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Item The dynamics of milk emulsion structure during in vitro neonatal gastric digestion : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Food Technology at Massey University, Palmerston North, New Zealand(Massey University, 2015) Lueamsaisuk, Chalida"Summary": Efficient fat digestion is an essential part of neonatal development. In this respect, it is noteworthy that the process by which infants digest fat differs from that in adults; key differences include the immaturity of the pancreatic function and elevated gastric pH. The digestion of emulsified lipids may accordingly be rendered less efficient in ambient conditions in the infant gastric lumen. For example, it may be postulated that covariation in optimal conditions of proteolytic and lipolytic digestion may differently affect the digestion and disruption of the droplet membrane, the interfacial accessibility of lipase and the subsequent fatty acid production. Differences between formulated emulsion structures may therefore influence the rate of digestion; previous human studies have indicated that infants digest formula feeds more slowly than they do breast milk (Splinter and Schreiner, 1999). To further explore this observation, the lipid digestion of native biological milk (human breast milk), commercial infant formulae (liquid and powder), and model emulsions (Intralipid containing lactoferrin) were investigated in an in vitro gastric system. The aim was to gain a better understanding on the changes in emulsion structure and fat digestibility with various interfacial layers and pH environments under simulated gastric conditions. The introduction and a rationale for the focus of this thesis are shown in Chapter 1. Chapter 2 gives a critical overview and review of the literature pertaining to this thesis, and presents possible explanations of how the properties of milk fat globules and their membranes are related to the digestion outcome in the digestive system of infants. The review also examines the effects of physicochemical factors on emulsion stability. Then, Chapter 3 presents the general materials and methods used in the experimental work. The first experimental design is described in Chapter 4. This chapter compares the characteristics and physicochemical properties of different types of milks. Infant formulae are prepared from cow’s milk and designed to mimic human milk as much as possible. However, even with the advances of technology, there are still differences observed between the breast milk and commercial infant formulae. Therefore the microstructure, droplet size and droplet charge of these different types of milk (human milk, raw cow’s milk, commercial liquid formulae and commercial powder formulae) were examined before studying the emulsion digestibility under simulated infant physiological conditions. Chapter 5 gives a description on how digestion affects emulsion structure of a typical formula emulsion at different pH levels (25.5) in an in vitro system that replicates the shear rates that would normally be encountered in the infant stomach. The system is designed to simulate infant gastric conditions using different combinations of porcine pepsin and fungal lipase (Rhizopus oryzae). Thus, digestion in the presence and absence of proteolytic and lipolytic enzymes was evaluated by observing changes in microstructure, particle size and surface charge. In liquid infant formulae, droplet size increased progressively by coalescence during in vitro digestion at pHs between 3.5 and 4.5 when both lipase and protease were present, but not when either enzyme was omitted or when pH levels were outside this range. Coalescence was augmented by shear, notably at rates above the normal physiological range. The fidelity of in vitro systems did not appear to be compromised by the use of fungal lipases but compromised by the use of inappropriately high stirring rates. The stability and structural properties of formula emulsions appeared to be influenced by disruption of the proteinaceous oil/water interface during digestion, being most susceptible to the concerted activity of pepsin and gastric lipase over a limited range of pH. Given that the onset of secretion of pepsin, lipase and hydrochloric acid does not occur synchronously in the developing infant stomach, inappropriately formulated milks may lower digestive efficiency. Chapter 6 progresses the findings from chapter 5, employing a model phospholipidstabilised emulsion which was digested alone, and in combination with the milk protein lactoferrin. It was postulated that the lactoferrin would form an electrostatic layer-on-layer complex with the phospholipid allowing comparison to be made between digestion of the phospholipidstabilised emulsion and the emulsion stabilised by lactoferrinphospholipid complex. Lipolysis of untreated Intralipid, as evidenced by the increase in droplet size i.e. d43 and by confocal microscopy, took place at pH levels between 3.5 and 5.5. Coalescence was evident with lipase alone and with mixtures