Chili fermentation is one of the most important processes in the production of Pixian Douban (PXDB), which determines the flavor and product quality of PXDB. However, the maturity of fermented chili mainly depends on empirical judgment, which can not satisfy the need for standardized production of PXDB. Therefore, this study aimed to investigate volatile and non-volatile substances during the maturation process and to find markers related to the maturity of fermented chili. Two-dimensional gas chromatography-mass spectrometry (GC × GC-MS) combined with multivariate statistical analysis and relative odor activity values (ROAV) analysis revealed that 2-methoxy-3-isobutyl pyrazine, linalool, 3-(methylthio)propionaldehyde, myrcene, and decanal (ROAV ≥ 1, VIP > 1, P < 0.05) were regarded as potentially active aromatic markers for differentiating fermentation time. Additionally, ultra-high performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry (UPLC-QTOF-MS) combined with multivariate statistical analysis revealed that 25 compounds could serve as differentiated non-volatile compounds. The correlation of maturity-related physicochemical indicators with volatile and non-volatile compounds revealed that four volatile compounds (2-methoxy-3-isobutylpyrazine, linalool, myrcene, and decanal) along with seven non-volatile compounds could serve as markers for evaluating the maturity of fermented chili. This study is expected to establish a standard for the determination of the maturity the fermented chili and lay the foundation for intelligent production of PXDB.

Umami peptides play important roles in the flavor of fermented broad bean paste (FBBP), and proteases produced by microorganisms contributed to the production of umami peptides. In order to reveal the formation of umami peptides and their relationships with protease-producing microorganisms during the natural fermentation of FBBP, peptidomics and virtual screening were used to identify and screen umami peptides. Meanwhile, macrogenomics was used to analyze the abundance of microbial-derived protease genes during FBBP fermentation. Then, based on the Pearson correlation coefficient, the correlation network diagram of each protease-producing microorganism with umami peptides was constructed. The results showed that a total of two exopeptidases and four endopeptidases were annotated from FBBP. Staphylococcus, Lactobacillus, Aspergillus, and Weissella can produce most proteases. The species Lactobacillus curvatus, Dyella jiangningensis, Erythrobacter sp., and unclassified_g_Pantoea had strong correlation with umami peptides, and they may contribute to the process of protein hydrolysis to produce umami peptides. This study is expected to reveal the formation mechanism of umami peptides in FBBP, and the results of this study provided a better understanding of the relationship between proteases, microbiota, and core umami peptides in FBBP, which could help to improve the umami taste of Pixian Douban paste during fermentation.