Effect of Extrusion Screw Speed on the Multiscale Structure of Starch in Restructured Rice

Abstract

The microstructure, the submicroscopic structure and fractal structure of starch paste system, and the long- and short-range ordered structures of amylose and amylopectin in restructured rice prepared by extrusion of broken rice at varying screw speeds were compared by scanning electron microscopy (SEM), small angle X-ray scattering (SAXS), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy. It was found that the helical conformation of rice starch changed after extrusion treatment, the number of holes on its surface increased, and the crystalline structure obviously altered. With the decrease in extrusion screw speed, the mass fractal dimension, relative crystallinity (RC) and degree of double helix of rice starch gradually decreased, and the system showed a loose and disordered state. Moreover, After separating amylose and amylopectin, it was found that the extrusion treatment led to the formation of small amounts of amylose-lipid complex as well as a maximum particle size of amylopectin of over 1 000 μm, and increased the surface roughness of the particles. This study has important implications for the restructuring and utilization of rice by-products.

Keywords

• extrusion treatment; long-range ordered; fine structure; amylose; amylopectin