ESR studies on γ-irradiated foods
Chapter 1 discusses the history, applications and effects (both beneficial and hazardous) of food irradiation and the techniques developed to detect irradiated foods. The basic radiation chemistry of major food components is reviewed. The preparation of 3,5-dimethyl-4-nitrosopyridine-1-oxide (DMNPO) and its dichloro- and dibromo- derivatives is described. Spin trapping of a variety of free radicals by DMNPO showed it to be an efficient trap for carbon-centred radicals but it did not form stable adducts with oxygen-centred radicals at room temperature as had been previously reported. The esr spectra were complicated by couplings arising from the hydrogens and nitrogen of the trap. The dichloro- and dibromo-analogues gave simpler spectra but were much more difficult to isolate. The effects of ionising radiation on spices and the methods used to detect these effects are reviewed. The measurement of free radical concentrations by esr spectroscopy was examined as a dosimetric method of identifying γ-irradiated spices. This proved to be impracticable because of the relatively rapid decay of the radicals and the variation in base-line radical concentrations. The short lived free radicals produced by irradiation were found to arise from the oleoresins. Identification of these radicals was attempted by irradiating the oleoresins and their major components, followed by spin trapping. In some cases, hydrogen abstraction gave the same radicals as those produced by irradiation. Separation of the spin adducts, formed from oleoresin components, by reverse phase HPLC is also described. Irradiation of food is known to cause destruction of vitamins. However, the processes involved are not fully understood. The solid state radiation chemistry of vitamins was investigated by spin trapping and esr spectroscopy. Irradiation of bones produces stable free radicals with characteristic esr spectra. It was shown that measurement of free radical concentrations in irradiated bones by esr spectroscopy could provide a dosimetric technique as the radical concentrations were stable and proportional to the applied dose.