal browning. These findings are in  
agreement with those of Smith et al. ( 1 987) who demonstrated that alcohol 
fo rmat i on  i n  app les  was' associ ated w i th  [02] ext be l ow  1 % at  l ow  
temperatures. 
There was no detectable AA or ETOH in the core cavity of either Cox's 
Orange Pippin or Granny Smith apples, irrespective of the [02]ext. It may be 
that at the time of internal atmosphere sampl ing, AA and ETOH may not have 
accumulated in sufficient concentrations to be detectable. Further resea rch is 
requi red to investigate this surprising finding . Acetaldehyde is a natural a roma 
component in  almost every fruit (Pesis and Frenkel ,  1 989).  Many resea rchers 
including Fidler ( 1 933,  1 968), Gerhardt and Ezel l ( 1 939), Janes and Frenkel 
(1 978) , Pesis et al. (1 991 ) and Pesis and Avissar (1 989, 1 990) reported that 
AA and ETOH are usual ly found in  f ruit in  trace amounts but they begin to 
accumu late as f ru its beg i n  to r ipen and i ncrease d u ri ng r ipen i n g  and 
senescence. Acetaldehyde also accumulates duri ng development of many 
physiological disorders, although its role in  deterioration is not clear (Avissar et 
al. , 1 989 ; Smagula and Bramlage, 1 977). Examining the 02 gradients i n  fruits 
in  relation to ripening, Biale and Young (1 981 ) indicated in  their review article 
that at the cl imacteric peak of respiration the 02 concentration could approach 
zero at the centre of a fruit. This is consistent with an earlier report by  Fidler 
(1 951 ) that certain apple varieties produce AA and ETOH when they ripen ;  th is 
impl ies that they contai n anaerobic tissue, even though they have 2 1 % 02 
outside. 
1 33 
It has long been reported that 02 is n ecessary for C2 H4 prod u ct io n  i n  
m a n y  f r u i t s  ( i n c l u d i n g a p p l e s )  a n d  w h e n  02 i s  a b s e n t  o r  u n d e r  a n o x i a  
c o n d i t i o n s  C 2 H 4 p r o d u c t i o n  c e a s e s  b e c a u s e  t h e  c o n v e r s i o n  o f  1 -
a m i nocyclopropane-ca rboxylic acid (ACC) to C2 H4 is inhibited. Th is res u lts i n  
a cc u m u lation of ACC in the tis s u e ,  s i n c e  e a r l i e r  steps in C 2 H 4 b iosynt hesis 
from meth ionine occu r in the absence of 02 (Adams and Yan g ,  1 979; Lu rssen 
et al. 1 979; M iyazaki and Yang, 1 987; Yang, 1 985; Yang and H offm a n ,  1 984) .  
However characte risi ng the relationship between the rates o f  C2 H4 prod u ction 
o r  [C2 H4] i and different 02 concentrations ( i e .  [02]ext or [02] i) h a s  not been 
report e d .  T h i s  s t u d y  sh owed that t h e  r e l a t i o n s h i p  b et w e e n  Re/C2 H 4 o r  
[ C 2 H 4] i a n d  [ 02 ] e x t  was s i g m o i d a l ,  b u t  t h e  r e l a t i on s h i p  w i t h  [ 02 ] i w a s  
exponential. T h e  d ifference in t h e  n ature of response ( ie. between ReIC2 H 4 o r  
[C2 H 4]i a n d  [02]ext o r  [02] i) was d u e  t o  t h e  presence of t h e  effects of R.  The 
p resence of R i m pl ies there exists a g rad ient i n  gas concent ration betwee n  t h e  
atmosphere i n side t h e  fru it a n d  t h e  external atmosphere. T h e  m ag n it u d e  of 
t h i s  g radient is a function of the skin of t h e  fruit to gas diffusion . 
The [02]ext va l ues at which ReIC2 H4 wa s half of t h e  upper asym ptotic 
va l u e  was higher in Cox's Orange P ippin than in G ranny S m ith apples. These 
d iffe ren ces c o u ld be re lated to the d i fferences i n  R. In b o t h  c u lt i va r s ,  t h e  
[02]e xt v a l u e s  a t  wh ich RelC2 H 4 was h a l f  t h e  upper asym ptotic va l u e  was 
h ig h e r  than the [02] i va l ue. The disparity is d u e  to the presence of R. T h i s  
f u rt h e r  em p h a s ises t h e  point m a d e  e a r l i e r  t h at f r u i t  re spo n se to CA/MA a r e  
l i k e l y t o  b e  m o r e  c o n s i s t e n t  w h e n  m e a s u r e d  i n  t e rm s o f  t h e  i n t e r n a l  
atm o sphere com position rather than that e xtern a l  atmosphere ( i e . [02 ]e xt ) to 
which they a re exposed, since it is t h e  02 i n s id e  t h e  f r u i t  t h at is t h e  d i re ct 
cause of inhibition of both C2H 4 production and [C2 H4] i rat h e r  t h a n  [02 1e xt , o n  
which [021 i i s  depen dent. 
It is interesting to note that the re lationsh i p  of ReIC2 H 4 vers us [02 ] i was 
we l l  desc ribed by an exponential type eq uation (equation [ 5 . 1 2] )  t h a n  by t h e  
Michae lis- Menten equ ation (equation [5 . 7] ;  f i g .  5- 1 7). ReIC2 H 4 appe a red to 
1 34 
reach an upper asymptotic value at lower [02]i values than might be predicted 
f rom  equat ion  [5 .7] . Th is  may be part ly  re lated to the fact that C2H4 
production from its immediate precursors involves at least two substrates (ACC 
and 02) and is therefore not strictly susceptible to Michaelis-Menten analysis. 
Keeping fruit in low 02 might be expected to result in accumulation of ACC 
within the tissue (because the breakdown of ACC to C2H4 requires 02 wh ilst 
the cleavage of S-adenosylmethionine (SAM) to yield ACC does not ;  Adams 
and Yang ,  1 979; lau et al. , 1 984; Miyazaki and Yang, 1 987; Yang, 1 985; Yang 
and Hoffman , 1 984) .  This could stimu late higher levels of C2H4 production 
f,om a piece of tissue in CA than would otherwise be expected from the same I �,f '''', 
piece of tissue based upon its rate of C2H4 production in air. An alternative 
. 
explanation could be that the rate of C2H4 production by the fruit in  air was not 
stable and i ncreased over t ime.  This again could have stimulated C2H4 
production at lower 02 levels giving higher rates than might be expected from 
the i r  rate of p roduction in a i r. However, the potential i nteractions o f  th is 
system at the biochemical level are quite complex and beyond the scope of 
this study;  consequently further work would be required to test this idea. 
To conclude, data on the 02 concentration around and within fruit have 
been uti l ised to examine the respi ratory behaviour as well as C2H4 production 
of  apples i n  response to 02 concentrat ions i n  t he  i nte rnal o r  exte rnal 
envi ronment. It is clear that fruit response to CA/MA storage are l ikely to be 
more cons istent when measu red i n  terms of the  i n te rna l  atmosphe re 
composition ( ie .  [02] i ) rather than that external atmosphere ( ie .  [02]ext) to 
which they are exposed, since it is the 02 inside the fru it that is the d i rect 
cause of inhibition of respi ration and C2H4 production rather than [02]ext , on 
which [02] i is  dependent. 
1 35 
5.7 LITERATURE CITED 
Adams, D. O. and Yang, S. F. 1 979. Ethylene biosynthesis: identification of  1 -
aminocyclopropane-carboxylic acid as an intermediate in  the conversion 
of methionine to ethylene. Proc. Nat. Acad. Sci. USA. 76 :1 70-1 74 . 
Andrich, G. ,  Fiorentini ,  R . ,  Tuci , A. and Galoppini ,  C. 1 989. Skin permeability 
to oxygen in  apples stored in controlled atmosphere. J .  Amer. Soc. Hort. 
Sci. 1 44 :770-775. 
Andrich, G . ,  Fiorent in i ,  R . ,  Tuci , A. , Z innai, A. and Sommovigo, G .  1 991 . A 
tentative model to describe the respi ration of stored apples. J .  A mer. 
Soc. Hort Sci . 1 1 6 :478-481 . 
ap Rees, T. 1 980. Assessment of the contributions of metabolic pathways to 
plant respirat ion.  I n :  The Biochemistry of Plants - A Comprehensive 
Treatise. Metabolism and Respi ration.  (D.  D.  Davies,  ed . )  Academ ic 
Press, New York, vol . 2 :1 -29. 
ap Rees, T. 1 985. The organisation of gylcolysis and the oxidative pentose 
phosphate pathway in plants. I n :  Encyclopedia of plant physiology.  (R.  
Douce and D .  D .  Days. eds.) Higher Plant Cell Respiration. Springer­
Verlag ,  Berlin .  New Series, vol . 1 8 : 391 -4 1 7. 
Avissar, I . ,  Marinansky, R.  and Pesis, E .  1 989. Postharvest decay contro l  of 
grape by acetaldehyde vapours. Acta Hort. 258 :655-660. 
Banks, N. H .  and Kays, S. J .  1 988. Measuring internal g ases and lenticel 
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1 36 
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1 37 
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1 38 
Gerhardt, F .  and Eze l l ,  B .  D .  1 939 .  A method for estimating the volatile 
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Kade r, A .  A .  1 987. Respi rati on and gas exchang e  of vegetab les .  I n :  
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metabolism of apple fruit tissue. J.  Sci . Food Agric. 24 :1 289-1 298.  
Knee ,  M .  1 980 .  Physio l og ical responses of app l e  f ru its to  o x yg e n  
concentration. Ann. Appl. BioI .  96 :243-253. 
Knee, M. 1 991 . Fruit Metaboli s m  a n d  practical p robl e m s  of fruit storage u nder 
hypoxia and anoxia. I n :  Plant Life Under Oxygen Deprivation .  (M.  B.  
J ackson ,  D.  D .  Dav ies  and H.  L a m b e r s .  eds . ) .  SPB Academic  
Publishing, The Hague, Net h e rl ands. pp. 229-243 .  
Laki n ,  W. D .  1 987. Computer aided he rmeti c  packa g e  d es i g n  a n d  s he l f  l ife 
predi ctio n .  J .  Packag i n g  Tech no l .  1 :82-86. 
Lam b e rs ,  H .  1 985. Respi rati o n  i n  i ntact plants a nd t i s s u e s : I t s  re g u l ation and 
d e p e n d e n c e  o n  e n v i ro n m e n t a l  f a c t o rs , m et a b o l i s m a n d  i n v ad e d  
org a n i s m s .  I n :  E ncyc l o pe d i a  o f  p l a nt phys i o l o g y .  ( R .  D o uce a n d  D .  D. 
D ay s .  eds . ) ,  H i g h er P l a nt C e l l  R e sp i rati o n .  S p ri n g e r- V e rl a g , B e rl i n .  
N e w  S e ries, vo l .  1 8 :4 1 8-473 . 
1 39 
'0 '" - ' � 
Lau ,  O. L. , Liu ,  Y. and Yang, S. F. 1 984. I nfluence of storage atmospheres 
and procedures on 1 -aminocyclopropane-carboxylic acid concentration 
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427. 
Leshuk ,  J .  A .  and Saltve it ,  M. E .  1 990.  A simple system for the  rapid  
determi nat ion o f  t he  anaerobic compensation poi nt o f  plant t issue. 
HortSci . 25:480-482. 
LO rssen ,  K . ,  Naumann ,  K.  and Sch roder, R .  1 979 . 1 -Aminocyclopropane- .'Y 
carboxylic acid : an i ntermediate in the ethylene biosynthesis i n  h igher 
plants. Z. Pflanzenphysiol . ,  92:285-294. 
Metlitski i ,  L. V. ,  Sal 'kova, E. G. ,  Volkind, N .  L., Bondarev, V .  I . ,  and Yanyuk, V. 
Y .  1 972 . Contro l led atmosphere sto rage of f ru i ts .  E ' ko n o mi ka 
Publ ishers, Moscow, 1 972 , Eng lish trans. by Dhote,  A. K. ,  Ameri nd 
Publishing Co. ,  New Delhi. 
Miyazaki , J. H .  and Yang, S. F. 1 987. The methionine salvage pathway in  
relation to ethylene and polyamine biosynthesis. Physiol .  Plant. 69 :366-
370. 
Montgomery, R . ,  Conway, T. W. and Spector, A. A. 1 990 . Biochemistry .  A 
Case-Oriented Approach. 5th edition. The C. V. Mosby Company, St. 
Louis, Baltimore, Philadelphia, Toronto. pp. 267-279. 
Pesis, E. and Avissar, I. 1 989. The postharvest quality of o range fru its as 
affected by prestorage t reatments with acetaldehyde vapou rs o r  
anaerobic conditions. J .  Hort. Sci . 64:1 07-1 1 3. 
Pes is ,  E .  and  Avissar ,  I .  1 990 .  Effects of postharvest app l icat i o n  of 
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acetaldehyde vapour on �trawberry decay, taste and certain volati les. J .  
Sci . Food Agric. 52:377-385. 
Pesis, E. and Frenkel , C. 1 989. Acetaldehyde vapours influence postharvest 
qual ity of table g rapes. HortSci . 24 :31 5-31 7 .  
1 40 
Pesis, E .  and Mari nansky, R. 1 992. Carbon dioxide and ethylene production by 
harvested grape berries i n  response to acetaldehyde and ethanol.  J. 
Amer. Soc. Hort. Sci . 1 1 0-1 1 3. 
Pesis, E . ,  Zauberman , G.  and Avissar, I .  1 99 1 . I nduction  of certain a roma 
volati les i n  �eijOa fruit by postharvest appl ication of acetaldehyde or 
anaerobic conditions. J .  Sci . Food Agric. 54 :329-337. 
Smagu la ,  J .  and Bramlage, W. 1 977. Measurement of acetaldehyde i n  
serlScing apple fruits. J .  Amer. Soc. Hort. Sci . 1 02 :31 8-320.  
Smith , S .  M., Geeson, J. D . ,  Browne, K.  M. ,  Genge, P. M. and Everson, K. P .  
1 987. Modified atmosphere retai l packaging of Discovery apples. J .  Sci. 
Food Agric. 40 : 1 65- 1 78. 
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of respi ratory d iminution. I n :  Control led atmospheres for storage and 
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1 70 .  
Solomos, T .  1 985. I nteractions between 02 levels, rate of respiration and gas 
d i ffus ion  i n  5 apple variet ies .  I n :  P roc. 4t h  Nat io nal  Con t ro l led 
Atmosphere Research Conference, North Caro l ina State U niversity, 
Raleigh ,  NC. (S. M. Blankenship, ed. ) ,  pp. 1 0-1 9. 
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Steel ,  R. G.  D. and Torrie, J .  H .  1 980. Pri nciples and procedures of statistics, 
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A biometrical 'pproach. McGraw-HiI I Book Co. ,  New York, NY, 2nd ed. 
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Plant Physiol .  62:249-255. 
Tucker, M. L. and Laties, G. G. 1 985 . . The dual role of oxygen in avocado fruit 
respirati o n :  K inetic analysis and computer mode l l i ng  of d i ffus ion­
affected respi ratory oxygen isotherms. Plant, Cell and Env. 8 : 1 1 7- 1 27. 
1 41 
Wade,  N .  L .  and G raham, D .  1 987.  A model  to descri be the mod i fied 
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ASEAN Food J. 3 :1 05-1 1 1 .  
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vegetables. New South Wales University Press, N ew South Wales, 
Australia. 1 71 pp. 
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humidity on the physical properties of apples. J. Hort. Sci . 40 :58-65 .  
Woll in, A .  S ,  Little, C .  R .  and Packer, J .  S .  1 985. Dynamic control of storage 
atmospheres. In Proceedings of the Postharvest horticu lture workshop 
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Yang, S. F. and Hoffman, N. E. 1 984. Ethylene biosynthesis and its regu lation 
in higher plants. Ann. Rev. Plant Physiol . 35 :1 55-1 89. 
1 42 
CHAPTER 6 
G AS D I F FUS ION  AND  QUALITY O F  APPLES  I N FLU E NCED  BY  
SURF ACTANT. 
6.1 ABSTRACT 
Granny Smith apples tend to deve lop g reasy skins after  e xtended 
storage which makes them s l ippery to touch and reduces the i r  aesthetic 
appeal .  Washi ng of Granny Smith apples in Tween 20 solut ions i nh ibited 
development of greasiness. This effect was associated with i ncreased R,  
��.l 
depressed [02]i , lower respi ration
"'-
and i ncreased [C02] i and [C2H4] i i n  the /I 
washed fruit compared to controls. The depression of  [02] i i n  Tween  20 
washed fruit was greater than the elevation of C02' suggesting that the Tween 
20 t reatment may have affected C02 production and rate of 02 uptake to 
different extents or alternatively the Tween 20 deposit on the fruit surface was 
differentially permeable to these two gases. 
Washed fruit also remai ned g reener and fi rmer than contro ls .  P re­
treatment by wiping without using Tween 20 solution had none of these effects 
but d id st imu late weight loss. None of the t reatments i nduced i nternal  
browning which is often associated with the  development of  g reasi ness i n  
Granny Smith apples. 
The positive effects of Tween 20 treatment appeared to be the result of 
modification of the fruit's gas exchange characteristics .  The mag nitude of 
modi f icat ion ach i eved by the Tween 20 t reatment was dependent upon 
temperatu re ,  period of sto rage and the concentration of wash ing mixture 
appl ied. 
1 43 
6.2 INTRODUCTION 
'G ranny  Smith ' is  an important export apple cult ivar grown in New 
Zealand and accounts for more than 35% of total production (New Zealand 
Apple and Pear Marketing B6ard, 1 986). Since New Zealand is far from export 
markets, most fruit are stored for some period of time. However, during  long 
term storage, the re is often an i ncrease in greasiness on the fruit surface 
(Martin ancY,f�niper, 1 970; Trout et al. , 1 953). Greasiness develops rapidly at 
ambient temperatures after removal of fru it from O°C i n  a i r  or CA storage 
(Leake et al. ,  1 989a) . This d imin ishes the aesthetic value and consumer 
appeal of the fruit as a marketable commodity. Greasiness i n  Granny  Smith 
apples has been of considerable concern to the New Zealand apple i ndustry 
over recent years. 
Apple fruit cuticle is primari ly  composed of cut in and waxy materials. 
Cutin, which is the major part of the cuticle, is i nsoluble i n  water and organic 
so lvents ( Hue l i n ,/ 1 959 ) .  On the basis of  the i r  chemistry and phys ical 
properties, the waxy materials have been divided into three separate groups 
namely u rsol ic acid, wax and oi l  (Leake £It al. 1 989a; U I I  et tiI: , 1 989) .  The 
onset of greasiness is a natural phenomenon associated with the wax and oi l 
composition of the fruit cuticle (Leake et al. 1 989a) . Major changes i n  the wax 
and oil fractions occur during fruit development (Knuth anc:l Stosser, 1 987) and 
duri ng storage (Mazl iak and Pommier-Miard , 1 963 ; Metl itskri et al. , 1 983) .  
Although  t he  wax f ract ion does not change much afte r harvest ,  the o i l  
component conti nues to increase markedly during storage (Li l l  e t  al. , 1 989, 
1 991 ; Leake et ai. , 1 989a;  Morice ani Shorland, 1 973) .  The oil is the fraction 
that is l iqu id at room temperature (Huel in  and Gallop, 1 951  a) . Whi lst these 
changes occur generally in apple cultivars such as Gala, Cox's Orange Pippin ,  
Stu rmer  etc . ,  they appear to occur  very markedly i n  G ranny Smith apples. 
Huel in and Gallop' { 1 951 b) showed that the oi l  fraction of the skin increased to 
3 - 4 times its original concentration during storage at O°C. 
1 44 
Development of the oi l f raction i ncreases skin resistance by blocking  
lenticels, thereby impeding gas exchange, modifying  the i nternal atmosphere � .......-
of the fruit (Eaks and ludi , 1 960 ; Huelin and Gallop, 1 951 a, 1 951  b ;  Trout et al. , 
1 94a.( 1 963) with the consequent potential for t ri ggeri ng  deve lopment of 
physiological disorders such as corefl ush (Little and "Minn is, 1 978). The fruit 
also become slippery to touch . 
Much research has been undertaken to understand the causes and 
prevention o f  the development o f  g reasiness in apples particularly G rann y  
Smith  (Huel in and Gallop, 1 95 1  a, b ;  Knuth et al. , 1 987; Leake eral. , 1 989a ;  
Markley and Sando, 1 931 ; Martin and Juniper, 1 970 ; Mazl iak and Pommie r­
Miard,  1 963 ;  Metl itski i er'al. , 1 983 ; Trout et al. , 1 953) . Solvents have bee n  
used to remove surface wax in apples i n  an attempt to study the chemical and 
physical properties of waxes (Horrocks, 1
-
964 ; Hal l , 1 966;  Li l l  et ' al. , 1 989,  
1 991 ) .  Leake et aC(1 989a) indicated that development of greasiness may be 
i nf luenced by time of harvest, storage period and position of fruit i n  the tree 
canopy, but fruit size was not a factor. 
In a prel iminary study (Appendix 2) with Granny Smith apples kept in a i r  
at 20°C, it was found that when fruit that had developed greasy surfaces were 
ha��1�9. by touching, thei r [02] i were lower than in non-handled controls. The 
[C02] i of fruit in both handled and non-hand led treatments we re h i g h  and  
when these fruit were cut open some had developed internal browni ng (see 
Appendix 3 ) .  The h igh  [C02] i and [02] i in  contro l  fruit compare d  to the 
handled fruit suggested that this treatment cou ld have caused blockage of 
lenticels through the redistribution of grease on the fruit surface. S ince 02 
effectively only diffuses via the lenticels (avai lable evidence indicates C02 can 
move through both the cuticle and epidermis [Banks, 1 984; Burton, 1 974] )  any 
treatment which blocks the lenticels on the fruit su rface is  l ikely to affect [02]i 
more than [C02]i ' A strong correlation (r = 0.63 ;  P < 0.0006) was measured 
1 45 
between the severity of i nternal browning (on a scale of 0 - 3) and [C02Ji . 
Based on these findings, it was reasoned that i f  some form of treatment was 
app l ied  to the fruit su rface to remove some of the su rface grease , gas 
exchange m ight be e n hanced and consequently development of i nternal 
browning could be reduced or prevented. Tween 20 solution was therefore 
chosen. 
Tween 20 is a surfactant routi nely used in fruit production either as an 
adjuvant i n  pesticide formulation or added to agricu ltu ral sprays main ly  to 
improve wetting and to enhance penetration of the active i ngredient i nto the 
/' 
plant material (Greene and Bukovac, 1 974).  Tween surfactant has been used 
to prevent post storage greening in potato tubers (Poapst et al. , '1 978 ; Poapst 
and  Forsyt h 1 974 ; 1 9 75 ) .  I n f o rmat i o n  o n  t he rate o f  pers ist e nce o r  
disappearance of Tween 20 sol ution in  apples i n  the f ield o r  i n  storage i s  
unavailable, however it is ' known to be nontoxic and used i n  the laboratory as a 
detergent (Poapst and Forsyth 1 974; 1 975). It is also used i n  pharmaceutical 
preparations as a surfactant for internal use (The Merck index ,  1 976) .  
An experiment was conducted in 1 989 to investigate whether removing 
grease from CA stored Granny Smith apples by washing in  Tween 20 solution 
enhanced gas exchange and prevented development of  i nternal brown ing .  
Contrary to i n it ial  expectat ion ,  the resu lts of  the experiment showed that 
redevelopment of greasiness in Granny Smith apples cou ld be inh ibited by the 
Tween 20 treatment,  however, th is was associated with g reater rather than 
lesser modification of the internal atmosphere of fruit. Based on these results, 
it was worthwhile to identify the optimum Tween 20 concentration that would 
prevent development of greasiness without causi ng excessive modificat ion of 
internal atmosphere composition of fruit. A further experiment was therefore 
u ndertaken i n  1 990 i n  which freshly harvested Granny Smith apples were 
washed in various concentrations of Tween 20 solution before storage at O°C 
1 46 
and subsequent transfer to 20°C with the objective of preventing development 
of g reasi ness and studying the i nternal atmosphere composition as well as 
some aspects of fru it quality. 
6.3 MATERIALS AND METHODS 
6.3.1 Fruit supply 
Granny Smith apples (Malus domestlca Borkh . ;  count 1 25; av. weight 
1 48 g) stored in CA (2% 02 and 2% C02) for approximately 4 months were 
obtained i n  1 989 as previously described in section 3 . 1 . Fru it were further 
stored at O°C in ai r for 1 4 days and subsequently transferred to 20±1 °C for 1 4 
days and during that period grease developed on fruit surface. 
In a second experiment in 1 990, freshly harvested Granny Smith apples 
(count 1 25 ;  av . weig ht 1 48 g) were also obtai ned from simi lar source as 
mentioned above. 
6.3.2 Treatment 
6.3.2.1 Experiment 1 
Fruit were divided into three lots of 1 5  and weighed individual ly before 
the following treatment application : 
1 .  control ( in the light of the results of the prel im inary experiment, fruit 
were handled by the stem (or peduncle) 
vi" 
2. fruit washed gently in Tween 20 solution (0. 1 5%) (Polyoxyethylene 
fI 
(20) - sorbitan monolaurate) and then ri nsed under runni ng water 
3. fruit wiped with soft tissue paper until they were shiny. 
Fru it were further sto red at 20±1 °C for 22 days to al low g rease to 
redevelop before measurements were made. Fruit were reweighed 1 and 22 
days after treatment appl ication. 
1 47 
6.3.2.2 Experiment 2 
Four fruit per treatment per assess�ent time were weighed and washed 
in 0, 0.05, 0 . 1 , 0.2 , 0 .4, 0 .8, 1 .6 and 3.2%lween 20 solution then rinsed u nder 
running water. Fruit were then stored at O°C in air for 0 ,  8, 1 6, and 24 weeks 
and subsequently t ransferred to 20±1 °C for 0 ,  1 ,  8 and 1 5  days be fore 
measurements were made. 
6.3.3 Assessment of g reasiness 
In both experiments 1 and 2, g reasiness was assessed quantitatively  by 
weighing the fru it on a Mettler AE 200 balance to the nearest 0.001 g before 
and after wiping thoroughly with soft t issue paper. The difference in weight 
provided a measure of grease weight (mg) .  
Greasi ness was also estimated subjectively in experiment 1 (Leake et 
al. , 1 989b) by rubb ing fru i t  agai nst the hand and sco r ing the degre e  of  
g reasiness on the fol lowing scale :  no greasiness (0), sl ight ( 1 ) ,  moderate (2) ,  
and severe (3) . 
6.3.4 Estimation of gas exchange variables 
In experiment 1 fruit respiration (C02 production)  and C2H4 production 
were measured on fruit kept in the dark (see 3.3.5.2) .  
I n  both expe riments , co re cavity 02 ' CO2 and C2H4 concentrat ions 
were measured by the di rect sampling method (see 3 .3 .4. 1  ) .  
RC02 and RC2H4 were a lso est imated (see  3 . 3 . 5 . 2 ) on f r u it i n  
experiment 1 .  
1 48 
6.3.5 Fruit quality assessment 
Fru it fi rmness, sol uble sol ids content and backg round colou r  were 
measured i n  both experiments 1 and 2 as previously described (see 3.3.8. 1 , 
3.3.8.2 and 3.3.8.3). 
Fruit were cut open across the equator and i nternal browning assessed 
subjectively by rating (0 - 3) the severity of browning as none, sl ight, moderate 
and severe respectively. 
6.3.6 Experimental design and analysis 
6.3.6.1 Experiment 1 
Fifteen  s i ng l e  f ru it rep l icates of each treatment were u s e d  i n  a 
completely randomised design .  Data were tested with analysis of variance 
procedure using General Linear Models (GLM) procedu re of SAS (see 3.3.9) .  
Mean comparisons were carried out using the Least s ign ificant d i fference 
(LSD) procedu re at 1 % level of significance (Steel and �� rrie ,  1 980 ; Litt le ,  
1 98 1 ) .  D ata o n  p e rcen tage  we i g ht l oss were s u bjected  to  a rcs i n 
t ransfo rmation (Mead and Cu rnow, "  1 983; Litt le ,  1 985)  p ri o r  to stat istical 
analysis and back transformed for presentation. 
6.3.6.2 Experiment 2 
Withi n the overall study, there were four  sampl ing times at Doe, each 
analysed as a separate expe riment. There were fou r  s ingle fru it repl icates, 
e ight Tween 20 concentrations and four  sampl ing t imes at 200e u sed  i n  a 
factorial design within each experiment.  Analysis of variance was carried out 
1 49 
usi ng General Li near Models procedu re (GLM) of SAS (see 3 .3 .9 ) .  The 
analysis inco rporated quantification of l i near, quadrat ic or cubic e ffects by 
regression (Steel and TQrrie, 1 980 ; Littfe, 1 981 ) .  
6.4 RESULTS 
6.4.1 Greasiness and internal browning 
6.4.1 .1 Experiment 1 
Redevelopment of g reasi ness, i n  f ruit measured objective ly as the 
d ifference in weight of the f ruit before and after  rubbing the fru it fre e  from 
g rease, was markedly reduced by washing in Tween 20 solution (P < 0.01 ; fig .  
6-1 ) .  Compared to the controls, washing of  fruit in Tween 20 solution resulted 
i n  58% reducti on i n  the subsequent g rease deve lopment. There was no 
significant d i fference in  g reasi ness between control and wiped fruit (at P = 
0 . 0 1 ) .  S im i l a r  resu lts we re obtai ned when g reas iness were assessed 
subjectively (fig. 6-2). There was a positive correlation between the objective 
and subjective methods of measuring g reas iness ( r  = 0.50;  P < 0 .0007) ,  
however the relationship was poorly  defined. No treatment induced i nternal 
browning. 
6.4.1 .2 Experiment 2 
Storage of Granny Smith apples at O°C and subsequent transfer to 20°C 
enhanced development of greasiness in Granny Smith apples. No significant 
differences (P = 0.05) were observed between treatments du ri ng the fi rst 1 5  
days storage at 20°C afte r harvest and t reatment app l icat ion  (fi g .  6-3a). 
However,  afte r 8, 1 6  or 24 wee ks sto rage at , O°C and  espec ia l ly  after 
subsequent t ransfer to 20°C, significant (P  < 0 'r001 ) reductions of g rease 6-
development were achieved by t reatment with Tween  20 solution (fig .  6-3) .  
These effects were greater for the higher Tween 20 treatment concentrations 
150 
50 �----�------�----��----�------�----� 
40 
-.. 
bO 
E 
'::' 30 
..c:: 
bO .... 
� 
� 20 
4) � 0 
10  
o L..--_ 
a 
control wIpmg 
Treatments 
washing 
Fig. 6- 1 .  Grease weight of Granny Smith apples after wiping or 
washing in Tween 20 solution and storage for 22 days at 20°C. 
Letters in common not significantly different at the 1 % level. Mean 
separation by Least significant difference (LSD) procedure. 
15 1 
4.0 
3 .5  
a a 
3 .0 
� 2.5 
0 
u � 
� 2.0 
� � 
0 1 .5 
1 .0 
0.5 
0.0 
control wIpmg washing 
Treatments 
Fig. 6-2. Grease score of Granny Smith apples after wIpmg or 
washing in Tween 20 solution and storage for 22 days at 20°C.  
Letters in common not significantly different at the 1 % level. Mean 
separation by Least significant difference · (LSD) procedure. 
30 �----------------------------� 
25 
20 
15  
10  
5 
- - 0 day at 'll-te 
•• • •. 1 day at wOe 
. _.  8 days at 200e 
-- IS days at 200e 
(a) 
o � ______________________________ � 
25 
20 
1 5  
co 1 0  
g 5 ..... 
..c 
(b) 
. .  ' ' .  
.� 0 
� �--------------------------------� � 
� 25 
� 
� 20 C) 
15  
10  
5 
o 
25 
20 
15  
10  
5 
o 
(c) 
�--------------------------------� 
(d) 
...... : . . . . . 
�---+�--------------------------� 
o 0.05 0. 1 0.2 0.4 0.8 1 .6 3 .2 
Tween concentration (%) 
Fig. 6-3 . Grease weight of Granny Smith apples after 
washing in different concentrations of Tween 20 solution, 
o stored (for (a)=O, (b)=8, (c)= 16, (d)=24 weeks) at 0 C and 
subsequent transfer to 20°C (for 0, 1 , 8 and 1 5  days). Vertical 
bars indicate standard errors of means. 
