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The lignans are a group of chemical compounds found in plants. Plant lignans are polyphenolic substances derived from phenylalanine via dimerization of substituted cinnamic alcohols (see cinnamic acid), known as monolignols, to a dibenzylbutane skeleton 2. This reaction is catalysed by oxidative enzymes and is often controlled by dirigent proteins. Many natural products, known as phenylpropanoids, are built up of C6C3 units (a propylbenzene skeleton 1) derived from cinnamyl units just as terpene chemistry builds on isoprene units. Structure 3 is a neolignan, a structure formed by joining the two propylbenzene residues at other than the β-carbon atom of the propyl side chain.〔(neolignane at en.wiktionary )〕 Some examples of lignans are pinoresinol, podophyllotoxin, and steganacin. When a part of the human diet, some plant lignans are metabolized by intestinal bacteria to mammalian lignans enterodiol (1) and enterolactone (2). Lignans that can be metabolized to mammalian lignans are pinoresinol, lariciresinol, secoisolariciresinol, matairesinol, hydroxymatairesinol, syringaresinol and sesamin. Lignans are one of the major classes of phytoestrogens, which are estrogen-like chemicals and also act as antioxidants. The other classes of phytoestrogens are isoflavones and coumestans. ==Food sources== Plant lignans are co-passengers of dietary fiber, and therefore fiber-rich food items are often good sources of lignans. Flax seed and sesame seed contain higher levels of lignans than most other foods. The principal lignan precursor found in flaxseed is secoisolariciresinol diglucoside. Other sources of lignans include cereals (rye, wheat, oat and barley - rye being the richest source), soybeans, cruciferous vegetables such as broccoli and cabbage, and some fruits, particularly apricots and strawberries.〔(Linus Pauling Institute at Oregon State University )〕 Secoisolariciresinol and matairesinol were the first plant lignans identified in foods. Pinoresinol and lariciresinol are more recently identified plant lignans that contribute substantially to the total dietary lignan intakes. Typically, lariciresinol and pinoresinol contribute about 75% to the total lignan intake whereas secoisolariciresinol and matairesinol contribute only about 25%.〔 This distribution may change as the contributions of syringaresinol and hydroxymatairesinol have not properly been quantified in foods. Sources of lignans: A recent study shows the complexity of mammalian lignan precursors in the diet. In the table below are a few examples of the 22 analyzed species and the 24 lignans identified in this study. Mammalian lignan precursors as aglycones (µg / 100 g). Major compound(s) in bold. 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「lignan」の詳細全文を読む スポンサード リンク
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