Assessment of milk protein digestion kinetics: effects of denaturation by heat and protein type used

Knowledge about how molecular properties of proteins affect their digestion kinetics is crucial to understand protein postprandial plasma amino acid (AA) responses. Previously it was found that a native whey protein isolate (NWPI) and heat denatured whey protein isolate (DWPI) elicit comparable postprandial plasma AA peak concentrations in neonatal piglets, while a protein base ingredient for infant formula (PBI, a β-casein-native whey protein mixture) caused a 39% higher peak AA concentration than NWPI. We hypothesized that both whey protein denaturation by heat as well as changing protein composition by including β-casein, increases the rate of intact protein loss, and that changing the protein composition (by including β-casein), but not whey protein denaturation, yields a faster absorbable product release. Therefore NWPI (91% native), DWPI (91% denatured) and PBI hydrolysis was investigated in a semi-dynamic in vitro digestion model (SIM). NWPI and DWPI hydrolysis were also compared in a dynamic digestion model with dialysis (TIM-1) to exclude potential product inhibition effects that may occur in a closed vessel digestion model as SIM. In both models, the degree of hydrolysis (DH), loss of intact protein, and release of absorbable products (SIM: