Effect of Extrusion on the Physicochemical Properties of Starch in Brown Rice
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Abstract:
The effects of extrusion on the gelatinization, thermal properties, crystalline structure, and the branch length of amylopectin chain of brown rice starch were studied. The results showed that the peak viscosity, setback, and enthalpy of starch all declined from 1811 cP, 1677 cP, and 9.41 J/g to 107 cP, 53 cP, and 0.97 J/g, respectively after extrusion, leading to gelatinization. Extrusion also changed the X-ray diffraction peaks and locations, and transformed the crystalline structure from A type to V type. Additionally, the relative crystallinity of brown rice starch decreased from 31.33% to 20.95% upon extrusion. The ratio of 1047 cm-1/1022 cm-1 in the Fourier transform infrared absorption spectra was also reduced from 0.811 to 0.732, which indicated that the proportion of crystalline regions in starch was reduced after extrusion. In addition, the absorption intensity of starch-iodine compounds increased after extrusion, which indicated that the proportion of amylose had also increased. The results of high-performance anion-exchange chromatography pulsed amperometric detection showed that the proportion of A chains (DP6-12) increased, while the proportion of B1 chains (DP13-24) and B2 chains (DP25-36) both decreased after extrusion, which indicated that amylopectin had been degraded. Moreover, the results of scanning electron microscopy showed that the starch granules of the extrudate were bigger; the starch surface was also rougher, and had more wrinkles and cracks after extrusion.
