ABSTRACT
As minor components of plant lipids, phytosterols function as structural components in membranes and as precursors to steroid hormones. They are similar in structure to, and thus analogous in functionality to, cholesterol in animal lipids. Due to their structural similarities to cholesterol, phytosterols are expected to undergo similar chemical reactions including oxidation (1). Many types of oxidation products have been found to result from cholesterol. This oxidation is thought to proceed by a free-radical process resulting in phytosterol oxides and phytosterol hydroperoxides. The refining of plant oils and food processing conditions commonly expose lipid components in foodstuffs to contact with heat, light, air, and metal surfaces that induce this free-radical oxidation. The many types of cholesterol oxide products (COPs) found in foods and their biological properties have been reviewed (2). The biological effects of such compounds are overwhelmingly negative. COPs have been implicated in the onset of arteriosclerosis and coronary heart disease in humans, with the epoxides having been found to be mutagenic (3,4). More recently, a very comprehensive review of the many COPs and their biological activity has appeared (5). The oxidation of phytosterols compared to cholesterol seems to be much more difficult, and the biological and safety aspects of phytosterol oxidation products (POPs) remain unclear (6). Much of the confusion with regard to the effects of POPs has resulted from the lack of research studies on the safety of phytosterols, as well as from the levels of consumption and thus concern by the general population. Problems with the analysis and isolation of resulting products have slowed research concerning their effects on biological systems (7).
