Virgin olive oil is considered to be the major ingredient in the traditional Mediterranean diet as it has high nutritional value and it provides various benefits on human health. The significance of virgin olive oil (VOO) is attributed not only to its high content of monounsaturated fatty acids (MUFA) and polyunsaturated fatty acids (PUFAs), but also to its antioxidant phenolic compounds. The major classes of phenolic compounds in olive oil areꓽ phenolic alcohols, secoiridoid derivatives, lignans, flavonoids, phenolic acids and hydroxy-isochromans; hydroxytyrosol, tyrosol and their secoiridoid derivatives are in abundance, making up around 90% of the total phenolic content of virgin olive oil.
Olive oil phenolic compounds have a broad spectrum of beneficial properties on human health, related to the platelet and cellular function, microbial activity, bone formation, the oxidative damage of cells and inflammation. In 2012, EFSA, assessing the biological activity of olive oil phenolic components issued a scientific opinion in favor of the specific health claim, pointing out that olive oil polyphenols contribute to the protection of blood lipids from oxidative damage (Regulation No 432/2012 of EC). The protective role of olive oil polyphenols on lipid oxidative damage is provided by the results of the EUROLIVE study. In particular, the most important results of this study were that the increase in HDL cholesterol and the decrease in the lipid oxidative damage were linear with the phenolic content of the olive oil consumed (Covas, De la Torre, and Fitó 2014). EUROLIVE was the main study contributing to the strengthening of the health claim for olive oil polyphenols, Regulation 432/2012. The claim points out that ‘olive oil polyphenols contribute to the protection of blood lipids from oxidative stress’ and it can only be used for olive oils that contain at least “5 mg of hydroxytyrosol and its derivatives (e.g., oleuropein complex and tyrosol) per 20 g of olive oil”.
However, this health claim presents some weaknesses regarding terminology and analytical methodology. Specifically, the term “olive oil polyphenols” is not entirely clear and accurate due to the fact that all biophenols referred to EFSA’s health claim do not belong to the chemical class of polyphenols (i.e., tyrosol and its derivatives). Ιt is worth noting that the phenolic content of the olive oil consumed during the EUROLIVE study includes phenolic compounds of simple phenols, secoiridoids, lignans, flavonoids and phenolic acids, for which their determination was made by the analytical method of de la Torre – Carbot (2005). This observation further intensifies the confusion about the health claim related phenolic compounds.
Another factor adding to the health claim weaknesses is the inexistence of an official analytical method for the quantitative determination of biophenols in olive oil. Many analytical methods based on HPLC-DAD, LC-MS, GC-MS, CE-DAD, NMR and spectrophotometry techniques have been proposed in literature for the determination of the phenolic components in olive oil and for the verification of EFSA’s health claim criteria concerning it. However, all these methods have limitations. The only recognized method is the one proposed by the International Olive Council (IOC) (Determination of biophenos in olive oils by HPLC-COI-/T.20/Doc No 29).
The Olive Research Group over the last 4 years, as part of a systematic mapping study of Greek olive oil, has developed specialized protocols and applies modern analytical methodologies, HP-TLC, HPLC-DAD, HP-SFC-DAD-MS, LC-HRMS, FT-ICR-MS, NMR, HPLC-DAD-CD for the determination of the main phenolic components of olive oil, including hydroxytyrosol, tyrosol, oleacein, oleocanthal, etc. However, in order to verify the health claim in olive oil meeting the EFSA criteria, the Olive Research Group has developed and is applying the HPLC analytical method, proposed by IOC.
