| Yeast in the beer fermentation process,in addition to metabolizing the main product ethanol,also metabolizes diacetyl,advanced alcohols,esters and other byproducts,these by-products are the main substances that constitute the flavor of beer,but excessive generation of by-products will affect the quality of beer.Diacetyl is a measure of beer maturity,according to national standards,the content of diacetyl must be less than 0.10 mg/L.If the diacetyl content is higher than 0.15 mg/L,it will produce an irritating taste,and if it is higher than 0.5 mg/L,it will produce a sour taste and affect the flavor of beer;senior alcohol is one of the main substances that make up the flavor of beer,and the right amount of senior alcohol will make the beer taste coordinated and soft.The right amount of advanced alcohol will make the beer taste harmonious and soft,but too much advanced alcohol will make the beer "head" after drinking,affecting the flavor and quality of beer.Therefore,selecting and breeding yeast strains with low diacetyl and high alcohols,and controlling the amount of diacetyl and high alcohols produced during beer fermentation can not only shorten the main fermentation cycle and save production costs,but also improve the flavor of beer and improve the quality of beer.Brewer's waste yeast is the yeast slurry at the end of beer fermentation.Although the waste yeast loses its fermentation function,it is very rich in nutrition and has important application value,which can be used in medicine,food and feed industries.This study mainly applies the waste yeast to the production of glutathione.The main content of this study is the selection and breeding of yeast strains with low diacetyl and high alcohol,analyzing the effect of mutagenic strains on the production cost and flavor quality of beer brewing,and screening the excellent yeast strains suitable for medium and high-end beer products.The utilization of waste yeast after beer fermentation was studied.Waste yeast was recovered after fermentation to produce glutathione.The changes in glutathione production of waste yeast after fermentation of mutated strain and original strain were compared,and the yield analysis of free yeast fermentation and immobilized yeast fermentation.Brewer's yeast was selected by UV-ultrasonic compound mutagenesis breeding technology and combined with the method of the tribenuron-methly resistance screening method,and mutagenic strain Y7 was obtained.Compared with the original strain C1,the difference in diacetyl production of mutagenized strain Y7 was highly significant(P <0.0001),which was reduced by 41.41%,but the content of higher alcohols did not change much.The mutagenic strain Y7 was subjected to pilot fermentation of beer,and the indexes of diacetyl,alcoholic strength,higher alcohol and fermentation degree were measured,and the beer fermentation process was optimized.After 10 generations of transmission,the content of diacetyl and other substances in beer brewed by this strain were not significantly different(P >0.05),and the genetic performance was stable.The mutagenic strain Y7 was confirmed by 26 S r DNA sequence analysis,NCBI comparison,and phylogenetic analysis using MEGA5.0 software.The mutagenic strain Y7 can improve the fermentability and resistance of beer to miscellaneous bacteria,improve the flavor quality of beer,shorten the fermentation cycle of beer and save the production cost.Since the yeast strain Y7 obtained by UV-ultrasonic compound mutagenesis breeding technology,the production of higher alcohols did not change much after fermentation,so a chemical mutagen,diethyl sulfate,was added,and the mutagenic strain Y7 obtained after was used as the original On this basis,the low-diacetyl and low-high alcohol brewer's yeast strain YB-Y1 was obtained by the method of diethyl sulfate-ultrasonic and ultraviolet composite mutagenesis.The main fermentation indexes were measured after pilot fermentation of beer,and the difference in the amount of high alcohol production of mutagenized strain YB-Y1 was highly significant(P <0.005)compared with that of original strain C1,which was 49.07% lower and 2.2% higher in alcoholic strength,while other fermentation indexes did not change much.After 10 generations of transmission,there was no significant difference(P >0.05)in the advanced alcohol and ethanol content of mutagenic strain YB-Y1,and the genetic performance of this strain was more stable.The mutagenic strain YB-Y1 was confirmed to be brewer's yeast by 26 S rDNA sequence analysis,NCBI comparison,and phylogenetic analysis using MEGA5.0 software.The differences of fermentation index and fermentation cycle of mutagenized strain YB-Y1 in beer brewing process and fermentation cycle were highly significant(P <0.0001),and the alcoholic strength increased by 2.2%,the true fermentation degree increased by 3.6%.Response surface analysis was performed using the software Design-Expert.V8.0.6.1,with higher alcohol,diacetyl,and alcoholic strength as the main factors and sensory score as the response value,and the response surface model test was used to optimize the flavor substance content of the beer with 75 mg/L of higher alcohol,0.092 mg/L of diacetyl,and 3.916% vol of alcoholic strength,and the sensory score of the finished beer was 92.1148.The fermentation indexes were determined by using mutagenic strain YB-Y1 in beer brewing,with 70.03 mg/L of higher alcohol,0.08 mg/L of diacetyl,and 4.2% vol of alcohol,and the sensory score of the finished beer was 92.The flavor of beer brewed by mutagenic strain YB-Y1 was better.To study the application of mutagenized yeast strains YB-Y1 in glutathione production,the yeast slurry after fermentation of mutagenized strains was recovered and used for fermentation to produce glutathione,and the yield of glutathione was increased by more than 30% for both compared with the original strain C1,in which mutagenized strain YB-Y1 was increased by 36.10%,and genetic stability test was conducted,and after10 generations of transmission,the content of glutathione after fermentation of mutagenized strain YB-The genetic stability test was carried out,and after generations,there was no significant difference in the glutathione content of mutagenic strain YB-Y1 after fermentation(P>0.05),and the genetic performance was more stable.After 20 the parallel test,the amount of glutathione production after fermentation was highly significant(P <0.0001)compared with the original strain C1,which proved that the mutagenic strain YB-Y1 was more stable.The mutagenic strain YB-Y1 were subjected to free yeast fermentation and immobilized yeast fermentation,respectively,to compare the glutathione production of different fermentation methods.The results showed that after immobilized yeast fermentation,the intracellular glutathione content and yield of mutagenic strain YB-Y1 were higher than those of free yeast fermentation,and the yield increase was more than 50%,and the immobilized yeast fermentation method could improve the yield of glutathione to a greater extent.Expands the field of application of yeast strains and reduces the environmental impact of beer production waste. |
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