Cholesterol oxides II. Measurement of the 5,6‐epoxides during cholesterol oxidation in aqueous dispersions

Abstract

Cholesterol in aqueous dispersion with sodium stearate or Triton surfactants was aerated at various pH values at 50 and 80 C. Analysis of the reaction mixtures by TLC during the oxidation produced qualitatively similar patterns regardless of pH or temperature. Major oxidation products observed were 7‐ketocholesterol, the isomeric 7‐hydroperoxy‐ and 7‐hydroxycholesterols, the isomeric 5,6‐epoxycholestanols and 3β,5α,6β‐trihydroxycholestanol. The concentrations of 3β,5α,6β‐trihydroxycholestanol and an unknown compound increased greatly at the lower pH values. Recovery of the 5,6‐epoxide isomers by preparative TLC followed by capillary GC allowed theα‐ andβ‐epoxide isomers to be quantitated. Oxidations at pH 8 and 12 produced increasing amounts of the epoxides with time, without significant changes in theα/β‐epoxide ratio. However, oxidations at the acidic pH values of 5.5 and 3 showed large changes in theα/β‐epoxide ratio during the oxidation. Measurement of the hydrolysis rates of the 5,6‐epoxides at pH 5.5 showed that theβ‐epoxide isomer is more labile than theα‐isomer by a factor of 2.5. The rate constant for the hydrolysis of theα‐epoxide isomer was 5.3 × 10−7 sec−1 and that of theβ‐isomer 13 × 10−7 sec−1.

Development of gas chromatographic method for determination of cholesterol oxides in meat products

“…Among these compounds there are some of the several cholesterol oxidation products (COPs) [2], whose toxicity is related to their potential mutagenic and carcinogenic activity and to their involvement in cardiovascular diseases and in atherosclerosis [3][4][5]. Several investigations have shown that 25-hydroxycholesterol and cholestane-3[~,5cx,6[~-triol are the most toxic agents [6,7].…”

Inhibition of cholesterol autoxidation by the nonsaponifiable fraction in rice bran in an aqueous model system

“…Crystalline cholesterol and aqueous cholesterol dispersions readily undergo oxidation at relatively mild temperatures when exposed to air, with the oxidation reactions producing a variety of products (1)(2)(3)(4)(5)(6). Some cholesterol oxidation products (COP) have been shown to be cytotoxic, atherogenic, mutagenic, and carcinogenic when ingested by laboratory animals (1)(2)(3)(4)(5)(6).…”

“…Some cholesterol oxidation products (COP) have been shown to be cytotoxic, atherogenic, mutagenic, and carcinogenic when ingested by laboratory animals (1)(2)(3)(4)(5)(6). These COP are formed in foods containing cholesterol during the cooking process or during prolonged storage (1).…”

“…An emulsion of fatty acids and aqueous buffer was used as a relatively simple model system for studying lipid oxidation of muscle-based foods (5,17). Systems containing biological membranes such as red blood cells are quite complex, but micellar systems are relatively simple, uniform, and well understood, although heterogeneous (5).…”

“…Systems containing biological membranes such as red blood cells are quite complex, but micellar systems are relatively simple, uniform, and well understood, although heterogeneous (5). In addition, colloidally dispersed cholesterol may be a more suitable model of the state of cholesterol in foods and in the aqueous fluids of animal tissues (17).…”