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This research follows on from previous work to evaluate the effectiveness of the current thermoluminesence (TL) and photo-stimulated luminescence (PSL) methods for the detection of irradiated foods. The project aims to develop new and improved luminescence approaches to detect blended mixtures of herbs, spices and seasonings containing irradiated products. Blending of such products takes place for many commercial reasons and many products are presented for sale as blends or mixtures of dried ingredients (e.g. curry powder, mixed herbs, seasoning mixes). In these instances a detection method is required that can be used for identifying an irradiated component rather than a product in pure form. <p>Physical and chemical methods have been established for a wide range of pure irradiated food types, however there has been little research on the detection of minor irradiated ingredients in blended products. Current luminescence techniques rely on TL and PSL criteria established for pure products for absolute classification. Blended products can produce results which fail to satisfy international validation criteria.
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This project aims to improve both TL and PSL approaches to the detection of blends by using new statistical approaches to TL and PSL analysis. It will also investigate single grain imaging methods which offer the promise of providing unambiguous distinction between individual irradiated and un-irradiated components from compound food samples.
A large data base of several thousand TL analyses is available at SUERC. Three approaches to the TL interpretation will be explored: 'kinetic deconvolution', 'multivariate analysis' and the application of 'neural networks'. The aim of this part of the work will be to optimise methods to detect minor proportions of irradiated material in various samples. <p>The second part of the work will be to address single grain imaging approaches to both PSL and TL, with the aim of developing advanced instrumental techniques for providing unambiguous results from mixed populations of irradiated and un-irradiated grains. Work will be undertaken to adapt a nitrogen-dye laser luminescence spectrometer to permit single grain stimulation at other wavelengths, and to investigate the feasibility of conducting single grain TL measurements based on laser-step heating systems developed at SUERC.
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PSL and TL are procedures for detecting irradiated food which make use of mineral grains that are present in small amounts in many foods . These mineral grains act as dosimeters which, when irradiated, store energy as charge centres trapped within their crystal lattice. When these minerals are exposed to some energy (heat for TL and infrared light for PSL), the stored energy is liberated as the charge centres are released from their energy traps, giving rise to the emission of light that can be measured using sensitive light-detecting instruments.
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Find more about this project and other FSA food safety-related projects at the <a href="http://www.food.gov.uk/science/research/" target="_blank">Food Standards Agency Research webpage</a>.