Fig. 1: Schematic diagram of study design.

Pasteurized milk was co-fermented by two probiotic strains, Bifidobacterium adolescentis B8589 and Lacticaseibacillus paracasei PC-01. Samples were collected every 12 h of fermentation until the pH reached 3.8 after 72 h. The probiotic viable count in the fermented milk was enumerated by flow cytometry. The milk metabolomes (at 0, 36, 60, and 72 h) were detected by ultra-performance liquid chromatography for tracking changes in metabolites and metabolic pathways of interest in the course of milk fermentation. Finally, enrichment analysis was performed on the identified differential metabolic pathways.