Integrated volatile metabolomic and microbiome profiling reveals flavor-driving compounds and interaction networks during long-term fermentation of Dazu preserved mustard

This study examined temporal variations in flavor-related metabolites and microbial ecology of Dazu preserved mustard, a representative Chinese semi-dry fermented vegetable, across multiple years of spontaneous fermentation. The dynamic metabolic fingerprints, microbial composition shifts, and corresponding biochemical functions were comprehensively profiled using 16S rRNA sequencing, and PICRUSt2-derived metabolic inference. Sequential transitions in flavor-active constituents were identified throughout fermentation: fruity esters (e.g., ethyl acetate and hexanoate esters) were prevalent initially, aromatic alcohols and aldehydes accumulated in the intermediate stage, conferring floral nuances, while the later phase exhibited an enrichment of sulfur volatiles like thiols, shaping a complex and stratified flavor matrix. Microbial diversity exhibited a dynamic, non-linear trajectory during fermentation, characterized by an initial increase, followed by a pronounced decline and a slight rebound at later stages. The bacterial community concurrently shifted from an initially diverse structure toward a composition increasingly dominated by Firmicutes (e.g., Lactobacillus ), Proteobacteria (e.g., Enterobacteriaceae ), and Actinobacteria. Lentibacillus persisted as a keystone taxon and correlated strongly with amino acid, carbohydrate, energy, and lipid metabolic pathways, suggesting its regulatory significance during the terminal stage. Microbe–metabolite co-occurrence networks displayed distinct positive and negative interactions, emphasizing that microbial composition intricately modulates the biochemical basis of flavor formation. Altogether, this study clarifies the microbial–metabolic coupling mechanisms underlying natural vegetable fermentation, providing foundational insights for process optimization, flavor control, and industrial scaling. • GC–MS revealed volatile flavor dynamics during long-term fermentation of Dazu mustard. • Fruity esters, floral alcohols, and acids dominated early, mid, and late stages. • Microbial succession shifted toward Firmicutes and Lentibacillus with stabilization. • Network analysis identified Lentibacillus as a key driver of late-stage flavor changes. • Findings support fermentation optimization and industrial quality control.