Modification of retrogradation property of rice starch by improved extrusion cooking technology.

Modifications of molecular structure, and of short- and long-term retrogradation properties, in rice starch by an "improved extrusion cooking technology" (IECT) were studied. IECT decreased starch molecular size in the order high speed / high temperature > low speed / high temperature > high speed / low temperature > low speed / low temperature. Degradation was mostly of amylopectin and insignificant for amylose. The reduction of water mobility and the increase of storage modulus were both less than normal in extrusion: IECT inhibited short-term retrogradation. Crystallinity and retrogradation enthalpy were increased after long storage: IECT accelerated the long-term retrogradation of starch. The greater the starch degradation by IECT, the more short-term retrogradation was inhibited and long-term retrogradation accelerated. These results show that, under appropriate conditions, IECT is a type of extrusion which can be used to change retrogradation properties of rice starch that have not been previously available.