Chlorophyll photosensitized oxidation of virgin olive oil: a comparison between selected unsaturated model esters and real oil samples

The effects of chlorophyll on photooxidation of virgin olive oil was evaluated. A purified chlorophyll fraction from spinach leaves was used as a photosensitiser to oxidise tiglic acid, as a model unsaturated compound that is useful to tune reaction conditions. Oleic and linoleic acid methyl esters were used to test photosensitised oxygenation. Virgin olive oil samples with the added spinach chlorophyll were photooxidised and the formation of hydroperoxides was monitored by 13C NMR. The virgin olive oil showed a behaviour similar to oleic acid methyl esters, as the olive oil contains more than 75% oleic acid. Headspace gas chromatography-mass spectrometry analysis of the irradiated reaction mixtures showed several short-chain products for the linoleic acid methyl esters, while for the oleic acid methyl esters, octane was the only product that was detected in any quantity. The analysis of photooxidised virgin olive oil confirmed the presence of octane, which can therefore be proposed as a marker for an irradiation step of the oil.