The Mediterranean Sea basin is the main olive-producing region all over the world. Greece constitutes one of the most important countries in olive culture, accounting for 13% and 5.3% of the global olive oil and table olive production, respectively (International Olive Oil Council, 2011). There are ≈60 olive tree cultivars originating from Greece, some of which are cultivated globally (i.e., ‘Koroneiki’, ‘Kalamon’), whereas most of them are found in local areas.
Phenolic compounds are secondary metabolites with a great structural diversity and a wide phylogenetic distribution (Harborne, 1989). Phenolic compounds influence the organoleptic properties of olive fruits and virgin olive oils and are important markers for studying fruit characteristics of different cultivars and controlling olive production processes. Their antioxidant effect is correlated to the high stability of virgin olive oil against heat oxidation and autoxidation processes overtime (Romani et al., 1999). Besides fruits, some studies considered the phenol fraction present in olive leaves (Briante et al., 2002b; Ranalli et al., 2006). Olive leaves are endowed with the most potent free radical scavenging power among the different parts of olive trees and provide considerable amounts of high added-value compounds (Japón-Luján et al., 2006). Olive leaves have phenol composition similar to that of olive fruit with oleuropein constituting the main phenolic compound followed by other phenol glycosides (Benavente-García et al., 2000).
Oleuropein is a heterosidic ester of β-glucosylated elenolic acid and hydroxytyrosol and can be easily transformed by endogenous or exogenous supply of the enzyme β-glucosidase into glucose and oleuropein aglycon (Ranalli et al., 2006). It is also the most abundant phenolic compound in olive leaves and fruits and is considered as the main responsible factor for the characteristic bitterness of olive fruit and the browning that occurs in green table olives either after impact and wounding during harvesting or during subsequent technological treatments (Malik and Bradford, 2006; Soler-Rivas et al., 2000; Therios, 2009). Health benefits of oleuropein have been extensively investigated. Specifically, it has been reported that oleuropein and other related phenolic compounds such as hydroxytyrosol, tyrosol, verbascoside, ligustroside, and demethyloleuropein act as antioxidants that contribute to a lower risk of coronary diseases (Beauchamp et al., 2005; Visioli et al., 1998; Wiseman et al., 1996) and several types of cancers (Owen et al., 2000; Tripoli et al., 2005). Furthermore, these compounds present antimicrobial and antiviral activity (Bisingnano et al., 1999; Uccella, 2001).
The chemical and biochemical composition of olives relies on some agronomical factors, one of which is the cultivar. Because phenolic compounds play an important role in olive fruit and virgin olive oil quality and present several health benefits, the aim of the present study was to determine the phenolic content and fruit antioxidant activity of 11 Greek olive cultivars. This is of great importance to explore phenolic concentration of the previously mentioned cultivars and identify those with high values to use them commercially for oleuropein production.
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