Effect of γ-radiation on free radicals formation, structural changes and functional properties of wheat starch

Wheat starch was treated by different gamma-radiation doses (3, 5, 10, 20, 35 and 50 kGy). The effects of gamma-radiation on on structural, thermal, physicochemical, morphological and rheological properties of wheat starch were studied. The presence of free radicals after gamma-radiation treatment, which number decreased with time was confirmed. Structural analysis revealed decreases in the intensities of the O-H and C-H stretches and glycosidic linkages indicating the depolymerization of amylose and probably amylopectin into shorter chain molecules, but showed that gamma-radiation treatment did not affect the crystalline structure. Differential scanning calorimetric (DSC) thermograms showed the absence of significant differences in the gelatinization temperatures, as well as the corresponding transition enthalpies since the DSC parameters are related to the crystalline ordering within the granules. Apparent amylose content decreased linearly with increasing irradiation dose leading to an increase in water solubility index. An increase in the swelling power was observed after irradiation treatment until 20 kGy, followed by a rapid decrease at higher doses. Microscopic observations showed that the effect of gamma-radiation was more visible on starch pastes than on starch granules. Rheological properties of the starch pastes decreased with increasing irradiation dose as a result of glycosidic bond cleavage. (C) 2015 Elsevier B.V. All rights reserved.