Modification of Micellar Casein Isolate Alters Protein Degradation Pathways and Peptide Generation during In Vivo Gastrointestinal Digestion

To elucidate how structural modification of micellar casein isolate (MCI) influences digestive protein breakdown, proteomics and peptidomics analyses were employed to characterize protein degradation and peptide profiles of formulas containing different MCIs during gastrointestinal digestion. Newborn piglets served as a digestion model mimicking infants' conditions and were fed formulas based on MCI, plasmin-treated MCI (PMCI), or calcium-reduced MCI (CaMCI) blended with whey protein concentrate (WPC). Plasmin prehydrolysis tended to increase the proportion of intact protein residues in gastric clots and a distinct peptide profile, while generating lower peptide diversity in gastric juice compared with other dietary groups. In contrast, the CaMCI group showed greater peptide diversity and abundance than other groups in the intestine (especially distally), resulting in higher levels of putative bioactive peptides associated with reported functions such as DPP-IV inhibition and cholesterol regulation. The peptide profiles observed across gastric and intestinal regions reflect structure-dependent digestion.