Effect of γ-irradiation on some physicochemical and thermal properties of cowpea (Vigna unguiculata L. Walp) starch

Previously, we reported that starch-related functional properties of cowpea flours and pastes were modified by 2, 10 and 50 kGy γ-irradiation doses. To elucidate some of the effects of γ-irradiation specifically on cowpea starch as well as the actual contribution of starch to the observed functional modifications at the flour and paste level, starch was isolated from irradiated cowpea flours and pastes and studied using differential scanning calorimetry (DSC), scanning electron microscopy (SEM), Fourier Transform Infra-Red (FTIR) spectroscopy, Rapid Visco-Analyser (RVA) pasting properties, and some functional properties. Pasting (peak, trough, breakdown, final, and setback viscosities) and swelling properties were significantly decreased in a dose-dependent manner. DSC of cowpea starch showed increases in peak gelatinisation temperature with increasing irradiation dose. SEM (2500×) microphotographs showed that up to 50 kGy irradiation did not present any visible physical effect on the cowpea starch granule. FTIR indicated that starch granule surface order (crystallinity) was not affected by the irradiation doses employed.