Abstract: Abstract: To investigate the microbial diversity and the relevance of their metabolites in traditional yak fermented dairy products featured, the present study analyzed the microbial diversity and metabolite profiles of three traditional yak dairy products, ghee, Qula, and yak yogurt, by using high-throughput sequencing and GC-TOF-MS, respectively. Results showed that the microbial communities of the three dairy products differed significantly at the genus level, with Lactobacillus being the superior bacterial genus in yogurt and Qula, and Lactococcus being leading in ghee; Geotrichum and yeasts were found in all fungal genera. In particular, a high abundance of Pichi was detected in yak yogurt and Qula, and unique Kluyveromyce was also present in yogurt, whereas the fungal genus composition varied considerably within the ghee. The results could provide a basis for labeling the dominant microflora of traditional dairy products. Metabolomics combined with multivariate statistical analysis identified a total of 51 differential metabolites. The characteristic metabolites of ghee were mostly lipids and lipid-like molecules; Qula was similar to yogurt in that the characteristic metabolites were organic acids and derivatives, in addition to lipid and lipid-like molecules. A total of 12 metabolic pathways involved in the regulation of flavor and quality of dairy products. Correlation analysis showed that Lactococcus and Geotrichum were negatively correlated with the metabolites screened, and Lactobacillus and Kluyveromyce were positively correlated with most of the metabolites screened. Differences in microbial structure could lead to quite different metabolites and nutrients in fermented yak dairy products, and the study provides a theoretical basis for better quality control of fermented foods.

Key words: Key words: Ghee, Qula, Yak Yogurt, Microbial Diversity, Metabolomics, Correlation