Mechanism of lower oxidizability of eicosapentaenoate than linoleate in aqueous micelles. II. Effect of antioxidants.
We have reported that the peroxyl radicals derived from methyl eicosapentaenoate (20:5n-3) are more polar than those from methyl linoleate (18:2n-6) since the former peroxyl radicals have at least two molecules of oxygen in a molecule while the latter peroxyl radical has one. This lowers the oxidizability for 20:5n-3 in aqueous Triton X-100 micelles by enhancing the termination reaction rate for peroxyl radicals and by reducing the rate of propagation since there may be more polar peroxyl radicals derived from 20:5n-3 at the surface than within the micelle core. In this study, we measured the effect of three antioxidants, di-tert-butyl-4-methylphenol (BHT), 2,2,5,7,8-pentamethyl-6-chromanol (PMC) and 2-carboxy-2,5,7,8-tetramethyl-6-chromanol (Trolox), on the oxidation of lipids in aqueous micelle. Antioxidants give a clear induction period during oxidation of 18:2n-6 initiated with a water-soluble radical initiator, and its induction length decreases in the order of BHT > PMC > Trolox. This is consistent with the proposed location of three antioxidants: being in the core of micelle, at the surface, or in aqueous phase, respectively. However, BHT does not inhibit the oxidation of 20:5n-3 efficiently, and its rate of oxidation is slower than that observed in the oxidation of 18:2n-6, supporting the idea that polar peroxyl radicals derived from 20:5n-3 are preferentially located at the surface of the micelle. Similar results were obtained when oxidation was initiated with a lipid-soluble radical initiator except antioxidants had lesser effect on the oxidation rate of 20:5n-3.
Yazu
K
K
Department of Energy Resources, National Institute for Resources and Environment, Tsukuba, Ibaraki, Japan.
Yamamoto
Y
Y
Niki
E
E
Miki
K
K
Ukegawa
K
K
D000332:Aerobiosis; D000975:Antioxidants / Q000494:pharmacology*; D001391:Azo Compounds / Q000494:pharmacology; D002084:Butylated Hydroxytoluene / Q000494:pharmacology; D002839:Chromans / Q000494:pharmacology; D015118:Eicosapentaenoic Acid / Q000737:chemistry*; D005609:Free Radicals / Q000737:chemistry; D066298:In Vitro Techniques; D019787:Linoleic Acid / Q000737:chemistry*; D008823:Micelles; D009570:Nitriles / Q000494:pharmacology; D010084:Oxidation-Reduction; D014867:Water
D000975:Antioxidants; D001391:Azo Compounds; D002839:Chromans; D005609:Free Radicals; D008823:Micelles; D009570:Nitriles; C055792:2,2'-azobis(2,4-dimethylvaleronitrile); D014867:Water; D002084:Butylated Hydroxytoluene; C029141:2,2,5,7,8-pentamethyl-1-hydroxychroman; D019787:Linoleic Acid; D015118:Eicosapentaenoic Acid; C010643:6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid