Metagenomic features of Tibetan kefir grains and its metabolomics analysis during fermentation

The microbial community diversity of Tibetan kefir grains (TKGs) contributes to intricate metabolite changes and metabolic interactions during milk fermentation. In present research, metagenomic sequencing analysis was used to reveal microflora composition of TKGs, indicating the presence of 522 species, with Lactobacillus kefiranofaciens as the most abundant species. Lactobacillus and Bifidobacterium were the most diverse probiotics. Subsequently, the metabolites changes of kefir were investigated using metabolomics with UHPLC - MS/MS. Datasets at the 8 h, 24 h and 36 h of fermentation (group A, B, C, respectively) were analyzed to reveal the apparent differences during fermentation. A total 192 differential metabolites were identified in the A vs B group, and 96 differential metabolites were identified in the C vs B group. In addition, 7 metabolic pathways were enriched based on the differential metabolites in group A vs B, and mainly related to lipid metabolism, amino acid biosynthesis, carbohydrate metabolism and phenylpropanoid biosynthesis. The differential metabolites in C vs B group covered 11 pathways, mainly involving amino acid metabolism, citrate cycle (TCA cycle), translation, membrane transport and biosynthesis of secondary metabolites. The study of metabolomics in kefir fermentation provides a theoretical foundation for visualization of the fermentation process in future studies.