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Item Heat-induced modifications of pea protein: Implications for solubility and digestion behaviour(Elsevier B.V., 2025-08-20) Li D; Ma Y; Acevedo-Fani A; Lu W; Singh H; Ye APlant proteins have become increasingly desirable due to their sustainability and proposed health benefits. This study initially examined the effects of heat treatment on the solubility of pea protein (PP) in a 3 % (w/w) protein solution, applying heat from 65 °C to 95 °C for varying durations across pH conditions ranging from 5.5 to 7.8. Subsequently, an advanced dynamic gastric digestion model—the Human Gastric Simulator—was employed to examine the in vitro gastric digestion behaviours of heat-treated and untreated PP. Results suggest that heat treatment reduces the protein aggregate size and enhances PP solubility, potentially due to a decrease in α-helix and β-turn structures or an increase in β-sheet content, as determined via Fourier transform infrared spectroscopy. Additionally, heat treatment elevated the surface hydrophobicity and free sulfhydryl group concentration of PP. During in vitro dynamic gastric digestion with pepsin, PP underwent notable structural and physical stability modifications. Unheated and heated PP exhibited small particles in the digesta and remained unaggregated throughout digestion. However, the heat-treated PP showed a smaller particle size during gastric digestion and a greater hydrolysis rate than the unheated protein. This study systematically evaluates the solubility and digestion behaviour of PP subjected to food processing conditions, highlighting its stability and structural changes that may influence the delivery of macronutrients from the stomach to the next phase of digestion.Item Probing structural modification of milk proteins in the presence of pepsin and/or acid using small- and ultra-small-angle neutron scattering(Elsevier Ltd, 2025-02) Yang M; Ye A; Yang Z; Everett DW; de Campo L; Singh H; Gilbert EPAcid- and pepsin-induced milk protein coagulation plays a crucial role in the gastric digestion of milk. Real-time structural evolution at a nano- (e.g. colloidal calcium phosphate (CCP) and micelle) and micro- (gel network) level of unheated and heated (85 °C for 30 min) bovine milk was examined under acidic conditions and at low and high concentrations of pepsin using ultra-small- and small-angle neutron scattering (USANS and SANS), small-amplitude oscillatory rheometry and confocal scanning laser microscopy. Milk was treated with glucono-δ-lactone (GDL), pepsin or a combination of GDL and pepsin to induce coagulation. Heat-treated milk showed a faster increase in elastic storage modulus (G′) and scattering intensity (USANS and SANS) compared with unheated milk when coagulated with GDL or the combination of GDL and pepsin. At pH 6.3, heat treatment retarded pepsin (1.10 U/mL)-induced milk coagulation, with slower increases in G′ and scattering intensity. At a high concentration of pepsin (2000 U/mL) that mimics the concentration found in the stomach, general proteolysis followed coagulation. Heat treatment retarded coagulation but accelerated curd proteolysis. This study demonstrates how time-resolved USANS and SANS can be used to investigate the structural evolution of protein coagulation and degradation under gastric environment conditions at nano- and micro-metre length scales.Item Studies on heat-induced protein interaction and digestion behavior of sheep milk : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Food Technology at Riddet Institute, Massey University, Palmerston North, New Zealand(Massey University, 2023) Pan, ZhengSheep milk has low heat stability, which results in undesirable changes after heat treatment, such as separation of milk fat, sediment formation, and phase separation. However, the mechanism of low heat stability of sheep milk has not yet been elucidated. Additionally, the protein interactions in sheep milk during heating and the digestion behaviors of differently processed sheep milk are also unknown. Therefore, the aim of this thesis was to explore the protein interactions of sheep milk during heat treatment (67.5–90 °C and 140 °C), and the mechanism of heat coagulation of sheep milk. In addition, the effect of the commercial processing treatment [homogenization (200/50 bar) and thermal (75 °C/15 s and 95 °C/5 min) processing] on the digestion behavior of sheep milk were determined. Sheep skim milk (SSM) was heated under various conditions (including temperatures, heating times and pH values) and the denaturation of whey protein and protein interactions occurring during heating were characterized using high-performance liquid chromatography. Casein micelle diameter increased upon heating, depending on the temperature and time. The association of whey protein with casein micelles and the aggregation of casein micelles occurred simultaneously and contributed to the increase in casein micelle size in SSM. SSM was stable to heat (140 °C) at pH 6.8–6.9 but became unstable at higher or lower pH. The low heat stability of sheep milk was attributed to the low proportion of κ-casein surrounding the casein micelles, high ionic calcium levels and ready dissociation of κ-casein from casein micelles upon heating at pH 7.0. The Human Gastric Simulator was used for in vitro dynamic