Differences in oxidation kinetics between conjugated and non-conjugated methyl linoleate.
The oxidation kinetics of conjugated methyl linoleate was compared with that of non-conjugated methyl linoleate under mild oxidation conditions (30 degrees C in the dark). Samples of methyl 9-cis,11-trans-linoleate, methyl 10-trans,12-cis linoleate and methyl 9-cis,12-cis linoleate were assayed separately and in mixtures. For comparative purposes, methyl alpha-linolenate and methyl oleate were also used. Two complementary analytical approaches were selected to monitor the progress of oxidation, (1) the traditional follow-up of residual substrate by gas liquid chromatography, and (2) an analytical procedure by high-performance size-exclusion chromatography (HPSEC) for direct measurement of the oxidation compounds formed. The HPSEC method enabled us to quantitate oxidized monomers, dimers and polymers concomitantly in a rapid and direct analysis. Results showed that conjugated methyl linoleate samples oxidized later than their non-conjugated counterparts, and showed a very different oxidation pattern. Thus, formation of oxidized monomers was negligible and the first and major compounds formed were polymerization products. Also, under the conditions used, non-conjugated and conjugated methyl linoleate samples in 1:1 mixtures led to decreased oxidation rate of non-conjugated methyl linoleate and increased oxidation rate of conjugated methyl linoleate. This study supports the view that oxidation kinetics of conjugated dienes differ substantially from that of methylene-interrupted dienes.
Luna
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P
Instituto del Frío (CSIC), José Antonio Novais, 10, 28040, Madrid, Spain. pluna@if.csic.es
de la Fuente
M A
MA
Salvador
D
D
Márquez-Ruiz
G
G
D002849:Chromatography, Gas; D002851:Chromatography, High Pressure Liquid; D007700:Kinetics; D008041:Linoleic Acids / Q000737:chemistry*; D044243:Linoleic Acids, Conjugated / Q000737:chemistry*; D010084:Oxidation-Reduction
D008041:Linoleic Acids; D044243:Linoleic Acids, Conjugated; C005575:methyl linoleate