Photo-Stimulated Luminescence Approach for Effective Identification of Irradiated Fruit

This work reports the results of a study carried out to verify the applicability of the CEN EN 13751 method, based on the photo-stimulated luminescence (PSL) technique, for the identification of irradiated fruit. A total of 15 types of fresh and dried fruit not irradiated and irradiated (0.5 and 1 kGy) were tested. Preliminary tests were performed on samples of fresh kiwis, lemons, mangoes, oranges, papayas, pineapples and tangerines, dried dates, dried prunes and raisins. Successively, an inter-comparative test was organized, whereby four Italian official control laboratories analyzed eight matrices, namely, kiwi, orange, dried fig, raisin, hazelnut, peanut, pistachio and walnut. The results indicated considerable differences in the radiation PSL sensitivities of the different types of fruit as well as among the PSL responses obtained from different batches of the same fruit. The best results were obtained with some types of dried fruit, namely, pistachios, peanuts, dried figs and raisins. Irradiated fresh fruit generally gave non-positive results, mainly intermediate and even very close to the negative threshold. Tests performed on kiwi, mango and orange samples indicated that the parts of the fruit peel close to the stem, which are more wrinkled, provide better results.