Bacterial community diversity of shilixiang baijiu Daqu based on metagenomics

Daqu is a fermentative saccharifying agent that is used to initiate fermentation in the production of Chinese baijiu. In this study, we performed metagenomic analysis of microorganisms present in shilixiang baijiu Daqu in order to analyze the bacterial community diversity of shilixiang baijiu Daqu from four different fermentation batches and determine the effect of fermentation process on microorganisms. An understanding of the composition and structure of bacterial communities of the shilixiang baijiu Daqu can provide a theoretical basis for the stability and quality evaluation of shilixiang baijiu Daqu-making technology. The results showed that the microbial community structure was different among Daqu samples from different fermentation batches, and at different fermentation days within the same fermentation batch. In general, the abundance and diversity of microorganisms found in Daqu samples from the four batches increased after 30 days of fermentation. The analysis of community structure showed that after 30 days of fermentation, Firmicutes was the predominant phylum in the four batches of the shilixiang baijiu Daqu samples. After 30 days of fermentation, the proportion of Lactobacillus, Pediococcus, and Staphylococcus increased, while the proportion of Pseudomonas decreased; Lactobacillus was the dominant microorganism in the shilixiang baijiu Daqu samples. We also determined that Lactobacillus, Pseudomonas, Leuconostoc, Lactococcus, Saccharopolyspora, and Enterococcus were present in Jannanchun, Maotai, and shilixiang baijiu Daqu samples. In addition, every batch had its own unique genus. We discovered genera that had not been found before in shilixiang baijiu Daqu samples. Through the prediction of functional gene composition, we confirmed that the bacterial population in shilixiang baijiu Daqu mainly had metabolic, genetic information processing, and environmental information processing functions. This study contributes to expanding our understanding of the functional characteristics of Daqu bacterial communities and provides new ideas for future in-depth studies of the diversity and functionality of Daqu bacteria. PRACTICAL APPLICATIONS: This study contributes to expanding our understanding of the functional characteristics of Daqu bacterial communities and provides new ideas for future in-depth studies of the diversity and functionality of Daqu bacteria. Based on these results, we can further select functional strains related to the performance of koji. The results of this study point out the direction for future studies on the formation mechanism of trace aroma substances in baijiu and the improvement of koji quality.