Dynamic Correlation Between Bacterial Communities and Volatile Compounds During Douchiba Fermentation

Douchiba is a traditional bacteria-fermented soybean product in Guizhou, refined through the following steps of soaking, steaming, koji-making, salt sprinkling, fermentation, pounding, drying, molding, and after-ripening. However, the dynamic alterations of microbiota and volatile compounds of Douchiba were seldom reported. In this work, the bacterial communities and volatile compounds during the fermentation process of Douchiba were explored by high-throughput sequencing and headspace solid-phase microextraction and gas chromatography-mass spectrometry (HS-SPME-GC-MS) techniques, respectively. Furthermore, the correlation between microbial communities and volatile compounds was analyzed with Spearman's method. The findings revealed that the diversity and evenness of bacteria increased during the fermentation process of Douchiba. The dominant bacteria genera included Bacillus, Staphylococcus, Tetragenococcus, Loigolactobacillus, and Virgibacillus. Bacillus dominated the bacterial communities throughout the fermentation process, and Staphylococcus, Tetragenococcus, Loigolactobacillus, and Virgibacillus also became the dominant genera in the fermentation and after-ripening stages. A total of 134 volatiles were identified. The main volatiles were ketones and alcohols in the koji-making stage, ketones and pyrazines in the fermentation stage, and acids in the after-ripening stage. In total, 26 compounds were selected as the main characteristic volatiles, including 2,3,5-trimethylpyrazine, 3-methyl-1-butanol, and indole, which endowed Douchiba with a specific flavor. Additionally, Bacillus was significantly positively correlated with isovaleraldehyde, benzaldehyde, and acetic acid. Staphylococcus was significantly positively correlated with indole, 3-methylbutanoic acid, and eucalyptol. Tetragenococcus, Loigolactobacillus, and Virgibacillus were significantly correlated with indole and estragole. The research establishes a theoretical foundation for better regulating the flavor quality of Douchiba products.