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Item Effect of protein polymorphisms on milk composition, coagulation properties, and protein profile in dairy sheep(Elsevier Ltd, 2025-01-01) Marshall AC; Vigolo V; De Marchi M; Lopez-Villalobos N; Loveday SM; Weeks M; McNabb WThe objective of this study was to quantify the effect of protein polymorphisms on milk composition, coagulation properties, and protein profile in dairy sheep from a New Zealand flock. A total of 470 test-day records, from 147 lactating ewes, were used in the statistical analyses. Protein polymorphisms observed in the RP-HPLC were self-named for purposes of the present study. Data were analyzed using a mixed linear model, including the fixed effects of ewe age, litter size, coat-colour, and stage of lactation, and, as a covariate, deviation from the median lambing date of the flock. The effects of protein polymorphisms were added to the model, one at a time. Protein polymorphisms were significantly (p < 0.05) associated with milk composition and protein profile. Polymorphisms of β-lactoglobulin were significantly associated with milk heat stability, being AB type more heat stable than AA. The other processability traits were not significantly affected by protein polymorphisms. Further studies are required to confirm the protein variants and the properties of individual protein polymorphisms.Item Differentiation between organic and conventionally produced milk in pasture based farming systems : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Animal Science at Massey University, Palmerston North, New Zealand(Massey University, 2017) Schwendel, Brigitte HeikeConsumer perception of organic cow’s milk is associated with the assumption that organic milk differs from conventionally produced milk. The value associated with this difference, justifies the premium retail price. It includes the perception that organic dairy farming is kinder on the environment, animals and people; that organic milk products are produced without the use of antibiotics, added hormones, synthetic chemicals and genetic modification and may have potential benefits for human health. Controlled studies investigating the chemical differences between organic and conventionally produced milk have so far fallen short of a conclusion as to whether or not these exist. Reasons for this are many folds, caused principally by the complexity of the research problem. A main complication is that farming practices and their impacts differ depending on country, region, year and season between and within organic and conventional systems. Factors influencing milk composition (e.g. diet, breed, and stage of lactation) have been studied individually, while interactions between multiple factors have been largely ignored. Studies fail to consider that factors other than the farming system (organic versus conventional) could have caused or contributed to, the reported differences in milk composition. These omissions make it impossible to determine whether there is a system related difference between organic and conventional milk, or not. The present study investigated the chemical differences between organic and conventionally produced milk in a pasture based farming system. Milk samples have been collected on two farm sets each comprised of one organic and one conventional farm. All farms applied year-round pasture grazing. Milk samples were collected from individual animals on Farm Set 1 and throughout the milking season on both farm sets. Milk samples have been analysed for fatty acid, free oligosaccharides, major casein and whey proteins, and milk fat volatiles, as well for a limited set of milk metabolites using a non-targeted NMR method. Considering the known influence factors on milk composition and the differences observed between the farms on the farm sets in our study, we postulated that fatty acids were influenced by breed and fertilizer application. Oligosaccharides differed between farming systems, with causes presently unknown. The farm set was the dominant influence factor on protein composition, while none of the compounds identified using NMR show any trend. Thus, the major conclusions from this study were that the factors influencing milk composition are not exclusive to either farming system, and pasture feeding conventional cows will most probably remove differences previously reported in other organic and conventionally produced milk studies.Item Phenotypic relationship between milk fatty acid profile and live weight change in early lactation in New Zealand dairy cattle : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Animal Science, Institute of Veterinary, Animal and Biomedical Sciences, Palmerstone North, New Zealand(Massey University, 2016) Mkunda, VedastusThe phenotypic relationship between milk fatty acid (FA) profile and live weight (LW) change in early lactation in grazing Friesian x Jersey (FxJ) cows was investigated in this study. Data used in this study compromised of 73,040 daily milk yields, 5,936 fortnightly