The role of abiotic and biotic factors of aged brine in directing microbial assembly and volatile profiles of Paocai during fermentation

Aged brine is a representative natural starter that evolves with stable abiotic and biotic conditions for reproducible quality of fermented vegetables. In this study, the role of aged brine in directing the quality formation of Paocai (a traditional fermented vegetable) was investigated by analyzing the contribution of abiotic and biotic factors to physicochemical properties, volatile compound profiles, microbial composition and function in Paocai. Results showed that the abiotic factors in aged brine promoted reducing sugar consumption and lactic acid accumulation by facilitating the growth of indigenous lactic acid bacteria (LAB) and yeasts. Also, the masking effect of abiotic factors on isothiocyanates and disulfide alleviated the pungent flavor of Paocai. The biotic factors introduced indigenous dominant LAB genera of Liquorilactobacillus, Levilactobacillus, Lactiplantibacillus, Secundilactobacillus, Pediococcus, Lentilactobacillus, Lacticaseibacillus, Lactobacillus and indigenous dominant yeast genera of Kazachstania and Brettanomyces into Paocai. LAB functioned in the production of acid and aldehyde, while yeasts contributed to the accumulation of esters and lactones. Both LAB and yeasts reduced the contents of pungent compounds in Paocai during fermentation. Analysis of microbial function revealed that the role of aged brine was related to the regulation of carbohydrate metabolism and carbohydrate-active enzymes of the microbial community. This study provided an understanding of the role of aged brine in shaping the quality of fermented vegetables.