Analysis of microbial structure and function in fermented grains during the fermentation process of Congjiang WeiJiu...

WeiJiu was a traditional specialty liquor from the Zhuang ethnic villages in Congjiang County, Qiandongnan Miao and Dong Autonomous Prefecture, Guizhou Province. It was brewed using glutinous Xianghe rice, mountain spring water, and ancestral koji as raw materials. Its core production processes consist of five stages: (1) raw material preparation; (2) spreading, cooling and yeast mixing; (3) fermentation and liquor extraction; (4) simmering treatment; (5) sealing and aging. WeiJiu had a dark brown color, a mellow, soft, and sweet taste, and featured the characteristic of becoming more aromatic as it ages. As an intangible cultural heritage item of Qiandongnan Prefecture, its craftsmanship inheritance had long been confined to an empirical paradigm. Due to the lack of research on the composition and function of the microbial community in Congjiang WeiJiu, the microbial changes and metabolite changes during the fermentation process, its quality characteristics and brewing mechanism remain unclear. Therefore, in-depth understanding of the brewing mechanism and essentially improving its quality and production was an urgent priority for research related to Congjiang WeiJiu.

In this study, the fermented grains of Congjiang WeiJiu at various fermentation stages: CQ: early fermentation stage (7 d), ZQ: middle fermentation stage (11 d) and WQ: late fermentation stage (15 d) were used as the research objects. High-throughput sequencing technology was employed to analyze microbial community structure and diversity. Functional annotations were performed against KEGG and CAZys databases to explore metabolic pathways and carbohydrate-active enzyme (CAZys) characteristics.

The microbial community exhibited significant stage-specific succession synchronized with fermentation processes. At the phylum level, Bacillota and Pseudomonadota dominated in CQ, Bacillota became predominant in ZQ, and Actinomycetota increased significantly in WQ. At the genus level, Aspergillus, Saccharomyces, and Hyphopichia served as core functional genera in respective stages. Functional annotations showed stage-specific expression of metabolic pathways: KEGG pathways focused on energy and amino acid metabolism (in CQ), carbohydrate metabolism (in ZQ), and stress adaptation (in WQ). CAZys families corresponded to fermentation substrates degradation (GH28, AA1 in CQ), macromolecule conversion (GH13, CBM50 in ZQ), and metabolite modification (GH18, GH16 in WQ). Core functional bacteria enhanced adaptability through evolutionary mechanisms such as horizontal gene transfer, genome streamlining, and plasmid-mediated gene acquisition. The unique simmering process and smoked cellar storage shaped the distinct microbial community and flavor, differing from traditional Luzhou-flavor liquor in yeast succession, lactic acid bacteria metabolism, and mold survival period.