gastric digestion and pH-stat for simulated small intestinal digestion. Heat treatment of sheep milk resulted in the incorporation of MFGs into the curds through casein‒whey protein or whey protein‒whey protein interactions; this hindered the formation of the closely knitted protein network and led to the formation of fragmented curds. Homogenization of sheep milk resulted in looser and more fragmented curd in comparison with unhomogenized sheep milk; this accelerated the protein hydrolysis and increased the rate of release of protein, fat, and calcium from the curds into the digesta. Processing treatments affected the lipolysis rate but not the lipolysis degree during small intestinal digestion. In conclusion, the findings of this study have advanced our understanding of the heat-induced protein interactions in sheep milk and provided insights into the digestion behavior of differently processed sheep milk within the gastrointestinal tract. This may help to design and develop sheep milk-based products with desired digestive and functional properties.Item Study of the interactions between milk proteins and hydroxyapatite particles : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Food Technology at Massey University, Riddet Institute, Palmerston North, New Zealand(Massey University, 2016) Tercinier, LucileHydroxyapatite (HA) and other insoluble calcium salts added to calcium-fortified milks are often described as inert, as they do not cause any protein aggregation and heat instability during heat treatment of the milk. However, it is well-known that proteins can interact with HA. The adsorption of milk proteins on HA has been demonstrated in many systems, for example in chromatography, bioceramic and dentistry applications, and has been shown to have consequence on the colloidal stability of HA, but has never been studied in food systems. The main objective of the present study was therefore to explore the adsorption of milk proteins onto HA particles under a range of physico-chemical conditions. The consequences of these interactions on the colloidal properties of the HA particles and on the stability of the milk proteins were investigated. It was shown that the five individual milk proteins αₛ₋casein, ß -casein, k-casein, ß-lactoglobulin and a-lactalbumin adsorbed onto the HA particles. A Langmuir model was used to fit the adsorption data and determine the affinity constant and maximum surface loads of the different proteins. The adsorption of the different milk proteins onto HA particles was found to be of competive nature. ß-casein and aS-casein were always preferred for adsorption over k-casein, ß-lactoglobulin and a-lactalbumin. This was attributed to the presence of phosphoserine clusters in ß-casein and αₛ₋casein, forming many anchor points capable of binding to the calcium sites of HA. ß-casein and αₛ₋casein also adsorbed to higher maximum levels compared to k-casein, ß-lactoglobulin and a-lactalbumin. Both ß-Casein and αₛ₋casein were considered to self-associate or associate together in the adsorbed layer, therefore forming a thick layer onto the HA surface. Conversely, ?-casein, ß-lactoglobulin and a-lactalbumin adsorbed to lower maximum amounts and had lower affinities for HA, which was attributed to adsorption in a monolayer through their carboxyl groups binding to the calcium sites of HA. The amount of protein adsorbing to the HA surface was affected by the physico-chemical properties of the solution such as pH and ionic strength, for all proteins. Decreasing pH and increasing ionic strength decreased the electrostatic repulsive forces between HA and the proteins and the electrostatic repulsive forces within the protein molecules, which allowed more protein to adsorb onto the HA surface. Milk serum ions such as calcium, phosphate and citrate bound specifically onto HA particles, therefore competing with the milk proteins for adsorption. In milk, it was shown the addition of HA in milk disrupted the mineral equilibrium and the milk protein phase. When HA particles were added to milk, the milk serum ions bound to the HA surface. This caused the colloidal calcium phosphate to be released from the casein micelles and the casein micelles to dissociate. Therefore the casein micelles did not bind as intact micelles but as individual molecules or small aggregates onto the HA particles. The adsorption of milk proteins onto HA particles affected the colloidal properties of the HA particles in suspension. The adsorption of both caseins and whey proteins onto HA particles resulted in the particles becoming negatively charged, thus improving their suspension stability. Whey protein adsorption probably provided only electrostatic stabilisation, whereas casein adsorption also provided steric stabilisation. Overall, this work has provided a detailed understanding of the interactions between milk proteins and HA particles. Calcium fortification of milk using insoluble calcium salts such as HA should be approached using an awareness of these interactions, as they may have consequences on the stability of calcium fortified milks.Item Surface modifications to increase dairy production run length : a thesis presented in partial fulfilment of the requirements for the degree of Master of Chemical Engineering at Massey University, [Manawatū], New Zealand.