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Item The interaction between sugars and acids and their effects on consumer acceptance of kiwifruit pulp : a thesis submitted for the degree of Master of Technology at Massey University(Massey University, 2000) Rossiter, K. LA model system using kiwifruit (Actinidia deliciosa (A. Chev) Liang et Ferguson var deliciosa cv Hayward) pulp has been developed so that consumer perceptions of sugar and acid can be explored in a realistic, homogenous product where natural variation between fruit and within fruit is eliminated. Use of a pulp model system enabled the sugar and acid level in kiwifruit to be manipulated using sugar and acid stock solutions. Fruit from an early harvest were selected to suppress the development of esters in the fruit at 'eating ripeness' so that sugar and acid relationships could be assessed without the influence of ester odour compounds. To compare and contrast sugar and acid relationships in kiwifruit with ester levels typical of fruit harvested at the recommended harvest maturity, odour compounds were incorporated into a portion of the pulp. Consumer's 'overall liking' ratings of the pulp increased with rising Brix. Increasing Brix level was also shown to increase 'sweetness liking', 'acidity liking', and perception of 'sweetness intensity'. Variations in Brix and acid level elicited the same consumer response to pulp with added odour compounds as to pulp without added odour compounds.Item Temperature effects on kiwifruit maturation : thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Horticultural Science at Massey University, Palmerston North, New Zealand(Massey University, 1993) Seager, Nicola GillianThe effect of temperature on rate of kiwifruit maturation was studied using container-grown vines placed in controlled environments and field-grown vines from four orchards (Kerikeri, Te Puke, Palmerston North and Riwaka) at the geographical extremes of the kiwifruit growing regions. Soluble solids concentration (SSC) and partitioning of carbohydrate between starch and total sugar concentrations were studied at different stages of maturation in both the controlled environment and field work. Flesh firmness, dry matter concentration and fruit growth changes during fruit maturation were also measured. The effect of carbohydrate status on fruit maturation was determined by manipulating it using girdling of field-grown vines. A model relating changes in SSC to temperature was derived using data collected from controlled environment treatments. This model was applied to field-grown vines using meteorological data from kiwifruit growing regions. Use of controlled environments quantified changes in kiwifruit during maturation. Increase in SSC and total sugar concentration, and decrease in starch concentration were faster at cooler than warmer mean temperatures, irrespective of minimum temperature per se or magnitude of the difference between maximum and minimum temperature. A temperature perturbation altered the partitioning of carbohydrate compared to treatments where a perturbation did not occur. In some years fruit were not responsive to any temperature treatments; these fruit had not reached the stage of development at which they were able to respond to temperature. Differences in rate of fruit maturation were found among orchard sites. Some of these differences, such as decrease in starch concentration and increase in total sugar and SSC could be attributed to the effect of temperature. Girdling kiwifruit laterals altered carbohydrate concentration and affected rate of fruit maturation. Carbohydrate concentration was higher in fruit from the 5:1 than 1:1 leaf:fruit ratio treatment. Fruit in the 5:1 treatment matured similarly to fruit from ungirdled vines, compared to delayed maturation in fruit from the 1:1 treatment. Carbohydrate concentration in this treatment may be insufficient to support fruit maturation. The model developed to predict the rate of change in SSC during kiwifruit maturation was made up of two components; a state-dependent physiological response function and a temperatu re-dependent rate function. The base + exponential model was chosen to represent the state-dependent physiological response function, based on SSC being separated into two components; basal SSC and maturation SSC. The temperature-dependent rate function from container-grown vines placed in controlled environments was successfully transported to fit SSC in field-grown vines at different orchard locations. The model was developed using continuous temperature records but was later modified to use daily maximum and minimum temperatures allowing greater practical application. The partial rate coefficient accounted for most of the physiological differences between years, orchards and experiments; it required fitting at each orchard location. Transportability of the partial rate coefficient was demonstrated between years for two orchard locations. The model, therefore, has great potential for prediction of harvest date of kiwifruit in different regions and seasons.Item Gas exchange, ripening behaviour and postharvest quality of coated pears : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Postharvest Physiology and Technology at Massey University, New Zealand(Massey University, 1998) Amarante, Cassandro Vidal Talamini do; Amarante, Cassandro Vidal Talamini doPear cultivars 'Bartlett', 'Beurre Bosc', 'Doyenne du Comice', and 'Packham's Triumph' were treated with different levels of deposits of a carnauba based wax on the skin and assessed for gas exchange, ripening behaviour and postharvest quality. The response to coating treatments was strongly dependent on cultivar, ripening stage and environmental temperature. 