herd-tests for fat, protein and lactose, 41,981 daily live weights, and 882 determinations of FA profiles from 300 second-lactation FxJ crossbred cows recorded during the production season 2003-04. Cows were classified based on the magnitude of LW change from calving to peak lactation into three groups: cows with low live weight loss (L; below -0.012kg), medium live weight loss (M; below -0.174kg and high live weight loss (H; below -0.340kg). LW change was considered as a proxy for energy balance. Correlations between LW change and individual FAs or group of FAs were estimated at the three stages of lactation (early, mid and late). Stage of lactation affected significantly (P>0.05) the concentration of all FAs considered in this study, except the concentration of C20:0. Higher concentration of C18:0 and C18:1 cis-9 was observed in early lactation relative to other lactation stages. Compared to the L and M cows, the H cows had higher concentration of C18:1 cis-9 in early lactation. Live weight loss in early lactation was significantly associated with higher concentrations of unsaturated (r = -0.19), long-chain FA (r = -0.17), C17:0 (r = -0.14), C18:1 cis-9 (r = -0.20) and C18:3 cis-9, cis-12, cis-15 (r = -0.21), but live weight loss was significantly associated with lower concentrations of saturated FA (r = 0.18), medium-chain FA (r = 0.16), C12:0 (r = 0.24), C14:0 (r = 0.17) and C15:0 (r = 0.22). The association between LW changes in early lactation and most of the FAs were not significant in mid and late lactation. If determination of FA can be implemented using mid-infrared spectroscopy, a conclusion from this study is that concentration C18:1 cis-9 in early lactation can be used as indicator of live weight change (energy balance). Further studies are required to evaluate the inclusion of concentrations of FAs in breeding programs to improve fertility in seasonal grazing dairy cattle.Item Physical and rennet coagulation properties of recombined cheese milk made from milk protein concentrate (MPC-56) : a thesis presented in partial fulfilment of the requirements for the degree of Master of Technology in Food Technology(Massey University, 1996) Pomprasirt, VisakaThe effects of heat treatment and homogenization on the physical and rennet coagulation properties of recombined cheese milk (40% total solids) made from reconstituted milk protein concentrate (MPC-56) (20%) and fresh frozen milkfat for recombination (FFMR) (20%) have been investigated. The effects of heat treatment of the concentrate prior to drying were also studied. Heat treatment, either during MPC powder manufacture or after reconstitution and recombination of MPC powder had a significant influence on whey protein denaturation, viscosity, and rennet coagulation properties of recombined cheese milk. The degree of whey protein denaturation, as determined by the decrease of soluble whey protein at pH 4.6, increased with increasing severity of heat treatment, and β-lactoglobulin A was more heat sensitive than β-lactoglobulin B and α-lactalbumin. Recombined cheese milk showed shear thinning behaviour, e.g. recombined cheese milks behaved as pseudoplastic materials. The viscosity of recombined cheese milk determined at a shear rate of 18.5 - 731 s increased with increasing severity of heat treatment, indicating aggregation of protein and fat particles. The changes in viscosity were related to the degree of whey protein denaturation and the interactions between whey proteins and casein micelles. The rennet coagulation properties of recombined cheese milk were determined in terms of gelation time (GT), storage modulus (G'), and the force required to fracture the renneted gels (yield force). In general, G' and yield force decreased with increasing severity of heat treatment. Gelation time appeared to remain unaffected by heat treatment, either of the recombined cheese milk or during MPC manufacture. There was an almost linear inverse relationship between G' or yield force and whey protein denaturation of up to ~ 60%. Further denaturation had no further effect. It is likely that denaturation and complex formation between whey proteins and casein micelles sterically interferes with the aggregation of altered casein micelles, resulting in slower increases in G' and yield force values. Compared to heat treatment, the degree of homogenization appeared to have a minor effect on the physical and rennet coagulation properties of recombined cheese milk. Increased homogenization pressure resulted in a decrease in average fat globule diameter and an increase in viscosity. Rheological parameters, i.e. G' and yield force of renneted-induced gels decreased as the homogenization pressure was increased. The changes in milk fat globule diameter and its surface composition are probably involved in this phenomenon. Microstructure examination and permeability measurements of renneted gels indicated that the casein networks were very strong and dense with limited porosity. Since increasing heat treatment and homogenization reduced