Optimisation of photostimulated luminescence detection for irradiated dietary supplements

Last updated:
24 March 2008
This project reviewed the performance of Photostimulated Luminescence (PSL) methods applied to food supplements and explored ways of enhancing the applicability and effectiveness of rapid detection methods for identification of irradiated products.
Study duration: March 2008 to March 2010
Project code: A05010
Contractor: Scottish Universities Environmental Research Centre (SUERC)


The work reported in this project represents an initial study of food supplements with a view to enhancing the performance of routine methods for detecting irradiated ingredients. Based on the published results of existing applications, which have been extremely successful in finding irradiated materials in the supply chain, PSL and TL methods are already effective means for detecting many of these products. The work conducted in this short project shows some of the ways in which the PSL method could be further improved to reduce non-detection probabilities for use in screening work.

Research Approach

The contract took some time in specification and final placement.

Once underway the initial review of existing data sets progressed rapidly and was informative. It took longer than originally anticipated to select sample matrices for study, and a revised schedule for the final stages of the work was agreed.


The end result of the project has been extremely interesting. With all of these types of investigation it is important to conduct experimental work at a high level of replication in order to quantify and manage the inevitable levels of variability in naturally derived products. The data sets obtained here, while from a relatively small number of sample types, represent a significant body of work in this field, and form a sound foundation for future work.

Additional Info

This has been a useful exploratory study, which has defined the context of divergent PSL-TL outcomes in the food supplement area, and provided solutions, based on preconcentration prior to PSL screening to one of the main problem areas: dealing with low sensitivity in mineral deficient samples.

Overall the concentration work produced results that would promote PSL results from irradiated products from “negative” band to” intermediate” band classification for the least sensitive samples, and from “intermediate” to “positive” bands for slightly more sensitive cases. Further work can now be considered to explore protocols for applying these methods in practice. As indicated in the project summary this might involve a structured combination of screening and calibrated PSL, followed by selection of samples for TL analysis or further concentration and re-classification. This should be considered for development in conjunction with laboratories working in the supply side, and in the regulatory sector, and if successful should be considered for validation through inter-laboratory trials.

Of the approaches explored to enhance discrimination between residual geological signals from samples with higher mineral loads, it appears that depletion rate analysis is also potentially useful. It is suggested that this approach now be extended to matrices with high mineral contents, and then considered for inter-laboratory implementation./

Further investigations of a broader range of food supplement ingredients should also be considered. Of these the use of solvents such as ethanol to remove the organic bulk from appropriate extracts has further potential. Additionally studies of the combined used of luminescence method together with some of the other EN standard methods (for example in conjunction with ESR for some of the excipients, and with the cyclobutanone method for certain extracts) appears to have potential for overcoming some of the matrix specific limitations of individual methods.

Finally it is noted that where undeclared irradiated samples have been identified in the past it has sometimes been assumed that infringement of the food irradiation regulations is the only food safety concern. This view is based on the understanding that the irradiation itself would not normally be expected to introduce a new food safety hazard. However there is a significant knowledge gap in the area of the broader food safety context behind the illegal use of food irradiation. Work to establish whether there are correlations between the underlying reasons for irradiation and other food hygiene or contamination issues does not appear to have been conducted. Studies to explore these additional characteristics of irradiated foods would add significantly to the literature, and assist in formulating appropriate policy responses.