Autoxidation of methyl linolenate and methyl linoleate: The effect of α‐tocopherol

Peers, Kenneth E.; Coxon, David T.; Chan, Henry

doi:10.1002/jsfa.2740320908

Cited by 75 publications

(45 citation statements)

References 15 publications

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“…Moreover, experiments with -tocopherol have provided evidence against direct pentadienyl radical isomerization. -Tocopherol, which acts in the autoxidation reaction at the level of the peroxyl radicals and not of the carbon radicals, has been shown to direct autoxidation toward the cis,trans products (Porter et al 1980;Peers et al 1981). If the loss of stereochemistry in the product hydroperoxides occurred by pentadienyl radical isomerization, then -tocopherol would have no effect on the product composition (Porter 1986).…”

Section: Figurementioning

confidence: 99%

“…In methyl linoleate autoxidation, -tocopherol inhibits the formation of the thermodynamic trans,trans conjugated diene hydroperoxides and thus favours the formation of the kinetic cis,trans products in a concentration-dependent manner (Porter et al 1980;Peers et al 1981;Weenen & Porter 1982;Mäkinen et al 2000). At high concentrations of -tocopherol (5%, 0.1 M) these effects dominate almost totally and the mixture of products is greatly simplified; only cis,trans isomers are forme d and the quantities of the positional isomers are equalized (Peers et al 1981). This effect oftocopherol has been used to advantage in the production of pure cis,trans hydroperoxides from methyl linoleate, methyl linolenate, and methyl arachidonate (Peers et al 1981;Peers & Coxon 1983).…”

Section: Figure 12mentioning

confidence: 99%

“…At high concentrations of -tocopherol (5%, 0.1 M) these effects dominate almost totally and the mixture of products is greatly simplified; only cis,trans isomers are forme d and the quantities of the positional isomers are equalized (Peers et al 1981). This effect oftocopherol has been used to advantage in the production of pure cis,trans hydroperoxides from methyl linoleate, methyl linolenate, and methyl arachidonate (Peers et al 1981;Peers & Coxon 1983). As discussed above in section 2.1.1, the product distribution and the ability of -tocopherol to direct the isomeric distribution of hydroperoxides has been rationalised based on the reversibility of oxygen addition.…”

Section: Figure 12mentioning

confidence: 99%

“…The high amount oftocopherol was therefore necessary for the production of sufficient amounts of hydroperoxides for the characterization. In addition, the high amount of -tocopherol was expected, as observed in the autoxidation of methyl linoleate (Peers et al 1981), to simplify the hydroperoxide mixture such that it consisted of only the kinetic products, thereby simplifying the separation of the isomers as well. The extent of oxidation was kept low; in the autoxidation of Me 9c,11t-CLA the extent of oxidation was 13% based on substrate consumption followed by GC, and the yield of hydroperoxides, which was estimated based on TLC and PV measurement, was 9% (II).…”

Section: Structure Of the Conjugated Linoleic Acid Methyl Ester Hydromentioning

confidence: 99%

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Autoxidation of Conjugated Linoleic Acid Methyl Ester in the Presence of α‐Tocopherol: The Hydroperoxide Pathway

Pajunen

Johansson

Hase

et al. 2008

Lipids

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The autoxidation of conjugated linoleic acid (CLA) is poorly understood in spite of increasing interest in the beneficial biological properties of CLA and growing consumption of CLA-rich foods. In this thesis, the autoxidation reactions of the two major CLA isomers, 9-cis,11-transoctadecadienoic acid and 10-trans,12-cis-octadecadienoic acid, are investigated. The results contribute to an understanding of the early stages of the autoxidation of CLA methyl ester, and provide for the first time a means of producing and separating intact CLA methyl ester hydroperoxides as well as basic knowledge on lipid hydroperoxides and their hydroxy derivatives.Conjugated diene allylic monohydroperoxides were discovered as primary autoxidation products formed during autoxidation of CLA methyl esters in the presence and absence oftocopherol. This established that one of the autoxidation pathways of CLA methyl ester is the hydroperoxide pathway.Hydroperoxides were produced from the two major CLA methyl esters by taking advantage of the effect of -tocopherol to promote hydroperoxide formation. The hydroperoxides were analysed and separated first as methyl hydroxyoctadecadienoates and then as intact hydroperoxides by HPLC. The isolated products were characterized by UV, GC-MS, and NMR techniques. In the presence of a high amount of -tocopherol, the autoxidation of CLA methyl ester yields six kinetically-controlled conjugated diene monohydroperoxides and is diastereoselective in favour of one particular geometric isomer as a pair of enantiomers. The primary autoxidation products produced from the two major CLA isomers include new positional isomers of conjugated diene monohydroperoxides, the 8-, 10-, 12-, and 14-hydroperoxyoctadecadienoates. Furthermore, two of these new positional isomers have an unusual structure for a cis,trans lipid hydroperoxide where the allylic methine carbon is adjacent to the cis instead of the usual trans double bond.The 1 H and 13 C NMR spectra of nine isomeric methyl hydroxyoctadecadienoates and of ten isomeric methyl hydroperoxyoctadecadienoates including the unusual cis,trans hydroperoxides, i.e. Me 8-OOH-9c,11t and Me 14-OOH-10t,12c, were fully assigned with the aid of 2D NMR spectroscopy. The assigned NMR data enabled determination of the effects of the hydroxyl and hydroperoxyl groups on the carbon chemical shifts of CLA isomers, identification of diagnostic signals, and determination of chemical shift differences of the olefinic resonances that may help with the assignment of structure to as yet unknown lipid hydroperoxides either as hydroxy derivatives or as intact hydroperoxides.A mechanism for the hydroperoxide pathway of CLA autoxidation in the presence of a high amount of -tocopherol was proposed based on the characterized primary products, their relative distribution, and theoretical calculations. This is an important step forward in CLA research, where exact mechanisms for the autoxidation of CLA have not been presented before. Knowledge of these hydroperoxide formation steps is of cr...

