Autoxidation linoleic acid

This mechanism illustrated by linoleic acid autoxidation is, however, typical for virtually all autoxidation processes. The general rate law based on stationary state kinetics is... 

Anthocyanin pigments, such as cyanidin 3-glucoside and its aglycone cyanidin, showed antioxidant activity in four different lipid oxidation sytems the linoleic acid autoxidation system, the egg lecithin liposomes system, the rabbit erythrocyte membrane system and the rat liver microsomal system [94]. Anthocyanins from eggplant [127], grape [91] and red beans [128], also show significant antioxidant activity. 

Figure 3.30 Minor primary products of linoleic acid autoxidation.

Figure 10.7 Autoxidation of a linoleic acid ester. In step 1 the reaction is initiated by the attack of a radical on one of the hydrogen atoms of the -CH2-group between the two double bonds this hydrogen abstraction produces a radical that is a resonance hybrid. In step 2 this radical reacts with oxygen in the first of two chain-propagating steps to produce an oxygen-containing radical, which in step 3 can abstract a hydrogen from another molecule of the linoleic ester (Lin-H). The result of this second chain-propagating step is the formation of a hydroperoxide and a radical (Lin ) that can bring about a repetition of step 2.

Dopamine, a strong water-soluble antioxidant, was identified in banana fruit (Musa cavendishii) by Kanazawa and Sakakibara (2000). Banana fruit contained high levels in the pulp and peel 2.5-10 mg/100 g and 80-560 mg/100 g, respectively. A banana water extract was reported to suppress the autoxidation of linoleic acid by 65-70% after a 5-day incubation in an emulsion system, as determined from peroxide value and thiobarbituric acid reactivity (Kanazawa and Sakakibara 2000). 

The effects of flavonoids on in vitro and in vivo lipid peroxidation have been thoroughly studied [123]. Torel et al. [124] found that the inhibitory effects of flavonoids on autoxidation of linoleic acid increased in the order fustin < catechin < quercetin < rutin = luteolin < kaempferol < morin. Robak and Gryglewski [109] determined /50 values for the inhibition of ascorbate-stimulated lipid peroxidation of boiled rat liver microsomes. All the flavonoids studied were very effective inhibitors of lipid peroxidation in model system, with I50 values changing from 1.4 pmol l-1 for myricetin to 71.9 pmol I 1 for rutin. However, as seen below, these /50 values differed significantly from those determined in other in vitro systems. Terao et al. [125] described the protective effect of epicatechin, epicatechin gallate, and quercetin on lipid peroxidation of phospholipid bilayers. 

Hill, R. D., Van Leeuwen, V. and Wilkinson, R. A. 1977. Some factors influencing the autoxidation of milks rich in linoleic acid. N.Z. J. Dairy Sci. Technol. 12, 69-77. 

Sidhu, G. S., Brown, M. A. and Johnson, A. R. 1975. Autoxidation in milk rich in linoleic acid. I. An objective method for measuring autoxidation and evaluating antioxidants. J. Dairy Res. 42, 185-195. 

Because autoxidation products of linoleic acid would confound the results, it is preferable to isolate linoleic acid by either TLC, HPLC, or silicic acid column chromatography before using it in the reaction. 

A small amount of hydroperoxides arising from autoxidation is not a major concern as it shortens the observed lag phase. Because of the insidious nature of autoxidation, the condition of the linoleic acid sample used to prepare the solution should be known. It is recommended that afresh sealed vial from the supplier is used. 

Aqueous solutions of linoleic acid tend to autoxidize more readily. 

Ullrich, F. and Grosch, W. 1987. Identification of the most intense volatile flavour compounds formed during autoxidation of linoleic acid. Z. Lebensm. Unters. Forsch. A. 184 277-282. 

Furimsky E, Howard JA, Selwyn J (1980) Absolute rate constants for hydrocarbon autoxidation. 28. A low temperature kinetic electron spin resonance study of the self- reactions of isopropylperoxy and related secondary alkylperoxy radicals in solution. Can J Chem 58 677-680 Gebicki JM, Allen AO (1969) Relationship between critical micelle concentration and rate of radiolysis of aqueous sodium linolenate. J Phys Chem 73 2443-2445 Gebicki JM, Bielski BHJ (1981) Comparison of the capacities of the perhydroxyl and the superoxide radicals to initiate chain oxidation of linoleic acid. J Am Chem Soc 103 7020-7022 Gilbert BC, Holmes RGG, Laue HAH, Norman ROC (1976) Electron spin resonance studies, part L. Reactions of alkoxyl radicals generated from alkylhydroperoxidesand titanium(lll) ion in aqueous solution. J Chem Soc Perkin Trans 2 1047-1052... 

Freyaldenhoven MA, Lehman PA, Franz TJ, Lloyd RV, Samokyszyn YM. Retinoic acid-dependent stimulation of 2,2 -azobis(2-amidinopropane)-initiated autoxidation of linoleic acid in sodium dodecyl sulfate micelles a novel prooxidant effect of retinoic acid. Chem Res Toxicol 1998 11 102-110. 

It is interesting to consider the concentrations of free radicals that result from lipid hydroperoxides in an in vitro model system. For example, my group has been studying the autoxidation of linoleic acid in SDS micelles at 37°C. We initiate the autoxidation by the decomposition of an initiator, as shown in Equation 3. 

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