Exploring The Effect Of Bioaugmentation On Biochemical Characteristics And Microbial Communities In Qishan Daqu

Daqu is an important liquefaction and saccharification starter in the vinegar solid-state fermentation(SSF)process,which affect the flavor and quality of vinegar products directly.The Daqu solid-state fermentation process is a complex biochemical interaction,including the growth and metabolism of microorganisms and the decomposition and transformation of raw materials.The main microbial bacteria,molds and yeasts in Daqu decompose the raw materials by producing amylase and glucoamylase,then metabolize to produce main volatile substances such as alcohols and esters that affect the flavor of vinegar.To investigate the influence of bioaugmentation with native microorganisms on Daqu SSF process,microorganisms with high amylase activity were screened and inoculated in Daqu,while physicochemical properties,microbial biomass,volatile substances and microbial communities were analyzed in lab-scale Daqu using qPCR,GC-MS analysis and high-throughput sequencing.The results showed that Bacillus amyloliquefaciens,Saccharomycopsis fibuligera and Absidia corymbifera had higher amylase ability,and the amylase activities reached 48.9 U/mL,51.5 U/mL and 52.7 U/mL,respectively.After solid-state fermentation,the physical and chemical indicators such as water content,pH value and acidity basically maintained a reasonable and stable range in Daqu.The final pH value was about 7.0,the water content was <13%,and the acidity was between 0.07 and0.14,which was not significantly different from the traditional Daqu.Moreover,the amylase activity of Daqu enhanced 6.35%±0.74% by inoculating Bacillus amyloliquefaciens,Saccharomycopsis fibuligera and Absidia corymbifera.A total of 22 volatile substances were detected in the mature Daqu,including 4 kinds of alcohols,4 kinds of acids and 5 kinds of esters.Slightly increase in the content of alcohols was found in the fungal inoculation(FI)group,including ethanol(46.58±1.36 mg/kg),and isoamyl alcohol(1.55±0.13 mg/kg).Based on qPCR analysis,the biomass increased at the beginning and then remained stable during the Daqu fermentation process.And the total number of bacteria in the dahuo and chengqu stages increased significantly(P < 0.05),which was nearly two orders of magnitude higher than the shangmei stage.Compared with the control group(6.7 Logcopies/g),the fungal biomass of the bacterial inoculation(BI)group in the chengqu stage was significantly increased(P < 0.05),reached 8.4 Log copies/g.In addition,Enterococcus,Bacillus,Saccharomycopsis,Rhizopus and Rhizomucor were the main Daqu microorganisms through high-throughput sequencing analysis.ANOSIM and MRPP analysis revealed that bioaugmentation increased the abundance of Daqu microbial community without affecting microbial community structure.This work explained that bioaugmentation had a positive impact on amylase activity,main volatile substances and microbial community richness in Daqu,which is of great significance to the improvement of Daqu production process and vinegar quality.