Photostimulated Luminescene (PSL)

What is food irradiation?
Food irradiation is the treatment of food items using controlled dose of ionizing radiation for a specific time to achieve a certain objective.


Why is it important to detect irradiated food?
Detection of irradiated food is essential to implement quality control at all levels. An ideal detection method should measure a specific radiation effect, which is proportional to the dose and should not be affected by processing parameters and storage conditions or the length of time between irradiation processing and analysis. Proper control of irradiation processing of food is critical to facilitate international trade of irradiated foods and to enhance consumer confidence, consumer choice, and safety.


What methods or techniques are available to detect irradiated food?
The detection of irradiated foods is mainly based on physical, chemical, microbiological and DNA (deoxyribonucleic acid) methods.


What is Photostimulated Luminescence (PSL) technique?
The photostimulated luminescence (PSL) technique is one that is used to detect irradiation of any food items that contain mineral debris, especially silicates mineral and bioinorganic materials such as calcite, which originate from shells or skeleton. The PSL technique is particularly suited to the investigation of wide range of food items containing mineral deposits, for instance herbs, spices, seasonings, fruits and vegetables, shellfish, meat products, cereals, bulbs and tubers. PSL measurement does not destroy the sample; therefore, measurement can be made repeatedly. It provides rapid, low cost methods for screening a wide range of food types to determine whether these have been irradiated.


How does PSL screening technique work?
The SUERC (Scottish Universities Environmental Research Centre) PPSL (Pulsed Photostimulated Luminescence) Irradiated Food Screening System is a portable laboratory instrument intended for indoor use. The PSL technique involves the detection from the small amount of mineral debris present in most foods. These materials store energy in charged carriers trapped at structural interstitial or impurities site. When exposed to ionizing radiation, optical stimulation of minerals released charges carriers. During optical stimulation, the trapped energy is released, resulting in a luminescense signal which can be measured and detected by PSL detector, as photon counts per second (PCs).



Where is PSL screening technique applied?
In Malaysia, research and services for screening of irradiated food have been developed at the Photostimulated Luminescence Laboratory, Malaysian Nuclear Agency. In PSL measurements technique, whole samples or a mixture of organic and inorganic materials can be used. The system is typically able to recognize more than 95% of irradiated herbs and spices. The findings of this study will be useful to facilitate control of food irradiation application in Malaysia.