Identification by epr spectroscopy of carvacrol and thymol as the major sources of free radicals in the oxidation of plant essential oils

The formation of stable free radicals upon reaction of the essential oils of 10 plant species with ultraviolet radiation and the superoxide radical anion, O2−, has been investigated by electron paramagnetic resonance (EPR) spectroscopy. Only the oils from oregano, summer savory and thyme produced EPR spectra and the results can be accounted for in terms of free radicals produced by the closely related phenolics, carvacrol and thymol. These observations are interpreted in terms of the known antioxidant properties of these molecules.