Unraveling the flavor profile and microbial roles during industrial Sichuan radish paocai fermentation by molecular sensory science and metatranscriptomics

In this study, the changes of flavor profile, the succession rules of active microorganisms and their correlation were analyzed during the fermentation process of industrial Sichuan radish paocai, in order to further explore the composition of ingredients that constitute the unique flavor characteristics of industrial Sichuan radish paocai, and the microorganisms and enzymes that may contribution to it. To this end, molecular sensory, high performance liquid chromatography and metatranscriptomics were employed to identify the aroma-active compounds, non-volatile compounds and active microorganisms during the 197-day fermentation process of industrial Sichuan radish paocai, respectively. Twenty aroma-active compounds were identified, of which 12 compounds had odor activity values ≥ 1, and some off-flavor compounds were significantly lower than those of fresh radish. After 100 days of fermentation, aroma-active compounds began to accumulate extensively with the dominant active microorganisms transforming from fungi to bacteria. Among the potential formation pathways of 14 aroma-active compounds, most of which were dominated by Lactobacillus and Debaryomyces, and were contributed by other microorganisms mainly belong to Lactobacillales, Saccharomycetales and Bacillales. This study provides new insights into the flavor formation and microbial metabolic roles of industrialized paocai, as well as valuable references for screening and isolation of functional strains, expression and characterization of flavor enzymes.