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Intensive study of the metabolome during the Douchi fermentation can provide new knowledge for optimizing the fermentation process. In this work, the metabolic characterization throughout the fermentation of Mucor racemosus Douchi was investigated using gas chromatography with time‐of‐flight mass spectrometry. A total of 511 peaks were found, and 114 metabolites were identified. The fermentation process was clearly distinguished into two main phases by principal components analysis and orthogonal partial least squares‐discriminant analysis. All the samples in the score plots were within the 95% Hotelling T2 ellipse. Two separated clusters can be seen clearly in the score plot, which represents the two stages of fermentation: koji‐making (within 48 hr) and postfermentation (after 48 hr). Besides, clear separation and discrimination by both methods were found among different fermentation time within 15 days, while the discrimination cannot be found with more than 15 days of fermentation, indicating that the fermentation of Douchi was finished in 15 days. Due to the synergistic effect of protease and hydrolase accumulated in the early stage, proteins and other big molecular substances are rapidly hydrolyzed into a large number of small molecule components. However, the activity of enzymes decreased with the further fermentation, and some free amino acids were consumed in Maillard reaction. Therefore, there was no significant change in the content of small molecular substances after 15 days of fermentation. Furthermore, the levels of some metabolites such as alanine and lysine involved in the fermentation varied significantly throughout the processes. This study provides new insights for the metabolomics characteristics of Douchi fermentation. [ABSTRACT FROM AUTHOR]

Liuyang Douchi is a kind of traditional fermented Aspergillus -type Douchi in China for excellent favor. However, studies on the microbial diversity and the characterization of predominate fungi of Liuyang Douchi are few. In present study, the Illumina HiSeq sequencing was performed to reveal the fluctuation characteristics of microbial diversity during fermentation. Results showed that Staphylococcus (33.86%), Staphylococcaceae_unclassified (27.39%) and Pediococcus (8.80%) were the dominated bacteria, while Petromyces (74.57%), Rhizopus (10.93%) and Penicillium (2.68%) were the most predominant fungi during entire fermentation period. Intriguingly, Petromyces was negatively correlated with Alternaria, Saccharomyces and Saccharomycetales_unclassified. Further, four non-aflatoxigenic Aspergillus flavus strains were first identified and isolated from Liuyang Douchi according to phylogenetic and macroscopic characteristics. These four Aspergillus flavus displayed high cellulase and protease activities, but weak lipase activity. This study could contribute to the quality control of Liuyang Douchi by providing an overview of the microbial diversity. • Staphylococcus and Pediococcus was the dominated bacteria in qu-making period and pile fermentation, respectively. • Petromyces were the predominant fungi in Douchi that was negative correlated with Alternaria and Saccharomyces. • Four Aspergillus flavus strains isolated from Douchi displayed high cellulase and protease activity. • No aflatoxin B1 was detected in these four strains in conditions provided. [ABSTRACT FROM AUTHOR]

[Display omitted] • 115 kinds of VOCs were identified and most of them were accumulated during the pile fermentation. • Most of alcohols and acids decreased while esters and pyrazines increased during fermentation. • Hexanol, hexanal and 2-pentylfuran might be responsible for the odors of unfermented black beans. • Esters and pyrazine (e.g. ethyl acetate) contributed to the aroma of matured Douchi. The present study investigates volatile organic compound (VOC) compositional changes in Liuyang Douchi during fermentation via a HS-GC-IMS and HS-SPME-GC-MS combination approach. A total of 115 VOCs were identified from Douchi, most of which were accumulated during pile fermentation. Notably, most alcohols and acids decreased with fermentation, while esters, ketones, pyrazines, and phenols accumulated during pile fermentation. Depending on the VOCs identified by GC-IMS/MS, the different fermentation stages of Douchi could be facilely distinguished. Of these, 49 VOCs were regarded as the marker VOCs of Douchi in different fermentation stage: hexanol, hexanal, and propanoic acid was the marker VOCs of the black beans before fermentation and contributing beany and grassy odors; 1-octen-3-ol and 3-octanone supplying a mushroom aroma to the Douchi fermented for 3–9 days; and esters and pyrazine, especially ethyl acetate and 2,6-dimethylpyrazine, contributing the cocoa, fruity, and nutty aromas of matured Douchi. [ABSTRACT FROM AUTHOR]

Color is one of the important indicators affecting the quality of fermented pepper sauces, and it is closely related to carotenoid composition. This study systematically analyzed the changes in carotenoids and related physiochemical indices during the fermentation of yellow lantern pepper sauce. The CIELab color values indicated that L* and C* displayed a significant decreasing trend during fermentation. After 35 days of fermentation, the total carotenoid content significantly reduced from 3446.36 to 1556.50 μg/g DW (p < 0.05), and the degradation rate was 54.84%. Among them, the total content of carotene decreased by 56.03% during fermentation, whereas the degradation rate of xanthophylls and their esters was 44.47%. According to correlation analysis, violaxanthin myristate and lutein played a pivotal role in L*, a *, b *, chroma (C*), and yellowness index (YI). Moreover, PCA analysis indicated that lactic acid and acetic acid were the important qualities affecting the stability of pigment in fermented yellow lantern pepper sauce, which might also be the inducement of the color change. This work gives additional information concerning the discoloration of yellow lantern pepper sauce during fermentation and provides theory evidence regulating and improving the sensory qualities of yellow lantern pepper sauce. [ABSTRACT FROM AUTHOR]