Interactions of ferric ions with olive oil phenolic compounds.
The ferric complexing capacity of four phenolic compounds, occurring in olives and virgin olive oil, namely, oleuropein, hydroxytyrosol, 3,4-dihydroxyphenylethanol-elenolic acid (3,4-DHPEA-EA), and 3,4-dihydroxyphenylethanol-elenolic acid dialdehyde (3,4-DHPEA-EDA), and their stability in the presence of ferric ions were studied. At pH 3.5, all compounds formed a reversible 1:1 complex with ferric ions, but hydroxytyrosol could also form complexes containing >1 ferric ion per phenol molecule. At pH 5.5, the complexes between ferric ions and 3,4-DHPEA-EA or 3,4-DHPEA-EDA were relatively stable, indicating that the antioxidant activity of 3,4-DHPEA-EA or 3,4-DHPEA-EDA at pH 5.5 is partly due to their metal-chelating activity. At pH 7.4, a complex containing >1 ferric ion per phenol molecule was formed with hydroxytyrosol. Oleuropein, 3,4-DHPEA-EA, and 3,4-DHPEA-EDA also formed insoluble complexes at this pH. There was no evidence for chelation of Fe(II) by hydroxytyrosol or its derivatives. At all pH values tested, hydroxytyrosol was the most stable compound in the absence of Fe(III) but the most sensitive to the presence of Fe(III).
Paiva-Martins
Fátima
F
Centro de Investigação em Química, Departamento de Química, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre, no. 687, 4169-007 Porto, Portugal. mpmartin@fc.up.pt
Gordon
Michael H
MH
D004355:Drug Stability; D005290:Ferric Compounds / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D057888:Iridoid Glucosides; D039823:Iridoids; D000069463:Olive Oil; D010636:Phenols / Q000737:chemistry*; D010626:Phenylethyl Alcohol / Q000031:analogs & derivatives* / Q000737:chemistry; D010938:Plant Oils / Q000737:chemistry*; D011714:Pyrans / Q000737:chemistry
C121925:3,4-dixydroxyphenylethanol elenolic acid; D005290:Ferric Compounds; D057888:Iridoid Glucosides; D039823:Iridoids; D000069463:Olive Oil; D010636:Phenols; D010938:Plant Oils; D011714:Pyrans; C005975:3,4-dihydroxyphenylethanol; C002769:oleuropein; D010626:Phenylethyl Alcohol