the strength of renneted gels, with only a small effect on gelation time, it might be possible to use these two processes to counter the gel firmness problem of recombined cheese made from MPC powder.Item Interactions of iron, protein and orthophosphate in milk systems : 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, 2014) Mittal, Vikas AshokAlthough iron deficiency is the largest nutritional disorder affecting the human population, few food products in daily use are fortified with adequate (25% of daily requirements per serving) concentrations of iron. The interaction of iron with food components and the consequential deteriorative effects on colour and taste thwart its use as a fortificant of choice. Milk proteins, especially caseins, are a class of metallo-protein which chelate iron and prevent its interaction with food matrix. However, addition of high levels of iron to protein solutions causes precipitation. As iron and calcium bind to similar sites on the proteins in milk, the effect of calcium depletion on the iron-binding properties of the milk proteins was examined. A weakly acidic cation-exchange resin was used to remove three different levels i.e. 18‒22, 50‒55 and 68–72% of calcium from milk, designated as low, medium and high CDM respectively. The depletion of calcium from milk by ion exchange affected its physico-chemical properties, with the extent being highly dependent on the level of calcium depletion. The integrity of the casein micelles was retained at up to ~ 20% calcium depletion from normal milk, but there was substantial disintegration of the casein micelles at calcium depletion levels of > 50%. Five levels of iron (5, 10, 15, 20 and 25 mM) were added to each of these calcium-depleted milks (CDM) and the resultant milks were analysed for particle size, microstructure and the distribution of protein and minerals between the colloidal and soluble phases. The properties of the milks with different calcium contents were variably affected by the addition of iron. In both normal milk and the low CDM, the majority (> 90%) of the added iron bound to caseins within the casein micelles, minimally affecting the hydrodynamic diameter, ζ-potential and protein distribution. Protein solubility was adversely affected in the medium CDM, whereas most of the protein and the added iron were associated with the non-sedimentable phase in the high CDM. The high concentration (~ 20 mM) of ferric iron in the non-sedimentable phase of the high CDM (~ 70% calcium depletion) presented a distinct advantage of the calcium depletion process over traditional processes for the iron fortification of milk systems. However, a reduction in aqueous phosphorus, in proportion to added iron, was observed in all milk systems. The addition of orthophosphate prevented aggregation and promoted the formation of small fibrous structure particles in calcium-depleted milk by reducing inter-particle iron bridging. In contrast, added orthophosphate promoted the formation larger unstable aggregates in calcium-depleted milk upon calcium re-addition. The differing effects of added orthophosphate on the iron and calcium-induced aggregation of proteins in calcium-depleted milk were related to the binding characteristic of respective cations. The inclusion of iron in the calcium-restored milk generated substantially smaller aggregates, which were promoted by the addition of orthophosphate. The presence of iron probably blocked the polymerisation pathway required for casein micelle structure formation but not the interaction of calcium with caseins. The effect of orthophosphate addition on the iron-induced aggregation of caseins in sodium caseinate was examined. The binding of iron at greater than equimolar concentration of organic phosphorus on caseins resulted in the precipitation of both the iron and caseins. In the presence of orthophosphate, however, higher concentrations of iron could be added to sodium caseinate solution (~ 6.9% by weight of casein) with little sedimentation of protein. The presence of orthophosphate prevented iron-induced casein precipitation in sodium caseinate solutions and also improved the solubility of iron. The formation of small aggregates upon iron addition to sodium caseinate solution containing orthophosphate was responsible for the high solubility of casein-iron complexes. The 31P-NMR study, SDS-PAGE and size exclusion chromatography analysis of the soluble casein-iron complexes revealed that a cluster of inorganic ferric phosphate was stabilised by caseins. The concentration of iron bound by caseins in the soluble form was at least 5 to 10 times higher than in previous studies, thus creating an opportunity to develop an iron ingredient for food fortification. The effect of exchanging the sequence of adding iron and orthophosphate to sodium caseinate solutions was examined. Surprisingly, the casein-iron precipitates (formed upon > 5 mM iron addition to sodium caseinate solutions) were redispersed upon orthophosphate addition. The added orthophosphate adsorbed