Electron Spin Resonance

Electron spin resonance (ESR) is a sensitive and versatile technique to identify and detect the irradiated foods. ESR can be used for the detection of food irradiation in a variety types of foodstuffs.

Figure 1. Electron spin resonance instrument for food irradiation testing

ESR detects molecules that contain unpaired electrons such as free organic radicals induced by ionizing radiation. Those radicals are trapped in the dry parts of irradiated foods. The stability of this technique depends on the moisture content of the tested food sample, and the crystallinity of the solid region of the food. The signals of ESR and other parameters that are induced by irradiation and used to identify irradiated foods should be specific to irradiation process, and the signals cannot be induced by other food processing steps. The signals and parameters should be absent in the non-irradiated foods. The ESR signals and parameters need to be present after the food irradiation with normal doses and should be stable during the testing process. The ESR signal is ideally proportional to the dose that applied on the tested foods.

ESR has been applied by the European Committee for Standardization as a standard method for food irradiation testing. There have been standardized detection methods based on ESR for foods containing cellulose, bone, and crystalline sugar. For plant-based foods, irradiation can form free radicals in crystalline sugars and cellulose which are considered as indicators for irradiation detection. The radicals that are induced by the irradiation typically occur in the dry and solid portions of foods. Free radicals are trapped in the rigid structure of food samples so the interaction between the free radicals and other food compounds in the wet parts of the foods is inhibited. ESR method is more applicable for the detection in foods with low moisture content such as foods containing shells, bones, and seeds. For foods with high moisture content, additional sample preparation steps are required.

ESR has an advantage of simple sample preparation. The dry parts of the food are relatively easy to separate from the soft tissues that can affect the signal. When analyzing seeds from fresh fruits, additional materials and instruments are usually needed to separate the seeds from the pulp. The radicals in the wet fruit parts are not stable and hard parts such as seeds are used for the analysis. For the samples with high moisture content, a vacuum oven or freeze dryer is generally used to dry the samples in order to minimize the effect of the water on the tuning of the spectrometer resonator. The temperature that is used for drying samples needs to be selected below a certain temperature to reduce any possible signals that are induced by the heat.

The procedure for the food irradiation testing includes sample preparation and pretreatment, 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 ESR 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.