Phenolic compounds represent a unique and functional part of the polar fraction of virgin olive oils. Many different approaches for the analysis of these compounds have been published, which has led to ambiguous results that are difficult to compare. In order to explain the controversial data reported in the literature, extraction techniques (solid-phase extraction, SPE, and liquid-liquid extraction, LLE), methods of analysis (HPLC and colorimetric assay) and quantification methods have been re-investigated with genuine olive oil phenols. The optimized LLE system led to high recovery of the nine major olive oil phenolics (93%) and, in addition, was at least as good as the SPE technique in view of costs, solvent and sample consumption, and analysis time. SPE was shown to be problematic because of the selectivity towards the individual phenolics, particularly the aglycone-type ones. The proposed LLE/HPLC method was compared with the traditional colorimetric assay (Folin-Ciocalteu method) by analyzing 23 samples of virgin olive oils. A strong correlation between both methods has been found, suggesting that the colorimetric assay is reasonably valid for a rough prediction of the total phenolic content. In the literature, the level of phenolics is expressed in several different units (reference compound equivalents in case of colorimetric measurements and ppm in HPLC measurements). As these units can differ in orders of magnitude, it is necessary to convert the data to a common base before comparing or combining them.

Three monovarietal extra virgin olive oils (EVOOs) were subjected to accelerated storage conditions (60 degrees C, dark) representative of the autoxidation process during shelf life. Oxidation markers, i.e., the peroxide value, conjugated dienes, the oil stability index, and minor components, were monitored. The changes in minor components, related to the stage of ongoing oxidation and expressed as a percentage of the induction period (IP), followed a similar pattern in all oils: o-diphenols diminished by the highest rate (halved within 15% of the IP), followed by alpha-tocopherol (halved within 35% of the IP). Carotenoids and chlorophylls were also affected by autoxidation, whereas squalene showed high stability (<20% loss within 100% of the IP). Polar phenols (especially o-diphenols) and alpha-tocopherol were deduced to be the most potent antioxidants of EVOO. They efficiently inhibited oxidative lipid deterioration and subsequent development of sensory defects (rancidity, discoloration), which occurred only after substantial depletion of these antioxidants. Therefore, they could also be used as markers for the oxidative status of EVOO particularly in the early stage of oxidation.

Research Paper 100 m CPSil TM 88 column). The amounts obtained by GC were generally higher than those determined by Ag + -HPLC due to co-eluting compounds.

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