Linoleic acid oxidation rate

The data in Table 1 show that when the oxidation of dilinolein, methyl linoleate, and monolinolein was followed in the presence of linoleic acid, their rates of oxidation were reduced relative to that of linoleic acid (Table 1, entries 1-3). 

The major fatty acids present in plant-derived fatty substances are oleic acid (9-octadecenoic, C18 l), linoleic acid (9,12-octadecadienoic, C18 2) and the conjugated isomers thereof and linolenic acid (9,12,15-octadecatrienoic, C18 3) (Scheme 31.1). Their rates of oxygen absorption are 100 40 1, respectively, hence partial hydrogenation with consequent lowering of the iodine number would lead to a significant increase in oxidative stabihty, particularly when C18 3 is reduced. 

The unsaturated fatty acid oxidation proceeds at a rate higher over that for saturated acids. For example, if the oxidation rate for saturated stearic acid is taken as a reference value, the oxidation rate for oleic acid is i 1 times, linolic acid, 114 times, linolenic acid, 170 times, and arachidonic acid, nearly 200 times as high as that for stearic acid. 

Fluie RE, Padmaja S (1993) The reaction of NO with superoxide. Free Rad ResCommun 18 195-199 FluieRE, Brault D, Neta P (1987) Rate constants for one-electron oxidation by theCFjCV, CCI3O2, and CBr302 radicals in aqueous solutions. Chem Biol Interact 62 227-235 Inouye S (1984) Site-specific cleavage of double-strand DNA by hydroperoxide of linoleic acid. FEBS Lett 172 231-234... 

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... 

The autooxidation of linoleic acid has been investigated as a function of polyoxyethylene(23) dodecanol (Brij 35) and linoleic acid concentration (Swarbrick and Rhodes, 1965). At constant surfactant concentration, the rate of oxidation increased linearly with increasing linoleic acid... 

That lipid alkoxyl radicals recombine (Reaction 71) at diffusion controlled rates (k= 10 M s ) (198, 305) probably accounts for the presence of low levels of peroxides even under mild conditions and low levels of oxidation. In one study, oxidation of linoleic acid at 30°C gave —C—O—O—C— dimers. Reactions 71-73 were found in linolenic acid oxidized under mild conditions to PV 585 this increased to > 50% at PV 4000 and to > 75% after heating to 40°C (276). Alkoxyl radicals from hydroperoxyepidioxides heated at 40°C generated > 90% dimers (276). 

Anisidine Value. Anisidine value is a measure of secondary oxidation or the past history of an oil. It is useful in determining the quahty of crude oils and the efficiency of processing procedures, but it is not suitable for the detection of oil oxidation or the evaluation of an oil that has been hydrogenated. AOCS Method Cd 18-90 has been standardized for anisidine value analysis (103). The analysis is based on the color reaction of anisidine and unsaturated aldehydes. An anisidine value of less than ten has been recommended for oils upon receipt and after processing (94). Inherent Oxidative Stability. The unsaturated fatty acids in all fats and oils are subject to oxidation, a chemical reaction that occurs with exposure to air. The eventual result is the development of an objectionable flavor and odor. The double bonds contained in the unsaturated fatty acids are the sites of this chemical activity. An oil s oxidation rate is roughly proportional to the degree of unsaturation for example, linolenic fatty acid (C18 3), with three double bonds, is more susceptible to oxidation than linoleic (C18 2), with only two double bonds, but it is ten times as susceptible as oleic (C18 l), with only one double bond. The relative reaction rates with oxygen for the three most prevelent unsaturated fatty acids in edible oils are ... 

Figure 40. HOect of the range of the pre-amplifier on the rate of increase in temperature, of a mixture of 50 jU L of linolic acid and 50 mg of cotton wool charged in the draft cell, into which oxygen gas is supplied at a flow rate of 2 cm7min at atmospheric pressure, and subjected to the adiabatie oxidatively-heating test started from a near 60 C, keeping ihe other conditions constant.

Types of lipids can also affect toxicant metabolism, as a high proportion of phospholipids is unsaturated due to the presence of linoleic acid (18 2) in the /3-position of triacylglycerol. Thus, dietary 18 2 is important in determining the normal levels of hepatic cytochrome P-450 concentration and the rate of oxidative demethylation in rat liver. 

Compounds that contain allylic and benzylic centres are especially prone to autoxidation, since the radicals formed on oxidation are stabilised by resonance. Oleic acid contains two allylic positions, linoleic acid contains two allylic positions and one double allylic position, while linolenic contains two allylic and two double allylic positions. We would therefore expect linolenic to be the most susceptible acid to oxidation, followed by linoleic and oleic. (The actual relative rates of autoxidation are linolenic (25) > linoleic (12) > oleic (1)). Precautions that can be employed to minimise oxidative deterioration are reducing the oxygen concentration in the container by, for example, the use of an inert atmosphere, and the use of a well-closed and well-filled container. It would also be advisable to store the product at low temperature and in a dark place. 

SLO follows an ordered, bi-uni mechanism, in which linoleic acid (LA) binds and reacts prior to O2 encounter [8], which has permitted a variety of steady-state and single-turnover studies into chemistry on SLO. The kinetic mechanism can be divided into a reductive half-reaction, described by the rate constant kcat/ffM(LA), and an oxidative half-reaction described by the rate constant fecat/KM(02). On the reductive half-reaction, SLO binds LA (ki), then the Fe +-OH cofactor abstracts the pro-S hydrogen from C-11 of LA (k2), forming a substrate-derived radical inter-... 

This equation was originally developed to express the inactivation kinetics of a-chymotrypsin and glucoamylase covalently bound to a water-insoluble support in an aqueous system (Kawamura et al., 1981). Equation 1.4 was successfully applied to express the oxidation kinetics of fish oil (EPA, eicosapentaenoic acid Yoshii et al., 2003) and linoleic acid powder (Ishidoh et al., 2002, 2003). The above-mentioned three equations are equivalent from the perspective of simulation of flavor release from spray-dried powder. All of the parameters, n in Equation 1.1, (3 in KWW s equation, and a Gaussian distribution with the standard deviation o in Equation 1.4, can be viewed as a consequence of the activation energy distribution of the release rate. 

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