Linoleate, oxidation

Liu, H. P. (1970b). Catalysts of lipid peroxidation in meats. 2. Linoleate oxidation catalyzed by tissue homogenates. 7. Food Sci. 35, 593-595. 

Haase, G. and Dunkley, W. L. 1969A. Ascorbic acid and copper in linoleate oxidation. I. Measurement of oxidation by ultraviolet spectrophotometry and the thiobarbituric acid test. J. Lipid Res. 10, 555-560. 

Haase, G. and Dunkley, W. L. 1969B. Ascorbic acid and copper in linoleate oxidation. 

As expected, the rate of oxidation was much faster at the higher temperature for both the adsorbed and the bulk samples. At 60°C ethyl linoleate oxidized faster when adsorbed on silica than when In bulk. On the other hand, oxidation of the bulk samples was faster at 180°C than that of the monolayers (Fig. 1). The faster oxidation of linoleate in monolayers at 60°C is probably due to the larger surface and the more facile exposure to oxygen. This, however, appears to be offset by the higher mobility of the substrate molecules and the faster radical transfer in bulk at the higher temperature. 

Figure 1. Rate of ethyl linoleate oxidation on silica and in bulk at 60 C and 180 C. (Reprinted with permission from ref. 39. Copyright 1988 American Oil Chemistry Society.)...

During the oxidation to form hydroperoxides, the natural cis,cis unsaturation of linoleate is converted to cis, trans and trans, trans isomers. Privett and co-workers (10) concluded that at least 90% of linoleate hydroperoxide preparations are conjugated. When the oxidation is conducted at 0°C the hydroperoxides are predominately cis, trans isomers, but room temperature oxidation produces a large amount of trans, trans unsaturation (11, 12). Ethyl or methyl linoleate hydroperoxides are relatively low melting and as a result purification by crystallization is difficult. Bailey and Barlow (13) prepared high melting p-phenylphenacyl linoleate, oxidized the ester in benzene solution, and isolated virtually pure hydroperoxide by crystallization. Infrared spectra of the 99% purity p-phenylphenacyl linoleate hydroperoxide correspond to a trans, trans conjugated isomer. 

In a study of 92 Finnish edible and nonedible plant materials, a total of 15 berry samples were screened for antioxidant activity (Kahkonen et al., 1999). The activity was compared with the total phenolic content of the samples. Inhibition of methyl linoleate oxidation was used as a measure of antioxidant activity of berry acetone extracts and total phenolics determined by the Folin-Ciocalteau method as GAE/g dry matter of extracts. Berry extracts were high in antioxidant activity among the... 

Grapes, wine and other berry products are acidic, and the anthocyanins are in the flavylium form. A hypothesis that the anthocyanins may be pH-transformed into their carbinol pseudo-base and quinoidal base, or the chalcone, in the intestine and blood system during digestion has been proposed by Lapidot et al. (1999). These compounds have been shown to have antioxidant activity and are also most likely absorbed from the gut into the blood system. The pseudo-base and the quinoidal base of malvidin and malvidin-3-glucoside remained as very effective antioxidants, both when tested by a linoleate-oxidizing assay and by a microsomal lipid peroxidation assay. 

Table 10.4 Partial structures of products of enzymic linoleate oxidation (C-8 to C-14 each structure represents two compounds)...

Free radicals may also undergo decomposition or scission reactions. Hexanal is a principal oxidation by-product of linoleate oxidation, one of the causes of the acrid smell during drying. 

Many of the classical mechanistic concepts of lipid oxidation were formulated on the basis of kinetic studies. Later developments in support of the general free radical mechanism of oxidation were based on structural studies of the primary hydroperoxide products. To simplify the kinetics of linoleate oxidation, the reactions were studied at early stages of oxidation, at low levels of conversion, at lower temperatures and in the presence of an appropriate initiator. Under these conditions, the propagation reactions producing hydroperoxides in high yields are emphasized, and the decomposition of hydroperoxides is minimized... 

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

Table 6.4. NMR and preparative HPLC analyses (rel %) of dienol isomers from hydroperoxides of methyl linoleate oxidized at different temperatures ...

Methyl linoleate Oxidized at 40°C in bulk or oU-in-water emulsions, monitor conjugated diene (234 nm), 72 hr oxidation Inappropriate substrate, one time point oxidation Kahkonen etcd. (1999, 2001, 2003)... 

Tappel, A. L. 1952. Linoleate oxidation catalyzed by hog muscle and adipose tissue extracts. Food Research 17, 550. 

Tne aim of present study was the search of NADPH-dependent MOX pathway of linoleate oxidation in pea seedlings. 

When ethyl linoleate (1.0 mM) was oxidized in distilled water, NaCl solution and cathodic solution under the presence of FeS04 (1.0 mM) and ascorbic acid (20.0 mM), it was easily oxidized in distilled water and in the NaCl solution with about a 60% loss of the substrate after only 24 h of oxidation (Figure 1, (A)). On the other hand, in the cathodic solution, it was very stable to oxidation, more than 90% of the substrate remaining unchanged after more than 100 h of oxidation (4). The antioxidative activity of the cathodic solution toward ethyl linoleate oxidation was also confirmed by measuring the increase in total... 

The properties of a lipoxidase from peas have been studied by Siddiqi and Tappel (660). Because their preparation possesses no fatty acid oxidase or fatty acid dehydrogenase activity and oxidizes linoleate but not oleate, it behaves like a true lipoxidase. The products of linoleate oxidation contain carbonyl groups although a correlation of the intenfflty of absorption with peroxide concentration suggests that the initial products of pea lipoxidase action are totally conjugated hydroperoxides. These appear to be very unstable under the conditions of formation, undergoing scission and polymerization to form aldehydes and trienes, detected by the presence of an absorption band at 280 m/t. 

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