Differences in spatial distribution of microbial communities in new and old pits and their effects on the flavor of Taorong-type Baijiu

The microbial communities of pit mud and fermented grains, and the volatile metabolite profiles of fermented grains and base liquor in the new and old pits of Taorong-type Baijiu were determined by high-throughput sequencing technology combined with flavor omics technology. Correlation analysis was conducted on these data by applying bioinformatics technology to deeply explore the differences in microorganisms between new and old pit mud and their influences on the main flavors of fermented grains and base liquor. The results showed that the fermented grains in old pits exhibited better physicochemical properties, with lower moisture content, higher acidity and more thorough starch degradation. The results indicated that significant differences in the composition of microbial communities in pit mud were observed between new and old pits. The microbial community in old pits has higher richness and more stable community structure. The main bacterial and fungal genera that cause differences in the community structure of the fermented grains were Lactobacillus and Rhizopus. A total of 26 and 27 volatile flavor components were detected in the base liquor produced by the new and old pits, respectively. Among the main volatile flavor compounds (esters, acids and alcohols) in base liquor produced by old pits, except isobutyric acid and isovaleric acid, the contents of all other compounds were higher than those in base liquor from new pits. A positive correlation was shown between the bacterial community in pit mud and the volatile flavor compounds in base liquor, such as major acids (hexanoic acid, butyric acid, etc.) and esters (ethyl hexanoate, ethyl butyrate, ethyl acetate, etc.), while a negative correlation was presented between the fungal community and volatile flavor compounds in base liguor. The main functional bacterial genera (e.g., Caproiciproducens, Caloramator, Clostridium) in pit mud related to the synthesis of flavor substances were found to have a positive correlation with acids and most esters, but a negative correlation with alcohols. The research results are considered to have certain guiding significance for the maintenance of Taorong-flavor Baijiu cellars and the promotion of the positive accumulation of flavor substances.