Untargeted mass spectrometry-based metabolomics approach unveils biochemical changes in compound probiotic fermented milk during fermentation

Probiotic functional products have drawn wide attention because of their increasing popularity. However, few studies have analyzed probiotic-specific metabolism in the fermentation process. This study applied UPLC-QE-MS-based metabolomics to track changes in the milk metabolomes in the course of fermentation by two probiotic strains, Lacticaseibacillus paracasei PC-01 and Bifidobacterium adolescentis B8589. We observed substantial changes in the probiotic fermented milk metabolome between 0 and 36 h of fermentation, and the differences between the milk metabolomes at the interim period (36 h and 60 h) and the ripening stage (60 h and 72 h) were less obvious. A number of time point-specific differential metabolites were identified, mainly belonging to organic acids, amino acids, and fatty acids. Nine of the identified differential metabolites are linked to the tricarboxylic acid cycle, glutamate metabolism, and fatty acid metabolism. The contents of pyruvic acid, γ-aminobutyric acid, and capric acid increased at the end of fermentation, which can contribute to the nutritional quality and functional properties of the probiotic fermented milk. This time-course metabolomics study analyzed probiotic-specific fermentative changes in milk, providing detailed information of probiotic metabolism in a milk matrix and the potential beneficial mechanism of probiotic fermented milk.