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Tocotrienols are members of the vitamin E family. An essential nutrient for the body, vitamin E is made up of four tocopherols (alpha, beta, gamma, delta) and four tocotrienols (alpha, beta, gamma, delta). The slight difference between tocotrienols and tocopherols lies in the unsaturated side chain of tocotrienols, having three double bonds in its farnesyl isoprenoid tail. Tocotrienols are named by analogy to tocopherols (from Greek words meaning ''to bear a pregnancy'' (see tocopherol); but with this word changed to include the chemical difference that tocotrienols are trienes, meaning that they share identical structure with the tocopherols except for the addition of the three double bonds to their side chains. Tocotrienols are natural compounds found in select vegetable oils, including rice bran oil and palm oil, wheat germ, barley, saw palmetto, anatto, and certain other types of seeds, nuts, grains, and the oils derived from them. This variant of vitamin E typically only occurs at very low levels in nature. Chemically, vitamin E in all of its forms functions as an antioxidant. All of the tocotrienol and tocopherol isomers have this antioxidant activity due to the ability to donate a hydrogen atom (a proton plus electron) from the hydroxyl group on the chromanol ring, to a free radical in the body. This process inactivates ("quenches") the free radical by effectively donating a single unpaired electron (which comes with the hydrogen atom) to the radical. Thus, one model for the function of vitamin E in the body is that it protects cell membranes, active enzyme sites, and DNA from free radical damage. Although the many vitamers of vitamin E have different distributions and metabolic fates, there is as yet no accepted evidence that any of the active forms of vitamin E are able to do any essential function in the body that each of the others is not also able to do. Specifically, symptoms caused by ''alpha''-tocopherol deficiency can be alleviated by tocotrienols. Thus, tocotrienols may be viewed as being members of the natural vitamin E family not only structurally but also functionally. While the majority of research on vitamin E has focused on ''alpha''-tocopherol, studies into tocotrienols account for less than 1% of all research into vitamin E. More recently, tocotrienols have been the subject of increased scientific attention, with research on tocotrienols accounting for nearly 30% of all peer-reviewed articles published on vitamin E between 2009 and 2010. The first-ever scientific compilation of tocotrienol research, ''Tocotrienols: Vitamin E Beyond Tocopherols'', was published in 2008 by CRC and AOCS Press, while a second edition was published in 2013.〔 Tocotrienols have only a single chiral center, which exists at the 2' chromanol ring carbon, at the point where the isoprenoid tail joins the ring. The other two corresponding centers in the phytyl tail of the corresponding tocopherols do not exist due to tocotrienol's unsaturation at these sites. Tocotrienols extracted from natural sources always consist of the dextrorotatory enantiomers only. These naturally occurring, dextrorotatory stereoisomers are generally abbreviated as the "d-" forms, for example, "d-tocotrienol" or "d-alpha-tocotrienol". In theory, the unnatural "l-tocotrienol" (levorotatory) forms of tocotrienols could exist as well, which would have a 2S (rather than 2R) configuration at the molecules' single chiral center. In practice, however, tocotrienols are only typically produced from natural sources, and neither the synthetic mixed stereoisomer ("dl-tocotrienol") or synthetic single stereoisomer ("l-tocotrienol") are marketed as dietary supplements. == History of tocotrienols== The discovery of tocotrienols was first reported by Pennock and Whittle in 1964, describing the isolation of tocotrienols from rubber. The biological significance of tocotrienols was clearly delineated in the early 1980s, when its ability to lower cholesterol was first reported by Qureshi and Elson in the ''Journal of Medicinal Chemistry''. During the 1990s, the anti-cancer properties of tocopherols and tocotrienols began to be delineated. The current commercial sources of tocotrienol are rice, palm, and annatto.〔Tan, B. and M.H. Saleh, Integrated process for recovery of carotenoids and tocotrienols from oil in USPTO 5,157,132. 1992〕 The ratios of tocopherol-to-tocotrienol extracted from rice, palm, and annatto sources are 50:50, 25:75, and 0.1:99.9, respectively. α-tocopherol makes up roughly 25–50% of palm and rice vitamin E mixtures, respectively, and has been shown to interfere with tocotrienol benefits. Annatto, on the other hand, naturally contains only δ- and γ-tocotrienols and is essentially tocopherol-free, hence not confined by α-tocopherol interference issues. Other natural tocotrienol sources include rice bran oil, coconut oil, cocoa butter, barley, and wheat germ. Sunflower, peanut, walnut, sesame, and olive oils, however contain only tocopherols. Some vitamin E supplements supply 50–200 mg/day of mixed tocotrienols. In a number of clinical trials, doses of tocotrienols as low as 42 mg/day have shown to reduce blood cholesterol levels by 5–35%. Tocotrienols are safe and human studies show no adverse effects with consumption of 240 mg/day for 48 months. Tocotrienol rich fractions from rice, palm, or annatto, used in nutritional supplements, functional foods, and anti-aging cosmetics, are available in the market at 20%, 35%, 50%, and 70% total vitamin E content. Molecular distillation occurs at lower temperatures and reduces the problem of thermal decomposition. High vacuum also eliminates oxidation that might occur in the presence of air. For the utility and quality it is desired for the absolute tocotrienol concentration to be highest, tocopherol to be the lowest, and the processing solvent-free. Annatto tocotrienol has the highest tocotrienol concentrations, and is tocopherol-free. Vitamin E, be it tocopherols or tocotrienols, is extremely sensitive to heat. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「tocotrienol」の詳細全文を読む スポンサード リンク
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