Natural polyphenols as chain-breaking antioxidants during methyl linoleate peroxidation

• Published in: European journal of lipid science and technology Vol. 112; no. 8; pp. 887 - 893
• Main Authors: Tichonov, Ivan, Roginsky, Vitaly, Pliss, Evgeny
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley-VCH Verlag 01.08.2010; WILEY-VCH Verlag; WILEY‐VCH Verlag
• Subjects: Antioxidant activity; Antioxidants; Lipid peroxidation; Methyl linoleate; Polyphenols
• ISSN: 1438-7697; 1438-9312
• DOI: 10.1002/ejlt.200900282

A technique based on monitoring oxygen consumption was applied to study 11 natural and model polyphenols (PP, QH₂) as well as four typical monophenolics as a chain-breaking antioxidant during the controlled chain oxidation of methyl linoleate (ML) in bulk at 37°C. The antioxidant activities of QH₂ were characterized by two parameters: the rate constant k₁ for reaction of QH₂ with the peroxy radical ${\rm LO}_{2}^{{\bf .}} $: (i) QH₂ + ${\rm LO}_{2}^{{\bf .}} $ [rightward arrow] ${\rm QH}^{{\bf .}} $ + LOOH and the stoichiometric factor of inhibition, f, which shows how many kinetic chains may be terminated by one molecule of QH₂. The rate constant k₁ were reduced significantly by factor of 4 -28 as compared to these determined during the oxidation of styrene in bulk; the effect was typically more pronounced for catechol derivatives than for pyrogallol derivatives. At the same time, f for QH₂ was found to be close to two independent of the number of active OH groups, similar to that determined earlier during the inhibited oxidation of styrene. The formation of H bond between OH group of QH₂ and carboxyl group of ML is suggested as a reason for reducing effect of ML on k₁.Practical applications: This work reports rate constants for the reaction of lipid peroxyl radical with phenolics and stoichiometric coefficient of inhibition, which characterize the antioxidant activity (AOA) of 15 natural and model PP, QH₂ during the controlled peroxidation of ML. The reactivity of PP, QH₂ during the oxidation of ML is routinely lower than the reactivity during the oxidation of non-polar model hydrocarbons. This information may be useful to estimate the AOA of natural PP, QH₂ in real systems of practical significance including plant oils, fats, food-stuffs, biological objects, and similar.