In Vitro Digestibility and Predicted Glycemic Index of Chemically Modified Rice Starch by One-Step Reactive Extrusion

The in vitro digestibility of chemically modified rice starch by one-step reactive extrusion (REX) via esterification, acetylation, hydroxypropylation, and cross-linking or dual-modification (hydroxypropylation-cross-linking and acetylation-cross-linking) is investigated. After REX processing, pasting viscosity is decreased, while the viscosity of esterification samples is lower than that of cross-linking samples. Molecular structure analysis suggests that the degradation of starch molecules is retarded by esterification whereas enhanced by cross-linking. Dual modification (hydroxypropylation and phosphorylation, hydroxypropylation-cross-linking (HP-CL) sample) involving hydroxypropylation and phosphorylation (HP-CL sample) is more conducive to preventing enzyme hydrolysis than the other modifications. HP-CL sample achieves the lowest predicted glycemic index (pGI) value (88.1) and the highest RS content (15.3%). Thus, the one-step REX is a useful method for reducing rice starch digestibility or pGI value.