Degradation of the polar lipid and fatty acid molecular species in extra virgin olive oil during storage based on shotgun lipidomics

Among the bioactive compounds present in extra-virgin olive oil, polar lipids and free fatty acids are minor compounds with well-known nutritional values and have been studied for traceability and adulteration investigations as well. In the present paper, the simultaneous characterization of polar lipids and free fatty acids in a pool of fifteen EVOO samples was achieved by means of reversed phase C18 analysis coupled to negative polarity high-resolution mass spectrometry. A total of 24 polar lipids, comprising 19 phospholipids and 5 sulfolipids, and 27 free fatty acids were tentatively identified, including several odd-chain and very long-chain fatty acids at trace levels. Moreover, a one-month study of lipid degradation on simulated storage conditions was carried out thanks to the set-up of a dedicated approach for degradation product analysis which was implemented of Compound Discoverer software. By virtue of the customized data processing workflow, more than forty compounds were tentatively identified, including compounds deriving from hydrolysis and oxidation reactions. Finally, by analysis of peak area trends, phosphoester hydrolyses of polar heads of phospholipids emerged as the fastest reactions, followed by glycerol ester hydrolyses and oxidative processes.