Study On The Screening Of Mead-producing Yeast And The Breeding Of Strains

Mead is a kind of wine fermentated by brewer's yeast through advanced fermaentation technology with honey as the material.The quality of mead is closely correlated with its nutritious component,sort of aroma component and contents.Mead fermentated only by brewer's yeast is rich in alcohol flavor but lack in aroma,which meas it's not good enough in taste.In order to improve the quality of mead,people did reseach from aspects like selection of honey,yeast and fermentation conditions.Screening and breeding aroma-producing yeast with high ester productivity,fine flavor and suitable for mead fermentation is significant in mead industry.This article compared influence of Hansenula,Candida,Dekkera,Saccharomycopsis fibuliqera and Geotrichum candidum on sensory characteristics of mead,aroma-producing capacity and aroma components.Meanwhile,fermentation characteristics of different strain combinations were discussed as well.Based on thediscussion,Saccharomycopsis fibuliqera Y7 was selected as the initial strain.By conducting NTG and UV mutation on haploid strain,mutant haploid strains with high esterifying enzyme activity and good fermentation proterty were obtained.Through hybridization between haploid strains,a high esterifying enzyme activity diploid strain which is suitable for mead fermentation was obtained.The main results of the research are as follow:(1)Influence of five aroma-producing yeast strains on sensory characteristics,limited component,aroma-producing property and aroma components were explored.The result indicated that all but Dekkera 30201 and 30202 could form pellicle under stationary state.The broth after fermentation was transparent light brown liquid.Hansenula had the highest ethyl acetate productivity and fusel oil content,among which 1437 could produce 773.860mg/L of ethyl acetate and 82.336mg/L of isoamylol,and 1312 could produce 43.140mg/L of isobutanol.Saccharomycopsis fibuliqera was not ester-productive,but could produce special aroma components,which made the wine smells and tastes fruity,and Y7 was the best.(2)Hybrid fermentated five aroma-producing yeast strains in different conbinations,in was discovered that abnormal-mutatnt-Hansenula-entered hybrid fermentation and Saccharomycopsis fibuliqera-centered hybrid fermentation produced mead in fine sensory characteristics.Mead produced through abnormal-mutatnt-Hansenula-entered hybrid fermentation had the highest ester and alchol contents,midium acidity,but fusel oil content was relatively high.Mead produced through Saccharomycopsis fibuliqera--centered hybrid fermentation had a fine taste and low fusel oil content.(3)Saccharomycopsis fibuliqera Y7,which could produce wine with fine taste and low fusel oil content,was selected from 23 aroma-producing yeast strains.Different mating types of haploid cells were isolated for UV and NTG mutation.After primary and secondary screen,haploid cells with high esterifying enzyme activity were isolated.By hybridization among different mating types,Y-2-3,an esterifying enzyme active diploid strain which was suitable for mead fermentation was finally obtained.By comparing to its parent strain Y7,incrase of total ester was obvious(P<0.05).Esterying enzyme activity of Y-2-3 was 5.692mg/100m,which was 1.49 times higher than its parent strain Y7.(4)5M3 fermentation tank was used to observe the fermentation property of Saccharomycopsis fibuliqera Y7 and selected strain Y7-2 in large-scaled producing condition.The results showed that mead produced by Y-2-3 had no difference in color and clarity in comparison to its parent strain Y7,but fragrance and flavor were better than Y7.Compared to Y7,ethyl acetate and isoamyl acetate concentration were increased in mead produced by mutant strain Y-2-3,which made the mead tastes richer in bouquet.By adding trace amount of Saccharomycopsis fibuliqera Y7 and selected strain Y7-2,the quality of disilled mead improved a lot.The flavor was more harmonized and softer,and the bitterness was decreased.The conclusion of the article are as follow:(1)The influence of five aroma-producing yeast strains on sensory characteristics,limited components,aroma-producing property and aroma components vary from each other,which can be referred when producing mead of different flavors.(2)Through hybrid fermentation,we discovered that abnormal-mutatnt-Hansenula-entered hybrid fermentation and Saccharomycopsis fibuliqera-centexed hybrid fermentation produced mead in fine sensory characteristics.In other words,they're suitable for mead fermentation and strain breeding.(3)Mutation and hybridization were conducted to different mating types of hiploid of Saccharmycopsis fibutqera Y7,an excellent diploid strain Y-2-3 with high esterying enzyme activity and mead fermentation performance was obtained.Its esterification capacity was 5.692mg/100mL,which was 1.49 times higher than its parent strain Y7.By passage and measure,it was genetically stable.(4)5M3 fermentation tank was used to observe the fermentation property of Saccharomycopsis frbuliqera Y7 and selected strain Y7-2 in large-scaled producing condition.Ethyl acetate and isoamyl acetate concentration were increased in mead produced by mutant strain Y-2-3,this fertated liquor could also improve the quality of distilled mead greatly.The innovative points of the article are:(1)Systematic comparison on sensory characteristics,aroma components and limited components of five aroma-producing yeast strains was accomplished.It could provide production of mead,other wines and condiments with reference.(2)Two strain conbinations with relatively good flavor were obtained and can be used in mead production.(3)Hiploid cells of Saccharomycopsis fibuliqera Y7 were mutated by UV and NTG Based on hiploid cell hybridization,Y-2-3,a mutant strain with better fermentation flavoer and high ester content was gained.(4)Y-2-3 was used in 5M3 fermentation tank and gained high quality mead,and this strain is practical in industraial production.