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Pasteurized egg products (whole egg, egg yolk and egg white) were tested for irradiation treatment in the German food control laboratories in Oldenburg/Niedersachsen and Kassel/Hessen as well as in the food irradiation laboratory of the German federal health office. Gas chromatographic/mass spectrometric measurements on the fat components of egg-products showed clearly whether the product had been irradiated or not. While in unirradiated samples no traces of special hydrocarbons (according to the fatty acid composition of egg) and no traces of the irradiation-specific compound 2-Dodecyl-cyclobutanone were found, irradiated control samples as well as products of two Belgian suppliers contained these substances. Additionally, regarding the rather high time consumption of gas chromatography, electron spin resonance (ESR)-measurements were carried out on the packaging material of egg products. Irradiated packaging material (cellulose) could be easily detected by the appearance of a signal pair in the ESR spectrum (cellulose radical). ESR measurements are very fast and easy to perform so that this method can be used for screening. Microbiological investigations showed remarkably reduced total numbers of microorganisms for some irradiated samples, but the microbiological status is influenced by other factors like storage-time and -temperature, so that microbiological tests can not be used successfully for screening on irradiation treatment.

Electron spin resonance spectroscopy can be used for the detection of irradiation of various groups of foodstuffs. The results of ESR-measurements on irradiated meat and fish and fresh fruit, as well as dried fruit, spices and nuts as performed by the food irradiation laboratory of the German Federal Health Office are summarized in this report. For the detection of irradiated meat and fish, we examined the bones. Using the results from 10 different animal bones, we were able to develop an official method according to the German law section 35 LMBG. A similar routine method for fish will be established in 1992 (at the moment, an intercomparison with German food control laboratories is in progress). Irradiated dried fruit can be identified easily, because unirradiated samples give no ESR-spectra, while irradiated fruit show a partially resolved spectrum, which is caused by radiation induced sugar radicals. Interestingly, the structure of the resulting spectra is not identical for all irradiated species of fruit. We found three different types of ESR-spectra for irradiated dried fruit. Irradiated nutshells show an ESR-spectrum which reveals two additional lines (from cellulose-radicals) beside the main signal, while unirradiated samples show only the main signal. An official method for identifying irradiated nuts will be proposed in 1992. Irradiation specific ESR-signals of the cellulose radical were not only found for nutshells but also for fresh fruit and some spices, while most of the irradiated spices and herbs could not be identified by ESR-measurements.