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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 Insights into wheat grain microstructure and composition for the development of novel flour with slow digestion properties and enhanced functional characteristics : 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, 2025) AbhilashaWheat has been consumed as whole grains, broken grains, flattened format, and puffed format other than the flour format, which has a wide application in different types of food preparations. Wheat flour possesses a unique ability to form a cohesive dough that has viscoelastic properties. A range of products with wheat as their major ingredient are high glycaemic index (GI) foods as wheat flour contains highly digestible starch. However, the consumption of high GI foods is associated with chronic diseases such as diabetes, coronary heart disease, and obesity due to a rapid increase in blood glucose levels and secretion of insulin. The major objective of the research studies of this thesis included creating slowly digestible flour with improved functionality using slowly digested starch sources and non-starch components. Modifying wheat grain through different processing techniques alters the microstructure, and therefore, starch digestibility is impacted. Microstructure modification through various processing techniques, which can control the access of digestive enzymes to starch, could help develop products with controlled starch digestibility. To advance the understanding of the impact of wheat grain microstructure on starch hydrolysis, Chapter 3 explored a study on whole wheat grain in different commercially available forms (kibbled, cut grains, and flour) to understand the influence of microstructural changes on in vitro starch digestibility. The process of size reduction from raw intact grains to kibbled grains and flour caused an increase in overall starch hydrolysis (%) during simulated digestion in the order of flour>kibbled>cut>intact whole wheat grains. Cooking of these formats further increased their starch hydrolysis. However, both cooked cut and intact grains were low glycaemic with the expected glycaemic indices (eGI) of values of 54.08±0.03 and 41.98±0.04, respectively, revealing the role of intact microstructure in starch hydrolysis of wheat grains. Based on the role of intact microstructure, Chapter 4 investigated the possibility of reducing the starch hydrolysis in wheat grain formats (whole, flakes, and flour) by hydrothermal treatment and low-temperature storage of whole wheat grains. The extent of starch hydrolysis after oral-gastro-small intestinal digestion in vitro was significantly lower (p<0.05) in intact grains, flakes, and flours from the cold-stored grains than their non-cold-stored counterparts. In this study, scanning electron micrographs, pasting properties, water retention capacities, and relative crystallinity of the resulting flours revealed an enhanced degree of gelatinisation with the treatment temperature; however, cold-storage of treated grains resulted in a change in these properties due to the retrogradation of the starch. This study indicates that hydrothermal pre-treatment of grains followed by low-temperature storage for prolonged periods might help to reduce the starch digestibility of wheat grains and their resulting products and could be an effective strategy in developing reduced glycaemic impact grain products. However, in our preliminary trials, the flours from hydrothermally treated and low-temperature stored grains resulted in doughs of inferior viscoelastic properties. Furthermore, intending to create slowly digestible flour, Chapter 5 employed two approaches to modify a resistant starch: one involving soluble extracts from wheat flour and vital gluten (water solubles, salt-assisted water-solubles, and acid-solubles) and the other utilising hydrocolloids (guar gum, xanthan gum, locust bean gum, and carboxymethyl cellulose). Modifications from both approaches resulted in modified starch morphology with the formation of starch clusters mimicking the wheat flour. Moreover, the modification with hydrocolloids resulted in an improved pasting profile. Furthermore, in vitro digestion studies revealed that the starch hydrolysis rate was decreased for most of the cooked modified starches with wheat solubles and a slower starch hydrolysis profile until 60 min of simulated small intestinal digestion for most of the hydrocolloids used, carboxymethyl cellulose being the least effective in slowing the starch hydrolysis rate. Additionally, Chapter 6 evaluates the functionality and starch digestibility of a wheat flour system (dough and flatbread-chapatti) by utilising the modified starches created in Chapter 5 as low glycaemic ingredients. The interaction of the modified starches with vital gluten and wheat flour components resulted in improved viscosity of the functional flour. The microstructure of the functional flour dough indicated that the modified starches with wheat solubles (soluble extracts from wheat flour and vital gluten) and hydrocolloids improved the starch-protein matrix and gluten network. Furthermore, the in vitro digestion study revealed the overall starch hydrolysis of chapattis from all the functional flour formulations was significantly lower than the wheat flour chapatti. In conclusion, structural modifications of wheat grain could help reduce