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

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. 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. 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. 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.