Domination of pit mud microbes in the formation of diverse flavour compounds during Chinese strong aroma-type Baijiu fermentation

Abstract The pit mud microbes are tightly correlated with the quality of Chinese strong aroma-type Baijiu. However, it is still unclear the explicit contributions of pit mud microbes to flavour formation. Through down-scaled fermentation with or without pit mud, we found that 85 genera from pit mud, dominating by Caproiciporducens, Caloramator, Sedimentibacter and Caldicoprobacter, migrated into fermented grains. These microbes increased the microbial diversity in fermented grains and resulted in an improved flavour profiles: 13 volatiles acids, 6 linear-chain alcohols and 37 esters were more abundant in the pit mud group. Most of these compounds were positively correlated with anaerobes derived from pit mud by network correlation analysis. Moreover, a synergistic effect of diverse esters formation was found between pit mud microbes and starter (Daqu). The pit mud microbes contributed to abundant volatile acids and linear-chain alcohols that were selectively esterified by Daqu (starter), and the metabolism of pit mud microbes elevated the pH of fermented grains, which further elevated the esterification capability of Daqu. These findings improve the understanding of the diverse flavour compounds formation during strong aroma-type Baijiu fermentation.