Application of branching enzyme in starch processing

Branching enzyme (BE; EC 2.4.1.18; (1 -> 4)-alpha-D-glucan:(1 -> 4)-alpha-D-glucan 6-alpha-D-[(1 -> 4)-alpha-D-glucano]-transferase) is a glucan transferase which is responsible for synthesis of alpha-1,6-glucosidic bonds in starch and glycogen in vivo. It has been demonstrated that at least three BEs catalyze cyclization reactions in addition to the branching reaction in vitro. A thermostable BE from Bacillus stearothermophilus has been used industrially for starch processing to synthesize a food ingredient, highly branched cyclic dextrin (HBCD). HBCD has a narrow molecular-weight distribution and relatively long side chains compared with conventional dextrins, partially hydrolyzed starch produced with (x-amylase. In order to further evaluate the potential of BE in starch processing, the action of BEs from several sources on amylopectin was analyzed. Many BEs tested in this study catalyzed similar reactions to B. stearothermophilus BE to produce HBCD. BE from Bacillus cereus catalyzed cyclization of amylopectin, but the chain-length distribution of the product was significantly different from HBCD. Noticeably, BE from kidney bean produced much larger molecules with shorter side chains than HBCD.