Irradiated herbs and spices detection: light-induced fading of the photo-stimulated luminescence response.

Reliability of the photo-stimulated luminescence (PSL) technique, both as screening and identification methods, has been tested with several kinds of irradiated herbs and spices over a long period of storage. To check the influence of storage modality on the PSL response, the samples were divided into groups kept in environments with different light exposure. The results clearly indicate a marked light-induced bleaching of the PSL signal, which may lead to a false negative classification, in a significant percentage, for spices stored in typical market conditions. To limit the occurrence of wrong classifications, the suggestion reported in the European Committee of Normalization Standard 13751 to draw the necessary amount of product from a light-protected position becomes mandatory. Thermoluminescence measurements, performed for comparison purposes, gave correct results for all the samples tested.