**3.1 Lipophilic hydroxytyrosol esters**

Many different hydroxytyrosol lipophilic analogues occur naturally in olive fruit and in virgin olive oil. The amount of these compounds is related to olive variety and ripeness, climate, location, type of crushing machine and oil extraction procedures. As an example, the concentration of hydroxytyrosyl acetate is similar to that of HT in some olive oil varieties such as Arbequina, twice as high in the Picual variety, and between one third and one fourth in the Manzanilla and Hojiblanca oils (Romero et al., 2007).

Due to the limited solubility of HT in lipid media, the search for new lipophilic hydroxytyrosol esters with enhanced properties is of great interest, both in food industry and in medicine. Studies on olive polyphenols have shown the importance of the lipophilicity of the antioxidants on the cell uptake and membrane crossing, and on the substrate to be protected (membrane constituents or LDL), (Grasso et al., 2007). These facts explain the efforts made in the development of new synthetic analogues with increased lipophilicity.
