Retrogradation behaviour of high-amylose rice starch prepared by improved extrusion cooking technology.

Native rice starch (NRS, amylose/28.9%) was gelatinized by improved extrusion cooking technology (IECT) and retrograded (RRS) after low temperature storage (4 °C). The retrogradation behaviour of RRS was changed to low retrogradation percentage and low retrogradation rate. The retrogradation resulted in a high compact morphology. The melt enthalpy change and percentage of retrogradation of RRS was 3.68 J/g and 37.7%, respectively, compared to those of NRS (9.75 J/g, 100%). The retrogradation percentage for RRS was low during storage as shown as a low retrogradation rate (0.21 d(-1)) and a high Avrami exponent (0.89). The pattern of rice starch changed from A-type to amorphous and B-type. Both the relative crystallinity of RRS (12.7%) by the X-ray diffractograms and the ratio of the band height (0.63) in the FTIR spectra were low. The analysis of retrogradation structure and short-range molecular order further confirmed the retrogradation behaviour of rice starch after IECT treatment.