Effects of copper on the antioxidant activity of olive polyphenols in bulk oil and oil-in-water emulsions

• Type: Article in International Scientific Journal
• Date: 2006

Authors

Paiva Martins, F (Author) FCUP; Santos, V (Author) Other; Mangericao, H (Author) Other; Gordon, MH (Author) Other

Journal

Title: Journal of Agricultural and Food Chemistry

Vol. 54

Pages: 3738-3743

ISSN: 0021-8561

Publisher: American Chemical Society

Indexing

ISI Web of Knowledge - 29 Citations

Scopus - 30 Citations

Scientific classification

FOS: Agrarian Sciences > Other Agrarian Sciences

Other information

Authenticus ID: P-004-KR5

DOI: 10.1021/jf060033j

Abstract (EN): The antioxidant activity and interactions with copper of four olive oil phenolic compounds, namely oleuropein, hydroxytyrosol, 3,4- dihydroxyphenylethanol- elenolic acid ( 1), and 3,4- dihydroxyphenyl-ethanolelenolic acid dialdehyde ( 2), in olive oil and oil- in- water emulsions stored at 60 degrees C were studied. All four phenolic compounds significantly extended the induction time of lipid oxidation in olive oil with the order of activity being hydroxytyrosol > compound 1 > compound 2 > oleuropein > alpha- tocopherol; but in the presence of Cu( II), the stability of oil samples containing phenolic compounds decreased by at least 90%, and the antioxidant activity of hydroxytyrosol and compounds 1 and 2 became similar. In oil- in- water emulsions prepared from olive oil stripped of tocopherols, hydroxytyrosol enhanced the prooxidant effect of copper at pH 5.5 but not at pH 7.4. The stability of samples containing copper at pH 5.5 was not significantly different if oleuropein was present from that of the control. Oleuropein at pH 7.4, and compounds 1 and 2 at both pH values tested, reduced the prooxidant effect of copper. The lower stability and the higher reducing capacity of all compounds at pH 7.4 could not explain the higher stability of emulsions containing phenolic compounds at this pH value. However, mixtures containing hydroxytyrosol or oleuropein with copper showed higher 1,1-diphenyl- 2- picrylhydrazyl radical scavenging activity at pH 7.4 than at pH 5.5. Moreover, the compound 2- copper complex showed higher radical scavenging activity then the uncomplexed compound at pH 5.5. It can be concluded that the formation of a copper complex with radical scavenging activity is a key step in the antioxidant action of the olive oil phenolic compounds in an emulsion containing copper ions.

Language: English

Type (Professor's evaluation): Scientific

No. of pages: 6