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Measurement of oxidation of polyunsaturated fatty acids by spectrophotometric assay of conjugated derivatives
Author(s) -
Fishwick Michael J.,
Swoboda Peter A. T.
Publication year - 1977
Publication title -
journal of the science of food and agriculture
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.782
H-Index - 142
eISSN - 1097-0010
pISSN - 0022-5142
DOI - 10.1002/jsfa.2740280412
Subject(s) - absorbance , polyunsaturated fatty acid , linolenate , conjugated system , chemistry , chromophore , fatty acid , sodium borohydride , organic chemistry , oxidative phosphorylation , chromatography , biochemistry , catalysis , polymer
A procedure has been developed for measuring the extent of oxidative deterioration of polyunsaturated fatty acids. The method is based on the conversion of fatty acid hydroperoxides and compounds derived from them, oxodienes and hydroxydienes, to conjugated fatty acids with strongly chromophoric triene and tetraene structures. This is done in two steps in which reduction with sodium borohydride is followed by dehydration under acid conditions; the chromophores produced are measured by absorbance in the ultraviolet. The method has been investigated using methyl linoleate and methyl linolenate as model compounds. Dienoic fatty acid oxidation products give rise to a conjugated triene chromophore whilst the more polyunsaturated fatty acids form a conjugated tetraene chromophore. The sum of absorbance changes at 268 and 301 nm measure the degree of oxidation. The ratio of absorbance change at 301 nm divided by that at 268 nm varies from zero for a pure triene to 2.8 for a pure tetraene and is a measure of the type of polyunsaturated fatty acid being oxidised. The concentration of oxodiene component present in the original mixture may be estimated separately by the decrease in the 275 nm region during the reduction step.