Effects of Bacillus megaterium L222 on quality and bacterial diversity of Sichuan paocai

Bacillus sp. was found in the Sichuan paocai, but their possible effects on Sichuan paocai fermentation are still elusive. In this study, the effect of Bacillus megaterium L222 isolated from high-quality homemade Sichuan paocai on the flavor characteristics and bacterial diversity was investigated. Overall, 7 organic acids, 16 free amino acids, and 48 volatile substances were detected in the B. megaterium L222-inoculated paocai (BMP) and spontaneously fermented paocai (SP) within 7 days. The metabolites produced in BMP were significantly different from that in SP, and 13 main flavor-related metabolites were the discriminant markers. The contents of free amino acids in BMP were much higher than that in SP. Compared to the SP group, the BMP group could better maintain the high level of alcohols, which improved the synthesis of esters, and controlled the increase of the content of sulfides. The representative bacteria in BMP were Weissella, Lactococcus, Bacillus, Leuconostoc, and the inoculation of B. megaterium L222 could significantly increase the amount of Weissella and inhibit the growth of opportunistic pathogen and other bacteria during the fermentation process of paocai. This study presents an important basis for the development of B. megaterium L222 as a starter for paocai fermentation.