152 
1 53 
(P  < 0 .000 1  fo r t he  l i near effect of 1092 {Tween  concentrat ion)  with no  
sign ificant quad ratic or cubic deviations). Greasiness developed rapid ly  i n  
control fruit at 20°C, particularly in  fruit stored fo r 1 6  and 24 weeks at O°C. 
This development of greasiness was totally inhibited during storage at 20°C in  
fruit coated with the h ighest concentrat ions of  Tween 20 ,  w i th  progre ssive 
amounts of i nh ibition  seen at the i ntermediate levels of treatment. These 
effects were confi rmed by the significance of the interaction of the effects of 
days and treatment concentration (P < 0.001 at 8, 1 6  and 24 weeks) .  None of 
the treatments induced internal browning. 
6.4.2 Skin resistance to gas diffusion 
Washing of Granny Smith apples i n  Tween 20 solution i ncreased both 
RC02 and RC2H4 (P < 0.01 ; fig. 6-4, experiment 1 ) . Skin resistance to C02 
diffusion of washed fru it was 33% more than controls and 23% more than 
wiped fruit. RC2H4 of washed fru it was 36% more than controls and 1 7% 
more than wiped fruit. The wiping treatment resulted in a mean increase of 
nearly 1 3% and 23% respectively for C02 and C2H4 diffusion compared to the 
controls. 
6.4.3 Respiration rate and ethylene production 
Wash ing of fruit in Tween 20 solut ion (experiment 1 )  S i gn if icant ly  
decreased the rate of C02 production from the fruit ( P  < 0.01 ; f ig. 6-5). Tween 
20 treated fruit were respiring approximately 36% less than the controls, whi le 
wiped fru it were respi ring nearly 30% more than the washed ones and only 
about 8% less than the controls (not significant). 
Rate of C2H4 evolution was not affected by the treatments (at P = 0.01  ; 
f ig. 6-6) ,  with an overal l mean of 29. 1 ± 1 .9 Ill/kg/hr. 
154 
b 
....-.. -
III RC02 
[ill RC2H4 
, 
E 
(..) 6 C'-l 
-
o 
control 
a 
a 
wlpmg 
Treatments 
washing 
Fig. 6-4. RC02 and RC2H4 of Granny Smith apples after wiping or 
washing in Tween 20 solution and storage for 22 days at 20°C. 
Letters in common for each gas not significantly different at the 1 % 
level. Mean separation by Least significant · difference (LSD) 
procedure. 
155 
1 0  
�----�----�------�----�------�-----. 
_-.. 8 
'"t: 
-, 
00 
� 
0 6  u 
r<) 
e u '--' 
§ 4 .-..... � '-.-
0.. VJ 
(l) 
� 2 
o '----
a 
control wlpmg 
Treatments 
washing 
Fig. 6-5 .  Respiration rate of Granny Smith apples after wiping or 
washing in Tween 20 solution and storage for 22 days at 20°C. 
Letters in common not significantly different at the 1 % level .  Mean 
separation by Least significant difference (LSD) procedure. 
156 
40 
35 a 
..-
"7..c 30 
-, 
Q.() 
� 25 
::t --
= .9  20 .... u 
::s 
"'0 
e 15  
0. 
"f" 
� 10  U 
5 
0 
control wlpmg washing 
Treatments 
Fig. 6-6. C2H4 production of Granny Smith apples after wiping or 
washing in Tween 20 solution and storage for 22 days at 20°C.  
Letters in common not significantly different at  the 1 % level. Mean 
separation by Least significant difference . (LSD) procedure .  
1 57 
6.4.4 Internal gas concentrations 
6.4.4.1 Experiment 1 
Compared to the control and wip ing t reatments . washi ng of G ranny 
Smith apples in Tween 20 solution decreased [02]i by two-th i rds (fig . 6-7). 
There were no sig nificant differences in [02]i between control and wiped fruit 
(P < 0.01 ) .  Inte rnal C02 was not affected by  any of the treatments (at P = 
0.01 ; fig .  6-7), with an overal l average of 4.8 ± 0.2%. On the other h and the 
washi ng treatment significantly i ncreased [C2H4] i (P < 0.01 ; fig .  6-8) by 30% 
compared to the controls.  The re were no marked d i fferences i n  [C2H4]i 
between control and wiped fruit. 
6.4.4.2 Experiment 2 
In  general during storage at O°C there was a progressive decline  i n  [02]i 
with increasing Tween 20 concentration. Fruit washed in various Tween 20 
concentrations before storage at O°C and subsequent transfer to 20°C (P  < 
0.00 1 ) had lower [02]i than control fruit and the magnitude of this e ffect was 
di rect ly proporti onal to the 1092 (Tween concentrat ion)  (fi g .  6-9) .  Marked 
depression of [02] i was observed 24 hours after t ransfer of fruit f ro m  cold 
storage (O°C) to ambient temperature (20°C). The magnitude of depression 
was more apparent in fruit washed in  the highest concentrations of Tween  20. 
I nternal 02 however increased thereafter. 
Simi larly, there was a consistent elevation of [C02]i duri ng storage at 
20°C i n  f ru it coated with the h ighest concentrat ions of Tween 20 .  with a 
prog ressive increase seen at the intermediate levels of treatment ( P  < 0.001 
for the l i near and quadratic effects of 1092 (Tween concent rat ion ) ,  wi th  no 
significant cubic deviations ; fig. 6- 1 0) .  A similar trend was observed i n  fruit 
14 
12 
.- 10 
� '-' 
.-..-. 
N 8 0 u ......... 
""0 
a 6 
,.-, 
N 0 ......... 4 
2 
0 
a 
control wlpmg 
Treatments 
• [02]j 
El [C02]j 
z 
washing 
158 
Fig. 6-7 .  [02] i and [C02]i of Granny Smith apples after wiping or 
washing in Tween 20 solution and storage for 22 days at 20°C. 
Letters in common for each gas not significantly different at the 1 % 
level. Mean separation by Least significant difference (LSD) 
procedure. 
159 
/ 
-'. \ 
/ '\ j 
l. ., 
1" -' 
700 �----�----�------�----�------�-----. 
600 
500 
200 
100 
0 1....---
control wlpmg 
Treatments 
b 
washing 
Fig . 6-8 .  [C2H4] i  of Granny Smith apples after wiping or washing in 
Tween 20 solution and storage for 22 days at 20°C. Letters in 
common not significantly different at the 1 % level. Mean separation 
by Least significant difference (LSD) procedure. 
25 
20 
15 
10 
5 
0 
20 
1 5  
1 0  
5 
,,-... 
� 0 --
,........, 
N 
Q 20 
15  
10  
5 
0 
20 
15  
10  
5 
0 
- - 0 day al '1J)°C 
• • • • •  1 day al '1J)°C 
• _. 8 days al 20°C 
- 15 days at 20°C 
1- - -: 1- - - .. _ _  + _ _  . _  
. .. , .. .. . ... . 
·· .. 
· · · · · · · i 
- ... " " " i- - - i 
._, 
.
. .. . . . . 
" . 
.
.. .. . , 
1- - - 1- - - +- - - + - - ... -. ...... i ...... 
... ... " " " 
'f 
(a) 
(b) 
(c) 
(d) 
o 0.05 0. 1 0.2 0.4 0.8 1 .6 3 .2 
Tween concentration (%)  
Fig. 6-9. Internal O2 concentrations of Granny Smith apples 
after washing in different concentrations of Tween 20 
solution, stored (for (a)=O, (b)=8, (c)= 16 ,  (d)=24 weeks) at 
o 0 o C and subsequent transfer to 20 C (for 0, 1 ,  8 and 1 5  
days). Vertical bars indicate standard errors of means. 
1 60 
20
�-
---------------------------� 
15 
10 
5 
o 
15  
10  
5 
.-
� 0 ---,......., 
N 0 U ....... 15  
10 
5 
0 
15  
10 
5 
o 
- - o day at 1Jle 
• • • • . 1 day at 'lJte 
._.  8 days at 20°C 
- IS days at 20°C 
(a) 
. ' 
t . . · ,...,.··"f!'·-· I 
_ ... -- ­
...- - - ... -
-
" - - "' -
-
"
-
,.. 
.-
-
-
"' -
-
"' - - "
-
-
.. 
-
_ .... ..... 
... . . . ·
· · · 1 
.... 
_ - -1 
_ - I  ,..-
.
.
..
.
.
.
. t. ·· · · · ·
· ·  
�--1 I ..
.
.
.
. .
. 
1 . . . . . . . . t- '.:;� ; .A.!.'::'::' : � .- '  
. -
! - · - �
·
- "r r 
t- I • I 
_ 
-f- _ - t 
..... - - � - - � - - ... - -
.. _ - .-1 -
(b) 
(d) 
o 0.05 0. 1 0.2 0.4 0.8 1 .6 3 .2 
Tween concentration (%) 
Fig. 6- 10. Internal CO2 concentrations of Granny Smith 
apples after washing in different concentrations of Tween  20 
solution, stored (for (a)=O, (b)=8, (c)= 16,  (d)=24 weeks) at 
o 0 o C and subsequent transfer to 20 C (for 0, 1 ,  8 and 15 
days). Vertical bars indicate standard errors of means. 
161  
1 62 
during storage at O°C, but thei r [C02] i was lower than those stored at 20°C.  In 
the fi rst 24 hou rs afte r  t ransfe r of  f ru it from O°C to 20°C,  there was a 
pronounced increase in  [C02]i ' The degree of increase was greater i n  fruit 
washed in  the higher Tween 20 concentrations. I nternal C02 concentrations 
however decreased thereafter at 20°C. The [C02]i in fruit treated with Tween 
20 ( 1 .6  or 3.2%) and after 24 weeks of cold storage and 1 day at 20°C were 
twice the level in  similar fruit at stored at 20°C for 1 5  days. 
There was no detectable [C2H4]i i n  fruit during the fi rst 1 5  days after 
harvest and treatment appl ication at 20°C (fig .  6-1 1 ) . During  storage at O°C 
[C2H41i in both control and treated fruit was low, but concentrations increased 
steadily duri ng storage at 20°C in contrast to the i ncrease then decrease seen 
for [C02] i ' Genera l ly ,  after  8, 1 6  or 24 weeks of  sto rage at O°C and 
subsequent transfe r to 20°C, there was a consistent trend of i ncreasing 
[C2H4] i in fruit washed with the h ig hest concentrations of Tween 20 ,  with 
progressive increase in [C2H4] i observed at i ntermediate concentrations of 
Tween 20. 
6.4.5 Percentage weight loss 
6.4.5.1 Experiment 1 
Twenty-two days after treatment appl ication, water loss was increased 
by about 25% in fruit wiped with a soft tissue paper compared to control fruit . 
There was no significant effect of washing with Tween 20 solution on water 
loss (at P = 0.05; fig .  6-1 2) .  
---, -
-::t '-" 
.� ....... '<t 
::r: ('I 
2500 
2000 
1 500 
1000 
500 
0 
2000 
1500 
1000 
500 
0 
- - 0 day at '}Ite 
. . • • . 1 day at 200e 
. _ .  8 days at 200e 
- IS days at 200e 
J----r---. ...--::._ ·r · _.  . _
. ' 1 ' "  · · · · ·1 :� ... � . . . . :�.+ . . . . . . .  
t - . . . . . . . . . . . . . . . f- . . . . . • .  
I -e - - '-'  
- - - � - - . - - + - - . - - � - -
(a> 
(b) 
� 2000 (c) 
1500 
1000 
500 
0 
2000 
1500 
1000 
500 
0 
-A--�.-.-1-·- 1 . ·- ·t ·_ ·+ ·- · . . . f 
I . .  . . . . . . t · · · · · · ·  .. · · ·:.:.  -t , . . . . . . . .  1 . . . . . . . . + . . . . . . . 1 . . . . . . . .  1 -I _ - -1 -
... - - ... - - .. - - . - _ . - -
-. _ .
- '  ·- ·-I-·_ j 
t · . . . . . . . . .��: 
.
. :.-::. . . . . . . .  . . . . . .  .� .� .� � .�.� 
...- - - - - - .. - - + - - . - - .. 
(d) 
o 0.05 0. 1 0.2 0.4 0.8 1 .6 3 .2 
Tween concentration (%) 
Fig. 6- 1 1 .  Internal C2H4 concentrations of Granny Smith 
apples after washing in different concentrations of Tween 20 
solution, stored (for (a)=O, (b)=8, (c)= 16,  (d)=24 weeks) at 
o 0 o C and subsequent transfer to 20 C (for 0, 1 ,  8 and 15 
days). Vertical bars indicate standard errors of means. 
163 
4 
V} 
V} 
0 -
.... 
� 3  .... 
0 � 
� 
2 
control 
b 
wlpmg 
Treatments 
164 
a 
washing 
Fig. 6- 12.  Percentage weight loss of Granny Smith apples  after 
wiping or washing in Tween 20 solution and storage for 22 d ays at 
20°C. Letters in common not significantly different at the 1 % level. 
Mean separation by Least significant difference (LSD) procedure. 
1 65 
' 6.4.5.2 Experiment 2 
Twenty-four  hours after treatment application and storage at 20oe, t here 
were no differences i n  percentage weight loss between controls and Twee n  20 
treated fruit. Weight loss increased with t ime of storage  at 20°C, wit h  fruit 
washed in h igher Tween 20 concentrations losing more weight (fig. 6-1 3a) . 
D u ri ng sto rage at ooe i t  was f ru it washed i n  t h e  h i g hest Tween  20 
concentrations that lost most weight and a similar pattern was seen for the 
elevated rate of weight loss during subsequent storage at 20°C. There was a 
progressive loss of weight in fruit during the period of storage at 200e after  a 
period of storage at ooe with the highest amount recorded on  the 1 5th day at 
20oe. Fruit stored for 24 weeks at ooe and subsequently transferred to 200e 
for 1 5  days lost nearly 6% of thei r  total weight. Generally, percentage weight 
loss increased with increasing Tween 20 concentrations applied. 
6.4.6 Qual ity indices 
6.4.6.1 Experiment 1 
Afte r twenty-two days of t reatment appl ication and storage at 20oe, 
control and wiped fruit markedly lost their g reen colour (fig . 6-1 4) .  In  contrast, 
fruit washed i n  Tween 20 solution retained their green colour (as i ndicated by 
the Hue angle values) (P <0.01 ; fig .  6- 1 5). Fruit treated with Tween 20 were 
approximately 6% and 9% fi rmer than control and wiped fruit respectively (P < 
0.01 ; fig .  6-1 6). The re were no treatment effects on soluble sol ids content of 
fruit (at P = 0.05, with overall mean of 1 1 .4 ± 0 .9%). 
6.4.6.2 Experiment 2 
When freshly harvested G ranny Smith fru it were -washed i n  various 
concentrations of Tween 20 solution and stored at 20°C for 1 ,  8 and 1 5  days 
there were no significant (at P = 0.05) differences i n  colour change between  
VJ 
VJ 
0 -.. 
� bO .-
� 
� 
10�------------------------------� 
8 
6 
4 
2 
o 
8 
6 
4 
2 
0 
8 
6 
4 
2 
0 
8 
6 
4 
2 
0 
- - 0 day at 1JtC 
• • • • .  1 day at 1JtC 
. _ .  8 days at 20°C - 15 days III 20°C 
.... I I • • .� 
_ _ . __ . _._._._._. + ._.-t 
. . . . . . . . .... . . . . . . . . . . .. . . . .. . . . . . . . .. . . . . . . . . .. . . . .. . . .. . . . . . . . .  
- • I I I �---/j 
. _ - . -- .-..-'- '-+-- ' - ·- ·r ·_·-t ...... . . . . . . . .  .. . . . . . . • . . • . . . . . .• . . . • . . .  ..oi� .- ;.J 
_ _  ���� _ _ _ _ _  �� - 1 - -
� T I � • I -, 1 • .-1 I , 1 -... .--f-- -t .-.-._- .-._ ._ .+- ._.+ .-. _1 . :l  . . . . . . . . .. . . . . . . .  � :;.·- · · ·t • . . . . .. . . . . . . . .. . . . . . . _ _  -1 - - .... ..=.. :..:.. _ ..... >..L._  9- - _ .. - -
r---I r---! I I I 1 
I-·-l- _/- ._ .-t ._ ·-t. - ·-j·- '-I- ·:.-j 
I · · · · · · · · �· · · · ·:.:.· .. . . . . . . . .. .  · · · · · · ·! · · · · · · · ·.· · · ·.;: ·.:.t··;. -r - - � - t - - � - - , - - ; -
11 , , 
<a> 
(b) 
(c) 
(d) 
o 0.05 0. 1 0.2 0.4 0.8 1 .6 3 .2 
Tween concentration (0/0) 
Fig. 6- 1 3 .  Percentage weight loss of Granny Smith apples 
after washing in different concentrations of Tween 20 
solution, stored (for (a)=O, (b)=8, (c)= 16 ,  (d)=24 weeks) at 
o 0 o C and subsequent transfer to 20 C (for 0, 1 ,  8 and 15  
days) .  Vertical bars indicate standard errors of means. 
166 
TREA TM£NTS APPLIED l' OCT08£JC 1 aa. 
w.-.SHED 
0.15. ... TWEEH 20 
167 
Fig. 6- 14. Photograph showing Granny Smith apples after wiping or 
washing in Tween 20 solution and storage for 22 days at 20°C. 
168 
120 �-
---�------��--�------�----�------� 
1 10 
90 "'---
control wIpmg 
Treatments 
b 
washing 
Fig.  6- 15 .  Hue angle of Granny Smith apples after wiping or washing 
in Tween 20 solution and storage for 22 days at 20°C. Letters in 
common not significantly different at the 1 % level. Mean separation 
by Least significant difference (LSD) procedure . 
80 
70 
60 
--. 
b 50 
V,) 
V,) 
Q) 
§ 40 
t.C 
..... 
·2 30 � 
20 
10 
0 
control wIpmg 
Treatments 
169 
b 
washing 
Fig. 6- 16.  Firmness of Granny Smith apples after wiping or washing 
in Tween 20 solution and storage for 22 days at 20oe.  Letters in 
common not significantly different at the 1 % level. Mean separation 
by Least significant difference (LSD) procedure. 
. 
1 70 
treatments (fig .  6-1 7). However hue angle declined during storage of treated 
fruit at Doe and especial ly fol lowing  subsequent t ransfer to 20°C. During  
storage at  Doe , there was a progressive inh ibit ion o f  degreen ing  i n  h ighe r  
treatment concentrat ions. Fruit washed in high Tween 20 concentrat ions 
before storage for 8 or 1 6  or 24 weeks at Doe and then stored at 200e were 
greener than their respective controls. There was a t rend of decreasing loss of 
g reenness with higher treatment concentrations in fruit stored at Doe for 24 
weeks and subsequently transferred to 20oe. 
Fru it f i rmness remai ned h igh  (mean of 80 Newto ns) and approximate ly  
constant (P < 0.05) duri ng the f i rst 1 5  days after  t reatment appl ication and 
storage at  20oe. However there were consistent t rends (P < 0.001 for t he 
l i near effect of 1092(Tween concentration)), of decreasing loss of fi rmness with 
h i g he r  Twee n  20 concentrat ions  after  a period of sto rage at Doe a n d  
subsequent storage at 20°C (fig .  6- 1 8) .  Fruit washed in  high ( 1 .6 or 3.20/0) 
Tween 20 solution were fi rmer than the controls during storage at ooe for 1 6  or  
24 weeks and subsequent storage at 20°C. 
There was no marked (not sign ificant at P = 0.05) effect of treatments on fruit 
soluble solids contents during storage at Doe and subsequent transfer to 200e 
(fig . 6-1 9) .  However there were significant differences in  the overall sol uble 
sol ids content of fruit stored at ooe for 8,  16 and 24 weeks and subsequent 
storage at 200e (P < 0.05). For example soluble sol ids content of control and 
most treated fruit increased by the 1 5th day at 200e (fig .  6- 1 9a) on  the o ther  
hand it decreased after 24 weeks at ooe and 15  days at 20°C (fig .  6- 1 9d) .  
10.0 r---------------------., 
7 .5 
5.0 
2.5 
0.0 
7.5 
5.0 
2.5 
0.0 
7.5 
5 .0 
2.5 
0.0 
- - O day at '2Ile 
•• . . . 1 day at 200e 
._- 8 days at 200e 
- 15 days 11 200e 
I ,--C·""·'· - - . - .  :f; .. -.. t --·4·.-.:: =1 . . . . . .  -J . . .  . _ . ..- . - . . . . .. . . . . 
I---t- -- -�-- .+ -
i-- r:-. :-:--r- _:7_ :-:_1..... --_:1:- -r .... - .1 . _ -_ .:..f ..... --- ....---- - i � ...... ..--., - -1- - -
(a) 
(b) 
(c) 
(d) 
o 0.05 0. 1 0.2 0.4 0.8 1 .6 3 .2  
Tween concentration (%) 
Fig. 6- 17 .  Percentage decrease in hue angle of Granny Smith 
apples after washing in different concentrations of Tween 20 
solution, stored (for (a)=O, (b)=8, (c)= 16,  (d)=24 weeks) at 
o 0 o C and subsequent transfer to 20 C (for 0,  1 ,  8 and 1 5  
days) . Vertical bars indicate standard errors of means. 
171  
80 
70 
60 
50 
80 
70 
60 
g 
r.IJ 50 r.IJ 
Q) 
I: 
� 80 
.... ..... 
� 70 
60 
50 
80 
70 
60 
50 
- - 0 day at wOe 
• • • . .  1 day at wOe 
._. 8 days at 200e 
- IS days al 200e 
(d) 
° 0.05 0. 1 0.2 0.4 0.8 1 .6 3 .2 
Tween concentration (%) 
Fig. 6- 18 .  Finnness of Granny Smith apples after washing in 
different concentrations of Tween 20 solution, stored (for 
° (a)=O, (b)=8, (c)=16, (d)=24 weeks) at 0 C and subsequent 
transfer to 20°C (for 0, 1 ,  8 and 1 5  days). Vertical bars 
indicate standard errors of means. 
172 
14�------------------------------� 
12  
10  
8 
:-;;:,:- . . . . . . . . . - .. . . - . . . . . -
r·-· .- . .... -.  
- - 0 day &1 200e 
• • • • •  1 day &1 200e 
.
_ .  8 days &1 20°C 
-- 15 days al 200e 
(a) 
6 ��==��----------------� 
12 
10 
8 
6 �------------------------------� 
12 
(c) 
10 
8 
6 �------�--�--------------------� 
12 ;' 
. �. - -
(d) 
;' 
10 
8 
6 �---M�--------------------------� 
o 0.05 0. 1 0.2 0.4 0.8 1 .6 3 .2  
Tween concentration (%) 
Fig. 6- 1 9. Soluble solids contents of Granny Smith apples 
after washing in different concentrations of Tween 20 
solution, stored (for (a)=O, (b)=8, (c)= 16 ,  (d)=24 weeks)  at 
o 0 o C and subsequent transfer to 20 C (for 0, 1 ,  8 and 15  
days). Vertical bars indicate standard errors of means. 
1 73 
1 74 
6.5 DISCUSSION 
The current study was i nitiated to exami ne the effects of Tween 20 
solution on removal and/or development of greasiness and effects on  browning 
in Granny Smith apples. I nit ial results obtai ned i ndicated that wash ing of 
g reasy Granny Smith apple fruit in  0. 1 5% Tween 20 solution markedly i nhibited 
subsequent g rease development. Similarly grease development was reduced 
when freshly harvested fruit were washed in Tween 20 concentrations of 0.8, 
1 .6 or  3.2% before storage at O°C for 1 6  or  24 weeks and subsequent t ransfer 
to 20°C. The high Tween 20 concentrations presumably exerted their effects 
on  g rease development through  modif icat ion of the  f ru it ski n su rface by 
blocki ng pores on fru it surface and consequently modifyi ng fru it i nternal 
atmosphere composition .  The h ig h temperatu re sto rage seems to  have 
exacerbated the development of g reasiness in the control and fruit washed i n  
low Tween 20 concentrations. 
Data obtai ned in experiment 1 demonstrated that wash ing  of fruit i n  
0 . 1 5% Tween 20 solution resulted in  marked depression of [021i , i ncreased 
[C2H41i ' but had no effect on [C02Ji . The increase in  [C2H41 i and depression 
of [021 i as a resu lt of the Tween 20 treatment was p resumably  due to 
i ncreased R. The low [021 i decreased fruit respi ration rate. The combined 
i ncrease i n  R and decreased respi rat ion apparently led to mai nten ance? 
[C02Ji . These findings are in agreement with similar findings by Banks ( 1 9,s) .  
The Tween 20 treatment generally increased RC02 and RC2H4 (fig. 6-
4) .  However, the relative effects of the treatment on the diffus ion of these 
gases were different. RC2H4 was h igher than RC02 i n  al l  the treatments 
(experiment 1 ) . The difference could be due to differences in the routes of 
diffusion of these two gases. C02 may move through both the cuticle and 
epidermis whi lst C2H4 l ike 02 diffuses only via the lenticels (Banks
( 
1 984 ;  
Burton, 1 974), so any treatment which blocks o r  affects the lenticels on the fruit 
1 75 
surface is likely to affect [C2H4]i more than [C021i - Hence RC2H4 was h igher 
s 
than that of RC02' This findi ng contrast" with the earlie r  findings reported in  
chapter 4. The disparity could be due to the appl ication of the treatments 
and/or the h i g h  amount of g rease on the fruit su rface wh ich presumably 
b locked lenticels in the present experiment (experiment 1 ) . The current 
f indings are consistent with the data publ ished by Trout etJ�/. ( 1 953) who 
showed that the type of treatment or material appl ied to apples can indeed 
alter the relative effects of skin resistance to these gases since these gases 
differ in the i r  paths of diffusion. 
Modification of internal atmosphere at 20°C was much greater than the 
modification ach ieved by the same treatment at O°C, presumably because of 
i ncreased resp i rat ion  at t he  h i ghe r  temperatu re .  The re was a marked 
depression of [02] i in both control and treated fru it one day after fruit were 
transferred from O°C to 20°C. However after the initial period of depression of 
[02] i and corresponding increase in [C02] i , fruit recovered (or establ ished a 
new physiolog ical equ i l ibrium at the new temperature ) ,  with an increase i n  
[02] i and decrease in  [C02]i ' There was no condensation on  the fruit at the 
time of measurement so, in the absence of grease development, R probably 
remained approximately constant. Therefore changes i n  inte rnal atmosphere 
composition presumably reflect change in respi ration :  adjustment of respiration 
(to low-02) appears to take longer than physical equi l ibration.  A similar findi ng 
was reported by Knee ( 19f!O) who showed that the response of fruit respi ration 
to changes in 02 concentration was delayed by 1 to 4 days depending u pon 
the time and direction of change. Knee considered this delay was longer than 
the time requi red for equil ibration of 02 concentrations inside and outside the 
fruit. On the other hand, Tucker and Laties ( 1 985) reported that with avocados 
only a t ime i nterval of 1 2h was requi red for re-establ ishment of a constant 
respi ration rate after a change in 02 concentration. 
1 76 
The depression of 02 levels i nside washed fruit was greater than the 
elevation of C02 , suggesting that washing in Tween 20 solution may have 
affected C02 evolut ion and 02 uptake to d ifferent extents. It seems more 
l ikely that skin  resistance to the two gases might have been altered to different 
extents because the Tween 20 deposit on the fruit surface was differentially 
permeable to these two gases. In general, washing of fruit with Tween  20 
solution i ncreased [C02]i , but because the solubi l ity of C02 in water and l ipids 
� ------- ---------. 
(Mitz, 1 979),is -aboUf2rr' frmes
-
greater than that of 0), the increase was usually ,/,_ 
less than that the  decrease for 02 . Furthermore ,  as menti oned i n  the 
preceding page, because of  the differences in the path of  diffusion of  these 
gases, any modification of the fruit skin surface which blocks pores is l ikely  to 
have greate r  effect on [02] i and [C2H4]i than on [C02J i . H igh Tween  20 
concentrat ions ( 1 .6 o r  3 .2%) resu lted i n  lower [02]i and h igher  [C02]i and 
[C2H4]i , and were most effective in preventing the development of greasi ness 
i n  G ranny  Smi th  app les .  The reduced [02] i were not low e no u g h  to 
significantly result in  any i nternal physiological damage to the fruit. In  both 
studies, in spite of the fact that some of the fruit developed high [C02]i , none 
of the treated fruit developed internal browning. It is interesting to note that in 
the prel im i nary experiment the [C02] i which was correlated with i n  i nternal 
browni ng were lower than those obtained in experiments 1 and 2 . Th is 
disparity could be due to the fact that development of internal browni ng was 
not only dependent on h igh [C02]i , but it may also be maturity o r  r ipeness 
related. Even though the use of Tween 20 solution elevated [C02]i it delayed 
ripen ing through the depression of respi ration and [02]i . 
poaps�71�(( 1 978) worki ng with potatoes indicated that application of 
Tween surfactant fo r the prevention of g reening in  cold-stored potato tubers 
resulted in high [C02Ji . They indicated that this was associated with reduced 
CO2 permeabil ity caused by the adhering surfactant fi lm �  In  their studies on  
potato tube rs ,  Poapst and Fo rsyt h  ( 1 975) also reported t hat the g reening 
control mechanism exerted by Tween surfactant was related to accumu lation 
'-' 1 
._-J' I t' , 1 ( . 1 77 
of C 02 with i n  the t u be r  and suggested that the s u rfactant formed a tem p or a ry 
f i l m  on t h e  t u b e r's s u rface . I n  the c u rrent st u d y  wash i ng o f  G ra n n y  S m it h  
a p p l e s  i n  Twee n  2 0 s u rfactant dep ressed [02] i m u c h  m o r e  than it e l e vated 
[C02]i ' S ince, Poapst and Forsyth d id n o t  m e a su re the [02 ] i thi s  raises the 
strong poss i b i l ity t h at their claim th at h ig h  C02 affects g reen ing could i n  fact 
b e  d u e m o re t o  r e d u c e d  02 i n s i d e  t h e  t u b e r s  t h a n  t o  i n c r e a s e d  C O 2 
concentration. 
W i p i n g  of G ra n n y  S m it h  apples with t iss u e  paper to rem ove s u rf a c e  
grease resu lted in a n  i ncrease i n  percentage weight l o s s  over the 22 days after 
t reatment application . The in creased we ight loss was probab l y  due to t h e  fact 
that m ost of the natura l  coating on the fruit s u rface had been removed b y  the 
w i p i n g  t rea t m e n t .  T h i s  is cons istent with the f i n d i ng s  b y  H a l l  (j.9-66) w h o  
.,..) w (L 
/� 
rep o rted that when the s u rfaces of G ranny S m it h  apples «Fe wiped with paper :-
wrappers, t h e i r  t r a n s p i rat i o n  rates increa sed a n d  t h is was pro b a bl y  d u e  t o  
rem o v a l  of s u rface w a x e s .  S i m i l a r  f i n d i n g s  h ave a l s o  b e en repo r t e d  (fo r 
o ra n ges, apples a n d  various k in ds of leaves) b y  othe r  i nvestigators i n c l u d i n g  
v/. 
Ben-Yehosh� ( 1 969) , Denna ( 1 970) ,  Mars h a l l  et al. ( 1 9 36 ) ,  Pieniazek ( 1 944) ,  
Scho n he r r  ( 1 9'76 ) ,  Sm ith ( 1, 932) ,  Soliday et al. ( 1 979) , Trout et�/. ( 1 95 3 ) .  
P e rcentage we ight l o s s  o f  washed a n d  control f r u it w e re s i m i l a r  a n d  
stat i s t i c a l l y  d ifferent f ro m  w i pe d  f r u it .  S i m i l a rly, d u ri n g  t h e  fi rst 2 4 h a fter 
treatment application percentage weight loss of control a n d  t reated f r u it w e re 
s i m i la r. H owever after a period of cold stora g e  a n d  s u b s e q uent t r a n sf e r  to 
h i g h  tem peratu re percentage weight loss of f r u i t  i n crea sed. T h is w o u ld b e  
expected from t h e  i ncrease in vapo u r  pressu re deficit ( a t  the h igh tem p e rat u re) 
experienced by the fruit ( B u rton. 1 982) .  It is also poss ible t h at the i n c re a s e  i n  
p e r c e n t a g e  w e i g ht l o s s  at t h e  h i g h  tem p e ra t u re co u l d  b e  c a u s e d  b y  a n  
i n c reased rate o f  res p i ration ( I n aba and C h ac h i n ,  1 98 8 ) .  W a s h e d  f r u it lost 
we ight more rapidly than the contro ls, with increasing treatm ent con c e n t ration 
agg ravating t h is effect. Th e Tween 20 treatm ent pres u m a b l y  affected w e ight 
loss through the removal of the su rface wax or a lternative ly t h ro u g h  p e rm a nent 
1 78 
penetration of the cuticle or inhibition of grease development. These findings 
are consistent with those of other i nvestigators i ncluding, Horr06ks ( 1 964) ,  }, 
Huel in and Gal lop ( 1 951 b), Markley and Sando ( 1 931 ) ,  PieniaZek ( 1 944) ,  ..... �J 
Richmond and Marti n ( 1 959), who demonstrated that use of  surfactant to 
remove surface deposits of wax embedded in apple cuticle i ncreased rates  of 
water loss and accelerated wi lting or shrivell ing. 