onto the casein-iron precipitate. This adsorption displaced a part of the organic phosphorus (contributed by caseins) bound to iron and increased the surface negative charge on the casein-iron precipitate, which probably led to the redispersion of caseins and iron. The adsorption of orthophosphate occured on ferric hydroxide formed in the absence of casein, but does not solubilise iron, suggesting that the presence of caseins was critical for redispersion of the precipitate. Precipitate with higher protein content could redisperse greater concentrations of iron, while requiring lower orthophosphate content. Optimally four moles of iron could be solubilised by one mole of casein in these experiments. The adsorption of orthophosphate onto protein-iron complexes and its consequent solubilisation is a novel finding with a potential to create a new iron fortificant. Overall, this research highlights the important role that orthophosphate plays in the binding of iron to milk proteins. The soluble protein‒iron complexes created in this work could be used to fortify liquid food products. Moreover, two processes involving entirely different mechanisms for the formation of soluble protein‒iron complexes have been proposed, which has opened up a number of avenues for further research. The products and processes as an outcome of this research are protected by a patent, namely “Micronutrient fortification process and its usage”, issued by the New Zealand Patent Office on 24 June 2014.Item A study of diurnal rhythms in milk and fat production in the cow : a thesis submitted in partial fulfilment of the requirements for the degree of Master of Agricultural Science in the University of New Zealand(Massey University, 1954) Linklater, Peter MunroWhen cows are milked under commercial conditions milk yields are normally greater in the morning than in the evening, mainly because a longer time interval precedes the morning milking. In addition the percentage of fat in the milk is generally lower in the morning and higher in the evening. The alternation of high milk yields of low fat percentage, with lower milk yields of higher fat percentage, form a diurnal rhythm. This will depend partially on the length of time between morning and evening milkings, for the difference in yield and fat percentage is reduced as the time intervals approach equal length. There is left in the udder after a normal milking an appreciable quantity of milk of high fat percentage which has been termed "residual milk". In a hypothetical case if the volume and fat percentage of this milk remained constant after each milking, then the yield obtained from the udder would represent synthesis, and any diurnal rhythm would be caused solely by synthesis. However, neither the amount, nor the fat percentage of the residual milk remains constant at morning and evening milkings. Thus the diurnal rhythm may be attributed to two general causes, firstly synthesis, and superimposed on to this a diurnal variation in residual milk.Item Changes in bovine mammary enzyme activities and milk composition : a thesis presented in part fulfilment for the degree of Master of Agricultural Science in Animal Science, Massey University(Massey University, 1969) Currie, William BrucePreface: Concurrent study of mammary biochemical parameters and changes in the composition of the secreted product allows an examination of possible causal relations and is fundamental in identifying sites of action of physiological factors influencing the secretory activity of the gland. Changes in biochemical parameters accompanying various physiological states are now well documented for rodent species, e.g. Baldwin & Milligan (1966), but the relationships these bear with trans-lactation changes in the composition of milk have not been studied. The bovine provides ample material of sufficient diversity to characterise changes in milk composition and the specie's importance as a food producer justifies any attempt to determine how milk production is controlled and seek possibilities of artificial regulation. Prerequisite to such a study is a technique for repeatedly obtaining tissue from lactating udders without seriously influencing future production. The present experiment was undertaken to develop such a sampling method and use it in a first attempt to study milk production at the synthetic level throughout whole lactations in dairy cattle.Item Properties of milks concentrated by reverse osmosis : a thesis presented in partial fulfilment of the requirements for the degreee [i.e. degree] of Doctor of Philosophy in Food Technology(Massey University, 1998) Kaw, Anil KumarReverse osmosis (RO) is an energy efficient way of concentrating milk that can be operated at ambient temperatures, avoiding the product damage associated with thermal processes, and resulting in concentrates with better functional and nutritional properties. The objectives of this study were to examine in detail the effects of RO concentration on the rheological properties of milks, the states of