Fatty acids in edible oils

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 ... 

In this paper, we describe the apparatus we use to make phase equilibrium measurements on mixtures of conqponents with greatly differing volatilities, putting particular emphasis on recent inqprove-ments over the previous version (6-7). We also describe quantitative measurements of the solubility of methyl oleate in supercritical fluids which can provide a basis for choosing a solvent to separate fatty acids in edible oils. In the following paper (JB.) we explore the utility of cubic equations of state to describe the results of supercritical fluid - liquid phase equilibrium measurements. Some additional experimental results on the mutual solubility of methyl linoleate and carbon dioxide are presented there also. 

The high temperatnre of a chemical catalytic hydrogenation process promotes the undesirable cis-to-trans isomerization of fatty acid donble bonds recent stndies have shown that the injestion of trans fatty acids in edible oils increases cholesterol blood levels and contribntes to coronary heart disease. The low-temperature electrochemical hydrogenation scheme rednces snch isomerization. 

Box 5 Saturated and unsaturated fatty acids in edible oils... 

Tatum, V. Chow C.K. Effects of processing and storage on fatty acids in edible oils. In Fatty acids in foods and their health implications. Chow, C.K. (Ed.), Marcel Deckker Inc. New York, 1992 pp. 337—351. 

Kinami, T. Analysis of conjugated fatty acids in edible oils. Master thesis, 2003, Hokkaido University, Hakodate, Japan. 

Polyunsaturated fatty acids in vegetable oils, particularly finolenic esters in soybean oil, are especially sensitive to oxidation. Even a slight degree of oxidation, commonly referred to as flavor reversion, results in undesirable flavors, eg, beany, grassy, painty, or fishy. Oxidation is controlled by the exclusion of metal contaminants, eg, iron and copper addition of metal inactivators such as citric acid minimum exposure to air, protection from light, and selective hydrogenation to decrease the finolenate content to ca 3% (74). Careful quality control is essential for the production of acceptable edible soybean oil products (75). 

Another processability factor is TOTOX value that is related to the degree of oil deterioration due to lipoxygenase action on polyunsaturated fatty acids in the oil (Mounts et al., 1990). Products of oxidation degrade flavor and stability of edible oils. A low TOTOX value <3.0 meq/kg is desirable. TOTOX was calculated as two times the peroxide value as determined by AOCS Method Ca9f-57 plus the anisidine value (AOCS, 1987). 

Fig. 1. The biosynthetic pathvay of the major fatty acids in edible vegetable oilseeds. The chain elongation pathway from oleic to eruclc acid is unique to the Brassica oil crops.

Sardine oil has similar fatty acids to other edible fats and oils and also contains longer-chain co-3 polyunsaturated fatty acids, such as eicosapentaenoic acid and docosahexanoic acid. Table 2 indicates that the principal polyunsaturated fatty acids of sardine oil are in the co-3 family. 

Kochar, S.P. (1983) Influence of processing on sterols in edible oils. Prog. Lipid Res., 22, 161-188. Krzynowek, J., Uljua, D.S., Panuzio, L.J. and Maney, R.S. (1992) Factors affecting fat, cholesterol, and omega-3 fatty acids in Maine sardines. J. Food Sci., 57, 63-65. 

Wolff, R.L. (1992) Hems-Polyunsaturated fatty acids in French edible rapeseed and soybean oils. J. Am. 

Contents of individual fatty acids in the fat of a species can vary by over 100 percent. Table 34.2 summarizes general fatty acids contents of the major edible fats and oils, and Table 34.3 does likewise for industrial fats and oils. 

Specifications, or typical analyses, of edible, industrial and feed animal fats are shown in Table 34.9.80,86 Much emphasis is placed on Titer, the solidification temperature of fatty acids in a saponified sample of the fat or oil (AOCS Method Cc 12-59). Feed ingredients in the United States may not be as aesthetically attractive as food ingredients, but are required to pass the same toxicology standards. 

The manufacture of fatty acids from triglycerides via their reaction with alkali followed by acidification is not used commercially. However, the recovery of fatty acids from alkali refining of fats/oils (to produce acid soaps) and soap reboiling operations (the recovery of fatty acids from the acidification of soap waste streams) are practiced still in special situations, for example, in edible oils refining where soap-stock that is generated from chemical (alkali) refining requires acidulation to produce acid oils with commercial value. 

To overcome the existing problems with the state-of-the-art technology in edible oil and free fatty acid hardening, we decided to have a look on hydrogenation reactions in sc CO2 using precious metal fixed bed catalysts on acid resistant supports. 

Considerable recent research has defined conditions for successful use of lipases and other enzymes in numerous lipid modification reactions, including a variety of types of interesterifications (69, 71, 76). For edible applications to date, they have been employed at industrial scales for the production of (1) cocoa butter substitutes, for which disaturated, monounsaturated acylglycerols with the unsaturated fatty acid in the sn-2 position are desired (77) (2) to produce human milkfat analogues, where 2-palmitoyl acylglycerols are desired (77) (3) in the synthesis of 1,3- di-acylglycerols (78) and in the production of diacylglycerols for edible applications. These reactions employ vegetable oils as feedstocks. 

Oxidative stability of edible oils depends primarily on their fatty acid composition and, to a lesser extent, in the stereospecific distribution of fatty acids in the triacyl-glycerol molecules. The presence of minor components in the oils also affects their oxidative stability. A detailed discussion of oxidative processes in fats and oils is provided elsewhere in this series. Oxidation may occur via different routes and includes autoxidation, photo-oxidation, thermal oxidation, and hydrolytic processes, all of which lead to production of undesirable flavor and products harmful to health. Flavor and odor defects may be detected by sensory analysis or by chemical and instrumental methods. However, chemical and instrumental procedures are often employed in the processing and during usage of edible oils. Indicators of oxidation are those that measure the primary or secondary products of oxidation as well as those from hydrolytic processes or from thermal oxidation, including polymers and polar components (15). 

The removal of the free fatty acids in the bleached oil is done by steam distillation in a deodorizer. This, simultaneously, deodorizes the oil. Because deodoriza-tion is, also, the last process normally carried out on edible oils, this step may be delayed until other processes, such as hydrogenation of the oil, have been done. 

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