A Study On The Screening And Application Of Ester-Producing Yeast From Shilixiang

Shilixiang wine has a long history,which is made from sorghum,rice,glutinous rice,wheat,corn.Daqu,which is made from wheat in the production process,is a starter.In the process of making Shilixiang,fermented grains and raw materials should be mixed well,distilled to obtain wine,mud cellar solid fermentation,and then through the jiuhai and pottery altar long-term constant temperature storage.Shilixiang is clear,transparent,fragrant,sweet,long aftertaste,which is one of the representatives of luzhou-flavor liquor in hebei province.This project is a cooperative project between Hebei university and Shili xiang co.,LTD.,aiming at screening the production of ester yeast in fermented wine fermentation and applying it to liquor fermentation,so as to improve liquor ester aroma and optimize the composition ratio of various esters.This study in combination with miles sweet white wine fermentation system and style,on the basis of reference for application of ester yeasts in other kinds of fermented foods,from different time periods fermented alcohol in the fermented grains out for miles sweet wine brewing good incense yeasts,comprehensive analysis of the characteristics and composition of skeleton of the senses,and research on its ester yield rule for further analysis,for miles sweet wine flavor to provide safe and reliable technical way and theoretical support.This research first analyzes the index of fermented grains and changes of fungus in fermented grains.Moisture,acidity,alcohol content in the fermented grains as fermentation time,reducing sugar as the fermentation time was reduced after the first rise trend,starch with the trend of fermentation time was reduced,and the trend of lower,which is consistent with the basic,due to gravity,in the late fermentation,the lower moisture content,acidity of fermented grains,the alcohol content is higher than the middle and upper fermented grains.With the advance of fermentation time,shannon,Simpson,chao1 and ACE of fermented grains in the upper,middle and lower layers showed an overall trend of first increasing and then slightly decreasing.The results showed that the dominant fungi were ascomycetes,accounting for 80.1%of the total abundance.The relative abundance of Ascomycetes and Candida remained relatively high in fermented grains,which were the dominant fungi in the brewing process of Shilixiang.In this study,culturable yeasts were screened,isolated and morphologically clustered.A total of 372 strains of yeast were isolated and divided into 19 different morphologies,of which morphologically 1 accounted for 28.6%,40.2%,33.8%and 22%respectively in the fermentation process,and 30.9%in the screened yeast.In the early stage of the fermentation process of Shilixiang,morphology 1 was the dominant yeast,but morphology 10 was the ester producing yeast studied in this paper.In this study,the esterification of yeast,the environmental adaptability of wine making and the molecular identification were studied.Through the qualitative,quantitative and molecular identification experiments of ester production,it was determined that form 10 yeast was Zygosaccharomyces bailii and could metabolize ethyl caproate.The yeast showed high esterase activity at 25-30?and pH5.0,but glucose had no significant effect on esterase activity.However,the presence of ethanol inhibited esterase activity,Cu²⁺,Zn²⁺and Pb²⁺all showed inhibition,and Ca²⁺,Mg²⁺,Mn²⁺,Fe³⁺,Na⁺and K⁺showed activation.In this paper,the expanded culture conditions of ester producing yeast were studied,and its combination with lactic acid bacteria was applied to production fermentation.The final conditions for extended culture were:glucose 4.63%,peptone 4%,yeast extract 3%,temperature 32?,pH 5.5,stirring rate 180r/min,ininoculation amount 8%.The introduction of lactic acid bacteria and bayer combined yeast could change the proportion of the four esters in fermented grains,and increase the proportion of ethyl hexyl in raw wine,but did not reverse the trend that the ratio of ethyl hexyl was less than 1.