Correlation between microbial communities, metabolites, and bioactivities in fermented mare's milk revealed by metagenomics and metabolomics.

Koumiss exhibits various functional properties, including antioxidant, hypoglycemic, and antihypertensive effects; however, natural fermentation is characterized by an uncontrollable microbial community structure, significant fluctuations in product quality, and a lack of specialized fermentation agents. The mechanisms underlying the links between microbial communities, functional metabolites, and bioactivity in natural and inoculated fermentation systems remain unclear. Therefore, this study employed bioactivity assays, metagenomics, and non-targeted metabolomics to systematically analyze differences in microbial communities, metabolite composition, and functional activities of mare's milk under different fermentation regimes. The results indicated that, compared with natural fermentation, inoculated fermentation with a mixed lactic acid bacteria (LAB) culture significantly enhanced the antioxidant, α-glucosidase, α-amylase inhibitory activities, and ACE inhibitory activity of mare's milk; microbial diversity in fermented samples was significantly reduced, with a more pronounced decrease in the inoculated group. Metabolomic analysis revealed that inoculated fermentation significantly enriched functional metabolites, including lipids and organic acids. Correlation analysis indicated that the abundance of Lactiplantibacillus and Limosilactobacillus was significantly positively correlated with beneficial metabolites (e.g., linoleic acid, α-linolenic acid) and functional activities. The lipid and amino acid metabolic pathways are closely associated with the differences in in vitro biological activity of inoculated fermented mare's milk. This study provides a fermentation starter that can improve the in vitro functional activity of mare's milk and reveals the potential metabolic links between LAB fermentation and the altered functional traits of mare's milk, thereby providing a theoretical basis and technical support for the development of high-value-added fermented mare's milk products.