Effect of γ-ray irradiation on starch granule structure and physicochemical properties of rice

Irradiation, an effective method to change starch structure and its functionalities, was carried out before traditional air-drying. Effect of irradiation on the structural and physicochemical properties of rice starch and contrast with that of non-irradiated and traditional air-dried rice was studied in this research. Micrology observation of microstructure of starch, at outer and inner layer rice endosperm, showed that the starch granules would be destroyed by gamma irradiation, and the breakage was increased with increasing dose. Effect of gamma irradiation on microstructures of inner endosperm was greater than that of outer endosperm. Chemistry examination and RVA rice viscosity analysis were carried out on the air-dried rice. Apparent amylose content, gel consistency and gelatinisation temperature were all affected by irradiation pre-treatment. Apparent amylose content was decreased, and gel consistency and gelatinisation temperature were increased with increasing dose. These affects generally related to the changes of starch structure. With the analysis of RVA, six major parameters of starch pasting properties, peak viscosity (PKV), hot pasting viscosity (HPV), cool pasting viscosity (CPV), setback (CPV minus PKV), breakdown (PKV minus HPV), and peak time (PKT), were significant decreased with the increasing dose by different velocity. There were high correlation coefficient between dose and individual major parameters of starch pasting properties (range from 0.961 to 0.998). These changes of pasting properties were also due to the breakage of starch granules caused by gamma irradiation. (c) 2006 Elsevier Ltd. All rights reserved.