Mechanisms for the autoxidation of polyunsaturated lipids

Porter, Ned A.

doi:10.1021/ar00129a001

Cited by 397 publications

(308 citation statements)

References 41 publications

Supporting

Mentioning

286

Contrasting

Unclassified

Order By: Relevance

“…With a high 1,4-cyclohexadiene concentration, the product mixtures became non-equivalent and reflected the stereochemistry of the particular diene precursor (Porter & Wujek 1984). The product distribution is, however, independent of oxygen pressure between 10 and 1000 mm Hg (Porter 1986). …”

Section: Hydroperoxide Formation During Autoxidation Of Nonconjugatedmentioning

confidence: 99%

“…Autoxidation of monoene and nonconjugated diene fatty acids has been extensively studied (reviewed in Swern 1961;Frankel 1985Frankel , 1998bPorter 1986;Chan & Coxon 1987;Gardner 1987Gardner , 1989Porter et al 1995). The overlapping stages of the autoxidation of polyunsaturated lipids are depicted in Fig.…”

Section: Autoxidation Of Monoene and Nonconjugated Diene Fatty Acidsmentioning

confidence: 99%

“…9-cis,12-trans-; 9-trans,12-cis-; and 9-trans,12-trans-octadecadienoic acid methyl ester (Porter & Wujek 1984). Isomeric distribution of the four hydroperoxides depends on the extent of oxidation, concentration of the fatty ester, and temperature (Porter 1986). The sum of total products formed from oxygen addition at C-9 is the same as products formed from oxygen addition at C-13.…”

Section: Hydroperoxide Formation During Autoxidation Of Nonconjugatedmentioning

confidence: 99%

“…-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). This mechanism also fails to account for the effects of hydrogen atom donors and the initial fatty ester concentration on product composition (Porter 1986).…”

Section: Figurementioning

confidence: 99%

“…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). This mechanism also fails to account for the effects of hydrogen atom donors and the initial fatty ester concentration on product composition (Porter 1986). …”

Section: Figurementioning

confidence: 99%

See 4 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

View full text Add to dashboard Cite

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...

show abstract

Section: Hydroperoxide Formation During Autoxidation Of Nonconjugatedmentioning

confidence: 99%

Section: Autoxidation Of Monoene and Nonconjugated Diene Fatty Acidsmentioning

confidence: 99%

Section: Hydroperoxide Formation During Autoxidation Of Nonconjugatedmentioning

confidence: 99%

Section: Figurementioning

confidence: 99%

Section: Figurementioning

confidence: 99%

See 3 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

View full text Add to dashboard Cite

show abstract

Lipid Oxidation: Theoretical Aspects

Schaich

2005

Bailey's Industrial Oil and Fat Products

128

121

View full text Add to dashboard Cite

Lipid oxidation has long been accepted as a classic free radical chain reaction mechanism with initiation, propagation, and termination stages. This view is not inaccurate, but it is incomplete. Initiation is generally treated as if it was spontaneous or random, but in reality, radical initiation is quite specific and varies with the source. Similarly, propagation is considered to involve only hydrogen abstraction where as internal cyclization, addition, scission, and disproportionation reactions are competitive or even dominant under some conditions, leading to variations in oxidation kinetics and, in particular, product mixes. Alternative reaction paths have been recognized for some time, but remain largely ignored in measurements of lipid oxidation. This chapter reviews initiation processes with a focus on differentiating rates, mechanisms, and specificity of radical formation; and it presents evidence for multiple propagation mechanisms that lead to different product mixes. Finally, a new integrated view of lipid oxidation is proposed to account for multiple propagation pathways. Practical application of this information should enable development of analyses that more accurately reflect the true extent of lipid oxidation and also antioxidant approaches that more effectively extend shelf life and preserve desirable food qualities.

show abstract

Lipid Oxidation: New Perspectives on an Old Reaction

Schaich

2020

Bailey's Industrial Oil and Fat Products

View full text Add to dashboard Cite

After lying in the doldrums during the no/low fat era, lipid oxidation is once again attracting intense interest for its effects on food quality, stability of personal care products, impairment of functional properties, and nutrition in foods, as well as toxic potential in tissues. Advanced analytical methods now detect lipid oxidation products with greater sensitivity and in more molecular detail, which provides greater power in elucidating reactions. At the same time, the comparative timing for the development of various products as well as the distribution of products under different conditions cannot be explained by the traditional free radical chain reaction driven solely by hydrogen abstractions. The previous edition of this article provided arguments for considering a number of alternate reactions of peroxyl and alkoxyl radicals that compete with hydrogen abstraction and alter outcomes of lipid oxidation, and then integrated these alternate pathways into a coherent reaction scheme that shows there interdependence and interrelationships. This article builds on that base, provides evidence for epoxides a product equal to hydroperoxides in importance, and introduces thinking about pathway changes induced by solvents, oxidation catalysts, and other environmental conditions.

show abstract

Mechanisms for the autoxidation of polyunsaturated lipids

Cited by 397 publications

References 41 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

Lipid Oxidation: Theoretical Aspects

Lipid Oxidation: New Perspectives on an Old Reaction

Contact Info

Product

Resources

About