Structure and enzymatic resistivity of debranched high temperature-pressure treated high-amylose corn starch

Abstract

High-amylose corn starch (HACS) was treated with high temperature-pressure (HTP) treatment and pullulanase debranching. It was found that 24 h storage was favorable for resistant starch (RS) formation. Structure (granular morphology, fractal structure, lamellar structure, crystalline structure, weight-average molecular weight) and properties (swelling power, solubility, enzymatic resistivity) were evaluated for native starch and the samples with 24 h storage. By modification, the surface became loose and rough fragmented and the birefringence crosses disappeared. All samples displayed a B + V crystalline structure. The scattering objects of native starch at the higher scale level were more compact than those of modified starches, and the latter displayed a mass fractal structure which became more compact as debranching increased. The native starch contained RS2 and RS5, while the modified samples included RS3 and RS5. The higher amount of V-type crystals and the starch chains with smaller molecular weight could lead to form more RS. Interestingly, a surface fractal structure with Ds2 was measured for the modified starches, leading to more RS, since some active sites of starch molecules were masked by the ordered-aggregations of molecular chains in the scattering objects. Furthermore, the more compact scattering objects with Dm1 contributed to forming more RS. © 2012 Elsevier Ltd.