Abstract: To investigate the microbial diversity and the correlation with metabolites in traditional fermented yak milk products, the study used high-throughput sequencing and gas chromatography-time-of-flight mass spectrometry (GC-TOF-MS) to analyze the microbial diversity and metabolite profiles of yak ghee, Qula, and yogurt. Results showed that the microbial communities of the three dairy products differed significantly at the genus level. The dominant bacterial genus in yak yogurt and Qula was Lactobacillus, while Lactococcus was dominant in ghee. The fungi Geotrichum and yeast were found in all samples. In particular, a high abundance of Pichi was detected in yak yogurt and Qula, and Kluyveromyce was exclusively present in yogurt, whereas the fungal genus composition varied considerably among ghee samples. Using metabolomics combined with multivariate statistical analysis, a total of 51 differential metabolites were identified. The characteristic metabolites of ghee were lipids and lipid-like molecules, and the characteristic metabolites of Qula and yogurt were similar, including organic acids and their derivatives as well as lipid and lipid-like molecules. A total of 12 metabolic pathways were found to be involved in the regulation of the flavor and quality of fermented yak milk products. Correlation analysis showed that Lactococcus and Geotrichum were negatively correlated with selected metabolites, while Lactobacillus and Kluyveromyce were positively correlated with most of the metabolites. Differences in the microbial community structure could lead to differences in the metabolite profile of fermented yak milk products. The results from this study provide a theoretical basis for better regulating the quality of fermented yak milk products.

Key words: ghee; Qula; yak yogurt; microbial diversity; metabolomics; correlation