PHENOLIC ANTIOXIDANT CONTENT OF OLIVE OILS AND THEIR POTENTIAL IN THE PREVENTION OF CANCER

The traditional (European) Mediterranean diet is characterized by an abundance of plant foods such as bread, pasta, vegetables, salad, legumes, fruit, nuts; olive oil as the principal source of fat; low to moderate amounts offish, poultry, dairy products and eggs; only small amounts of red meat; low to moderate amounts of wine, normally consumed with meals. This diet is low in saturated fatty acids, rich in carbohydrate and fibre, and has a high content of monounsaturated fatty acids (MUFA). These are primarily derived from olive oil. Despite a wealth of general knowledge concerning the major classes of compounds present in olives and olive oil, detailed knowledge of the phenolic antioxidant content has been lacking. Therefore the aim of the study was to evaluate the phenolic antioxidant content in a range of olive and seed oils. While seed oils were devoid, on average, the olive oils contained $196{\pm}19mg/kg$ total phenolics as judged by HPLC analysis, but the value for extravirgin ($232{\pm}15 mg/kg$) was significantly higher than that of refined virgin olive oil ($62{\pm}12mg/kg$; P<0.0001). Appreciable quantities of simple phenols (hydroxytyrosol and tyrosol) were detected in olive oils, with significant differences between extravirgin ($41.87{\pm}6.17$) and refined virgin olive oils ($4.72{\pm}2.15$; P<0.01). The major linked phenols were secoiridoids and lignans. Although extravirgin contained higher concentrations of secoiridoids ($27.72{\pm}6.84$) than refined olive oils ($9.30{\pm}3.81$) this difference was not significant. On the other hand the concentration of lignans was significantly higher (P<0.001) in extravirgin ($41.53{\pm}3.93$) compared to refined virgin olive oils ($7.29{\pm}2.56$). All classes of phenolics were shown to be potent antioxidants. In future epidemiolgic studies, both the nature and source of olive oil consumed should be differentiated in ascertaining cancer risk.