Dual-Enzymatic Modification of Waxy Wheat A- and B-Type Starch and Its Effects on Structure and Digestibility

A-type and B-type starch separated from waxy wheat starch were separately mixed with high-amylose corn starch and treated with pullulanase and/or branching enzymes. The granular morphology, crystalline structure, apparent amylose content, solubility, swelling power and other physicochemical properties of the modified starch were determined, and their digestion characteristics were also investigated. The results showed that the predicted glycemic index (pGI) of waxy wheat A- and B-type starch were significantly reduced by the dual-enzymatic modification, and the content of apparent amylose was increased significantly. The solubility increased with temperature, while the swelling power remained basically unchanged. Under a scanning electron microscope (SEM), the microstructure of the enzymatically modified starch granules exhibited holes. The relative crystallinity (RC) and the ratio between the intensities of the peaks at 1047 and 1022 cm^-1 were obtained by X-ray diffraction and Fourier infrared spectroscopy, respectively, revealing that the long-range and the short-range ordered structures of starch were significantly improved by the dual-enzymatic modification. Furthermore, sequential treatment with pullulanase and branching enzymes could significantly improve the digestion characteristics of waxy wheat A-type and B-type starch.