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Section: Figurementioning

confidence: 99%

Section: Figure 12mentioning

confidence: 99%

Section: Figure 12mentioning

confidence: 99%

Section: Structure Of the Conjugated Linoleic Acid Methyl Ester Hydromentioning

confidence: 99%

See 2 more Smart Citations

Autoxidation of Conjugated Linoleic Acid Methyl Ester in the Presence of α‐Tocopherol: The Hydroperoxide Pathway

Pajunen

Johansson

Hase

et al. 2008

Lipids

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“…When oxygen is present in trace amounts, c!-tocopherol can react directly with alkyl radicals (Evans et al, 1992;Yamauchi et al, 1993). c!-Tocopherol at high concentrations induces the formation of lipid hydroperoxides (Peers et al, 1981;Koskas et al, 1984;Terao & Matsushita, 1986). The pro-oxidant effect of c!-tocopherol was related to the reaction of c!-tocopheroxyl radicals with lipids (Terao & Matsushita, 1986;Bowry & Stocker, 1993;Mukai et al, 1993aMukai et al, , 1993b The reaction products of c!-tocopherol with lipid free radicals are described in the following sections.…”

Section: A-tocopherol As the Free Radical Scavengermentioning

confidence: 99%

Vitamin E: Mechanism of Its Antioxidant Activity.

Yamauchi

1997

FSTI

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The antioxidant activity of vitamin E (a-tocopherol) during the peroxidation of unsaturated lipids has been reviewed based on its reaction products. Free-radical scavenging reactions of a-tocopherol take place via the a-tocopheroxyl radical as an intermediate. If a suitable free radical is present, a non-radical product can be formed from the coupling of the free radical with the a-tocopheroxyl radical. The reaction products of a-tocopherol with lipid-peroxyl radicals are 8a-(lipid-dioxy)-a-tocopherones which are hydrolyzed to a-tocopherylquinone. If the supply of oxygen is insufficient, a-tocopherol can trap the carbon-centered radicals of lipids to form 6-0-(lipidalkyl)-a-tocopherols. On the other hand, the dimer and trimer of a-tocopherol is formed by the bimolecular self-reaction of the a-tocopheroxyl radical in a reaction mixture containing a large amount of a-tocopherol. The other product-forming pathway yields isomeric epoxy-a-tocopherylquinones and their precursors, epoxyhydroperoxy-a-tocopherones, but the mechanism of this pathway remains unknown. The reaction products of other vitamin E compounds (7-and 6-tocopherols) during lipid peroxidation are almost the same as those formed from the a-tocopherol. The tocopheroxyl radicals of 7-and 6-tocopherols prefer to react with each other to form dimeric products that are still effective as antioxidants.

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Stability of pumpkin seed oil

Murkovic

Pfannhauser

2000

Eur. J. Lipid Sci. Technol.

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Autoxidation of methyl linolenate and methyl linoleate: The effect of α‐tocopherol

Cited by 75 publications

References 15 publications

Autoxidation of Conjugated Linoleic Acid Methyl Ester in the Presence of α‐Tocopherol: The Hydroperoxide Pathway

Autoxidation of Conjugated Linoleic Acid Methyl Ester in the Presence of α‐Tocopherol: The Hydroperoxide Pathway

Vitamin E: Mechanism of Its Antioxidant Activity.

Stability of pumpkin seed oil

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