Research Of The Formation Mechanism Of Esters In Process Of Liquor Fermentation

Esters are the largest flavor substances in liquor.Research of the formation of esters in the process of liquor fermentation can provide a theoretical basis for the regulation of esters in liquor production,and it has great significance for improving the quality of liquor.From the perspective of the ester-producing yeast strains,esterifying enzyme of Daqu,esterifying enzyme of pure monascus and rhizopus koji,and lipase,this study aimed to research the formation rules of ethyl acetate,ethyl lactate,ethyl hexanoate and ethyl butyrate in liquor.(1)The effects of oxygen supply conditions,pH and temperature on the ethanol fermentation and the ester production of ester-producing yeast strains were investigated which were represented by Pichia cactophila,Candida krusei,Hansenula anomala var.anomala,Torulopsis globose and Saccharomyces cerevisiae.The results demonstrated the oxygen supply had a significant influence on ester-producing yeast strains except Saccharomyces cerevisiae.As oxygen supply was reduced,the alcohol content and fermentation degree of yeasts were weaker.Moderate oxygen supply is beneficial to esters production of yeasts.The pH had a certain effect on the ester-producing yeast strains.The optimum pH for wine production and the optimum pH for the production of ester were different.The effects of temperature on ester-producing yeast strains were more significant.When the temperature was lower than 28?,yeasts had lower alcohol and fermentation degree,but it was beneficial to ester production(except for Torulopsis globose),The optimal temperature of Torulopsis globose was 28 ?.It can be seen that Saccharomyces cerevisiae is widely used,and the other four kinds of ester-producing yeast strains cannot be directly pit entry fermentation,but it can be made into esterification liquid or solid flavoring fermented grains,then proceeded pit entry fermentation or mixed with fermented grains and distilled.(2)Under the different acid concentration and pH,the different characteristics of esterifying enzyme of different flavor Daqu were studied.The results showed that in catalyzing and synthesizing ethyl acetate and ethyl butyrate,the enzyme activity of light-flavor Daqu was the largest;in catalyzing and synthesizing ethyl lactate and ethyl caproate,the enzyme activity of strong-flavor Daqu was the largest;the enzyme activity of maotai-flavor was small.The effects of acid concentration and pH on esterifying enzyme activity of Daqu were significant.For Daqu,the optimum pH was within the range of 4.0-5.0 in catalyzing and synthesizing ethyl acetate,ethyl caproate and ethyl butyrate.The optimum pH in catalyzing and synthesizing ethyl lactate respectively was 7.0-8.0.The results indicated the reason of the imbalance of the proportion between the acids and esters in liquor,and it was effective improve the quality of liquor by the rational use of the esterifying enzyme of Daqu.(3)Under the different acid concentration and pH,the different characteristics of esterifying enzyme of different of bran koji were studied.The results demonstrated that in catalyzing and synthesizing ethyl acetate,ethyl caproate and ethyl butyrate,the enzyme activity of Monascus fulginosus koji was the strongest;in catalyzing and synthesizing ethyl lactate,the enzyme activity of Rhizopus oryzae koji was the strongest.The acid concentration and pH had a certain effect on the enzyme activity of bran koji.The optimum pH was in the fermentation range of liquor in catalyzing and synthesizing ethyl acetate,ethyl caproate and ethyl butyrate.But the optimum pH in catalyzing and synthesizing ethyl lactate respectively was 6.0-7.0.(4)Under the different acid concentration and pH,the different characteristics of lipases were studied.The results showed that in catalyzing and synthesizing ethyl acetate,ethyl lactate and ethyl butyrate,the activity of Novozym435 was higher;in catalyzing and synthesizing ethyl caproate,the activity of enzyme from South China Science and Technology was higher.The optimum pH was in the fermentation range of liquor in catalyzing and synthesizing four esters.