Study On Performance Analysis As Well As Preferred Selection Of Saccharomyces Cerevisiae And Optimization Of Fermentation Technology Of Kiwifruit Wine

In this dissertation,‘Xuxiang' kiwifruit(Actinidia deliciosa cv.)were fermented with seven different Saccharomyces cerevisiae Strains(F15,BM 4×4,RA17,RC212,WLP77,JH-2,CR476)in order to revealed their influence on physicochemical indexes,phenolic components,volatile aroma components and sensory evaluation of kiwifruit wines.Additionally,selecting the specific strains with high producing-ester ability were used to mixed fermentation for the sake of improving the categories and quantities of ester and the quality of kiwifruit wine.The main research results were as follows:1.The fermented attributes about nine S.cerevisiae strains(F15,BM 4×4,RA17,RC212,WLP77,JH-2,CR476,PF11,F20)contained some differences.RA17,BM4×4,RC212 strains had higher fermentation ability,longer fermentation time and stronger tolerance of alcohol as well as SO2,but contained lower flocculating ability.PF11 and F20 strains had the lowest growth rates,lower fermentation ability and poor tolerance of alcohol and SO2,which demonstrated PF11 and F20 strains could not quickly adapt the kiwifruit juice.So these two strains were not studied any more.2.This character was focus on the effects of different S.cerevisiae strains on the physicochemical indexes and phenolic components of the kiwifruit wines.The results showed that the effects of strains on physicochemical indexes were not obvious except for the soluble solid content.Nevertheless there were some differences in the specific level of each index,due to the comprehensive effect with adaptability,growth rate and fermentation ability of strain.In the aspect of phenolic profiles,some polyphenol contents and DPPH free radical scavenging rate had significant differences.Especially for epicatechin,catechin and protocatechuic acid,they all showed extremely significant differences(P < 0.001).Regarding to the total phenolic content,wine with BM 4×4 contained the highest amount of 317 mg/L,while wine with CR476 only had 214 mg/L.Talking about DPPH,the BM 4×4 also achieved the greatest amount of 201 mg/L,which showed this strain had the relatively weak decomposition ability as well as breaking ability of kiwifruit juice and preserved the antioxidant substances in raw juice.3.The influences of S.cerevisiae strains on the aroma substances and sensory evaluation were performed.The results indicated kiwifruit wines with different strains had some discrepancies of types and contents of aroma substances.Wines with RA17 and BM4×4 were good sources of ester,which was significantly higher than the ester of other treatment groups.The wines with these strains were ester-type by using PCA.RC212 and JH-2 wines had higher amount of ethyl hexanoate,ethyl octanoate and octanoic acid,possessing typical aroma characteristics of pear,strawberry and banana,while CR476 wine had more 2-nonanol and 2-phenethyl alcohol,containing typical aroma characteristics of honey and rose.F15 wine showed the eugenol of 38.9 ?g/L,giving clove aroma to kiwifruit wine.Besides,sensory evaluation of kiwifruit wines also performed some differences,but did not show regularity.The score of RA17 and BM4×4 wines were higher,particularly for fruity flavor,balance,complexity.Above all,BM4×4 and RA17 strains were the most suitable strains for making kiwifruit wine.4.According to the traditional preparation method for yeast,BM4×4 and RA17 strains were selected in order to mix and make the special yeast for kiwifruit wine.Through single factor test and response surface analysis,optimum culture condition was determined: inoculum amount of strain was 5.3 g,the ratio of RA17 to BM4×4 was 2:1,culture temperature was 26.5 ?,culture time was 8d.Under this condition,the number of yeast was 6.36×107 CFU,total ester amount was 6.52 mg/L and alcohol content was 15.8 % vol,which were all more than fermented by single strain.5.The kiwifruit wine was made by the means of the mixed yeast.Later,the four important factors,including the amount of yeast,the amount of nutritional agent,fermentation temperature,fermentation time,were studied by single factor test and response surface test The optimum fermentation conditions were ensured: the amount of yeast was 16.5%,the additive amount of nutrient was 0.18 g/L,fermentation temperature was 26.0?,fermentation time was 15.5 d.Under this condition,the kiwifruit wine was not only clear and bright,but also had mellow taste,unique flavor and fruity fragrance.Additionally,the alcohol was 11.2% vol,the soluble solids content was 4.3 °Brix,the total acid was 10.2 g/L,the content of Vc was 32.85 mg/100 g and the sensory score was 98.More importantly,the total ester content of 6.70 g/L and volatile ester content of 49.896 mg/L were significantly improved.