Identification of radiation treatment of wheat ( Triticum aestivum. L) and rice ( Oryza sativa. L) samples using thermoluminescence of contaminating minerals

Abstract

Food irradiation is gaining popularity worldwide and this technology is important to improve quality and reduce the post harvest losses of food. Because of the rapid commercialization of irradiated foods throughout the world, compliance of different regulations relating to use of technology in different countries and demand of consumers for clear labelling of irradiated foods, there is need for the development of analytical methods to detect radiation treatment of food. Among several methods studied so far, thermoluminescence (TL) is an important method that can be used to find out the irradiation history of food that contain even a very minute amount of dust particles. In this study, the irradiated and unirradiated wheat and rice samples were analyzed using the TL method. The samples were purchased from the local market of Peshawar and irradiated to radiation doses of 0.5 and 1.0 kGy using Co-60 gamma irradiator at the Nuclear Institute for Food and Agriculture (NIFA), Peshawar. The mineral contaminants were isolated by jet water, ultrasonic treatment, and density gradient. TL glow curves of the isolated minerals from irradiated and unirradiated samples were recorded between the temperature ranges of 50—500°C using a TL reader. Generally, the glow curves for irradiated samples showed much higher TL intensities (TL 1) than the unirradiated samples. The results were normalized by re-irradiation of mineral samples to gamma-ray dose of 1.0 kGy followed by determination of the second glow curves (TL 2). The ratio of the area of first glow curve to that of second glow curve (TL 1/TL 2) was calculated for selected temperature intervals and compared with the recommended values for unirradiated and irradiated samples. Finally, the shapes of the glow curves for irradiated and unirradiated samples were also analyzed. On the basis of these results (comparison of TL-intensities, TL 1/TL 2 ratios and shapes of the glow curves), all the irradiated and unirradiated samples of wheat and rice were unequivocally identified.