Screening And Identification Of Saccharomyces Cerevisiae And Research On Fermentation Characteristics In Jiangsu And Anhui Regions

This thesis aims to screen high quality Saccharomyces cerevisiae,enrich the strain resources of native yeast,and provide theoretical basis for brewing dry red wine with local characteristics.In the experiment,the grape producing areas in Jiangsu and Anhui provinces were used as the sample collection sites,and the typical yeast strains were obtained after separation and purification of the samples.The fermentation ability,tolerance and basic characteristics were screened.The excellent yeast strains were identified by strain identification,and they were applied to dry red wine fermentation with commercial yeasts,respectively.The effects of different yeasts on the physicochemical indexes and aroma components of wine were analyzed.Combined with sensory evaluation,the native Saccharomyces cerevisiae with the best brewing quality and taste was screened out.The main research results are as follows:（1）Isolation and screening of yeast strains.The collected grape samples,rhizosphere soil and fermented mash were enriched,cultured,separated and purified to obtain 90indigenous yeast strains.The fermentation ability and tolerance of five yeast strains were studied by Duchet tube gas production test,and five yeast strains with excellent properties were BA1,BI1,BN3,CE1 and NL1.All the five yeasts could ferment within 24 h,and could tolerate 15%alcohol,400 mg/L SO₂,60%glucose,42°C high temperature and 6°C low temperature.BA1 and NL1 could tolerate p H 1.6,BI1,BN3 and CE1 could tolerate p H 2.1.In the study of basic characteristics,5 strains were low-yield hydrogen sulfide,high-yield ester and low-yield foam yeast,BA1 was medium-yield alcohol yeast,and 4strains were high-yield alcohol yeast.（2）Simulated fermentation test of yeast strains.Five yeast strains were used for small-pot wine simulation fermentation.The reducing sugar content was 3.48～3.99 g/L,the alcohol content was 13.0～13.3%vol,and the total acid content was 7.48～7.94 g/L.The content of each index met the relevant national brewing standards.Combined with physical and chemical indicators and sensory evaluation results,CE1 and NL1 were retained as the preferred yeast strains.（3）Identification of preferred yeast strains.CE1 and NL1 were identified as Saccharomyces cerevisiae by physiological and biochemical identification and WL medium identification.（4）Quality analysis of Cabernet Sauvignon dry red wine fermented by Saccharomyces cerevisiae.Two optimal Saccharomyces cerevisiae strains and two commercial yeast strains were used to ferment Cabernet Sauvignon dry red wine.Through the determination of physical and chemical indexes in the fermentation process,it was found that the reducing sugar content was reduced to below 4 g/L,the alcohol content was between 14.1%vol and 15.1%vol,the total acid content was between 7.02 and 7.30 g/L,the total phenol content was between 1468.61 and 1713.33 mg/L,the tannin content was between 179.37 and 203.52 mg/L,and the anthocyanin content was between 377.28 and331.26 mg/L.All meet the national brewing standards and wine content range requirements.（5）Determination of aroma components and sensory evaluation of Cabernet Sauvignon dry red wine.The aroma components of wines were determined by GC-MS.The aroma components of wines fermented by NL1 and CE1 were 48 and 47,respectively,and the total relative contents were higher than those of wines fermented by two commercial yeasts.The sensory evaluation score of NL1 was 88,which was higher than that of commercial yeast F15,and the score of CE1 was 83.The comprehensive quality analysis showed that the brewing characteristics and liquor quality of NL1 were better than those of commercial yeast F15 and Saccharomyces cerevisiae CE1,which could be used as high-quality native Saccharomyces cerevisiae.