Autoxidation arachidonic acid

In meat, oct-l-en-3-ol and oct-l-en-3-one are produced analogously by decomposition of 12-hydroperoxy-5,8,10,14-eico-satetraenoic acid, which is one of the arachidonic acid autoxidation products. When this decomposition occurs, it may cause an off-flavour. 

Heat treatment of eggs by cooking and frying creates a variety of other volatile compounds, more from egg yolk than from egg white. The main volatile components are aldehydes, alcohols, free fatty acids, esters and other compounds. Those occurring in the highest quantities are (2Z,4Z)- and (2Z,4E)-deca-2,4-dienals, (Z)-oct-2-enal, nonanal, hexanal, phenylacetaldehyde and hexyl butyrate. Egg white odour resembles (2E,4Z,7Z)-2,4,7-tridecatrienal, which arises as a product of arachidonic acid autoxidation (see Section 3.8.1.12.1). Its odour threshold was estimated to be 0.07ng/1 air. Sulfane and ammonia are also important protein degradation products. 

Second-derivative spectrophotometry has been used to monitor the time-dependent production of cis,tmns-(Xmax 242 nm) and trans, tram- (Xmax 232 nm) diene conjugates of microsomal PUFAs following the exposure of rats to carbon tetrachloride (CCU) (Corongui et al., 1986). These signals have been postulated to be derived from mixtures of peroxidized substrates. Previous studies using chemical model systems have established that autoxidation of linolenic or arachidonic acid results in the production of cis, trans- and tmns, trawr-conjugated diene... 

Peroxyl radicals are the species that propagate autoxidation of the unsaturated fatty acid residues of phospholipids (50). In addition, peroxyl radicals are intermediates in the metabolism of certain drugs such as phenylbutazone (51). Epoxidation of BP-7,8-dihydrodiol has been detected during lipid peroxidation induced in rat liver microsomes by ascorbate or NADPH and during the peroxidatic oxidation of phenylbutazone (52,53). These findings suggest that peroxyl radical-mediated epoxidation of BP-7,8-dihydrodiol is general and may serve as the prototype for similar epoxidations of other olefins in a variety of biochemical systems. In addition, peroxyl radical-dependent epoxidation of BP-7,8-dihydrodiol exhibits the same stereochemistry as the arachidonic acid-stimulated epoxidation by ram seminal vesicle microsomes. This not only provides additional... 

Figure 111 Overview of the complex autoxidation pathways of arachidonic acid.

Blank, I., Lin, J., Arce Vera, F, Welti, D.H., Fay, L.B. Identification of potent odorants formed by autoxidation of arachidonic acid structure elucidation and synthesis of ( ,Z,Z)-2,4,7-tiidecatrie-nal. J. Agric. Food Chem. 2001, 42, 2959-2965. 

Figure 5.1 Autoxidation of arachidonic acid and fi-scission of a bicydic endoperoxide to generate MDA. (a) Following initial hydrogen abstraction from C7 on arachidonic acid, an inner peroxyl radical forms leading to the...

At least one vitamin E deficiency sign is known to occur only when a certain class of polyunsaturated fatty acids is furnished in the diet. For instance, encephalomalacia in chicks appears when the diet contains linoleic or arachidonic acid, but not when the diet is fat free or contains linolenic acid. It is possible that encephalomalacia is due to the lack of an antioxidant effect, but attempts to demonstrate autoxidation products in the affected tissue have not been successful. 

Porter et al, in two significant papers, have offered a unified mechanism of polyene autoxidation. This seeks to account for the various products obtained particularly from linoleic acid and from arachidonic acid (six hydroperoxides with one E double bond, six hydroperoxides with two E double bonds, and four hydroperoxy cyclic peroxides). The serial cyclisation of peroxy radicals observed with (51) is interesting in that the 1,5-diene units give rise to six-membered cyclic peroxides whilst the 1,4-diene units in natural... 

Porter NA, Wolf RA, Yarbro EM and Weenen H Ihe autoxidation of arachidonic acid formation of the proposed SRS-A intermediate. Bloakm Blophy Ro6 Commun 89 1058-1064, 1979. 

Polyunsaturated fatty acids, such as linoleic acid, a-linolenic acid, arachidonic acid and docosahexaenoic acid have characteristic physiological activities and are essential for human health. However, when these polyunsaturated fatty acids are exposed to oxygen, they are oxidized to form conqjlex oxidation products. Since autoxidation of unsaturated fatty acids decreases their biological availability in foods and produces offensive odors and... 

The relative rates of autoxidation of different unsaturated fatty acids and esters were compared on the basis of oxygen absorption measurements (Table 1.1). In neat systems without added initiator, linoleate was 40 times more reactive than oleate, linolenate was 2.4 times more reactive than linoleate, and arachidonate was 2 times more reactive than linolenate. The oxidizability of polyunsaturated fatty acid (PUFA) esters was also compared on the basis of oxygen uptake measured kinetically by the induction period method described above, in solution in the presence of azo initiators. The oxidizability of 18 2,18 3,20 4, and 22 6 was linearly related to the number of bis-aUyUc positions present in the fatty esters. From this relationship, the oxidizability of each PUFA was increased approximately two fold for each active bis-allylic methylene group. Thus, the oxidizability of 22 6 was 5 times greater than that of 18 2. 

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