Fatty acids autoxidation

Porter NA, Lehman LS, Weber BA, Smith KJ (1981) Unified mechanism for polyunsaturated fatty acid autoxidation. Competition of peroxy radical hydrogen atom abstraction, p-scission, and cyclization. J Am Chem Soc 103 6447-6455... 

Cooking oils contain esters of polyunsaturated fatty acids. You need not worry now about what esters are we will discuss them in Chapter 14. The important point here is that all vegetable oils contain fatty acids with long hydrocarbon chains, many of which have one or more carbon-carbon double bonds. (See Problem 4.44 for the structures of three of these fatty acids.) Autoxidation takes place at a carbon ac acent to a double bond— that is, at an allylic carbon. 

Autoxida.tlon. The autoxidation (7) of unsaturated fatty acids in phosphoHpids is similar to that of free acids. Primary products are diene hydroperoxides formed in a free-radical process. 

Figure 1.7 Typical zero-order and corresponding second-derivative electronic absorption spectra of ethanol-reconstituted lipid/chloroform extracts of autoxidized model polyunsaturated fatty-acid compounds and inflammatory synovial fluid obtained after (1) reduction with NaBH4 and (2) dehydration with alcoholic H2S04- (a) Methyl linoleate subsequent to autoxidation in air at ambient temperature for a period of 72 h (—), or exposure to a Fenton reaction system containing EDTA (5.75 x 10 mol/dm ), H2O2 (1.14 X 10 mol/dm ) and Fe(ll) (5.75 x IO mol/dm ) as an aqueous suspension (—) (b) as (a) but with methyl linolenate (c) untreated rheumatoid knee-joint synovial fluid.

Dahle, L.K., Hill, E.G. and HoUman, RT. (1962). The TBA reaction and the autoxidation of polyunsaturated fatty acid methyl esters. Arch. Biochem. 98, 253-259. 

Autoxidation of unsaturated fatty acids is well known. Modifications of the extraction and separation procedures were made to investigate the possibility that these oxygenated fatty acids (OFAs) arise as artefacts. When exposure to light and air were minimized, no changes were noted in TLC and HPLC. 

Are used to accelerate autoxidation and hardening of oxidisable coatings. Metal soaps, used as paint driers, can be made from a variety of carboxylic acids, including the commercially important naphthenic and 2-ethyl hexanoic acids, tall oil, fatty acids, neodecanoic and isononanoic acid. Cobalt is unquestionably the most active drier metal available. Metallic driers such as cobalt naphthenate or octoate and zinc salts can interact with UVAs, HALS, or AOs. 

As a reasonable biogenetie pathway for the enzymatic conversion of the polyunsaturated fatty acid 3 into the bicyclic peroxide 4, the free radical mechanism in Equation 3 was postulated 9). That such a free radical process is a viable mechanism has been indicated by model studies in which prostaglandin-like products were obtained from the autoxidation of methyl linolenate 10> and from the treatment of unsaturated lipid hydroperoxides with free radical initiators U). 

The photobleaching of P-carotene by fluorescent light in fatty acid ester solutions showed an autoxidation kinetic profile with the rate of degradation of P-carotene in the order laurate > oleate > linoleate (Carnevale et al. 1979). The presence of a radical scavenger retarded the autoxidation, thus leading to the view that protection against autoxidation is built into the system by the unsaturation in the fatty acid. 

Yin, H. and Porter, N.A. (2005) Newinsights regarding the autoxidation of polyunsaturated fatty acids. Antioxidants el Redox Signaling, 7, 170—184. 

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... 

In plant tissues, various enzymes convert the hydroperoxides produced by LOX to other products, some of which are important as flavor compounds. These enzymes include hydroperoxide lyase, which catalyzes the formation of aldehydes and oxo acids hydroperoxide-dependent peroxygenase and epoxygenase, which catalyze the formation of epoxy and hydroxy fatty acids, and hydroperoxide isomerase, which catalyzes the formation of epoxyhydroxy fatty acids and trihydroxy fatty acids. LOX produces flavor volatiles similar to those produced during autoxidation, although the relative proportions of the products may vary widely, depending on the specificity of the enzyme and the reaction conditions. 

Emulsion oxidation of alkylaromatic compounds appeared to be more efficient for the production of hydroperoxides. The first paper devoted to emulsion oxidation of cumene appeared in 1950 [1], The kinetics of emulsion oxidation of cumene was intensely studied by Kucher et al. [2-16], Autoxidation of cumene in the bulk and emulsion occurs with an induction period and autoacceleration. The simple addition of water inhibits the reaction [6], However, the addition of an aqueous solution of Na2C03 or NaOH in combination with vigorous agitation of this system accelerates the oxidation process [1-17]. The addition of an aqueous phase accelerates the oxidation and withdrawal of water retards it [6]. The addition of surfactants such as salts of fatty acids accelerates the oxidation of cumene in emulsion [3], The higher the surfactant concentration the faster the cumene autoxidation in emulsion [17]. The rates of cumene emulsion oxidation after an induction period are given below (T = 353 K, [RH] [H20] = 2 3 (v/v), p02 = 98 kPa [17]). 

The secretion of the red hartebeest is characterized by its high aldehyde content. Of an estimated 100 detectable constituents, 25 are saturated and unsaturated aliphatic aldehydes [138]. Because the aldehydes are highly susceptible to autoxidation, the secretion could therefore only be used for shortterm territorial marking. On the other hand, the conversion of the aldehydes to carboxylic acids could also be transmitting information with a date stamp . In this regard, it is debatable whether fatty acids, which are almost ubiquitous in the animal world, really are such major carriers of semiochemical information in all of the many species in which they are purported to fulfill this role. 

Cosgrove, J. P., Church, D. F., and Pryor, W. A., 1987, The kinetics ofthe autoxidation of polyunsaturated fatty acids, Lipids 22 299-304. 

Oxygen-mediated autoxidation can occur with unsaturated acid components of fats and oils, which are esters of fatty acids with glycerol (see Box 7.16). This leads initially to hydroperoxides that decompose further to produce... 

Volatile compounds formed by anabolic or catabolic pathways include fatty acid derivatives, terpenes and phenolics. In contrast, volatile compounds formed during tissue damage are typically formed through enzymatic degradation and/ or autoxidation reactions of primary and/or secondary metabolites and includes lipids, amino acids, glucosinolates, terpenoids and phenolics. 

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