Bifidobacterium adolescentis B8589- and Lacticaseibacillus paracasei PC-01-co-fermented milk has more γ-aminobutyric acid and short-chain fatty acids than Lacticaseibacillus paracasei PC-01-fermented milk

Probiotics are increasingly used in the fermentation industry owing to their probiotic properties. However, most previous studies of milk fermentation are based on single-strain fermentation or focused on interactions between the starter strains without considering the role of probiotics in the microbial ecosystem. Thus, in this study, we compared the differences in the fermented milk metabolomes of single-strain fermentation with Lacticaseibacillus paracasei PC-01 (PC-01) versus dual-strain fermentation with both PC-01 and a probiotic, Bifidobacterium adolescentis B8589 (B8589), with the aim of revealing the metabolic effect of adding B8589 in the milk fermentation process. Although co-fermenting with B8589 did not influence the growth of PC-01, non-targeted metabolomics revealed significant changes in the dual-strain fermented milk metabolomes, characterized by increased levels of amino acid metabolites. Targeted metabolomics analysis confirmed that, by adding B8589 as the co-fermentation culture, the level of γ-aminobutyric acid increased by seven times; and the contents of acetate, propionate, butyrate, valerate, and citrate were also significantly enriched. Our results suggested that B8589 metabolically interacts with PC-01, which increases the amounts of functional metabolites in the co-fermented milk. This study provides interesting insights into the metabolic interaction between probiotic and starter culture in an industrial fermentation process.