The Properties of Glycosidases of Vitis vinifera and a Comparison of Their β-Glucosidase Activity with that of Exogenous Enzymes. An Assessment of Possible Applications in Enology

Abstract

Glycosidases of Muscat of Alexandria were isolated and further purified. Two β-glucosidases, a β-galactosidase, and two weak α-glucosidases were found. The β-glucosidases, which were located mainly in the juice of the grape, had increased activity with berry maturity. They both had optimal activity at pH 5.0 and were relatively tolerant to 10% ethanol, but they were inhibited by glucose. Chardonnay, Gewürztraminer, Muscat Hamburg, and Thompson Seedless grape varieties had β-glucosidase enzymes with similar properties to those of Muscat of Alexandria. The properties of the β-glucosidases of a commercial pectolytic enzyme, Rohapect C, and of almond emulsin (β-glucosidase, EC 3.2.1.21) were compared with the grape enzymes. The β-glucosidase of Rohapect C was strongly inhibited by glucose. Studies with a mixture of natural monoterpene glycosides from grape showed all the plant-derived enzymes to have an aglycone specificity discriminating against glycosides of tertiary alcohols. The properties of the endogenous and exogenous glycosidases examined limit their usefulness for the release of glycosidically bound flavorants in juice processing or winemaking.