Correlation Study Of Enzymatic Activities And Chemical Composition During Chinese Liquor Fermentation.

Chinese liquor flavor substances are mainly derivated from degradation products ofstarch, protein and other ingredients in grains metabolized by microbial enzymes. Toexplore the mechanism of flavor compounds, firstly, the reversible synthesis andhydrolysis of four main esters in aqueous and solvent system was analyzed; secondly,the enzymatic activities and chemical composition in solid-fermentation process ofChinese liquor were traced. On this basis, liquid-state light-flavor liquor fermentationwas conducted.The reversible synthesis and hydrolysis of four main esters was analyzed.Esterification in aqueous phase and organic phase were conducted using Novozym435. The highest synthesis rates of ethyl acetate, ethyl butyrate, ethyl hexanoate andethyl lactate in aqueous phase were8.9%,29.1%,16.7%and5.7%, respectively,which are40.3%~76%lower than in organic phase. The hydrolysis rates of the fouresters in aqueous phase can reach to80%, which are higher than synthesis rates. Soesters prefer hydrolysis than synthesis in aqueous phase while they prefer synthesis inorganic phase.Enzymatic activities and chemical composition in the solid-state brewing process oflight-flavor liquor were traced. During the fermentation, moisture, acidity andalcoholic content increased6.9%,27.8,5.2%, respectively. Content of starchdecreased from27.09%to17.37%. High activities of amylase, protease and xylanasewere detected, so that they had greater impact on the fermentation. The cellulaseactivity was low, showing which had low impact. Furthermore, major volatile flavorcompounds, such as ethyl acetate, ethyl lactate, n-propanol, isobutanol, weremonitored.Enzymatic starch hydrolysis simulating liquor fermentation process was optimized.The optimal liquefaction and saccharification conditions were determined takingsorghum, corn, wheat, rice as the raw materials, the liquefaction DE is16.3%andsaccharification DE is99.4%.Four microbial strains were inoculated in liquid liquor fermentation mediumincluding starch and protein hydrolysates. Then acids, esters and other flavorcompounds were analyzed. Acetic acid bacteria, lactic acid bacteria, andester-producing yeast produced acetic acid, lactic acid, ethyl acetate1.2g/L,7.3g/L,2.5g/L, respectively, in single strain fermentation. Mixed strain sequential fermentation of Saccharomyces cerevisiae and ester-producing yeast produced44%more esters than single strain fermentation. The content of flavor compoundsincreased substantially when relevant flavor producing strains were used in mixedstrain fermentaion.Comparative analysis of flavor compounds revealed that flavor composition inliquid-state fermentation was similar to that in solid-state fermentation.