Determination of cholesterol oxidation products in cheese under photo-oxidative stress using QuEChERS and LC-MS

The QuEChERS approach was optimized for extracting cholesterol oxidation products in cheese, followed by LC-APCI-MS/MS analysis. Optimization of the method, including evaluations of saponification step, sample weight, and d-SPE purification resulted in good recoveries for each analyte, ensuring a reliable determination of these contaminants in cheese samples. In addition, the method was successfully validated by testing linearity of response, analytical limits (LOD and LLOQ), and precision. Sliced cheese samples wrapped in various packaging materials underwent a challenging test to simulate refrigerated storage conditions under fluorescent light, inducing photo-oxidative stress. The validated QuEChERS method revealed that only seasoned hard cow's cheese showed an increase in the concentration of 7-ketocholesterol and its chemical precursors, 7 beta-hydroxycholesterol, and 7 alpha-hydroxycholesterol, reaching levels of 0.45, 0.35, and 0.35 mu g g-1, respectively. Conversely, opaque packaging and the use of a double film were found to be effective in preventing the formation of COPs in cheese samples subjected to photo-oxidative stress, such as smoked cheese and melted cheese slices (sottilette). A trade-off must be found between ensuring cheese protection and meeting the consumer's desire to see the product.