**2. Nutritional value of olive oil**

Mediterranean food tradition is sustained by three basic essentials: wheat, olives and grapes. Nevertheless, olive oil is the central element inherent to this diet, and its importance is due to the increasing consumption around the world, because of its nutritional and sensory properties. European Union (EU) is the leading producer of olive oil and within the EU, the Mediterranean members are the biggest producers, in fact Mediterranean area accounts for 95% of world production and 85% of world consumption of olive oil (IOOC, 2007).

Several clinical data have shown that consumption of olive oil can provide heart health benefits, such as favourable effects on cholesterol regulation and LDL cholesterol oxidation, and that it exerts anti-inflammatory, antithrombotic and antihypertensive effects (Lairon, 2007; Perez-Jimenez et al., 2007).

Virgin olive oil is a genuine fruit juice obtained from olive drupes (*Olea europaea* L.), using exclusively mechanical procedures, without further treatments or chemical additions. The saponifiable fraction is more representative (about 98%) than the unsaponifiable one and it comprises principally triacylglycerols, esters formed by glycerol and fatty acids, mainly unsaturated acids whose the major is oleic acid (about 65-80%). The olive oil contains also a relatively reduced level of polyunsaturated essential fatty acids (PUFA), linoleic and linolenic acids (C18:2 ω-6, C18:3 ω-3). Such composition gives good resistance to chemical and biological oxidation, in contrast with other edible oils in which polyunsaturated fatty acids prevail on monounsaturated ones (Rastrelli et al., 2002). Thus, the importance of virgin olive oil is related to its high levels of monounsaturated fatty acids but also to the presence of minor components including aliphatic and triterpenic alcohols, sterols, hydrocarbons, volatile compounds, and several antioxidants. In fact, the unsaponifiable fraction which covers a small percentage (0,5-3%) plays a significant role on human health.

Among the antioxidant compounds, squalene, a triterpenoid hydrocarbon and precursor of sterol biosynthesis, occurs in olive oil with a high concentration (up to 1%). Other active constituents in the olive oil are represented by tocopherols α-, β -, γ -, δ -: the concentration of α–tocopherol (Vitamin E), traditionally considered as the major antioxidant, covers almost 88% of the total tocopherols. The tocopherol content of olive oil depends not only on the presence of these compounds in olive fruit but also on several other factors, involved in the transportation, storage and olive fruit processing. Normally in animal fluids and tissues, vitamin E works in synergy with coenzyme Q (CoQ) to protect cells and tissues against lipoperoxidation, and some authors detected CoQ9 and CoQ10 in olive oil (Pregnolato et al., 1994; Psomiadou & Tsimidou, 1998). According to Viola (1997), the ratio of vitamin-E to polyunsaturated fatty acids in olive oils is better than in other edible oils.

Phenolic compounds make an important contribute to the nutritional properties, sensory characteristics and the shelf life of olive oil, because they improve the resistance to the autoxidation. Olive fruit contains simple and complex phenolic compounds: those derived from the hydrolysis of oleuropein contribute to the intensity of the bitterness of virgin olive oil, and especially hydroxytyrosol, tyrosol, caffeic, coumaric and *p*-hydroxybenzoic acids influence the sensory characteristics of olive oil (Kiritsakis, 1998). The concentration and composition of phenolic compounds in virgin olive oil is strongly affected by many agronomical and technological factors, such as olive cultivar (Tura et al., 2007), place of cultivation (Vinha et al., 2005), climate, degree of maturation (Kalua et al., 2005; Sicari et al., 2009; Giuffrè et al., 2010), crop season (Gómez-Alonso et al., 2002), irrigation (Tovar et al., 2001) and production process (Cinquanta et al., 1997; Ranalli et al., 2001).

Regarding other compounds in the olive oil, its colour is mainly related to the presence of chlorophyll and pheophytin a (Psomiadou & Tsimidou, 2001).

Carotenoids are also responsible for the colour of olive oil: the major are β-carotene and lutein in virgin olive oil (Gandul-Rojas & Mínguez-Mosquera, 1996). The presence of these constituents depends on several factors, such as cultivar, soil and climate, and fruit maturation as well as applied conditions during olive fruit processing (Gallardo-Guerrero et al., 2002).
