INTERPRETING THE OIL STABILITY INDEX

It has been found that the Oil Stability Index (OSI) as determined wit h a Rancimat apparatus on blends of triglyceride oils and fats can be expressed as: [GRAPHICS] wherein R = OSI value of the blend x(i) = mas s fraction of component i a(i) = net anti oxidative property of compon ent i v(i) = rate of oxidation of component i. By measuring the OSI va lue of 48 series of binary blends of 20 different commonly used compon ents such as liquid oils, hydrogenated oils and fats, the a values and the upsilon values of these components have been determined. The upsi lon values thus determined can be correlated with the fatty acid compo sition (in wt%) of the components by using the following weighting fac tors: saturated fatty acids 0.0023 mono-unsaturated fatty acids 0.0030 linoleic acid and isomers 0.3887 linolenic acid and isomers 0.4150 wh ereby the upsilon value of a soybean oil hydrogenated to a melting poi nt of 44 degrees C has been arbitrarily set to equal 1.00. Consequentl y, upsilon values vary over a wide range. The a values cover a much sm aller range and vary somewhat between oil types, between liquid and hy drogenated oils of the same type and also between batches of the same oil product. Accordingly, the OSI value of a product is fairly predict able, and routine OSI determinations should only aim at detecting outl iers.