Analysis of Microbial Diversity Dominating Nitrite Enzymatic Degradation and Acidic Degradation in the Fermentation Broth of Northeast Sauerkraut

Nitrite hazard is an important food safety issue in the production process of Chinese Northeastern sauerkraut, but this nitrite can be eliminated through microbial enzymatic degradation and acidic degradation as fermentation progresses. Therefore, analyzing the microbial diversity that dominates nitrite degradation in Chinese Northeastern sauerkraut can provide a reference for its safe production. In this study, based on the dynamic monitoring of nitrite concentration, pH, and the abundance of nitrite reductase genes (<i>nirK</i> and <i>nirS</i>) and the application of high-throughput sequencing technology and various statistical analysis methods, the microbial groups associated with nitrite enzymatic degradation and acidic degradation in Northeast sauerkraut fermentation broth were analyzed. During the nitrite peak period of Northeast sauerkraut fermentation broth, the nitrite concentration reached 32.15 mg/kg, the pH was 4.7, and the abundances of the nitrite reductase genes <i>nirK</i> and <i>nirS</i> were 3.0 × 10⁴ and 4.9 × 10⁴ copies/μL, respectively. At this stage, nitrite degradation was likely dominated by enzymatic activities. Microbial phyla such as <i>Bacteroidetes</i> (38.8%), <i>Proteobacteria</i> (19.2%), and the archaeal phylum <i>Euryarchaeota</i> (1.1%) showed strong correlations with nitrite. Among the genera within these three phyla, <i>Chryseobacterium</i>, <i>Elizabethkingia,</i> and <i>Aeromonas</i> exhibited significant differences in abundance compared to the late fermentation stage and were identified as the primary microbial groups likely driving the enzymatic degradation. During the nitrite degradation period, the nitrite concentration decreased to 0.04 mg/kg, the pH dropped to 3.6, and the abundances of <i>nirK</i> and <i>nirS</i> genes were reduced to 1.0 × 10³ copies/μL. At this stage, the nitrite degradation was primarily driven by acid activity. The bacterial phylum <i>Firmicutes</i> (99%) exhibited a strong correlation with pH. Within this phylum, the genus <i>Lactobacillus</i>, which showed significant differences in abundance compared to the early fermentation stage, was identified as the primary microbial group indirectly contributing to acidic degradation. This study provides guidance for the isolation of food-grade prokaryotic microbial strains capable of nitrite degradation. Additionally, the findings offer a methodological reference for conducting future research on nitrite-degrading microorganisms in fermented vegetable broths.