Abstract
The isomalto- and nigero-oligosaccharides are usually produced from starch by the combination of α-glucosidase and starch degrading enzymes, such as α- and β-amylases. In this study, a new reaction system for the production from starch of two α-1,4 glucans having α-1,6- and α-1,3-linked glucosyl residues at or near the non-reducing end was established. These glucans were efficiently produced by the coupled reaction of α-glucosidase and cyclodextrin glucanotransferase (CGTase) with negligible cyclodextrin production. The produced glucans underwent very little hydrolyzation by β-amylase but α-amylase clearly enhanced the digestion of glucan. This indicated that glucosidic linkage other than α-1,4-linkage was introduced at or near the non-reducing end of the glucan and the reducing end part of the glucan was mainly composed of α-1,4-linkages. The glucosidic linkage introduced was dependent on the specificity of α-glucosidase for glucosidic linkage. α-Glucosidases from Aspergillus niger (ANG) and Acremonium strictum (ASG) produced α-1,6- and α-1,3-glucosidic linkages, respectively. The chain length distribution also varied according to the specificity of α-glucosidases for substrate chain length. The major DP of the glucans produced by ANG and ASG were 4-6 and 6-10, respectively. The glucan produced by the coupled reaction was highly resistant to retrogradation. The syrup including this glucan maintained transparency following storage at room temperature for 1 month. In contrast, control syrup including the starch hydrolysate lost transparency despite the lower content of long-chain glucan. This indicates that the glucosyl residue linked by α-1,3-linkage present at or near the non-reducing end of glucan strongly inhibits aggregation of glucan and provides retrogradation tolerance.
