Screening Of Excellent Yeast In Fermentation System Of Maotai-flavor Liquor

Yeast is the main microorganism of maotai-flavor liquor fermentation,separating it from the fermentation system,carrying out a comprehensive performance evaluation of excellent strains,and further evaluating the fermentation performance about alcohol and flavor compounds,which is of great significance to the cognition of dominant microorganisms in maotai-flavor liquor fermentation process,and can provide support for microbial resources through yeast strengthening and transformation of brewing process.In this experiment,305 yeast strains were isolated from the fermented grains of a maotai-flavor liquor distillery in 1-7 rounds.Combined with the morphology of single colony on WL medium,cell morphology under microscope and the determination and comparison of D1/D2 region sequence of 26 S r DNA,the yeast strains isolated were divided into 5 genera and 8 species,which were as follows: Saccharomyces cerevisiae,Wickerhamomyces anomalus,Schizosaccharomyces pombe,Zygosaccharomyces bisporus,Zygosaccharomyces bailii,Zygosaccharomyces rouxii,Pichia manshurica,Pichia kudriavzevii.The fermentation capacity and tolerance(alcohol,lactic acid,acetic acid and high temperature)of 305 strains were evaluated by Duchenne tube fermentation method,and the alcohol production capacity,β-glucosidase production capacity and esterase production capacity of 305 strains were evaluated by TTC colorimetry,heptanoside semi-quantitative colorimetry and transparent circle production method.According to the comprehensive evaluation of the strains,36 excellent strains were selected.The sorghum hydrolysate was used as raw material for single-bacteria fermentation,and the contents of alcohol and main flavor compounds in the liquor samples were detected by high performance liquid chromatography and gas chromatography.It was found that ethyl acetate content produced by W.anomalus,Z.bisporus,Z.bailii and P.kudriavzevii was significantly higher than that of control strain AY12 and the highest can reach 29.71 times.In terms of higher alcohols,it was found that the content of phenylethanol produced by all non-S.cerevisiae was lower than AY12,and S.pombe did not produce phenylethanol.In addition,W.anomalus could produce lower isobutanol,active amyl alcohol and isoamyl alcohol.S.pombe could produce lower npropanol,isobutanol,active amyl alcohol and isoamyl alcohol,Z.disporus could produce lower active amyl alcohol and Z.bailii could produce lower isoamyl alcohol.P.kudriavzevii produced n-propanol,active amyl alcohol and iso-amyl alcohol at low yields.Otherwise,a strain of S.cerevisiae was isolated,which could produce n-propanol,isobutanol and active pentanol at low yield.