'Bartlett', 'Comice' and 'Packham's', with non-lignified skin, had substantial reductions in skin permeance (P'j) with small increases in coating deposit. Magnitudes of reduction in P'j to different gases were observed in the order: P'O2 > P'CO2>> P'H2O. The skin of 'Bosc', with lignified cells, had high P'H2O and low P'CO2' and increasing the amount of coating deposited on the skin resulted in small reductions of P'H2O and a gradual reduction of P'O2 and P'CO2. 'Bartlett' and 'Bosc' had a high risk of developing internal disorders caused by excessive internal accumulation of CO2 at low temperatures when treated with substantial coating deposits, as a result of high respiration rate ('Bartlett') or low P'CO2 of coated skin ('Bosc'). These cultivars were also less tolerant to hypoxia (expressed in terms of internal lower O2 limit, LOLi) created by high coating concentrations, and their level of tolerance reduced with increasing ripeness. 'Comice' and 'Packham's' were highly tolerant of hypoxia [the fruit did not ferment despite of an internal O2 partial pressure (piO2)@ 0 kPa]. Respiration rates, softening and colour change followed a Michaelis-Menten model when plotted against piO2, while internal CO2 partial pressure (piCO2) had virtually no explanatory power for these variables during shelf life. Variable cover of skin pores in cultivars having high P'j might result in variable P'O2 and, consequently, variable piO2. This could increase the naturally high ripening variability of pears treated with a given coating concentration. Softening had a lower Michaelis-Menten constant for pio2 than skin colour. Therefore, coated pears with intermediary pio2 might have variable postharvest quality mainly in terms of colour change, and the fruit may still soften while being unable to change in colour. For 'Comice', higher levels of coating deposit resulted in more substantial modification of internal atmosphere during cold storage, slightly increasing ripening delay. These treatments reduced wastage by diminishing the incidence of senescent breakdown and senescent scald after long term storage and by reducing skin friction discolouration during shelf life. Increasing the amount of coating deposit improved skin gloss and reduced senescent breakdown of 'Bartlett', 'Comice' and 'Packham's' during shelf life. The results show that optimisation of surface coatings should take into account differences between cultivars, ripening stage when the fruit is coated and storage temperature to avoid the risk of fermentation and physiological disorders. Even though there are some quality problems due to uneven ripening, wax coatings represent a technology with high potential for the pear industry, improving the finish of the skin, reducing water loss, delaying ripening and reducing the incidence of senescence related disorders.Item The role of ethylene in kiwifruit softening : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Plant Science at Massey University(Massey University, 1999) Kim, Hyun OkPremature fruit softening during storage at 0°C is a serious and costly problem for the New Zealand kiwifruit industry. Ethylene gas (C2H4) is a potent promoter of fruit softening; it is involved in regulation of fruit ripening and influences a number of processes, including ethylene production, respiration rate and fruit softening. Exogenous ethylene increases softening rate in kiwifruit at 20°C and at 0°C; a concentration of 0.01µl/1 will enhance softening at 0°C. The precise relationship between kiwifruit softening and endogenous ethylene concentration is not known. The influences of low temperature, an ethylene synthesis inhibitor (aminovinylglycine (AVG)), an inhibitor of ethylene action (1-methylcyclopropene (1-MCP)) and application of ethylene at different maturities were investigated in an attempt to elucidate ethylene's role in initiating kiwifruit softening. Exposing fruit to 0°C for more than 52 days hastened ethylene production upon removal to 20°C compared with fruit maintained at 20°C continuously after harvest; this enhanced ethylene was associated with increased 1-aminocyclopropane-1-carboxylic acid (ACC) concentration and ACC oxidase (ACO) activity. Kiwifruit softening at 0°C occurred even though ethylene production was low and constant between 0.02 to 0.06µl/kg/h (corresponding to internal ethylene concentrations (IEC) 0.2 to 0.6µl/1). This softening was associated with low ACC concentrations varying between 0.2 to 0.5nmole/g and ACO activity varying between 0.01 to 0.66nl/g/h These results indicate that very low concentrations of ethylene may play an essential role in kiwifruit softening. In kiwifruit treated with AVG (500ppm) 4 weeks before harvest, ethylene biosynthesis, manifested as reduced ACC concentration, ACO activity and ethylene production, was significantly inhibited both at 20°C and after storage at 0°C. AVG application resulted in a slower softening rate and firmer fruit than in untreated controls. Rates of softening were 0.4N/day and 1.9N/day in the AVG treated fruit and control fruit respectively during 14 days at 20°C. However, the AVG effect was reduced after storage at 0°C for 14 days, indicating that the AVG effect was only temporary and may not be sufficient to warrant possible commercial use for longer storage. Application of 250ppm AVG 2 or 4 weeks before harvest, and 500ppm AVG 2 weeks before harvest had no effect on ethylene production or fruit firmness. Fruit infected with B. cinerea produced more ethylene than non-infected fruit at 0°, 4°, 10° and 20°C. An increase in ethylene production, induced by B. cinerea