|
Lecithin is a generic term to designate any group of yellow-brownish fatty substances occurring in animal and plant tissues, which are amphiphilic - they attract both water (and so are hydrophilic) and fatty substances (lipophilic), and are used for smoothing food textures, dissolving powders (emulsifiers), homogenizing liquid mixtures, and repelling sticking materials.〔(Lecithin ) (Merriam Webster Dictionary online)〕〔(Lecithins: Sources, Manufacture & