Macromolecular alpha-glucans with alpha-1,3/alpha-1,4 branching structures produced using dual glycosyltransferases: Elucidation of physicochemical and slowly digestible properties

Abstract

Amylosucrase from Neisseria polysaccharea (NpAS) produces the linear amylose-like a-glucans by the elongation property from sucrose, and 4,3-a-glucanotransferase from Lactobacillus fermentum NCC 2970 (4,3-aGT) newly synthesizes the a-1,3 linkages after cleaving the a-1,4 linkages by the glycosyltransferring property. This study focused on the synthesis of high molecular a-1,3/a-1,4-linked glucans by combining NpAS and 4,3-aGT and analyzed their structural and digestive properties. The enzymatically synthesized a-glucans have a molecular weight of >1.6 x 107 g mol-1, and the a-4,3 branching ratios on the structures increased as the amount of 4,3-aGT increased. The synthesized a-glucans were hydrolyzed to linear maltooligosaccharides and a-4,3 branched a-limit dextrins (a-LDx) by human pancreatic a-amylase, and the amounts of produced a-LDx were increased depending on the ratio of synthesized a-1,3 linkages. In addition, approximately 80 % of the synthesized products were partially hydrolyzed by mammalian a-glucosidases, and the glucose generation rates decelerated as the amounts of a-1,3 linkages increased. In conclusion, new types of a-glucans with a-1,4 and a-1,3 linkages were successfully synthesized by a dual enzyme reaction. These can be utilized as slowly digestible and prebiotic ingredients in the gastrointestinal tract due to their novel linkage patterns and high molecular weights.