Application of Thermo-luminescence (TL) Method for the Identification of Food Mixtures Containing Irradiated Ingredients

Thermo-luminescence (TL) method was employed to identify irradiated garlic or ginger powder mixed at different proportions into the food base. The identification of irradiation was carried out by analyzing the shapes of the glow curves and the TL ratios in the temperature ranges of 150–250 °C. Four independent laboratories participated in the study. Garlic or ginger powder was irradiated at 1 or 10 kGy with gamma ray and mixed into a non-irradiated single food base at ratios 0, 0.5, 1, 5, and 10 % for analysis. Detectable TL glows were observed for the samples containing more than 5 % of irradiated ginger or garlic powder. However, the TL ratios of the samples containing more than 5 % were not always positive. In order to identify irradiation in complicated food matrices, garlic or ginger powder irradiated at 10 kGy was added to curry powder and black bean sauce powder at different ratios, namely, 0, 5, 10, 15, and 20 %. In case of curry powder, identification of irradiated garlic and ginger was possible for samples containing more than 5 and 15 %, respectively. On the other hand, identification was possible for black bean sauce powder containing more than 5 % irradiated garlic and 10 % irradiated ginger. The results showed that the detection sensitivity of the TL method decreased substantially in complicated food matrices. In addition, the observed detection limits were too high as compared to the commercial food products. The study showed that the identification of irradiated food ingredients by the TL method was dependent on the irradiation dose, food type, and proportion of irradiated ingredients mixed with the food. Further study is required on how to reduce the variance of the detection limit of irradiated materials in food mixtures.