Four different spices produced in Mexico, namely black pepper, two kinds of chilli and oregano, were studied by electron paramagnetic resonance (EPR) technique for detection purposes. In all the non-irradiated spices we tested, the same single line signal at g ¼ 2.0041 (native signal) was registered. Irradiation induced at least two EPR signals overlapping the native signal: an intense singlet and, with the exclusion of oregano, a weak triplet with hyperfine splitting of 3 mT due to cellulose free radicals. The recombination time of the free radicals produced by irradiation was short compared with the shelf-life of the spices, thus limiting the application of the EPR technique for detection. To extend the time when these products may be identified as irradiated, the method proposed by Yordanov and Gancheva (Appl Radiat Isot 2000;52:195) was applied to the spices, but with no success. Thermoluminescence tests provided correct results for all the spices, even 2 years after irradiation.

For the Atomic Energy Commission Under U.S~ Government Contract W7405 eng 26

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