Linolenic acid relative oxidation reaction rate

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 rate of the oxidation reactions is higher for the fatty acids that contain more double bonds. However, even saturated fatty acids undergo oxidation. The relative reaction rates of oleic (Cig.i), linoleic ( ,8,2), and linolenic acid ( ,8,3) with oxygen are 1, 10, 25, respectively [18]. Therefore, the inherent stability to oxidation, expressing the relative reaction rate with oxygen of oil depends on the fatty acid content of its triglycerides and can be calculated as [18] ... 

The mutual annihilation of free radicals is known as the termination stage (Reactions 12.5 through 12.7), when the free radicals R and ROO" interact to form stable, non-radical products. The rate of oxidation of fatty acids increases with their degree of unsaturation. The relative rate of autoxidation of oleate, linoleate, and linolenate is in the order of 1 40 100 on the basis of oxygen uptake and 1 12 25 on the basis of peroxide formation. ... 

The selectivity ratio for linolenic to linoleic acid is 5 n = kilk2, and for linoleic to oleic acid, S = kjk. In a simple system the reaction proceeds in a stepwise manner because 5 is greater than 5. However, because of the complexity of triglyceride systems, impurities in the oil and the effect of processing conditions, in reality all the steps of the sequence take place simultaneously and the selectivity of the reaction depends on the relative rates at which they occur. Reactions in which polyunsaturated acids are hydrogenated in preference to monounsaturated, i.e. high selectivity, are required for improving the oxidative stability of an oil. 

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