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Antioxidant activity and phenolic contents of Olea europaea L. leaves sprayed with different copper formulations

Ferreira, I.C.F.R., Barros, L., Soares, M.E., Bastos, M.L., Pereira, J.A.
Food chemistry 2007 v.103 no.1 pp. 188-195
antioxidant activity, phenolic compounds, Olea europaea, olives, leaves, foliar spraying, copper, antioxidants, chemical constituents of plants, chemical composition
Olive trees (Olea europaea L. Cv. Cobrançosa) from the northeast of Portugal were sprayed with three different copper formulations [bordeaux mixture (copper sulphate + calcium hydroxide - 20% Cu), copper hydroxide (40% Cu) and copper oxychloride (50% Cu)] to control olive fungal diseases. The residues of copper in olive leaves, harvested at different times, were evaluated by atomic absorption spectrometry. At all the collection times, treated olive leaves had significantly higher copper contents, compared to the control. The different copper amounts in pesticide formulations lowered the leaves contents in total phenols and hence their antioxidant properties. Olive leaves sprayed with copper oxychloride possessed the highest copper levels and the lowest content in phenols, which influenced its antioxidant activity (higher EC₅₀ values for reducing power, scavenging effect on DPPH radicals and inhibition of erythrocyte hemolysis). Leaves without copper residues proved to be a good natural source of antioxidants, giving values comparable to the reference compounds.