Investigating the variations in microbiome and volatilome characteristics of sauce-flavor Muqu across different grades and production rounds

Muqu is the starter of high-temperature Daqu; however, the mechanisms underlying its quality formation remain unclear. Therefore, the effects of grade and round on Muqu quality were investigated. Biochemical activities were closely associated with grade, while moisture and fat content were linked to round. The volatilome was also significantly influenced by grade, with levels of differential compounds such as trimethylpyrazine, 2,3-butanediol, and methyl hexanoate showing a positive correlation with grade. In contrast, bacterial and fungal diversities were regulated by grade and round, respectively, resulting in distinct interaction patterns within the co-occurrence network. Acidity and amino acid nitrogen levels were key factors driving community assembly, and Virgibacillus, Kroppenstedtia, Thermoactinomyces, Aspergillus, and Byssochlamys were identified as the primary flavor producers. Functional predictions indicated the pivotal role of bacterial communities in flavor synthesis and fungal communities in carbohydrate metabolism. These findings provide new insights into improving Daqu quality via the Muqu grading strategy.