The Microbiota Dynamics During The Solid-State Fermentation Process Of Medium-Temperature And Hightemperature Daqu Starters

Daqu starter is traditional saccharifying and fermenting agent for the brewing of of traditional vinegar and Chinese liquor,and plays a significant role on the flavor formation of final fermented products.According to maximum incubation temperature,Daqu can be categorized into three types,low-temperature,medium-temperature and high-temperature Daqu,each type of Daqu possess unique microbiota communities and functional enzymes.The inoculation temperature during solid-state fermentation process is controlled by a traditional ventilation.In this study,the dynamics of physical indicators,microbial diversity and volatile flavoring compounds during the solid-state fermentation process of medium-temperature(defined as R4)and high-temperature(defined as R10)Daqu starters,which was sampled from a vinegar factory in Shanxi province,was determined and analyzed.The results indicated that the tendency of moisture,p H,acidity,reducing sugar is similary,comparing R4 to R10.The glucoamylase activity of R4 is 893 U/g at 32 d,which higher than R10's 606 U/g.However,the amylase activities of R4 and R10 behave a similar tendency,which is 1.37 U/g and 1.36 U/g at 32 d,respectively.Quantitative PCR results indicated that the difference of microbial biomass was displayed during 12 d to 14 d,while the biomass of fungi in R4 higer than R10 at 32 d.We performed Illumina Mi Seq sequencing combined with PCR–denaturing gradient gel electrophoresis to trace the microbiota dynamics,and the results indicated that the microbial dynamics during the solid-state fermentation process of R4 and R10 was similar,Saccharomycetales only dominated earlier stages,Mucorales,Saccharomycetales,Eurotiales dominated mid-stages,Mucorales,Saccharomycetales dominated final stages,Enterobacteriales,Lactobacillales,Bacillales dominated throughout the solid-state fermentation process.However,the abundance of Bacillales and Saccharomycetales of R4 higher than R10.The volatile compounds including 12 esters,3 carboxylic acids,14 alcohols,7 aldehydes,4 ketones,8 alkanes,4 heterocyclic,4 benzenes and 8 other aromatic compounds,and the esters are the main volatile compounds during solid-state fermentation.However,the content of of ethyl acetate and tetramethylpyrazine differed between R4 and R10,the content of ethyl acetate of R4 is 0.38 mg/100 g at 32 d,while R10 didn't detected at 32 d,and the content of tetramethylpyrazine of R4 is 1.11 mg/100 g higer than R10's 0.29 mg/100 g.PCA and cluster analyses revealed the high correlation between the dynamics of bacterial community and metabolites.This is an important report to study the dynamics of microbiota community and volatile flavoring compounds during solid-state fermentation process,and can be used as a guide for further fermentation experiments of solid-state fermentation to improve the quality of Daqu.