Changes in Microbial Diversity, Physicochemical Characteristics, and Flavor Substances During Maotai-Flavored Liquor Fermentation and Their Correlations

The aim of this study was to investigate the composition and function of microorganisms during the production of high-temperature Daqu, high-temperature stacking process, and in-pit fermentation with genomic DNA extraction at different periods. The microbial diversity of each fermentation period was analyzed using high-throughput sequencing. Results show that the quantity and distribution of the microbial flora in the diverse environment of high-temperature Daqu, stacking fermentation, and bacterial community are identical. The differences in the ecological environment between high-temperature Daqu and stacking fermentation leads to dominance of different bacteria. The dominant microorganisms in the high-temperature production process included Clostridium sensu stricto (cluster I), Escherichia-Shigella, Lactobacillus, Streptococcus, Alternaria, Issatchenkia, Pyrenochaetopsis, and Pichia, whereas the dominant microorganisms of fermented grains in stacking fermentation included Escherichia-Shigella, Lactobacillus, Clostridium sensu stricto (cluster I), Streptococcus, Actinobacillus, Bifidobacterium, and Alternaria. In agreement with flavor characteristics, the activities of protease, lipase, alpha-amylase, and glucoamylase in the "second round" of fermentation showed regular changes. The activities of protease, lipase, and alpha-amylase in the high-temperature stacking process were higher than that in in-pit fermentation. However, glucoamylase activity showed an opposite trend. The contents of some acids, such as acetic acid, isobutyric acid, and propionic acid in the in-pit fermentation were higher than those in stacking fermentation, whereas ethyl lactate content showed a different trend. The content of alcohol, total acids, and total lipids decreased with time. In addition, the liquor quality reached the best character in the third, fourth, and fifth liquor rounds, which preliminarily justifies brewing Maotai-flavored liquor with microorganisms in different fermentation periods. In addition, the flavor substances formed correlated with the microbial flora. Lactobacillus, Escherichia-Shigella, and Clostridium sensu stricto (cluster I) were the dominant microorganisms. Certain dominant yeasts and molds with possible antagonistic and agonistic interactions among themselves and different fungi can produce metabolites related to Daqu production, which further affect liquor flavor and quality.