Biological Effects of Phytosterol Oxidation Products, Future Research Areas and Concluding Remarks

• These compounds are minor components of foods. They often represent <1% of phytosterols, which is a very small amount in food. • The intestinal absorption of phytosterols is low, and it was anticipated that the absorption of their oxides was also low. Considering the very low levels in foods and their low absorption, it was thought that their biological roles in vivo were negligible. • The precise analysis of the oxysterols is difficult, as was described in earlier chapters. In the case of oxyphytosterols, the difficulty is increased by the frequent overlapping of compounds coming from the oxidation of different sterols: for example, the use of gas chromatography (GC) on a DB5 column does not allow the separation of the TMS derivatives of α-epoxysitosterol, campestanetriol (1), and 26-hydroxycholesterol (Grandgirard et al., unpublished results). Under the same conditions, the TMS derivatives of 25-hydroxycholesterol and 7β-hydroxysitosterol have the same retention time.