proteins and fat globules in milk, the stability of RO concentrates towards ultra high temperature (UHT) processing, and changes in the UHT sterilized product during storage. Whole milk, homogenized milk and skim milk were concentrated to 1.5X, 2.0X, 2.5X and 3.0X by RO, and rheological properties were measured at 5, 15, 25, 40 and 60 °C before and after 48 h storage at 5 °C, using a Bohlin VOR rheometer. The values of k (the consistency index) and n (the flow behaviour index) were obtained by analysis of the flow curves using the power law model. These values indicated that the samples were generally very slightly shear thinning (i.e. pseudoplastic). k increased with decreasing temperature and increasing concentration. A shift factor approach was used to develop a relationship between k, temperature and total solids concentration (as n remained virtually constant). The equation can be used to predict the flow behaviour of RO concentrated milk at various total solids contents and temperatures. The data was also analysed using the Fernandez-Martin approach (1972); this was found to be more successful at modelling the effects of concentration and temperature on k. The viscosity data was also analysed using a hydrodynamic approach by means of Eilers' equation. A closer relationship was found between experimental values of basic viscosity and those predicted values by Eilers' equation when lactose was included in the equation as a component contributing to the volume fraction of the dispersed phase, rather than as a component contributing to the continuous phase viscosity. Concentration by RO results in inevitable homogenization of whole milk, by the back pressure device needed to maintain the pressure driving force for concentration in the RO plant. Analysis of RO milks by particle size distribution measurement and electron microscopy revealed that the original fat globules were broken up into new globules in the size range 0.02-0.3 μm; these globules were smaller overall than in milks homogenized with conventional valve homogenizers. The microstructures of protein membranes around the fat globules in RO concentrated milks were very different from those in milks homogenized conventionally. There were very few intact or semi-intact casein micelles at the surfaces of fat globules or in the serum. There were numbers of small fat globules grouped together, apparently held together by quantities of protein. Some unique particles were observed, which appeared to be similar to casein micelles, but had a number of very small fat globules embedded within their structure. Particle size measurements and electron micrographs of samples clearly showed that UHT treatment of RO concentrated milks resulted in the formation of large aggregates of intact fat globules. This aggregation was protein-mediated and no evidence of fat globule coalescence was observed. When milks containing native fat globule membrane (non-homogenized reblended concentrated milks) were UHT treated, the large aggregates formed consisted of protein alone with no inclusion of fat globules. In RO concentrated milks, the extent of formation of aggregates, as well the aggregate size, decreased with increase in milk pH from 6.3 to 7.2 or with the addition of disodium phosphate (DSP) prior to UHT treatment. UHT treated KU concentrated milks were examined for physico-chemical and structural changes during storage at 5, 20 and 37 °C. The effects of various processing variables (forewarming prior to concentration, post-UHT homogenization and the addition of phosphates prior to UHT treatment) on the storage-induced changes were also investigated. The results showed that irrespective of processing treatment, there was a decrease in pH with storage time, the extent of pH decrease being greater at higher storage temperatures. Gel formation, determined by a penetration test, correlated with the particle size distribution determined by light scattering. Samples stored at higher temperature showed greater quantities of large particles and gelled more quickly than those stored at lower temperature. The viscosity (measured at storage temperature) increased with storage time, the greater rate of increase being observed at the lowest storage temperature of 5 °C. The non-protein nitrogen content of all samples increased with storage time (indicating protein breakdown), the greatest rate of increase being observed at the highest storage temperature of 37 °C. Homogenization of concentrates after UHT treatment had no appreciable effect on gel formation during storage for pasteurized milk concentrates, but it decreased the rate of gel formation for concentrates that had been made from milk forewarmed prior to concentration. While forewarming decreased the rate of gelation for homogenized milks, an opposite trend was observed for concentrates that had not been homogenized. Results from electrophoresis analysis and electron microscopy showed minimum changes in the samples stored at 5 °C, whereas storage of samples at 37 °C for 25 weeks resulted