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 ofNPDE 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 mixturescontaining various starches revealed the accumulation of maltooctaose (G8) with glucose and maltose. Based on the novelenzymatic properties of NPDE, an MO mixture containing more than 60% G8 with yield of 18 g G8 for 100g starch wasprepared 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-stepprocess for the production of a G8-rich mixture was developed involving the enzymatic hydrolysis of starch by NPDE.