Abstract: The bacterial community structure of bacterial-type naturally fermented dried douchi (a Chinese fermented soybean product) produced in Zunyi was analyzed by high-throughput sequencing, and its flavor quality was evaluated. According to the diversity index and the relative abundance of operational taxonomic units (OTUs), it was found that the major bacterial contributor for the bacterial-type douchi was Bacillus, and a small amount of Lactobacillus also played an important role in its fermentation. Therefore, both bacterial species could cooperate to produce douchi with a unique flavor. A total of 16 amino acids including 6 essential ones were identified in the douchi, as well as 26 free fatty acids including 15 saturated ones and 11 unsaturated ones. In addition, the relative contents and thresholds of the major aroma contributors in the douchi were compared using the major volatile substances contributing to the flavor of douchi as references, revealing that the relative content of acids in the douchi was the highest (44.529%), followed by nitrogen-containing substances, and the contents of alcohol, ketone and ester substances were very low. The results of this study can provide a basis for understanding the correlation between the microbial flora structure of bacterial-type douchi and the formation of its flavor substances and for the development of direct vat set starters for douchi.

Key words: bacterial-type douchi; high-throughput sequencing; bacterial community structure; flavor quality