BACKGROUND: Extra virgin olive oil is a food with a recognized health claim in the EU related to its phenolic content. Based on nuclear magnetic resonance (NMR) analysis, we observed for the first time that most high‐phenolic olive oils also contain significant quantities of another potential beneficial ingredient, S‐(E)‐elenolide, which is a non‐phenolic compound related to oleuropein or ligstroside. Elenolide had only been found in olive leaves and fruits as the Z isomer or had been synthesized and had been recognized as an antihypertensive agent. RESULTS: (E)‐Elenolide was isolated from olive oil and its structure was elucidated and completely characterized for the first time using 1D and 2D NMR and gas chromatography–mass spectrometry. In addition, we developed a method of quantitative measurement based on qNMR. Investigation of 2120 olive oil samples showed that elenolide was present in the majority of samples, in quantities ranging from 0 to 2821 mg kg−1. Although elenolic acid, which is a hydrated derivative of elenolide, had been reported as an olive oil ingredient, this is the first time that elenolide has proved to be transformed to elenolic acid after reaction with water. Finally, it was found that the quantity of elenolide in olive oil depends on the quantity of water remaining in the olive oil during storage. CONCLUSION: S‐(E)‐Elenolide is a new important substance of olive oil and could be used as marker of high‐quality oils with low water content. © 2019 Society of Chemical Industry [ABSTRACT FROM AUTHOR]
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