Phytosterols (i.e. campesterols, stigmasterol and sitosterol) in soybean (Fig. 17.3) are obtained as by-products during crude oil processing for toco-pherol extraction. They share a common identical ring structure with animal cholesterol, but differ in the side chain. Campesterol and sitosterol are distinguished from each other by the presence of a methyl group for the former and an ethyl group for the latter at carbon 24. Stigmasterol is characterized by the presence of unsaturation at carbon 22. The total phytosterol content, as determined by gas liquid chromatography, in soybean seed is in the range of 0.202-0.843 mg g-1. Sitosterol makes up the largest proportion of total sterols, followed by campesterol and stigmasterol (Yamaya et al., 2007). Several clinical studies have shown that a diet moderately enriched with phytosterols results in a 10% reduction of the total cholesterol content and a 15% reduction in the LDL cholesterol content in human subjects (Law, 2000; Matvienko et al., 2002). Phytosterols lower the cholesterol content by inhibiting its incorporation into micelle, and hence its absorption through the intestine.
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