A Comparison of Three Physical Techniques for the Identification of Irradiated Eggs

Within the framework of a project financed by the Italian Ministry of Health, eggs of different brands and types (farming method, color, size), both irradiated (0.5–5 kGy) and non-irradiated, were examined by the laboratories of the Istituto Superiore di Sanità (ISS) and the Istituto Zooprofilattico Sperimentale della Puglia e della Basilicata (IZSPB) using Photo-stimulated Luminescence (PSL) and Thermoluminescence (TL) techniques, which identify irradiated foods through the luminescence emitted from certain types of minerals present in the food matrix (biominerals) or in contaminating dust (silicates). The data obtained with both techniques indicate that the content of luminescent minerals in the shells is rather low, probably due to the cleaning of the eggs during production. The PSL technique applied to 144 irradiated samples results in 75% false negatives and 23% unclassifiable intermediates, with only 3 positive samples originating from eggs with markedly different characteristics (small and white). As for TL technique, the silicates extracted from 6 eggshells were generally sufficient for the analysis but provided rather weak TL signals. The ESR technique applied to eggshells produced excellent results for the identification of X-ray treatment. Furthermore, from the tenth day after irradiation onward, the ESR signal showed no time-dependent attenuation. The relationship between signal intensity and irradiation dose was not linear but exponential up to 1 kGy and logarithmic between 1 and 5 kGy.