Random forest-guided decoding of multiplex role of initial brine salinity in shaping dichotomous equilibrium of microbial assembly and flavor compound in liquid phase and solid phase of radish Paocai during fermentation.

The aim of this study was to investigate the effect of brine salinity (3 %, 6 %, 9 % and 18 %) on the dichotomous equilibrium of flavor compounds and microbial composition in the liquid and solid of radish Paocai during fermentation by incorporating non-metric multidimensional scaling analysis and random forest model. Results showed that salinity of 6 % and 9 % facilitated more balanced microbial distribution, whereas salinity of 3 % and 6 % promoted balanced accumulation of lactate, esters and aldehydes, and enhanced degradation of glucosinolates into sulfur-containing compounds. Random forest model indicated that diffusion of salt from liquid into solid drove microbial assembly via regulating response intensity of microbiota, especially dominant Kazachstania, Candida, Pediococcus and Lactiplantibacillus to salinity, contributing to divergent dichotomous equilibrium of flavor compounds of radish Paocai. This study provided understanding of the multiplex role of salinity in shaping the quality of fermented vegetable during dichotomous phase fermentation beyond regulating osmosis.