Peptidome and Metabolome Profiling of Fermented Milk Products Reveal Accumulation of Bioactive Compounds During Cold Storage

This study assessed the metabolome and peptidome profiles of cow’s milk and four traditional fermented milk products produced using standard sets of starter cultures. Many of these microbe-generated molecules exhibit biological activities that can affect human health. We used non-targeted metabolomic methods to assess semi-quantified concentrations of four types of molecules in the final products: peptides; amino acids; long-, medium-, and short-chain fatty acids; and mono- and disaccharides and their derivatives. Ultra-performance liquid chromatography–mass spectrometry (UPLC-MS/MS) was performed on the peptidomes. For all other fractions, we used gas chromatography–mass spectrometry (GC-MS), with a method adapted to specific metabolite conditions. The metabolome and peptidome of 15 dairy milk products, including yogurt (Y), fermented milk (FM), kefir made with commercial cultures (K) and kefir made with grains (KG), were analyzed on days 7 and 14 of shelf life at +4 °C, and milk (M) samples with various fat content were used as a reference. A total of 348 peptides, 37 amino acids, 30 fatty acids, and 23 mono- and disaccharides were identified in the products. Among them, 41 putative bioactive peptides were annotated via in silico database mining, and together with branch-chained amino acids (BCAAs), orotic acid (vitamin B13), d-phenyllactic acid, 5-phenylvaleric acid and myo-inositol (vitamin B8), accumulated in fermented products during storage. Bioactivities were not experimentally validated in this study.