Gastrointestinal digestion of dairy and soy proteins in infant formulas: An in vitro study

- α-Lactalbumin and β-lactoglobulin resist in vitro infant gastric proteolysis.
- β-Lactoglobulin and caseins completely hydrolyse in the in vitro infant duodenal phase.
- Degradation of proteins is highest for formulations with the highest casein fraction.
- Glycinin and β-conglycinin partially hydrolyse in the infant in vitro digestion.
- Pepsinolysis decreases the particle size distribution of the protein aggregates.

An in vitro digestion simulating infant gastrointestinal tract studied the digestion of caseins, whey and soy proteins, commonly used in infant formulations, in the presence of proteases only (without lipolytic enzymes). 60 min of gastric phase and 120 min of intestinal phase coupled with gel electrophoresis, confocal microscopy, mastersizer and pH were employed to monitor the degradation of proteins, microstructure, particle size distribution and pH drop of the digesta through the in vitro digestion process. Obtained results showed around 20% of caseins and almost no components of whey were hydrolysed after 60 min in the simulated stomach. In the simulated duodenal phase, 8% of α-lactalbumin was hydrolysed while caseins and β-lactoglobulin completely digested immediately and 30 min respectively after addition of duodenal digestive proteases. Overall, soy proteins indicated lower level of hydrolysis than dairy proteins during in vitro infant digestion as observed by SDS-PAGE.The soy protein fractions glycinin and β-conglycinin were partially hydrolysed during the gastrointestinal phase. The observed pH drop confirms that caseins are easily digested in the duodenal phase compared to whey and soy protein. Gastric digestion resulted in a decrease of the particle size of protein aggregates, but no fat coalescence was observed during both gastric and duodenal digestions in the given conditions.