title: Antioxidant protective effect of flavonoids on linoleic acid peroxidation induced by copper(II)/ascorbic acid system.
abstract: Antioxidants are compounds that can delay or inhibit lipid oxidation. The peroxidation of linoleic acid (LA) in the absence and presence of Cu(II) ion-ascorbate combinations was investigated in aerated and incubated emulsions at 37°C and pH 7. LA peroxidation induced by copper(II)-ascorbic acid system followed first order kinetics with respect to hydroperoxides concentration. The extent of copper-initiated peroxide production in a LA system assayed by ferric thiocyanate method was used to determine possible antioxidant and prooxidant activities of the added flavonoids. The effects of three different flavonoids of similar structure, i.e. quercetin (QR), morin (MR) and catechin (CT), as potential antioxidant protectors were studied in the selected peroxidation system. The inhibitive order of flavonoids in the protection of LA peroxidation was: morin>catechin≥quercetin, i.e. agreeing with that of formal reduction potentials versus NHE at pH 7, i.e. 0.60, 0.57 and 0.33V for MR, CT, and QR, respectively. Morin showed antioxidant effect at all concentrations whereas catechin and quercetin showed both antioxidant and prooxidant effects depending on their concentrations. The structural requirements for antioxidant activity in flavonoids interestingly coincide with those for Cu(II)-induced prooxidant activity, because as the reducing power of a flavonoid increases, Cu(II)-Cu(I) reduction is facilitated that may end up with the production of reactive species. The findings of this study were evaluated in the light of structure-activity relationships of flavonoids, and the results are believed to be useful to better understand the actual conditions where flavonoids may act as prooxidants in the preservation of heterogeneous food samples containing traces of transition metal ions.
authors.affiliation: Yildiz Technical University, Science and Arts Faculty, Chemistry Department, Esenler, Istanbul, Turkey.
authors.forename: Bilge Yıldoğan
authors.initials: BY
authors.lastname: Beker
authors.forename: Temelkan
authors.initials: T
authors.lastname: Bakır
authors.forename: Inci
authors.initials: I
authors.lastname: Sönmezoğlu
authors.forename: Filiz
authors.initials: F
authors.lastname: Imer
authors.forename: Reşat
authors.initials: R
authors.lastname: Apak
mesh_terms: D000975:Antioxidants / Q000494:pharmacology*; D001205:Ascorbic Acid / Q000737:chemistry*; D002392:Catechin; D003300:Copper / Q000737:chemistry*; D005419:Flavonoids / Q000494:pharmacology; D019787:Linoleic Acid; D015227:Lipid Peroxidation / Q000187:drug effects*; D010084:Oxidation-Reduction; D020011:Protective Agents; D011794:Quercetin; D013329:Structure-Activity Relationship; D047309:Flavones
chemical_list: D000975:Antioxidants; D001205:Ascorbic Acid; D002392:Catechin; D003300:Copper; D005419:Flavonoids; D019787:Linoleic Acid; D020011:Protective Agents; D011794:Quercetin; C008548:morin; D047309:Flavones