Dynamic analysis of physicochemical characteristics and microbial communities of Aspergillus-type douchi during fermentation

This study aimed to analyze the potential relationship between bacterial community succession and the physicochemical properties of Aspergillus Douchi. Combing the cultivable method, high-throughput sequencing technology and physical and chemical properties determination during fermentation, the physicochemical parameters, microorganism number, and bacterial community diversity were investigated. The fermentation temperature in Douchi firstly increased and then decreased, most of them were around 45 ℃; the pH value continued to drop and finally reached to 4.86; the salt content was maintained at approximately 6%; and amino nitrogen and total acid contents increased steadily, while the contents of reducing sugar and total sugar continued to decline. The culture-dependent and real-time quantitative PCR results showed that the number of fungi and bacteria in Douchi decreased. The 16S rRNA gene sequencing revealed that the bacterial composition of Aspergillus-type Douchi in the early fermentation stages was dominated by Lactobacillus spp., Staphylococcus spp. and few Bacillus spp.. In the middle-late stages, the dominant bacteria shifted from Staphylococcus spp. and Lactobacillus spp. to Bacillus spp. Redundancy analysis showed that the fermentation environment influenced the bacterial community succession. Particularly, pH and temperature are important environmental parameters that promote the bacterial flora structure transformation and influence the diversity distribution. This study lays the foundation of the theoretical for the precise controlling of the Douchi fermentation.