Intragastric restructuring dictates the digestive kinetics of heat-set milk protein gels of contrasting textures

• Published in: Food research international Vol. 195; p. 114944
• Main Authors: Li, Siqi, Mungure, Tanyaradzwa, Ye, Aiqian, Loveday, Simon M., Ellis, Ashling, Weeks, Mike, Singh, Harjinder
• Format: Journal Article
• Language: English
• Published: Canada Elsevier Ltd 01.11.2024
• Subjects: Animals; Caseins - chemistry; Caseins - metabolism; Digestion - physiology; Food Handling - methods; Food structure; Gastric Emptying; Gastric restructuring; Gels - chemistry; Hot Temperature; Hydrogen-Ion Concentration; In vitro digestion; Kinetics; Milk protein gels; Milk Proteins - chemistry; Milk Proteins - metabolism; Pepsin A - metabolism; Protein digestion; Proteolysis; In vitro digestion; Gastric restructuring; Food structure; Protein digestion; Milk protein gels
• ISSN: 0963-9969; 1873-7145; 1873-7145
• DOI: 10.1016/j.foodres.2024.114944

[Display omitted] •Two heat-set milk protein gels of contrasting textures were studied for gastric digestion behaviour.•The firm gel (pH 5.65) underwent gradual breakdown during gastric digestion.•The soft gel (pH 6.55) became compact and sustained longer in the stomach.•Intragastric restructuring reversed the textural difference of the two gels.•pH effect on pepsin activity and specificity possibly played a key role. The gelation of milk proteins can be achieved by various means, enabling the development of diverse products. In this study, heat-set milk protein gels (15 % protein) of diverse textures were made by pH modulation and two gels were selected for dynamic in vitro gastric digestion: a spoonable soft gel (SG, pH 6.55′ Gʹ of ∼100 Pa) and a sliceable firm gel (FG, pH 5.65; Gʹ of ∼7000 Pa). The two gels displayed markedly different structural changes and digestion kinetics during gastric digestion. The SG underwent substantial structural compaction during the first 120 min of gastric digestion into a denser and firmer gastric chyme (26.3 % crude protein, G* of ∼8500 Pa) than the chyme of the FG (15.7 % crude protein, G* of ∼3000 Pa). These contrasting intragastric structural changes of the gels reversed their original textural differences, which led to slower digestion and gastric emptying of proteins from the SG compared with the FG. The different intragastric pH profiles during the digestion of the two gels likely played a key role by modulating the proteolytic activity and specificity (to κ-casein) of pepsin. Preferential early cleavage of κ-casein in SG stimulated coagulation and compaction of solid chyme, whereas rapid hydrolysis of αS- and β-caseins in the FG weakened coagulation. This study provided new insights into controlling the structural development of dairy-based foods during gastric digestion and modulating digestion kinetics.