Wash ing of G ranny Smith  apples i n  Tween 20 so lut ion markedly 
reduced colour change. The retention of green colour in  washed fruit cou ld  be 
associated with the depressed [02] i and/or depressed respi ration rate . Any 
t reatment which retards fruit respi ration was associated with retention of colour 
./ 
change (Trout et al . . 1 953) . Studies by other researchers have also s hown 
that t he  l oss of g reen  co lou r  in apples was de layed i n  MA o r  low-02 
atmosphe res  (Hewett  et af. '; 1 989 ; Kader. 1'-986 ;  Knee .  1 975..-' 1 98.0) .  
Alternatively, the retention of g reen colour could also be due to elevatio n  in 
[C02] i as a result of the Tween 20 treatment. This finding is consistent with 
that of Burton,  ( 1 974) who indicated in a review article that high C02 ( 1 0%) 
could retain the green colour of apples. 
Fru it washed i n  Tween 20 solution were firmer than the i r  respective 
controls. In experiment 2 there was an effect of Tween 20 solution on fi rmness 
changes even at O°C. The effect of Tween 20 solution on firmness changes 
could presumably be mediated through the depression of [02] i and respiration 
and/or e levation of [C02] i ' There are several reports of the use of coating 
materials. CA or MA to delay loss of firmness in  apples (Kader. 1 986 ; Knee • 
./ , 
1 980 ; Trout et al . •  1.�2 ; Hulme./'1 949 ;  Tomkins. 1 968) and these are also 
thought to have been effective through modif icat ion of the fru it 's i nte rnal 
atmosphere. Results obtained in the current study confirm these assertions .  
I n  conclusion  these fi ndi ngs demonstrate that wash ing of  g re ased 
G ran ny Sm i t h  app les  i n  0 . 1 5% Tween 2 0 so lu t ion  markedly red uced 
subsequent g rease deve lopment. Wash ing f reshly harvested f ru it in h igh  
1 79 
Tween 20 concentrations ( 1 .6 o r  3.2%) was most effective in preventi ng the 
deve lopment of g reasi ness.  The Tween  20 concentrat ions presumably 
exerted their effects on grease development by blocking pores on fruit surface 
and consequent ly modifyi ng  fru it i nte rnal atmosphere composit i o n  and 
respi ration. Fruit were greener and fi rmer and there was no noticeable i nternal 
b rown ing  which is often associated with the  development of g reas i ness. 
These findings indicate that some form of coati ng treatment could be used to 
prevent the development of greasiness in Granny Smith apples. 
In the commercial situation, coating treatment of this type cou ld  easily 
be i ncorpo rated i nto the packi ng chain of the grower or pack h ouse.  I f  
maximum benefits of the Tween 20 treatment are to  be  achieved i t  i s  essential 
that the temperature at which fruit are stored are properly controlled i n  v iew of 
the fact that high Tween 20 concentrations tend to exacerbate water loss and 
modification of gas exchange characteristics of the fruit. 
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633 pp. 
Tomkins, R. G. 1 968. The effects of treatments with silicones on the ripening 
and loss of water from fruit. Annu. Rpt. Ditton Lab. 1 967- 1 968: 29-33.  
Trout, S. A. ,  Hal l ,  E. G. , Robertson ,  R .  N . ,  Hackney, F .  M.  V. and Sykes, S.  M. 
1 942. Studies in  the metabolism of apples. 1 .  Preliminary i nvestigations 
\./ 
on internal gas composition and its relation to changes in  stored G ranny . ./ 
Smith apples. Aust. J .  Expt. BioI. Med. Sci . 20 :21 0-23 1 . 
Trout, S. A. ,  Hal l ,  E .  G. and Sykes, S. M. 1 953. Effects of ski n coatings on  the 
behav i ou r of  app les  in s torage .  I .  P hys i o l og ica l  a nd  g e n e ra l  
investigations. Aust. J .  Sci. Res. 4 :57-81 . 
Tucker, M. L. and Laties, G.  G. 1 985. The dual role of oxygen in  avocado fruit 
respirat ion : Ki net ic analysis and computer mode l l i ng of d i ffus i on ­
affected respiratory oxygen isotherms. Plant, Cell and Env. 8 : 1 1 7- 1 27.  
\ 
� 
184  
CHAPTER 7 
TEMPERATURE EFFECTS ON INTERNAL ATMOSPHERE COMPOSITION, 
RESPIRATION,  ETHYLENE PRODUCTION AND SKIN RESISTANC E  TO 
GAS DIFFUSION OF APPLES. 
7.1 ABSTRACT 
T h e  re l a t i o n s h i p  b e t w e e n  t e m p e r a t u re a n d  i n t e r n a l  a t m o s p h e re 
co m p o s i t io n ,  r e s p i rat i o n ,  ra te of C2 H 4 p rod uction a n d  R of C ox's O ra n g e  
CA ... J 
Pippi n ,  G a l a ,  Royal G ala, G olden Del iciou s ,  Red Delicious" Splendou r a pp le s  
was ascertained after equ i l i brating fruit at tem pe ratu res ran g i ng from 0 - 3 0 ° C  
f o r  72h .  
There was a progress ive decline in [02] i with correspon d i ng increa se i n  
[C02] i in respo n se to increasing temperatures. B ra eb u rn apples con s i st e n t l y  
h ad lower [ 02] i a n d  h i ghe r [C02 ] i than t h e  o t h e r  cu l t i va r s .  T h i s  c o�.Id b e  
related to t h e i r  h igh R, low i ntercel l u la r  space vo l u m e  a s  wel l  a s  interm e d iate 
re s p i rati on rate . I n  cont rast S p l e n d o u r  a p p l es h ad h i gh e r  [ 02 ] i and l o w e r  
[C02] i t h a n  th e other cu lt ivars. The reason cou ld b e  d u e  to t h e i r  low R, l ow , 
respiration rate, presence of open calyx and n u merous lenticels h���e �as�r � 
gas d iffu sion. 
Between 0 a n d  1 0°C both [C2 H 4] i a n d  rate of C2 H4 prod ucti o n  were 
low, h o weve r c o n c e n t rat i o n s  i n c rea sed r a p i d l y  i n  res p o n se to i n c r e a s i n g  
tem perature to a maximum a t  25°C above wh ich concentrations decl i n e d ,wtth­
�er-temJ30ra.tllre increase . T h e  m a g n it u d e  of d e c l i n e  v a r ied b e t w e e n  
c u l t i v a r s .  A t  3 0 ° C  t h e  c a p a c i t y  t o  p ro d u c e C 2 H 4 d e c l i n e d m a r k e d l y .  
Splendo u r  apples had the l east capacity to accumu late and produce C2 H 4 ' 
1 85 
Fruit respiration rate increased in  response to increasing temperatures. 
Cox's Orange P ippin apples equi l ibrated at 30°C were respi ri ng  nearly ten 
times more rapidly than those stored at O°C. Th� capacity to produce C02 (for 
al l t h e  temperatu re reg imes)  was markedly lower i n  Splendour  apples 
compared to the other cultivars. 
RC02 and RC2H4 appeared to be i ndependent of tem pe ratu re .  
However, R varied between cultivar with Braeburn apples having the h ighest 
mean RC02 and RC2H4 compared to the other cultivars. 
Braeburn apples were firmer than the other cultivars. Fruit soften ing 
was accelerated by high temperatu res. Soluble sol ids content varied with 
cultivar but was not affected by temperature. 
7.2 INTRODUCTION 
Temperature is the single most important environmental factor affecti ng 
the rate of respi ration and hence i nternal atmosphere composition  of fru its 
including apples (Eaks, �,�78 ; Kader et al., .1 985, 1989 ;  Maxie et al. 1 974) .  I n  I­
harvested apples, the rate of respi ratory activity as measured by 02-C02 
exchange, is an index of the rate of metabolism and hence the length of life of 
the fruit (Porritt, 1'951 ; Porritt and Lidster, 1 978). A depression i n ' [02]i and 
elevation of [C02]i as well as respi ration rate of fruits (i ncluding apples) occurs 
i n  response to increasing temperature (Kader et al. , 1 985,' 1 989 ; Kidd, and 
West, 1 930 ; Magness, 1 9;0 ;  Magness and Diehl, 1 924 ; Trout e!;BI. , 1 942) .  A 
review of temperature as a factor affecting the internal atmosphere of fru it is  
present in  chapter 2 . However, detailed information on the effects of  a range 
of temperatures on the internal atmosphere composition 'and respi ration rate of 
i ntact apples of different cultivars is l imited or meager. 
1 86 
Information on the effect of temperature on R of various apple cultivars 
is also largely unavailable. Various i nvestigators have measured apple R but 
generally  only at one or two temperatures (Banks, 1 985; Burg ,  1 962 ; Burg and 
Burg ,  1 965; Burton, 1..974, 1 978;  Cameron,  )982 ; Cameron and Yaog', 1 982 ; 
Kidd and West , 1 949 ;  Kney·1 99 1 ) .  I nfo rmat ion o n  the  effect of various 
storage temperatures on R as wel l  as i nternal atmosphere composit ion of 
various cultivars of apples could help in our understanding of the physiological 
behaviour of fruit during storage. For instance, Granny Smith apples develop a 
g reasy surface after a pe riod of cold storage and subsequent transfer to 
ambient temperatures; this increases R,  impedes gas exchange thus modifying 
the i nternal atmosphere of fruit (this subject is addressed in  more detail i n  the 
precedi ng  chapter) . As a result the development of certain physio log ical 
disorders such as i nternal browni ng may be triggered (Trout et al. , 1 942) . ../ 
Consequently, knowledge of the effect of varying temperatures on R may help 
in our u nderstand ing  of the deve lopment of some of t hese phys io log ical 
disorders that develop in apples during storage. 
Review articles on the physiology of C2H4 by Abeles l1973}, Lieb��man 
(1 979), Roberts and Tuc!5er' (1 985} and Osborne ( 1 978) have presented l im ited 
i nformat ion on various storage temperature-i nduced effects on [C2H4]i and 
rate of C2H4 production by fruits, particularly apples. This is largely because 
of t he  g e n e ral pauc ity of  i n format i o n  and u nt i l  re ce n t l y  t h e  l ac k  o f  
u nderstand i ng  o f  C2H4 biosynthes is  (F ie ld ,  1 985 ; Lyons et al. , 1 979) .  
Considering the significance of temperature as a major environmental variable 
and its known influence on many physiological process it is su rprising that it 
has received relatively scant attention. As a corollary, relatively few reports on 
C2H4 physiology include information on the temperature effects on [C2H4]i of 
apples. In spite of the numerous research that has been conducted to study 
the accumulation and production of C2H4 in apples, there is sti l l  a dearth of 
informat ion on the effects of a range of temperatures on [C2H41 i and C2H4 
product ion  of i ntact apple cu l t ivars .  Such i nformat ion  may he lp i n  our  
1 87 
understanding of the physio logical response to varying temperatures by apple 
cu lt ivars after low temperatu re storage and subsequent transfer to h igher  
temperatures during the distribution chain.  
The cu rrent research was therefore in itiated to study the effects of a 
ran ge  of temperatu res ( 0  - 30°C)  o n  in te rna l  atmosphere compos it ion ,  
respi ration rate , C2H4 evolution , R and some aspects of qual ity o f  e ight 
commercial apple cultivars grown in  New Zealand. 
7.3 MATERIALS AND METHODS 
7.3.1 Materials 
Fresh l y  ha rvested fru it of  e i gh t  commerc ia l  export app le (Malus 
domestica Borkh .) cultivars (Cox's Orange Pippin,  Gala, Royal Gala, Golden 
Del ic ious, Red Del ic ious, Splendour,  Braeburn and Granny  Sm ith apples;  
count 1 25; av. weight 1 48 g) differ ing in  date of harvest and matur ity were 
obtained as previously described in 3.
·1-. -F-r� it were "stored in cii"r Oaf aoe for -4 . .  " (3 
weeks. Prior to starting each experiment, fruit were taken directly from storage 
and carefully selected for un iformity in size and freedom from blemishes. A set 
it-<U"-.. �+� hCJI (1:;1 
of e ight  fru it from each cu lt ivar was p laced in the  dark in thermostieafly 
control led temperature cabinets maintained at 0, 5, 1 0, 1 5, 20,  25 and 30±1 °C 
respect ive ly for 72h to a l l ow f ru it to eq u i l i b rate with t he  app rop r iate  
temperatures. A temperature probe was inserted into a representative sample 
of fou r  fru it to ensure that fru it were at temperature equ i l i br ium with the i r  
surroundings before measurements were made. This was because ( in  chapter 
5) respiration took time to reach an equi l ibrium when fruit were transferred to 
new 02 levels, so it was thought that it wou ld be worthwh ile to leave fruit for 
sim ilar period to regain steady state at the new temperature. 
7.3.2 Methods 
7.3.2.1 Estimation of gas exchange variables 
1 88  
Respiration (C02 production) and C2H4 production were measured on 
fruit kept in the dark as previously described in 3.3.5.2 . 
Core cavity 02. C02 and C2H4 concentrations were measured by the 
direct sampl ing method (see 3.3.4. 1 ) and gas samples analysed as described 
in 3.3. 
RC02 and RC2H4 were est imated by t he steady-state method (see 
3.3.5.2). 
7.3.2.2 Fruit quality assessment 
Fru it fi rmness was measu red as previously described (see 3 . 3.8 . 1 ) . 
So l ub l e  so l i ds content was a lso  measu red  w i t h a n  Atago N - 1  h and 
refractometer (see 3.3.8.2) on a small volume of  fruit ju ice extracted from fruit 
using a blender (Phil ips, type HR 2290/A) . 
7.3.2.3 Experimental design and analysis 
Eight randomly selected s ing le fru it rep l icates of each apple cu lt ivar 
(complete ly randomised design)  were kept at each of the seven temperature 
regimes. Experiments were repeated at least once. Data were analysed as 
p rev ious ly  descr ibed i n  sect i on  3 .3 .9 .  Reg ress ion analyses we re also 
performed according to the methods described by Steel  and 1Pfri e  ( 1 980). 
Methods of comparison of reg ression l i nes were undertaken as described by 
Kleinbaum and Kupper .( 1 978) . Mean comparisons were also carried out by 
the Least s ign ificant difference (LSD) procedu re at 1 % level of sign ificance 
(Little and Hi l ls, 1 978) to test cultivar differences. 
1 89 
7.4 RESULTS 
7.4.1 Internal 02 concentration 
There was a consistent decline in fruit [02]i in response to increasing 
temperatures (figs. 7- 1 and 7-2) .  The magn itude of response varied with 
cu lt ivar. After  equ i l ib rat ion at O°C , [02]i in al l the cultivars was h igh  and 
s imi lar, however with i ncreasing temperatures concentrat ions decl i ned.  At 
.N � l  
25°C the average [02] i o f  Splendour apples .wefe' nearly 1 9% as aga inst 
approximately 1 2% in  Braeburn and 1 5% in  Granny Smith or  Red Del icious. 
For al l  the temperature reg imes studied, Splendour, Gala, Royal Gala and 
Golden Delicious apples consistently contain higher [02]i (even at 30°C, mean 
[021 i approximately 1 8%) than Braeburn or Granny Smith apples (1 0% and 
1 3% respectively). 
Regression analysis revealed that plots of [02]i versus temperatu re 
were li near with no significant deviations from the fitted l ines (P  < 0 .0001 ; figs. 
7-1 and 7-2) .  Comparison of the intercepts and slopes of the regression l ines 
re lat i ng  [021 i of apples to temperatu re showed that the i ntercepts for al l  
cultivars were similar at about 20.6% 02 though differences between cultivars 
were i n  many cases statistical ly h ighly significant (Table 7- 1 ) . On the other 
hand the slopes of the regression l i nes were different with a range of 0 .090/0 
02 °C- 1  (for Splendour) to 0.34% 02 oC-1  (for Braeburn) (figs. 7-1 and 7-2 ; 
Table 7-2) .  
190 
191  
24 2 
Y=20.69-0. 101x; R =0.90 
.. • (a) 20 • • 
• • ... 
1 6  
1 2  
8 2 
Y=20.77-0. 1 1 5x; R =0.86 
0- Q (b) 20 0 
0 0 0 � 
16  
12  
-.. 
� '-" 8 ,...-., 2 (c) C"I Y=20.33-0. 1 1 5x; R =0.73 0 '--' 
---20 • • 
• • • _. 
16  
12 
8 2 Y=20.70-0.212x; R =0.87 
20 
(d) 
16  
0 
1 2  
8 
0 5 10 15  20 25 30 
0 Temperature ( C) 
Fig.  7-2. Relationship between temperature and [02] j 
(a)=Gala (b)=Royal Gala (c)=Golden Delicious (d)=Red 
of 
Delicious apples with fitted regression. 
1 92 
Table 7-1 . Comparison of significant differences between the intercepts of the 
regression l ines relating [021i of apples to temperature. 
APPLE CUL TIVAR 
Cultivar COP G GD GS RD RG S 
8raeburn (88) ••• .* • .** 
• 
*. ••• .*. • •• 
Cox's Orange Pippin (COP) .* NS NS NS • •• 
Gala (G) NS ***  .* NS NS 
Golden Delicious (GO) ** • NS NS 
Granny Smith (GS) NS  ••• ••• 
Red Delicious (RD) •• ••• 
Royal Gala (RG) NS  
NS ,  . , . * ,  * . *  = Nons ign i f ica nt o r  s i gn i f icant a t  P = 0 .05 ,  0 . 0 1 , 0 . 00 1  
respectively. 
S = Splendour apple. 
1 93 
Table 7-2. Comparison of significant d ifferences between the slopes of the 
regression l ines relating [02]i of apples to temperature. 
APPLE CUL TIVAR 
Cultlvar COP G GD GS RD RG S 
Braeburn (BB) ***  *** *** ** ***  *** *** 
Cox's Orange Pippin (COP) ** * ** NS * *** 
Gala (G) NS *** ***  NS NS  
Golden Del icious (GO) *** *** NS NS  
Granny Smith (GS) NS *** *** 
Red Delicious (RD) *** *** 
Royal Gala (RG) NS 
NS ,  * ,  * * ,  ***  = Nons ign i f icant or  s i gn i f icant at P = 0 .05 ,  0 . 0 1 , 0 .00 1 
respectively. 
S = Splendour apple. 
1 94 
7.4.2 Internal C02 concentration 
Temperature had s ign if icant (P < 0 .0001 ) effect on [C02] i a nd the 
response of fruit [C02]i to temperatures was cultivar dependent (figs. 7-3 and 
7-4) .  At low temperatures (0 - 1 0°C) [C02]i were low, however concentrations 
i ncreased progressively in response to i ncreasi ng temperatures. At 25°C, 
Braeburn and Cox's Orange P ippin apples contained nearly 8 and 7%  C02 
respectively as opposed to approximately 3% i n  Splendour, Gala o r  Royal 
Gala. At 30°C the [C02]i of Braeburn apples was nearly eight times higher 
t han  t h ose at ooe,  compared  to  a t h reefo ld i ncrease ove r t h e  same 
temperature range for Splendour. 
Regression analysis indicated that fru it [C02] j was l inearly related to 
temperature (P < 0.001 ; figs. 7-3 and 7-4; with no sign ificant quadratic or cubic 
dev iat ions) .  Comparison of the i ntercepts of the reg ression l i nes relat ing 
[C02]i to temperature indicated cu ltivar differences rang ing from 0.32% C02 
(i n Royal Gala) to 0.97% C02 ( in Braeburn) and in some cases differences 
between cultivars were statistically highly significant (Table 7-3) . Similarly, the 
slopes of the regression l i nes were also different with a range of 0.09% C02 
°C- 1  (for Splendour) to 0 .27% C02 °C- 1  (for Braebu rn )  and d iffe rences 
between cultivars were statist ically highly significant i n  some cases (figs. 7-3 
and 7-3; Table 7-4) .  
7.4.3 Fruit respiration rate 
Tempe ra tu re had a p ro nounced ( P  < 0 .000 1 )  e ffect o n  rate o f  
respiration and varied with cultivar (figs. 7-5 and 7-6) . Respi ration rates of fruit 
were low at low temperatures (0 or 5°C). but rates increased progressively as 
temperature increased to 30°C. The magnitude of i ncrease diffe red between 
cultivars. Splendour apples had the lowest average respiration rate compared 
to the other cultivars, whilst Cox's Orange P ippin apples had the highest 
10  
8 
6 
4 
2 
0 
8 
6 
4 
2 
...-
� 0 --
,......., 
C"I 0 u 8 '--' 
6 
4 
2 
0 
8 
6 
4 
2 
0 
2 Y=0.97+0.272x; R =0.96 
2 Y=0.41+0.2 16x; R =0.90 
(a) 
(c) 
(d) 
o 
o 5 10 15  20 25 30 
o Temperature ( C) 
195 
Fig. 7-3 . Relationship between temperature and [C02]i 
concentrations of (a)=Cox 's Orange Pippin (b )=Braebum 
(c)=Splendour (d)=Granny Smith apples with fitted regression. 
196 
10  
8 (a) 
6 
4 
2 
0 
2 Y=0.32+0. 1 13x; R =0.91 
8 (b) 
6 
4 
2 
-. 
� 0 '-.-..--, 
N 0 (c) u 8 ....... 
6 
4 
2 
0 
2 Y=0.41+0. l95x; R =0.91  
8 (d) 
6 
4 
2 
0 
0 5 10 15 20 25 30  
0 Temperature ( C) 
Fig. 7-4. Relationship between temperature and [C02]i of 
(a)=Gala (b)=Royal Gala (c)=Golden Delicious (d)=Red 
Delicious apples with fitted regression. 
1 97 
Table 7-3. Comparison of significant differences between the intercepts of the 
regression l i nes relating [C02]i of apples to temperature.  
APPLE CUL TIVAR 
Cultivar COP G GD GS RD RG S 
Braeburn (BB) * *** *** • * .*. .* • *** 
Cox's Orange Pippin (COP) *.* * •• NS • • *. .* • 
Gala (G) NS .** .* NS NS 
Golden Delicious (GO) • NS  NS * 
Granny Smith (GS) NS  .*. .** 
Red Del icious (RD) ** .*. 
Royal Gala (RG) NS 
NS, . ,  • •  , . * *  = Nons ign i f icant o r  s ign if icant at P = 0 .05 ,  0 . 0 1 , 0 . 0 0 1  
respectively. 
S = Splendour apple. 
1 98 
Table 7-4. Comparison of significant differences between the slopes of the 
regression l ines relating [C02]i of apples to temperature. 
APPLE CUL TIVAR 
Cultivar COP G GD GS RD RG S 
Braeburn (BB) • ••• • •• •• • •• ••• • •• 
Cox's Orange Pippin (COP) ••• ••• NS NS ••• ••• 
Gala (G) NS ••• ••• NS  NS 
Golden Delicious (GD) ••• •• NS  • 
Granny Smith (GS) NS ••• • •• 
Red Delicious (RD) ••• • •• 
Royal Gala (RG) NS 
NS ,  ., * * ,  •••  = Nons ign i f icant or  s i gn i f icant at P = 0 .05 ,  0 . 0 1 , 0 . 0 0 1  
respectively. 
S = Splendour apple. 
35 
28 
2 1  
14  
7 
0 
28 
__ 2 1  -
',.c 
- 14  , 
b.O 
� 
N 7 0 U 
f<'l 0 E (,) --
� 28 
E! 
§ 21  .-� t'\! .� 14 0.. � 
Q) 
� 7 
0 
28 
2 1  
14  
7 
0 
2 2 Y=2.75+0.0455x+0.0244x ; R =0.99 
2 2 Y=0.94+0.3554x+0.OO33x ; R =0.94 
2 2 Y=1 .49+0. 1786x+0.OO49x ; R =0.93 
2 2 Y=1.81+0.2105x+0.OO82x ; R =0.97 
o 5 10 15  20 
o Temperature ( C) 
1 99 
(b) 
(c) 
(d) 
25 30 
Fig. 7-5 . Relationship between temperature and respiration rate 
of (a)=Cox 's Orange Pippin (b)=Braebum (c)=Splendour 
(d)=Granny Smith apples with fitted regression. 
35 
28 
2 1  
14  
7 
0 
28 
__ 2 1  
-, 
..c 
- 14  , 
00 
� 
N 7 0 
U 
(") 0 E 
u --
B 28 
r: 
§ 21 .... .... � .= 14  0.. tI.) 
� 
� 7 
0 
28 
21  
14  
7 
0 
2 2 Y=2.07+0.3 186x+0.OO57x ; R =0.95 
2 2 Y=1.33+0.4512x+0.OO15x ; R =0.96 
2 2 Y=3. 1 7+0.3771x+0.OO68x ; R =0.95 
2 2 Y=2.33+0. 1780x+0.0182x ; R =0.97 
0 5 10 15  20 
0 Temperature ( C) 
200 
(a) 
(b) 
(c) 
(d)  
25 3 0  
Fig . 7-6. Relationship between temperature and respiration rate 
of (a)=Gala (b)=Royal Gala (c)=Golden Delicious (d)=Red 
Delicious apples with fitted regression. 
201 
respiration rate. At 30°C, Cox's Orange Pippin apples were respiring over 50% 
more rapidly than Splendour apples. Cox's Orange Pippin apples equi l ibrated 
at 30°C were respi ring nearly ten times more than at O°C. 
Regression analysis showed that with the exception of Cox's Orange 
P ipp i n  apples ,  i n  which the response of respi rati on to temperatu re was 
decidedly curvi l inear, in most cases the response was largely l inear with a 
minor quadratic component (figs. 7-5 and 7-6). 
7.4.4 Internal C2H4 concentration 
Fruit [C2H4]i were markedly affected by equi l ibration temperatures with 
significant l i near, quadratic and cubic effects of temperature (Table 7-5) . The 
response patt e rn d iffered between cu l t ivars (f igs .  7-7 and 7 -8 ) .  Low 
equ i l i b rat ion  temperatures between 0 and 1 0°C markedly depressed fruit 
-- - . . ..  . _ ..... . " .- _ .  �--. - . .  - --. -- _.  
[C2H4] i (P < 0 .00 1 ) .  However concentrati ons i ncreased progressive ly  i n  
response t6 further increase i n  temperatu re to a maximum at 25°C above 
which i nternal concentrations declined with further temperature increase. The 
magnitude of decl ine varied with cultivar. At 30°C most of the cultivars lost the 
capacity to accumulate C2H4' 
Expos ing fru i t  to 30°C sig nif icantly (P  < 0.00 1 ) depressed [C2H4]i 
re lative to that found at 25°C. The magnitude of this depression varied with 
cultivar. For example, Royal Gala apples stored at 30°C were found to contain 
only about one seventh as much C2H4 as at 25°C as opposed to about a th i rd 
as much as i n  Cox's Orange Pippin ,  approximately half as much i n  Golden 
Delicious and almost the same amount in  Granny Smith.  
Of al l  the cultivars studied Splendour apples had the least capacity to 
accumulate C2H4 over all the temperature regimes. For i nstance, Splendour 
apples equil ibrated at O°C and 25°C had mean [C2H4]i of nearly 1 5  and 66 III 
202 
Table 7-5. Relationship between [C2H4]i and temperature of apples. 
Level of significance 
Cultivar Regression equation L Q 
Cox's Orange 
Pippin Y=97.45 - 34.47x + 4.93x2 - 0. 1 2x3 •• •••• 
Braeburn Y=94.65 - 64.39x + B.24x2 - 0.20x3 ••• •• * • 
Splendour Y=1 7.32 - 2.0Sx + 0.SSx2 - 0.02x3 • • 
Granny Smith Y=S9.06 - 1 B.96x + 2.37x2 - 0.OSx3 • •• 
Gala Y=B3.0B - 44.2Sx + 7.23x2 - 0. 1 9x3 •• *.* • 
Royal Gala Y=S7.79 - 3S.B4x + 6.39x2 - 0. 1 7x3 ••• *.* • 
Golden 
Del icious Y=1 27.B2 -: 1 9.79x + 4. 1 6x2 - 0 . 1 1 x3 •• •••• 
Red Delicious Y =9B.26 - 1 B.28x + 2.85x2 - 0.07x3 •• * ••• 
• , •• , ••• , •••• = significant at P = O.OS, 0.01 , 0.001 , or 0 .0001 respectively.  
L, Q and C = Linear, Quadratic and Cubic 
C 
.*.* 
•••• 
•• 
•• 
._ .. 
•••• 
_
.
_-
**** 
750 
600 
450 
300 
150 
o 
600 
450 
-. 300 
-
I -
-a 1 50 
--. -,........., 
:;: 0 
� 600 
450 
300 
150 
o 
600 
450 
300 
150 
o 
I I I 
..... 
..... 
_ - -I 
_ .. - - _ .. --
... - -
I I I I 
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. . .
. . . . .
. . .•. . . . . . . . . . . � . . 
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. - . _ . ---._. _ . -.- . 
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I I 
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I I 
i I 
/·�
l/ 
J 
., 
I 
.,�  
I 
A., . . 
\ 
.
. 
�. 
I I 
\ 
\ 
(a> 
\ 
\ 
\ 
1 
(b) 
'1 
(c) 
I --:--. I 
(d) 
././1-'-'-1 
I 1 
o 5 10 1 5  20 25 30 
o Temperature ( C) 
Fig. 7-7, Temperature effects on [C2H4]j of (a)=Cox's Orange 
Pippin (b)=Braeburn (c)=Splendour and (d)=Granny Smith 
apples. Vertical bars represent standard error of the means. 
203 
7 50 r---.,.---r-"""'T"""-,...---r-r--.,.--..,....-�--r--,-..,--, 
600 
450 
300 
150 
- ­... -
/ 
f- - - - I (a) / \ / \ / \ / \ 
� / \ � \ 
�
� \ 
� � \ 
- - � .. - t 
o �--��-+--r-+--r-+�r-+--r-+--� 
600 
450 
(b) 
,- 300 
-, -
'"a 150 
'-" 
� . .. . . . . . .. . . . ... 
� O r---+--r-+�r-+-�-+�--+-�-+�� 
� (c) 
� 600 
450 
300 
150 
o r---+-�-+�--+-�-r�--+-�-+�� 
600 
450 
300 
150 
/ . ..1', /' " � . , 
....... . - .-.. , .. - ' , 
(d) 
-t -' . . -t-.-.  . , t - ·- "£ 
o ������--����--�����
o 5 10 15  20 25 30 
Temperature (QC) 
204 
Fig. 7-8. Temperature effects on [C2H4] j of (a)=Gala (b)=Royal 
Gala (c)=Golden Delicious (d)=Red Delicious apples .  Vertical 
bars represent standard error of the means. 
205 
1-1  respectively, compared to 43 and 684 I.d 1-1 in Braeburn ; 63 and 52 1 � r 1 
in  Cox's Orange Pippin ;  50 and 600 �I r 1 i n  Gala; and 1 03 and 583 J.1.I r1 i n  
Golden Delicious. 
7.4.5 C2H4 production 
Temperature had pronounced effect on the rate of C2H4 product ion  
(Table 7-6 ;  with significant l inear, quadratic and cubic effects) and varied with 
cultivar (figs. 7-9 and 7- 1 0). At low temperatu res between 0 and 1 0°C the 
rates of C2H4 production were low but production increased progressively with 
i ncreasi ng temperatu re to a max imum  at 25°C above which product i on  
decl i ned. The capacity to produce C2H4 obviously decl ined markedly a t  30oe. 
However the magnitude of decl ine was cultivar dependent. The rates of C2H4 
production of Braeburn, Royal Gala, Gala, Cox's Orange Pippin and Granny 
Smith apples at 25°C were 20,  1 5 , 1 2 1 0  and 8 t imes h igher than at ooe 
(respectively) . At 25°C,  Golden Del icious and Gala apples produced nearly 
twelve times more C2H4 than Splendour. At 30°C, Golden Delicious and Gala 
apples were respectively producing approximately one half and one fifth as 
much C2H4 as at 25°C. Over all the temperature ranges, Splendour apples 
had the lowest rate of C2H4 production compared to the other cultivars. 
