Routine high-performance liquid chromatographic determination of free 7-ketocholesterol in some foods by two different analytical methods

Two methods for routine analysis of free 7-ketocholesterol (7-k) in foods by high-performance liquid chromatography (HPLC) were compared. The analyzed samples were egg noodles, biscuits prepared with eggs, sweet snacks, grated Parmesan cheeses, and some ingredients utilized in the food industry (whole-milk and whole-egg powder). The enrichment of cholesterol oxides was carried out by solid-phase separation of the total lipids with florisil and silica cartridges for methods A and B, respectively. The 7-k analyses were run in normal-phase HPLC for method A, and a reverse-phase process was used in method B. Identification of the 7-k peak was confirmed by gas chromatography/mass spectrometry analysis and peak purity checkvia spectral analysis with a diode array detector. The quantitation of 7-k was carried out with an internal standard for method A and with a calibration curve for method B. The limit of quantitation (LQ) was 3 × 10⁻⁹ g/injection; the limit of detection was ten times lower than the LQ for both methods. The two methods showed good recovery (99%) and good repeatability (coefficient of variation of 3.9 and 3.7% for methods A and B, respectively). These methods allow a fast, sensitive, and reliable determination of one cholesterol oxidation product, which is present at a high concentration level in the first stages of the oxidation process.