Effect of Filtration Systems on the Phenolic Content of Virgin Olive Oils by HPLC-DAD-MSD

Virgin olive oil is dominated by secoiridoid derivatives, followed by flavonoids and phenolic alcohols. These derived compounds appear in virgin olive oil and possess antioxidant activity and a lower polarity compared to those in olive fruits (as glycosidic compounds). The partition coefficients between olive oil and water depend on the structure of these compounds and the number of hydroxyl groups. The most abundant secoiridoids in virgin olive oil are the dialdehydic forms of elenolic acid linked to hydroxytyrosol or tyrosol (3,4-DHPEA-EDA or p-DHPEA-EDA) and an isomer of the oleuropein aglycone (3,4-DHPEA-EA). This can be explained by the fact that 3,4-DHPEA-EDA and 3,4-DHPEA-EDA are the compounds with the highest partition coefficients, as reported by Servili et al. [2006]. It is known that olive oil has a low quantity of water and for this reason olive oil can be considered as a water-in-oil emulsion. The presence of phenolic compounds in virgin olive oil and their high antioxidant activity can be explained by the so-called “polar paradox” dictating that: “polar antioxidants are more effective in non polar lipids, whereas non-polar antioxidants are more active in polar lipid emulsions”. An important factor to consider is the visual appearance of virgin olive oil, as it will strongly influence consumer preference. Color is an intrinsic characteristic of each food product and helps to identify it, to the extent that the consumer is disconcerted if the color changes. From a hedonistic point of view, the color of olive oil can be considered an important organoleptic attribute that is a basic criterion in assessing quality, according to consumer preferences. The compounds responsible for the color and appearance of virgin olive oil are chlorophylls, carotenoids, flavones (as apigenin and luteolin) but also water content. Chlorophylls give olive oil its yellow-green color, carotenoids contribute in the yellow-red range and flavones, having an absorbance maximum at around 330-350 nm, provide a yellow color.