Formation of Ethyl α-D-Glucoside in Saké Brewing

Abstract

A remarkable formation of ethyl α-D-glucoside (α-EG) was observed in the regular process of saké brewing, while its formation was slight in a modified process, in which Koji as the enzyme source was replaced with a mixture of mold enzyme preparations, Takadiastase (Aspergillus oryzae) and glucoamylase (Rhizopus delemar). An enzyme preparation was fractionated from Koji extract and partially purified. The enzyme fraction catalyzed the formation of α-EG from ethanol and α-1, 4-glucans having various degrees of polymerization as sugar substrate by a transglucosidation reaction in parallel with hydrolysis of the glucans to glucose. Thus, it was concluded that α-EG in saké was synthesized by the action of the Koji-enzyme from those glucans and ethanol in the system of usual saké brewing. Although Takadiastase also showed some activity of α-EG forming enzyme, the activity in the modified process was estimated to be very lower than in the regular one, because only a small quantity of the preparation was introduced.