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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]