Analysis Of Enzymes And Metabolomics In Daqu,and Application Of Compound Enzyme-producing Bacillus From Daqu

Daqu,as the most commonly used starter in solid-state fermentation of Baijiu,is rich in enzymes and chemical compositions,which is crucial for the quality and flavor of Baijiu.It makes Daqu become irreplaceable saccharifying stater of Baijiu.Daqu is made by a natural fermentation process running for a few weeks such that a complex microbial succession occurs.However,Daqu is only limited to the fermentation of Baijiu at present,and it has not given full play to its advantages as a strain library.Therefore,this study aimed to explore the distribution of hydrolases and metabolites in Daqu,and on this basis,screen of strains producing compound enzymes in Daqu as starter to expand the application scope of Daqu.The main contents are as follows:(1)Amylase,protease and esterase were analyzed in 32 Daqu samples collected from 16 Baijiu factories.The results indicated that the highest amylase activities and diversities were found in Daqu which had light-flavor.Proteases play a significant role in determining the quality of Daqu samples which owned sauce-flavor.Moreover,we found that enzymes in raw materials of Daqu such as barley,wheat,and pea may play an important role in providing excellent hydrolytic enzymes.(2)The volatile metabolites of different Daqu samples were analyzed and identified by HS-SPME-GC-MS and 1H NMR technique.Alcohols in different types of Daqu were significantly higher than that of others;And heterocyclic in strong-flavor and sauce-flavor Daqu were significantly higher than that in light-flavor Daqu.In addition,by the correlation analysis of enzyme activities and metabolites in Daqu,it was found that amylase activities were positively correlated with the key substances in the metabolic pathway of sugar in Daqu samples.Esterase activities were positively correlated with most metabolites in light-flavor Daqu,and negatively correlated with most metabolites in strong-flavor and sauce-flavor Daqu.(3)Amylase and protease activities of 105 strains from different Daqu samples were analyzed.The Bacillus subtilis B.S-1 and Bacillus licheniformis B.L-1,which have a higher yield of amylase and protease.Based on zymogram analysis,the results showed that proteases in B.S-1 and B.L-1 fermented broth were abundant.(4)Analysis of the changes of proteases in commercial sufu during fermentation,it was found that the internal and external protein hydrolysis were simultaneous in sufu.Then Bacillus licheniformis B.L-1 from light-flavor Daqu was used to make bacterial fermented sufu.The non-volatile metabolites during the production of sufu were analyzed by 1H NMR.A total of 55 kinds of metabolites were detected.Ethylene glycol,lactic acid,glucose,tryptophan,betaine,ascorbic acid,serine and aspartate were key compounds during fermentation of sufu.