In vitro digestion of soymilk using a human gastric simulator: Impact of structural changes on kinetics of release of proteins and lipids

Abstract

Soymilk (about 3% protein and 1.8% lipids), prepared by wet disintegration of soaked soybeans, was heated at 108 °C for 15 min and then subjected to in vitro gastric digestion using an advanced dynamic digestion model (i.e. a human gastric simulator). Microstructural changes, physicochemical stability and protein digestibility were studied; the release of protein and lipid during digestion was also quantified. Gastric digestion significantly influenced the colloidal stability of soymilk, resulting in coagulation of the soy proteins because of the action of pepsin and the acidic pH. The soymilk oil bodies appeared to be entrapped within the coagulated protein particles. With continued digestion, protein hydrolysis by pepsin resulted in the disruption of the coagulum structure, leading to an accelerated gastric emptying of both protein and lipid in the first 45 min. Gastric-induced coagulation did not have a significant impact on either protein or lipid emptying, except for an initial delay of lipid emptying in the first 15 min. No extensive coalescence of soymilk oil bodies was observed under a confocal microscope. This study provides further understanding of the fate of soymilk in the digestive tract and may be useful in the microstructural design of foods to achieve a controlled physiological response during digestion.