Thermal oxidation methyl linoleate

The comparison of the antioxidant potency of hydroxytyrosol, tyrosol, oleuropein with respect to vitamin E and BHT and the synergistic effect with vitamin E were studied in thermal initiated oxidation of methyl linoleate in the presence of azo-compounds, in heptanol or propanohwater. The activity of the phenols was expressed as increase of induction period and extent of reaction inhibition [47]. The azo compounds initiated oxidation is a free radical chain process. Confirming the results from a previous study [43], this study showed that hydroxytyrosol and oleuropein were much more effective than BHT and vitamin E in extending the induction period. Tyrosol was devoid of activity and no synergistic effect on the preservation of methyl linoleate was foxmd when vitamin E was used together with tyrosol. 

Oleuropein appears to interfere with some biological processes such as lipoprotein oxidation, platelet aggregation, platelet and leukocyte eicosanoid production and cardiovascular control too. As previously described, oleuropein and hydroxy-tyrosol are characterised by a catechol moiety that appears to be needed for their scavenger and antioxidant activities. In fact, it was demonstrated that these compounds prevent thermally initiated autoxidation of methyl linoleate in homogenous solutions [56], protect LDL from oxidation [57] and inhibit production of... 

Frankel, E.N., Neff, W.E., Selke, E. and Weisleder, D. Photosensitized oxidation of methyl linoleate. Secondary and volatile thermal decomposition products. Lipids 17, 11-18 (1982). 

In mixtures, 2-nonenal and 2,4-heptadienal are more rapidly oxidized than methyl linoleate and linolenate, and these fatty esters are more readily oxidized than nonanal. Therefore, during the more advanced stages of oxidation the saturated aldehydes accumulate and the unsaturated aldehydes are further oxidized to lower aldehydes and dialdehydes. At elevated temperatures, saturated aldehydes and dialdehydes are further oxidized into mono- and dibasic acids. The formation of low molecular weight volatile acids is used as a measure of thermal oxidation of fats, and is the basis for detection in some high temperature stability tests (Chapter 7). 

Methyl linoleate Dodecane solution oxidized at 110°C with Oj hubbhng, monitor residual linoleate Not sensitive, significant thermal decomposition of hydroperoxides, favors lipophilic antioxidants, inappropriate substrate, not sensitive or specific Cuvelier et al. (1990,1992)... 

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