Exploring the typical flavours formation by combined with metatranscriptomics and metabolomics during Chinese Sichuan paocai fermentation

Microbial metabolism is considered to have an important influence on the formation of taste, aroma and flavour compounds during vegetable fermentation. However, the relationship between microbial gene expression and the biosynthetic sources of flavor compounds are still unclear. In this study, genetic and metabolite profiles were used to characterize flavour development during Sichuan paocai (SCP) fermentation. Metatranscriptomic results showed that gene expression and enzyme activity by Enterobacteriaceae and Lactobacillaceae were strongly involved in SCP fermentation. Differential expression of 666 genes involving 27 metabolic pathways – most associated with amino acids– accompanied the accumulation of 17 amino acids (from 31.5 μg/mL to 738.4 μg/mL). In addition, 239 volatile organic compounds (VOCs) were identified and odour activity values showed 10 volatile organic compounds (include 5 sulphur compounds) exert an important influence on the aroma of SCP. Sulphur compounds, Glu, Asp, Lactic acid, acetic acid and maltic acid exert an important influence on the sour, umami and sulphur flavour of SCP. The cysteine and methionine metabolism asparate and glutamate biosynthesis and metabolism and pyruvate metabolism were responsible for the key flavours formation. This study provides significant guidance in the aroma, flavour and tastes regulation in SCP fermentation and new product development.