Preparation of Branched Starch by Α-Amylase and Thermophilic Glycogen Branching Enzyme Modification

Abstract

Maltogenic α-amylase (MA, EC 3.2.1.133), which shows high thermal stability, can cleave long amylose, provide glucan chains for glycogen branching enzyme (GBE, EC 2.4.1.18) and further improve its branching effect. The direct starch enzyme-modification at high temperature can make up for the deficiency of traditional starch modification method. Therefore, we synergized ungelatinised normal corn starch (NCS) emulsions at 70℃ using MA and the heat-stable mutant Pyrococcus horikoshii (Ph) OT3 GBE (H415W and T508K), in order to achieve dual enzyme branching modification of starch. The results demonstrated that pre-treatment with MA increased the proportion of short chains (degree of polymerisation, DP < 13) by 8.44% compared to unmodified NCS. Subsequent branching by Ph GBEs further enhanced the degree of branching, reduced content of amylose, and improved starch properties. Specifically, the dual enzyme treatment decreased rapid digestibility by 23.07% and retrograde enthalpy (ΔH) by 5.51 J/g.

Keywords: Keywords: Glycogen branching enzyme, Maltogenic α-amylase, Normal corn starch, Starch swelling, Branched starch