infection, occurred in tissue slices from the invasion zone (the infection front containing both infected tissue and sound tissue immediately ahead of the infection front) and adjacent zone (sound tissue ahead of the invasion zone) of kiwifruit. The increased ethylene in infected fruit was associated with increased ACO activity in tissue from adjacent and distal (sound tissue at the distal end of the fruit) zones. Application of 500ppm AVG to kiwifruit vines before harvest reduced ACC concentration and ACO activity and ethylene production induced by B. cinerea at 20°C. However this AVG reduced ethylene production from B. cinerea infected fruit after 4 weeks at 0°C was insufficient to prevent rapid growth of B. cinerea. Therefore, such an AVG treatment can not be used to reduce B. cinerea infection during storage at 0°C. As kiwifruit matured, softening was enhanced increasingly by exogenous ethylene, indicating that tissue sensitivity to this growth regulator increased with time. The sensitivity of kiwifruit was reduced by treatment with 1-MCP, an inhibitor of ethylene action. When applied to kiwifruit at harvest, 1-MCP reduced ethylene production and respiration rate, resulting in a slower fruit softening and firmer fruit during storage at both 0°C and 20°C. Kiwifruit treated with 1-MCP plus ethylene at harvest, remained firmer than fruit exposed to ethylene alone for 4 days at 20°C and 8 days at 0°C, after which this 1-MCP effect disappeared with firmness being the same for both ethylene plus 1-MCP and ethylene treated fruit at the two temperatures. When both 1-MCP plus ethylene were applied after storage at 0°C, 1-MCP negated the ethylene-induced softening with treated fruit having a softening rate 4 times less than for fruit treated with ethylene alone. Softening rate of control and 1-MCP treated fruit was the same as those treated with 1-MCP plus ethylene (approximately 0.06 ('Kiwifirm'unit)/day) compared with 0.2 ('Kiwifirm'unit)/day for fruit treated with ethylene alone. Since 1-MCP binds to the ethylene receptor sites irreversibly, it is suggested that kiwifruit can synthesis new ethylene receptors with time during storage at 0°C and 20°C, making kiwifruit increasingly sensitive to endogenous ethylene. Over several different experiments in 3 seasons, kiwifruit softened from ≈ 90N to 10~19N while endogenous ethylene production remained low (below 0.1~0.2 µl/kg/h) and constant at 20°C. Increased ethylene production only occurred as fruit softened from 10N~19N to eating ripe (6~8N). These results have led to a model being proposed for ethylene action during ripening of kiwifruit. Kiwifruit softening (phases 1 and 2) occurs even though ethylene production is low as is ACS and ACO activity. It is possible that this basal level of ethylene corresponds to System 1 ethylene production which is thought be associated with basal metabolic maintenance; this ethylene probably binds to System 1 ethylene receptors. The changing ability of fruit to soften with increased maturity is due to increasing sensitivity to such low ethylene concentration resulting from the progressive formation of new ethylene receptors in the fruit. Application of AVG and 1-MCP reduced ethylene production, leading to a delay in ethylene-induced softening. It is possible that low endogenous ethylene (System 1 ethylene) is sufficient to induce starch degradation and solubilization of pectins in cell walls caused by hydrolase enzymes such as amylase, β-galactosidase and xyloglucan endotransglycosylase early in ripening. Alternatively oligomers derived from cell wall breakdown may induce ethylene production even though such oligomer elicitors have not been reported to exist in kiwifruit. Maximal cell wall swelling, depolymerization of the solubilized pectin by polygalacturonase and breakdown of the middle lamella only occur when kiwifruit already have softened to <20N (phase 3 of softening), and these events are associated with or co-ordinated by System 2 autocatalytic ethylene. This autocatalytic ethylene is associated with high ACS and ACO activity and may bind to System 2 ethylene receptors, leading to ethylene dependent responses such as PG activation which results in ready-to eat fruit with a firmness of 6~8N. In conclusion, kiwifruit softening from 90N to 10~19N occurs with low and constant ethylene production. Because new ethylene receptors of kiwifruit can be formed with time at both 0°C and 20°C, it appears that kiwifruit sensitivity to low ethylene concentration also increases with time in storage. It is possible that different cultivars of kiwifruit with different softening rates, may have different amounts or rates of formation of new ethylene receptors. By comparing physiological, biochemical and molecular attributes of Hayward and other kiwifruit cultivars and selections, it should be possible to provide information on their responsiveness and sensitivity to ethylene. This will allow plant breeders to create new cultivars that have both low ethylene production and low sensitivity to ethylene that would provide a range of commercial cultivars with prolonged and different storage lives for the international kiwifruit market. Application of inhibitors of ethylene biosynthesis (AVG) and ethylene action (1-MCP) reduced ethylene production and softening rate of kiwifruit with 1-MCP being more effective for longer than AVG. Although 1-MCP showed promise as a tool to delay softening during storage at 0°C and shelf life at 20°C, further research is required to determine optimum concentration, time and frequency of application, and efficiency when applied at 0°C in order to derive treatments that may have significant commercial applications.