Oxidation of phytosterols in a simulated model food system

Phytosterols are plant lipid components that are structurally analogous to cholesterol in animal fats. Cholesterol oxidation products have been found to have negative effects at the cellular level and have been implicated in the onset of arteriosclerosis and coronary heart disease in humans. Compared to cholesterol oxidation, there have been few reports on phytosterol oxidation. The oxidative stability of phytosterols in canola, coconut, peanut, and soybean oil was examined under simulated frying conditions. The degree of oxidative decomposition was assessed by the loss of phytosterols, accumulation of phytosterol oxides, and the change in fatty acid profiles of the oils. The use of metal containers for heat treatment was observed to increase the rate of loss of the phytosterols compared to an all glass apparatus. The oxides produced in the oils were identified using mass spectroscopy.;Phytosterols and tocopherols coexist naturally in plant derived oils. Tocopherols have been shown to provide plant lipids with protection from oxidation. The effects of tocopherols on the oxidation of phytosterols and the change in fatty acid profiles was examined in a simulated frying oil model system. Corn oil, commercially stripped of its native tocopherols and soybean oil containing its natural level of tocopherols were subjected to heat treatments. The losses in phytosterols and changes in fatty acid profiles were compared. Tocopherols were found to offer little protection to the phytosterols against oxidative losses but did provide protection to the unsaturated fatty acids.;Synthetic compounds known as phenolics and lipid compounds such as phospholipids have been shown to provide antioxidant protection to food lipids. Phenolics have limited use at high temperatures and the action of phospholipids is unclear. The antioxidant activity of tertiary butylhydroquinone (TBHQ), sphingomyelin, soy lecithin, and lysophophatidylcholine on the oxidation of corn, coconut, and soybean oils was examined. Oils were heat treated in metal containers for 20 hours at 100°C and 180°C and changes in fatty acid profiles and sterol content were monitored. Some degree of protection was offered to soybean oil and corn oil by all the additives at 100°C, with TBHQ and lecithin showing the greatest effect. At the higher temperature, lecithin appeared more effective than TBHQ. All the additives were found to offer some degree of protection at 180°C. None of additives offered protection to coconut oil, a highly saturated oil.;The effects of cooking on the content of cholesterol and phytosterols was compared in two breaded shrimp products. Phytosterol concentrations increased during cooking due to moisture loss and oil absorption by the sample components. oxidation products of cholesterol, but not of the phytosterols were found after cooking. The oil used for heat transfer demonstrated oxidative losses of phytosterols and polyunsaturated fatty acids.;Cholesterol oxidizes much more readily than phytosterols. Oxidation products can be found in cholesterol containing foods after short cooking times. Phytosterol oxidation requires harsher conditions. Studies are needed to determine how the mechanism of phytosterol oxidation differs from that of cholesterol.