Analysis of microbial community succession and its metabolic characteristics in the first and second rounds of cave-brewed sauce-flavor Baijiu

The natural cave located on the bank of the Chishui River in Guizhou is currently the only base in the country for brewing sauce-flavor Baijiu in the cave. Utilizing the natural cave for brewing not only enriches the microbial source of sauce-flavor Baijiu, but also helps in conserving land resources. This article studied the microbial communities and flavor compounds of fermented grains and the environmental microorganisms during the first and second rounds of heap fermentation in cave-brewed sauce-flavor Baijiu (CBSB). The results indicated that Thermomyces, Torulaspora, and Thermoascus were the dominant fungal genera during heap fermentation, while Virgibacillus, Kroppenstedtia, and Bacillus were the dominant bacteria. Daqu contributed 92.28% of the bacterial community and 73.89% of the fungal community to the fermented grains, while the cave air contributed 11.77% of the fungal community. During the heap fermentation process, a total of 79 volatile metabolites were identified, dominated by esters and alcohols. At the same time, 134 non-volatile metabolites were detected and most amino acids content increased gradually with heap fermentation time, while flavonoids showed the opposite trend. Correlations revealed that Saccharomyces was positively correlated with a number of esters and alcohols, and that Oceanobacillus promoted the synthesis of most flavonoids and organic oxides. The study provides data parameters for the environmental microbiology of the cave and also supports the exploration of the fermentation mechanism of CBSB.