Photooxidation of phytosterols in oil matrix: Effects of the light, photosensitizers and unsaturation degree of the lipids.

In this work we studied the stability of phytosterols in oil matrix under photooxidation (with different light intensity, existence/absence of photosensitizers and unsaturated lipids). Results revealed that the photooxidation of phytosterols fit a first order kinetic model (R2 > 0.96). When the intensity of light was higher, the rate constants increased and phytosterols oxidized faster. The progress could be also accelerated by photosensitizers, whereas the unsaturated matrix inhibited the formation of oxidation products. Phytosterols oxidation products (POPs) were detected in all model matrix samples. 7β-hydroxy was the main oxidation products in most cases during the whole treatment under light, which represented about one third of the total phytosterol oxides, followed by 7α-hydroxy, 5β,6β-epoxy, 7-keto, 5α,6α-epoxy and 6β-hydroxy. And the oxidation at C7 on the Ring B of steroid nucleus was the most important pathway of phytosterols photooxidation.