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

Abstract

AbstractSpin 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.