the overall starch hydrolysis of wheat grain products. Moreover, the wheat grain components have the potential to modify resistant starch sources to improve their functionality while retaining their slow digestion property. Also, utilising hydrocolloids to modify resistant starch sources could be an effective strategy to enhance the functionality of resistant starches in wheat-based systems. Modified resistant starches created using wheat solubles (soluble extracts from wheat flour and vital gluten) and hydrocolloids have potential applications with slow digestibility and improved functionality in wheat-based products.Item Heat-induced dissociation and association of proteins in hempseed protein bodies(Elsevier Ltd, 2025-10) Do DT; Ye A; Singh H; Acevedo-Fani AProtein bodies (PBs) are naturally occurring storage organelles in seeds. In hempseeds, the major storage proteins, including edestin (11S globulin) and albumin, are primarily located in the crystalloids and proteinaceous matrices of hemp protein bodies (HPBs), respectively. The retention of native PB structures in flours and dry-fractionated protein ingredients has important implications for protein functionality and digestibility, especially when heat treatment is applied during processing. While the thermal behaviour of hempseed proteins has been studied in protein isolate systems, to the best of our knowledge, it has not yet been explored in HPB systems. In this study, we isolated native HPBs using an enzymatic method. Aqueous suspensions of HPBs (4 % protein, w/w) were heated at selected temperatures (60–100 °C) and pH 7 for 20 min, followed by hydrolysis with trypsin at pH 7 and 37 °C for 120 min. The thermal aggregation of proteins in HPBs was characterised using confocal laser scanning microscopy (CLSM) and sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE). The hydrolysis of HPBs by trypsin was monitored over 120 min by measuring the degree of protein hydrolysis (DH) and analysing SDS-PAGE. Aggregation of edestin in HPBs, primarily driven by disulfide bond formation, occurred upon heating, most noticeably at temperatures above 80 °C. Heating increased DH and altered protein degradation patterns of both acidic and basic subunits of edestin. This may be related to conformational changes in the HPB structure resulting from heat-induced dissociation-association of multiple HPB protein fractions, including 11S edestin, 7S globulin, and 2S albumin. These findings contribute to our understanding of the structure-hydrolysis relationships of HPBs, potentially leading to their use as a new plant-based material for food applications.Item Understanding the Effects of Lactose Hydrolysis Modeling on the Main Oligosaccharides in Goat Milk Whey Permeate(MDPI (Basel, Switzerland), 2019-09-10) Thum C; Weinborn V; Barile D; McNabb WC; Roy NC; Leite Nobrega de Moura Bell JM; Moreno DA; Villaño DEnzymatic hydrolysis of lactose is a crucial step to improve the efficiency and selectivity of membrane-based separations toward the recovery of milk oligosaccharides free from simple sugars. Response surface methodology was used to investigate the effects temperature (25.9 to 54.1 °C) and amount of enzyme (0.17 to 0.32% w/w) at 1, 2, and 4 h of reaction on the efficiency of lactose hydrolysis by Aspergillus oryzae β-galactosidase, preservation of major goat whey oligosaccharides, and on the de-novo formation of oligosaccharides. Lactose hydrolysis above 99% was achieved at 1, 2, and 4 h, not being significantly affected by temperature and amount of enzyme within the tested conditions. Formation of 4 Hexose (Hex) and 4 Hex 1 Hex and an increased de-novo formation of 2 Hex 1 N-Acetyl-Neuraminic Acid (NeuAc) and 2 Hex 1 N-Glycolylneuraminic acid (NeuGc) was observed in all treatments. Overall, processing conditions using temperatures ≤40 °C and enzyme concentration ≤0.25% resulted in higher preservation/formation of goat whey oligosaccharides.Item Influence of food macrostructure on the kinetics of acidification in the pig stomach after the consumption of rice- and wheat-based foods: Implications for starch hydrolysis and starch emptying rate(Elsevier Ltd, 2022-11-15) Nadia J; Olenskyj AG; Subramanian P; Hodgkinson S; Stroebinger N; Estevez TG; Singh RP; Singh H; Bornhorst GMHow the stomach can serve as a biochemical environment for starch digestion and the implications on starch emptying are not well-understood. Biochemical changes during gastric digestion of cooked wheat- and rice-based diets of varying particle size and microstructure were investigated using a growing pig model. In larger-particle size diets (rice grain, rice noodle, pasta), pH >3 was maintained in the proximal stomach digesta even until 240 min digestion, resulting in extended remaining amylase activity and accumulation of maltose from starch hydrolysis in the stomach. In smaller-particle size diets (couscous, rice couscous, semolina porridge), gastric acidification occurred faster to produce homogeneous intragastric pH and deactivated amylase. The hypothesis of the study was that food macrostructure would impact gastric acidification kinetics, and the resulting biochemical environment for starch hydrolysis in the stomach may further affect the mechanisms of food breakdown in the stomach and gastric emptying of starch.Item Kinetics of pepsin-induced hydrolysis and the coagulation of milk proteins(Elsevier Inc and the Federation