Phenolic compounds have a fundamental importance in the nutritional and sensory characteristics of virgin olive oil. Problems regarding their qualitative and quantitative evaluation have not been completely solved; hence, in this paper the extractive and HPLC methods of analysis are examined and some modifications are presented. By means of these techniques, elenolic acid and four unknown compounds having phenolic behavior were separated from virgin olive oil. Four of them were correlated with total phenols evaluated by means of the Folin-Ciocalteu reagent, and two of them were correlated with olive oil autoxidation stability.

Hydrophilic phenols are the most abundant natural antioxidants of virgin olive oil (VOO), in which, however, tocopherols and carotenes are also present. The prevalent classes of hydrophilic phenols found in VOO are phenolic alcohols, phenolic acids, flavonoids, lignans and secoiridoids. Secoiridoids, that include aglycon derivatives of oleuropein, demethyloleuropein and ligstroside, that are present in olive fruit, are the most abundant phenolic antioxidants of VOO. The sensory and healthy proprieties of VOO hydrophilic phenols as well as the agronomic and technological parameters that affect their concentration in the oil are discussed in this paper.

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The antioxidant effects of hydrophilic phenols and tocopherols on the oxidative stability in virgin olive oils and in purified olive oil have been evaluated. Total hydrophilic phenols and the oleosidic forms of 3,4‐dihydroxyphenolethanol (3,4‐DHPEA) were correlated (r=0.97) with the oxidative stability of virgin olive oil. On the contrary, tocopherols showed low correlation (r=0.05). Purified olive oil with the dialdehydic form of elenolic acid linked to 3,4‐DHPEA, an isomer of oleuropeine aglycon, and 3,4‐DHPEA had good oxidative stability. A synergistic effect was observed in the mixture of 3,4‐DHPEA and its oleosidic forms with α‐tocopherol in purified olive oil by the Rancimat method at 120°C.

The stimulation of the human sensory receptors by volatile compounds present in virgin olive oils gives rise to the sensory attributes that describe its delicate and fragrant aroma. The composition of the volatile compounds and their biogenesis is briefly illustrated. Analytical methodologies for evaluating the volatile fraction and the sensory properties of virgin olive oils are elucidated. Compounds responsible for typical flavours are examined and the influence of the main factors on the composition of volatile compounds is discussed. The origin of off-flavours are also described and the consequent changes of volatile composition and of sensory characteristics are analysed. The relationships between volatile compounds and sensory attributes are discussed.