of pepsin and lipase at pH 3.5, but did not occur in the presence of pepsin alone. Conversely, no coalescence was evident on digestion of Intralipid treated with lactoferrin, with lipase alone at pH levels below 5.5. However, coalescence of droplets in treated Intralipid did take place at pH levels above 2 when both pepsin and lipase were present. Changes in surface potential indicated that interfacial proteolysis was required for lipase-mediated coalescence to occur. Findings indicated that the interaction of lactoferrin with the oil/water interface of soybean oil droplets may have inhibited the action of lipase pending digestion by pepsin. The findings of Chapter 5 and 6 demonstrate the co-dependent role of proteolytic and lipolytic enzymes on the stability of emulsions during digestion, and the contribution of pH on enzymatic function. This knowledge should be a key factor for the design of emulsion structures in infant formula emulsions. Chapter 7 describes how digestion affects the structure of human breast milk. Fat droplets showed no significant propensity towards flocculation and aggregation during incubation both with and without either enzyme at all pH. Additionally, the breast milk emulsion was seen to be resistant to coalescence across all pH’s and enzymatic conditions studied. The difference in structural behaviour is attributed to variance in lipid composition of the MFG relative to the emulsion systems studied in chapters 5 and 6. Accordingly, it is suggested that the by-products of lipolysis of the breast milk emulsion may serve to stabilise droplets rather than cause instability. Thus the MFGM of maternal milk is not considered inhibitory to the action of either of these two enzymes (porcine pepsin and fungal lipase) under in vitro simulation of infant gastric conditions. Chapter 8 describes the overall conclusions and addresses the major findings and recommendations for future work.Item The effect of milk fat globule membrane damage in the absence of air on fouling in heat exchangers : a thesis presented in partial fulfilment of the requirements for the degree of Master of Technology in Food Technology of Massey University(Massey University, 1998) Fang, LeThe fouling by whole milk of processing plant surfaces, especially in heat exchangers, is a serious problem, but is incompletely understood despite extensive past investigations. While milk fat has generally been thought to play a minor role in fouling, the results of some previous work suggest that this is not always the case. The state and form of the fat, as well as processing conditions, may have effects on milk fouling behaviour. Careless mechanical handling of whole milk is known to cause fat damage. The present study set out to investigate the effect on fouling of damage to the milk fat globule membrane (MFGM) by mechanical stresses in the absence of air. Pasteurised non-homogenised whole milk was deliberately stressed to differing degrees by passing it through a cavitating pump a variable number of times. The extent of damage was measured using four different techniques: a free fat (FF) test (a modified extraction method), a lipolysable free fat (LFF) test (free fatty acid determination after incubation of the sample with pig pancreatic lipase, a technique developed during this work), particle size distribution (PSD) measurement by laser light scattering, and confocal laser scanning microscopy (CLSM). The fouling behaviour of both damaged and undamaged milk was investigated by heating the milk from about 4°C to about 94°C in a custom built double pipe heat exchanger, which could be disassembled easily to access the fouling layer. Milk flowed in the annulus, with a Reynolds number range of about 220-310. The fouling rate was measured and expressed as the rate of increase of the overall resistance to heat transfer, normalized using the overall heat transfer coefficient determined at the start of a run. The fouling rate exhibited by damaged milk (normalized by the rate for undamaged milk, to account for batch-to-batch variation) was found to increase significantly with the extent of cavitation treatment. There was also a clear positive relationship between both the FF and LFF contents of milk and the extent of cavitation treatment, suggesting strongly that the observed increases in fouling rate were the result of increased MFGM damage. PSD measurement and CLSM both showed that cavitation caused the appearance in the milk of some large, irregularly shaped fat globules, presumably the result of coalescence. The FF results, and observation by CLSM, indicated that only a small proportion (> 6°C) of the total milk fat had to be measurably damaged to cause extensive fouling. The fat contents of the fouling layers were found to be very high (>45% on a dry weight basis). Although some of the experimental conditions, especially the low Reynolds numbers, may have contributed to this result, other fouling investigations made in New Zealand have produced similar results. It is hypothesised that large globules formed by the coalescence of