Enzymatic Preparation of Maltooctaose-rich Mixture from Starch Using a Debranching Enzyme of Nostoc punctiforme

The debranching enzyme of Nostoc punctiforme (NPDE) is a novel enzyme that catalyzes the hydrolysis of α-1,6-glycosidic linkages in starch, followed by the sequential hydrolysis of α-1,4-glycosidic linkages. The debranching activity of NPDE is highly specific for branched chains with a degree of polymerization (DP)＞8. Moreover, the rate of hydrolysis of α-1,4-linkages by NPDE is greatly enhanced for maltooligosaccharides (MOs) with a DP＞8. An analysis of reaction mixtures containing various starches revealed the accumulation of maltooctaose (G8) with glucose and maltose. Based on the novel enzymatic properties of NPDE, an MO mixture containing more than 60% G8 with yield of 18 g G8 for 100 g starch was prepared by the reaction of NPDE with soluble starch, followed by ethanol precipitation and gel permeation chromatography (GPC). The yield of the G8-rich mixture was significantly improved by the addition of isoamylase. In summary, a 4-step process for the production of a G8-rich mixture was developed involving the enzymatic hydrolysis of starch by NPDE.