STARCH MODIFICATION BY RECOMBINANT 4-α-GLUCANOTRANSFERASE FROM CASSAVA Manihot esculenta Crantz

Abstract

4-α-Glucanotransferase or disproportionating enzyme (D-enzyme, DPE) (E.C.2.4.1.25) catalyzes the α-1,4 glycosyl transfer between oligosaccharides. Type I D-enzyme (DPEI) can transfer maltosyl unit from one 1,4-α-D-glucan to an acceptor mono- or oligo-saccharide, which reflects its physiological role in plant starch degradation. In this study, the purified recombinant DPEI from Manihot esculenta Crantz cultivar KU50 (MeDPEI) was used to modify cassava starch. Optimum conditions for cassava starch modification was achieved at 30 units/g starch of enzyme at 37 °C for 12 hours and 5% w/v cassava starch. Cycloamyloses were produced with size distribution in the ranges 18-57 glucose units. When side chain distribution were analyzed by HPAEC-PAD on Carbopac PA-1 column, the treated starch showed lower amount of side chains distribution compared to untreated starch but the size distribution were similar. Apparent amylose content of the treated starch, determined by iodine binding, was also lower. Retrogradation of the treated starch determined by Differential Scanning Calorimeter (DSC) showed lower retrogradation of amylopectin. Percentage of syneresis from freeze-thaw process was lower compared to native starch. Modified corn starch at the same modification condition showed the same results as modified cassava starch. Starches modified by MeDPEI showed suitable properties for further studies in industrial applications.