Oxidation linoleic acid degradation

Multiply unsaturated linolenic and linoleic acid residues make triglycerides more vulnerable to oxidative degradation than oleic acid which is relatively stable. It is therefore desirable to hydrogenate the most unsaturated residues selectively without production of large quantities of stearic (fully saturated) acid. The stepwise reduction of an unsaturated oil may be visualized as ... 

Exposure of cardiolipin to oxygen gas resulted in a substantial loss of the lipid and most of the degradation products were hydroperoxide derivatives. Even though we have not done the comparative experiment, our experience tells us that cardiolipin is more sensitive to oxidative stress than free linoleic acid or trilinolein. Taking into account that mitochondria is the site where reactive oxygen species are often produced, we propose that peroxidation of cardiolipin may easily take place once the intracellular oxidative stress occurs. 

Unsaturated fatty acids usually contain a cis double bond at position 9 or 12—e.g., linoleic acid (18 2 9,12). As with saturated fatty acids, degradation in this case occurs via p-oxida-tion until the C-9-ds double bond is reached. Since enoyl-CoA hydratase only accepts substrates with trans double bonds, the corresponding enoyl-CoA is converted by an iso-merase from the ds-A, cis- A isomer into the trans-A, cis-A isomer [1]. Degradation by p-oxidation can now continue until a shortened trans-A, ds-A derivative occurs in the next cycle. This cannot be isomerized in the same way as before, and instead is reduced in an NADPH-dependent way to the trans-A compound [2]. After rearrangement by enoyl-CoA isomerase [1 ], degradation can finally be completed via normal p-oxidation. 

As shown in Table 34.4, oxidation and hydrogenation reactivity of a fatty acid, in free form or as part of a TAG, increases with the number of double bonds.34 Oxidation of fatty acids and TAG (aldehyde formation, breakdown into shorter chains, and crosslinking to form polymers) is initiated at double-bond sites. However, linoleic acid, Cl8 2 n-6, does not decompose into a mixture of C9, C3, and C6 compounds. Instead, as the molecule starts degrading, positions of the double bonds migrate and provide many opportunities for splitting. Over 250 different breakdown... 

It was generally assumed that oxidation products from oils and fats are poorly absorbed. Indeed, animals can be resistant to the effects of abused oils in their diet (29,30). Nevertheless, orally administered oxidized C-linoleic acid was incorporated into chylomicrons and very low density lipoprotein (VLDL) particles in rats. The absorbed oxidation products were subsequently identified as hydroxy fatty acids (31). Interestingly, dietary glutathione (GSH) reduced the absorption of peroxidized linoleate (32), presumably due to the activity of selenium-dependrait GSH peroxidase present in the intestinal epithelial cell (33). However, these absorption studies used free fatty adds, not triglycerides thus, they cannot address the role of pancreatic lipase and phospholipase. The fate of polymerized fatty adds has not been studied specifically. Whether the intestinal flora could degrade fliese polymers and hence allow their absorption remains to be seen. What is clear is that very little is known about the absorption of oxidized fat in animals and even less in humans. 

The metabolism of CLA in peroxisomes shows interesting aspects in terms of a possible role in the formation and concentration of eicosanoids, especially as effected in different pathologic conditions. By either competing with linoleic acid for desaturation and elongation, or via peroxisomal P-oxidation, CLA may interfere with eicosanoid production and degradation. It is likely however that its action may depend on its incorporation and thereby its concentration in different tissues. The different rate of peroxisomal P-oxidation between t 0,c 2 and c9,tll, may also explain the different biological activities of the two isomers. Also, enhanced fatty acid oxidation... 

Although less sensitive, this method is relatively precise. However, the test is not specific, and the results can be misleading because many primary and secondary oxidation products formTBA-reactive substances. This test is more sensitive with polyunsaturated fats containing three or more double bonds and not sensitive for the oxidation products of oleic and linoleic acids. The results overestimate the amount of Hpid oxidation, because extraneous materials in foods such as browning reaction products, protein and sugar degradation products interfere with the TBA test (see Chapter 5). 

Chen, J.F., Tai, C.-Y., Chen, Y.C., and Chen, B.H. (2001) Effects of Conjugated Linoleic Acid on the Degradation and Oxidation Stability of Model Lipids During Heating and Illumination, Food Chem. 72, 199-206. 

Linoleic acid is found in soybean, safflower and com oil, nuts, seeds, and some vegetables. a-Linolenic acid is found in flaxseeds, walnuts, and their oils canola oil is also a good source of a-linolenic acid. Edible oils rich in monounsaturated fatty acids are stable, flavorful, and nutritious for humans and animals. Oleic acid-rich soybean oil is more resistant to degradation by heat and oxidation and requires little... 

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