A Little Accumulation Of Sulfur Dioxide In Beer Yeast Breeding

Six beer yeasts(Saccharomyces cerevisiae) were employed for test. The fermentation characteristics which affect the beer flavor were determined. Beer yeast SY-8 with better flocculation ability, medium fermentation degree, faster fermentation velocity and higher concentration of SO2 was selected as parent strain.The yields of SO2 and H2S of SY-8 in different conditions were determined. The results of beer fermentation showed that the production of SO2 varied when the wort was different in initial pH values, contents of amino acids and salts with the same other fermentation conditions. Production of SO2 reached the maximum when pH value was 6.0. Also, the production of SO2 was proportional to the concentration of all kinds of salts and amino acid within the concentration of 0.05%. The SO2 production could be 3 times more than blank control when adding 0.02% sodium sulfide or 1.45 times more with 0.02% cysteine.After DES (diethyl sulfate) treatment, lead different medium plates containing different sulfur sources were used as screening plates, twelve Saccharomyces cerevisiae strains with higher production of SO2 were selected from original strain SY-8. The basic effected characteristics on fermentation of the mutations were determined, and the results showed that MS-10 was best of all them. SO2 production of MS-10 was 25.32mg·L-1, which is much more than original strain SY-8.The genetic substances of beer yeast SY-8 and MS-10 were analyzed with RAPD. The results of RAPD by random primer showed a different electrophoretic band which was 852bp by DNA sequencing. The protein analysis showed that there was no significant difference between the two strains. Thus it could be seen that MS-10 was a new Saccharomyces cerevisiae strain with higher SO2-producing.Comparing with SY-8, the results of beer fermentation by MS-10 indicated that in terms of beer flavor compounds, the concentration of fusel oil decreased obviously with the others changing a bit. As a result, we found mutation MS-10 was much better than parent SY-8 viewing the situation as a whole.