Effective production of glycosyl-steviosides by alpha-1,6 transglucosylation of dextrin dextranase

Dextrin dextranase (EC 2.4.1.2; DDase), which is produced by Acetobacter capsulatus ATCC 11894, acted on a mixture of stevioside and starch hydrolysate with isoamylase, so that the enzyme was found to convert stevioside to predominantly mono-glucosyl-stevioside (SG1) and di-glucosyl-stevioside (SG2), and little of the stevioside initially added remained. SG1 was separated into two compounds (SG1a and SG1b) by reversed-phase high-pressure liquid chromatography. The structures of SG1a, SG1b, and SG2 were analyzed and concluded to be 13-O-(6-alpha-glucosyl-2-beta-glucosyl-beta-glucosyl)-19-O-beta-glucosyl -steviol, 13-O-[(6-alpha-glucosyl)(2-beta-glucosyl)-beta-glucosyl]-19-O- glucosyl-steviol, and 13-O-[(6-alpha-glucosyl)(6-alpha-glucosyl-2-beta- glucosyl)-beta-glucosyl]-19-O-beta-glucosyl-steviol, respectively. During the reaction for production of glycosyl-steviosides, DDase catalyzes transglucosylations from glucosyl donor compounds to stevioside to be SG1a and SG1b, and to SG1b to be SG2 rapidly forming alpha-1,6 glucosidic linkages. However transglucosylation to SG1a to be SG2 rarely occurred, and the conversions among stevioside and these glycosyl-steviosides were catalyzed by the action of DDase to transfer alpha-1,6 linked glucosyl residues, forming alpha-1,6 linkages.