Preparation of branched starch by α-amylase and thermophilic glycogen branching enzyme modification

Maltogenic α-amylase (MA, EC 3.2.1.133), which shows high thermal stability, can cleave long starch chains linked by α-1,4 glycosidic bonds. And glycogen branching enzyme (GBE, EC 2.4.1.18) can increase the branching degree of starch. At high temperatures, Elevated temperatures enhanced starch solubilization, improving the accessibility of both MA and GBE to glucan chains. Therefore, ungelatinized normal corn starch (NCS) emulsion (20 % w /w, dry basis) was first pretreated with α-amylase (MA) at 70 °C for 2 h, followed by enzymatic modification using the thermostable Pyrococcus horikoshii OT3 GBE mutants (H415W and T508K) for an additional 10 h modification. The physicochemical properties of the modified starch were determined by scanning electron microscopy and X-ray diffraction, etc. The results demonstrated that the dual enzyme treatment decreased rapid digestibility by 23.07 % and retrograde enthalpy by 5.51 J/g compared to NCS. This study provides guidance for the industrial enzymatic preparation of highly branched starch.