Abstract DNA comet assay was applied to detect radia- tion treatment of some fresh and frozen samples of meats and freshseafood. Electrophoresis of irradiated cells caused stretching of the fragmented DNA in the gel in the form of a comet. The unirradiated and irradiated samples of meat (fresh and frozen lamb, beef and turkey) were clearly distinguishable on the basis of stained pat- terns of DNA in the form of round (or conical) intact cells or longer comets, respectively. One sample of sea- food (salmon) could also be identified successfully as irradiated or unirradiated using comet assay. This dis- crimination was not possible with other samples of sea- food, either due to the same kinds of migration patterns of DNA in both unirradiated and irradiated samples, or that the cells or nuclei could not be extracted, such as in squid and saithe samples. Validity of the comet test as a function of storage time was also studied, and in most of the cases the test was successful up to at least 6 days after irradiation. For most of the fresh or frozen meat samples investigated and for salmon, using suitable con- ditions, DNA comet assay can be applied as a rapid and inexpensive screening method for detection of irradiation treatment. Keywords Irradiation detection · DNA comet assay · Meat · Fish · Seafood Introduction The radiation treatment of foods like meat, seafood, and poultry is gaining in importance throughout the world [1, 2, 3]. This process decreases or eliminates food-born pathogens such as Salmonella, Campylobacter, Escheri chia coli O157:H7, Clostridium etc., and protozoan para sites such as Toxoplasma gondii [4, 5, 6, 7, 8], thereby reducing food-borne illnesses and their associated med cal and productivity costs [9, 10]. Proper control of radiation treatment of food is important in order to facilitate international trade in irr diated food, but also to enhance consumer confiden and to ensure consumers' free choice. Analytical de tion of radiation treatment of food is an important mean to implement such control, once the food items have lef the irradiation facility. In 1996, the European Committe of Standardization adopted several methods for the tection of irradiated foods such as electron spin re nance spectroscopy (EN 1786, EN 1787), thermolum nescence measurements (EN 1788) and gas chroma graphic analysis of lipid-derived radiolytic products (EN 1784, EN 1785) [11]. These five detection methods have also been endorsed as general Codex Methods [12 However, thesevalidated methods require expensive instrumentation and/or are time consuming. Therefo efforts have been made to develop rapid and inexpensiv detection tests. Since ionizing radiation causes DNA damage, micro- gel electrophoresis of single cells or nuclei, also ca “DNA comet assay” [13, 14], could be used to det irradiated food. Irradiated cells will appear as com with regular tails of definite shapes and sizes dependin upon the applied radiation dose. Unirradiated cells stai as nuclei without tails or with very short dispersed tails The application of this technique to detect irradiation treatment of some foods has been described [15, 16, 17 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32 33, 34, 35, 36, 37, 38]. In the meantime the method has been standardized on a European level as EN 1378 [39]. In the Standard it is recommended that each type of foodstuff shall be tested before unknown sample are analysed. Since at present, knowledge of DNA come patterns for various foodstuffs is still limited, it is desir able to gain more experience with the variability of com A.A. Khan · H.M. Khan National Center of Excellence in Physical Chemistry, University of Peshawar, Peshawar-25120, Pakistan H. Delincée ( ✉ ) Institute of Nutritional Physiology, Federal Research Centre for Nutrition, Haid-und-Neu-Strasse 9, 76131 Karlsruhe, Germany e-mail: henry.delincee@bfe.uni-karlsruhe.de Tel.: +49-721-6625-405, Fax: +49-721-6625-404 Eur Food Res Technol (2003) 216:88–92 DOI 10.1007/s00217-002-0595-x O R I G I N A L PA P E R Ashfaq A. Khan · Hasan M. Khan · Henry Delincée “DNA comet assay” – a validity assessment for the identificatio of radiation treatment of meats and seafood Received: 31 May 2002 / Revised: 22 July 2002 / Published online: 17 September 2002 © Springer-Verlag 2002