Study On Bacteria And Optimization Of Process Of Alcohol Fermentation In Shanhe Vinegar

Yeast has been regarded as one of the main functional microzyme in Daqu sorghum,and plays an important role in the production rate and flavor quality of vinegar.Thus it is of great significance to increase the concentration of yeast in the fermentation broth.In this experiment,the yeast strains were isolated from Daqu sorghum and liquor msah,and then purified;identified by morphological and physiological biochemical tests;alcohol resistance,alcohol production,and ester-producing ability of the yeast strains were analyzed;The volatile components of yeast with higher total ester content was analyzed by gas chromatography-mass spectrometer(GC-MS).The best selection of yeast strains was the basis for subsequent studies.The ratio of inoculation of Daqu sorghum and yeast strains was determined using orthogonal test.The optimal process parameters for alcohol fermentation were determined by plackett-Burman test and response surface test,promoting fermentation.The results of study are as follows:1.Separation and identification of yeasts:68 strains with typical yeast characteristics were isolated from Daqu sorghum and liquor msah.One representative strain was selected from each group for a total of 12 strains.According to the colony morphological characteristics,physiological and biochemical experiments identified:2 strains were Hansenula;2 strains were Kloeckera;3 strains were Saccharomyces;3 strains were Candida;1 strain is Pichia;1 strain is Schizosaccharomyces.2.Production performance of yeast:Among the 12 strains,strains LY14,LY27,and QY15 had high alcohol resistance,tolerance to alcoholicity of 15%vol,and 15.4%higher than strain SHY.The strains LY14 and QY15 had strong alcohol production capacity,the alcoholicity was 9.4%vol and 9.1%vol,respectively,which were higher than the strain SHY(7.2%vol).The strain QY13 had outstanding ester-producing ability and the total ester content reached 0.783g·100mL-1.It is 34.1%higher than strain SHY.3.Determination of volatile aroma components:The results showed that most of the substances with the characteristic flavor of vinegar were detected in strain QY18 sorghum fermentation broth,whice had 7 kinds,namely phenylethyl alcohol,ethyl acetate,phenyl ethyl acetate,and acetate Amyl ester,ethyl palmitate,2-methyl butyric acid and phenyl acetaldehyde.4.Proportioning of strains and parameters of fermentation process:According to the analysis of orthogonal experiments,the ratio of the best alcohol-producing fermentation was:Daqu:LY14:QY18 =20:2:1;the optimal proportion of ester-producing fermentation was:Daqu:LY14:QY18=20:1:2.Three significant factors were screened by Plackett-Burman test:material-water ratio,inoculum size and fermentation time.Using response surface tests,the ratio of material to water was 33:100,inoculum size was 45%,fermentation time was 7d,fermentation temperature was 35 ?,pH value at normal,alcohol content of sorghum fermentation liquid reached 13.82%vol,total ester content reached 0.732g·100mL-1,the amount of residual sugar was 0.86 g·100 mL-1.Under these conditions,seven substances with vinegar-characteristic flavor were detected in sorghum broth,namely phenylethyl alcohol,ethyl acetate,isoamyl acetate,ethyl palmitate,ethyl oleate,2-methyl butyl Acid and phenylacetaldehyde.