| Abstract: | Electron spin resonance (ESR) spectroscopy has been used to examine components from γ-irradiated fish, meat and fruit produce in order to identify areas in which the technique may be of use in detecting an irradiation history. Results show that, in the studied samples of the flesh of meat, fish and fruit, stable radical species are not formed on irradiation, thus indicating that ESR will have no applications for determining a radiation history of such specimens. However, stable ESR signals are obtained in components where radical centres can be stabilised within a crystalline or protein matrix. Thus bone from meat or fish yields a characteristic ESR signal at levels likely to be used commercially, although signal intensity appears to be related to the degree of crystallinity of the hydroxyapatite. This would be a complicating factor in determining quantitative radiation exposure measurements. Similarly a radiation-induced ESR signal can be observed in scampi shell. The signal appears to be associated with the chitin component and thus cooking, either before or after irradiation, can result in a major decrease in signal intensity as a result of chitin degradation. Several radical species were observed in irradiated animal fat, one of which had spectral parameters similar to those obtained from organic peroxy radicals. These species were of limited stability restricting any practical ESR determination to within a few days of treatment. Stable free radical centres are produced in the seeds of fruit, but their spectra generally resemble those of the naturally occurring melanin-type pigments. Since the concentrations of the latter may vary considerably as a result of natural factors such as exposure to sunlight, ESR has limited applications in the diagnosis of an irradiation history in such materials. With irradiated grapes a weak spectral component that was not present in unirradiated specimens was observed in the seeds. It is possible, therefore, that the ESR method could be useful for detecting irradiated grapes. |
