Determination of cholesterol oxidation products in milk powders: Methods comparison and validation

Many papers have been published during the past 15 years on suitable methodologies for the analysis of cholesterol oxidation products (COPs) in foodstuff. Regarding milk powders, data found in the literature are difficult to compare, if not contradictory. Therefore, the aim of the present study was to compare four of the most frequently used methods for COP analysis to identify the best. A method with direct saponification of the sample was compared with three methods involving preliminary fat extraction (Folch's, Radin's, and Maxwell's methods). After saponification all of the samples were enriched by solid-phase extraction (SPE) on aminopropyl cartridges and analyzed by CC-MS. [H-2(6)]cholesterol was used to monitor artifact formation. The four methods were applied to the analysis of three milk powders containing different levels of COPs (low, medium, and high contents). The method offering the best compromise was found to be direct saponification of the milk powder, without preliminary fat extraction, followed by aminopropyl-SPE and CC-MS quantification.