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

Abstract

Abstract 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 check via 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.