Oxidation of phytosterols in a test food system

The oxidative stability of phytosterols in canola, coconut, peanut, and soybean oils was examined under simulated frying conditions of 100, 150, and 180 degreesC for 20 h. The degree of oxidative decomposition was assessed by the loss of phytosterols, accumulation of phytosterol oxides, and the change in fatty acid profiles. The phytosterol oxides produced in the oils were identified using mass spectroscopy. Oils with higher levels of polyunsaturated fatty acids showed greater amounts of sterol loss; however, the sterol loss was less complete than in the more saturated oils. A greater variety of sterol oxides was observed at the lower temperatures of 100 and 150 degreesC compared to 180 degreesC. This study demonstrates that under conditions similar to frying, there is a loss of phytosterols and polyunsaturated fatty acids. The accumulation of phytosterol oxides may be temperature-limited because of further breakdown into products not measurable by typical gas chromatography-mass spectrometry techniques.