Exploring the differences in sauce-flavour Daqu from different regions and its contribution to Baijiu brewing based on microbial communities and flavours

Abstract Daqu is an essential saccharification and fermentation agent in Baijiu brewing, and its characteristics affect the yield, quality, and flavour of Baijiu. The fundamental reason is that Daqu can provide rich microbial resources, complex enzyme systems, and raw materials for the Baijiu brewing process. In this study, three sauce-flavour Daqu from two production areas, Beijing and Guizhou, were selected to focus on discussing and analysing the main contributions of sauce-flavour Daqu itself to Baijiu brewing without interference from the external environment. The differences in the flavour composition and microbial communities of three Daqu were analysed. Microbial biomarkers were analysed by Lefse multilevel discriminant analysis for three Daqu. We found that different regions have their own biomarkers. Citrobacter, Rhodococcus, and Pseudomonas, were biomarkers of HD Daqu. Oceanobacillus, Aspergillus and Pichia were biomarkers of MT Daqu. Bacillus, Pediococcus and Fusarium were biomarkers of WM Daqu. A solid-state simulation fermentation experiment was carried out to analyse changes in the flavour composition and microbial communities of fermented grains after 35 days of fermentation. The results showed that the microbial communities and the flavour composition in the Daqu and fermented samples differed significantly. The dominant microorganism genus evolved from Citrobacter, Rhodococcus, and Thermomyces to Lactobacillus, Pediococcus, and Pichia HD sample. The dominant microorganism genus in WM sample changed from Virgibacillus, Oceanobacillus, and Thermomyces to Lactobacillus, Pediococcus, and Pichia. Whereas in MT sample, the dominant microorganism genus evolved from Virgibacillus, Kroppenstedtia, and Thermomyces to Lactobacillus, Pediococcus, and Pichia. Additionally, the main flavour composition also changed after fermentation, which in the late fermentation period were phenylethyl alcohol, ethyl palmitate, tetramethylpyrazine, and 3-methylbutanoic acid. These findings can provide support to explain the importance and contribution of sauce-flavour Daqu in Baijiu brewing scientifically.