7.4.6 Skin resistance to gas diffusion 
RC02 and RC2H4 , est imated using the steady-state method , were 
cu l t ivar dependent ( f igs 7- 1 1 ,  7 - 1 2 and f igs .  7- 1 3 , 7 - 1 4 respect ive ly ) .  
Statistically equil ibration temperature had no Significant (at P = 0.05) effect on  
RC02 and RC2H4 ' However there were marked differences in  Reo2 and  
RC2H4 between temperatures in  some of the cultivars. For example at Qoe, 
RC02 and RC2H4 of Braeburn apples were markedly (P < 0.01 ) lower than at 
5 or 1 0°C. RC02 and RC2H4 of Braeburn apples over all the temperatu re 
206 
Table 7-6. Relationship between C2H4 production and temperature of apples. 
Level of significance 
Cultlvar Regression equation L Q 
Cox's Orange 
Pippin Y=51 .69 - 2 1 .59x + 2.98x2 - 0.07x3 •• .*** 
Braeburn Y=23.51 - 1 8.71 x + 2.26x2 - 0.05x3 ••• **** 
Splendour Y=1 2.44 - 2 .9 1 x + 0.48x2 - 0.01 x3 • •• 
Granny Smith Y=19.65 - 5.44x + 0.67x2 - 0.01 x3 • •• 
Gala Y=68. 1 2 - 36.69x + 6.1 4x2 - 0.1 6x3 ••• **** 
Royal Gala Y =43.50 - 32.73x + 5.66x2 - 0.1 5x3 **** **** 
Golden 
Delicious Y = 1 09.53 - 23.75x + 4.38x2 - 0. 1 1 x3 •• **.* 
Red Delicious Y=33.41 - 9.06x + 1 .56x2 - 0.04x3 •• •• 
•• ••• •••• •••• = significant at P = 0.05. 0.01 . 0.001 . or 0 .0001 respectively. 
L. Q and C = Linear. Quadratic and Cubic 
C 
•••• 
***. 
• •• 
•• 
***. 
**** 
**** 
• •• 
600 
500 
400 
300 
200 
100 
o 
500 
400 
"7-- 300 
.t:: 
"7 bl) 200 
� 
"'a 100 
� 
§ 0 ..... .... 
g 500 "0 
o 
5.400 
"<t 
� 300 u 
200 
100 
o 
500 
400 
300 
200 
100 
o 
I I I 
- - _ .f "  - -
- - - - ;-
- -
I 
•. . . . . . . . .  · t· . . . .  I 
I 
1 I I I 
. . . . . . ... . .
. 
. . . . .... . .  I I I 
j I I 
I 
...... 
..... 
...... t 
, , 
I I 
. . ' . . . . .
. 1 · · · . ' 
I I 
. 
I I 
I 
..... � 
..... , 
i I 
. . ' I. . . ' 
.1 I 
..L 
, 
. 
(a) 
, 
, 
, i 
(b) 
. . 
. 
., 
(c) 
I ----:--. I 
(d) 
.f-._ ._J 
.... . -
.-
- '  
,..- ,, -- " 
t - · - · �· - · -�· - · - · 1 I 
o 5 10 1 5  20 
o Temperature ( C) 
i i 
25 30 
Fig .  7-9. Temperature effects on C2H4 production of  (a)=Cox's 
Orange Pippin (b)=Braebum (c)=Splendour and (d)=Granny 
Smith apples .  Vertical bars represent standard error of the 
means. 
207 
600r---���1I�-.�--r-�.-��� 
500 
400 
300 
200 
100 
o �--���--r-�-+��+--r�--r-�� 
500 
400 
--:-- 300 
..c:: 
--: bO 200 
� 
� 100 
'-" . ' 
...
...
.. .
...
.. , .
. . 
• .1.' 
. . ..
.. 
I·
· · · · · · ·
· · · i 
. ..
... .. 
(b) 
• § 
0 �-.'-" '�" -" '-" �.'�--+-����+--r�--+-�� ..... .... 
g 500 
"8 
6.. 400 
� 
� 300 u 
200 
100 
(c) 
o �--���--r-���--+--r�--r-�� 
500 
400 
300 
200 
100 
. + . _ . _ . 1 +._.- I' ., -- '  . 
_ .--'  , _ . ---1. - - - -
. " 
(d) 
o �����--����--���--���
o 5 10 15  20 
o Temperature ( C) 
25 30 
208 
Fig .  7- 10. Temperature effects on C2H4 production of (a) =Gala 
(b)=Royal Gala (c)=Golden Delicious and (d)=Red Delicious 
apples. Vertical bars represent standard error of the means. 
209 
40 
32 <a) 
24 
16  
8 
0 
32 
24 
1 6  
,,-... - 8 I E 
u 
Cl:) 0 0 
8 
32 -
(c) 
� '-' 
N 24 0 
U 
� 1 6  
8 
0 
32 (d) 
24 
1 6  
8 
0 
o 5 10 15  20 25 30 
o Temperature ( C) 
Fig. 7- 1 1 .  Temperature effects on RC02 of (a)=Cox's Orange 
Pippin (b)=Braeburn (c)=Splendour and (d)=Granny Smith 
apples. Vertical bars represent standard error of the means. 
210 
40 
32 <a) 
24 
1 6  
8 
0 
32 (b) 
24 
1 6  
--. - 8 . E 
(.) 
Cl:) 0 
§ 
32 -
(c) 
� --
N 24 0 
U 
� 1 6  
8 
0 
32 (d) 
24 
16  
8 
0 
o 5 10 1 5  20 25 30 
o Temperature ( C) 
Fig. 7- 1 2. Temperature effects on RC02 of (a)=Gala (b)=Royal 
Gala (c)=Golden Delicious and (d)=Red Delicious apples .  
Vertical bars represent standard error of the means. 
40 
32 
24 
16  
8 
0 
32 
24 
16  
-. -, 8 E 
(,) 
tI.l 
8 0 
0 - 32 � '-" 
� 
::r:: 24 C"I 
U 
c:.:: 16 
8 
0 
32 
24 
16 
8 
0 
0 5 10 15  20 
o Temperature ( C) 
2 1 1  
(a) 
(b) 
(c) 
(d) 
25 30  
Fig. 7- 13 .  Temperature effects on RC2H4 of (a)=Cox's Orange 
Pippin (b)=Braebum (c)=Splendour and (d)=Granny Smith 
apples. Vertical bars represent standard error of the means. 
40 
32 (a) 
24 
1 6  
8 
0 
32 (b) 
24 
1 6  
-.. -. 8 E 
u 
t'-l 
8 0 
0 (c) - 32 � --
'o:t 
:::t 24 N 
U 
� 16  
8 
0 
32 (d) 
24 
16  
8 
0 
o 5 10 15  20 25 30 
o Temperature ( C) 
Fig. 7- 14.  Temperature effects on RC2H4 of (a) =Gala (b)=Royal 
Gala (c)=Golden Delicious and (d)=Red Delicious apples .  
Vertical bars represent standard error of the means . 
212 
21 3  
regimes were higher than the other cultivars. For instance at 30°C. RC02 and 
RC2H4 of Braeburn apples was more than 3 times greater than Gala apples 
(which had the lowest R). 
7.4.7 Quality indices 
Fru it  fi rmness varied between  cu lt ivars and it was s i gn i f i cant ly  
i nfluenced by temperature (P < 0.001 ; figs. 7- 1 5  and 7- 1 6). Genera l ly  fruit 
equi l ibrated at low temperatures were fi rmer than their counterparts at h igher 
temperatu res. Fruit fi rmness decli ned as temperatu re increased. For al l  the 
tempe ratu res , Braeburn apples were f irmer than the other cultivars .  For 
example, at 30°C, the mean firmness of Braeburn apples was 80 Newtons as 
against 47 and 42 Newtons in Golden Del icious and Cox's Orange Pippin 
apples respectively. 
Soluble solids differed among cultivars but there was no significant (P = 
0.05) effect of equi l ibration temperature on the soluble sol ids content of apples 
(figs. 7-1 7 and 7-1 8). However there were some differences in soluble sol ids 
content between temperatures in some of the cu ltivars. For example at O°C 
the soluble solids content of Golden Del icious and Splendour app les  were 
lower than those at 5°C, while i n  Royal Gala it was the opposite. G enerally 
Splendour apples contained higher soluble sol ids than the other cultivars . For 
� 
i nstance at 30°C the average soluble sol id content of Splendour apple s  was " 
approx imately 1 4% compared to 1 2 .5% i n  Red Del icious ,  1 2% i n  Go lden 
Del icious and Cox's Orange Pippin and 1 1  % in  Gala, Royal Gala or Braeburn. 
100 
90 
80 
70 
60 
50 
40 
90 
80 
70 
-. 60 Z 
';' 50 
v:l 
Cl) c 40 E 
u: 90 
80 
70 
60 
50 
40 
90 
80 
70 
60 
50 
40 
0 5 10 15  20 
o Temperature ( C) 
214 
(a) 
25 30  
Fig. 7 - 15 .  Relationship between temperature and finnness of 
(a)=Cox's Orange Pippin (b)=Braebum (c)=Splendour 
(d)=Granny Smith apples. Vertical bars represent standard error 
of the means. 
100 
90 
80 
70 
60 
50 
40 
90 
80 
70 
__ 60 Z 
':;' 50 
c.fl 
� 
c 40 E 
tt 90 
80 
70 
60 
50 
40 
90 
80 
70 
60 
50 
40 
0 5 10 1 5  20 
Temperature (C) 
25 
2 15 
<a) 
<b) 
(c) 
30  
Fig . 7- 1 6. Relationship between temperature and finnness of 
(a)=Gala (b)=Royal Gala (c)=Golden Delicious and (d)=Red 
Delicious apples. Vertical bars represent standard error of the 
means. 
16 r-
-----------------------------, 
14 
14  
14 
12 
10 
8 
o 5 10 15  20 
Temperature tC) 
25 
(a) 
(b) 
(d) 
30 
216  
Fig. 7- 1 7. Temperature effects on soluble solids contents of 
(a)=Cox 's Orange Pippin (b)=Braebum (c)=Splendour and 
(d)=Granny Smith apples. Vertical bars represent standard error 
of the means. 
16  
14 
12  
10 
8 
14 
12 -.. 
� '-" 
.... 10 t:: 0 .... 
t:: 
0 
8 (,) 
r.fJ 
"0 
:.::::= 
0 14 r.fJ 
0 -
..0 
::s 
12 -0 
Cl') 
10 
8 
14 
12 
10 
8 
0 5 10 15  20 
o Temperature ( C) 
25 
2 17 
(a) 
(b) 
(c) 
30 
Fig. 7- 1 8 . Temperature effects on soluble solids contents of 
(a)=Gala (b)=Royal Gala (c)=Golden Delicious and (d)=Red 
Delicious apples . Vertical bars represent standard error of the 
means. 
21 8  
7.5 DISCUSSION 
Temperature markedly i nfluenced the internal atmosphere composition 
of apples. Results obtained in the present study (figs. 7-1 , 7-2 and figs .  7-3, 7-
4) clearly demonstrated that the 02 concentrations i nside the fruit decreased 
with a concomitant increase in [C02]i in response to i ncreasing temperatures. 
This may be explained primarily on the basis of increased 02 utilisatio n  in the 
fruit as tempe ratu re i ncreased ( ie .  Increasing  temperatu res i nc re ase 02 
consumpt ion t h rough resp i rat ion  and decrease 02 so lubi l ity i n  t he  fruit 
t issues ) .  These fi nd ings are co nsistent  with those repo rted b y  othe r  
i nvestigators i ncluding,  Anzueto and Riki ( 1 985) ·who reported that apples 
stored at lower temperatu res had lower [C02]i and hig her [02] i than  their  
counterparts at h igher temperatures. S im i larly, as early as 1 920rt.Magness 
also showed that the 02 in the intercel lular spaces of apples decreases when 
fruit are held at higher temperatures, and C02 within the tissues 
correspondingly increases. 
I n  Braeburn apples both the intercept and slope of the regress ion l i ne 
relat ing [02] i and [C02]i to temperature were significantly different from the 
other cultivars. In physiological terms this cou ld be interpreted to mean that 
Braeburn apples consistently had lower [02]i and higher [C02]i than the other 
cultivars at al l the temperature reg imes and the rate of change in  [02]i and 
[C02]i with respect to temperature in Braeburn apples was higher than the 
other  cultivars. The reason for the difference could be due to the fact that 
B raeb u rn app l e s  have h i g h R a nd  l ow  i n t e rce l l u l a r space v o l ume  
(approximately 1 4 . 1  % Rajapaskse et ai, 1 990) coupled with i ntermediate 
respiration rate. High skin resistance therefore affec�gas movement across 
the fruit ski n and results in lower [02] i and higher [C02]i for a g iven respiration 
rate and external atmosphere composit ion. In  contrast, Splendour apples had 
higher [02]i and lower [C02]i than the other cultivars. The reaSon could be 
attr ibuted to the i r  low R, low respirat ion rate , presence of open  calyx  and 
numerous lenticels hence easier gas diffusion. 
21 9 
Temperature had a marked effect on fruit respiration rate which varied 
between cultivars. Respiration rates of fruit were low after equil ibratio n  at O°C. 
A low respiration rate at low temperatures i ndicates an inhibitory effect on  the 
overa l l  metabo l ic  system of the  fruit (Wang ,  1 990) .  In most cu l tivars, 
�. 
respiration rates i ncreased l inearly i n  response to i ncreasing temperatures, 
except i n  Cox's Orange Pippi n apples i n  which an exponent ial  type of 
response was observed which is simi lar to that reported for many crops and 
forms the basis of tempe ratu re quotient (Johnson and Tjlorn ley ,  1 985) .  
Perhaps the increased rate in respi ration was partially offset by the decreased 
02 solubil ity at higher temperatures. This would mean that for a given i nternal 
atmosphere composit ion,  02 content of t he ce l l  sap wou ld be reduced at 
h igher temperatu res. At 30°C, Cox's Orange Pippin apples were respi ri ng 
approximately ten t imes faster than at O°C and over 50% more rapidly than 
Splendour (at 30°C). High temperatures coupled with the high respirat ion rate 
and the h i gh  [C02] i of Cox's Orange Pippin apples could exacerbate the 
cu ltivar's h igh  susceptibi l ity to C02 i njury and h igh incidence of  postharvest 
disorders such as core flush or internal browning. 
High storage temperatures i ncrease respi ration metabolism, probably by 
enhanci ng the activity of enzymes involved in the breakdown of resp iratory 
tU- "'\' )  
substrates and production of C02 (Kader" 1 985; Kn�e, 1 990). On  the contrary ). 
l ow  t empe ratu re s  dep ress t h e  act i v i t y  o f  resp i rato ry e n zy m es and  
consequently decl ine in  C02 production (Abeles, 1 973 ; Knee, 1 990 ;  Wang ,  
1 990) .  Low temperatu res have been shown to  reduce respi ratio n  rate of 
apples (Johnson and Ert�n, 1 983) .  Hansen ( 1 942) working with pears fou nd 
that respi rat ion i ncreases i n  inte nSity t h roughout the  range of 0 - 40°C .  
Although C02 content was high in the fruit tissue with correspondingly low 02 
content, Hansen i ndicated that this was not the factor l imiting C2H4 p roduction 
at 40°C. 
220 
Since the rate of deterioration of harvested apples is inversely related to 
their rate of respiration, fruit stored at higher temperatures would be expected 
to have shorter she lf-life because of the i ncreased rate of respi rat ion at h igh 
temperatures (Johnson and Enan, 1 983 ; Kader et al. , 1 985, 1-989) .  On this 
basis, exposing cultivars �uch as Cox's Orange Pippin apples which have  h igh 
resp i rati on  rates to h igh tempe ratu res cou ld  resu lt i n  shorter s h e lf- l i fe 
compared to Splendour apples which have low respiration rates. 
Temperature had pronounced effects on [C2H4]i and rate of C2H4 
production and varied between cu lt ivar. Low equ i l ibrat ion  tem peratu res 
between 0 and 1 0°C depressed both [C2H4]i and rate of C2H4 product ion i n  
a l l  the apple cult ivars ,  however concentrat ions increased i n  respon se to 
i ncreas ing  temperatu res reach ing  a maximum at 25°C and decl i n ed i n  
response to further temperature increase. This is the first time the effects of a 
range  of tempe ratu res o n  [C2H4] i of d i fferent  apple cu ltivars has  been 
C\r'!-
characte rised.  These f ind ingsAconsistent with those reported by  othe r  
i nvest i gators i n cl ud i ng  B u rg ( 1 962) who contended that l ow s to rage 
temperatures depressed rate of C2H4 evolution by slowing down the synthesis 
and/or activity of the enzymes (ie. 1 -aminocyclopropane- 1 -carboxyl i c  acid 
(ACC) synthase and/or ethylene-forming enzymes (EFE» necessary for C2H4 
product ion .  S im i lar concl us ions have be rep.one-et by-othe.r�vest igators <�-l 
i ncluding Abeles ( 1 973), Field ( 1 9� 1 9�91(JObl ing et al:/( 1 99y� and Knee 
( 1 985{ 1�88). Vu et al. ( 1 980), and Klein ( 1 989)�S� of f ruit at 
h igh temperatures inhibited C2H4 production at the step of conversion of ACC 
to C2H4 (ie. EFE activity) , as opposed to Biggs et ak(1 988) who i ndicated that 
ACC synthase is the primary site affected by hig h temperatu res, with EFE  
activity only affected secondarily. 
Many f ru its and a variety of tissues produce low amounts of C2H4 at 
low temperatu res, reaching a maximum between 20 and 30°C, and a lmost 
none at 40°C (Bu rg ,  !_�62) .  This was fi rst i ndicated by experiments with 
221 
comice pear, in which Hansen (1 942) found that small amounts of C2H4 were 
produced at low temperatures, large quantities were evolved by the fruit at 
20°C but negl ig ible amounts at 40°C .  On the other hand Mclntosh apples 
produced maximum amount of C2H4 at 32°C, but almost none during one hour 
at 40°C (Burg and T.bjmann, 1 959). In this research, fruit [C2H4]i and rate of 
C2H4 production  increased to a maximum at 25°C however the choice of the 
temperatu re ranges did not permit accurate identificat ion of the opt imum 
temperature for [C2H4]i and C2H4 production, nevertheless the shape of the 
graphs (figs. 7-9 and 7- 1 0) i ndicate that the optimum could l ie any where 
between 20 and 30°C. 
Literature dealing with C2H4 contains conflicting reports on  the opt imum 
temperatu re for C2H4 evolution in apples. For i nstance, Burg and Thimann 
( 1 959 )  wo rki n g  with app le t i ssue  secti ons  reported t hat the  o pt i mum 
temperatu re for  C2H4 p roduct io n was _ �?OC ,and above t h is opt i m um ,  
production declined rapidly. They further i ndicated that at 40°C and above, 
C2H4 production ceased. However, inhibition was reversible when fruits were 
transferred to lower temperatures. Mattoo et al . . ( 1 977) and Vu et al. ( 1 980), 
using apple fruit plugs, reported a sl ightly lower optimum temperature of 30°C, 
while Apelbaum et al. �1 )  obtained an optimum of 29°C when working with 
apple fruit discs. All of these workers determined the optimum temperature for 
C2H4 evo lut ion  on sections of apples. Although I do not  dispute  these 
conclusions, i t  may be that data obtained in experiments with fruit slices, discs, 
or tissue sections may not necessarily be applicable to the metabolism of the 
intact fru it. Sl iced fruit may well behave differently from  whole i ntact f ru i t · 
because of the stimulation of C2H4 production and respi ration by wounding 
(Abeles, 1 g73 ; Rosen and I:Sader, 1 989). Abeles ( 1 973)  i ndicated that an 
..., 
example of a process which is controlled by an i ncrease in the rate of C2H4 
production is wound-induced protein synthesis. Tissue damage results in an 
increase in C2H4 production (Field, 1 985) . In addition, the combined effects of 
222 
physical wou nding and temperatu re may simply be additiv.e in fresh ly-cut 
sections wh ich could i ncrease rate of C2H4 product ion (Field, 1 985) and 
perhaps also affect the optimum temperature. 
Afte r storage at 30°C most of the apple cu ltivars l ost much of their 
capacity to accumulate and produce C2H4. The decl i ne  in rate of C2H4 
evolution beyond the maximum suggests a loss of i ntegrity of the C2H4-
synthesising system (Field, 1�1 ; Saltveit and Djlley, 1 978) . More specifically . 
the high temperature may perturb membrane structure, leading to increases in 
activation energy of membrane-bound enzymes and hence the reduced rate of 
C2H4 synthesis (Field, 1 981 ) .  The, 
decl ine in rate of C2H4 production after 
reach ing  t h e  max imum and eventual cessat ion  at h igher  temperatures 
suggests t hat production of C2H4 was enzyme dependent (Spency, 1 969). 
Enzymes are well known to be denatured at h igh temperatures (Forward, r 
1 960) and this presumably accounted for the decline in  capacity to accumulate 
and produce C2H4. In several cases, e.g.  apples, pears and bananas, i t  has 
been ascertained that C02 production has not yet reached its maximum value 
at the temperature which causes total inhibition of C2H4 evolution, suggesting 
that the effes� of temperature is directly on the mechanism of C2H4 synthesis 
(Burg ,  1�). Osborne Jj-978) i ndicated that as temperatu re i ncreases the 
enzymes concerned with C2H4 biosynthesis appear to be relatively labi le 
compared w i th  t hose of  the resp i ratory pat hway. The  ab i l i ty  of h i g h  
temperatu res to reduce drastical ly o r  total ly prevent C2H4 evolution may be 
reflected in the fai lure of many fruits to ripen normally above 30°C to 35°C, if 
.I • 
they ripen at al l (Burg ,  1 �92 ; Hansen)945; Yu et,�/; 1 980) .  
Splendour apples compared to the other cultivars had the least capacity 
to accumulate and/or produce C2H4. It has long been known that there are 
cu l t ivar d i ff e re nces i n  rates of C2H4 producti on  and t h i s cou ld be a 
determinant of storage life (Nelson, 1 940). The formation and accumu lat ion of 
C2H4 i n  fruit t issues is a vital factor  in  the natural ri pen ing of apples and 
consequently in  their rate of deterioration (Kidd and West, 1 937) . 
223 
Evidence p resented i n  th is  study demonstrated that equ i l i b rati on  
tempe ratures ( 0  - 30°C) had no  consistent s ignificant effect on  RC02 and 
RC2H4 of apples. A temperature change of 5°C had l ittle or  no effect on  skin  
resistance, even though product ion rates and internal gas concentrations 
changed substantially. This might be expected since resistance to diffusion is 
a p h ys ica l  pa ramet e r  and he nce s hou ld be re lat ive l y  u n affected  by  
temperature (Cameron and �, 1 982). Leonard and Wqrdlaw ( 1 94 1 ), i n  thei r 
. '  
work with banana, reported that a temperature change of 8°C had little or no 
effect on R.  RC02 and RC2H4 varied between cultivars, with Braeburn apples 
having higher RC02 and RC2H4 (for al l the equi l ibration temperatures) than 
the other cultivars. 
G e n e ral l y  fru i t  were f i rme r  at low temperatu res  but i ncreas i n g  
temperatures accelerated softening and varied with cultivar. The findings of 
this study are compatible with those reported by Magnes�d Diehl ( 1 924) 
who indicated in their studies with six cultivars of apples that softening of fruits 
were greatly accelerated by higher temperatu res. Simi larly, Bou rne ( 1 982) 
reported that with some exception , most horticultural fruits and vegetables 
showed a decl ine in fi rmness with increasing . temperature over the range 0 -
45°C. Mitcham and M�onald ( 1 992 ) also reported that loss of f irmness by 
fruit during storage at � igh temperatures could be related to moisture loss. 
Temperatu re could affect firmness in two ways, fi rst, it could have reversible 
effect with di rect effect on fruit texture and secondly, it could accelerate the 
process of soften ing and th is is essential ly i rreversible. Softening of pome 
f ru its includ ing apples are associated with a reduct ion in  m iddle l ame l la  
cohesion and is  characterised by  so lub i l i sat ion  of  pect in  (Knee ,  1 982 ) .  
Temperature did not affect the soluble solids content of fruit. " 
, -
224 
It can be concluded that the internal atmosphere composit ion, C2H4 
evolut ion,  respi rat ion rate and f irmness of apples  respond to i ncreas i ng  
temperatures. The magnitude of response was cultivar dependent. Fruit [02]i 
decreased wh i le  [C02] i and respi rati on rates i ncreased i n  response to 
i ncreasing tem peratu res . I nte rnal C2H4 and C2H4 product ion i n  apples 
reached a maximum at 25°C. At 30°C the abil ity to produce C2H4 declined 
markedly i n  most apple cult ivars. Temperature did not affect R and soluble 
solids content of apples. 
The temperature at which an apple cu ltivar i s  stored after harvest and 
du ri n g  t h e  post harvest hand l i n g  cha in  is a v ita l  factor to  the rate o f  
deterio rat ion  and hence sto rage l i fe .  Fresh fru its i nc lud ing  app les  are 
assuming a pOSition of increasing importance in the diet of the human race. If 
a supply of this fruit is to be available to the ultimate consumers throughout the 
year, suitable storage temperatures are essential throughout the distribution 
network. Not only does proper storage temperature management e nsure 
regular supply, but it also stimulates consumption and stabil ises prices for the 
grower through its effects on quality. 
7.6 LITERATURE CITED 
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Anzueto, C. R and Rizvi, S. S. H. 1 985. Individual packaging of apples for shelf 
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Banks, N .  H .  1 985. Estimating skin resistance to gas diffusion in  apples and 
potatoes. J.  Expt. Bot. 36 : 1 842- 1 850. 
'/ 
225 
Biggs, M. S. ,  Woodson ,  W. R. and Handa, A. K. 1 988. Biochemical basis of 
high-temperatu re inhibition of ethylene biosynthesis i n  ripening tomato v/' 
fruits. Physiol. Plant. 72 :572-578. 
Bou rne,  M. C .  1 982. Effect of temperatu re on  firmness of raw fru its anj 
vegetables. J. Food Sci. 47 :440-444. 
Burg ,  S. P. and Thimann, K. V. 1 959. The physiology of ethylene formation i n  
apples. Proc. Nat. Acad. Sci. (U.S.A.) 45:335-344. 
Bu rg ,  S .  P .  1 962 . The physio logy of ethylene formation, Ann. Rev. Plant 
Physiol . 1 3 :265-302. 
Bu rg ,  S .  P .  and Burg ,  E .  A. 1 965. Gas exchange in  f ru its . Physio l .  P lant.  
1 8 :870-884. 
Burton ,  W. G .  1 974. Some biophysical pri ncip les underlyi ng  the cont ro l led 
atmosphere storage of plant material . Ann. Appl. Bio I .  78:1 49-1 68 .  
" 
/ " 
Bu rto n ,  W.  G .  1 978 .  B iochemical and phys io log ical effects of m od i fied 
atmospheres and thei r  rol e  i n  qual ity maintenance. In  'Postharvest v' 
biology and biotechnology'. (H. O. Hultin and M. Milner. eds.) Food and 
Nutrition Press, Westport, Conn. pp. 97-1 1 0. 
Cameron ,  A.  C .  1 982 . Gas diffusion i n  bu lky plant o rgans .  Ph .D .  thesis, 
University of California, Davis. 1 1 7 pp. 
Cameron, A. C. and Yang, S. F. 1 982. A Simple method for the determination 
of resistance to gas diffusion in plant organs. Plant Physiol .  70 :2 1 -23 .  
Cameron ,  A.  C .  and Reid, M.  S .  1 982. Diffusion resistance : importance and 
measu rements in contro l l ed atmosphe re storage .  I n :  Con t ro l l ed v 
atmospheres for sto rage and t ranspo rt of pe rishable ag ri cu l t u ral 
commodities. (D. G. Richardson and M. Meheriuk, eds.) .  Oregon State 
Un iversity School of Agricultu re ,  Symposium Series No. 1 ,  Timber  
Press, Beaverton, Oregon. pp. 1 71 - 1 80. 
Eaks, I .  L .  1 978. R ipeni ng , respi rat ion and ethylene product ion of 'Hass' 
avocado fruits at 20°C to 40°C. J. Amer. Soc. Hort. Sci . 1 03:576-578. 
Field, R. J. 1 981 . A relationship between membrane permeability and ethylene , 
production at high temperature i n  leaf tissue of Phaseo/us vulgaris L. t/ 
Ann. Bot. 48:33-39. 
226 
Field, R. J .  1 985. The effects of temperature on ethylene production by plant 
tissues. I n :  Ethylene and plant development. (J. A. Roberts and G. A. 
Tucker eds . ) .  Butte rworths,  Robert Hartnol l  Ltd, Bodmin ,  Cornwall ,  
Eng land. pp. 47-69. 
Field, R. J. 1 989. Temperature-induced changes in ethylene production and 
imp l icat io ns fo r post- ha rvest p hys io logy .  I n :  B iochem ica l  and 
physiological aspects o f  ethylene production in lower and higher  p lants. 
(H .  C l ijsters, De P roft , M . ,  Marce l le ,  R. and Van Poucke, M. eds. ) .  
Kluwer Academic Publishers. London. pp. 1 9 1 - 1 99. 
Forward, D. F. 1 960. Effects of temperature on respi ration. I n :  Encyclopedia of 
Plant Physiology. Springer-Verlag , Berl i n .  Gott i ngen .  He ide lberg . 
X I I/2 :234-258. 
Hansen ,  E .  1 942 . Quantitative study of ethylene product ion in re lat ion to 
respiration of pears. Bot. Gaz. 1 03 :543-558. 
Hansen, E .  1 945.  Quantitative study of ethylene production i n  apple varieties. 
Plant Physiol .  20 :631 -635. "//"  
Jobl ing ,  J. , McGlasson ,  W. B. ,  and Dil ley, D.  R. 1 991 . I nduction of ethylene 
synthesizing competency in  G ranny Smith apples by exposure to low 
temperature in  ai r. Postharvest Biology and Technology 1 :1 1 1 -1 1 8. 
\! 
Johnson, D.  S .  and Ertan, U .  1 983. I nteraction of temperatu re and o xygen 
level on the respiration rate and quality of Idared apples. J .  Hort .  Sci . .. 
58 :527-533. 
Johnson, I .  R. and Thornley, J. H. M. 1 985. Temperature dependence of plant 
and crop processes. Ann. Bot. 55 :1 -24 . 
Kader, A. A . ,  Kasmire, R. F. ,  Mitche� F. G . ,  Reid, M. S . ,  Sommer, N .  F. and 
Thompson, J.  F. 1 985. Postharvest Technology of Horticultural C rops. 
University of Cal ifornia Press, Berkeley. 1 92 pp. 
Kader, A. A . ,  Zagory, D. and Kerbe l ,  E. L.  1 989 . Modif ied atmosphe re 
packaging of fruits and vegetables .  CRC Crit . Rev.  Food Sci . Nutr. 
28 : 1 -30 . 
'/ 
'.. 
227 
Kidd, F. and West, C.  1 930. Physiology of fruit. I. Changes in the respi ratory 
activity of apples duri ng their senescence at different temperatures. '/ 
Proc. Roy. Soc. London Series. B. 1 06 :93-1 09. 
Kidd, F. and West, C. 1 937. Effects of ethylene on the respi ratory activity and 
climacteric of apples. Great Brit. Dept. Sci. Ind. Res. Rept. Food Invest. 
Bd. 1 937: 1 08-1 1 4. 
Kidd, F .  and West , C .  1 949.  Resistance of the sk in of the apple fruit to 
gaseous exchange. Rep. Food. Invest. Bd, Lond. (1 949) :57-64. 
Kleinbaum,  D .  G.  and Kupper, L. L. 1 978. Appl ied reg ression analysis and 
oth e r  mu l t iva r iab le  met hods .  Duxbu ry P ress , No rth  Sc i t uate , 
Massachusetts. pp. 95-207. 
K lel i n ,  J .  D .  1 989 . Ethy lene biosynthes is  i n  heat-treated apples .  I n :  
Biochemical and physiological aspects of ethylene production i n  lower 
and h igher  p lants. (H .  Cl ijsters, De P roft ,  M . ,  Marce l le ,  R. and  Van 
Poucke, M.  eds. ) .  Kluwer Academic Publishers. London. pp. 1 81 - 1 89. 
Knee, M. 1 982. Fruit softening : I l l . Requirement of oxygen and pH effects. J.  
\/ .. 
Expt. Bot. 33 :1 263-1 269. L--- -
Knee,  M .  1 985. Evaluati ng the practical s i gn if icance of ethylene  i n  fruit 
storage. I n :  Ethylene and plant development. (J. A. Roberts and G. A. 
