Methyl linoleate oxidation products

Figure 4.24. Volatile decomposition products from hydroperoxy epidioxides of methyl linoleate oxidized with singlet oxygen (Frankel etal, 1982).

Yamauchi, R. and K. Kato (1998). Products formed by peroxyl radical-mediated oxidation of canthaxanthin in benzene and in methyl linoleate. J. Agric. Food Chem. 46(12) 5066-5071. 

Yamauchi, R. et al. (1998). Oxidation products of beta-carotene during the peroxidation of methyl linoleate in the bulk phase. Biosci. Biotechnol. Biochem. 62(7) 1301-1306. 

Horvat, R.J., McFadden, W.H., Hawkins, N.G., Black, D.R., Lane, W.G., Teeter, R.M. 1965. Volatile products from mild oxidation of methyl linoleate. Analysis by combined mass spectrometry-gas chromatography. J. Am. Oil Chem. Soc. 42, 1112-1115. 

Yamauchi, R., Matsushita, S. 1977. Quenching effect of tocopherols on methyl linoleate photooxidation and their oxidation products. Agric. Biol. Chem. 41, 1425-1430. 

Ha, K.-H. and Igarashi, O. 1990. The Oxidation Products from Two Kinds of Tocopherols Co-Existing in Autoxidation System of Methyl Linoleate. J. Nutr. Sci. Vitaminol. 36 411—421. 

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... 

Autoxidation and photo-oxygenation are two aspects of the non-enzymic reaction between oxygen and unsaturated fatty acids. The enzymic reactions are discussed in Section 10.3. Oxidation of lipids during storage and handling, involving complex substrates and ill-defined reaction conditions, proved difficult to understand. This difficulty is enhanced by the fact that the primary oxidation products are labile and readily converted to secondary oxidation products of several kinds. Understanding of these processes has come from studies of simpler substrates such as methyl oleate or methyl linoleate under clearly defined reaction conditions. 

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). 

Figure 4.12. Cleavage products from 9- and 13-hydroperoxides formed by autoxidation of methyl linoleate (Frankel etaL, 1981). Relative percent values shown in parentheses are for autoxidation and photosensitized oxidation respectively ( ) = not detected.

Volatile decomposition products from autoxidized linoleic acid and methyl linoleate were characterized for their intense aroma and flavor impact by capillary gas chromatography-olfactometry. This technique involves sniffing the gas chromatograph effluent after stepwise dilution of the volatile extract. The most intense volatiles included hexanal, c/ -2-octenal, /ra. s-2-nonenal, l-octene-3-one, 3-octene-2-one and trans-l-ociQmX (Table 4.2). This analytical approach does not, however, consider the effects of complex interactions of volatiles occurring in mixtures produced in oxidized food lipids. 

As with oleate and linoleate, some volatile decomposition compounds are formed from linolenate hydroperoxides that cannot be explained by the classical A and B cleavage mechanisms, including acetaldehyde, butanal, 2-butyl furan, methyl heptanoate, 4,5-epoxyhepta-2-enal, methyl nonanoate, methyl 8-oxooctanoate, and methyl lO-oxo-8-decenoate. Some of these minor volatile oxidation products can be attributed to further oxidation of unsaturated aldehydes. Other factors contribute to the complexity of volatile products formed from hydroperoxides, including temperature of oxidation, metal catalysts, stability of volatile products and competing secondary reactions including dimerization, cyclization, epoxidation and dihydroperoxidation (Section E). 

The hydroperoxy epidioxides formed from photosensitized oxidized methyl linoleate are important precursors of volatile compounds, which are similar to those formed from the corresponding monohydroperoxides. Thus, 13-hydroperoxy-10,12-epidioxy-tra 5 -8-enoic acid produces hexanal and methyl lO-oxo-8-decenoate as major volatiles (Figure 4.24). The 9-hydroperoxy-10,12-epidioxy-rrans-13-enoic acid produces 2-heptenal and methyl 9-oxononanoate. Other minor volatile products include two volatiles common to those formed from the monohydroperoxides, pentane and methyl octanoate, and two that are unique, 2-heptanone and 3-octene-2-one. The hydroperoxy epidioxides formed from autoxidized methyl linolenate produce the volatiles expected from the cleavage reactions of linolenate hydroperoxides, and significant amounts of the unique compound 3,5-octadiene-2-one. This vinyl ketone has a low threshold value or minimum detectable level, and may contribute to the flavor impact of fats containing oxidized linolenate (Chapter 5). 

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