Oleic acid oxidation rate

Reactions in monolayers (38b) also provide direct chemical evidence for the dependence of molecular orientation on the surface area. The rates of oxidation and halogenation of double bonds midway along the carbon chain of oleic acid, the rate of lactoniza-... 

Another example, similar to that of the oleic acid oxidation, is provided by the study (Mittelmann and Palmer, 36) of the rate of oxidation of triolein films. Their results will be considered in more detail below, where their mathematical analysis will be discussed. 

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. 

More importantly, lipid peroxidation can be controlled or minimized by design of formulation. While saturated lipids (e.g., MCTs) will themselves not be susceptible to peroxidation, they may contain sufLcient unsaturated impuritiesto be problematic. Similarly, monounsaturated lipids (e.g., oleic acid glycerides) are much less susceptible to peroxidation. The relative rates of peroxidation of oleic, linoleic, and linolenic acids are 6 64 100, respectively (Swern, 1995). Monounsaturated lipids may, however, may contain polyunsaturated impurities, which will catalyze the oxidation ofthe monounsaturated components (Swern, 1995). Surfactants, particularly those based on PEG, may contain peroxides that can promote lipid peroxidation thus, particular attention should be paid to the purity and source of all formulation components. 

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 ... 

The relative oxidation rates of pure fatty acid esters based on peroxide formation are shown in Table 1 (6). This table is based on a common factor of one that has been arbitrarily assigned for the oxidation rate of oleic acid. 

The number of double bonds in a fatty ester radical significantly affects both physical and chemical properties of the triacylglycerol. The highly unsaturated (three double bonds) linolenic acid (18 3) is unstable to oxidation, and undesirable odors and flavors can develop. The rate of oxidation 18 3 is 15-fold greater than that of oleic acid (18 1). 

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. 

The production of DOD from oleic acid is unique in that it involves an addition of two hydroxy groups at two positions and a rearrangement of the double bond of the substrate molecule. The reaction at the A9,10 position resembles hydration, and the reaction at the C-7 position seems like a hydroxylation. Subsequent investigation of reactions catalyzed by PR3 led to the isolation of another new compound, 10-hy-droxy-8-octadecenoic acid (HOD) (34). From the structure similarity between HOD and DOD, it is likely that HOD is an intermediate in the formation of DOD from oleic acid by strain PR3. Kinetic studies (34) showed that the conversion from HOD to DOD is not a rate-limiting step. The bioconversion pathway for flie production of DOD from oleic acid is postulated as follows (Fig. 3) a hydratase in strain PR3 attacks oleic acid at the C-10 position, introduces a hydroxy group, and at the same time shifts the double bond from C-9 to C-8. The resulting product (HOD) is then oxidized by a hydroxylase at the C-7 position to produce DOD. 

Clouet, R, Niot, I. Bezard, J. (1989) Biochem. J., 263, 867-873. Pathway of a-linolenic acid through the mitochondrial outer membrane in the rat liver and influence on the rate of oxidation. Comparison with linoleio and oleic acids. 

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