Tucker eds . ) .  Butte rworths ,  Robert Hartnol l  Ltd, Bodmin ,  Cornwal l ,  
England. pp. 297-31 5. 
Knee, M.  1 988. Effects of temperature and daminozide on the induction of 
ethylene synthesis in two varieties of apples. J. Plant Growth Regul . ,  
7: 1 1 1 - 1 1 9. 
Knee ,  M .  1 990 .  E thy lene effects i n  co ntro l l ed atmosphere sto rage  of 
horticultural crops. In: Food preservation by modified atmospheres. (M. t 
Calderon and R .  Barkai-Goldon , eds. ) .  CRC Press. Boca Raton Ann. 
Arbor Boston. pp.  225-235. 
Knee, M. 1 991 . Rapid measurement of diffusive resistance .to gases in apple 
fruits. HortSci . 26:885-887. 
228 
Leonard, E. R. and Wardlaw, C .  W. 1 941 .  Studies i n  t ropical fruits. XI I .  The 
respiration of bananas during storage at 53°F and ripening at controlled :/ 
temperatures. Ann. Bot. NS. 5 :379-423. 
Lieberman, M. 1 979. Biosynthesis and act ion of ethylene .  Ann. Rev. Plant 
Physiol .  30 :533-591 . 
Little ,  T. M. and Hi l ls ,  F. J .  1 978. Agricultural experimentation - design  and 
,../ analysis. Wiley, New York. 345 pp. 
Lyons, J .  M. Graham, D. and Raison, J .  K. 1 979. Low temperature stress in 
crop plants. Academic Press, London . 358 pp. \,... ...
. 
Magness, J .  R. 1 920. Comparison of gases i n  intercel lu lar spaces of apples 
and potatoes. Bot. Gaz. 70 :308-3 1 6. 
Magness, J .  R. and Dieh l ,  H .  C .  1 924. Physiological studies on apples in  
storage. J.  Agr. Res. 27 : 1 -38. 
Mattoo, A. K. ,  Baker, J. E. Chalutz, E .  and Lieberman , M. 1 977. E ffects of 
temperature on the ethylene-synthesizing systems in apple, tomato and 
Penicillium digitatum. Plant and Cell Physiol . 1 8 :71 5-7 1 9. 
'. 
/ 
Maxie,  E .  C . ,  M itchel l ,  G .  C. and Sommer, N .  P .  1 974 . Effect of e levated 
temperatu res on ripen ing of Bartlett pears.  J .  Amer. Soc. Hort. Sci . ./ 
99 :344-348. 
Mitcham, E. J .  and McDonald, R. E .  1 992. Effect of h igh temperature on cel l  
wal l  mod ifications associated with tomato fru it ripen ing .  Postharvest 
Biology and Technology. 1 :257-264. 
Nelson, R. C. 1 9$ . Studies on production of ethylene in  the ripening process 
of apple and banana. Food Res. 4 :1 73-1 90. 
Osborne, D. J .  1 978. Ethylene. I n :  Phytohormones and related compounds: A 
comp re he ns ive  t reat i se , v o l .  1 : 265-2 94 . T h e  b i ochem is t ry o f  
phytohormones and related compounds. (D .  S .  Letham, P .  B.  Goodwin 
and T. J. V. Higgins. ed). E lservier/North Holland, Amsterdam. 
, .. /1' 
Porritt, S. W. 1 951 . The role of ethylene in fruit storage.  Sci. Agric. 31  :99-1 1 2 . . 
Porritt , S .  W. and Lidster, P .  D.  1 978. The effects of p restorage heating on 
ripening and senescence of apples duri ng cold storage. J.  Amer. Soc. ' 
Hort. Sci . 1 03 :583-585. 
229 
Rajapakse,  N .  C . ,  Banks, N .  H . ,  Hewett, E .  W.  and Cle land, D.  J .  1 990. 
Development of oxygen concentration gradients in flesh tissues of bulky V' 
plant o rgans. J .  Amer. Soc. Hort. Sci . 1 1 5 :793-797. 
Roberts, J .  A. and Tucker, G. A. 1 985. Ethylene and plant development. 
.. / 
Butterworths, Robert Hartnoll Ltd, Bodmin,  Cornwall ,  England. 41 6  pp. 
Rosen ,  J. C .  and Kader, A. A. 1 989 . Postharvest p� iO logy and q ual i ty 
maintenance of sl iced pear and strawbe rry fruits. J. Food Sci . 54 :656- v' 
659. 
Saltveit, M .  E .  and D il ley, D .  R. 1 978. Rapid induced wound ethy lene from 
excise segments of etiolated Pisum sativum L. ,  cv. Alaska. 1 1 . Oxygen 
and temperature dependency. Plant Physiol . 6 1  :675-679. 
Spencer, M. 1 969. Ethylene in nature .  Fortschritte der chemie organischer 
naturstoffe. 27:31 -80. 
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A biometrical Approach . McGraw-HiI I  Book Co., New York, NY, 2nd ed. ", ' 
633 pp. 
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1 942. Studies in the metabolism of apples. 1 .  Prel iminary investigations 
on i nternal gas composition and its relation to changes in stored Granny 
Smith apples. Aust. J .  Expt. BioI. Med. Sci . 20:21 0-231 . 
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Boca Raton Ann Arbor Boston. pp. 1 97-223. 
t/ 
Yu, Y. ,  Adams, D. O. and Yang, S. F. 1 980. I nhibition of ethylene production ) 
by 2 ,4-Dinitrophenol and high temperature. Plant Physiol . 66:286-290. \/ 
230 
CHAPTER 8 
VARIATION IN INTERNAL ATMOSPHERE COMPOSITION WITHIN  SINGLE 
APPLES 
8.1 ABSTRACT 
Gas concentration g radients within individual fruit have previously been  
conside red to  be  neg l ig ible. I n  this work, large 02 and C02 concentration 
differences were fou nd between the equato r and calyx e nd of Gala,  Royal 
Gala, Braeburn and Cox's Orange Pippin ,  while smal ler differences were found 
in Golden Delicious, Red Del iciousjGranny Smith and Splendour apples at 
20±1 °C. The average 02 concentration difference i n  Gala apples was nearly 
n i ne t imes hig her  than  i n  Splendour, and e ight t imes h igher t han i n  Red 
Delicious or Granny Smith apples. 
S imi larly, 02 and CO2 concentration differences were also observed 
between the equator and caylx end shoulder. These concentration differences 
were much greater than those which have h itherto been measured between 
the core cavity and the fru i t  su rface of other  cultivars.  Oxygen  and C02 
concentration differences between the core cavity and the equatorial surface of 
the fruit were small but statistically significant i n  cultivars such as Braeburn and 
Cox's Orange Pippin apples. 
Tissues at the  calyx reg ion of Braeburn and G ranny Sm ith  apples 
consistently had lower 02 but higher C02 and C2H4 concentrations than any 
other position on the fruit surface , whilst tissues at the equator had h ighe r  02 
and lower  C02 and  C2H4 concentrat ions  than  oth e r  parts of t h e  fruit .  
Braebu rn had h igher  CO2 and C2H4, and lower 02 concentrat ions  at the 
different positions beneath the skin surface compared to G ranny Smith apples. 
231 
These gas concentration differences at the various positions on the fruit 
surface may be related to local ised variation in intercellular space volume as 
well as d ifferences in R and fruit respiration rate. 
Modified atmosphere treatments are effective through the effects they 
have on  fru it internal atmosphere composit ion. The discovery that i nternal 
atmosphere composit ion i n  apple f ru i t  i s  hete rogeneous has i m po rtant 
impl ications for the way in  which we attempt to model the gas exchange of 
these fruit and the effects of CAJMA on their physiology. It may also provide a 
mechan ism which explains the pattern of development of atmosphere-related 
disorders develop within fruit stored in CAJMAs. 
8.2 INTRODUCTION 
Postharvest deterioration of harvested apples can be delayed in storage 
atmospheres i n  which the concentrations of gases surrounding the p roduce 
are alte red re lat ive to the composit ion of a i r  (Burt��/ .. ·1'982) .  The l imit of 
atmospheric modification for maximum benefits depends upon the p roduce 
characte ristics such as gas d iffus ion across the ski n and f lesh t issues,  
response to low 02 and/or high C02 and the abi l ity of the produce to maintain 
essential physiological processes at these conditions without causi ng i njuries 
to i nternal tissues (Kader et�(1 989).  However, when respiratory gases are 
p roduced o r  co nsumed , part icu la rl y  fo r bu lky o rgans such as app l es ,  
concentration g radients are established which result in  tissues experiencing 
i nternal concentrat ions which differ from the exte rnal atmosphere (Bu)1on,  
1 982 ; Came ron and Reid ,  1 982 ; Kader et  al. , 1 989 ; Knee ,/f99 1 ) .  The 
./ 
magn itude of these g radients are a funct ion of sk in resistance ,  effective 
d i ffus iv i ty of t he  gas i n  the fru i t  f lesh ,  f ru it s ize and respi  rat i o n  rate .  
Furthermore, it i s  sites of production and util isation of these gases that dictate 
the di rection of flux of gases resulti ng in these gradients (Burg and �rg , 1 965; 
Burton, }982) .  
232 
Gas concentration gradients within individual apple fruit have previously 
been considered by some authors to be negligible due to the relatively l arge 
i ntercel lu lar space- ·volume. and hence to have no physiological i mportance 
(Burton .  1 9�rg and Burg{1 965; Trout e�k ( 1 942). Available evidence 
indicated that. i nside the skin. the composition of the i nternal atmosphere of an 
apple f ruit is practical ly uniform (Andrich-.BfBl . •  1 989. 1 g91; Ca�n. 1 982 ; 
Hardy. !JM9) .  However.  Banks an�'ays ( 1 988) found s ign if icant f lesh 
resistance to gas diffusion in potatoes, in wh ich i ntercel lular space volume is 
much sma l l e r  t han that o f  app les ( Bu rtollv·1 982 ) .  Due  to  t he  l i m ited  
i ntercel lu lar space volume,  the flesh o f  dense organs such as potato tubers 
and avocado fruit might be expected to exert considerable resistance to gas 
diffusion .  Ben-Yehoshua et a�963) and Burg and BU'J}{' 965) i l lustrated 
that the flesh tissues of immature and climacteric avocado fruit exert sign ificant 
resistance to C02 diffusion,  thus creating large concentration g radients across 
the flesh t issues. Solomos ( 1J81) also reported the existence of significant 
C02 g radients between the core and surface of peeled apples. More recently 
Rajapakse et al. ( 1,989, 1 990) have demonstrated the existence of significant '"-" 
02 g radients i n  apple cultivars Cox's Orange Pippin ,  B raeburn and Golden 
Delicious, and Asian pear cultivars, Hosui and Kosui .  
A p re l im i nary experiment (appendix 4) ,  with G ranny Smith app les 
identified significant heterogeneity in 02 concentration at five positions on  the 
fruit surface beneath the skin. Much research effort has been geared towards 
studying commodity response to external ly imposed atmospheres. Howeve r, 
knowledge of i nternal atmospheres of these commodities is also important in 
developing CA/MA treatments for extended shelf-l ife (Anzueto and Rizvi ,  1 985; 
Banks,  1 984a ;  F id le r  and, Ncfrth ,  1 97 1 ; Hul n"�< 1 95 1 ) .  Knowledge of the  
'./ \!I"" 
distribution of i nternal gas concentrations will enhance our  understanding of 
the  mechan i sms  by which ri pen i ng  is retarded and atm osphe re- re lated 
disorders develop within fruit stored in CA/MA. Furthermore ,  impai red diffusion  
233 
of these gases across the ski n and flesh could result in extremely low 02 or  
h igh  C02 and C2H4 in  the i nte rnal t issues causi ng physiolog ical i njury to 
p roduce sto red u nder MA/CA condit ions. Therefore knowledge of f lesh 
resistance to gas movement is  important i n  determining the critical m inimum 
external 02 that can safely be used in CA/MA storage. 
The foregoi ng studies clearly indicate that fruit flesh resistance to gas 
diffusion may not be negl ig ible  as p reviously thought by some i nvest igators 
and should therefore be taken into consideration in  our attempts to u nderstand 
the physiological effects of fru it  response to CA/MA storage. A series of 
studies were therefore in it iated to quantify gas concentration differences ( 1 ) 
between the equator and calyx end, (2) between the equator and calyx end 
shoulder, and (3) between the equator and core cavity of freshly harvested 
eight cultivars of apples grown in New Zealand. 
I n  addit i o n ,  further experi ments  we re i n i t iated to i nvesti g at e  t he  
distribution of i nternal atmospheres at ( 1 ) the stem end, equator and calyx end 
and (2) at five different positions on the surface beneath the skin of B raeburn 
and G ran ny Smith apples stored fo r var ious periods of t ime  at aoc and 
subsequently held at 20°C. I n  th is way i t  was hoped to  be  able to i dentify 
whethe r  the  development of la rge  g rad ients was someth i ng  wh ich  was 
exacerbated with the decline in tissue condition associated with increased t ime 
i n  sto rage .  Th i s  m i g ht p rov ide  a s i mp le  mechan i sm  to  e xp l a i n t h e  
development of some fruit long term storage disorders. Furthermo re such 
information could help in the development of models p redict ing the effects of 
CA/MA on apple fruit and also in the study of gas exchange characteristics of 
fruits stored in CA/MA. 
234 
8.3 MATERIALS AND METHODS 
8.3.1 Fruit supply 
Freshly harvested apples (Malus domestica Borkh .) of eight cultivars 
(Cox's O range Pippin ,  Gala, Royal Gala, Golden Del icious, Red De l icious, 
Braeburn, Splendour. _and- -Granny Smith apples (count 1 25; av. weight 1 48 g)  
,. �".' 
---
were obtained--as previously described in 3. 1 .  All experiments were conducted 
at 20±1 cC. �-- --- -- - -- - -
I n  a second experiment freshly harvested Braeburn and Granny  Smith 
apples (count 1 25; av. weight 1 48 g) were obtained from a s imilar source as 
mentioned above and fru it were stored at O°C for 0, 4 , 8 and 1 2 weeks and 
subsequently transferred to 20±1 °C for 3, 1 0  and 1 7  days. Both experiments 
were conducted in 1 990. 
8.3.2 Methods 
8.3.2.1 Experiment 1 
8.3.2.1 .1  Estimation of 02 and C02 concentration differences 
Two 2 ml g lass vials from which bottoms had been removed were stuck, 
using polyvinyl acetate adhesive (PVA) , on twelve fruit of each cu ltivar at 
(a) the equator and the calyx end (fig. 8- 1 )  and 
(b) the equator and calyx end shoulder (fig. 8-2) 
Sub-epidermal 02 and C02 concentrations were estimated (see 3 .3. 1 ) 
as equil ibrated gas concentrations in the g lass chambers on each apple after 
40 - 90h at 20±1 cC in air (see appendix 1 ) . 
.,.--", 
, , 
I \ 
. 1  A I \ ; \ , \ , , J � , "'-
235 
c l 
Fig . 8- 1 .  Arra ngement of glass s a mpl i n g chambers on t he s u rface of 
a n  apple fru i t .  
A. Core cavity 1 .  Equator 
B. Fruit s u rface 2. Calyx e nd 
C .  G lass chamber 
D. Sept u m  cap 
E .  Sil icone t u be wit h water 
,--..... 
, , 
I \ 
I A ' 1 • \ : \ , , / \. , .... -
236 
1 
c 
2. 
Fig . 8-2 . A rra ngement of g l ass s a m p l i n g  cham b e rs on the s u rface of 
an apple fruit. 
A. Core cavity 1 .  E q u at o r  
B. Fruit s u rface 2. C alyx end shoulder 
C .  G lass c h am ber 
D. Sept u m  cap 
E. Sil ico ne t u b e  with water 
237 
Core cavity 02 and C02 concentrat ions were measured by the d i rect 
sampl ing method (see 3.3.4 . 1 )  and analysed for 02 and C02 as previously 
described (see 3.3 . 1 ) . Gas concentration differences were estimated as the 
difference in  gas concentrations between any two positions on the fruit. 
8.3.2.2 Experiment 2 
8 . 3 . 2 . 2 . 1  Dete rm inat ion  of d i s t r i bu t i on  of  i nt e rna l  a tmos phere  
composition 
Three 2 ml  glass vials were stuck as previously described, at the stem 
end,  equator and calyx end (fig .  8-3) of twelve fruit after  t ransfer from 0 to 
20±1 °C. 
Similarly, in another paral lel experiment, five 2 ml g lass vial were stuck 
(as previously described) over one or more lenticels on the surface (see fig .  8-
4) of twelve fruit after transfer from 0 to 20±1 °C. 
Gas samples (90�I) were then taken from each g lass vial on the 3rd ,  
1 0th and 1 7th day after seal ing the vial at 20°C using a gas-tight syringe and 
analysed for 02 , C02 and C2H4 as previously described (see 3.3 . 1 ) . 
Immediately after sampl ing from vials on the 1 7th  day at 20°C,  core 
cavity gas concentrations were obtai ned by the di rect sampl ing method and 
analysed for 02 , C02 and C2H4 as previously described (see 3.3 . 1 ) . 
8.3.2.2.2 Fruit quality assessment 
Fruit fi rmness,  so lub le sol ids content and backg round colour  were 
measured as previously described in 3 .3.8. 1 ,  3 .3.8.2 and 3 .3.8.3 respectively. 
,--.... , , , I \ l A I 
t ; \ , \ I \ / \. , ..... -
238 
2 
c 
Fig . 8-3.  A rra ngement of glass s a m p l i n g  c h a m b e rs on the s u rface of 
an apple fruit .  
A. C o re cavity 1 .  Stem e nd 
B. F ru it s u rface 2 . Equato r 
C. G l ass c h a mber 3. Calyx end 
D. Sept u m  cap 
E .  S i l icone t u be with water 
..,.--.... 
, , 
I \ 
I A I , ; \ I \ , , / \. , ..... -
239 
3 
c 
Fig . 8-4. Arra n g e ment of glass sampl i n g  cham b e rs on the s u rface of 
an apple fru it. 
A .  C o re cavity 
B .  F ruit s u rface 
C .  G lass chamber 
D. Sept u m  cap 
E .  S i l i cone t u be with water 
1 .  Ste m e nd s h o u lder 
2. Betwee n Ste m end s h o u ld e r  
and e q u ator 
3. Eq u ator 
4. Between t h e  equator a nd 
calyx e nd s ho u ld e r  
5. £alyx e nd s h oulder , . j ,  
I 
240 
8.3.2.3 Experimental design and analysis 
8.3.2.3.1 Experiment 1 
Twelve s ing le  fruit rep l icates of each apple cultivar were used i n  a 
completely randomised order. Data were analysed as described i n  section 
3.3.9. Mean comparisons were carried out by Duncan's multiple range test at 
1 % level of significance (Duncan J 955), to test difference between cultivars. 
/" 
Student's pai red t-tests (Steel and TO!rie ,  1 980) were also performed to 
compare gas concentration differences between the equator and calyx end, 
between  the equator and calyx end shoulder and between the equator and 
core cavity in each cultivar. 
8.3.2.3.2 Experiment 2 
Within the overall study there were four sampling times at ooe and two 
cultivars, each analysed as a separate experiment .  There were twelve si ngle 
fru it repl icates of each cult ivar and three sampl i ng t imes at 200e used in  a 
factorial design with in each experiment. Analysis of variance (Steel and Torrie,  ./ 
1 980;  litt le ,  1 98 1 ) was carried out usi ng General Li n ear Models p rocedure 
(GLM) of SAS (see 3.3.9) .  
8.4 RESULTS 
8.4.1 Experiment 1 
8.4. 1 . 1 02 and C02 concentration differences between the equator and 
calyx end 
.". . .. .. - , 
Oxygen concentration differences between the equator and calyx end, 
differed between cultivars (P < 0.0 1 ; f ig. 8-5) .  Markedly higher 02 differences 
were estimated i n  �.:al
:
� 
"
�ppr?�
"
i�
"
�t� ly 9o/0)Jsraeburn (5.7%), Royal Gala (5%) 
and Cox's Orange Pippin (4.9%) compared to 0. 1 % in Splendour, 1 % in Red 
_ 1 2  
� ........ 
� 1 0  
u 
c: 
Cl.) L. 
Cl.) - 8 -"0 
c: 
0 
o+J 6 0 L. o+J 
c: 
Cl.) 
u c: 
0 4 u 
N 
o 
U 
"0 2 
c: 
o 
N 
o 0 
a 
• C02 
d b 
COX'S GALA ROYA L GOLDEN RED BRAEBURN SPLENDOUR GRANNY 
ORANGE GA L A  D E L ICIOUS D E LICIOUS SMITH 
P IPP IN 
F ig .  8-5. Oxgyen and carbon d iox ide concentrat ion differences between the equator 
and ca lyx end of fresh ly  harvested app les at 20·C . Letters in common for each gas 
not s i gn i f icant ly d i fferent at the 1 % l eve l .  Mean separation by Duncon's mu l t ip l e  
range test.  
242 
Delicious and Granny Smith and 2% in Golden Del icious apples. The mean 
02 concentration difference in Gala apples was nearly nine times higher than 
in Splendour, and eight times h igher than in Red Delicious or Granny Smith 
apples. 
The re we re s i g n i f icant ( P  < 0 . 0 1 ) cu lt iva r d i ffe re nces i n  C02 
concentration differences between the equator and calyx end. The average 
C02 concentration differences in Cox's Orange P ippin ,  Gala, Royal Gala and 
Braeburn were nearly three t imes higher than in  Splendour and twice higher 
than in Red Del icious or Golden Del icious apples (fig .  8-5) .  
I n  al l  the cultivars, the mean C02 concentration differences were lower 
than the 02 differences. For example, i n  Gala the mean C02 concentration 
difference was 2.6% compared to 9% for 02' 
8.4 . 1 .2 02 and C02 concentration d ifferences between the equator and 
calyx end shoulder 
Oxygen concentrat ion  d i ffere nces esti mated as the d i ffe re nce i n  
equi l ibrated 02 concentrations between the equator and calyx end shoulder 
we re large ly cu lt ivar specif ic (P < 0 .0 1 ; f ig .8-6) .  Mean 02 concentration 
diffe rences in  Gala apples were about six times h ighe r than i n  Splendour, 
Granny Smith or Golden Delicious, nearly  five t imes g reate r than in  Cox's 
Orange Pippi n and three times greater than in Braebu rn or Royal Gala. 
Similarly C02 concentration difference varied with cultivar (P < 0.01 ; f ig. 
8-6) .  The CO2 concentration difference in Braeburn was approximately fou r  
times higher than in Cox's Orange Pippin and about one fourth greater than in  
Gala apples (but  not sign ificantly different) .  I n  general the average 02 and 
C02 concentration differences estimated between the equator and calyx end 
(fig .  8-5) in al l the cultivars, were consistently h igher  than those est imated 
between the equator and calyx end shoulder (fig . 8-6) .  
_ 8  
� 
In 
Cl) 
u 
� 6 L. 
Cl) -..... 
c: 
o 
.... 
o 4 L. .... c: 
Cl) 
u c: 
o 
u 
� 2 
u 
'lJ c: 
o 
N 0 0 
COX'S 
ORANGE 
PIPPIN 
a 
GALA ROYA L 
GA L A  
GOLDEN 
D E L ICIOUS 
RED 
D E L ICIOUS 
BRAEBURN SPLENDOUR 
• C02 
b 
GRANNY 
SMITH 
F ig .  8- 6. Oxgyen and carbon d iox ide concentrat ion d i fferences between the equator 
and ca lyx end shou l der of fresh ly  harvested app l es at  2 0·C . Letters in common for 
each gas not s i gnif icant ly  d i fferent at the 1 % l eve l .  Mean separat ion by Duncan's 
mu l t i p l e  range test.  
N � w 
244 
8.4.1 .3 02 and C02 concentration differences between the equator and 
core cavity 
Gas concentration diffe rences between the equator and core cavity 
differed between cultivar (P < 0.01 ; fig. 8-7). Significantly (P < 0.01 ) h igher 02 
concentration  differences were observed in Braeburn and Cox's Orange Pippin 
apples compared to nearly none in  Gala, Royal Gala, Golden Delicious, Red 
Delicious, Splendour or Granny Smith apples. 
Carbon dioxide concentration differences in Braeburn and Cox's Orange 
Pippin apples were 0.47% and 0 . 1 6% respectively as against nearly zero i n  
Gala, Royal Gala, Golden Del icious , Red Del icious, Splendour o r  Granny 
Smith apples. I n  al l the cultivars, the average gas concentration differences 
estimated between the equator and core cavity (fig.  8-7) were much lower than 
those estimated between the equator and calyx end (fig .  8-5), or  calyx end 
shoulder (fig .  8-6). 
8.4.2 Experiment 2 
8.4.2.1 D istribution of gas concentrations at the stem end, equator and 
calyx end 
8.4.2.1 .1 02 concentrations 
The overall mean 02 concentrations (for each experiment) estimated at 
the stem end, equator and calyx end of Braeburn (fig .  8-8) apples after storage 
at O°C fo r  0 ,  4 , 8, and 1 2 weeks and subsequent  t ransfe r to a m bi e nt 
temperature for 3, 1 0 , and 1 7  days were lower than i n  G ranny Smith apples 
(fig .  8-9 ; P < 0.01 ) .  The average 02 concentrations at the equator in both 
cultivars were consistently higher than at the stem end (P < 0.05) or calyx end 
(P < 0.0 1 ) .  For instance during storage at O°C for 0 weeks and 1 7  days at 
20°C, the 02 concentrations at the equator of Braeburn and Granny Smith 
_ 6  
t.e ......... 
� 5 
u 
c: 
Q) \.. 
Q) 
� 4 
"0 
c: 
0 
� 3  \.. o+J c: 
Q) 
u c 
o 2 u 
N 0 u ,  
"0 
C 
0 
N 0 0 
a 
b b c b c b 
a 
c b c b c 
III 0 2  
• C 0 2  
b c 
COX'S GALA ROYA L GOLDEN REO BRAEBURN SPL ENDOUR GRANNY 
ORANGE GA L A  D E L ICIOUS D E LICIOUS S�ITH 
PIPPIN 
F i g . 8-7 . Oxgyen and carbon d iox ide concentrat ion d i fferences between the equator 
and core cavity of fresh ly  harvested app les at 2 0 ·C . Letters in common for each 
gas not s i gn i ficant ly d i fferent at the 1 % l eve l .  Mean separat ion by Duncan 's  mu l t ip l e  
range test .  
N � Con 
20 
1 6  
1 2  
8 
4 
0 
20 
16  
12  
,-... 
� 8 '-'" 
tn 
I: 4 0 .-.... ro 
0 '"'" .... I: 
8 20 
I: 
0 
u 1 6  (".I 
0 
12 
8 
4 
0 
20 
16  
12  
8 
4 
0 
r - - - - - - I-. , 
. . . . . . . . . . . . . . . . . . . . ... " . ... . " 
- - 3 days at wOe 
• . . . .  10 days at 200e 
- 17 days at 200e 
':.::. �. ::.::-.:":'.;-:- . 
- - - -
- ­
. . .. . . .. .. . .  
. . . . .. . . . . .  
. ..  :'T. r:'
. :-:'  .. ::":' - -
... ... ... .... 
... 
, 
, 
· .. ·i 
Stem end Equator Calyx end 
Position on fruit surface 
246 
(a) 
(b) 
(c) 
(d) 
Fig .  8-8. Oxygen concentration at the stem end, equator and 
calyx end of Braebum apples stored (for (a)=O, (b)=4, (c)=8 ,  
o 0 (d)= 1 2  weeks) at 0 C and subsequent transfer to 20 C (for 3 ,  1 0  
and 1 7  days). Vertical bars represent standard error of the means. 
20 
1 6  
1 2  
8 
4 
0 
20 
1 6  
1 2  
;--.. 
� 8 '-' 
f.I.) 
c 4 0 . -.... � 
0 '-.... c 
8 20 
c 
0 
C,) 1 6  N 
0 
1 2  
8 
4 
0 
20 
1 6  
1 2  
8 
4 
0 
- - 3 days at 'lIte 
. . . . .  10 days at 200e 
- 17 days at 200e 
r:.:-:.:-:.:-:-.:-:-.:-:.:-: . .  - -· · · · · · =7· �· :-:-·::· t 
Stem end Equator Calyx end 
Position on fruit surface 
247 
(a) 
(b) 
(c) 
(d) 
Fig. 8-9. Oxygen concentration at the stem end, equator and 
calyx end of Granny Smith apples stored (for (a)=O, (b)=4, 
o 0 (c)=8, (d)=1 2  weeks) at 0 C and subsequent transfer to 20 C (for 
3 ,  1 0  and 1 7  days). Vertical bars represent standard error of the 
means. 
248 
apples were nearly 1 1  and 1 6% respectively as against approximately 4 and 
1 3% respectively at the calyx end and 9 and 1 5% at the stem end. There were 
consistent trends of h igh 02 concentrations at the stem end, peaking  at the 
equator and decl ining at the calyx end. The magnitude of decline was cultivar 
dependent. After storage at ooe for 1 2 weeks and subsequent transfer to 20°C 
for 1 7  days, the 02 concentrations at the equator of Braeburn apples were 
nearly 3 times higher than at the calyx end, while i n  Granny Smith it was 1 .3 
t imes hig her. Duri ng the fi rst 1 7  days at 20°C, 02 concentration s  at the 
various positions on the fruit surface were high ,  however after a period of cold 
storage and subsequent transfer to 20°C, there seemed to be a decl ine in 02 
concentrations. In  addition, 02 concentrations at the stem end, equator and 
calyx end in  both cultivars declined with time of storage at 20°C. For i nstance, 
i n  Braeburn apples, after the 3rd day of storage at 20°C (fig .  8-8a) , the mean 
02 concentrations at the stem end, equator and calyx end were approximately 
1 2 , 1 3  and 6% respectively. However by the 1 7th day at 20°C, concentrations 
had dropped to nearly 9 ,  1 1  and 4% respectively.  After 4 , 8 or 1 2 weeks at 
ooe and subsequent storage at 20°C for 3days, 02 concentrat ions at the 
various positions were lower than the initial concentrations before cold storage 
(fig .  8-8a) . Similar trends were also observed in Granny Smith, however i n  this 
case, 02 concentrations were much higher than those observed in Braeburn 
apples. 
Core cavity 02 concent rat ions est imated on the 1 7th  day at 20°C 
differed between the two cultivars (fig .  8-1 0 ;  P < 0.01 ) .  I t  was observed that 
whi lst the 02 concentrations i n  the core cavity of Braebu rn apples d i d  n ot 
change with t ime of storage at ooe and subsequent storage at 20°C for 1 7  
days, 02 concentrations in  Granny Smith apples varied markedly (P  < 0 .0 1 ) 
over the period . 
20r-
----�----�----�----�------��--�_. 
-.. 
� 1 6  '-" 
VJ c: 
o .-0  .... � 1-0 
t: 1 2  
8 
§ 
U 
N o 8 o .-0  
� 
U 
� o 4 u 
o 
11 Braebum 
[]] Granny Smith 
o 1 2  
249 
Fig. 8- 1 0. Core cavity O2 concentrations of Braebum and Granny 
Smith apples stored at OOC for 0, 4, 8 and 12  weeks and subsequent 
storage at 20°C for 1 7  days. Vertical bars represent standard error of 
the means .  
. 
250 
8.4.2.1 .2 C02 concentrations 
Carbon dioxide concentrations at the stem end, equator and caly x  end 
differed between cu
·
ltivars. After storage at O°C and subsequent storage at 
20°C, CO2 concentrations in Braeburn apples were mostly greater than 6% 
and increased during storage at 20°C to about 9 or 1 0% (fig. 8- 1 1 ) . compared 
to Granny Smith in which concentrations were greater than 3% but increased 
to approximately 6 or 7% during the same period (fig.  8- 1 2).  Carbon d ioxide 
concentrations at the calyx end in both cultivars were consistently higher  than 
at the stem end or equator, however, concentrations in Braeburn were much 
higher than in Granny Smith apples. For example, C02 concentrations at the 
calyx end of Braeburn and Granny Smith apples after 8 weeks of cold storage 
and subsequent storage at ambient temperature for 1 7  days were respectively 
1 0.6 and 7.9% as against 7.7 and 6.4% at the equator and 8. 1 and 6.7% at the 
stem end. Throughout the storage periods there were consistent patterns of 
h igh  C02 concentrat ions at the calyx end ,  decl i n ing  at the  equat o r  and 
increasing at the stem end. Core cavity CO2 concentrations differed between 
t h e  two cu l t i vars (f i g .  8 - 1 3 ; P < 0 . 0 1 ) w i th  on l y  g radual i ncrea se  i n  
concentrations with storage time at 20°C (not significantly different) .  
