Autoxidation of cholesterol in tallows heated under deep frying conditions: evaluation of oxysterols by GLC and TLC-FID.

The products of cholesterol autoxidation (oxysterols) in heated animal food fat were determined qualitatively and quantitatively to evaluate their toxicity and those of the foods in which they occur. Samples of beef tallow were taken from deep-fat fryers while they were in use. The oxysterols were identified and assayed by gas liquid chromatography and thin layer chromatography on Chromarods with flame ionization detection (TLC-FID). The two methods were compared and the TLC-FID method was found more convenient for a rapid estimation of autoxidation. Of the original cholesterol, 25% was destroyed during cooking and partly transformed into 3 beta-5-6 beta-trihydroxy-5 alpha-cholestane, 7 alpha-hydroxy-, 7 beta-hydroxy-, 7-oxo-cholesterol, 7-oxo-cholesta-3-5-diene and cholesterol epoxides. Certain other oxysterols were present in smaller quantities.