Screeing Of Low-yield Acetic Acid Saccharomyces Cerevisiae Strains And Evaluate The Performance Of Fermentation

As by-product of wine-making yeast fermentation, the content of acetic acid in beer is very low, but small fluctuations will make a significant impact on beer flavor. High content of acetic acid can cause an adverse taste of beer, a "sour outcrop" is one of the main reasons on incompatible flavor of beer. In order to control the content of acetic acid in beer, improve beer flavor, this project tries to choose good, stable and low-yielding acetic acid saccharomyces yeast used for industrial production of beer and seeks technical way to improve the quality of beer flavor.Parent strain using EMS, according to the acetic acid in fermentation liquid of mutant strains of acetic acid and other flavor compounds and the determination results of fermentation performance, the research selects a strain of low-yield acetic acid saccharomyces yeast, over the study of laboratory yeast strains by the small pilot-scale low-temperature fermentation and genetic stability, we found that this target strains can reduce the acetic acid content of 30.7%, and the main fermentation characteristics can be genetic stably.In order to study and analysis the feasibility of this low-yield acetic acid saccharomyces yeast used in beer production, pilot fermentation has carried out in this research, we got comprehensive evaluation from both the fermentation performance and sensory evaluation. The result shows that:the target strains can reduce the content of acetic acid, diacetyl, acetaldehyde, total higher alcohol content 15.4%,15.7%,25.85%,9.6%, the acid feeling gets more coordinated, the beer gets fine quality of soft and refreshing, in line with beer characteristics of saccharomyces yeast.To further study the low production of acetic acid of target strains, this research optimizes the extraction method of acetaldehyde dehydrogenase in yeast strains cells, according to study of activity of aldehyde dehydrogenase and the changes of content of acetic acid in fermentation liquid during fermentation, we get the result that:the activity decline of acetaldehyde dehydrogenase in the mutant stains A12 causes the content decline of acetic acid in fermentation liquid.By extracting the genes of target strains and initial saccharomyces yeast strains and amplification via PCR technical to get ALD6 gene, after sequence analysis, the team found: the mutation of base group in low-yield acetic acid saccharomyces yeast ALD6 gene suppresses activity expression of aldehyde dehydrogenase, then control the produces of acetic acid during yeast fermentation process.The phenomenon of high acetic acid content in beer is widespread, which can affect the beer quality. Using such low-yielding acetic acid saccharomyces yeast to fermentate, may reduce the content of acetic acid in beer furtherly and improve the beer flavor quality on a certain degree.