Composition and Antioxidant Activity of Olive Leaf Extracts from Greek Olive Cultivars |
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Authors: | Kostas Kiritsakis M G Kontominas C Kontogiorgis D Hadjipavlou-Litina A Moustakas A Kiritsakis |
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Affiliation: | (1) Alexander Technological Educational Institute of Thessaloniki, Sindos, Thessaloniki, Greece;(2) Department of Chemistry, University of Ioannina, Ioannina, Greece;(3) Department of Pharmaceutical Chemistry, School of Pharmacy, Aristotle University of Thessaloniki, Thessaloniki, Greece;(4) Technical University of Crete, Chanea, Greece |
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Abstract: | The olive leaf phenolic composition of the Greek cultivars koroneiki, megaritiki and kalamon was determined using LC/MS. Furthermore, the antioxidant activity of olive leaf extracts from the above three cultivars,
using solvents of increasing polarity (petroleum ether, dichloromethane, methanol and methanol/water: 60/40) was evaluated
using the stable free radical diphenylpicrylhydrazyl (DPPH) test. Furthermore the oxidative stability index (OSI) was compared
to that of the synthetic antioxidant TBHQ and commercial oleoresin (rosemary extract). The ability of phenolic compounds to
inhibit the lipoxygenase (LOX) activity was also investigated. The ten main components determined in the olive tree leaf extracts
for the cultivars koroneiki and kalamon were: secologanoside, dimethyloleuropein, oleuropein diglucoside, luteolin-7-O-glucoside, rutin, oleuropein, oleuroside, quercetin, ligstroside and verbascoside. Respective compounds for the cultivar
megaritiki were: secologanoside, dimethyloleuropein, oleuropein diglucoside, luteolin7-O-glucoside, oleuropein, oleuroside, quercetin and ligstroside. In all three cultivars, oleuropein represented the main phenolic
component. The solvent polarity influenced the total amount of the phenolic compounds determined. When methanol/water (60/40)
was used, as solvent, more phenolic compounds were determined. The total amounts of phenols determined in the extracts, obtained
by successive extractions using the above solvents, were 6,094, 5,579 and 6,196 mg/kg (mg gallic acid/kg dried olive leaves)
for the cultivars megaritiki, kalamon and koroneiki, respectively. Among all extracts, methanol/water extracts exhibited the highest antioxidant activity as shown through the
application of the DPPH and OSI methods. The OSI antioxidant activity followed the sequence: synthetic antioxidant TBHQ > commercial
oleoresin > olive tree leaf extracts > control. Likewise, methanol/water olive leaf extracts significantly inhibited soybean
lipoxygenase, although some small differences in the activity among the olive leaf extracts of the different cultivars were
observed. The solvent polarity as well as the amount of the extract influenced the inhibitory activity. A positive correlation
was shown between the antioxidant activity of leaf extracts and the total phenol content. |
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