Photostimulated Luminescence

Photostimulated luminescence (PSL) is a common method that can be applied in the detection of irradiated foods containing mineral debris such as bioinorganic materials and silicates. This method is applicable to detect a wide range of foods including shellfish, fruits, vegetables, cereals, and spices.

Figure 1. Photostimulated luminescence system for food irradiation testing

The energy in charge carriers is stored at the minerals within food samples and trapped at the structural sites. When the ionizing radiation is applied, the charge carriers are released from the optical stimulation of minerals which are shown in the excitation spectroscopy. The principle of this technique is based on the fact that the sample induced by irradiation emits light in the range of 300 - 400 nm. The amount of light emitted from the sample can indicate that the food has been applied with irradiation. This technique is mostly used as a screening approach to identify food irradiation and helpful to the controlling of the application of food irradiation. Most irradiated food samples generate a strong signal above the upper threshold level. When the signal is below the threshold, the foods are not irradiated.

The whole samples and a mixture of inorganic and organic materials can be used for the PSL measurement. It only needs minimal sample preparation steps. Irradiated food samples should be kept in darkness when not in use to reduce the effects of signal bleaching. PSL is a non-destructive method and the measurement can be repeated with the same sample. However, the PSL signal may decrease with the repeated times of the same sample is measured. It is a rapid method to screen a variety of different types of food to determine whether the foods have been irradiated with low cost. This method generally has an initial screening measurement with PSL to establish the sample status and an optional measurement with a calibration process to determine the PSL sensitivity of the tested sample.

PSL technique has been adopted by the European Committee for Standardization and the Codex Alimentarius Commission as a standard method for the detection of irradiated foods. The sensitivity of PSL technique is dependent on the amount and types of minerals in the food sample. Some irradiated materials with low sensitivity such as peppers may result in the signals below the lower threshold. These materials need to be investigated with additional calibration process or other analysis. The upper threshold materials can separate adequately the irradiated products. Therefore, calibrated PSL measurement is recommended for foods like shellfish and spices with low mineral contents in order to eliminate the possible negative results. PSL is a leading physical method for the detection of irradiated herbs, nuts, and dried fruits.

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 PSL 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 analysis.