Physicochemical Properties of Low and High Amylose Cross-Linked Rice Starches

Background and Objectives: As chemical methods are commonly used to modify the starch properties, in this study, the influence of chemical modification using POCl3 on the rice starch function was evaluated. Materials and Methods: Rice starch was isolated by alkaline extraction of the proteins and cross-linked rice starches were prepared from reactions between native rice starch (low and high amylose) and varied concentrations of POCl3 (0.1, 0.2 and 0.3 % w/w). The physicochemical, rheological and morphological properties of rice starches (water absorption and solubility, pasting viscosity parameters, light transmittance, freeze-thaw stability, and scanning electron microscopy) were evaluated. Results: According to SEM micrographs, cross-linking did not affect granule size or shape. The cross-linked starches showed lower solubility than that of the native starches and solubility decreased with increasing the concentration of cross-linking agent. Cross-linking decreased the capability of starches to absorb water at high concentration of cross-linking agent (0.3%). The paste clarity and pasting viscosity parameters of cross-linked samples were lower than their native starches and decreased with POCl3 concentration. The freeze-thaw stability of rice starches improved by cross-linking and increased with an increase in cross-linking agent concentration. Regarding amylose content, low amylose rice starches showed lower water solubility, water absorption and freeze-thaw stability and higher pasting viscosity parameters than those of high amylose ones. Conclusions: The results of this study suggest that high amylose cross-linked rice starch can be used in food systems in which higher stability, or controlled increase of viscosity is desired during their processing.