(Massey University, 2013) Runwal, SiddharthFouling is the build-up of undesired deposits on surfaces. In the dairy industry, fouling is mainly seen in heat exchangers where dairy fluid is heated or concentrated. It is one of the primary reasons for restricted run length, causing financial losses from downtime, the use of cleaning chemicals and reduced product quality. Fouling is a complex process and is due to number of factors including the properties of the heat transfer surface. A silica based coating is known to alter the surface properties. This study was carried out to investigate the effect of a silica based coating on fouling by whole milk in a falling film evaporator. Seven independent trials were conducted. In each trial, a control run was carried out followed by a full cleaning of the equipment and then either another control run or a coating run with pasteurized milk from the same batch. There was a six hour interval between the start of the control run and start of the coating run. Since prolonged milk storage may have some effect on fouling rate, control-control runs were carried out to see the effect of prolonged storage. The results obtained from control-control runs were used in analysing the effect of the coating on fouling rate. All coating trials showed consistently lower fouling rate as compared with corresponding control trials. The Pearson’s correlation coefficient of 0.83 showed a strong effect of coating on the fouling rate. Further, a regression analysis gave a p-value of 0.033, indicating that, at the 96.7% level of confidence, coating reduced the fouling rate. The extent of reduction in fouling rate varied from trial to trial. It was estimated that the coating had the potential to increase the run length by a maximum of 34% under the conditions these experiments were carried out.Item Heat-induced colloidal interactions of whey proteins, sodium caseinate and gum arabic in binary and ternary mixtures(Elsevier Ltd, 2013-11) Loveday SM; Ye A; Anema SG; Singh HMany food-grade proteins and polysaccharides will aggregate together when acidified or heated, due to electrostatic and hydrophobic interactions. At low concentrations, aggregates are soluble and colloidally stable, and they have potential applications as Pickering emulsifiers and nutrient carriers. Sodium caseinate (SC) and gum arabic (GA) at pH. 7 will form colloidal aggregates when heated, but aggregation is largely reversed on cooling. Whey proteins (in the form of whey protein isolate, WPI) will aggregate irreversibly with GA when they are heated together, but aggregation is often so rapid and extensive that aggregates precipitate. Here we sought to overcome those limitations, and to develop an in situ method for quantifying heat-induced aggregation. Aggregation was measured using temperature-controlled dynamic light scattering equipment and transmission electron microscopy. Combinations of SC, WPI and GA were heated at either pH. 7 or 3.5, and the weight ratio of protein to polysaccharide was held at 1:5 for simplicity. Heat-induced colloidally stable aggregates of SC. +. WPI. +. GA did not dissociate on cooling. Aggregation was measured in situ, both in temperature ramps and with isothermal experiments. In situ measurement allowed us to avoid potential artefacts stemming from the temperature changes and measurement delays associated with ex situ measurements. This work demonstrated how the size and heat-stability of colloidal protein-polysaccharide aggregates can be tailored by judicious selection of proteins, pH and heat treatment.Item The development of a chemical analogue of thermal destruction of bacterial spores : a thesis presented in partial fulfilment of the requirements for the Degree of Doctor of Philosophy at Massey University(Massey University, 1967) Packer, Gordon John KitchCanning as a method of food preservation has its origin in the work of Nicolas Appert (1750-1841) who was the first to use heat as a means of preserving food in hermetically sealed containers. Although he did not understand the principles of his method, his systematic experimentation (and generous sharing of his discoveries) laid the foundations of thermal food preservation methods. Appert initially processed his food in cork sealed glass jars and bottles in boiling water baths for periods varying from 15 minutes to two and a half hours. Storage trials were the basis of his processing methods, some foods being kept up to ten years. His products ranged from meats, soups and vegetables to fruit and even cream and evaporated milk. He recognized the value of quick clean handling of good quality raw materials. Blanching was used with some products, and he was also aware of the distinction between acid and low-acid foods in regard to their length of processing. Appert's understanding of the process was that heating eliminated the "air" which was believed to be the cause of spoilage. This belief was to persist for nearly 100 years. Appert's work in glass containers led to the development in England about 1815-20 of tin containers for preserved foods. Appert himself used cans in some of his later work. Some time before 1830 the autoclave was introduced (apparently by Appert) as a means of cooking canned foods under pressure. By 1870, autoclaves were being used quite widely in industrial canning.