Association of Cellar Microbial Communities with Differences in Flavor of Base Baijiu across Fermentation Rounds during Mechanized Production of Jiangxiangxing Baijiu

This study investigated the association of cellar microbial communities with the differences in the flavor of base Baijiu obtained after the 2nd to 4th rounds of fermentation during the mechanized production of Jiangxiangxing Baijiu. It systematically analyzed the variations in physicochemical indicators of fermented grains, the succession pattern and assembly mechanism of microbial communities, and the flavor components of base Baijiu. The core microbial community in each fermentation round was identified and differential flavor compounds among fermentation rounds were selected. Furthermore, correlation analysis was performed to elucidate the mechanism underlying the differences in the flavor of base Baijiu across fermentation rounds. The results showed that the moisture and total titratable acidity in fermented grains exhibited a similar increasing trend with increasing fermentation rounds. Meanwhile, the dynamic changes and succession patterns of the microbial communities revealed that Candida and Geotrichum were detected only in the 2nd round, while Lactobacillus and Pichia were common dominant microorganisms in each fermentation round. The top 13 bacterial genera and the top 17 fungal genera identified by the random forest algorithm were considered as core microorganisms across all rounds. The Mantel test results showed that the total titratable acidity, moisture, and starch content of fermented grains drove microbial community succession. In total, 11 differential flavor compounds were identified by orthogonal partial least square-discriminant analysis (OPLS-DA) with their contents in base Baijiu varying among all fermentation rounds and among the upper, middle, and bottom layers of fermented grains. The Spearman correlation analysis between differential flavor compounds and core microbiota indicated that Planococcus, Kazachstania, and Zygosaccharomyces might influence the formation of ethyl acetate and acetal in base Baijiu. Through neutral community model analysis, it was found that the contribution of the random processes (e.g., random migration, birth-death events, environmental disturbances, and probabilistic dispersal) to shaping the microbial communities decreased with increasing fermentation rounds, while that of the deterministic factors (e.g., fermentation temperature, humidity, and pH) exhibited a reverse trend. The research results can provide a theoretical basis and technical support for the high-quality mechanized production and quality and flavor regulation of Jiangxiangxing Baijiu.