native globules whose membrane have been damaged could migrate more easily to the stainless steel heating surface. There, they could act as anchor points for the build-up of a fouling layer with a continuous protein phase. This hypothesis is supported by CLS micrographs of the fouling layer. Further investigation is warranted. Recommendations are made for improving the methods used to measure MFGM damage, fouling and fouling rate, and the structure of the fouling layer.Item The effect of a milk lipid fraction on bone properties of growing female rats and the growth and function of bone cells : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Human Nutrition at Massey University, Manawatu, Palmerston North, New Zealand(Massey University, 2014) Cao, ZhonglingObjective: To investigate the effects of a milk lipid fraction (MLF) on the accruel of bone mass in growing rats by evaluating the effects of MLF on growth and bone parameters such as bone mineral content (BMC), bone mineral density (BMD) and biomechanical properties in growing rats and the effects of MLF on the development and activity of bone cells, including osteoblasts and osteoclasts. Methods: There were one hundred and eight 3-month old female Sprague-Dawley rats were randomly allocated into three groups: a control group (n=48), a low-dose MLF group (n=30) fed with 250 mg/rat/day of MLF, and a high-dose MLF group (n=30) fed with 500 mg/rat/day of MLF. Forty-five rats (n=15 for each group) were selected to terminate at month 3 for biomechanical testing while sixty-three continued into a second arm of the trial after ovariectomy. Body composition and bone parameters of animals (n=108) were measured in vivo by Dual Energy X-Ray Absorptiometry (DEXA) at baseline and week 12 of the study. Length and diaphyseal width and thickness of the left femur were measured. The three-point bending test was used to evaluate the biomechanical characteristics of the left femur of rat. The effect of MLF on proliferation, differentiation and mineralization of murine osteoblasts were investigated using the osteoblastic cell line MC3T3-E1. The cells were cultured with 0-1,000 µg/ml or 0-100 µg/ml MLF for 5, 9 and 24 days, respectively for proliferation, differentiation and mineralization. Cell proliferation was determined using the methyl-thiazolyl tetrazolium (MTT) assay. The differentiation of osteoblasts was detected using the alkaline phosphatase (ALP) activity assay. Mineralized nodules were examined using an Alizarin red histochemistry assay. The effect of MLF on RANKL-induced osteoclastogenesis was evaluated in the murine monocytic cell line RAW264.7. The cells were cultured with 0-100 µg/ml MLF for five days. Osteoclastogenesis was determined using the tartrate-resistant acid phosphatase (TRAP) staining assay and counting numbers of TRAP-positive multinucleated cells. Results: Rats fed with the high-dose MLF diet had a significant increase in body lean mass compared with those fed with the control and low-dose MLF diets. The high-dose MLF group also had significant gains in BMC at the femur and in BMD at the femur and lumbar spine compared with the control group. There were no significant differences in dimensional and biomechanical results among groups. The MLF significantly increased the proliferation of MC3T3-E1 at 0.1, 1.0 and 100 µg/ml. There was a dose-dependent, but not significant increase in the differentiation of osteoblasts cultured with MLF for 9 days. After 24-days of cell culture, the MLF at the low concentrations of 0.1 and 1.0 µg/ml led to non-significant increase in calcium deposition by the differentiated osteoblasts. MLF at 10 and 100 µg/ml significantly inhibited calcium nodule formation. RANKL-stimulated osteoclastogenesis was significantly increased in RAW 264.7 cells cultured with the MLF at concentrations up to 10 µg/ml. Conclusion: These results indicated that oral administration of MLF to the growing rats improved bone accrual and has a favourable effect on achievement of peak bone mass. The MLF increased the proliferation of MC3T3-E1 pre-osteoblast cell line, but there was no effect on osteoblast differentiation and the higher concentration of MLF may have inhibited the function of mature osteoblast. Additionally, the MLF stimulated osteoclastogenesis from RAW264.7 cells. Further studies are required to investigate some of the contradictory findings presented in this report.Item Blood metabolite and hormone concentrations of dairy calves differing in genetic potential for milk fat production : a thesis presented in partial fulfilment of the requirements for the degree of Masterate of Agricultural Science in Animal Science at Massey University(Massey University, 1985) Xing, Guo QiangThe present study was conducted at the Massey University Dairy Research Unit to investigate the effect of genetic merit for milk fat production on the physiology and metabolism of Friesian calves. Twenty four Friesian calves divided into four groups namely High Breeding Index (HBI) heifers, HBI bulls, Low Breeding Index (LBI) heifers, and LBI bulls were challenged with four different experimental treatments, ie. fasting, feeding, intravenous arginine infusion, and subcutaneous synthetic corticosteroid injection at ten to eighteen days of age. A total of eighteen blood samples were collected from each calf through an indwelling jugular cannula and the concentrations of plasma glucose, insulin, GH and cortisol were determined. Some statistically significant differences were found in plasma metabolite and hormone concentrations between the HBI and LBI groups. 