From Soybean Sterols

The chemistry for providing steroid raw materials from the far more readily available soybean sterols was developed somewhat later. The so-called unsaponifiable fraction 

The byproduct sitosterol was for many years quite useless due to the lack of a chemical point of attack on the side chain that would permit its removal. Extensive efforts on the part of many laboratories eventually led to the discovery of a pseudomonas microbe that efficiently effected that transformation. Fermentation of (4-1) digests the entire aliphatic side chain at 17 to afford a mixture of 17-keto products including dehydroepiandrosterone (4-2) [4]. 

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The oxidative stability of an oil depends on the fatty acid (FA) composition and triacyl-glycerol (TAG) structure, as well as on non-TAG components, such as tocopherols, carotenoids, ascorbic acid, citric acid, free fatty acids, and sterols, which may either prevent or promote oxidation. Several investigations have reported correlations of FA composition, TAG structure, and oxidative stability (135-140). For example, the oxidative stability of purified TAG from soybean oil (SBO) in air in the dark at 60°C is correlated positively with a greater concentration of oleic acid (O) and lower concentrations of linoleic (L) and linolenic (Ln) acids of SBO TAG. 

Nagao, T., Kobayashi, T., Hirota, Y., Kitano, M., Kishimoto, N., Fujita, T., Watanabe, Y., and Shimada, Y. 2005. Improvement of a process for purification of tocopherols and sterols from soybean oil deodorizer distillate. J. Mol. Catal. B Enzym., 37, 56-62. 

Shi, J., Gonazales, R. and Bhattacharyya, M. (1996) Identification and characterization of an S-adenosyl-L-methionine A24-sterol-C-methyltransferase cDNA from soybean.. Biol. Chem., 271,9384—9. 

The chemical structure of phytosterols is similar to that of cholesterol so that these compounds may be involved in oxidative reactions. Przybylski and Eskin (42) found some oxidation products formed from plant sterols during storage of fried food products. Similar oxidation products were found in soybean oil and wheat flour (43). In light of health concerns associated with cholesterol oxidation products, potential health risks of phytosterol oxidation products are now receiving serious attention. 

The preparation of high-purity tocopherols and phytosterols involves steps such as molecular distillation, adduct formation, liquid-liquid extraction, supercritical fluid extraction, saponification, and chromatography (175). The extraction of tocopherols from soybean oil deodorizer distillate by urea inclusion and saponification of free fatty acids resulted in good recovery of tocopherols (208). To improve the separation of sterols and tocopherols, Shimada et al. (209) used a lipase to esterify sterols with free fatty acids. Then the steryl esters and tocopherols were separated better by molecular distillation. Chang et al. (210) used supercritical fluid CO2 extraction to recover tocopherols and sterols from soybean oil deodorizer distillate. A patent by Sumner et al. (211) advocated treatment of the distillate with methanol to converted free fatty acids and other fatty acid esters to methyl esters that can then be removed by a stripping operation. Then separation of sterols and tocopherols could be carried out by molecular distillation. 

Supercritical CO2 column fractionation of soybean (57, 86, 88, 89) and rice bran oil (57) deodorizer distillates has been investigated to enrich their sterol and tocopherol contents. Brunner et al. (89) reported that the FFA were enriched in the top (in the extract), whereas the monoacylglycerols, tocopherols, and diacylglycerols were enriched in the bottom (in the raffinate) fraction during the fractionation of soybean oil deodorizer distillate. Saure and Brunner (88) achieved a tocopherol concentration of more than 70% (w/w) using continuous column fractionation of soybean deodorizer distillate where squalene was almost completely found in the top product, whereas sterols and tocopherols were enriched in the bottom product. King and Dunford (57) developed a two-step column fractionation scheme (13.6 MPa and 27.2 MPa at 313 K) for the enrichment of phytosterols from soybean and rice bran oil deodorizer distillates such that the FFA were removed in the first step and sterols were enriched in the oil fraction in the second step. 

It will be noted that stigmasterol also represents a commercial route to progesterone. This abundant plant sterol that is readily available from soybean with its C22-C23 double bond, easily converts to progesterone in four steps and has therefore become a preferred substrate for various steroidal drugs. Cholesterol itself, which is the natural substrate for all mammalian steroid hormones, and is readily available from various sources (e.g., wool grease), is now also convertible to desirable steroid intermediates utilizing biotransforma-tion chemistry. The same is true of P-sitosterol (Chapter 11), which is another plant sterol available from soybean. 

Julian worked for Glidden for seventeen years, developing several new products from soybeans. He mapped out commercially viable syntheses of progesterone, testosterone, and cortisone from soya sterols. From soya protein he developed Aero-Foam, a fire extinguishing foam for oil and gasoline fires, which saw use by the U.S. armed forces during World War II. 

Natural mixed tocopherols (E306), natural D-a tocopherol, natural o-a tocopherol acetate, natural D-a tocopherol succinate from soybean sources Vegetable oil-derived phytosterols and phytosterol esters from soybean sources Plant stanol ester produced from vegetable oil sterols from soybean sources Whey used in distillates for spirits Lactitol... 

Clark, J.P. Tocopherols and sterols from soybeans. Lipid Technology, 8,111-114. 1996. 

Definition PEG deriv. of sterols obtained from soybean oil with avg. 30 moles EO Properties Nonionic Uses Emulsifier in cosmetics PEG-40 soy sterol... 

J.P. Clark, Tocopherols and sterols from soybeans. Lipid Technology, 1996, 8, 111-114. T. Netscher, lipid Synthesis and Manufacture (ed. F.D. Gunstone) Sheffield Academic Press,... 

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