Flavor remodeling in Paocai during round spontaneous fermentation: an integrative analysis of active microbial...

Traditional paocai is a representative Chinese fermented vegetable that is typically produced through successive fermentation cycles. However, the mechanisms underlying flavor differences between paocai fermented in fresh and aged brine during continuous fermentation remain unclear, particularly the dynamic coupling among environmental variation, active microbial communities, and flavor development across fermentation rounds. Here, comprehensive two-dimensional gas chromatography-mass spectrometry and metatranscriptomic analyses were integrated with nonlinear modeling, machine learning, and time-decay relationship analysis to investigate physicochemical evolution, microbial succession, and flavor formation during continuous fermentation of traditional paocai. The results showed that pH, organic acids, and microbial diversity exhibited pronounced nonlinear dynamics across 11 successive fermentation rounds. Random forest analysis identified Phenylethyl alcohol, Hexadecanoic acid, ethyl ester, and Tetradecanoic acid, ethyl ester as key volatile compounds discriminating fermentation rounds. Lactiplantibacillus plantarum and Lactobacillus japonicus were identified as core microorganisms throughout continuous fermentation, while microbial community structures progressively diverged from their initial states, consistent with a significant time-decay relationship. Multi-omics integration using O2PLS further revealed tight and complex cross-omics associations between active microbial taxa and volatile flavor compounds, enabling reconstruction of key flavor-related metabolic pathways during successive fermentation rounds of Sichuan paocai. Comparative metatranscriptomic analyses between fresh and aged paocai clarified the metabolic basis underlying flavor differentiation at later fermentation stages. Overall, this study elucidates flavor evolution in paocai under continuous round fermentation from microbial ecological and metabolic perspectives, providing a theoretical basis for flavor regulation and quality stabilization in traditional fermented foods.