Analysis of Polar Cholesterol Oxidation Products: Evaluation of a New Method Involving Transesterification, Solid Phase Extraction, and Gas Chromatography

Monitoring cholesterol oxidation products is important in the evaluation of the potential health risks associated with lipid oxidation. In the present study, a method allowing quick and reliable analysis of polar cholesterol oxidation products was evaluated. After Soxhlet-lipid extraction, the fat was transesterified under mild conditions, thereby minimizing degradation and allowing determination of the free and esterified cholesterol oxides. Sample fractionation was achieved with aminopropyl solid phase extraction cartridges and a stepwise elution with hexane, hexane/methyl tert -butyl ether, and acetone to separate polar cholesterol oxides from cholesterol and other lipid products. Further analysis of the trimethylsilyl derivatives was performed by gas chromatography with detection by flame ionization or mass spectrometry. A phytosterol oxide such as sitosterol α-epoxide (24α-ethyl-5α,6α-epoxycholestan-3β-ol) was employed for the first time as an internal standard for the quantification of cholesterol oxides in foodstuffs of animal origin.