Bacterial Community And Metabolic Mechanism During Fermentation Of Aspergillus Type Douchi

Douchi is a kind of traditional flavored food produced by the use of cooked soybeans or black beans as a substrate and the use of various microorganisms.It has a history of thousands of years in China.In the ancient Chinese medical records,it was found that the Douchi has the effects of spleen and digestion,clear the heat and cold.Modern scientific research has also proved that soybean meal has the effects of preventing cardiovascular disease and reducing osteoporosis.This paper focused on the physicochemical properties and functional substances of Aspergillus type Douchi produced by Jiangxi Nanchang Daoxiangyuan Flavoring Food Co.,Ltd.,and the bacterial microbial diversity was analyzed.Analyzed the correlation between bacterial microorganisms and flavor substances and found the dominant genus in the fermentation process.The main research results are:(1)The moisture of 8 samples in Aspergillus type Douchi decreased from 36.47% to 32.01%.The acidity increased from 2.37% to 3.62%,and it did not changed in the middle stage of fermentation.The content of reducing sugar was very obvious in the first three days.It was stable at about 14 mg/mL in the middle and late stages,and decreased at the end stage.The total alcohol content increased from 1.54 mg/mL to 3.02 mg/mL in the middle and early stages,and decreased in the late stage of fermentation.(2)High-throughput sequencing analysis of bacterial microbes on Douchi samples,which were classified into 423 bacterial OTUs,were classified into 15 bacteria and 240 genera;The α-diversity analysis found that the species diversity of the bacterial flora at the initial stage of soybean meal fermentation was lower than that in the middle and late stages;the richness analysis found that the dominant bacteria in the fermentation process were Firmicutes,Proteobacteria and Actinobacteria,and the dominant species were Bacillus,Anaerosalibacter,Weissella and Lactobacillus.(3)There are a total of 16 free amino acids determined by the amino acid analyzer in samples,among which Gly,Ala,Ser,Thr,and Lys are sweet,Val,Leu,Ile,Met,Phe,Arg His is a bitter taste;42 volatile components were determined by headspace-solid phase microextraction-gas chromatography-mass spectrometry,including 14 esters,6 acids,5 pyrazines,4 phenols,and aldehydes.There are 3 kinds of alcohols and 2 kinds of alcohols;the plasmin activity measured by the fibrin plate method increased from the initial 56.29 IU/mL to 116.01 IU/mL;the protease activity measured by the forinol reagent method was from the initial 78.19 μg/mL increased to 118.61 μg/mL;the changes of four isoflavone contents were determined by HPLC.The content of bound isoflavones changed from 193.30 μg/mL to 78.91 μg/mL,and the free isoflavones changed from 790.94 μg/mL to 980.47 μg/mL.(4)Bidirectional Orthogonal Partial Least Squares(O2PLS)was used to analyze the relationship between 42 volatile substances and 16 free amino acids and bacterial microbial flora in the fermentation of soybean meal.It is found that there are 57 genera of bacterial microorganisms which have an important influence on flavor;12 species of bacteria belonging to four amino acids with more content;64 kinds of esters of bacteria belonging to bacteria belonging to better volatile substances,pyridinium There are 23 kinds of azines,39 kinds of acids,39 kinds of aldehydes,18 kinds of phenols,25 kinds of alcohols,and found 9 kinds of core functional bacteria.In this paper,we studied the physicochemical properties,bacterial microbial diversity and functional flavors of Aspergillus type Douchi produced in Nanchang Daoxiangyuan,and analyzed the correlation between flavor substances and bacterial microorganisms.Finally laid a theoretical foundation for the research and development of Aspergillus type Douchi pure microorganism production.