. '  8.4.2. 1 .3 C2H4 concentrations ..... � .. <. ,  i , . ..:,'-: r- .' 
1\ 
The mean C2H4 concentrations at the stem end, equator and calyx  end . ': ' . .! " 
of Braebu rn (fig .  8-1 4) apples were higher (P < 0.001 ) than in Granny Smith ' 
(fig .  8- 1 5) .  H ighest concentrations were estimated at the calyx end, s l ightly 
less at the stem end and least at the equator. During th� 3rd and 1 0th d ay at 
20°C (fig .  8- 1 5a) C2H4 was not detected in any of the positions in G ranny 
Smith apples, however, by the 1 7th day, the calyx end (1 36 III r 1 ) had more 
C2H4 than the stem end (1 09 III r 1 ) and equatorial surface (97 III 1 - 1 ) .  After 
cold storage for 4 , 8 and 1 2 weeks and subsequent storage at 20°C for 3 ,  1 0  
1 2  
9 
6 
3 
0 
1 2  
9 
--. 
6 � "-" 
CI:l 
c:: 3 0 .-.... 
� .... 0 c:: tU 
(,) 1 2  c:: 
0 (,) 
N 9 0 u 
6 
3 
0 
12  
9 
6 
3 
0 
- - 3 days at wOe 
• . . . .  10 days at 20·C 
- 17 days at 20·C 
. .. . .. . . . . .. . . .. . . . . . .. .  - - - - - -
.. ..  �.:,.- :.: :.: .. .. .. .. .. .. .. .. .. .. .. 
- - - - - -
Stem end Equator Calyx end 
Position on fruit surface 
25 1 
(a) 
(b) 
(c) 
(d) 
Fig. 8- 1 1 .  Carbon dioxide concentration at the stem end, equator 
and calyx end of Braebum apples stored (for (a)=O, (b)=4, (c)=8, 
o 0 (d)= 1 2  weeks) at 0 C and subsequent transfer to 20 C (for 3, 1 0  
and 1 7  days). Vertical bars represent standard error of the means. 
1 2  
9 
6 
3 
0 
12 
9 
-. 6 � 
--
V,) 
c 3 0 .
... 
... 
e 
... 0 c 
0 u 12 c 
0 U 
N 9 0 
u 
6 
3 
0 
12  
9 
6 
3 
0 
- - 3 days at wOe 
• • . • .  10 days a1 200e 
- 17 days a1 200e 
::. .. . . .. ..
.
.
. .
.
..
.
.
. 
. 
-
-
-
... - .... 
-
-
-
. .  :.:.- :.:, .. :.:.- :..:,-:.:.-:..:. 
Stem end Equator Calyx end 
Position on fruit surface 
252 
(a) 
(b) 
(c) 
(d) 
Fig. 8- 12. Carbon dioxide concentration at the stem end, equator 
and calyx end of Granny Smith apples stored (for (a)=O, (b)=4, 
o 0 (c)=8, (d)=1 2  weeks) at 0 C and subsequent transfer to 20 C (for 
3,  10  and 1 7  days). Vertical bars represent standard error of the 
means. 
253 
1 2  �----�----�----�------��--�----�--, 
11 Braebum 
!El Granny Smith 
sg 9  
o .... 
� 
= 
8 
= 
8 6  
C"l 
o 
u 
;>.. .... .... 
> � 
() 3 � 
o 
U 
o 
o 4 8 12 
Weeks at OOC 
Fig. 8- 1 3 .  Core cavity CO2 concentrations of Braeburn and Granny 
Smith apples stored at OOC for 0, 4, 8 and 1 2  weeks and subsequent 
storage at 20°C for 1 7  days .  Vertical bars represent standard error of 
the means. 
1600 
1200 
800 
400 
0 
1600 
-. 1200 -. -
-
800 � '-' 
v.I 
= 
0 400 .-.... COd ""' .... 
= 0 Q) (,) 
1 600 = 0 
(,) 
v 
::r: 1200 N 
u 
800 
400 
0 
1600 
1200 
800 
400 
0 
- - 3 days at 2tJ°e 
. • . . . 10 days at 200e 
- 17 days at 20°C 
I -i I . . . . . . . . . 1 
� i · · ·
· · " :,:.::.::.�.�.��.�._ - - - -I  
t-----t":: . . . 
J- - - - - - -I- - - - - - - I 
. .. - . . .. . . . . . .. . . .. . . . . .. -
_ .t  
1- _ _  
- - - -
r .." ..,  
J- - - - - - _ r "' 
.... 
Stem end Equator Calyx end 
Position on fruit surface 
254 
<a> 
(b) 
(c) 
(d) 
Fig. 8- 14 .  Ethylene concentration at the stem end, equator and 
calyx end of Braebum apples stored (for (a)=O, (b)=4, (c)=8, 
o 0 (d)= 12  weeks) at 0 C and subsequent transfer to 20 C (for 3 ,  1 0  
and 1 7  days) . Vertical bars represent standard error of the means. 
1 600 
1 200 
800 
400 
0 
1600 
__ 1200 -
I ...... 
...... 
800 :t '-'" 
r.I.) c: 0 400 ..... ..... � '"'" ..... c: 0 Q) (,) 
1 600 c: 0 
(,) 
'<t 
::I:: 1200 C'I 
u 
800 
400 
0 
1600 
1200 
800 
400 
0 
- - 3 days at 'lJte 
• • • • . 10 days at 20De 
- 17 days at 20De 
. _._. _. _. _. -
. . . .. .. . . . . . . .. .. - - - -
. . . . . .  . . . . 
I- - - - - _ _ t- - - -
Stem end Equator Calyx end 
Position on fruit surface 
255 
(a) 
(b) 
(c) 
(d) 
Fig. 8- 15 .  Ethylene concentration at the stem end, equator and 
calyx end of Granny Smith apples stored (for (a)=O, (b)=4, 
o 0 (c)=8, (d)=12 weeks) at 0 C and subsequent transfer to 20 C (for 
3 ,  10  and 17  days) .  Vertical bars represent standard error of the 
means. 
256 
and 1 7  days, the concentrations of C2H4 in both cu ltivars increased over the 
periods at 20°C with highest concentrations at the calyx end. The mean C2H4 
concentrat io n  at the calyx end of Braebu rn apples after 1 2 weeks of cold 
storage and 1 7  days at ambient temperatures was 35% h igher than at the 
equator and 30% h igher than at the stem end, whilst in Granny Smith apples it 
was approximately 1 8% and 6% respectively. 
The mean C2H4 concentrations in the core cavity of Braeburn apples \. ". 
were h igher than in Granny Sm ith (f ig. 8- 1 6; P < 0 .00 1 ) .  I n  Grann y  Sm ith 
apples (apart from the 1 2th week at O°C) core cavity C2H4 concentrat ions 
i ncreased s ign ificantly with increasing periods of  storage. In contrast in  
Braeburn apples the increase in C2H4 concentrations after 0 weeks at O°C 
was not sign ificantly different over the periods of storage. 
8.4.2.2 Quality indices 
Braeburn apples were firmer than Granny Smith (P  < 0.0 1 ) . Generally 
fruit firmness decreased with increasing time of storage at O°C and subsequent 
storage at 20°C for 1 7  days (fig. 8- 17) .  
There were n o  d ifferences ( P  < 0.05) in  so l ub le  so l ids  content o f  
Braeburn and Granny Smith apples during the periods of storage at O°C and 
subsequent storage at 20°C (fig. 8- 1 8) .  
As  ind icated by  the hue  angle val ues,  Granny  Sm i th  app les  were 
greener than B raeburn (fig .  8- 1 9; P < 0.0 1 ) .  However wh i le G ranny  Sm ith 
apples lost greenness during the period of storage (at O°C and subsequent 
storage at 20°C), there were no marked (P < 0.05) colour changes in Braeburn 
apples. 
1500 r-----r---��-__.___--.....,........--__r_--___r_____. 
--
-
-:; 1200 
v:l 
§ .... � � 
C 900 o u 
§ 
U 
"<t 
� 600 u 
o .... 
> 
� u � 300 
o u 
o 
11 Braebum 
EJ Granny Smith 
257 
Fig. 8-16. Core cavity C2H4 concentrations of B raebum and Granny 
Smith apples stored at OOC for 0, 4, 8 and 12  weeks and subsequent 
storage at 20°C for 17 days. Vertical bars represent standard error of 
the means. 
. 
258 
100�----�----�--��------�----�----�--� 
11 Braebum 
Eill Granny Smith 
80 
40 
20 
o 4 8 12  
Weeks at oOe 
Fig. 8- 17 .  Finnness of Braebum and Granny Smith apples stored at 
° ° o e for 0, 4, 8 and 1 2  weeks and subsequent storage at 20 e for 1 7  
days . Vertical bars represent standard error of the means.  
259 
1 8  .-�--�----�------�----�----�------�-, 
III Braebum 
15  []I Granny Smith 
3 
o 4 8 12  
Weeks at oOe 
Fig. 8- 1 8 . Soluble solids content of Braebum and Granny Smith 
° apples stored at 0 C for 0, 4, 8 and 12  weeks and subsequent storage 
at 200e for 17  days . Vertical bars represent standard error of the 
means. 
160 �----�----�----�----�----�------�� 
III Braebum 
140 EJ Granny Smith 
120 
80 
60 
40 
Fig. 8- 1 9. Hue angle of Braebum and Granny Smith apples 
° stored at 0 e for 0, 4, 8 and 12  weeks and subsequent storage at 
200e for 1 7  days . Vertical bars represent standard error of the 
means. 
260 
261 
8.4.2.3 Distribution of gas concentrations at five positions on the fruit 
surface 
8.4.2.3.1 02 concentrations 
Steady state mean distribution of 02 concentrations at five d iffere nt 
positions on the  surface of Braeburn (fig .  8-20) were lower than i n  Granny 
Smith apples (fig .  8-21 ;  P < 0.0 1 ) . I n  general, during storage at ooe for 0 ,  4,  8 
and 1 2 weeks and subsequent storage at 20oe, the mean 02 concentration at 
the equator was consistently h igher than the other parts of the fruit ,  wh i lst 
t issues at t he  calyx end  reg ion  (posit i on 5) consistent ly h ad low e r 02 
concentrations than the other parts of the fruit . For example, the mean  02 
concentrations at the equator of Braeburn and G ranny Smith apples after 4 
weeks storage at O°C and 3 days at 200e were, approximately 1 2 .3 and 1 6. 5% 
respectively  as against 8.6 and 1 1 .7% in  the t issues nearest the calyx  end 
region (position 5) .  After 8 weeks of cold storage and 1 7  days at ambient 
temperature,  the difference between the mean 02 concentration at the equator 
and position 5 was approximately 4.4% in Braeburn and 3.0% in Granny  Smith 
apples. 
There was a trend of h igh 02 concentrations at position 1 (stem end 
shou lder) ,  more at posit ion 3 (equator) and less at position 5 (ca lyx e nd 
shoulder). General ly, 02 concentrations at the five positions i n  both cu ltivars 
decreased during  the period of storage at 20°C, however the magn itude of 
decrease differed between the two cultivars. 
Core cavity 02 concentrations sampled on the 1 7th day at 200e d i ffered 
between cultivar and time of storage (P < 0.01 ; fig . 8-22) .  G ranny  Sm ith  
apples were found to contain higher 02 in the core cavity than Braeburn and 
the  concentration in the former decl i ned markedly (P < 0.05) with incre asi ng 
time of cold storage and subsequent storage at 20°C for 1 7  days. 
20 
1 6  
1 2  
8 
4 
- _  ... ...... 
_ _ _  -1 - - ...... ...... ... . . . . . . . . . ' " 
- i-
J.:----t-...  - . . . . . . . . . . .... .... 
- - 3 days al wOe 
. • . . .  10 days at 200e 
- 17 days at 20°C 
" . .... " . ..... ' . 0. 
(a) 
o � ________________________________ � 
,.-., 
20 
1 6  
1 2  
� 8 -­
V) 
§ 4 .-... 
(b) 
r - - - -1 - - - - ... ..... ..... 
� 0 c �--------------------------------� 
8 20 
c 
o 
C) 1 6  N 
o 
12  
8 
4 
(c) 
o r-��r-�-4--'--;--'--;--'--;--'-� 
20 
1 6  
1 2  
8 
4 
(d) 
o ������ __ �� __ �� __ �� __ �� 
1 2 3 4 5 
Position on fruit surface 
262 
Fig . 8-20. Distribution of O2 concentrations at five positions in 
the sub-epidennis of Braebum apples stored (for (a)=O, (b)=4,  
o 0 (c)=8, (d)= 12  weeks)  at 0 C and subsequent transfer to 20 C (for 
3 ,  10  and 17  days). Vertical bars represent standard error of the 
means. 
20 
1 6  
1 2  
8 
4 
0 
20 
1 6  
1 2  
-. 
� 8 
'-" 
V) 
t:: 4 0 
.... 
... � 
0 .... ... 
t:: 
8 20 t:: 0 u 1 6  N 0 
1 2  
8 
4 
0 
20 
1 6  
12  
8 
4 
0 
t- - -;:1- - - - t -
. .. ..  :-: . . . . . . . � . . . . . . . . . . . . . . . . �.". . ..
. 't.� -... . . . . . .  :.::1 
- - 3 days at UlC 
. . . . .  10 days at 20°C 
- 17 days at 20°C 
� - - - -f- - - - +  _ _ 
- - + -.... - - - � - - -
-
-
--.. 
.
, . . · · · · · · · · ·4· · · . - - - .... t ·· · · · · · · · ·  
� 
" 
. . .
. . . . . . .
.
.
. , 
t- - - - -4 - - - - + - - _ _  
, . . . . . . . . . . . . . . . . . . .. ". ..... .:- - -t 
...... 
1 2 3 4 5 
Position on fruit surface 
263 
(a) 
(b) 
(c) 
(d) 
Fig. 8-2 1 .  Distribution of O2 concentrations at five positions in 
the sub-epidermis of Granny Smith apples stored (for (a)=O, 
° (b)=4, (c)=8, (d)= 1 2  weeks) at 0 C and subsequent transfer to 
20°C (for 3, 10 and 17 days). Vertical bars represent standard 
error of the means . 
24 �----�----�------�----�----�------�� 
� 20 
'-' 
Cl'.) c: o ·c 16  e .... 
c: 
Cl) C) 
§ 12  C) 
C"l 
o 
� .... . > 8 
� C) 
� o U 4 
o 
11 Braebum 
El1 Granny Smith 
264 
Fig. 8-22. Core cavity O2 concentrations of Braebum and Granny 
Smith apples stored at OOC for 0, 4, 8 and 1 2  weeks and subsequent 
storage at 20°C for 17 days. Vertical bars represent standard error of 
the means . 
265 
8.4.2.3.2 C02 concentrations 
During the period of storage at O°C and subsequent storage at 20°C.  
C02 concentrations at the five positions in  the sub-epidermis were found to be 
higher in Braebum (fig. 8-23) than in Granny Smith apples (fig .  8-24) .  Tissues 
at the calyx end region consistently contained higher C02 concentrations than 
the other parts of the fruit. Whi lst the equatorial  reg ion beneath the skin 
surface had lower C02 concentrations than any other parts of the fruit. After 8 
weeks of cold storage and 1 7  days at 20°C. the C02 concentrations at the 
calyx end shou lder (position 5) of Braebum and Granny Smith apples were 
about a th ird higher than the equator. Carbon dioxide concentrations showed 
a trend of decrease from position 1 towards positions 2 and 3 and an increase 
towards positions 4 and 5. The magnitude of increase was higher in Braeburn 
than in  G ranny Smith  apples. Carbon d ioxide concent rat ions at t he  five 
positions were found to increase with time of storage at 20°C. 
Braeburn contained higher C02 concentrations in the core cavity than in 
Granny Smith apples (fig.  8-25) and concentrations increased with peri od of 
storage at O°C and subsequent storage at 20°C for 1 7  days. 
8.4.2.3.3 C2H4 concentrations 
After storage at O°C and subsequent storage at 20°C Braeburn (fig.  8-
26) had h igher  mean C2H4 concentrat ions at the five d iffe rent pos itions 
compared to Granny Smith app les (fi g .  8-27) .  Tissues at the  ca lyx e nd 
shoulder contained h igher C2H4 concentrations than any other parts of  the 
fruit. For example, after 1 2 weeks of cold storage and 1 7  days at 20°C. C2H4 
concentrations at the calyx end shoulder of Braeburn and Granny Smith apples 
were nearly two thi rds and one fifth (respectively) h igher than at the equator. 
1 5  r-
1 2  f-
9 f-
6 r 
3 r 
0 r 
15  t-
12  r-
9 r-
,,-... 
� 
6 '-" V,) f-c: 0 3 .... 
..... 
r-
e 
..... 0 c: � f-u 15  t: f-0 U 
N 12  0 r U 9 r 
6 f-
3 r-
0 I-
15  f-
12  r-
9 r-
6 f-
3 f-
0 f-
- - 3 days at wOe 
.
.. .
. . 
-
10 days at 200e 
17 days at 200e 
� ... " ... � lz· · · · ·  . . · · ·;4;.£· ... · _·-I· _· ... · :.:.·:..;. ._ -
.. ca .. LE .... ca = ca _ • cs Lt cc t:: ... . . . .  q 
F - �" "'.:..:
.
!!j 9- - .. · · · ·r· · ·;;·
;; ·;.. - -
I I 
- - .,.,. 
. 
I I I 
oF ,,� I ... . . . � .
.
. . .
.
.
. . . . . t . . . . . . . ;! - - - -� - - -
-
- - - - -
I I I I I 
1 2 3 4 5 
Position on fruit surface 
266 
-
<a) 
-
-
-
-
-
-
<b) 
-
-
-
-
-
-
(c) 
-
-
-
-
-
-
(d) 
-
-
-
-
-
Fig. 8-23 . Distribution of CO2 concentrations at five positions in 
the sub-epidennis of Braebum apples stored (for (a)=O, (b )=4, 
(c)=8, (d)= 1 2  weeks) at OOC and subsequent transfer to 20°C (for 
3 ,  10  and 1 7  days). Vertical bars represent standard error of the 
means. 
15  
12  
9 
6 
- - 3 days at 'lite 
. . . . .  10 days at 200e 
- 17 days at 200e 
-
3 - . . . . . . . . . . . ""· ... · ... · ... · ...... · ... · :..o ·�·t· · · ·�· :·: -... ... 
(a) 
o � ________________________________ � 
-. 
15  
12  
9 
� 
-- 6 � 
c .g 3 
e 
(b) 
c 0 V �------------------------� g 15  
o 
� 12  
o 
u 9 
6 
3 
o 
15  
12  
9 
6 
3 
o 
(c) 
..... .... . ... ... ... 0.:... t�ZI - - - -" ' 
r--r--�-r--r--r--��--T-�--;-�--� 
I:!' co. _- _ ...... __ 
1 2 
.= • 
3 
..,. 
4 
Position on fruit surface 
(d) 
. _
.::1 
5 
267 
Fig. 8-24. Distribution of CO2 concentrations at five positions in 
the sub-epidennis of Granny Smith apples stored (for a=O, b=4, 
o 0 c=8 , d= 12 weeks) at 0 C and subsequent transfer to 20 C .  (for 3 ,  
10  and 1 7  days) . Vertical bars represent standard error of  the 
means . 
268 
1 5  �----�----�------�--��----�------�--, 
III Braebum 
-. 
� 1 2  EJ Granny Smith 
c;I'.) 
§ .... .... 
e ... 
� 9 () 
§ 
() 
� 
o 
u 6 
>. .... .... 
> 
� 
() 
� 3 
u 
o 
Fig. 8-25 . Core cavity CO2 concentrations of Braebum and Granny 
Smith apples stored at O°C for 0, 4, 8 and 12  weeks and subsequent 
storage at 20°C for 1 7  days. Vertical bars represent standard error of 
the means. 
1600 
1200 
800 
400 
1600 
-.. 1200 -I -
-
::t "-" 
Cl:) 800 c 0 . -..... � 1-0 400 ..... c � u c 1600 0 u 
:C 
N 1200 u 
800 
400 
1600 
1200 
800 
400 
- - 3 days at wOe 
• • • • . 10 days at 200e 
- 17 days at 200e 
I I I� 
� 
.
. . . . . . . . . 
�' 
. . . . . . . . . . . t" 
.
.
. . . .
. . . . 
�
.
t-
-
- - -1 - - -
- - - - - - -
-1 f- - - - -1  f- - - - - - - - t - - - -
t- - -
-1 
1- - - - -1 - - - - t - - - - -
. 
. 
_ - - I . .
. . . 
., 1 -
1 2 3 4 5 
Position on fruit surface 
269 
(a) 
(b) 
(c) 
(d) 
Fig .  8-26. Distribution of C2H4 concentrations at five positions 
in the sub-epidennis of Braebum apples stored (for (a)=O, (b)=4, 
o 0 (c)=8, (d)=12  weeks) at 0 C and subsequent transfer to 20 C (for 
3, 10  and 17 days). Vertical bars represent standard error of the 
means.  
1600 -
1200 I-
800 I-
400 I-
1600 f-
-;- 1200 f-
-
-
::t ........-
v:l 800 = I-0 .-.... t':j 
b 400 = I-� u = 1600 0 f-u 
� 
::r:: 
N 1200 u I-
800 I-
400 ,.. 
1600 I-
1200 I-
800 l-
400 I-
- - 3 days at 'lIte 
. . � . .  
-
10 days at 200e 
17 days at 200e 
-f I . . . .. . . . . . . . . . . . ... ;.:. . . . . . . . . . . ... . . . . . . . . . . . . .. . . . . . . .  :,: .:,: � - - - � - - - -1- - - _ + - -
-f 
i I �  . . . . . . . . . . . -t 
t · · · ·  . . . . . . of • • • • - -i � . . . . . . . . . . . . . . ., . . . t- - -- - - --1 - _  
_
-
-- - of -
I I I I I 
t· · · ·  _I 
i- - -i- � 
. , . . . . . . . . . . .  � 
_ _ _ � _ _ .�. - r - - -
I 
1 
- -
I 
2 
I I 
3 4 
Position on fruit surface 
I 
5 
270 
-
(a) . 
-
-
-
-
(b) 
-
-
-
-
(c) 
-
-
-
-
(d) 
-
-
-
Fig. 8-27. Distribution of C2H4 concentrations at five positions 
in the sub-epidermis of Granny Smith apples stored (for (a)=O, 
o (b)=4, (c)=8, (d)= 12 weeks) at 0 C and subsequent transfer to 
20°C (for 3 ,  10 and 17  days), Vertical bars represent standard 
error of the means. 
271 
After the 3rd and 1 0th day at 200e (fig. 8-27a) C2H4 was not detected i n  any 
of the different positions on Granny Smith apples, however, by the 1 7th  day, 
2.5J.l1 1-1 C2H4 was measured at position 5 compared to 0.38, 0.23, 0 . 1 2 and 
0.48J.l1 r 1 respectively at positions 1 ,  2, 3 and 4. After a period of sto rage at 
ooe and at 20oe, C2H4 concentrations increased (over time at 200e) , with the 
highest concentrations measured at position 5 .  Ethylene concentrations at the 
various positions in the sub-epidermis in both  cultivars increased during the 
period of storage at 20oe. 
The mean C2H4 concentrations in the core cavity during the period of 
storage at ooe and at 20°C were consistent ly h igher i n  Braeburn t han i n  
Granny Smith apples (fig.  8-28). In  Braeburn apples there were no sign ificant 
differences in core cavity C2H4 concentrations over the period of storage at 
ooe and subsequent transfer to 20°C for 1 7  days. In contrast in Granny  Smith 
apples C2H4 concentrations increased after 0 weeks at ooe and subsequent 
t ransfer t o  20°C fo r 1 7  days and thereafte r t he re we re no  s i g n if icant  
differences in e2H4 concentrations. 
8.4.2.4 Quality indices 
During the period of storage for 0, 4, 8 and 1 2 at ooe and subsequent 
storage at 20°C for 1 7  days, Braeburn apples were found to be firmer (P < 
0.05) than Granny Smith apples. Fruit softeni ng increased with increasing  time 
of storage (fig .  8-29) . 
There were no significant (P < 0.05) effects of duration of storage on the 
soluble solids content of both cultivars (fig .  8-30) . 
As expected, Granny Smith were greener than Braeburn apples (fig . 8-
3 1 ) .  I n  either cu ltivar, background colour as indicated by hue angle values 
were similar over the storage period. 
--
3 1200 
'c o .... 
� t: 900 (1) (,) 
§ 
(,) 
'V 
� 600 u 
>... ..... .... 
> 
� 
� 300 
o u 
o 
272 
III Braebum 
El Granny Smith 
Fig. 8-28. Core cavity C2H4 concentrations of Braebum and Granny 
Smith apples stored at OOC for 0, 4, 8 and 12  weeks and subsequent 
storage at 20°C for 17 days. Vertical bars represent standard error of 
the means. 
273 
100�----�----�----�----�------�----�-, 
I!!IIII Braebum 
EJ Granny Smith 
80 
40 
20 
Fig .  8-29. Finnness of Braebum and Granny Smith apples stored at 
o 0 o C for 0, 4, 8 and 12 weeks and subsequent storage at 20 C for 1 7  
days. Vertical bars indicate standard error of the means.  
--
� -­
.... 
274 
1 8��-
-�----�----�------�----�----�--� 
II!!I Braebum 
1 5  
EJ Granny Smith 
.§ 1 2  c:: o U 
ell 
"0 .-
"0 9 ell 
a) ..-
oD 
::l ..-
r55 6 
3 
Fig. 8-30. Soluble solids content of B raebum and Granny Smith 
D apples stored at 0 C for 0, 4, 8 and 12  weeks and subsequent storage 
at 20De for 17 days. Vertical bars indicate standard error the of 
means.  
275 
160�----�----�----�----�----��----�-. 
IIlII Braebum 
140 EIl Granny Smith 
120 
80 
60 
40 
Fig . 8-3 1 .  Hue angle of Braebum and Granny Smith apples stored at 
o 0 o C for 0, 4, 8 and 12  weeks and subsequent storage at 20 C for 1 7  
days . Vertical bars indicate standard error of the means. 
276 
8.5 DISCUSSION 
Steady state mean 02 and C02 concentration differences between  the 
equator and calyx end of Gala, Braeburn ,  Royal Gala, Red Delicious ,  and 
Cox's Orange Pippin apples were high considering that the average [02]i and 
[C02]i in a freshly harvested fruit at ambient temperature and 02 condit ion is 
about 1 6-1 8% and 1 -2% respectively. Under MA conditions these differences 
would be expected to be reduced owing to the depressed respi ratory activity of 
the fruit but it appears as though they could sti l l be very significant. One may 
argue  that coveri ng  the calyx end  may be t he  cause for the  h i g h g as 
concentration differences estimated, since it may be an important route to gas 
exchange. However data presented in fig. 8-6 in which the calyx end was not 
covered, showed simi lar but s l ightly smal ler  gas concentrat ion diffe rences 
between the equator and calyx end shoulder for Gala, Royal Gala, B raeburn ,  
Red Del icious, and Cox's Orange Pippin apples. Fruit without vials over the 
calyx end had higher [02] i and lower [C02]i compared to those with vials over 
the calyx end. This suggests that the calyx end may be an important route to 
gas exchange  in apples.  Th is fi nd ing is consistent with those of othe r  
researchers i ncluding Cameran ( 1 982) ,  Cameran and Re�'(1 982) ,  MaI'cell in 
��� � . 
(1 974) ,11. Markley and Sando (1 �;3 1 a,. 
b) who showed that the calyx open ing  of 
apples contribute to gas exchange. For instance, Cameron  ( 1 982) o bserved 
that in Golden Delicious apples, the calyx end provided for the diffusion of 42% 
of the C2H4' 24% of the C02, and only 2% of the water. 
Gas concentration diffe rences between the equator and calyx end or 
between the equator and calyx end shoulder were much greater than those 
which have hitherto been measu red between the core cavity and t h e  fruit 
surface of other cultivars (Rajapakse et al. 1 9�9, 1 990).. Anatomical studies of 
Golden Delicious apples by Soudain and Phan Phuc ( 1 979) have shown that 
"r 
i ntercellular spaces are greatest at the equator than the other parts of the  fruit 
hence easier gas diffusion through the tissues at the equator and consequently 
smaller gas concentration difference. 
Smal l  but s ign ificant 02 and C02 concentrat ion d i fferences were 
observed between the equator and core cavity of Braeburn and Cox's Orange 
P ipp in  apples and none in the other  cu ltivars .  These d iffe rences in gas 
concentration between apple cultivars could be associated with differences in 
i ntercel lu lar space volume as wel l  as d ifferences in skin resistance and fruit 
resp i ration rate . These fi ndings are i n  ag reement with t hose publ ished by 
Rajapakse et al. ( 1 990). 
�./ 
Steady state mean C02 concentration differences estimated in al l  e ight 
apple cultivars were lower than those for 02' This cou ld also be due partly to 
different pathways of diffusion of these gases Le, unl ike 02 (which is thought 
to move v ia the lenticels) C02 may a lso diffuse th rough  the cut ic le and 
epidermis of the fruit (Banks, � 984b ;  Burton, 1 974) .  The presence of these 
concentration  differences confirms the existence of resistance to 02 and C02 
transfer through the flesh of the commodity. The data further show that the 
f lesh of the apple fruit is more permeable to C02 than to 02, despite the fact 
that the diffusivity of 02 in air (0. 1 78 cm2 . s- 1 at O°C) is h igher than that of 
C02 (0. 1 38 cm2 . s- 1  at O°C) (Burg and Burg, 1 965). 
v 
The foregoing results clearly demonstrate that there are significant gas 
concentration differences between apple cultivars and the magnitude of these 
differences are cultivar dependent. This could have important implications for 
modified atmosphere storage of cultivars with relatively large flesh resistance 
at ambient temperatures. In determin ing the critical external 02 levels i n  
CA/MA storage of apples, the gas concentration difference (gradient) between 
the fruit surface or the calyx end and centre should be taken i nto consideration 
to avoid development of certain physiological disorders. ' At a low external 02 
concentration i n  CA/MA storage, tissues at the fruit centre would experience 
278 
lower 02 concentrations than the surface and would therefore be l ikely to have 
lower rates of respiration and ripening. It would be i nterest ing if further work 
could include investigation of MA effects on the size of these gradients. 
Gas concentrat ions i ns ide t he  app le f ru i t  have previo us l y  been 
considered to  be is  practical ly homogeneous (Andrich et al. , 1 989,(1 991 ; 
Cameron,  1 982 ; Hardy',�t949) . The cu rrent study has demonstrated that the 
� 
i nternal atmosphere composition of apples varied substantially from one part of 
the fruit to another. After  sto rage at O°C for 0 ,  4 , 8 and 1 2 weeks and 
subsequent storage at 20°C for 3, 1 0  and 1 7  days tissues nearer the calyx end 
region of Braeburn and Granny Smith apples consistently had lower 02 and 
h igher C02 and C2H4 concentrations than the other parts of the fruit, while 
those at the equator had higher 02 and lower CO2 and C2H4 concentrations 
than any other positions on  the fruit surface. This may be related to localised 
variation in i ntercel lular space volume. As previously mentioned, studies have 
shown that i ntercel lular space volume at the equatorial reg ion was higher  than 
the other parts of the apple fruit (Soudain and. Phan P h uc, 1 979) .  H igh  
porosity would therefore, be expected to  facil itate gas diffusion.  
The 02 concentrations measured at the calyx end region at 20°C u nder 
normal ambient 02 condition were low in these cu ltivars, thus u nder l ow-02 
atmospheres it would be expected that the 02 concentrations at this region 
would be extremely low or in  some case tissues at the calyx end may even 
experience anaerobic conditions and this cou ld trigger the development of 
certain physiological disorders such as browning, decay, or necrotic lesions in 
th is region of the fru it .  I n  a st�'di!� by Nichols ano-''Patterson ( 1 987)  they 
v 
reported that after 8 weeks of storage of Del icious apples in  0% 02 ' external 
symptoms of anaerobic i njury (ie. sunken, brown, necrotic areas) were seen 
especially at the calyx end of fruit. Although the localisation of the symptoms 
at the calyx end of the fruit could be due to a number of factors (such as fungal 
, ' . , '. , . 
't"  r I : I = . 
. ..... , 
279 
infection) , the findi ngs of this study i ndicate that the disorder could partly be 
associated with the low 02 and/or high C02 concentrations at the calyx end of 
• 
. ... .. .. . 
the fruit. 
