Low Diacetyl Brewer's Yeast Mutation Breeding Research

Diacetyl is one of the main flavor substance in beer,whose leak point is very low in beer(0.1～0.15mg/mL), if exeeeding this standard,the beer will have unpleasant taste.So that the content of diaeetyl in beer is the important signal of the quality's.Superscale of diacetyl had become restrictive factors and outstanding contradictions of improving beer qualities,especially in producing low cost beer products fermented by elevating fermentation temperature,shortening fermentation period and increasing content of subsidiary materials. In this thesis, the low diacetyl Saccharomyces cerevisiae were obtained by mutation breeding and screening of SM.In order to improve the resistant to SM of Saccharomyces cerevisiae, UV, NTG and microwave were used to mutagenize Saccharomyces cerevisiae, respectively. The optimum irradiation time of UV is 40 seconds at 30cm distance with 15 W. Screening obtain Saccharomyces cerevisiae srtains ZW-HDY-005. The fermentation productions diacetyl conten was 0.23mg/L and alcohol conten was 2.03%. The optimum dosage of NTG is about 2mg/mL,15min. Screening obtain Saccharomyces cerevisiae srtains N-T-HDY-006. The fermentation productions diacetyl conten was 0.25mg/L and alcohol conten was 1.93%.The ZW-HDY-005 for NTG mutagenesis, screening obtain SM resistance strains FH-HDY-03. The fermentation productions diacetyl conten was 0.19mg/L and alcohol conten was 2.02%. The optimum irradiation time of microwave is 120 seconds. Screening obtain Saccharomyces cerevisiae srtains WB-HDY-006. The fermentation productions diacetyl conten was 0.17mg/L and alcohol conten was 2.05%. Also genetic charaeteristies of obtained strains were stbale atfer 10 generations of inoeulation.WB-HDY-006 and HDY-01 are different in the number and fermentation productions content such as sugar, alcohol, diacetyl in fermentation experiment. Yeast WB-HDY-006 can keep more numbers in the fermentation courses than HDY-01.The sugar content of WB-HDY-006 is 5.50%, while HDY-01's content is 5.87%, 6.3% descend compared with the original strain HDY-01. WB-HDY-006 ethanol yield is 3.85%, while HDY-01's is 2.76%, increased 41.92% than the original strain HDY-01. WB-HDY-006 diacetyl yield is 0.06mg/L, while HDY-01's is 0.23mg/L, 73.91% descend compared with the original strain HDY-01.And the fermentation period of WB-HDY-006 is 6 days'shorter than original strain HDY-01.