Exploring the Core Functional Microbiota Related to Flavor Compounds in Douchi from the Sichuan–Chongqing Region

Douchi is a traditional Chinese fermented soybean product. In the Sichuan-Chongqing region, <i>Mucor</i>-type douchi was particularly famous for its distinctive flavor. Nevertheless, the association between microorganisms and douchi flavor is still poorly understood. In this study, high-throughput sequencing, amino acid analysis, and gas chromatography-mass spectrometry (GC-MS) were used to investigate the bacterial and fungal profiles as well as the flavor compounds (sixteen amino acids and one-hundred volatile flavor compounds) of seven different types of douchi. High levels of glutamic and aspartic acids were observed. Microbial analysis found that <i>Bacillus</i>, <i>Tetragenococcus</i>, <i>Weissella</i>, <i>Aspergillus</i>, <i>Mucor</i>, and <i>Penicillium</i> were the prime microorganisms. In total, 100 volatile components were detected; however, none of them was common to all the douchi products, although most volatile components had the aromas of flowers, fruits, caramel, and cocoa. An analysis of the flavor compounds was conducted using two-way orthogonal partial least-squares discriminant analysis (O2PLS-DA). Based on the analysis, it was found that Glu had negative correlations with most microorganisms, and <i>Aspergillus</i> had positive correlations with 2-pentylfuran and phenylacetaldehyde. This study provides a theoretical foundation for the regulation and enhancement of douchi flavor.