Use of ESR spectroscopy for the detection of irradiated whiting (Merlangius merlangus)

Previously frozen whiting were thawed overnight and irradiated the following day with doses of 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 kGy, with four replicates per treatment. Four unirradiated whiting were used as controls. The fins, scales and vertebrae were removed from each fish and freeze dried prior to determination of the free radical concentration using electron spin resonance spectroscopy. The spectra which were derived from each of the components could be used to qualitatively detect irradiation. The signal strength increased significantly with increasing irradiation dose for both the vertebrae and fins although the response was more significant for the vertebrae. Thus the technique has potential for the quantification of the irradiation dose received. A further 20 defrosted whiting were irradiated at 5 kGy and an additional four served as unirradiated controls. After irradiation, the samples were stored in four groups each containing one control and five irradiated samples and analysed after storage periods of 0, 7, 14 and 21 days at 3 +/- 1 degrees C. This simulates normal storage conditions for fresh fish. The signal from irradiated, freeze dried, ground vertebrae did not change significantly as storage time increased.