Peptidomic Characterization and Functional Properties of Goat and Cow Milk Kefir before and after In Vitro Digestion.

Kefir is a fermented beverage produced from goat or cow milk. This study evaluated the bioactive potential and peptidomic profile of kefirs from both species before and after in vitro digestion. Peptides from undigested, gastric, and intestinal phases were characterized by LC-MS/MS. In silico tools identified sequences homologous to known bioactive peptides, with functions such as antihypertensive, immunomodulatory, and anticancer. β-casein was identified as the main precursor protein, with the highest number of peptides identified during the gastric phase. Undigested kefir showed antioxidant activity in ABTS and FRAP assays, and peptide extracts from both kefirs exhibited activity in all antioxidant assays across digestion phases. Antimicrobial activity against E. coli and S. aureus was observed before digestion for both kefir peptides; however, after digestion, only goat kefir peptides remained active against E. coli. This data indicates that kefir peptides are promising bioactive compounds for food and pharmaceutical applications.