Impacts of Whey Protein on Digestion of Lotus Seed Starch Subjected to a Dynamic In Vitro Gastric Digestion

The exogenous protein (e.g. whey protein isolate, WPI) is commonly used to fortify and modify the functionality of starchy food, that might influence starch hydrolysis during gastric digestion. In this study, the effect of whey protein on the digestion of lotus seed starch (LS) subjected to a dynamic in vitro gastric digestion was investigated. The particle size distribution, the swelling power of the starch and the changes in pH, viscosity, microstructure and hydrolysis of 2% LS and blends of 2% LS with 1, 2 and 4% WPI were investigated. The presence of whey protein caused decreases in the particle size and the swelling power and an increase in the viscosity of the LS granules. The presence of whey protein also delayed the decrease in the pH and increased the hydrolysis of LS during the in vitro gastric digestion. WPI surrounded or encapsulated the LS granules observed using confocal laser scanning microscopy, and may have been the reason for the decrease in swelling power of the starch granules. The increased degree of gastric digestion of LS with the addition of WPI was largely related to the delayed decrease in the gastric pH rather than to alterations in the swelling power and viscosity and WPI’s physical barrier toward starch.