1. The basal glucose concentration in HBI group was significantly higher than that in LBI group (P<0.05). The basal plasma insulin concentration was also significantly higher in HBI group than in LBI group (P<0.01). The basal GH concentration in HBI calves was higher in HBI calves than in LBI calves, but the difference was not quite significance at 5% level (P=0.059). 2. Following feeding, plasma insulin and GH concentrations in HBI group were significantly higher than those in LBI group (P<0.01, P<0.05 respectively). 3. Acute intravenous arginine infusion induced hyperinsulinemia and hypoglycemia in all calves. LBI calves had significantly higher increments of plasma insulin measured as a percentage of basal levels than HBI calves. The response of GH concentration to arginine challenge differed significantly in terms of level and pattern between HBI and LBI groups, with the HBI calves having more prolonged higher GH concentration than LBI calves (P<0.05). 4. Subcutaneous injection of synthetic corticosteroid resulted in significant increments in plasma glucose and insulin concentrations, and a significant decrease in endogenous cortisol production in all calves. (P<0.01, P=0.05, P<0.01 respectively). But no significant differences were detected between HBI and LBI groups. Effects of sex on plasma metabolite and hormone concentrations were also found in the present study. Plasma insulin concentration was consistantly higher in bulls than in heifers and the differences were significant at the time of fasting, after feeding, and after arginine infusion (P<0.01). Plasma glucose concentrations following feeding were significantly higher in bulls than in heifers (P<0.05). GH concentration was slightly but not significantly higher in bulls than in heifers for most of the experiment. It was concluded that differences exist in some important metabolic and endocrinological characteristics between HBI and LBI calves, and these differences could become significant under certain physiological conditions and experimental treatments such as those applied in the present study. This study also showed the promise of identifying genetically superior Friesian dairy cattle at an early age by using physiological markers. However this possibility has yet to be tested by earring out measurements on calves for which breeding index value for milk fat production will be determined by methods such as progeny test.Item Behaviour of fat globules and membrane proteins under different processing environments as related to milk powder manufacture : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Food Technology(Massey University, 2003) Ye, AiqianThe objective of the first part in this study was to gain a better understanding of the protein components of the milk fat globule membrane (MFGM). In the second part, the influence of processing factors on the fat globules and the MFGM during the manufacture of whole milk powder were examined. Relationships between the state of the MFGM in whole milk powders and their reconstitutions properties were also explored. The MFGM proteins, isolated from early-, mid- and late-season fresh whole milks, were characterized using one- and two-dimensional sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) under reducing and non-reducing conditions. SDS-PAGE under reducing conditions showed the presence of about 40 protein bands, ranging in molecular weight from 15 to 200 kDa. The major MFGM proteins e.g., xanthan oxidase, butyrophilin, PAS 6 and PAS 7 constituted 60-70% of total MFGM proteins while 20-30% were minor proteins. Two-dimensional SDS-PAGE indicated that xanthine oxidase and butyrophilin might be complexed via intermolecular disulfide bonds in the natural MFGM. The examination of MFGM proteins heated at > 60 °C in the absence of skim milk proteins (caseins and whey proteins) showed that xanthine oxidase and butyrophilin interacted further to form very high molecular weight protein complexes, whereas PAS 6 and PAS 7 were relatively heat stable and did not form complexes. Heat treatment of fresh whole milk in the temperature range 65-95 °C caused incorporation of β-lactoglobulin (β-1g) into the MFGM. Small amounts of α- lactalbumin (α-la) and κ-casein were also observed in the MFGM material of heated milk. The amounts of β-lg and α-la that associated with the MFGM increased with an increase in temperature up to 80 °C, and then remained almost constant. The maximum values for β-lg and α-la association with the MFGM were ~1.0 mg/g fat and ~0.2 mg/g fat, respectively. Association