Determination of 7-ketocholesterol and 7-hydroxycholesterol in meat samples by TLC with densitometric detection

Concentrations of two oxycholesterols: 7-ketocholesterol and 7-hydroxycholesterol in meat samples (raw and cooked) were determined by TLC with densitometric detection. To obtain the oxycholesterols fraction, a multistage clean-up procedure based on liquid extraction and solid-phase extraction (SPE) was performed on silica gel and Florisil columns. The oxycholesterol fractions isolated from meat samples were separated by TLC on silica gel in an horizontal chamber. Quantitation was performed densitometrically directly after the TLC separation for 7-ketocholesterol and after Liebermann-Burchard reaction for 7-hydroxycholesterol. The presence of oxycholesterols determined by TLC was confirmed by GC-MS analysis of oxysterols derivatized to trimethylsilyl ethers. The investigations showed that the 7-ketocholesterol and 7-hydroxycholesterol content of the meat eaten most often in Poland ranged from approximately 40 ng g(-1) to 3.5 mug g(-1) of the sample.