Effects of Agronomic and Oil Processing Conditions on Natural Antioxidative Phenolics in Olive (Oleaeuropaea L.)

Olive fruits contain appreciable amounts of phenolic compounds which are valuable antioxidants and bioactives. Secoiridoids, such as oleuropein, demethyloleuropein, oleuropein aglycone and ligstroside are the predominant classes of phenolic compounds in intact olive fruits, while 4-Hydroxyphenylethanol (4-HPEA), 3,4-Dihydroxyphenylethanol (3,4-DHPEA), the dialdehydic form of decarboxymethyl elenolic acid linked to 3,4-DHPEA (3,4-DHPEA-EDA) and oleuropein aglycone (3,4-DHPEA-EA) are the principal phenolic constituents of Virgin Olive Oil (VOO). The phenolic compounds originally present in the olive fruit are substantially changed by the conditions of oil processing (crushing, malaxation and phase separation) and distributed among the final product (VOO) and by-products in various ways. They may undergo further changes during storage. This paper reviews the effects of the processing steps on the transfer of phenolic compounds from intact fruit to the final product (VOO), as well as the effects of agronomic factors (cultivar, maturity and irrigation) on the phenolic constituents of olive fruits at harvest.