Proteolysis and peptide release during in vitro digestion at infant conditions of bovine casein ingredients in comparison with human milk.

The present study evaluated in vitro gastrointestinal digestion behavior and peptide generation in infant conditions of simplified milk protein blends composed of micellar casein isolates (MCI) and whey protein concentrate (WPC) blends (40,60, 1.2% w/w total protein). Standard MCI, plasmin-treated (PMCI), and calcium-reduced (CaMCI) forms of MCI were compared, alongside pure WPC and human milk (HM) as references. During gastric digestion, caseins were rapidly hydrolyzed, whereas whey proteins remained largely intact until intestinal digestion. Plasmin pre-hydrolysis generated peptides and exposed additional pepsin cleavage sites, resulting in enhanced gastric hydrolysis and peptide release in PMCI:WPC compared with MCI:WPC. Decalcification also facilitated digestion, but its effect was pronounced most in intestinal phase, where CaMCI:WPC produced a markedly higher level of peptides due to improved protease accessibility. Both treatments yielded higher levels of bioactive peptides than MCI:WPC. HM produced more diverse but less abundant peptides, and bioactive peptides were less than protein mixtures.