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Mechanism of lower oxidizability of eicosapentaenoate than linoleate in aqueous micelles. II. Effect of antioxidants
Author(s) -
Yazu Kazumasa,
Yamamoto Yorihiro,
Niki Etsuo,
Miki Keiji,
Ukegawa Koji
Publication year - 1998
Publication title -
lipids
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.601
H-Index - 120
eISSN - 1558-9307
pISSN - 0024-4201
DOI - 10.1007/s11745-998-0245-3
Subject(s) - trolox , chemistry , micelle , radical , aqueous solution , photochemistry , aqueous two phase system , organic chemistry , antioxidant , antioxidant capacity
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.