of β-lg and α-la with the MFGM was described by a first-order reaction (65-85 °C for β-lg and 70-80 °C for α-la) in the low temperature range and by a second-order reaction in the high temperature range (85-95 °C for β-lg and 80-95 °C for α-la). Arrhenius plots showed an abrupt change in temperature dependence of the rate constants at 85 °C for β-lg and 80 °C for α-la. Of the major original MFGM proteins, xanthine oxidase and butyrophilin were not affected by the heat treatment of whole milk, whereas PAS 6 and PAS 7 decreased during heating. Interestingly, this behaviour is in contrast to that shown by these proteins in systems containing no skim milk proteins. The changes in fat globule size and MFGM proteins during the manufacture of whole milk powder were determined using light scattering, SDS-PAGE, confocal laser scanning microscopy (CLSM) and transmission electron microscopy (TEM). Heat treatment of whole milk by direct stream injection (DSI) prior to evaporation caused a decrease in the fat globule size and an increase in the MFGM protein, through the association of caseins and whey proteins with the MFGM material. Evaporation of milk by a multiple-effect falling film evaporator caused a gradual decrease in the fat globule size and an increase in the MFGM protein after each effect. Caseins dominated the total MFGM protein, indicating the adsorption of casein micelles to the newly formed surface of the fat globules during evaporation. When whole milk was preheated (95 °C for 20 s) before evaporation, the amounts of total MFGM protein were higher (~6 mg/m2 compared to ~4 mg/m2 for the non-preheated whole milk) because of association of whey proteins with the native MFGM proteins and casein micelles. The average fat globule size decreased further upon homogenisation of the concentrated milk. The amount of MFGM protein (mg/m2) of concentrated milk also increased after homogenisation, the extent of the increase being dependent upon the temperature and pressure of homogenisation. Furthermore, heat treatment of concentrated milk to 79 °C either before or after homogenisation also increased the amount of MFGM protein. However, at the same homogenisation temperature and pressure, the amounts of whey proteins in the MFGM of the concentrated milk that was heated after homogenisation were higher than the concentrated milk that was heated followed by homogenisation. The amounts of the major native MFGM proteins did not change during homogenisation, indicating that the skim milk proteins did not displace the native MFGM proteins but adsorbed onto the newly formed surface. The fat globule size of homogenized concentrated milk decreased after spray drying, while the amount of MFGM protein (mg/m2) decreased slightly. Some "uncovered fat" was observed on the surface of powder particles. It is possible that the proteins do not adsorb to all newly formed fat surfaces during spray drying. The reconstitution properties of whole milk powders produced using different processing treatments were determined. High homogenization pressure and temperature used before spray drying resulted in poor reconstitution properties of the powder, particularly when the heat treatment was carried out after homogenization. It is suggested that the proteins adsorbed at the fat globule surfaces during homogenisation of the concentrated milk and their subsequent aggregation during heat treatment play a key role in determining the reconstitution properties of whole milk powders.Item Modifications in the structure of the triacylglycerols of bovine milk fat : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Biochemistry at Massey University(Massey University, 1976) Morrison, Ian MalcolmA pair of monozygous twin cows was used to investigate the influence of the increased availability of linoleic acid (18:2) to the mammary gland, on the structure and physical properties of the milk triacylglycerols (TGs). The cows were grazing fresh pasture, and in addition one of the pair was provided with a daily supplement of encapsulated sunflower oil. The milk fat of the cow given the supplement (18:2-rich milk fat) contained 15.5% 18:2 compared with 1.8% 18:2 in the milk fat of the other cow (control milk fat). This increase in the proportion of 18:2 in the milk fat was accompanied by decreases in the proportions of myristic acid (14:0) and palmitic acid (16:0). The effect of this altered fatty acid (FA) composition on the TG composition of the 18:2-rich milk fat was to increase the proportions of TGs with 40, 52 and 54 acyl carbons and to decrease the proportions of TGs with 34, 36, 38, 44, 46, 48 and 50 acyl carbons relative to the proportions in the control milk fat. Both milk fat samples were separated, by column chromatography on silicic acid, into TG fractions of high, medium and low molecular weight. The relative proportions of the TG fractions of high, medium and low mol. wt. in the 18:2-rich milk fat were 43.0, 19.5 and 37.5% respectively compared with 36.1, 19.7 end 44.2% respectively in the control milk fat. Stereospecific analysis of