Correlation Analysis between Microbial Community and Volatile Flavor Compounds in Fermented Grains during the Second Round of Stacking Fermentation of Cave-Brewed Jiangxiangxing Baijiu

To investigate the dynamic changes in fermented grains during the second round of stacking fermentation of cave-brewed Jiangxiangxing Baijiu, gas chromatography-mass spectrometry (GC-MS) and high-throughput sequencing were employed to systematically analyze the composition of volatile flavor compounds and the structure of the microbial community. The results demonstrated that as fermentation progressed, the temperature and moisture content of fermented grains significantly increased from 29.67 ℃ and 45.12% to 44.33 ℃ and 54.94%, respectively. Additionally, the starch content decreased from 32.24% to 25.82%. A total of 364 bacterial genera and 97 fungal genera were detected, with the dominant bacterial genera being Virgibacillus, Oceanobacillus, and Kroppenstedtia. The dominant fungal genera were Thermomyces, Thermoascus, and Saccharomycopsis. During fermentation, the abundance of dominant bacteria such as Virgibacillus initially increased and then decreased; regarding the fungal community, the abundance of Thermomyces gradually decreased and Monascus became enriched. A total of 44 volatile flavor compounds were detected during the fermentation process, predominantly esters, aldehydes, and alcohols. Correlation analysis demonstrated that Lactobacillus and Monascus exhibited significant positive correlations (|r| > 0.7, P < 0.05) with the contents of various esters, suggesting their important roles in the flavor formation of cave-brewed Jiangxiangxing Baijiu. This study systematically elucidated the dynamic correlations among the physicochemical properties, microbial community succession, and flavor metabolite formation of fermented grains during the second round of stacking fermentation of cave-brewed Jiangxiangxing Baijiu, providing a theoretical basis for in-depth research on its fermentation mechanism and process optimization.