Refined, unhydrogenated soybean oil and edible beef tallow were interesterified with sodium methoxide. This was done as an alternative to hydrogenation for the production of plastic fats for use as margarine oils. Using 0.5% sodium methoxide at 80 C, interesterification was complete in 30 min as determined by lipase hydrolysis. A blend of 60% soybean oil and 40% edible beef tallow was found to have physical characteristics (melting point, solid fat index) similar to those of commercial tub margarine oils. The level of polyunsaturated fatty acids was slightly lower and the level of saturated fatty acids slightly higher than the commercial margarine oils. Iodine value and trans fatty acid determinations indicated no discernible effect on the degree of unsaturation or the level of isomeric fatty acids by the interesterification process. The interesterified blend did contain 3.0% trams fatty acids which were originally present in the tallow. Oxidative stability of the interesterified oils was estimated by peroxide value determinations over several days on samples stored at 60 C. Experimental blends treated with 0.1% citric acid had poorer stability than the partially hydrogenated margarine oils; however, 0.01% BHA significantly delayed oxidation of the experimental samples.

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