Journal Articles

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Subject: search.filters.subject.Pepsin

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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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    In vitro gastric digestion of heat-induced aggregates of β-lg
    (Elsevier Inc., 2012) Loveday, SM; Singh, Harjinder; Ye, Aiqian; Peram, Malleswara R.
    An in vitro gastric digestion of heat-induced aggregates of β-lactoglobulin (β-lg) in simulated gastric fluid was investigated using sodium dodecyl sulfate-PAGE under nonreducing and reducing conditions, native-PAGE, 2-dimensional electrophoresis, and size exclusion chromatography. Heating at 90ºC significantly increased the digestibility of β-lg, with a high initial digestion rate followed by a relatively constant rate of digestion at a high enzyme:substrate (E:S) ratio of 3:1. At a low E:S ratio (1:6), the rate of digestion of β-lg was slower, and intermediate and low molecular weight species could be seen. The high molecular weight nonnative aggregates (pentamers, tetramers, trimers, etc.) were digested relatively rapidly, whereas some of the nonnative dimers were resistant to digestion and others were digested rapidly. The intermediate molecular weight species (21 to 23 kDa) were digested slowly. These results indicated that the digestibility of nonnative β-lg aggregates varied significantly depending on the E:S ratio and the types of aggregate. Further investigation is necessary to identify and characterize slowly digested dimers and intermediate molecular weight species.