of Animal Science Societies on behalf of the American Dairy Science Association, 2022-02) Yang M; Ye A; Yang Z; Everett DW; Gilbert EP; Singh HHydrolysis-induced coagulation of casein micelles by pepsin occurs during the digestion of milk. In this study, the effect of pH (6.7–5.3) and pepsin concentration (0.110–2.75 U/mL) on the hydrolysis of κ-casein and the coagulation of the casein micelles in bovine skim milk was investigated at 37°C using reverse-phase HPLC, oscillatory rheology, and confocal laser scanning microscopy. The hydrolysis of κ-casein followed a combined kinetic model of first-order hydrolysis and putative pepsin denaturation. The hydrolysis rate increased with increasing pepsin concentration at a given pH, was pH dependent, and reached a maximum at pH ~6.0. Both the increase in pepsin concentration and decrease in pH resulted in a shorter coagulation time. The extent of κ-casein hydrolysis required for coagulation was independent of the pepsin concentration at a given pH and, because of the lower electrostatic repulsion between para-casein micelles at lower pH, decreased markedly from ~73% to ~33% when pH decreased from 6.3 to 5.3. In addition, the rheological properties and the microstructures of the coagulum were markedly affected by the pH and the pepsin concentration. The knowledge obtained from this study provides further understanding on the mechanism of milk coagulation, occurring at the initial stage of transiting into gastric conditions with high pH and low pepsin concentration.Item Effect of Gel Structure on the In Vitro Gastrointestinal Digestion Behaviour of Whey Protein Emulsion Gels and the Bioaccessibility of Capsaicinoids(MDPI (Basel, Switzerland), 2021-03-04) Luo N; Ye A; Wolber FM; Singh H; Kontominas MGThis study investigated the effect of gel structure on the digestion of heat-set whey protein emulsion gels containing capsaicinoids (CAP), including the bioaccessibility of CAP. Upon heat treatment at 90 °C, whey protein emulsion gels containing CAP (10 wt% whey protein isolate, 20 wt% soybean oil, 0.02 wt% CAP) with different structures and gel mechanical strengths were formed by varying ionic strength. The hard gel (i.e., oil droplet size d4,3 ~ 0.5 μm, 200 mM NaCl), with compact particulate gel structure, led to slower disintegration of the gel particles and slower hydrolysis of the whey proteins during gastric digestion compared with the soft gel (i.e., d4,3 ~ 0.5 μm, 10 mM NaCl). The oil droplets started to coalesce after 60 min of gastric digestion in the soft gel, whereas minor oil droplet coalescence was observed for the hard gel at the end of the gastric digestion. In general, during intestinal digestion, the gastric digesta from the hard gel was disintegrated more slowly than that from the soft gel. A power-law fit between the bioaccessibility of CAP (Y) and the extent of lipid digestion (X) was established: Y = 49.2 × (X - 305.3)0.104, with R2 = 0.84. A greater extent of lipid digestion would lead to greater release of CAP from the food matrix; also, more lipolytic products would be produced and would participate in micelle formation, which would help to solubilize the released CAP and therefore result in their higher bioaccessibility.Item Controlled Hydrolysis of TiO2 from HCl Digestion Liquors of Ilmenite(American Chemical Society, 2022-05-18) Haverkamp RG; Wallwork KS; Waterland MR; Gu Q; Kimpton JATraditionally, industrial scale production of the TiO2 pigment is achieved by hydrolysis from H2SO4 solution or by hydrolysis of TiCl4. However, the H2SO4 route produces FeSO4 waste, which is problematic, and the TiCl4 route requires a high grade rutile feedstock or chemically upgraded ilmenite (FeTiO3). Here, we investigate a direct route from ilmenite to TiO2 using aqueous HCl. New Zealand ilmenite digested in 35 wt % HCl to achieve a solution containing typically 1.18 mol kg-1 Fe(aq)2+ and 1.14 mol kg-1 Ti(aq)4+ was hydrolyzed under reflux, after seed preparation in water, or with phosphoric or citric acid. The structure of the seed was determined by Raman spectroscopy and X-ray powder diffraction using pair distribution function analysis, the latter enabling the identification of short-range order in poorly crystalline materials. TiO2 hydrate was precipitated from HCl in either the anatase or the rutile structure. Unlike from H2SO4, the natural structure formed without the use of structure determining agents is rutile. However, seed preparation using 0.4 mol H3PO4 per mole of Ti (resulting in 0.35 wt% H3PO4 in the hydrate) results in anatase hydrate formation. Sodium citrate or citric acid addition also seed anatase hydrate. The mechanism for polymorph control may be kinetic rather than a structural template or surface adsorption. This process has the potential to be used for the commercial scale production of the TiO2 pigment. Anatase hydrate has the advantage that traces of iron may be more readily removed by washing than from rutile precipitate, making the HCl process from ilmenite feasible for pigment grade material.Item Beef hydrolysis by Zyactinase™ enzymes : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy at Massey University, Auckland, New Zealand.