The correlation between flavor formation and microbial community dynamics during the fermentation of zha cai.

BACKGROUND: Zha cai, a pickled vegetable with unique flavors, is produced by fermenting fresh mustard tubers. In this study, the main physicochemical indices and volatile flavor compounds were determined in three fermentation periods. The bacterial and fungal communities in the three fermentation periods of zha cai were also monitored using high-throughput sequencing. Key microbial communities were identified based on significant correlations with flavor substances. RESULTS: Firmicutes and Proteobacteria were the main bacterial phyla found within the three fermentation periods. Lactic acid bacteria, namely Lactobacillus, was the predominant bacteria found at the genus level. Ascomycetes and Stenotrophomonas were the major fungal phyla found in the three fermentation periods. Yeast, namely Debaryomyces, was the predominant fungus found at the genus level. A total of 42 bacterial genera were negatively correlated with volatile flavor substances of zha cai, and 37 bacterial genera were positively correlated. Meanwhile, a total of 47 genera of fungi were negatively correlated with the volatile flavor substances of zha cai, while 50 genera were positively correlated. Several microbial genera were significantly correlated with volatile flavor compounds, including Lactobacillus, Halomonas, Rhodococcus, and Debaryomyces. CONCLUSION: This study identified the microbial classes that positively regulate the flavor of zha cai which could provide valuable help for flavor modulation in zha cai production. © 2024 Society of Chemical Industry.

Inhibition of Lactobacillus fermentum SHY10 on the white membrane production of soaked pickled radish.

The formation of white bio-membrane (shenghua) on the surface of pickle leads to uneatable and spoiled products, which has been the key problem restricting the development of Sichuan pickle industry. In this study, the 17 microorganisms in the white membrane of pickled radish were screened and identified, of which Candida parapsilosis was the main strain causing "shenghua". The membrane-forming ability of Candida parapsilosis was determined by crystal violet staining to explore its adaptability to the fermentation environment concerning temperature and oxygen. It was found that Candida parapsilosis had the strongest membrane-forming capacity under the aerobic condition at 37°C, with the highest OD595 nm value reached to 3.473 ± 0.07 at 72 h post inoculation. This research identified Lactobacillus fermentum SHY10 to be the inhibitor of the membrane production of Candida parapsilosis via the Oxford cup method on a Petri dish, and via co-inoculation with Candida parapsilosis in pickles. Furthermore, this study specified that the cell-free supernatant (CFS) of L. fermentum SHY10 had the most significant inhibitory effects and likely to result from protein substances in the CFS. Proteases treated CFS had significantly reduced inhibitory effects against membrane formation, which confirmed that the active component was protein substances. Overall, this study identified a functional LAB strain with significant inhibitory effects against the white membrane formation in pickles, which provide a safe and consumer-friendly solution for the membrane problem in the fermented vegetable industry.