Study of bacterial community succession and reconstruction of the core lactic acid bacteria to enhance the flavor of paocai

Paocai is a widely consumed traditional Chinese fermented vegetable product. To study the effects of bacterial community succession and core microbial reconstruction on the flavor of paocai, culture-dependent and culture-independent methods were used to analyze the bacterial community structure of naturally fermented paocai. HPLC and GC-MS were used to investigate changes in flavor compounds during the fermentation of paocai. Key odorants were identified by olfactometry combined with GC-MS. The results showed that dominant bacteria in the paocai fermentation were mostly cultivable. Leuconostoc mesenteroides, Weissella cibaria, and Lactococcus lactis appeared at the start of fermentation, Leu. mesenteroides, L. lactis, Lactiplantibacillus plantarum, and Levilactobacillus brevis appeared in the middle of fermentation, and L. plantarum dominated fermentation in the late stage. Leuconostoc mesenteroides CPTCC 1R3 (LEM), Weissella cibaria CPTCC 1R15 (WC), Levilactobacillus brevis CPTCC 3R8 (LB), and Lactiplantibacillus plantarum CPTCC 5R10 (LP) were screened from naturally fermented paocai and used for microbial reconstruction, revealing that the growth and fermentation profiles of the strains were closely related to the evolution of the bacterial community. Paocai inoculated with LEM had the following characteristics: fast fermentation, quickly disappearance of pungent odor of the raw materials, and the improved flavor and taste. Paocai inoculated with WC and LB contained ethanol and mannitol, but inoculated strains were poorly acid-tolerated. However, they can be used as auxiliary strains to enhance the flavor of paocai. Sample inoculated with LP resulted in slow fermentation and massive acid production. Mixed culture fermentation of paocai has more advantages than pure culture fermentation. Leu. mesenteroides and L. plantarum were the core microorganisms related to the flavor formation of paocai. These findings contributed to the better understanding of mechanisms underlie in the microbial community succession and flavor formation during paocai fermentation.