Screening And Identification Of Esterase-Producing Strains And Its Application In Flavor Enhancement Of Xiaoqu Rice Wine

Traditional Chinese liquor has a long history of development.There are Han,Tang,and Southern Song talks about its origin.After the founding of New China,with the improvement of people’s material requirements,the smell and taste of liquor were gradually raised.With higher requirements,the exploration of the process of enhancing the aroma of liquor began.A complex microbial system involved in the process of liquor brewing.Esterification enzymes produced by the metabolism of certain microorganisms catalyze the synthesis of esters that determine the degree of aroma of the wine body from acid alcohol substrates.Esterification enzymes that convert body substances into aroma substances are mainly derived from the metabolites of yeasts,bacteria,molds and other microorganisms,so they have a wide range of screening space.Traditional rice wine is a large category in white wine because of the single raw material and fermentation method.The problem has led to the fact that the aroma in the wine has not been able to achieve good aroma effects.In order to increase the content of aroma substances in traditional rice wine,this project is dedicated to screening esterified strains from the natural environment and using the interaction of the complex strains in the fermentation process in rice wine to explore the aroma-enhancing technology of rice wine.This technique can increase the content of ethyl acetate,ethyl lactate,ethyl caproate andβ-phenylethanol in the wine body to obtain a flavor prominent laboratory semi-finished rice wine.The main findings are as follows:1.Twenty-one wild strains that produce esterase with transparent circles around colonies on tributyrin plates were initially screened from sludge and koji samples using by a transparent circle method and acid-base titration method.Among them,the yeast strain TZC-5 produces 17.36 U/m L esterase activity,and the bacteria strain TZC-6 produces 13.89 U/m L esterase activity.The esterase activity of the primary strains were then detected using the method according to the QB/T 5188-2017 light work industry standard for brewing red yeast rice with slight modification that the reaction product concentration was directly measured by GC instead of the saponification titration.The results showed that TZC-5 has the highest esterification power（135.116mg/m L·100 h）among yeast and TZC-8 has the highest esterification power of among bacteria（120.339 mg/m L·100 h）.The esterification power of 5 strains of molds is above 35 mg/g·100 h,all higher than the esterification power standard（30 mg/g·100 h）in QB/T 5188-2017,of which TZC-14 has the highest esterification power of 78.5889 mg/g·100h.2.Morphological and molecular identification of the strains with esterification ability,the main results are:4 strains of Candida tropicalis（Candida tropicalis）,1 strain of Candida parapsilosis（Candida parapsilosis）,1 strain Trichosporon（Trichosporon）,2 Saccharomyces cerevisiae（Saccharomyces cerevisiae）,4 Bacillus subtilis（Bacillus subtilis）,1 Acinetobacter（Acinetobacter）,3 Penicillium chrysogenum（Penicillium chrysogenum）,1 smoke Aspergillus（Aspergillus fumigatus）;3.The esterification yeast was screened for its ethanol production capacity.When the substrate of 10%glucose was used,the maximum ethanol concentration of GX-UN120 in the fermentation broth was 39.61 g/L,followed by the ethanol concentration of TZC-5 at 35.41 g./L;and use the esterified strains after screening and identification in the traditional fermentation process of rice wine,and the flavor substances in the wine body（ethyl acetate,ethyl lactate,ethyl caproate,β-benzene Ethanol）compared with the improvement of non-inoculated fermented wine as an indicator,the inoculation amount of yeast,bacteria and mold solid koji was screened.Finally,the solid koji cultured for 72 hours with 2%rooting 2 added,6%yeast TZC-5 grown to an OD₆₀₀ of 29.53,and 4%bacteria TZC-6 grown to an OD₆₀₀ of 3.8593 were selected.Applied to the traditional fermentation process of rice wine,the alcohol content increased from 11.77%vol to 15.61%vol,an increase of 32.63%;the concentration of ethyl acetate increased from 0 to 41.3 mg/L;the concentration of ethyl lactate increased from 0 to 165.69 mg/L;The concentration of ethyl caproate increased from 1698.65 mg/L to 2208.25mg/L,an increase of about 1.3 times,and the concentration ofβ-phenylethanol increased from 60.88 mg/L to 157.31 mg/L,an increase of about 2.58 times.