these triacylglycerol fractions demonstrated that in fractions of similar mol. wt., the distribution of fatty acids within the TG molecule in the presence of high levels of 18:2, was not appreciably altered from that in the triacylglycerol fractions of the control milk fat. The positional distribution of fatty acids in the triacylglycerols of the total milk, fats was also similar. In the milk fat, containing high levels of linoleic acid, 18:2 showed a preference for positions 1 and 2 in the triacylglycerols of the low and medium mol. wt. fractions, and for positions 2 and 3 of the high mol. wt. fraction. The three TG fractions of each milk fat were further resolved into TG classes of differing levels of unsaturation. The 18:2-rich milk fat contained higier levels of the unsaturated TGs, namely the diene, triene and tetraene TGs, and lower levels of the saturated TGs and to a lesser extent the monoene TGs. The diene TGs of the 18:2-rich milk fat included combinations of 18:2 with two saturated FAs, which are a minor constituent of normal milk fats. Likewise the triene TGs reflected the presence of 18:2 in combination with 18:1 and a saturated FA. The thermal properties of the two milk fats were examined to investigate the influence of the altered TG composition and structure on the physical characteristics of the milk fat. The 18:2-rich milk fat melted at a lower temperature than the control milk fat with a large proportion of the sample melting over the narrow temperature range between 5 and 15°C. In contrast the control milk fat melted over a much wider temperature range.Item The physical properties of triacylglycerols in relation to milkfat : a thesis presented for the degree of Doctor of Philosophy in Chemistry at Massey University(Massey University, 1977) Norris, RobertEnantiomeric and racemic triacylglycerols (TGs) representative of the major structural classes in milkfat were synthesised and their polymorphism was characterised by differential scanning calorimetry (DSC) and infrared (IR) spectroscopy. With butyric (B), oleic (O), palmitic (P) and stearic (S) acids as starting materials, 22 racemic TGs were prepared. The main TG classes were: 1) palmitoyl-stearoyl TGs (e.g. PSS), 2) 1-butyryl TGs (BPS), 3) 1-oleoyl TGs (OPS), 4) 2-oleoyl TGs (POS), 5) 1-butyryl-2-oleoyl TGs (BOS) and 6) 1,2-dioleoyl TGs (OOS). Three TGs containing elaidic acid (E) were also synthesised (BES, ESS and SES). In addition, enantiomers of three of the racemic TGs belonging to the 1-butyryl and 1-oleoyl classes were prepared (sn-SSB, -SSO and -PPO). The polymorphic forms of each TG were classified as α, β' or β by comparison of their the spectra with the spectra of the polymorphic forms of monoacid TGs. Solvent crystallised forms were also characterised by X-ray powder diffraction. Melting points of all polymorphs and heats of fusion of the least stable (α) and most stable forms were determined by DSC. However, the determination of the polymorphic assignment and heat of fusion of the intermediate forms was often uncertain because of the difficulty in obtaining a pure phase. The principal findings were:- 1) Corresponding enantiomeric and racemic TGs exhibited similar polymorphic behaviour except that the α forms of the enantiomers transformed more rapidly than those of their racemates. 2) For TGs in which one fatty acid was very different from the other two (e.g. BSS, OOS), the position of the unusual acid determined the chain packing of the stable form. If the acid was in a primary position, the TG was β'-stable (e.g. BSS, OSS, OOS), while if it was in the secondary position, the TG was β-stable (e.g. SOS, SBS). 3) There were close parallels between the stable forms of corresponding butyryl and oleoyl TGs (e.g. BSS, OSS; SBS, SOS; BOS, OOS), although in other respects their polymorphism had little in common. The stable forms of BSP and OSP showed anomalous thermal, diffraction and spectral data compared with the remaining 1-butyryl and 1-oleoyl TGs. 4) The results obtained for the 1-oleoyl, 2-oleoyl and 1,2-dioleoyl TGs were in general agreement with earlier reports, although some differences were noted in the transformation of OSP, OPS, SOS and POP. Furthermore, previously undetected transitions were observed for all the oleoyl TGs, although these were minor. A new polymorph of OPP was also characterised. With the exception of POS, all monooleoyl TGs showed anomalous crystallisation behaviour. 