Study On The Quality And Key Influencing Factors Of Sake Flavor

Due to the lack of special fermented strains and rice in the domestic sake industry,there are few reports about the factors that influence the flavor quality of sake.Furthermore,domestic sake has an inconsistent quality,and its flavor is still similar to that of Huangjiu.Therefore,based on the current situation of domestic sake production,being oriented to the flavor of Japanese sake（ginjo particularly）and analyzing the effects of different sake brewing process and brewing parameters on the flavor of sake to provide a theoretical reference for improving the flavor quality of sake.The main research contents were as follows:（1）Following an analysis of physicochemical indexes and sensory characteristics of Japanese sake（Daiginjo and Junmai）,the basic physicochemical indexes of Daiginjo(15.0%alcohol content and 22.00 g·L^-1 total sugar)were chosen as the targets for enzymatic sake.Combining gas chromatography-mass spectrometry with orthogonal partial least squares discriminant analysis,it was determined that ethyl caproate,isoamyl acetate,ethyl butyrate,ethyl acetate,phenethyl alcohol,phenethyl acetate,ethyl caprylate,and ethyl heptanoate,were the aroma compounds that distinguish Daiginjo from Junmai.Among them,ethyl caproate in Daiginjo contributed significantly to the formation of the ginjo and had an odor activity value more than four times that of Junmai.（2）By using cerulenin plate screen and fermentation experiment,a strain of Saccharomyces cerevisiae JN5 was obtained that had a high output of ethyl caproate(580.63μg·L^-1).The best process for enzymatic brewing of sake was obtained,which was a material-liquid ratio of 1:2.5,anα-amylase addition of 0.22%,liquefaction for 80 min,a DSM compound enzyme addition of 0.60%and enzymatic digestion for 4 h.The alcohol content and total sugar of sake brewed were 15.0%and 21.59 g·L^-1,respectively.Compared with the traditional fermentation process,the enzymatic brewing process shortened the fermentation period by approximately 13 d,increased the alcohol yield by 43.9%and the total aroma compounds content by 48.2%that was much higher than that of Junmai（635.4%higher）,making ginjo stronger.Due to the similarity of the ginjo flavor compounds（isoamyl acetate,ethyl heptanoate,ethyl caprylate,phenethyl alcohol and isoamyl alcohol）in the enzymatic sake,they displayed aggregation with Daiginjo in principal component analysis.（3）By monitoring the changes of flavor compounds during fermentation,it was discovered that the greatest increases in total flavor compounds and the dramatical increases in ginjo compounds were at the first 6 d of fermentation,which increased 97.72-fold and 239.49-fold,respectively.Acids,aldehydes,ketones and other compounds were primarily produced at the first 4 d of fermentation,while the accumulation of alcohols,esters and ginjo compounds predominately occurred during the 4～6 d of fermentation.（4）The flavor compounds of enzymatic sake brewed from different rice,yeast and fermentation temperature revealed that all 3 factors could lead to changes in the content of flavor compounds of enzymatic sake,which yeast and temperature had the most significant effect.Japonica sake had a clear advantage in the content of total volatile flavor compounds（3.3%higher than that of indica sake）and ginjo esters（12.1%higher than that of indica sake）.S.cerevisiae SY3,SY4 and JN5 were suitable for brewing sake with high ester content.Among them,JN5 had the greatest ability to produce ginjo compounds(9650.93μg·L^-1).The best temperature for the production of ginjo compounds was 15°C and the sake fermented at this temperature had the maximum content of total aroma and ginjo compounds,there were differences of 10.0%～50.4%and 11.9%～57.1%compared with other samples,respectively.