The Changes and Driving Mechanism of Bacterial Community Structure during Paocai Fermentation

The standardization of paocai quality depends on the microbial community structure in the fermentation process. In this study, high-throughput sequencing technology was used to study the dynamic changes of bacterial community structure composition, detect the dynamic changes of physical and chemical factors, reveal the correlation between them, and carry out functional prediction and metabolic pathway analysis. The results showed that: Simpson index in SI stage was significantly higher than that in S2 and S3 stage, while Shannon index was significantly lower than that in S2 and S3 stage (P<0.05), indicating that the diversity of bacterial community was low in the early fermentation stage. The bacterial species detected from 9 samples of paocai belong to 6 phylum, 9 classes, 29 orders, 47 families, 59 genera, 83 species. Firmicutes and Proteobacteria were the dominant phyla in paocai fermentation. The dominant genera were Pseudomonas, Lactobacillus, Enterobacteriaceae and Lactococcus. The relative abundance of Firmicutes was 10.61%, 64.83% and 77.51% at the beginning, middle and end of fermentation respectively, while Proteobacteria decreased from 84.18% to 17.91%, and Pseudomonas decreased from 33.19% at the beginning of fermentation. The relative abundance of Lactobacillus increased rapidly from less than 1% to 67.65% in the end fermentation period. L. curvatus was the main Lactobacillus in the middle fermentation period, L. plantarum was the main Lactobacillus in the late fermentation period. Correlation analysis and Redundancy analysis showed that titratable acid and nitrite were the main driving factors of bacterial community structure change, and had the greatest influence on bacterial community composition. Nitrite was positively correlated with the community at the early fermentation stage, amino acid ammonia mainly affected the community at the middle fermentation stage, soluble protein and TTA had a greater impact on the community structure at the late fermentation stage. Titratable acids were significantly positively correlated with Lactobacillus and negatively correlated with Pseudomonas. The acidic environment created by lactic acid bacteria through lactic acid fermentation could significantly inhibit the growth of Pseudomonas and other harmful microorganisms. In this study, the community composition and differences of naturally fermented paocai in different stages were elucidated, and the driving factors affecting its composition were explained, which provided help for the production of paocai. © 2023 Journal of Chinese Institute of Food Science and Technology. All rights reserved.