in an increase in non-disulphide covalent cross links, and increases in fibre-like material and proteinacious particles in the serum. The addition of sodium hexametaphosphate (SHMP) resulted in the formation of smaller aggregates during storage, whereas the addition of DSP resulted in the formation of larger aggregates, suggesting that SHMP provides some stabilization of the concentrates. Electron microscopy and electrophoresis results did not show any significant differences between the samples with added SHMP or added DSP. Based on these results, a gelation mechanism in RO concentrated milks is proposed. RO concentrated milks have unique structures; recommendation are made for further work aimed at a better understanding of such milks, and at the development of new or improved dairy products that utilize their unique functional properties.Item An investigation of factors affecting the composition of milk and of methods for the analysis of milk components : a thesis presented to Massey University in partial fulfilment of the requirements of the degree of Doctor of Philosophy, Massey University, Palmerston North, New Zealand(Massey University, 1966) Wallace, G. M.Low solids-not-fat (S.N.F.) levels in the liquid Milk industry prompted an enquiry into the problem of meeting the minimum legal requirements for S.N.F. (8.5%) and into Methods for determining the S.N.F. content and the protein content of the milk. The methods, for determining the S.N.F., which were investigated were based mainly on the hydrometric or density technique which gives an indirect but rapid indication of the composition, whilst the amido black technique was examined with a view to assessing its suitability as a routine method for the protein determination. There is a growing awareness of the nutritional advantages of milk protein and of other nutritives in the solids-not-fat content of milk. Waite et al. have stated "In recent years the solids-not-fat content of milk has come to be regarded as of equal, or of greater importance, than the fat percentage. This change is the result of an increased awareness of the nutritive value of milk protein and other non-fatty constituents, in particular calcium and vitamins." Hansson in the same year wrote "The growing competition between fats of animal and plant origin has also led to the conclusion that the non-fat components of the milk will be emphasized more correctly in the future." Furthermore, it is considered that there is an urgent need to maintain milk composition up to the legal requirements when it is delivered to the consumer.Item Electrolyte systems relating to milk : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Chemistry at Massey University(Massey University, 1972) Pearce, Kevin NeilA pH titration method using a glass electrode/saturated calomel electrode cell has been applied to the determination of acidity and stability constants in dilute aqueous solutions at 25°C. Two computer programs in FORTRAN have been written and used to calculate the constants from the titration data. Acidity constants for the homologous series of aliphatic ωdicarboxylic acids (succinic acid to sebacic acid inclusive) have been determined. Acidity constants for tricarballylic, citric and a number of other carboxylic acids have also been determined and the values obtained are in good agreement with values reported by other workers. A new set of micro acidity constants, differing from those reported by other workers, has been obtained for citric acid from a pH titration study of various methyl esters of citric acid. The stability constants for the magnesium and calcium complexes of citric acid have been redetermined. The method of calculating acidity constants from substituent effects has been refined to distinguish between macro and micro acidity constants and has been used with some success in the prediction of both micro and macro acidity constants. Good values have been obtained for the first and second but not the third acidity constants for citric acid using this technique. An analogous method for calculating stability constants from substituent effects has been tested and found promising but its application is hampered by the lack of suitable experimental data. The thermodynamic basis of the cation exchange resin method of determining cation activities in solution has been described and a new method of resin calibration using two parameter equations developed. The ion exchange resin method has been applied to studies of the seasonal variation of milk composition and to brief studies of the effects of milk pH adjustment, the factors affecting the renneting time of milk and the determination of cation activities in non bovine milks. Some of the problems associated with calculating cation activities in milk have been briefly discussed. In a preliminary study of synthetic whey, comparisons have been made between cation activities determined experimentally and those calculated from a knowledge of composition and of the relevant acidity and stability constants.