Illumination and reconstruction of keystone microbiota for reproduction of key flavor-active volatile compounds during paocai (a traditional fermented vegetable) fermentation

Keystone microbiota is an integrative member in constructing and stabilizing the microbial community in fermented vegetables, which is crucial for reproducible flavor. Herein, reused Paocai brine was subjected to analysis of flavor-active volatile compounds profiles by SBSE-GC-O/MS and microbial community structure by metagenomics sequencing to understand the composition of keystone microbiota in volatile flavor formation of Paocai (a traditional fermented vegetable) during fermentation. SBSE-GC-O/MS identified 8 key flavor-active volatile compounds in Paocai, including dimethyl disulfide, dimethyl trisulfide, 3-butenyl isothiocyanate, erucin, phenylethyl alcohol, nonanal, decanal, and decanoic acid. By Venn analysis of abundance, co-occurring pattern and redundancy analysis (RDA) based on metagenomics, Liquorilactobacillus nagelii, Pediococcus ethanolidurans, Lentilactobacillus buchneri were found to be dominant species for performing acid-production and stabilizing co-occurrence network of microbial community. Spearman correlation analysis revealed that Liquorilactobacillus nagelii, Pediococcus ethanolidurans, Lentilactobacillus buchneri were responsible for mitigating pungent flavor; Kazachstania exigua played a crucial role in promoting mild and fragrant flavor. These species were isolated and reconstructed into synthetic keystone microbiota as starter culture for Paocai. Principal component analysis (PCA) showed that Paocai fermented with synthetic keystone microbiota was able to reproduce the composition of volatile organic compounds as that in Paocai fermented with reused brine. This study provided a strategy for identification and reconstruction of keystone microbiota for production of fermented vegetables with tractable and reproducible flavor.