Correlation Study Between Flavor Substances And Daqu Microbes In Fen-flavor Liquor

Liquor brewing is the essence of macromolecular substances,such as starch,protein in the materials,will be decomposed into small molecules,in turn,which is used to produce complex flavor substances by microbes.Daqu is the main source of microorganisms.To study the generation of flavor substances in the brewing process of Fen-flavor liquor,firstly,microbial diversity of Qingxiang Daqu was analyzed and bacteria and yeast were isolated from Daqu;secondly,separated microorganisms were used to carry out the single strain and mixed strains liquid fermentation;finally,the correlation of amino acids metabolism and higher alcohols in yeast was analyzed.In order to analyze microbial diversity in Qingxiang Daqu,16S rDNA V4 region in bacteria and ITS1 region in fungi were analyzed by high-throughput sequencing technology.The varieties of bacteria was more abundant than that of fungi;lactic acid bacteria were found to be predominant bacteria,candida was predominant fungi.Bacteria and yeast are isolated from Daqu by traditional microbial separation methods,including Bacillus amyloliquefaciens,Bacillus licheniformis（2）,Bacillus mojavensis,Cronobacter sakazakii,Bacillus aerius,Pediococcus pentosaceus,Saccharomyces cerevisiae,Pichia kudriavzevii,Candida elateridarum.Enzymatic activities and chemical composition in the process of single bacteria liquid fermentation were traced.Six bacteria can decompose macromolecular substances,the degradation ability of starch and protein of Bacillus amyloliquefaciens is strongest,followed by Bacillus licheniformis（B₃）,Bacillus aerius,Bacillus licheniformis（B₂）,Bacillus mojavensis,Cronobacter sakazakii.Formation of flavor substances such as esters and alcohols through lactic acid bacteria and yeast liquid fermentation which use sorghum starch hydrolyzate as fermentation medium were analyzed.Saccharomyces cerevisiae and Pichia kudriavzevii have strong ability to produce higher alcohols,Hansenula sp has strong ability to produce ethyl acetate.New flavor substances are not detected in mixed yeast liquid fermentation,addition of four amino acids mixture can improve the content of four higher alcohols.Ethyl lactate is not detected in the mixed fermentation of yeast and lactic acid bacteria.The correlation of amino acids metabolism and higher alcohols in four kinds of yeast was analyzed,addition of four precursor amino acids mixture significantly improve the content of four higher alcohols,the ability of Saccharomyces cerevisiae and Pichia kudriazevii producing higher alcohols are stronger than Hansenula sp,Candida elateridarum is the weakest.In view of Saccharomyces cerevisiae,addition experiment of single amino acid and different combination of amino acids was designed,added individually showed that leucine,isoleucine,valine,threonine can improve the content of isoamyl alcohol,active amyl alcohol,isobutanol,butanol;there is no effect on the yield of higher alchol by amino acids combination.Based on the above researches,the role of bacteria and yeast in liquor-making process and production process of esters and alcohols were understood,which is greatly significant for regulating the content of alcohols,esters in liquor.