.. .. t ........... -::, ."" . . . .  .., .--: --., • 
Braebu rn cons istent ly had h ighe r C02 and C2H4. and I O";;�
�-
, 
concentrations at the different positions beneath the ski n surface compared to \ 
Granny Smith apples. Anatomical differences such as differences i n  size of I 
intercel lular spaces ;  size, number and distribution of functional lenticels on  the 
fruit  surface ; thickness and nature of wax deposits of the cuticle as well as 
differences in R and fruit respi ration rate (refer to chapter 4 for details on  this 
subject) may have contributed to these di fferences in gas concentration 
between the two cultivars. Decl ine i n  fru it porosity that occurs with ripen ing 
and senescence could also affect the size of the gas concentratio n  (at the 
different positions) .  For  instance , low porosity would i ncrease the i nte rnal 
res istance to gas d i ffus ion and t he refo re i ncrease t he  g radient i n  gas 
concentration between the centre and outside of the fruit . 
Braeburn apples were firmer and had less colour change during storage 
at O°C and subsequent storage at 20°C than in Granny Smith apples.  As 
previously reported in chapter 4, the fi rmness of Braeburn could be related to 
their low intercel lular space volume (approximately 1 4. 1  %). The soluble solids 
contents of Braeburn and Granny Smith were similar. 
I n  concl us ion ,  MA treatments exe rt the i r  effects on fruit physiology 
through modification of the fruit's internal atmosphere composition . Fol lowing 
the work of Burg and BUrQ' ( 1 965) , fru it internal atmosphere composition has 
been treated as being essentially homogeneous. However, the current study 
provides f i rm evidence that the i nternal atmosphe re composit ion of apples 
varies substantially from one part of the fruit to another and this has important 
impl ications for the way in which we attempt to mode l  the gas exchange of 
these fruits and the effects of CAlMAs on their physiology. The heterogeneous 
280 
d i st ri buti on of gases with in  i nd iv idual fruit wou ld p resumably affect the 
tendency of  i ndiv idual t issues to deve lop low-02 or  h igh C02 disorders, 
particularly for fruit stored in MAs at elevated temperatures. This study further 
indicates that development of gas concentration difference (gradients) may be 
related to anatomical features in addition to depth of tissues within the fruit. 
Fu rther work could be undertaken to establish the l i nk between anatomical 
variation and the varying tendency to develop large g radients in d i fferent 
cultivars. 
8.6 LITERATURE CITED 
Andrich, G. ,  Fiorentini ,  R., Tuci , A. and Galoppini , C. 1 989. Skin permeabil ity 
to oxygen in  apples stored in controlled atmosphere. J .  Amer. Soc. Hort. 
Sci. 1 44:770-775. 
Andrich, G. ,  Fiorenti n i ,  R. , Tuci , A. , Z innai, A. and Sommovigo, G. 1 991 . A 
tentative model to describe the respi ration of stored apples. J .  Amer. 
Soc. Hort. Sci . 1 1 6:478-481 . 
Anzueto , C.  R .  and Rizvi, S. S. H .  1 985. I ndividual packaging of apples for 
shelf l ife extension. J. Food Sci . 50 :897-904. 
Banks, N .  H .  1 984a. Internal atmosphere modificatio n i n  P ro-long coated 
apples. Acta Hort. 1 57:1 05-1 1 2 . 
Banks, N .  H .  1 984b .  Some effects of TAL PrO-long  coat ing o n  r i p en i ng 
bananas. J .  Expt. Bot. 35 : 1 27-1 37. 
Banks, N .  H. and Kays, S. J .  1 988. Measuring internal gases and lenticel 
resistance to gas diffusion in  potato tubers. J. Amer. Soc. Hort. Sci. 
1 1 3 :577-580. 
Ben-Yehoshua, S . ,  Robertson ,  R. N .  and Biale,  J. B. 1 963. Respirat ion and 
internal atmosphere of the avocado fruit. Plant Physiol .  28 : 1 94-20 1 . 
Burg,  S .  P .  and Burg,  E .  A.  1 965.  Gas exchange i n  fruits. Physiol . P lant. 
1 8 :870-884. 
Burton ,  W. G.  1 974. Some biophysical principles u nderly ing the control led 
atmosphere storage of plant material . Ann. Appl. Bioi . 78 : 1 49- 1 68.  
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Burton, W. G .  1 982. Post-harvest physiology of food crops. Longman, London. 
� �. / 
Cameron, A.  C. 1 982. Gas diffusion in bulky plant organs. Ph.D. dissertation, 
University of California, Davis. 1 1 7 pp. 
Cameron, A. C. and Reid, M.  S. 1 982. D iffusion resistance : importance and 
measu rements in contro l led atmosphere storage. I n :  Contro l led 
atmospheres  fo r sto rage  and tra nsport of perishable ag ricu ltu ral  
commodities. (D.G.  Richardson and M. Meheriuk. eds) . Oregon State 
University School of Agriculture, Symposium Series No. 1 ,  Timber Press, 
Beaverton, Oregon. pp. 1 71 -1 80. 
Duncan, D.  B. 1 955. Multiple range and multiple F test. Biometrics 1 1  : 1 -42. ..-/ 
Fidler, J .  C.  and North, C. J. 1 971 . The effect of conditions of storage on the 
respiration of apples. V. The relatio nship between temperature, rate of 
respirat ion and composition of the i nternal atmosphere of the fruit. J .  
Hort. Sci. 46 :229-235. 
Hardy, J. K. 1 949.  Diffusion of gases in fruit: The solubi l ity of carbon dioxide 
,/ 
and other constants for Cox's Orange Pippin apples. Rep. Food I nvest. v/ 
Bd. (1 949) : 1 05-1 09. 
Hulme, A. C. 1 951 . An apparatus for the measurement of gaseous conditions /. 
inside an apple fruit. J. Expt. Bot. 1 1 :2 1 65-21 85. 
Kade r, A.  A. ,  Zagory, D. and Kerbe l ,  E. L. 1 989.  Modif ied atmosphere 
packaging of fruits and vegetables. C ri .  Rev. Food Sei. Nutr. 28: 1 -30. 
Knee , M. 1 991 . Rapid measurement of diffusive resistance to gases in apple 
fruits. HortSci. 26:885-887. 
Litt le, T. M. 1 981 . I nterpretation and presentation of results. HortSci . 1 6 : 1 9-
22. 
Litt le,  T. M. and H i l ls, F. J .  1 978. Ag ricultural experimentation :  Design and 
analys is .  J o h n  Wi ley  and Sons,  New York, Ch ichester ,  B risbane ,  
Toronto. 350 pp. 
Marcel l i n ,  P. 1 974. Conditions physiques de la circu lation des gaz respiratoi res 
a t ravers la masses des fru its et maturation .  In Colloques i nternationaux 
CNRS, No 238. Facteurs et regulation de la maturation des fru its. pp. 
241 -251 . 
282 
Markley, K. S. and Sando, C. E .  1 931 a. P rogressive changes in  the wax-l ike 
coating of the surface of apple during g rowth and storage. J. Agric. Res. 
v/ 42:705-722. 
Markley, K. S. and Sando, C. E .  1 931  b. Permeabil ity ot the skin of apples as 
measured by evaporation loss. Plant Physiol. 6 :54 1 -547. ./ ,,/ 
Nichols, W.  C.  and Patterson, M .  E.  1 987. Ethanol accumulation and post 
storage qual ity of 'Del ic ious' apples du ring  short-term,  low-02 , CA v'" 
storage. HortSci . 22:89-92. 
Rajapakse , N .  C . ,  Banks, N .  H . ,  Hewett , E .  W.  and C le land,  D .  J .  1 989. 
Oxygen diffusion i n  apple fruit flesh . Proc. 5th I nt .  Cont.  Amt. Res. 
Cont . ,  June 1 4- 1 6, 1 989, Wenatchee, Washi ngton ,  U .S.A. pp. 1 3-2 1 .  
Rajapakse,  N .  C . ,  Banks, N .  H . ,  Hewett, E .  W. and C le land ,  D .  J .  1 990. 
Development of oxygen concentration g radients i n  flesh tissues ot bulky 
plant organs. J .  Amer. Soc. Hort. Sci. 1 1 5 :793-797. 
Solomos, T. 1 987. Pri nciples of gas exchange in bulky plant tissues. HortSci. 
22 :766-771 .  
Soudain ,  P .  and Phan Phuc, A. 1 979. La d iffusion des gaz dans les tissus 
.... ../ 
vegetaux e n  rappo rt avec la  struct u re d es o rg anes mass i fs .  I n  '" 
Perspectives nouvel les dans la conservation des fru its et legumes frais. 
Semi nai re I nte rnat ional o rgan ise par le Centre d e  Recherches  en 
Sciences Appliquees a l 'Al imentation, Universite du Quebec, Montreal , 
1 4- 1 5 Apri l  1 978. pp. 67-86. 
Steel, R. G. D. and Torrie, J. H. 1 980. Principles and procedures of statistics, 
A biometrical approach. McGraw-HiI I Book Co., New York, NY, 2nd ed. 
633 pp. 
Trout, S. A, Hal l ,  E. G, Robertson, R. N, Hackney, F. M. V. and Sykes, S. M.  
1 942. Studies in the metabolism of apples. 1 .  Pre l iminary invest igations 
on inte rnal gas composition and its relation to changes in stored Granny 
Smith apples. Aust. J .  Expt. BioI. Med. Sci . 20 :2 1 0�23 1 . 
\ 
t 
283 
CHAPTER 9 
GENERAL DISCUSSION 
Postharvest deterioration of apples can be delayed by the use of low 02 
and/o r h i gh  C02 atmospheres  du ri ng CA/MA sto rage.  The low [02]ext 
depress the [02] i of apples which in t u rn l im it some of the phys io logical 
processes (such as respi ration ,  C2H4 production ,  loss of g reen colou r  and 
softening) leading to deterioration (Blanke, 1 991 ; Burton, 1 982; Kader, 1 986) .  
The physiological consequences of low 02 atmospheres are thought to  arise 
from the general depression of metabolism and, in particular, the reduction of 
fruit respiration. The success of CA or MA therefore is largely determi ned by 
the commodity's respiratory response to low 02 and/o r h igh C02 a nd the 
abi l ity of the produce to maintai n essential physiolog ical processes under 
these conditions without causing injuries to internal tissues. 
Most fru its and vegetables which are stored under CA/MAs are bulky 
t iss u es .  The  movement  of gases i n to t he  t i ssues from t h e  e xte rna l  
atmosphere, via the  surface pores, into the  internal atmosphere i n  the  organ 
i nvolves d iffusion in the gaseous phase. Th is i nternal atmosphere ,  which 
occupies from about 1 -2% of the internal volume in potato tubers and up  to 
30% in  some varieties of apples (Blanke , 1 991 ; Burton , 1 982 ; Kader  et al. , 
1 989) ,  forms an inter-connecting system throughout the organ . The efficacy of 
the i nternal atmosphere in aerating the tissues depends upon its volu me ,  its · 
continuity and the degree to wh ich it is fil l ed with gas or i njected with l iquid or 
cell sap (associated with over-ripeness). The internal atmosphere to wh ich the 
fruit tissues are di rectly exposed is effective in  bringing about the reduced rate 
of deteriorat ion seen in  CA/MA-stored produce. Consequently factors which 
affect inte rnal atmosphere composition are effective in regulating the rate of 
284 
deterioration and hence shelf-l ife of the fruit. However, most previous studies 
on fruit responses to CA/MA have related them to the composit i on  of the 
external , rather than the i nternal atmosphere (eg. see Knee, 1 980 in which 
rates of chlorophyll loss and softening are reported for d ifferent [021ext). In  
many cases, th is may in part be due to the lack of appreciation of just how 
substantial an effect the gradient between i nternal and external atmospheres 
can have i n  the  observed responses of t he fruit to a n  i mposed CA/MA. 
However, Knee ( 1 991 b) has recently considered in some detail the potential 
role of th is g radient i n  explain i ng the variabi l ity of i ndiv idual fruit to CA/MA 
reg imes and poi nted out that resolution of current u ncertainty ove r  [021 i i n  
apples might improve the efficiency of CA storage. It i s  t herefore perhaps the 
destructive nature of most methods of internal atmosphere sampling wh ich has 
prevented this approach from being adopted before. This, i n  combination  with 
the extra effort involved in internal , rather than external atmosphere mon itoring 
may explain the absence of th is type of study from existin g  l iterature. 
In  this study, a combination of a non-invasive technique for mon itoring 
internal atmospheres and the use of fruit immersion ( in  water) i n  p reventing 
contami nat ion of d i rect removal samples h���e enabled facto rs affect i ng  
internal atmospheres, and fruit responses to internal atmosphere modification,  
to be studied in some detai l .  This thesis has focused on [02]i (and [C021i and 
[C2H4] i ) by studying the relationship between internal atmosphere composition 
of apples and factors such as respiration, [021ext, R, temperature and artificial 
barriers .  In the preceding chapters these relati onships have been examined 
and it is clear that these factors do influence the atmosphere inside the apple 
and hence have the potential to affect important aspects of quality such as 
rates of softening and loss of g reen colour. 
The interactions of these variables in the final res-ponse of the fruit to a 
g iven t reatment are quite complex. Fig .  9-1  d raws together  the i nd ividual 
relationships identified in this thesis in a schematic model ,  which demonstrates 
F =  
285 
L\[021 = F * (R/A) 
F i g .  9-1 . Sche matic model i l l u strati ng the relation s h i ps 
between [02]ext' [02], F or resp i ration rate , � [02] and R.  
(RI A )  rep resent sum of a l l  resistances/su rface a re a  
between i nte rnal a n d  external atmosphere .  
286 
the mutual interdependence of each of these variables. The model i l lustrates 
the  sequence of causal i ty i nvolved i n  the  system ,  based on a cycle of 
interactions between some of the key variables. At any given steady state, the 
rate at which 02 is being consumed by respi ration is the same as the rate at 
wh ich 02 is d iffus i ng into  the fruit (F) ;  i ndeed, t h i s  is the way i n  wh ich 
respi rati o n  is measu red on who le  fru i t .  Combi ned with the fru it 's sk in  
resistance to gas diffusion (R)  and surface area (A) ie .  (R/A) , this inward flux 
results in  the presence of a certain 02 concentration g radient (�[02] )  ie. 
F *  (R/A) [9. 1  ] 
For this particular �[02] and the fruit's external atmosphere (ie. [02]ext) ,  this 
results in a certain internal 02 concentration ([02] i) ' ie.  
= [9 .2] 
The [02] i itself affects respi rato ry 02 uptake (equ ivalent ,  at steady 
state, to F), and can therefore be seen to be both cause and an effect i n  this 
system. The model makes the simpl ifying assumption that changes to any of 
the key variables are very gradual, so that at any g iven time,  respi ratory 02 
uptake can be treated as being equal to F. 
F is affected by a number of other factors, including temperatu re and 
stage of fruit development. Both of these operate through affecting the level of 
maximum flux  or maximum respiration rate (Fmax) :  as temperatu re increases 
or the climacteric develops, so Fmax becomes greater. The rate of respi ration 
287 
itself is thus dependent on maturity at harvest and time and temperature since 
harvest. If Fmax is increased, for example by i ncreasing temperature , this 
would increase F: 
F = 
and thereby decrease [021i = 
= [02]ext - (F* R/A) 
[5.2] 
[9.3] 
Let us now examine the effects of increasing R, as occurs throug h  the 
development of greasiness or application of a coating for a fruit which remains 
in air th roughout. This increases �[02] which therefore decreases [02]i a nd F. 
The decreased F resu lts i n  a reduct ion i n  �[02] ,  so t hat [02] i i ncreases 
slightly. However after a few cycles through the system, a new steady state is 
reached in  which the fruit with elevated R has a lower [02] i and respiratio n  rate 
than before R was i ncreased. 
If [02]ext is gradually reduced over time, [02]i is reduced as a resu lt of 
the difference between [02]ext and �[02] (equation 9.2). Fol lowing around the 
cycle i n  F i g .  9- 1 , t h is reduced [02] i depresses resp i rat ion  rate (F)  and 
therefore �[02] '  As [02]ext is reduced to its final level, the fruit develops a 
new steady state [02]i , respiration rate and L\[02] ,  all of which are lower than 
the orig inal values for the fru it in ai r. 
Specif ic aspects of the model i l l ustrat ing the re l at ionsh ip  between 
[02]ext and [02] i , respiration (ie. rate of 02 uptake and C02 production )  and 
288 
C2H4 concentration as well as the effects of coating or  washing treatment on 
gas exchange cha racte r ist ics of  app les a re d iscussed i n  deta i l  i n  the  
subsequent pages. 
9.1 Relationship between [021ext and [021i, respiration and C2H4 
9.1 .1 Relationship between [021ext and [02]i 
Oxygen concentrations between 1 and 5% have generally been used i n  
CA storage of apples (Meheriuk, 1990 ; Knee, 1 99 1 b) .  These lowered [02]ext 
depress [02] i as has been outl ined above. Characterisation of the relatio nship 
between [02]ext and [02]i of intact apples under different 02 atmospheres has 
to date only been attempted with l imited success (Brandle, 1 968) presumably 
because of the d i ff icu lt ies (as out l i ned above ; see a lso Knee , 1 973)  i n  
obtaining i nternal gas samples from fruit. In a review article published by Knee 
(1 991  b),  he indicated that, Pekmezci ( 1 971 ) used an 02 micro-elect rode to 
measu re cel l -sap 02 concent rat ions i n  fru it as the level  in  the i r  e xternal 
environment was reduced : when the data presented as partial pressu res i n  
mm Hg were recalculated in  kPa they often exceeded the  partial pressures 
external to the fruit. The source of this discrepancy may partly be due to the 
fact that the internal atmosphere of the fruit may not have equi l ibrated with the 
exte rnal atmosphere at the t ime of sampl ing .  Knee ( 1 973) i nd icated that 
analysis of gas extracted from apples under vacuum gave 02 levels very close 
to those of the su rrounding atmosphere, so that un less there was a la rge or  
significant .1[°2] .  the [02] i were in error. 
The techn iques used i n  this study resu lted i n  re l iable est imates of 
internal gas samples being obtained from individual apple fruit under d i fferent 
02 concentrations. Fruit were left for several times the period requi red for 
physical equi l ibration with the ir new atmosphere before samples were taken.  
These were carefu l ly  protected from atmospheric contaminat ion by water 
289 
barrie rs at every conceivable problem pOint. A combination of Fick's law of 
d iffusion and the Michael is-Menten equation (equation [5.4] )  deve loped to 
describe [02]i as a function of [02]ext indicated that at high [021ext, [021i of 
Cox's Orange Pippin and Granny Smith apples declined l inearly in response to 
decreasing [02]ext (fig.  5-2). This would be expected if respi ration (and hence 
.1[02]) was not sig nificantly affected over this range of 02 concentrations: as 
.1[02] remained constant ,  [02] i shou ld decrease by the same amount as 
[02]ext. However, as [021ext became progressively more l imiting there was a 
deviation from l i nearity which reflected the decreased .1[02] caused by the 
lowe red rate of 02 uptake by the fru it . The magnitude of deviat ion f rom  
l inearity and .1[02] was cultivar dependent. For instance, at 2% [021ext the 
fitted l ine i ndicated that .1[02] fo r Cox's Orange Pippin and G ranny Smith  
apples was 1 .6 and 1 .0% respectively. The difference cou ld be  rel ated to 
differences in  respi ration rate (h igher in  Cox's Orange Pippin than in G ranny 
Smith apples). The high respi ration rate in Cox's Orange Pippin would result in 
greater uti l isation of 02 and hence higher .1[02] than in Granny Smith apples. 
This appears to have been more important than the difference in  R values 
(only 1 0%) between the two cultivars which would have had the opposite effect 
on .1[02] '  
With the exception of the fruit of Braeburn apples which had respi ration 
rates in the range of about 8 .5  and 1 1 . 5 cm3 C02 kg- 1  h - 1  and RC2H6 
ranging from 1 5,000 and 45,000 s cm- 1 , most of the fruit of the other cultivars 
(put together) had respiration rates within the range of about 7 .5  and 20 cm3 
C02 kg- 1  h- 1  and RC2H6 between approximately 3,000 and 1 2 ,000 s cm-1 
(fig .  4-7). It is clear that there was a wide range of values for both of these 
variables within each apple cultivar used in this study. Similarly, Knee ( 1 99 1  b) 
reported data from a survey on Cox apples from d ifferent o rchards, that al l  
possible combi nations of h i gh  and l ow respi rati on a-nd h igh  and low skin 
resistance occurred. This variabil ity gave rise to nearly a threefold variat ion i n  
calculated [02] i values for the fruit in h is study. The multiple effects o f  these 
290 
g as exchange variables on i nternal atmosphere composit ion (especial ly on 
[0.2]i) could be partly responsible for differences in the response of different 
cu ltivars of apples to CA/MA storage (Knee , 1 991  b) .  Variation i n  the gas 
exchange variables within and between apple cultivars implies that the re wil l  
not be a single critical 02 level even for a single variety of apple. For  instance, 
Braeburn had three-fold higher R and only about 1 0% lower respiratio n  rates 
than Royal Gala apples, so that when these two cultivars are sto red under 
s im i lar 02 atmospheres such as 2%, it would be expected that Braeburn 
apples would have higher 6[02] and lower [02] i and hence greater probabil ity 
of fruit becoming anaerobic compared to the other cultivar. 
I n  v iew of the variation i n  the gas exchange variables betwee n  and 
within cultivars, atmospheres recommended for commercial use are generally 
designed to avoid hypoxic or anoxic conditions and harmful levels of C02 in 
the centre of fruit. These are typical ly between 1 -3% 02 and <1 -3% C02 for 
fruit stored at low temperatures (O-SOC; Meheriuk, 1 990) .  Recommended 02 
leve ls  have become  lower and lower  as t he  tech no logy  for contro l l i ng  
atmosp he ri c  compos i t ion  and  our  u nderstand i n g  o f  f ru it to l e ra n ce to  
atmospheric modification have improved. Further improvements in  s lowing 
dete r io rat i on  th rough  CA may depend  upon  ide nt i f i cat io n  of o pt imum  
atmosphere composition o n  a batch by batch basis. This would have to  take 
i nto accou nt the gas exchange variables d iscussed above. Clearly ,  any 
commercia l ly  viable system would also be subject to other ,  ope rat iona l  
constraints i nvolved in  the loading of store loads of  fru it. 
9.1 .2 Relationship between respiration and 02 concentration 
9.1 .2.1 Rate of 02 uptake 
Respi ration rate (or rate of 02 uptake) of apples and i ndeed several 
plant o rgans is lowe r  in low 02 atmospheres than in air  (Fidler and North ,  
1 967) and is  stimulated by 02 concentrations greater than that in ai r (Mapson 
291 
and Burton, 1 962; Theologis and Laties, 1 978, 1 982 ; Tucker and Laties, 1 985). 
The rel ationsh ip  between respi ration and [02]ext has been documented 
(Andrich et al. , 1 99 1 ; Cameron ,  1 985 ;  Solomos, 1 985, 1 988 ; Tucker and 
Laties, 1 985) but characterisation of the relationship with [02]i in  intact fruit has 
only been attempted indi rectly through mathematical models (And rich et al. , 
1 989 , 1 99 1  ; Banks et al. , 1 989 ; Cameron et al. , 1 989 ; Chevi l lotte , 1 973 ; 
Solomos, 1 985, 1 988 ; Tucker and Laties, 1 985) presumably because of the 
difficulties involved with concurrent monitoring of [02]i and respi ration rate in  
d iffe rent [02]ext. The techniques used in th is  study to overcome t hese 
difficulties (as outlined above) enabled the  relationship between rate of 02 
uptake ( ie. Re102) and [02] i o r  [02]ext to be characterised . This i nv olved 
studyi ng  the variat ion in the magnitude of 02 concent rat ion d iffe rences 
between the internal and external atmospheres (�[02] )  of  i ndividual a pples 
maintained i n  different 02 atmospheres. The relationship was hyperbolic and 
appeared to conform at least approximately to the Michaelis-Menten kinetics 
(figs. 5-3 and 5-4). A small change in  02 concentration (ie. [02]i o r  [02]ext) at 
low concentration therefore has a g reater effect on Rel02 than the same 
change at h i ghe r  concentrat ions.  Reductions in  the rate of dete rio ration 
associated with depressed respi rat ion would therefore be expected to be 
proportionally much greater as [02]i is  depressed further and further, as the 
depression in respiration rate per unit [02]i decrease is much g reater at l ow 02 
levels. 
It is ,  however, not clear whether  the gaseous envi ronment affects 
respi ration di rectly or whether it inhibits other metabolic processes or enzymes 
whose energy demands affect respi ratory rates. Various suggestions have 
been put forward by a number of investigators. For instance , Forward ( 1 965) 
suggested th ree alternative scenarios. In one, respi ratory 02 uptake was 
thought to be entirely catalysed by cytoch rome oxidase , but diffusion of 02 
through bulky plant tissues was slow, and the actual concentration of 02 at the 
s ite of the enzyme activity was very much lower than that in  the e xternal 
292 
atmosphere. This led to loweri ng of the enzyme's rate of 02 uptake. In the 
second scheme, she indicated that, a substantial part of respiration was not 
mediated by cytochrome oxidase, but rather by terminal oxidases with a much 
lower affin ity for 02 (than that of cytochrome oxidase). In the third scheme, 
she indicated that, in the intact plant organ , rate of respiration was l imited by 
02-dependent steps other than the final  steps in the transfer of electrons to 
°2' 
In  l ine with Forward's second scheme, Solomos' (1 982) view was that 
the decrease in  respi ration rate in response to decreased 02 concentration 
was not the  resu l t  of depress ion  of t he  basal metabol ism mediated by 
cytoch rome oxidase. Rather, it was thought that the reduction stems from the 
d im inut ion of the activity of other  oxidases (such as polyphenol oxidase, 
ascorbic acid oxidase and g lycolic acid oxidase) whose affinity for 02 may be 
five to six times lower than that of cytochrome oxidase. On the other hand, 
Knee ( 1 991  b) , suggested that the effects of 02 on fruit respiration does not 
involve di rect action on the terminal oxidase , but that there is some other site 
of action  of 02 which indi rectly affects respi ratory rate. This site of act ion 
might be an 02 consuming step i n  secondary metabol ism involved in fruit 
ripening;  inhibition of such an oxygenase could restrict the rate of metabolism 
and hence reduce the demand fo r respi rato ry energy.  Alternatively,  Knee 
(1 991  b) further suggested that there may be mechanisms whereby fru it cells 
sense hypoxic conditions and l imit respi ratory rate so as to min imise the 
production of toxic metabol ites under anticipated anoxia. 
In this study, the 02 concentration at which RelO2 was half maximal (ie. 
50% inhibition) was 7.5% for [02]ext and 2.5% for [02] i . Such levels of 02 are 
not expected to i nhibit cytoch rome oxidase because the Km of cytochrome 
ox idase is < 0 . 1 % 02 in the gas phase (Butt , 1 99 1 ; 
- Bu rton ,  1 978;  Knee,  
1 99 1  b) .  Therefore, the restriction (or 50% inhibition) of respiration at relatively 
high 02 concentrations was presumably due to the cu rtai lment of other  02 
293 
requ i ri ng p rocesses o r  other 'enzyme(s) ' (such as ascorbic oxidase and 
g lycol ic acid oxidase) which may be di rectly or ind i rectly involved in the 
respiratory machinery and the 02 affinities of which are much lower than that 
of cytochrome oxidase (Burton, 1 982 ; Butt, 1 991 ). It may be that, through  one 
of these oxidases, glycolytic flux is more di rectly affected than 02 uptake, as 
suggested by Tucker and Laties (1 985). 
The differences in the shapes of the curves in the relationship between 
RelO2 and [021ext (fig. 5-3) or [021i (fig. 5-4) as well as the difference between 
the [021 i and [021ext values at which RelO2 is half maximal ,  clearly i l l ustrate 
the advantages of consideri ng fru it physiol og ical responses to CA/MAs in  
terms of  t he i r  i nte rnal atmosphe re composition  rat he r  than the e xternal 
atmosphere to which they are exposed. The presence of the skin ,  with its finite 
res istance to gas d i ffus io n ,  means that t here must a lways be  a n  02 
concentration difference between the fruit's internal and external atmospheres 
(equation [5. 1 n. The magnitude of this difference wou ld depend largely upon 
the fruit's rate of respi ration and the value of R. The greate r the resistance, the 
greater the difference for any given rate of respi ration. Variation in R coupled 
with respiration rate therefore determines the [021i for a given [02]ext and  so it 
affects the shape of the relat ionship between Rel02 and [02]ext. H igh  R 
would result i n  a decrease i n  [02] i for a g iven rate of respiration and hence 
h i gh [021ext requ i red fo r ha l f maxi mal act iv i ty .  O n  t h e  same  bas is ,  
temperature (through its effect on respi ration) might be  expected to affect the 
measured Km for respi ration versus [021ext . Elevated temperatu res  would 
increase respi ration rate which, in  turn, would depress [02] i for a given [021ext 
and therefore increase the [021ext requi red for half maximal activity. 
Skin resistance characteristics therefore determine the fruit's respi ratory 
response to CNMA. They also dictate the lower l imit of [02]ext which can be 
tolerated by the fruit since they control the gradient which exists between the 
internal atmosphere of the tissue and its external environment for a g iven fruit 
294 
respiration rate. I n  a similar way, the decli ne i n  fruit porosity that occurs with 
ripening and senescence may affect the outcome of CA/MA treatments. Low 
porosity would increase the internal resistance to gas diffusion and therefo re 
i ncrease the gradient in gas concentration between the centre and outside of 
the fruit. 
There was a marked depression of [02]i with corresponding elevat ion i n  
[C02]i o f  G ranny Smith apples 24h after f ruit were t ransferred f rom  O°C to 
20°C (this effect was more pronounced i n  coated fruit than in the controls;  
chapter 6) .  Howeve r, after the i n it ia l  period of dep ression of [02] i and 
co rrespond ing i ncrease i n  [C02] i , f ru i t  recovered (or  establ ished a new 
physiological equi l ibrium at the new temperature), with an increase in  [02] i and 
decrease in [C02]i ' Changes in i nternal atmosphere composition presumably 
reflect changes in respiration .  A similar observation was made by Blackman 
(1 954) ,  who indicated that when apples were t ransferred from 2 to 22°C there 
was an 'overshoot' in respi ration rate before attai nment of a new equi l ibrium 
with the new temperatu re. Jobl i ng et al. ( 1 99 1 ) reported that the [C02]i in  
G ranny  Sm ith  app les showed a s i m i la r  'overshoot' phenomenon  which 
increased i n  intensity with increased duration of  exposu re to low temperatures 
up  to 32 days.  I n  the current study some of the apples had been in cool 
storage (O°C) fo r much longer periods (0, 4 , 8, 1 6  and 24 weeks)  befo re 
t ransfer to 20°C. The magn itude of the 'overshoot' at 20°C appeared to 
increase with longer periods in cool storage, consistent with the data p resented 
by Jobling et al. ( 1 991 ) .  
The effect of th is 'overshoot' i n  resp i rat ion rate on  [02] i wou ld be 
expected to be greater for coated fruit (than the controls) because a g reater 
concentration  difference between the i nte rnal and exte rnal atmospheres 
(�[02] )  would be generated ( i n  coated fruit than the c
·ontrols) for a g iven 
respiration rate. The subsequent reduction in these concentration d ifferences 
might simply reflect the subsidence of respiration rate as fruit equi l ibrate to the 
295 
new temperatu re .  Alternatively, for coated fruit, th is response cou ld  also 
reflect the delayed physiological equi l ibration of respiration rate to the lowered 
02 status i n  the tissue. A s imi lar phenomenon was noted by Knee ( 1 991 b) 
who observed that the delay between placing fruit in  a reduced 02 atmosphere 
and observing a reduction i n  respi ration rate (C02 production) was about 4 
days , l o nge r  t han  the  t ime  requ i red for phys ica l  e q ui l i b rat ion  of 02 
concentrations inside and outside the fruit. This contrasts with the fi nd ings of 
Tucker and Laties ( 1 985) who reported that with avocados only 1 2h was 
required for re-establ ishment of a · constant respirat ion rate after a change in 
02 concentration. The delays involved in development of a new physiological 
steady state seen i n  these tissues presumably represent the various times 
required for substrates and enzyme activities to reach new steady levels.  
I n  terms of the model presented i n  fig . 9-1 , the 'overshoot' i n  respi ration 
rate in response to temperature increase would be due to a n  i ncrease i n  Fmax 
which , at a given [02]i would result in an increase in F. Combined with  R, this 
would augment �[02] and decrease [02] i and F. After a few cycles t h rough 
the system a new steady state would be reached in which F and �[02] would 
be higher and [02] i lower than before the fruit was warmed. This effect would 
be exaggerated i n  the presence of coating due to the h ig her value of R/A in  
coated fruit. 
