Study On Breeding Of Aroma-improving Yeast Strain In Cider

This study was based upon the internal and external research situation, constructed cider yeast strain having aroma-improving ability and intense fermentability by protoplast fusion. Though protoplast fusion was already a ripe systematic technique, and many researchers in home and abroad wildly used it to breed new microorganism strains, there were a few research reports of constructing aroma-improving yeast strain.Five yeast strains were selected as experimental material in this study. According to the synthetic analysis of physic-chemical characteristics and organoleptic evaluation on ciders, strain 5# was chosen as optimal cider yeast. Then strain 5# was treated by ethyl methanesulfonate(EMS), strain E2, which has a stable hereditary marker, was isolated from mutants.Protoplasts of strain E2 were fused with inactivated protoplasts of strain 3# having intense fermentability, many stable fusants were obtained. A brewing trail with the excellent fusants and the parental strains was carried out, and the aroma components of different ciders were analyzed and identified by gas chromatography-mass spectrometry. Three fusants having beneficial characters of parental strains and aroma-improving ability were selected out. The main results in this study showed:(1) strain 5# was chosen as optimal cider yeast according to the synthetic analysis of different ciders brewed by the five yeast strains, and treated by EMS, strain E2, which is a lysine auxotrophic strain, was selected out from mutants for one parental stain in protoplast fusion.(2) strain 3#, which has intense fermentability, was chosen as another parental stain in protoplast fusion according to fermentative velocities of different strains and characteristics of different fermented apple juices.(3) The logarithmic growth phase of parental stains was from 2nd hour to 10th hour and the forepart phase was from 2nd hour to 4th hour according to the growth curve, therefore we used the parental cells incubated 4 hour to make protoplast.(4) The protoplast formation rate was 93.5% for parental stain of E2 and 92.4% for parental stain of 3# in the optimal reaction condition of at 35℃, 80min of reaction time, 1% final concentration of snailenzyme. and the protoplast regeneration rate was 30.7% and 29.5%,respectively.(5) The protoplast of strain 3# could be completely inactivated by 60℃ of water bath treatment for 15min.(6) The results obtained from analysis of different ciders by gas chromatography -mass spectrometry and sensory taste suggest that three fusants have better aroma-improving ability.