Activation of microbial community and enhancement of quality by inoculating Zygosaccharomyces rouxii during the post-fermentation stage of Doubanjiang.

The prolonged post-fermentation stage of Doubanjiang imparts unique flavors but may reduce microbial vitality and increase contamination, affecting quality. This study investigated the effect of Zygosaccharomyces rouxii inoculation during post-fermentation. Results showed a 46.7% increase in amino nitrogen and a significant rise in volatile compounds like phenethyl alcohol, 3-methyl-1-butanol, and ethyl octanoate. The relative abundances of Staphylococcus and Pantoea increased among bacteria, while Pichia, Wickerhamiella, and Zygosaccharomyces increased among fungi. Redundancy analysis showed a positive correlation between these genera and the main volatiles. Microbial ecological network analysis showed that inoculating Z. rouxii increased nodes and edges, resulting in tighter inter-module connections and enhanced robustness. Key genera included Zygosaccharomyces, Staphylococcus, Kazachstania, and Weissella. Metaproteomic results demonstrated that upregulated proteins were predominantly enriched in pathways related to flavor formation, while downregulated proteins were associated with ribosome and DNA synthesis-related pathways. PICRUSt2 analysis results showed higher expression of enzymes related to volatiles in innoculated samples. Inoculating Z. rouxii during the post-fermentation could boost core microorganisms, curb foodborne pathogens, stabilize the microbial community, and enhance Doubanjiang quality.