Effect of irradiation dose, storage time and temperature on the ESR signal in irradiated chicken bone

Two‐hundred pairs of chicken bones (drumsticks) were irradiated at 2.5, 5.0, 7.5 and 10.0 kGy and stored for 0, 7, 14, 21 and 28 days at −20°C or + 5°C thus giving five replicates per treatment. Five unirradiated pairs of bones were stored at 5°C, one sample being analysed at each storage time. The samples were fragmented, freeze dried and ground prior to determination of the free radical concentration using electron spin resonance (ESR) spectroscopy. ESR signal strength increased significantly as irradiation dose increased, and decreased with storage time. Temperature alone had no significant effect on free radical concentration but, as the storage time increased, the bones stored at 5°C showed a significantly greater reduction in free radical concentration than those stored at −20°C. Correction of the ESR signal to a standard P or Ca concentration did not significantly reduce the variability of the results but did eliminate the interaction between storage temperature and storage time.