Bacterial diversity, bioactive peptides, and enhanced immunomodulatory effects in raw milk kefir made with defined starter cultures versus backslopping

Abstract

This study compared the microbial composition, peptide profiles, and immunomodulatory effects of raw milk kefir produced using a defined starter culture (RMK-S) versus backslopping (RMK-B). RMK-B exhibited significantly higher microbial loads, with a 10-fold increase in total plate counts and 35-fold increase in lactic acid bacteria compared to RMK-S. This correlated with higher peptide content in RMK-B kefir, though RMK-S displayed higher bacterial diversity and a more diverse, bioactive peptide pool. Microbial analysis revealed RMK-S retained the starter culture's profile, while RMK-B was dominated by Lactococcus lactis and consistent yeast species, including Kazachstania, Klyveromyces, and Galactomyces. In a murine food allergy model, RMK-S kefir significantly reduced the allergic skin response and increased IFN-γ production, demonstrating enhanced immune modulation. RMK-B did not exhibit these protective effects. These findings point towards the role of bacterial diversity and peptide composition in kefir's health benefits, favoring defined starter cultures over backslopping.