5) The results for the polymorphism of the palmitoyl-stearoyl and elaidoyl-stearoyl TGs were also in accord with previous reports. The presence of a β'2 form was confirmed for all TGs except SPS and PSP. The heats of fusion of the β forms of SPS and PSP were comparable with those of their unsymmetrical counterparts, PSS and PPS, but the heats of fusion of their stable β' forms were much higher than those of β' SSS, PSS, PPS and PPP. These findings are discussed in relation to the principles of close packing and their relevance to the phase behaviour of milkfat.Item A study of the structure of triacylglycerols of bovine milk fat : a thesis presented for the degree of Doctor of Philosophy in Biochemistry at Massey University(Massey University, 1973) Taylor, Michael WilliamSamples of milk fat obtained at different stages of the dairying season were investigated to determine the influence of the observed seasonal changes in the fatty acid (FA) compositions of New Zealand milk fats on the structure of milk triacylglycerols (TG1s) . Of the three milk fats studied the January and March samples had FA compositions typical of hard summer milk fat, while the September sample had a FA composition typical of soft spring milk fat . Each of the three selected samples of milk fat was effectively separated into TG fractions of high, medium and low molecular weight which had distinctly different FA and TG compositions. Stereo specific analyses o f these fractions showed that in TG fractions of similar average molecular weight the arrangement of FA 's within the TG ' s was similar and that in all TG fractions the FA 's were arranged within positions 1 , 2 and 3 of the TG1s in a highly selective manner. The TG fractions were separated into TG classes of different degrees of unsaturation. Corresponding TG c lasses of the three samples of milk fat had generally comparable FA compositions. However an important distinguishing feature was that each TG fraction of the September sample contained a higher proportion of unsaturated TG's than the corresponding TG fractions of the January and March samples. Thus in New Zealand milk fats of differing FA composition, the nature of the TG species is similar but there exist differences in the relative proportions of the TG species. The variation in the proportions of the constituent TG species of New Zealand milk fat would appear to be the overriding factor whic h influences the seasonal variation in its physical characteristics. The thermal properties of TG fractions of milk fat were examined with a view to determining the influence of TG structure on the physical characteristics of milk fat. It was found that the unsaturated TG's of low molecular weight , were largely responsible for the considerable proportion of milk fat which melted below 0º C and consequently for the wide melting range which is characteristic of milk fat. The structural difference between these TG's and the remaining TG' s of milk fat was found to be sufficiently large to prevent significant formation of solid solutions. Consequently the wide melting range of milk fat is due to both the large number of different TG species and to the large structural difference between the various TG species.Item Structure and properties of liposomes prepared from milk phospholipids : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Food Technology(Massey University, 2005) Thompson, Abby KerrinThe isolation of milk fat globule membrane (MFGM) material from buttermilk on a commercial scale has provided a new ingredient rich in phospholipids and sphingolipids. The aim of this project was to explore the possibility of producing liposomes from MFGM-derived phospholipid matieral (Phospholac) and to compare the properties of these liposomes with those produced from commercial soy phospholipid fractions (SigP3644 and Ultralec). The technique used for liposome production was to be suitable for use in the food industry. All three phospholipid fractions were primarily composed of phosphatidyl choline and phosphatidyl ethanolamine, but the dairy-derived Phospholac also contained approximately a third sphingomyelin. It also had a more highly saturated fatty acid profile, and contained a significantly higher proportion of protein than the soy-derived fractions. The phospholipid fractions were dispersed in an aqueous system and cycled through a Microfluidizer® (a high-pressure homogeniser) to successfully produce liposomes. These were then characterised using a wide range of techniques. The hydrodynamic diameter of the liposomes, measured using Photon Correlation Spectroscopy, ranged from an average of ~95 nm for the Phospholac dispersion to ~80 nm for the SigP3644 and Ultralec samples. All three dispersions had a very wide particle size distribution. Electron microscopy showed that all three dispersions appeared to be primarily unilamellar, but there was a small percentage of multilamellar and multivesicular liposomes. The unilamellar nature of the dispersions was further supported by the small-angle X-ray diffraction images and 31P-NMR results. The SigP3644 dispersion had a much higher permeability than either the Phospholae or Ultralec sample, with minimal difference between the Phospholac and Ultralec samples at either 20 or 40 °C. Differential scanning calorimetry (DSC) found that SigP3644 and Ultralec had phase transition temperatures below 0 °C, while Phospholae dispersions showed a very broad transition with a centre between 28 and 30 °C. However, these differences did not appear to relate to the membrane permeability at its phase transition temperature. The Phospholae and Ultralec bilayers were approximately 20% thicker than SigP3644 membranes, with