EPR spectroscopy:: A tool to characterize gamma-irradiated foods

The gamma-radiation induced changes in ground black pepper (Piper nigrum L.), allspice berries (Pimenta officinalis L.), ginger root (Zingiber officinale Row.), dried clove buds (Caryophyllus aromaticus L.) and dry oregano leaves (Origanum vulgare L.) exposed to doses from 2.5 to 30 kGy using Co-60 source were studied by EPR spectroscopy. Influence of the dose on the character of generated paramagnetic structures, as well as their thermal stability and lifetime were investigated. EPR spectrum of all reference (non-irradiated) samples consists of a broad singlet line with unresolved hyperfine splitting, attributable to Mn(II) ions, upon which an additional narrow EPR signal (g = 2.0022; Delta B-pp similar to 1 mT) is superimposed, assigned to stable semiquinone radicals produced by the oxidation of polyphenolics in plants. The analysis of individual EPR spectra of gamma-radiation treated spice showed the formation of new paramagnetic structures of different origin (mostly cellulose and carbohydrate), which exhibited diverse thermal stability and lifetime. Ethanolic extracts of reference spice samples showed considerable radical scavenging ability using the 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical as an oxidant. The influence of gamma-radiation dose on the ability of spice extracts to terminate DPPH was also investigated. The results indicated that the antioxidant capacity was only slightly affected by the radiation treatment.