Release Of Varietal Aroma Compounds During Alcoholic Fermentation Of Cabernet Gernischt Wine

The varietal flavour of wine is mainly existed as glycosides bond forms that are derived from grape, and can be hydrolyzed to free volatile compounds by β-glucosidases in the wine-making process, so that given flavor characteristics of wine varieties. As the main microorganism to induce alcoholic fermentation, saccharomyces cerevisiae are the main sources of β-glucosidases in winemaking, thus it is important to enhance β-glucosidases activities by modifying wine- making conditions. Therefore, achieving the release of varietal flavor is key issue to be solved in the study of wine aroma improvement. Cabernet Gernischt Grapes in Hexi Corridor of Gansu province were used as raw materials in this study, the key factors in the alcoholic fermentation affected β- glucosidase activity from yeast were studied, and mechanisms of releasing and regulating varietal flavour of Gernischt wine were also investigated, with a view to the production of high-quality wine by aroma enhancement fermentation that provided theoretical basis and technical support. The main results are as follows:1. Both the type and content of aroma compounds in skin of Gernischt grape were higher than plup. A remarkable increase was found in the content of terpenes, sesquiterpenes and norisoprenoids after enzymatic hydrolysis. Combined with the results of principal component analysis, varietal flavour of Gernischt grapes including 8 terpenes, 14 sesquiterpenes and 3 norisoprenoids were preliminarily determined.2. The main factors affected the β-glucosidase activity in the model grape juice were initial p H, fermentation temperature and the amount of nitrogen source, respectively. The maximum β-glucosidase activity was reached at p H4.2, fermentation temperature 20℃ and the amount of diammonium phosphate 3 g/L. Cellobiose, SO2, vitamins and trace mineral elements had little influence on β-glucosidase activity, while tannins have negative influence.3. The fermentation temperature and initial p H were the main factors that influenced β-glucosidase activity during alcoholic fermentation. The amount of nitrogen and pomace contact period had no significant effect on the β-glucosidase activity; Under the condition of fermentation temperature 20℃, initial p H4.2 to make wine, the β-glucosidase activity was significantly higher than the control sample(p<0.05).4. After alcoholic fermentation, the contents of varietal flavor such as linalool, nerol, citronellyl acetate, β- damascenone in the treatment group were higher than the contents in the control group. The correlation analysis showed that the β-glucosidase activity had high significantly positive correlation(p<0.01)with the change of terpenol and C13-norisoprenoids, while had low correlation(r = 0.454) with terpene acetate compounds.