INVESTIGATION BY FRACTIONAL CRYSTALLIZATION OF CLASSES OF COMPOUNDS FORMED DURING FRYING OF VEGETABLE-OILS

In an effort to standardize a rapid and reliable method for the characterization of thermally abused vegetable oils, the technique of fractional crystallization was applied to heated samples of cottonseed and corn oil. Using this method an insoluble fraction enriched mainly in polar compounds, which form during the heating process, was obtained. These compounds, mostly of high molecular weight, are responsible for the increase in viscosity of the oil and are retained in a gas chromatographic column used for fatty acid methyl ester analysis. It was found that the above insoluble fraction formed when heated samples contained 25% polar constituents, a value which is widely accepted as the upper limit for use of heated vegetable oils. It is proposed that the technique of fractional crystallization can be used as a method for rapid quality assessment of frying oils such as non-hydrogenated vegetable oils. © 1990.