Bacterial community structure and metabolomic pathways in yak milk and cattle-yak milk during refrigeration: analysis of interspecific differences in dairy spoilage

Raw milk usually needs to be refrigerated at 4 before production, and microbial contamination during this process can cause spoilage of refrigerated raw milk. However, there is currently almost no research on plateau characteristic milk (yak milk and cattle-yak milk) (YM and CYM). In this study, significant differences in bacterial communities and their succession patterns were found between YM and CYM during 4 refrigeration, while Lactococcus, Pseudomonas, and Serratia revealed significant differences between the two groups of milk by Ancom2 analysis. And the microbial community in CYM exhibits higher network complexity and tighter interactions. The enzymes exhibiting stronger correlations identified in YM are more abundant than those in CYM predicted by PICRUSt2. Through metabolomics methods, the metabolome profiles between CYM and YM during refrigeration were significantly different. With the extension of storage time, the relative abundances of lipids and lipid-like molecules, and organic nitrogen compounds were decreased, the relative abundances of organic acids and derivatives was increased (YM is more obvious than CYM). Moreover, 8 metabolites gradually increases with the extension of storage time, and has a good correlation with Psychropliles growth. These metabolites have the potential to serve as markers of plateau characteristic milk deterioration. The results will provide a theoretical basis for improving the quality and safety of plateau characteristic milk and its products.