Applied Chemistry Division Commission on Food Chemistry* Analytical Methods for Post-irradiation Dosimetry of Foods

The trade and acceptance of foods treated with ionizing radiation, gamma radiation or x-rays, require appropriate means of control. A foolproof test to detect whether or not food has been irradiated, and eventually to quantify the amount of radiation, is vital to verify the labelling and enforce legislation. Such an assay also provides the information for avoiding repeated irradiations which are likely to degrade the food in terms of organoleptic acceptability and nutritional quality. METHODS OF ANALYSIS An ideal analytical method should measure a specific radiation effect which is proportional to the dose, and is unaffected by processing and storage conditions or by the length of time between irradiation treatment and analysis. Futhermore, the test should distinguish irradiated food even in the absence of a nonirradiated, control sample. If properly carried out, the irradiation process is a remarkably gentle treatment and the changes induced are generally very small and nonspecific. As a matter of fact, in spite of the strenuous efforts driven by toxicological concerns, no unique radiolytic products have ever been isolated from foods irradiated within the limits of recommended doses. In addition, the physical differences and natural variability in food composition, make it unlikely that a universal postirradiation dosimetry method for all foods will be found. The legislative and commercial interest, combined with the scientific challenge, has prompted extensive efforts to develop methods that permit the identification of irradiated foods (Raffi and Belliardo 1991, IAEA A multitude of approaches have been evaluated. They can be classified in several groups based on detection of the following radiation-induced changes: 1. Radiolysis of lipids 2. Modification of amino acids 3. Modification of DNA 4. Modification of carbohydrates 5. Formation of free radicals 6 . Release of hydrogen gas 7. Alterations of microbiological flora 8. Measurements of biological differences 9. Other physical measurements 1991). 1. Radiolysis of lipids The radiolytic splitting of fat molecules does not occur randomly; two hydrocarbons are produced preferentially from each fatty acid. One, resulting from preferential cleavage at the carbon-carbon bond alpha to the carbonyl group, has a carbon atom less than the parent fatty acid. The other, has two carbons less than the parent fatty acid and an extra double bond, and results from cleavage at the carbon-carbon bond beta to the carbonyl group (Fig. 1). 0 ii , I YH20-C t C H z + R CH I CH2 -