The effects of moisture on microorganisms, quality, and flavor of Liuyang douchi during the pile fermentation period

Abstract

Objective: Pile fermentation is an important process for the formation of Liuyang Douchi flavor, the initial moisture of the douchi qu during pile fermentation could induce the temperature changes which might further affected the microbial community and flavor compounds formation. Methods: In this paper, metagenomic sequencing, combined with headspace solid-phase microextraction-gas chromatography-mass spectrometry （HS-SPME-GC-MS）, was used to investigate the effects of different moisture （low 35%, medium 42%, high 50%） of the douchi qu on the bacterial community changes and volatile composition of Liuyang Douchi during pile fermentation. Results: The results showed that bacteria in high moisture douchi qu proliferated faster due to the lower center temperature. In detail, the relative abundance of Corynebacterium during the first and second stages of pile-fermentation was positively correlated with pile fermentation moisture, while Staphylococcus during the first stage of pile-fermentation was negatively correlated with pile fermentation moisture; Staphylococcus and Pediococcus during the second stage of pile-fermentation were also negatively correlated with pile fermentation moisture. For volatile compounds, the Douchi pile-fermented with medium moisture had the richest variety of volatile substances, especially pyrazine, but the content of aldehydes and acids were lower. Further correlation analysis showed that Staphylococcus had the greatest impact on differential volatile substances and was significantly positively correlated with six differential volatile substances such as 2,3,5-trimethylpyrazine and 2-ethyl-3,5,6 -Trimethylpyrazine, guaiacol, etc. are significantly positively correlated, followed by Oceanobacillus which was significantly positively correlated with five differential volatile substances. Conclusion: The moisture content of pile fermentation affects the quality of Liuyang Douchi by altering bacterial diversity.

Keywords

• liuyang douchi
• pile fermentation
• moisture
• volatile components
• bacterial diversity