Thermoluminescence

Thermoluminescence (TL) is a reliable method to identify irradiated foods containing silicate minerals and a sufficient amount of silicate minerals need to be isolated from the foodstuffs.

Figure 1. Thermoregulator for thermoluminescence analysis in food irradiation testing

The principle of TL is based on the physical changes of minerals from dust and sand which are concomitant to many food products. The post-irradiation energy is stored in silicate minerals by trapping charge carriers at defect or impurity parts. Then the trapped charge can be released by the heat stimulation in the form of light. The subsequent luminous relaxation emits the detectable light for the readout stage and the amount of the light is measured by a thermoluminescence reader during controlled heating. The silicate minerals are isolated from food samples mainly through a density separation step. The isolated silicate minerals need to be free of organic constituents.

The TL technique used for the detection of irradiated foods with minerals has been improved by normalization such as re-irradiation of the minerals. The second irradiation applied on the isolated minerals grains allows the technique to measure different compositions in minerals. Two glows of the separated minerals extracts are usually recorded due to the possible variable integrated TL intensities after irradiation that are exhibited from different types or amounts of minerals. The ratio of the two TL glows is calculated and used to represent the radiation treatment of the food sample. The irradiated foods theoretically generate higher TL glow ratios than that of the non-irradiated foods. The parameters of the glow shape provide additional information to identify food irradiation. The analysis of irradiated foods by TL technique is only dependent on the silicate minerals that can be separated from foodstuffs. Therefore, the testing results using this method is not affected by the type of the food sample.

TL technique has been extended to detect other foods containing concomitant minerals including some fruits, vegetables, and shellfish. Other studies also show that this technique is capable to be applied in a wide variety of foodstuffs. TL technique has been adopted by the European Committee for Standardization as a standard method for the identification of irradiated foods such as spices, herbs and their mixtures. Currently TL is a routinely used method in laboratories for the identification of food irradiation. TL is an approach to differentiate between irradiated and non-irradiated pure minerals and mineral mixtures. The stability and detection limits of TL method are related to the types and amounts of minerals that can be recovered from food samples. The selected intervals of glow temperature also affect the detection performance.

The procedure for the food irradiation testing using TL includes sample preparation and pretreatment, silicate minerals isolation, and detection/ identification. We have expertise in the sample preparation of a variety types of food matrices. The sample preparation has a significant effect on the accuracy of the level measured in the food samples.

We offer an accurate and validated TL platform for the identification and detection that have been widely applied in the food irradiation testing to meet customers' needs. We also maintain high quality assurance for the food irradiation analysis.