Physicochemical properties, microbial diversity, metabolites and their potential relationships of traditional Chinese Zhacai fermented for different periods

In this study, we investigated the physicochemical properties, dominant microorganisms, non-volatile metabolites and their relationships of traditional Chinese Zhacai (TCZ) at the “second-time pickling and pressing” stage fermentation. pH and amino acid nitrogen contents exhibited an increasing and then decreasing trend. Metagenomics analysis revealed the dominant bacterial species Lactiplantibacillus (Lpb.) plantarum and Latilactobacillus (Lat.) sakei, and fungal species Debaryomyces (D.) hansenii. LEfSe analysis identified a total of 47 differentially abundant bacteria, including Lpb. plantarum and Lat. Sakei. Metabolomics analysis indicated organic acids and their derivatives, organic heterocyclic compounds, lipids and lipid-like molecules as the major differential metabolites. Spearman's correlation results showed significant correlations among differential bacteria, non-volatile metabolites and physicochemical properties. Unexpectedly, differential fungi were not observed in TCZ at this fermentation period. Pathway enrichment identified phenylpropanoid biosynthesis and tryptophan metabolism as dominant metabolic pathways, both influencing the TCZ flavor development. This study contributes to further understanding of quality formation of TCZ, providing a foundational resource for future optimization and industrial application.