Unsaturated fatty acids lipid oxidation

Rebrovic, L., and F.D. Gunstone, Oxidative Cleavage of Unsaturated Fatty Acids, Lipid Technol. 78 135-137 (1996). 

Figure 1. A schematic of die potential reaction pathways that intact the oxidative deterioration of foods. Mn and Mn " are transition metals in their reduced and oxidized states RH, ROOH and AOH are an unsaturated fatty acid, lipid hydroperoxide and chain breaking antioxidant and R , RO ROO are alkyl, alkoxyl and peroxyl radicals, and Oj and LOX are singlet oxygen and lipoxygenase, respectively.

L Rebrovic and F.D. Gunstone, Oxidative cleavage of unsaturated fatty acids, Lipid Technology, 1996, 8, 135-137. 

M.J. Caupin, Lipid Technologies and Applications, (ed. F.D. Gunstone and F.B. Padley) Marcel Dekker, New York, 1997, pp.787-795. L.Rebrovic and F.D. Gunstone, Oxidative cleavage of unsaturated fatty acids. Lipid Technology, 1996, 8, 135-137. 

Lipids are hydrolyzed by moisture and heat into free fatty acids, though hydrolytic enzymes may be deactivated by extrusion. Also, unsaturated fatty acids may imdergo oxidative rancidity (Camire et al., 1990). 

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... 

It should be noted that Reaction (4) is not a one-stage process.) Both free radical N02 and highly reactive peroxynitrite are the initiators of lipid peroxidation although the elementary stages of initiation by these compounds are not fully understood. (Crow et al. [45] suggested that trans-ONOO is protonated into trans peroxynitrous acid, which is isomerized into the unstable cis form. The latter is easily decomposed to form hydroxyl radical.) Another possible mechanism of prooxidant activity of nitric oxide is the modification of unsaturated fatty acids and lipids through the formation of active nitrated lipid derivatives. 

It is commonly known that lipids, carbohydrates, and glycolipids are present in the Golgi apparatus (27). The determination of the components that react with the ZIO mixture was carried out by removing each component from tissues before incubation in the ZIO mixture. After lipid extraction by acetone (14), chloroform-methanol (15), or propylene oxide (27), no osmium-zinc precipitates could be detected in structures that normally reacted with ZIO. Blumcke et al. (15) summarized the nature of the lipids that react with the ZIO mixture as follows lipids and lipoproteins of cell membranes, neutral fat droplets (41), and lipid globules of type II pneumocytes and alveolar macrophages were, however, not as electron dense as the normally reactive lamellae containing highly unsaturated fatty acids. 

Flavor is one of the major characteristics that restricts the use of legume flours and proteins in foods. Processing of soybeans, peas and other legumes often results in a wide variety of volatile compounds that contribute flavor notes, such as grassy, beany and rancid flavors. Many of the objectionable flavors come from oxidative deterioration of the unsaturated lipids. The lipoxygenase-catalyzed conversion of unsaturated fatty acids to hydroperoxides, followed by their degradation to volatile and non-volatile compounds, has been identified as one of the important sources of flavor and aroma components of fruits and vegetables. An enzyme-active system, such as raw pea flour, may have most of the necessary enzymes to produce short chain carbonyl compounds. 

UV-induced ROS are extremely toxic to cells by causing oxidative damage to all biomolecules (Sies 1991). For instance, lipids, which are major compounds of all biological membranes, may be destroyed by ROS. After a first initiation reaction an unsaturated fatty acid is converted to a peroxyl radical, which in turn attacks another unsaturated fatty acid finally leading to free radical cascades. This photochemical peroxidation of unsaturated fatty acids may be particularly damaging for membrane structure and function (Bischof et al 2006a). 

In lipid metabolism, ds-trans isomerism is particularly important. For example, double bonds in natural fatty acids (see p.48) usually have a as configuration. By contrast, unsaturated intermediates of p oxidation have a trans configuration. This makes the breakdown of unsaturated fatty acids more complicated (see p. 166). Light-induced cis-trans isomerization of retinal is of central importance in the visual cycle (see p.358). 

Fatty acid hydroperoxides can be separated from each other and other lipids by MEKC followed by FLD according to equation 34 with 106a, using as catalyst microperoxidase-11 immobilized on the wall of a small capillary coupled at the end of the electrophoresis track. MEKC with DA-UVD can be applied for separation of unsaturated fatty acids from the mixture of hydroperoxides obtained on oxidation with 102 . ... 

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