no significant change in thickness between 20 and 40 °C. The liposomes produced from the Phospholac fraction showed considerably improved stability under a variety of environmental conditions than those produced from soy phospholipids. The Phospholac dispersions were able to withstand more severe processing treatments, were stable for longer periods at higher storage temperatures, and were less affected by changes in pH and in ionic concentration. It is thought that these differences are due to the high sphingomyelin concentration and more saturated fatty-acid profile of the dairy-derived fraction. There were noticeable differences in entrapment characteristics of the fractions. It was found that the entrapment efficiency of hydrophobic compounds was directly proportional to the solubility of the compound in the solvent phase used for dispersion. Hydrophilic entrapment was also investigated, but the rapid diffusion of the small hydrophilic molecules through the liposome membrane prevented quantification of the entrapment efficiency. To produce liposome dispersions suitable for the encapsulation of hydrophilic material, further work must be completed to reduce the membrane permeability. Differences in the properties of the liposome dispersions appear to be related to the composition differences between the phospholipid fractions, and it may be possible to exploit the unique composition of the MFGM phospholipid material in the delivery of bioactives in functional foods.Item Studies on the effects of heat and high pressure treatmeants on fat globule surface layers in recombined milk : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Food Technology at Massey University, Manawatu, New Zealand(Massey University, 2011) Anantawat, VisakaThe present study examined the effects of heat treatment, high pressure (HP) treatment or combined heat and HP treatments, either before or after homogenization, on recombined milk systems. The main focus was to explore the changes induced by these treatments on the surface layers of recombined fat globules, milk proteins and rheological properties of acid gels. Heat treatments caused denaturation of whey proteins; the degree of denaturation was dependent on temperature, holding time and to a lesser extent on the placement of heat treatment. Recombined milks that underwent heat treatment before or after homogenization had similar levels of whey protein denaturation. The amounts of caseins and denatured whey proteins adsorbed on the surface of fat globules of recombined milk heated before homogenization were significantly lower than those heated after homogenization, indicating different interaction mechanisms in these two systems. Increases in treatment pressure used in HP treatment resulted in decreased amounts of caseins, while whey proteins adsorbed onto the surface layers of fat globules increased. This was probably due to the dissociation of casein micelles under HP treatment and the interactions between HP-induced denatured whey proteins and casein particles on the surface layers of fat globules. Combined heat and HP treatments induced changes on adsorbed caseins and whey proteins on fat globule surface layers. HP treatment induced additional denaturation of whey proteins in heated milks, resulting in slightly increased amounts of denatured whey protein adsorbed onto the surface layers. Gelation pH, final G? and yield stress values of acid gels prepared from recombined milks heated before or after homogenization were dependent on temperature, holding time and the placement of heat treatment. These changes were attributed to the extent of denaturation of the whey proteins and their interactions with casein particles adsorbed onto the fat globule surface and in the serum. Differences in acid gels prepared from recombined milks heated before and after homogenization were attributed to the relative proportions of caseins and whey proteins at the surface layers of fat globules resulting in different interactions with protein strands in the gel network. The acid gels prepared from recombined milks HP-treated either before or after homogenization had shorter gelation times, higher gelation pH, final G? and yield stress values compared with untreated recombined milk and the effects were dependent on treatment pressure, temperature, holding time and the placement of HP treatment. The denaturation of whey proteins and their interactions with casein particles were responsible for these changes. In HP-treated recombined milks the proportions of caseins and denatured whey proteins adsorbed onto the surface layers of fat globules had significant effects on the acid gel structure. When HP treatment was applied after homogenization, the proteins on the surface layer were present as a layer which might provide better sites for the interactions with the protein strands in the gel matrix. The application of these processing treatments to recombined milk could provide new avenues to the dairy industry for manufacturing novel products with enhanced texture and nutritional properties.