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Light-Induced Oxidation of Unsaturated Lipids as Sensitized by Flavins

Triplet-excited riboflavin (3RF*) was found by laser flash photolysis to be quenched by polyunsaturated fatty acid methyl esters in tert-butanol/water (7:3, v/v) in a second-order reaction with k ∼ 3.0 × 105 L mol−1 s−1 at 25 °C for methyl linoleate and 3.1 × 106 L mol−1 s−1, with ΔH ‡ = 22.6 kJ mol...

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Bibliographic Details
Published in:The journal of physical chemistry. B 2010-04, Vol.114 (16), p.5583-5593
Main Authors: Huvaere, Kevin, Cardoso, Daniel R, Homem-de-Mello, Paula, Westermann, Signe, Skibsted, Leif H
Format: Article
Language:English
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Summary:Triplet-excited riboflavin (3RF*) was found by laser flash photolysis to be quenched by polyunsaturated fatty acid methyl esters in tert-butanol/water (7:3, v/v) in a second-order reaction with k ∼ 3.0 × 105 L mol−1 s−1 at 25 °C for methyl linoleate and 3.1 × 106 L mol−1 s−1, with ΔH ‡ = 22.6 kJ mol−1 and ΔS ‡ = −62.3 J K−1 mol−1, for methyl linolenate in acetonitrile/water (8:2, v/v). For methyl oleate, k was 0 for electron transfer. Interaction of methyl esters with 3RF* is considered as initiation of the radical chain, which is subsequently propagated by combination reactions with residual oxygen. In this respect, carbon-centered and alkoxyl radicals were detected using the spin trapping technique in combination with electron paramagnetic resonance spectroscopy. Moreover, quenching of 3RF* yields, directly or indirectly, radical species which are capable of initiating oxidation in unsaturated fatty acid methyl esters. Still, deactivation of triplet-excited flavins by lipid derivatives was slower than by proteins (factor up to 104), which react preferentially by electron transfer. Depending on the reaction environment in biological systems (including food), protein radicals are expected to interfere in the mechanism of light-induced lipid oxidation.
ISSN:1520-6106
1520-5207
DOI:10.1021/jp9121744