Virgin olive oil: Free radical production studied with spin-trapping electron paramagnetic resonance spectroscopy

Spin trapping using 5,5-dimethyl-1-pyrroline N-oxide (DMPO) has been used to detect and distinguish free radicals in samples of Greek extra virgin olive oils. A number of the samples examined immediately after the addition of the spin trap showed a spontaneous complex electron paramagnetic resonance (EPR) signal. The majority of DMPO-radical adducts formed (80–90%) represented peroxyl and alkoxyl radical adducts. Similar spectra were recorded when DMPO was added in oxidized triolein and then treated with Fe²⁺, Fe³⁺, or Cu²⁺ or when EPR-silent olive oil samples were treated with these metallic ions. Metal ion-catalyzed decomposition of triolein hydroperoxides, as recorded by EPR signal intensity, increased with increasing metal ion concentration in the micromolar range. The relative concentration of alkoxyl-DMPO adducts increased with increasing Fe²⁺ or Fe³⁺ concentration, whereas that of peroxyl-DMPO species decreased. In contrast, the relative concentrations of alkoxyl and peroxyl species produced by Cu²⁺ were similar over the whole metal concentration range examined. Exposure of EPR-silent virgin olive oil or oxidized triolein to ultraviolet light in the presence of DMPO resulted in the detection of a three-line spectrum characterized by wide line widths.