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Start date: 2020Subject: search.filters.subject.Heat treatment

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    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 A
    Plant 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.
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    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 EP
    Acid- 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.
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    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, Zheng
    Sheep 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.