白酒中四大乙酯在酿造发酵中形成的探讨

Study on the Formation Mechanism of Four Main Kinds of Ethyl Esters in the Fermentation of Liquors

四大乙酯(己酸乙酯、乙酸乙酯、乳酸乙酯和丁酸乙酯)是我国白酒中的主要香气成分,其含量占总酯的90%～95%,乳酸乙酯含量高是我国白酒的显著特征之一。己酸乙酯是己酸与乙醇经酯化而形成,研究结果表明,具有酯化能力的微生物有酵母菌和霉菌。酵母菌在生长活动期,其胞内酶将己酸酯化合成为己酸乙酯,而曲霉菌则是胞外酶合成己酸乙酯,主要有红曲霉和根霉菌。乙酸乙酯的形成有3条途径:一是酵母菌在酒精发酵时的副产物;二是酒醅中多量乙酸经微生物酯化而成;三是其他微生物发酵的代谢物。乳酸乙酯一是配醅带入,二是发酵过程中乳酸菌产生大量乳酸而形成。丁酸乙酯是由丁酸菌或己酸菌产生的丁酸与乙醇经生化反应而合成。(一平)

The four kinds of ethyl esters(ethyl caproate,ethyl acetate,ethyl lactate and ethyl butyrate)are the main flavoring com-ponents of Chinese liquors.The content of these ethyl esters accounted for90%～95%of the total esters and high content of ethyl lac-tate is one of the distinctive characteristics of Chinese liquors.Ethyl caproate formed by the esterification of ethanol and caproic acid,and the study results indicated that the microbes with esterifying capability included yeasts and mold.During the growth period and ac-tive stage,the intracellular enzyme of yeasts esterified caproic acid into ethyl caproate.However,the extracellular enzyme of mold mainly including monascus and rhizopus esterified caproic acid into ethyl caproate.The formation of ethyl caproate has three pathways:1.the byproduct of yeast during the fermentation of alcohol;2.esterification of the acetic acid in fermented grains;3.the metabolite by the fermentation of other microbes.Ethyl lactate is attended by the compounding of fermented grains or it formes by the large amount of lactic acid(produced by lactic acid bacteria during fermentation).Ethyl butyrate is formed by the biochemical action of al-cohol and butyric acid(produced by butyric acid bacteria or caproic acid bacteria).(Tran.by YUE Yang)