**5.2 Compositional markers**

There are several parameters, major and minor compositional markers, with varied discriminant power used for *olive oil* traceability according to the variety of olive participated in the production of the oil (Arvanitoyannis et al., 2007).

To relate the fatty acid composition of *olive oil*s with the cultivar, Mannina et al. (2003) studied *olive oil* in a well- limited geographical region, with no consideration of the pedoclimatic factor (soil characteristics such as temperature and humidity). A relationship between the fatty acid composition and some specific cultivars has been observed (Montealegre et al., 2010).

The *volatile fraction* in *olive oil*s, which represents one of the most important qualitative aspects of this oil, consists of a complex mixture of more than 100 compounds, but the most important substances useful for olive cultivar differentiation are the products of the lipoxygenase pathway (LOX). Only a subset of volatile compounds and a combination among them could provide valuable information for olive cultivar differentiation (Montealegre et al., 2010). Three volatile compounds [hexyl acetate, hexanal, and (E)-hex-2 enal] and the total concentration of ketones have nominated to distinguish the olive varieties (Tena et al., 2007) hich consequently could be used for olive oil, as well. However, it has been found that the level of (E)-hex-2-enal in the analyzed samples showed a variability that suggest an influence of genetic factors on the biosynthesis of this compound. In fact, genetic (Tura et al., 2008; Mahjoub-Haddada et al., 2007) and geographic (Mahjoub-Haddada et al., 2007) factors influence the volatile compound production of the olive fruits and affect the differentiation of *olive oil*s according to their olive variety. The volatile compound contents allowed differentiation among monovarietal *olive oil*s and even identification of the technique used for *olive oil* production (Torres Vaz-Freire et al., 2009).

The color of a virgin *olive oil* is due to the solubilization of the lipophilic chlorophyll and carotenoid pigments present in the fruit. The green-yellowish color is due to various pigments, that is, chlorophylls, pheophytins, and carotenoids (Cichelli & Pertesana, 2004). Chlorophyll a is the major chlorophyll pigment, followed by chlorophyll b. The carotenoid fraction is included lutein, violaxanthin, neoxanthin, β-carotene, β-cryptoxanthin, and luteoxanthin (Montealegre et al., 2010).

Several researchers reported the same qualitative composition in chlorophyll and carotenoid pigments, independent of the olive variety and the time of picking (Giuffrida et al., 2007 ; Roca et al., 2003).

Cerretani et al. (2006) showed that the carotenoid and chlorophyll content determination using UV-vis spectrophotometry was not useful to discriminate oils produced from different olive varieties. Lutein/β-carotene ratio has been reported as a tool to differentiate oils from a single cultivar.

Tocopherols and hydrocarbons are the compositional markers less studied to date to differentiate *olive oil*s. An important common aspect is that the content and composition of these markers are highly affected by the environmental conditions, the fruit ripening, and the extraction technology (Montealegre et al., 2010).
