Abstract:Malolactic fermentation (MLF) carried out by Oenococcus oeni(O.oeni) is the main method to reduce the acidity of the wine. Meanwhile, the synthesis and release of a variety of glycosidase will have a positive effect on the conversion of glycosylated precursor compounds originated from grapes. In this experiment, two O.oeni autochthonous strains ZX-1 and GF-2 isolated and identified from Hexi Corridor Region and the commercial strain VP41 were used as test and control strains, respectively. To analyze and discuss the effects of single fermentation conditions (initial pH value, ethanol concentration, SO2 addition and fermentation temperature) and the compound fermenting condition on the cumulative βD glucosidase and diglycosidase activities of the tested O.oeni strains. The changes of terpene aroma substances in the Chardonnay dry white wine fermented by the tested strains were analyzed by the microvinification experiment. The results showed that the cumulative glycosidase activity of the all tested strains was increased first and then decreased with the increase of ethanol concentration and SO2 addition. Higher pH value was more conducive to the synthesis of glycosidase produced by O.oeni strains, and there were differences in the response regulation of βD glucosidase and diglycosidase activity to fermentation temperature. Under the compound fermenting condition, diglycosidase activity of the O.oeni autochthonous strains were significantly higher than that of the commercial strain VP41 （P<0.05), but βD glucosidase activity were slightly lower than that of strain VP41. The SO2 addition had a very significant impact on the glycosidase activity of the all tested strains （P<0.01), and the pH value and ethanol concentration had a significant impact on the glycosidase activity of strains ZX-1, GF-2 and VP41 （P<0.05). The fermentation temperature only had a significant effect on the βD glucosidase activity of strain ZX-1 and VP41 as well as the diglycosidase activity of VP41 （P<0.05). The optimum conditions for glycosidase production of the tested strains were ethanol concentration of 12%, SO2 addition of 30mg/L, pH value of 3.6, and fermentation temperature of 22℃. Under the above conditions, the highest cumulative diglycosidase activity produced by strain GF-2 was 46.137mU/mL, followed by ZX-1 of 45.932mU/mL and VP41 of 37.011mU/mL. Results of the microvinification experiment showed that although the types of terpene compounds in the wine sample fermented by O.oeni autochthonous strain ZX-1 were less than that in VP41 fermented wine, the total content of terpenes were higher. The contents of α-terpineol, citronellol, damastone and linalool in the ZX-1 fermented wine were higher than the threshold, which effectively enhanced the varietal aroma characteristics of Chardonnay dry white wine.
