Dynamics in microbial communities and flavor characteristics before and after the end-point of Zhenjiang aromatic vinegar fermentation revealed by macro-transcriptomics and metabolomics.

Multi-strain microbial fermentation plays an important role in the formation of rich flavor of cereal vinegar, but it also brings challenges to the control of fermentation process and the judgment of fermentation end point. In this study, the differences of microbial community structure and metabolites composition in fermented grains (termed CuPei in Chinese) of Zhenjiang aromatic vinegar before and after acetic acid fermentation were compared. First, the physical and chemical indicators of CuPei during acetic acid fermentation of Zhenjiang aromatic vinegar were used to identify the fermentation endpoint. Second, the changes of metabolites in CuPei before and after the fermentation endpoint were investigated using metabolomics. A total of 43 differentially expressed metabolites were identified, including 18 esters, 9 acids, 2 alcohols, 5 ketones and 3 aldehydes. Hereinto, formamide, pyrazine and dibutylphthalate were the key intermediate metabolites. Furthermore, five species, including Komagataeibacter sp., Limosilactobacillus panis, Lactobacillus acetoolerans, Limosilactobacillus pontis and Acetilactobacillus jinshanensis were identified as key functional microorganisms involved in the production of these unique metabolites by metatranscriptomics. These findings improve our understanding of the relationship between microbial succession and flavour formation in the acetic acid fermentation process of Zhenjiang aromatic vinegar, thereby improving the accuracy of judging the fermentation endpoint of Zhenjiang aromatic vinegar, and improving the flavour quality of the product.