The changes in the microbial community structure and the synthesis of volatile flavor compounds in fermented grains (Jiupei) for nongxiangxing baijiu in the presence of Bacillus velezensis was analyzed to understand the effect of microorganisms in Daqu, a traditional fermentation starter for the production of baijiu, on microorganisms in Jiupei and their metabolism. Fermentation experiments were carried out by inoculating a strain of B. velezensis isolated from medium- and high-temperature Daqu into Jiupei. Headspace solid phase microextraction combined with gas chromatography-mass spectrometry (HS-SPME-GC-MS) was used to detect the volatile flavor compounds of the control and experimental Jiupei, and the microbial community structure of the control and experimental Jiupei was studied by amplicon sequencing. Partial least squares-discriminant analysis (PLS-DA) was used to explore the differential volatile flavor compounds between the control and experimental samples, and Spearman correlation analysis was used to analyze the correlation between the dominant microbial community and the differential volatile flavor compounds in Jiupei. The results showed that the abundance and uniformity of microorganisms in the experimental group did not change significantly compared with the control group, and there was no significant difference in the microbial community structure during the whole fermentation process. The contents of volatile flavor substances such as acids, esters, and alcohols in the experimental group were significantly increased compared with the control group. A total of 15 significantly differential volatile flavor compounds were identified between the control and experimental groups. The contents of caproic acid and ethyl caproate in the experimental group increased significantly. Caproic acid had a significantly positive correlation with Lactobacillus, and ethyl caproate was positively correlated with Pichia and Wickerhamomyces, but negatively correlated with Thermoascus, Bacillus and Weissella. The results of this study can help to understand the perturbation effect of Daqu microorganisms on Jiupei microorganisms and the changes of metabolites.

The changes in the microbial niche and community assembly of fermented grains for Nongxiangxing baijiu during fermentation by Saccharomyces cerevisiae were analyzed to explore the mechanism for the influence of inoculation with S. cerevisiae on the microbial succession of fermented grains. In this study, a strain of S. cerevisiae isolated from fermented grains for Nongxiangxing baijiu was inoculated into distilled grains for fermentation experiments, and the microbial community structures of fermented grains with (experimental) and without (control) inoculation with S. cerevisiae were studied by high-throughput sequencing technology, and the niche changes of the control and experimental groups were studied by statistical analysis, and the mechanism of microbial community assembly was analyzed by the zero model. The results showed that compared with the control group, the diversity, species composition and niche width of microbial communities in the experimental group decreased, and the relative content of specialized species groups increased. In the co-occurrence network, the relative abundance of specialized species in the major modules of the experimental group increased, and the network complexity increased. The assembly of microbial communities in the two groups was mainly dominated by random processes, while ecological drift and homogeneous diffusion in the experimental group were less important for community construction, which made the microbial community succession more certain. This study revealed the ecological function of S. cerevisiae in Nongxiangxing baijiu fermentation, which could have an important impact on baijiu fermentation.