Unraveling the microbial community and succession during the maturation of Chinese cereal vinegar Daqu and their relationships with flavor formation.

Daqu, the fermentation starter of Shanxi aged vinegar (a traditional Chinese cereal vinegar), is produced by natural fermentation of barley and/or peas under conditions of open environment. However, the succession of microbial communities and its effects on volatile compounds during Daqu maturation were still unclear, which are closely related to the flavor and quality of Shanxi aged vinegar. In this study, the dynamics of physicochemical properties, microbial communities, and volatile compounds and their inter-relationships during the production of Shanxi aged vinegar Daqu were investigated. High-throughput sequencing analysis showed that Lactobacillus and Rhizopus were the most abundant bacteria and fungi during Daqu maturation, respectively. Co-occurrence network analysis showed that Lactobacillus, Saccharopolyspora, Leuconostoc, and Weissella were the important taxa affecting the diversity of Daqu microbial community. Spearman correlation analysis showed that Leuconostoc, Aspergillus, Rhizopus, and Wickerhamomyces were positively correlated with starch and reducing sugars; Wickerhamomyces, Aspergillus, and Bacillus were positively correlated with esterification; Lactobacillus, Enterobacter, Bacillus, Aspergillus, and Rhizopus were positively correlated with lactic acid and acetic acid. Based on the Mean Decrease Accuracy index analysis showed that, ethyl acetate, 1-nonanal, 1-octen-3-ol, ethylbenzene, 3-furanmethanol, and methyl isovalerate were the volatile characteristic compounds during Daqu maturation, respectively. Aspergillus, Byssochlamys, Lichtheimia, Rasamsonia, Rhizopus, Syncephalastrum, Enterobacter, Lactobacillus, Leuconostoc, and Staphylococcus were strongly correlated with volatile compounds; among them, fungi had a greater impact on volatile compounds than bacteria. This study may further improve our understanding concerning the microbial system and microbial roles of Chinese cereal vinegar Daqu and may contribute to optimize the production process of Daqu.