レシチン (卵由来)

化学的特性Lecithins vary greatly in their physical form, from viscous semiliquids to powders, depending upon the free fatty acid content. They may also vary in color from brown to light yellow, depending upon whether they are bleached or unbleached or on the degree of purity. When they are exposed to air, rapid oxidation occurs, also resulting in a dark yellow or brown color. Lecithins have practically no odor. Those derived from vegetable sources have a bland or nutlike taste, similar to that of soybean oil.

解説ホスファチジルコリン，1,2-diacyl-sn-glycerol 3-phosphorylcholine．レシチン(lecithin)ともいう．動物，植物，酵母，かび類に広く分布している代表的なグリセロリン脂質．ほ乳動物組織では，全リン脂質の50％ 近くを占め，生体膜の主要構成成分である．卵黄ではグリセロリン脂質の約70％ がホスファチジルコリンであり，残りの大部分がホスファチジルエタノールアミンである．生物体から抽出された全リン脂質混合物からアセトン不溶のリン脂質をとり，塩化カドミウムなどの金属塩との複合体の溶解度差を利用した精製法か，あるいはアルミナやシリカゲルのカラムクロマトグラフィーにより精製する．天然物はL-α-体で，白または微黄色の樹脂状あるいはろう状物質である．炭素数16～23の飽和あるいは不飽和脂肪酸を含むが，一般にグリセロールの1位に飽和脂肪酸，2位に不飽和脂肪酸が結合しているものが多い．不飽和脂肪酸の多い天然のものは，酸化を受けやすく不安定である．E. Baerらによる全合成法や酵素反応を利用した調製法も報告されている．メタノール，エタノール，ベンゼン，エーテル，石油エーテル，クロロホルムに可溶，アセトン，酢酸エチルに不溶．水溶液中に懸濁させると脂質二重膜の小胞を形成する．大豆からとったホスファチジルコリン(soya lecithin)などは，食用かつ消化しうる界面活性剤，食品や医薬品の乳化剤，高脂血症の治療薬として用いられている．生体内では，ジグリセリドとCDP-コリンの反応，またはホスファチジルエタノールアミンのメチル化により生合成される．

用途phospholipaseの酵素基質。レシチンを用いた各種研究用。

用途生体膜や再構成の研究用。

用途界面活性剤。

説明Food-grade lecithin is obtained from soybeans and other plant sources. It is a complex mixture of acetone-insoluble phosphatides that consists chiefly of phosphatidyl choline, phosphatidyl etha nolamine, and phosphatidyl inositol, combined with various amounts of other substances such as triglycerides, fatty acids, and carbohydrates. Refined grades of lecithin may contain any of these components in varying proportions and combinations depending on the type of fractionation used. In its oil-free form, the prepon-derance of triglycerides and fatty acids is removed and the product contains 90% or more of phosphatides representing all or certain fractions of the total phosphatide complex. The consistency of both natural grades and refined grades of lecithin may vary from plastic to fluid, depending upon free fatty acid and oil content, and upon the presence or absence of other diluents. Its color varies from light yellow to brown, depending on the source, on crop variations, and on whether it is bleached or unbleached. It is odorless or has a characteristic, slight nutlike odor and a bland taste. Edible diluents, such as cocoa butter and vegetable oils, often replace soybean oil to improve functional and flavor characteris tics. Lecithin is only partially soluble in water, but it readily hydrates to form emulsions. The oil-free phosphatides are soluble in fatty acids, but are practically insoluble in fixed oils. When all phosphatide fractions are present, lecithin is partially soluble in alcohol and practically insoluble in acetone.

天然物の起源Lecithin is found in foods such as eggs, beef liver, and peanuts. Commercial sources are available

使用lecithin (hydrogenated) is an emulsifier.

Lecithins are essential components of cell membranes and, in principle, may be obtained from a wide variety of living matter. In practice, however, lecithins are usually obtained from vegetable products such as soybean, peanut, cottonseed, sunflower, rapeseed, corn, or groundnut oils. Soybean lecithin is the most commercially important vegetable lecithin. Lecithin obtained from eggs is also commercially important and was the first lecithin to be discovered. Vegetable lecithins are obtained as a by-product in the vegetable oil refining process. Polar lipids are extracted with hexane and, after removal of the solvent, a crude vegetable oil is obtained. Lecithin is then removed from the crude oil by water extraction. Following drying, the lecithin may be further purified. With egg lecithin, a different manufacturing process must be used since the lecithin in egg yolks is more tightly bound to proteins than in vegetable sources. Egg lecithin is thus obtained by solvent extraction from liquid egg yolks using acetone or from freeze-dried egg yolks using ethanol (95%). Synthetic lecithins may also be produced.

純化方法Lecithin from hen egg white is purified by solvent extraction and chromatography on alumina. It is suspended in H2O and kept frozen until required [Lee & Hunt J Am Chem Soc 106 7411 1984, Singleton et al. J Am Oil Chem Soc 42 53 1965]. For purification of commercial egg lecithin, see Pangborn [J Biol Chem 188 471 1951].