In order to clarify the succession pattern and potential functions of the microbial communities in fermented grains for Nongxiangxing baijiu, high-throughput sequencing was used to investigate the dynamic change of microbial community structure, and the correlations between microbial community structure and physicochemical indicators were analyzed at different fermentation stages. Phylogenetic Investigation of Communities by Reconstruction of Unobserved States (PICRUSt) was used to predict the potential functions of microbial communities in fermented grains. The results showed that Firmicutes, Proteobacteria, Actinobacteriota, Ascomycota, and Basidiomycota were the dominant phyla in fermented grains. The dominant genera were Lactobacillus, Bacillus, Staphylococcus, Thermoactinomyces, Kazachstania, Wickerhamomyces, Penicillium, Candida, Aspergillus, Meyerozyma, Debaryomyces, with Lactobacillus, Kazachstania and Wickerhamomyces being the absolutely dominant ones. The contents of reducing sugar and starch showed a significantly positive correlation with 8 bacterial genera (P < 0.05). Acidity and moisture content showed a significantly negative correlation with 10 bacterial genera. Some fungi were significantly correlated with physicochemical indicators. PICRUSt analysis showed that the relative abundance of functional enzymes was significantly different at different fermentation stages, and the dominant microorganisms in fermented grains participated in glycolysis, acid metabolism and ethanol synthesis to form a complete metabolic chain, indicating that the microbial community succession of fermented grains could be the major reason for the differences in metabolism at different fermentation stages. The findings of this study would provide a theoretical basis for the study of the metabolic mechanisms of microorganisms used for baijiu brewing.

In order to increase the content of ethyl acetate in Xiaoqu Baijiu, a strain of Saccharomycopsis fibuligera M1 with strong ester-producing capacity isolated from Daqu was used as the starting strain for preparing Fuqu (M1-Fuqu), which was subsequently used for the brewing of Xiaoqu Baijiu. The effect of enhanced fermentation of M1-Fuqu on volatile compounds of Xiaoqu Baijiu. The results showed that the optimal cultivation conditions for M1-Fuqu were 40% of water content, 28 ℃ of cultivation temperature, 6 mmol/100 g of initial acidity, and 48 h of cultivation time. The brewing experiments showed that the contents of acetic acid and ethyl acetate significantly increased (P < 0.05), and the contents of isobutanol and isoamyl alcohol significantly decreased in the M1-Fuqu group compared with the control group (traditional Xiaoqu Baijiu) (P < 0.01). Differences in the microbial community structure of fermented grains were observed between the control and experimental groups during the fermentation process, and the relative abundance of S. fibuligera and Weissella significantly increased in the experimental group. In addition, PICRUSt2 functional prediction confirmed that the abundance of enzymes involved in the metabolism of acetic acid and ethyl acetate was higher in the experimental group than in the control group during the fermentation process. In conclusion, the present study highlighted that the application of S. fibuligera M1-added Fuqu could increase the content of ethyl acetate in Xiaoqu Baijiu, which is reference significance for the quality improvement of Xiaoqu Baijiu.