Determination of cholesterol oxides content in milk products by solid phase extraction and gas chromatography-mass spectrometry

A method for quick and reliable analysis of cholesterol oxidation products (COPs) in dairy products has been developed. After lipid extraction, fat was transesterified under mild conditions to avoid degradation of the target compounds. Isolation of the COPs studied from other components in the lipid fraction was carried out on an aminopropyl SPE cartridge. Finally, analytes were analysed by GC-MS without derivatisation. The method developed provides high specificity and good sensitivity, allowing the direct and unambiguous determination of the underivatized COPs investigated. Application of the method to dairy food analysis revealed the presence of COPs in powder milks and milk-based infant formulas commercially available in Spain, showing that attention should be focused on reduction of cholesterol oxidation levels during both the processing and the storage of these types of foodstuffs.