Effect of various parameters on detection of irradiated fish and oregano using the ESR and PSL methods

Control of irradiated food on the market is a requirement of EU regulations. In order to improve checks of irradiated food in Greece, electron spin resonance (ESR) and photostimulated luminescence (PSL) were tested to detect electron beam radiation treatment of representative samples, namely fish (herring) and aromatic plant (oregano). The absorbed irradiation doses for both food samples were 1, 4 and 10 kGy. The effect of thermal treatment and storage time of fish samples on the sensitivity of ESR method as well as the effect of light exposure (after irradiation treatment) and storage time of oregano samples on the sensitivity of PSL method was studied. In addition, the suitability of both methods for two food samples was studied. For fish samples, the detection of irradiation treatment was based on ESR or PSL signal of fish bones. The results showed that PSL is a sensitive detection method for irradiated oregano samples allowing verification of irradiation treatment for all absorbed doses but this is not a sensitive detection method for irradiated herring containing bones. In contrast, ESR allowed verification of the irradiation treatment of fish bone samples but this is not a sensitive method for irradiated oregano samples. Daylight exposure of oregano samples (10 klux, 9 h) produced a strong effect on the PSL signal of all irradiated samples decreasing or disappearing the irradiation signal, while the thermal treatment (100 ± 1 °C, 1 h) of fish bones was produced a clear decreasing effect on the ESR signal of irradiated samples mainly for the higher dose of 10 kGy. The storage time strongly affected the PSL signal intensity of oregano samples as well as the ESR signal intensity of herring bone samples but the samples could be correctly identified as irradiated after a storage time of seven months.