Microbial succession and genome-resolved metabolic functions shape flavor evolution during sauce-flavor Baijiu fermentation.

Sauce-flavor Baijiu (SFB) fermentation is characterized by a unique multi-round solid-state process, during which complex microbial succession drives flavor formation. However, the functional differentiation and metabolic mechanisms of microbial communities across successive fermentation rounds remain poorly understood. In this study, the physicochemical properties, microbial assembly, and metabolic profiles of fermented grains (FG) were investigated across seven production rounds (R1-R7). The results revealed that as fermentation rounds progressed, the FG environment evolved toward elevated acidity and reduced pH, driving a directional shift in the microbial community from an initially diverse assemblage to a structure dominated by acid-tolerant Acetilactobacillus, which established pronounced ecological dominance in later rounds. Metabolomic analysis further indicated that this dynamic adjustment of microbial structure drove the evolution of the flavor profile, specifically manifesting as differential accumulation of compounds such as esters, alcohols, and pyrazines across the various rounds. Co-occurrence network analysis demonstrated that positive microbial interactions significantly predominated within the fermentation system, and that community function exhibited a convergent trend as the rounds increased. Furthermore, 158 metagenome-assembled genomes (MAGs) were recovered, and metabolic reconstruction elucidated the potential contributions of genera such as Pediococcus, Bacillus, and Oceanobacillus to key metabolic pathways, including glycolysis, phenylalanine metabolism, and pyrazine biosynthesis. This work provides important insights into microbial regulation and quality improvement in SFB fermentation.