Comparative Study of Three Diverse Glycogen Branching Enzymes for Efficient Generation of Highly Surface Branched Starch Granules with Enhanced Digestive Resistance

Glycogen branching enzymes (GBEs) are widely applied to functionalize starch. However, modification of granular starch is challenging, and among GBEs, so far, only GBEs from Geobacillus thermoglucosidans (GtGBE) and Rhodothermus obamensis (RoGBE) have been used. To further develop their modification, starch granules of waxy, normal, and three types of high-amylose maize starches were treated with GBEs from Petrotoga mobilis (PmGBE), Rhodothermus marinus (RmGBE), and RoGBE as a benchmark. PmBE most effectively and rapidly added short branches, causing a reduced crystallinity and surface order of the starch granules. Furthermore, digestibility analysis indicated that PmGBE boosted the content of resistant starch. Along with its high activity, PmGBE showed a superior binding capacity to starch granules. Based on structural comparison, surface binding sites and the N-terminal domain of unknown function in PmGBE are proposed to influence activity and substrate specificity. Thus, PmGBE showed potential as an effective tool for the future modification of starch granules.