Exploring the Successions in Microbial Community and Flavor of Daqu during Fermentation Produced by Different Pressing Patterns

Abstract

<i>Daqu</i> can be divided into artificially pressed <i>daqu</i> (A-<i>Daqu</i>) and mechanically pressed <i>daqu</i> (M-<i>Daqu</i>) based on pressing patterns. Here, we compared the discrepancies in physicochemical properties, volatile metabolites, and microbiota features between A-<i>Daqu</i> and M-<i>Daqu</i> during fermentation and further investigated the factors causing those differences. A-<i>Daqu</i> microbiota was characterized by six genera (e.g., <i>Bacillus</i> and <i>Thermoactinomyces</i>), while five genera (e.g., <i>Bacillus</i> and <i>Thermomyces</i>) dominated in M-<i>Daqu</i>. The flavor compounds analysis revealed that no obvious difference was observed in the type of esters between the two types of <i>daqu</i>, and M-<i>Daqu</i> was enriched with more alcohols. The factors related to differences between the two types of <i>daqu</i> were five genera (e.g., <i>Hyphopichia</i>). The functional prediction of microbial communities revealed that the functional discrepancies between the two types of <i>daqu</i> were mainly related to ethanol metabolism and 2,3-butanediol metabolism. This study provided a theoretical basis for understanding the heterogeneity of <i>daqu</i> due to the different pressing patterns.