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.Item Formation and stability of oil-in-water emulsions : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Food Technology at Massey University(Massey University, 1998) Srinivasan, MageshThe main objective of this study was to gain a better understanding of the formation, stability and microstructure of oil-in-water emulsions stabilized by commercial sodium (ALANATE 180) and calcium caseinates (ALANATE 380). The study also determined the effects of heat treatment and NaCI addition on the formation and stability of these emulsions. Emulsions were prepared using various concentrations of sodium or calcium caseinate solutions (0.5 to 5.0%) and 30% soya oil. Surface protein coverage (mg/m2) in freshly prepared emulsions was determined from analysis of the aqueous phase after centrifugation of emulsions at 45,000 g for 40 minutes, using the Kjeldahl method. SDS-PAGE was used to identify the adsorbed protein components in the cream phase. Creaming stability was determined after storage of emulsions for 24 hours at 20°C by a low speed centrifugation method. The microstructure of these emulsions was determined using confocal laser scanning microscopy. The aggregation state of caseins in sodium and calcium caseinate solutions was determined by successive centrifugation, gel permeation chromatography and multi-angle laser light scattering techniques. For emulsions stabilized with sodium caseinate, the surface protein concentration increased gradually with protein concentration up to 3%, but the increase was much smaller at higher concentrations. By comparison, the surface protein coverage in emulsions stabilized with calcium caseinate showed an almost linear increase with protein concentration (0.5 to 5.0%). At all protein concentrations, the surface protein coverage of emulsions stabilized with calcium caseinate was higher than that of sodium caseinate emulsions. β-Casein was adsorbed in preference to other caseins in emulsions made using ≤ 2.0% sodium caseinate, but αs-casein (αs1- + αs2-) appeared to adsorb in preference to other caseins when emulsions were made using > 2.0% sodium caseinate. In calcium caseinate-stabilized emulsions, αs-casein was found to adsorb in preference to other caseins at all protein concentrations used. Heat treatment (121°C for 15 min) of sodium caseinate emulsions or heat treatment of sodium caseinate solutions prior to emulsion formation, at all caseinate concentrations, resulted in an increase in surface protein coverage and altered the proportions of individual caseins at the droplet surface. The surface protein coverage of emulsions formed with calcium caseinate solutions increased markedly when the emulsions were heated (121°C for 15 min) or when calcium caseinate solutions were heated prior to emulsion formation. The preferential adsorption of αs-casein, observed in the unheated calcium caseinate emulsions, diminished after heating, which was due to polymerization of αs-casein during heating and/or degradation of this casein. In sodium caseinate emulsions, the surface protein coverage and the composition of emulsion droplets were influenced by the presence of NaCl prior to emulsion formation. The surface protein coverage in emulsions made with 1 and 3% sodium caseinate increased with an increase in NaCl concentration up to 40 mM, with a large increase in the adsorption of αs-casein at the droplet surface. Addition of NaCl beyond 40 mM had no further effects on surface coverage and composition. Similar trends were observed when NaCl was added to the emulsions after they were formed. By contrast, in calcium caseinate emulsions, the surface protein coverage decreased with increase in NaCl concentration up to 40 mM, but with further increase in NaCl concentration the surface protein coverage increased slightly. In these emulsions, the composition of the interface remained largely unafffected by NaCl addition; αs-casein was adsorbed in preference to other caseins. Creaming stability of calcium caseinate emulsions, after storage at 20°C for 24 hours, increased with an increase in protein concentration. However, the creaming stability of sodium caseinate emulsions decreased markedly as the protein concentration was increased above 2%. This decrease in stability was attributed to the reversible flocculation arising from a 'depletion flocculation' mechanism. This flocculation in turn resulted in enhanced creaming at high caseinate concentrations. In sodium caseinate emulsions, the appearance of the droplets in the confocal micrographs was dependent on the concentration of protein used for making emulsions. Emulsions formed with low concentrations of sodium caseinate (0.5 and 1.0%) appeared to be homogenous with no sign of flocculation. However the emulsions made with > 2% sodium caseinate showed some irregular flocs, which appeared to be forming a network structure at higher concentrations of protein. In contrast, confocal micrographs of emulsions formed with calcium caseinate at all protein concentrations showed individual droplets. The creaming stability of these emulsions improved, when the emulsions were heated or when emulsions were made using heated sodium or calcium caseinate solutions. The presence of 200 mM NaCl prior to emulsion formation resulted in improved creaming stability and a reduced degree of flocculation.