Structural changes of chemically modified rice starch by one-step reactive extrusion

Structural changes of chemically modified rice starch (CMRS) by one-step reactive extrusion (REX) via esterification, acetylation, hydroxypropylation, and cross-linking or dual-modification (hydroxypropylation-cross-linking and acetylation-cross-linking) were investigated. REX treatments exhibited a significant effect on the structure of rice starch granules, resulting in the destruction of the starch crystalline structure and formation of new crystalline complexes. The original A-type crystalline structure was transformed to V_H-type after REX treatments, which were further confirmed by DSC experiments since a new endotherm at 100-122 °C was detected. Due to the susceptibility differences in shear-induced breakdown of amylopectin and amylose, the molecular degradation was heterogeneous and retarded by esterification but enhanced by cross-linking. Morphology analysis showed that the original starch granular structure was lost and replaced with a rougher and more irregular structure. In consequence, REX process exerted significant influences on rice starch granules which enhanced its resistance to enzyme hydrolysis.