Over-production of the major exoglucanase of Saccharomyces cerevisiae leads to an increase in the aroma of wine

A Saccharomyces cerevisiae wine strain over-producing an endogenous exoglucanase encoded by the EXG1 gene has been constructed to investigate the possible role of this enzyme in increasing wine aroma through the release of a glycosidic precursor. Purification and biochemical characterization of the EXG1 protein has been performed revealing an apparent molecular mass of 61 kDa and an optimal pH and temperature of 4-5 and 55 °C, respectively. No activity loss due to ethanol, SO2, glucose or fructose at concentrations typically found in wine and must has been detected. The production of exoglucanase activity by two wine yeast strain transformants in which the expression of EXG1 was driven by either the S. cerevisiae actin or EXG1 gene promoters has been monitored in culture medium and in grape must during the fermentation process. Various alcohols and terpenes were enhanced in the aroma profiles of wines produced by inoculation with the exoglucanase over-expressing yeasts, though the transformant strain carrying EXG1 under the control of the actin promoter yielded higher levels of free volatiles in wine.