(Massey University, 2016) Ahmad, Noriza BintiProtein hydrolysis is the term that applies to all possible ways of splitting proteins to produce products with lower molecular weight. There is a continuous search for novel products derived from waste materials. In the developed nations considerable amount of meat off-cuts are discarded each year. Utilizing these leftovers by developing new technology for protein recovery and modification and production of a broad spectrum of food ingredients greatly enhances its final value. The aim of this research was to partially hydrolyse beef meat protein with a commercial kiwifruit product called ZyactinaseTM, which is essentially freeze-dried kiwifruit to determine the effect of various processing conditions that influence the extent of beef meat hydrolysis. Secondly to determine the peptide and amino acid profile of the beef meat sample after hydrolysis. Thirdly to determine the relative reaction of ZyactinaseTM on various beef meat protein fractions. This study also aimed to evaluate the rate and the extent of partial enzymic hydrolysis of lean beef using ZyactinaseTM enzymes in order to obtain a better understanding of protein hydrolysis reaction. Lean beef minced was partially hydrolysed using the Zyactinase enzymes for different processing times (up to 360 minutes), temperatures (27°C to 70°C) and varying enzyme concentrations. No pH adjustment on the raw material was carried out except for pH studies. The hydrolysates were collected and analysed for total nitrogen content and degree of hydrolysis. The method used to characterize the extent of protein hydrolysis was SN-TCA index (fraction of nitrogen soluble in trichloroacetic acid) also called non-protein nitrogen NPN. Peptide and amino acid in protein hydrolysates were analysed by HPLC and different protein fractions in the hydrolysates were characterised by SDS-PAGE. The relationship between the reaction temperature, enzyme concentration and processing time to the total nitrogen and NPN were determined. The total nitrogen content remained relatively constant throughout the hydrolysis process. In addition, the NPN content increased as the temperature, processing time and enzyme concentration increased. The optimum pH range for the enzyme’s activity was 4 – 5.6 and optimum temperature was 60°C. Furthermore, most of the higher molecular weight protein bands on SDS- PAGE disappeared after hydrolysis and lower molecular weight protein bands increased in intensity. Zyactinase was also found to digest protein in the myobrilla and sarcoplasmic meat fractions at similar rates as whole beef meat. The results provide basic understanding of the kiwifruit enzymes action toward protein that may lead to improved methods for recovering meat protein or developing new food materials.Item Lactose hydrolysis by immobilized whole cells of K. lactis CBS 2357 : a thesis presented in partial fulfilment of the requirements for the degree of Master of Technology in Bioprocess Engineering at Massey University(Massey University, 1999) Marasabessy, AhmadThe application of immobilized yeast for lactose hydrolysis was investigated. The enzyme stability was tested as a function of pretreatment. The stability of K. lactis CBS 2357 cells after treatment with glutaraldehyde (GA) and the β-galactosidase activity of whole cells after immobilization in alginate bead and corn particles were studied. Permeabilization using ethanol and chloroform (10% and 2%, respectively) at 37 °C and 120 rpm for 5 min, followed by stabilization with 10 mM glutaraldehyde at 30 °C for 1 hour with gently shaking deactivated 2.5% of the initial whole cells β-galactosidase activity, tested with the ONPG method. The glutaraldehyde treatment could significantly maintain β-galactosidase activity in phosphate buffer pH 6.5 containing 0.1 mM MnCl2. Manganese and potassium ions in the Mn-Buffer were found to be essential to enhance the activity. The biomass activity of GA stabilized cells in Mn-Buffer can be maintained above 70% during 72 hours of incubation at 30 °C. An increase of incubation temperature from 30 to 37 °C deactivated 10% of biomass activity after 72 hours. Direct stabilization of alginate biocatalyst with glutaraldehyde caused a significant reduction of β-galactosidase activity with the resulting deactivation depending on glutaraldehyde and alginate concentrations. When 40 g of biocatalyst containing 2x109 cells/g alginate was stabilized in 100 ml of 0 to 4 mM glutaraldehyde, the optimum range of glutaraldehyde concentration was between 0.5 to 1.0 mM. When this concentration range was applied to stabilize 2%- to 3%-alginate biocatalyst, the average biocatalyst activity remained within 56-74% of the initial activity. It was shown that the adsorption of K. lactis on corn particles through a "double liquid cultivation stage" followed by permeabilization of biocatalyst gave a higher activity. The activity obtained was 0.84 μmol lactose hydrolyzed /min/g biocatalyst under the conditions tested. This activity was about 5 times higher than the case without permeabilization and about 2 times higher than that of the permeabilized biocatalyst prepared with a "single liquid cultivation stage". When tested in the packed-bed reactor, during the initial stages the degree of hydrolysis (d.h.) was 45% within the operational conditions tested. Free enzyme was detected during the first 5 hours of operation, especially when non-stabilized corn biocatalyst was used. After 5 hours, free enzyme was no longer detected in the reactor outlet, suggesting that direct adsorption might have rendered good cell confinement inside the corn particles.