In vitro digestion of infant formulations with hydrolysed and non-hydrolysed proteins from dairy and soybean.

Digestion of hydrolysed and non-hydrolysed dairy (casein and whey proteins) and soy proteins commonly used in infant formulations was studied under in vitro gastrointestinal (without lipases) conditions for 60 and 120 minutes in the stomach and small intestine, respectively. The pH-drop, gel electrophoresis, microstructure, particle size distribution, and ninhydrin-reactive amino nitrogen of the digesta were monitored over the digestion period. The obtained results suggested that hydrolysed proteins were completely digested in the small intestine, while non-hydrolysed proteins (caseins, α-lactalbumin, β-lactoglobulin, conglycinin, glycinin) were only partially digested in the simulated gastrointestinal tract. Although the observed pH-drop for non-hydrolysed protein formulations was lower, significantly higher levels of ninhydrin-reactive amino nitrogen in hydrolysed proteins suggested higher digestibility of hydrolysed proteins than their non-hydrolysed counterparts. Only formulations containing caseins showed a decrease in the particle size of protein aggregates during gastric digestion. No fat globule coalescence was observed during both gastric and intestinal digestions under the given conditions.