9.1 .2.2 Rate of C02 production 
When express ing C02 evolution as a funct ion o f  02 concentration,  
most fruits including apples exhibit a classic respi ratory response and Pasteur  
effect (ie. the acceleration of  sugar uti l isation in  respiration under conditions of 
low 02 ; Boersig et al. 1 988 ; Turner, 1 951 ) .  The relationship between the  rate 
of CO2 production and [02]ext has been characterised by various resea rchers 
including Boersig et al. (1 988), Cameron (1 985), Kader ( 1 987) and Leshuk and 
Saltveit ( 1 990) and i nvolves two physiolog ical processes, anaerob ic and 
296 
aerobic respi ration. However, combin ing mathematical equations to d escribe 
the two physiological processes has not been reported. Cameron ( 1 985) 
attempted to fit a model describing only the aerobic phase of the process. In 
this study a mathematical model (equation [5.8] )  developed to describe the 
re lat io nsh i p  between Re/C02 o r  [C02] i and  [02]ext  or  [02] i h ad two 
components, each describing one of the two physiological processes. 
Oxygen concentrations below 2 - 5% (Biale, 1 969) or below 5% (Tucker 
and Laties , 1 985) may cause a switch from aerobic. to anaerobic processes 
(such as fermentation and alcohol formation) which reverse the reduction i n  
C02 production and can raise its concentration in affected fruit to levels above 
those for the same fruit kept i n  ai r (Blanke, 1 991 ; Burton, 1 982) .  I n  recent 
years, the use of low 02 atmospheres as a potential quarantine treatment for 
insect contro l  has renewed interest i n  anaerobic respi ratio n  of horticultural 
crops (Boersig et al. , 1 988; Ke et al. , 1 99 1 ; Yahia et al. , 1 991 . 1 992) .  Of 
special interest is the anaerobic compensation point (ACP) . which is defined as 
the 02 concentration at which C02 production was min imum (Boersig et al . •  
1 988 ) . A n  att empt was t h e re fo re made  to est i mate t he  a n ae rob i c  
compensation point (ACP) for both [02]i ([ACP]i ' 0.3%) and [02]ext ([ACP]ext. 
0.5%) in both Cox's Orange Pippin apples and Granny Smith apples. 
An i ncreased density of data points in the lower quadrant of the graphs 
cou ld have assisted in the accu rate est imat ion  of ACP ,  neve rt he less 
extrapolat ing the curves shown in f igs. 5-5 and 5-7 to the x-axis p rovided 
estimates of the point of interception of the two processes.  In  fact these plots 
make it clear that anaerobic respiration actual ly begins at an [02]ext somewhat 
higher than the ACP. It is below this point (recently termed the 'RQ breakpoint' 
by A .  C. Cameron) that RQ would be expected to rise f rom the plateau level 
observed at h igher  02 concentrat ions .  The steepness of the dec l ine  i n  
anaerobic respi ration versus 02 concentrat ion clearly  dete rmines the RQ 
breakpoi nt ( ie. the [02]ext at which al l anaerobic respi ration is exti nguished). 
297 
A less steep  s lope m i ght suggest that t he re was s ign if icant ana e robic 
respiration at 02 concentrations considerably h igher than the [ACP]ext. This 
might have accounted for the g radual decl ine in relative respiratory quotient 
(ReJRQ) seen in  Cox's Orange Pippin and Granny Smith apples (figs. 5-9 and 
5-1 0) over 02 concentrations ranging from 0 to 1 0%: these fruit apparently had 
a high RQ breakpoint. 
Even if [ACP]i is unaffected by temperature, there would sti l l  b e  large 
effects of tempe ratu re and R on [ACP]ext . H igh  temperatu re (th rough  its 
effects on fruit respiration rate) , coupled with high R, would lead to high .1[02] 
and hence low [02] i (Fig .  9-1 ) .  If [ACP]i remains the same, [ACP]ext wou ld be 
higher at high than at low temperature, since : 
[ACP]ext = [ACP]i + .1[02] [9.4] 
On this basis, a Braeburn apple kept at 25°C would be expected to have 
a much higher [ACP]ext than a Royal Gala apple kept at O°C (because of the 
high R of Braebu rn and the i ncrease in  respiration at the h igh  temperature) .  
An optimised MA package maintains fruit in an [02]ext just above [ACP]ext (ie. 
it minimises respi ration rate without i nducing anaerobic respi ration) .  Design of 
such a package should therefore take i nto account the temperature at which 
the packages will be kept as wel l  as inherent cultivar differences in resp i ration 
rate and R. In  th is study, estimates of [ACP]i and [ACP]ext were obtain ed for 
Cox's Orange Pippin and Granny Smith apples and their respiration rates and 
R values would not lead us to expect a substantial difference in  [ACP]i and 
[ACP]ext. However, it would be interesting to investigate cultivars with very 
different values for these variables to establish whether or not this prediction is 
correct. 
9.1 .3 Relationship between [02]ext and C2H4 f- .. . . � , 
298 
Ethy lene p roduct ion i n  fru its is known to be dependent upon  02 
concentrat ion (Adams and Yang , 1 979 ; B(�,n pie.d' __ ���J; Yang, 1 985,  1 987; Yang and Hoffman , 1 984) ,  and i nh i bit ion  of both C2H4 product ion  and 
respi ration by low 02 atmospheres is  an important component i n  the success 
of CA storage of fruits i ncluding apples. Most i nvestigators have looked at the 
impact of [02]ext rather than [02] i on  C2H4 product ion  and resp i ration .  
However, i t  i s  the 02 inside the fruit that is the most di rect cause of inh ibition of 
both C2H4 production and respi ration rather than [02]ext on which [02] i is 
dependent. In this study, the relationship between ReC2H4 or  [C2H4]i and 
[02]i (figs. 5- 1 7  and 5- 1 8) was more closely described by an exponential than 
a Michaelis-Menten type hyperbolic curve. Nevertheless, the overall shape of 
t he re lati onsh ip  conforms to t he  expectat ion  that smal l  changes  i n  02 
concentration have much greater effect at low [02]i than they do at h igh [02]i '  
The  p resence o f  d i ffus ion barr i e rs (such as ski n and f lesh) resu lted i n  
development of an apparent 'Iag phase' i n  the relationship between ReIC2H4 
or [C2H4]i and [02]ext such that it was no longer described by an exponential 
type equation and became essentially sigmoidal (figs. 5-1 5 and 5- 1 6) .  Some 
physiological corol laries of these observations are discussed below. 
Comparison of the re lat ionships between Re/C2H4 (fig. 5- 1 5) ,  on the 
one hand , and Rel02 (fig .  5-3) on the other hand, against [02]ext provides 
indi rect information on the nature of these two processes. If the 02 affin ities of 
these two processes (ie. respi ration and C2H4 production) were simi lar then 
they should yield simi lar response curves. The difference between the s hapes 
of the two curves indicates that two different enzyme systems may be i nvolved , 
presumably with differing affinities for 02' It also gives some indication  of the 
relative contrib\Jtions each makes to the 02 consumption 
·of the fru it tissues. 
299 
Assuming that an apple fruit produces 1 00).11 kg-1 h-1 of C2H4 (ie. 0 . 1  ml 
kg- 1 h - 1 ) and that for eve ry mole of C2H4 produced, one mole of 02 is 
consumed, then 02 consumption due to C2H4 production would only be 0.1 ml 
kg-1 h-1 . I f  in  the same fruit 02 uptake by respi ration is  1 0ml kg-1  h-1  then 02 
uptake by respiration is 1 00 times greater than 02 uptake by C2H4 production. 
Thus respi ration is the major 02 consuming  process in  the fruit tissue  and 
C2H4 production is only a minor consumer. The major 02 consuming process 
would not be expected to have the 'Iag phase' seen in fig .  5-1 5, as reductions 
in the avai labil ity of 02 with in the fru it tissue would be expected to resu lt in 
proportionate reductions in the rate of uptake by that process. Thus, the major 
02 consumi ng process should follow approximately Michael is-Menten type 
kinetics with regard to both [02] i and [02]ext. I n  contrast, minor consumers of 
02 might show a 'Iag phase' in thei r relationship with [02]ext which wou ld be 
related to the relative affin ities of the different processes involved for 02 and 
would be a reflection of their abil ities to compete for the available 02' H igh  02 
affin ity processes wou ld have a much less pronounced o r  non-existent 'Iag 
phase' compared to those with a low 02 affinity. These data therefore i ndicate 
that C2H4 production (compared to respi ration) is only a minor consumer  of 
02 in apple fruit tissue and that the process has an 02 affin ity considerably 
less than that of respiration .  
This observation appears to be at odds with the estimates of Km values 
for these processes which were higher for Rel02 than ReC2H4 (2.5% and 
1 .5% [02]i respectively, averaged across both cultivars). However, this can be 
explai ned by the th i rd model of respi rato ry control by low 02 proposed by 
Forward (1 965) : rate of respiration is l imited by 02-dependent steps othe r  than 
the f inal steps i n  the t ransfe r of e lectrons to 02 ' Thus ,  the h igh  affi n ity 
cytochrome oxidase is di rectly responsible for uptake of 02 by respi ration and 
therefore is efficient at competing for avai lable 02' However, the overall rate 
of respiration is moderated by some other 02 consuming process which g ives 
the overall process of respiration a lower apparent affi nity than observed for 
300 
Re1C2H4. This effect would become exaggerated if there were sign i fi cant 
gradients in 02 availabil ity between the i ntercel lular spaces and the sites of 02 
consumption with i n  the t issues (Fo rward 's fi rst mode l ) .  Clearly ,  f urthe r  
biochemical work would be requ ired to reach any fi rm conclusions reg arding 
the mechanisms involved in  these effects. 
The other two factors which could affect the degree of the lag seen here 
fo r Re/C2H4 versus [02]ext have al ready been ment i oned :  i e .  R a nd  
respiration rate . R varies considerably not only between cultivars but  also 
between i ndividual apples with in a cultivar (chapter 4) .  R can also change 
during storage as a result of developi ng greasiness (chapter 6) or ripen i ng at 
different humidities (Wilkinson ,  1 965). These natural sources of variation  i n  R 
could lead to l arge differences in  the size of the 02 concent ration g radient 
between the internal and external atmospheres and therefore in  the degree to 
which this lag phase might be expected to develop. In addition, R may be 
augmented intentional ly through the appl ication of coating materials (chapter 
6). All of these factors could change the shape of the relationship between 
ReK;2H4 or  [C2H4]i and [02]ext . 
Variation in respi ration rate, particularly in the presence of high R,  would 
also affect the form of this relationship. All of those processes which augment 
respiration rate (eg. elevated temperature and conti nued fruit deve lopment 
(cl imacteric)) would emphasise the lag phase ; the converse would also fol low. 
Keeping f ruit at low temperatu res would reduce the degree to which th is lag 
would be seen in cool storage. Transferring artificial ly coated fruit from cool 
storage to ambient temperatu re (chapter 6) duri ng that period in wh ich the 
fruit's respiration rate only gradually equi l ibrates with the depressed 02 levels 
which develop within it, wou ld therefore be expected to provide an e xtreme 
example of  the lag phase. Modified atmospheres would affect each of the 
ripening processes to an extent which wou ld reflect its affin ity for  02 and the 
301 
internal 02 l evels: a given [02]ext could have quite different effects on one 
process for fruit held at diffe rent temperatures or with diffe rent values of R 
(chapters 4 and 7). 
9.2 Effects of washing or coating on gas exchange 
Tween 20 coating i ncreased R of Granny Smith apples. This resulted in 
an increase in  gas concentration gradient between the inside and outside of 
the fruit and a decrease in [021; (and an increase in [C02]i) '  These effects 
would in  tu rn have depressed the rate of respiration and hence caused a 
decli ne in 02 uptake (fig. 9-2) .  
Depression of [02] i also results in  inhibition of other 02 dependent (and 
C02 i nhibited) processes and the depression in respi rat ion itself resu lts i n  
inh ibition o f  respi ration dependent processes (fig .  9-2) .  S imilar observations 
have been made fo r the coating of bananas (Banks ,  1 984a, b) and pears 
(Meheriuk and Lau ,  1 988 ; Meheriuk and Sholberg, 1 990), waxing of bananas 
(Ben-Yehoshua, 1 966) and avocados (Durand et al. 1 984) and also for various 
coatings on apples (Smith et al. , 1 987). Banks ( 1 984b) suggested that since 
coating involves the application of large molecules to the fruit surface, it m ight 
be expected that coating would exert its effects by increasing R and modifying 
the fruit's i nternal atmosphere composition rather than by any d i rect chemical 
effect. Coating or washing of fruit in Tween 20 solution resu lted in alteration of 
the gaseous mixture inside the fruit and in this way the technique m ight be 
considered to be analogous to that of MA storage. This was presumably the 
mechanism by which Tween 20 so l ut ion i n h i bited grease development i n  
Granny Smith apples. 
One inherent featu re in fruit , including apples, is variabil ity in all of thei r 
physiological characteristics. In apples, rates of respi ration ,  C2H4 production 
as well as R are also variable between cultivars and even between ind ividual 
Fig . 9-2. Schematic representation of the effects of wash ing or  
coating with Tween 20  solution on R,  [02] i ,  [C02] i, F or 
respi ration rate and O2 uptake of apples. 
302 
303 
fruit with in  a cu ltivar (chapter 4) .  Local ised variation i n  cuticular st ructure 
"f 
would cause differences in wettabi l ity or  extent" occlusion of the pores by a 
coating solution .  Th is would result in any given washing or coat ing material 
having a variable cover on different areas of a single fruit. Naturally, this wou ld 
cause variabil ity in the resistance of these areas on  the fruit to gas d iffusion 
and variation in R between individual fru it. This in turn would lead to variation 
i n  i n t e rn a l atmo s phere  com pos i t i o n  wh ich wou ld cause va r iab i l ity i n  
physiolog ical response. This i s  probably one  of the reasons why t he  great 
potential for surface coatings predicted by many workers in research papers 
( E l  Ghaouth e t  a l. ,  1 99 1 ;  Ben-Yehosh ua ,  1 987;  Eaks and Lud i ,  1 960;  
Hagenmaier and Shaw, 1 992; Trout et  al. ,  1 953) has not been fully rea l ised in  
commercial practice. 
Other prob lems with coatings include the substant ial increase in the 
extent of internal atmosphere modification achieved at different temperatures 
(Banks, 1 985a). However, Hagenmaier and Shaw ( 1 99 1 )  have recently shown 
that 02 permeabi l ity of a shel lac coating material rough ly doubled between 
30°C and 40°C. This ind icates the potentia l ,  at least, for permeabi l ity of the 
skins of coated fruits to adjust for variat ions in  fruit respiration rate at d ifferent 
temperatures. 
Evidence p resented in chapter 6 demonstrated that the d ifference 
(gradient) in 02 concentration between the internal and external atm ospheres 
in coated apples was much greater than that for C02 ' If we assume  that the 
majority of the movement of al l of gases into and out of the fruit occurred via 
the lenticels (ie. that the resistances of the fruit surface to 02 and CO2 were 
sim ilar) ,  then we must also assume that the coating or washing treatment was 
differential ly permeable to the different gases. S ince the  molecu lar size of 
C02 is greater than that of 02. the development of th is differential permeabil ity 
would probably have depended on some other characteristic of the two gases. 
Hagenmaier and Shaw (1 992) showed that the permeabil ity to C02 of coating 
304 
materials used on fruits is typically a factor of four greater than the permeabil ity 
to 02 ' Thus, the effects of Tween 20 coating on the i nternal atmosphere of 
apples were probably in large part due to the d ifferential permeabi l ity of the 
coating deposit on the fruit surface. 
At this point, with no data on the relative permeabil ities of Tween 20 
fi lms to 02 and C02' we cannot exclude the possibil ity that the application of 
the Tween 20 treatment reduced the movement of 02 and C02 through  the 
lenticels to a similar extent. I f  this is the case, then we must assume that the 
routes for entry of 02 into the apple fruit and those involved in the exit of C02 
are different. This would fit with data from Chapter 8 for non-coated B raeburn 
and Granny Smith apples coolstored for 1 2 weeks and then equi l i b rated at 
20°C for 3 days. These fruit had a much greater gradient i n  02 concentration 
between the i nterna l  and external  atmospheres than they d id  fo r C02 
concentration.  
Burton ( 1 974) indicated that the low solubi l ity of  02 in  water would l imit 
significant exchange of this gas across the fruit surface to pathways i nvolving 
only gaseous diffusion. Carbon dioxide on the contrary, by virtue of its high 
solubil ity in water might move at significant rates via pathways involv ing liquid 
water. The factor l imiting movement through the skin in the gas phase would 
comprise the effective apertures of the lenticels. If we assume that C02 was 
released from the general fruit surface as well as via the lenticels ,  t hen by 
blocking the lenticels we would exert a marked effect on the resistance to 02 
. (and C2H4) and some effect on the resistance to CO2, The magnitude of this 
effect wou ld depend on the th ickness and po rosity of the  deposit  i n  the 
aperture and the proportion of the total number of  lenticels blocked. If we also 
suppose that the  resistance of the ep ide rmis  and/o r  the  cuti c l e  to the 
movement of  gases was greater than that offered by the layer of the Tween 20 
solution appl ied to the fruit surface then the presence of washing treatment or 
coating over the rest of the fruit surface could have l ittle add itional effect on the 
305 
resistance of the fruit skin to C02' This provides an alternative account for the 
differential effects on the resistance of the fruit ski n to C02 exerted by coating 
with Tween 20 solution. 
It is i nte rest ing to note that the d ifferences i n  g radients for t he  two 
respi ratory gases were not present in the freshly harvested fruit and that they 
deve loped  i n  mag n itude ove r t ime .  It  may the refo re be that t he  most 
appropriate model of gas exchange through  the fruit skin is the first of those 
presented above " ". , i n  which al l of the; gas exchange takes place 
through the lenticels .  Subsequent development of wax on  the fru it surface 
then might lead to partial blocking of the lenticels and generate the observed 
differential gradients in a manner similar to that achieved by coating. 
Burton ( 1 974) has noted the importance of considering the vari ation in 
skin  resistance of individual fruit skins to gases when produci ng 
recommendations for the concentrations of 02 in CA storage of fruits. The 
same point must be borne in mind when suggesting suitable concentrations of 
a coating or washing treatment for fruits. Inherent differences in the resistance 
of both the skin and the internal t issues to the movement of gases may affect 
the relative effects of coating on 02-dependent physiological processes. 
9.3 A model describing the form of relationships between [021 i , R and 
respiration. 
A tentative model describing the general form of relationships between 
[021 i , total R ( i .e. the natu ral resistance of the skin ,  presence of coat ings, or 
g reasi ness , or packag ing) and temperature is shown in fig .  9-3. The curves 
R1 ' R2, R3 and R4' show that for any particular R value ,  the [021 i decreases 
with i nc reas ing temperatu re and that as the res ista"nce is i ncreased ( ie .  
naturally through the development of greasiness, o r  artificial ly through coating, 
306 
-
� o -
....-. 
C\I 
o ......... 
D 
a b 
Incre as i n g  temperatu re 
Fig. 9-3. Tentative model  describing the form of relationsh ips between 
[021j, skin res istance to gas d iffusion (R) and temperature. Curves  R 1  
to R4 represent fruit with d iffering levels of ski n resistance (R 1  = low, 
R4 = high) .  
307 
waxing or packaging)  th is effect of temperatu re becomes g reater . . These 
temperatu re effects are brought about by variation in respiration rate at the 
different temperatures. 
If the [02] i falls below a critical value (perhaps 1 % represented by the 
l ine CD), i nternal injury could occur (eg . because the [02]i is lower than the 
[ACP]i) .  The temperatures a, b, etc. corresponding to the points of i ntersection 
of the resistance curves and the 1 % [02] i l ine ,  CD, would therefore be the 
maximum temperatures at which the f ruit could be stored without deve loping 
injury. For a fruit kept in air, R would have to have very large values before the 
tissues wou ld begin to respire anaerobically because of the high concentration 
of 02 avai lable in the external atmosphere. However, the same overal l type of 
response to temperature would occur for fruit kept in modified atmospheres, in 
which only modest L\[021 would be needed to render the tissues anaerobic. 
The concept of an opti mum [02] ext , at wh ich resp i rat ion is max imal ly  
suppressed without i nducing anaerobiosis, is therefore not one of  a constant 
for a g iven fruit type in all environments. Rather, the optimum value for [02]ext 
fo r a g iven  popu lat io n of fru it wou ld  be depende nt u pon  t he  i n h e rent  
differences in R and respiration as well as the temperature at which these fruit 
are kept. 
Clearly ,  the predominance of temperatu re as an envi ronmental factor 
affecti ng  the physiological behaviour of apples th rough  its effects o n  fru it 
respi ration and internal atmosphere composition is reaffi rmed by this analysis. 
9.4 Recommendations for further research 
The o ri g i nal i ntent ion of th is wo rk was to attempt to ascertai n the 
re lat ionsh ip  between the i nte rnal atmosphere compositi on of apples and 
factors such as [02]ext, respiration, R, artificial barriers and temperatu re .  On 
reflection it would seem that in common with most other physiolog ical studies, 
308 
th is  research has raised more questions than were orig inal ly envisaged. 
Nevertheless, this work wil l help to focus subsequent inquiry. I n  the light of the 
findings of the current study, it is recommended that the following avenues of 
research would be worthwhile. 
Further  research is requi red to ascertain whethe r  the rel at ionsh i p  
between resp i rat ion and [02] i changes with fru it matu rity and duri ng  the 
cl imacte ric. The mechan ism by wh ich low 02 atmospheres affect fruit  
respi ration sti l l  remains obscure. I t  is hoped that in future additional efforts wil l 
be d i rected towards improvi ng our  u nde rstand ing  of h ow low 02 l evels 
influence respiration metabolism, C2H4 production and compositional changes 
related to qual ity attributes of apples. Such information wil l  no doubt he lp i n  
our understanding of the mode of action of CA and MA on fruit physiology and 
therefore improve our  chances of expandi ng the use of CA or MA du ri ng  
transport and storage of apples and other fruits. 
In this project there was no detectable AA or ETOH in the core cavity of 
apple fruit i rrespective of the [02]ext. It may be that at the time of i nternal 
atmosphere sampl i ng ,  AA and ETOH had not accumu lated i n  su ff ic ient 
concentrations to be detectable. This seems odd because the two vapours 
were present in the vials equi l ibrated with the internal atmosphere via a pore i n  
the fruit surface, despite the fact that their contents would lag at least several 
hours beh ind the changes in contents of the internal atmosphere of the fru it. 
Further research is required to investigate this surprising finding. It wou ld  also 
be i nterest ing if the distribution of AA and ETOH i n  the fruit is ascertained, 
someth ing which could be ach ieved non-destructive ly using the vial system 
employed extensively in  th is study. This would be of part icu lar i nte rest i n  
compari ng the re lative tendenci es towards accumulat ion of a naerob ic by­
products in the calyx end of the fruit with those regions which in this work have 
been shown to have higher levels of 02. 
309 
G iven  the importance of gas d iffus ion i n  successfu l CA sto rage of 
apples, additional information is required on the changes of R of apples during  
storage under low 02 atmospheres. I n  addition there was a large degree of 
variat ion in  R of individual apples with in  each cultivar; fu rther  research  is 
warranted to ascertain the physiolog ical and commercial importance of such 
variability in  apples during CA storage .  
In  th is  study Splendour  apples compared to the other cultivars had h igh 
[02]i ' low [C02]i , low 'respiration, low R,  high soluble solids contents and h igh 
storage potential . However one major disadvantage of this cultivar is its h igh 
suscepti b i l i ty to bru is ing damage .  I t  wou ld  therefore be  a com me rc ial 
advantage to the apple industry in New Zealand if some of these beneficial 
qual ities inherent in Splendou r apples cou ld be introduced into poor stori ng 
cultivars or alternatively to breed Splendour apples with better skin that does 
not affect the good qualities of this cultivar. i , " ,� ,;, .� 
In  view of the spacing of the temperature regimes used in  this research 
(chapter 7) ,  it was not possible to establish the optimum temperature for C2H4 
evolution of the apple cultivars studied. Above 25°C, most of the cultivars lost 
some of their capacity to produce C2H4' It would be interesting to establ ish 
the optimum temperature for C2H4 evolution and to study in detail why fruit 
lost their capacity to produce C2H4' This may be of value in  understanding the 
response of fruits to different temperature regimes eg o heat shock treatments. 
Tween  20 so l ut ion was effective in p revent i ng  the deve lopment of 
greasiness in Granny Smith apples as well as retardation of colour change and 
fi rmness . Whi lst it is beyond the scope of th is thesis ,  further research  to 
ascertain the mode of action of Tween 20 solution in  inhibiti ng development of 
greasiness, retardation of colour change and firmness wou ld be worthwhi le .  
310  
Following the discovery that the internal atmosphere composition within 
apples is heterogeneous, i t  is  hoped that in future further research efforts 
would be di rected towards establishing the physiological significance of such 
heterogeneity in apples under CA/MA conditions. It has been established that 
the calyx region of apples contained lower 02 and higher C02 and C2H4 than 
the other parts of the fruit. Further research is clearly warranted to study if this 
pattern is retai ned during storage of apples under low 02 atmospheres. If th is 
is so, does the development of certain physiological disorders in  apples under 
low 02 commence or occur at the calyx region of the fru it, where the 02 
concentrat ions are low even fo r fruit kept i n  a i r ? The researc h  shou ld 
incorporate anatom ical studies as wel l  as estimation  of i nterce l lu lar space 
volume. 
9.5 CONCLUSION 
To conclude,  data on gas exchange characteristics of apples have been 
uti l ised to examine  the form of re lationsh ips between internal atmosphere 
composition and factors such as [02]ext , R ,  respi rati on ,  temperatu re and 
artificial barriers .  It is clear that these factors do inf luence the atmosphere 
inside the apple and hence have the potential to affect important aspects of 
qual ity such as rates of softening and loss of green colour. Whi lst the scatter 
in some of the data sets made it difficult to be defi nitive about the exact shapes 
of some of the relationships, nevertheless the principles, results, d iscussions, 
mathematical equations and suggestions presented in this thesis has provided 
fu rt he r  i ns ig ht i n  t he  way these factors affect t he  i n ternal atmosphere 
composit ion of apples. The information assembled i n  th is  thes is  wou ld  
hopefu lly contribute to further study of these relationships as well as the effects 
of low 02 atmospheres on fru it respiration and C2H4 production. 
31 1 
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�. 
--
� '-" 
c:: 0 ..... 
� .... = � u = 0 u 
C"l 0 
336 
20 
15  
10  
5 
o 20 40 60 80 100 1 20 140 1 60 1 80 
Time (hr) 
Appendix 1 .  Change in glass vial O2 concentrations with time.  
Vertical bars indicate standard errors of means.  Points to  the left of 
the arrow were the average values for thirty-six fruit during 
equilibration in air. To the right of the arrow indicates equilib'ation of 
one fruit in 3.78% O2 (similar equilibration time was obta'ined for 
each of the thirty-six fruit (per cultivar) kept in different O2 
atmospheres) . 
337 
14  
12  
_ 10 
� '-" 
,........, 
N 0 u '--' 
"0 
� 
.-,........, 
N 0 '--' 
8 
6 
4 
2 
0 
handled non-handled 
Treatments 
Appendix 2 .  Effects of handling by touching on [02] i and [C02] i of 
greasy Granny Smith apples stored for 1 7  days at 20°C.  Vertical bars 
indicate standard errors of means. 
Appendix 3 .  Photograph showing browning around the core 
cavity of Granny Smith apple. 
338 
Appendi x  4 
VARIATION IN INTERNAL ATMOSPHERE COMPOSITION WITHIN SINGLE APPLES 
B . K. DADZIE* , NtH.  BANKS , E .W .  HEWETT AND D . J . CLELAND 
Department of Horticultural Science 
Massey University , Palmerston North (New Zealand )  
339 
INTRODUCTION - Precise knowledge of t he distribution of i nternal  gas concentrations in  
fruit  will  enhal)ce our understanding of  the mechanisms by which ripening i s  reta rded 
and atmosphere related-disorders develop within fruit  stored i n  modi f ied o r  cont rol l ed 
atmospheres . The internal atmosphere composition of an apple has been reported to be 
practicall y  homogeneous ( Solomos ,  1 981 ) . However,  recent  evidence demons t rates  that  
there may  be  s igni ficant heterogenei ty  in  02 concentrat i on wi  thin the flesh o f  some 
apple cult iva rs . The present study deals  with the dist ribu t i on o f  O2 c oncent rations  
within individual apples kept at  20°C . 
METHOD - Granny Smith  apples ( Mal us syl vestris  Hil l ,  cv G ranny Smi th ,  count 1 2 5 ) , 
stored in  a i r  for  2 months  a t  OOC were used in this  experiment . Glass  vials  ( 2ml") 
were stuck over 
f ruit ( Fig . 1 ) . 
were ta ken f rom 
an 02 elec t rode 
one or more lenticels  at each of f ive posit ions  on the s u r face of t he 
After 54hr  of equ ilibration at 2 0°C in the dark,  gas s ample s  ( 90�1 ) 
each glass chamber using a gas-tight syringe a nd analysed for  O2 using 
(Banks,  1 9 8 6 ) . 
RESULTS - The s teady state  mean  O2 concentrat ions of  
the  f ive v a r ious  posi t i ons  a re presented on Fi g .  2 
Oxygen concent ration at the equator was higher than any 
of the other  positions  on the f r ui t ,  whi l s t  t i s sues 
n e a r t h e  c a l y x e n d  c o n s i s t e n t l y  h a d  l owe r 0 2 
concent rations than other parts  of the f ruit . This may 
be re lated  t o  l oca l i sed vari a t i on i n  i n t e rcel lul a r  
space  v o l ume , s i nce s t udies  w i t h  Golden De l ic ious  
apples  have  shown that intercellular  space vol ume are 
greatest i n  the equatorial  region compared to  the other  
pa rts  of the fruit . High porosity  would be expected to  
f acil itate  gas  di f fusion . 
CONCLUSION - Internal atmosphere composition of Granny 
Smi t h  app l e s  v a r i ed f r om one pa rt  o f  t he  f ru i t  t o  
another  and thi s has important  implicat ions for  the way  
i n  which  we attempt to model the  gas exchange of  these 
f ruit and the e f fects of  modi fied atmospheres on the ir  
phy s i o l og y . A s  a r e s u l t  o f  t he h e t e r ogene o u s  
di s t r i bu t i on o f  02 concent r a t i ons  w i �hin  i ndividua l  
c 
•• I AltR.A.tlO, ... C2HT OF GUSS SAMl'LIHG Cll"'fllr:r:� 
ON TIt!: SUVAC£ OF AN APrLE fltlrrT 
I. Stna ........... 
.... . ...-
It !\ .. ,.. "",,""I" J. � .... 
f ruit ,  t issues at  the fruit  cent re would experience l ower O2 concentrat ions  than  those 
at t he s u r face . Deepe r t i ssues would therefore be l i kely  to  have lower r espi ra t i on 
I · 
! 
I 
I 
r a t e s  and  p re s umabl y a g r e a t e r  tende n c y  t ow a rd s  t he  
deve l opme n t  o f  1 0w-0 2 d i s o rde r s  in  f r u i t  s t � r ed  i n  
mod i f ied a tmosphe res  at e levated  tempe ra t u re s  s u c h  a s  
2 0°C . 
REFERENCES 
Banks,  N . H .  Appa ratus  for determining oxygen in sma l l  gas  
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Sol omos ,  
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T .  P r inciples  o f  g as  exchange in bul k y  p l an t  
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Fig.2. Di.uibutioll ofO'Yltll Concellultion within .inllc applCl. 
Oral abstract No . 2461 , 23rd I nternat i ona l  Hort i cu l tural  Congress , 
F i renze ( I taly ) . August 27-September 1 1 990 . 
.. 
Fruit used i n  this study were sampled from those suppl ied by the New 
Zealand apple and pear marketing board as follows: 
I n  chapters 4, 5, 6  and 7, fruit used in each experiment were sampled at 
random from four  cartons (one carton from each of 4 growers) pe� cultivar. 
Growers used for the different cultivars were not necessarily the same. 
I n  chapter 8, fruit used in experiment 2 were s imi larl y  sampled at 
random from four  cartons (one carton per grower) per cultivar. On the other  
hand, those used in experiment 1 were sampled from six cartons (one carton 
per g rower) per cultivar.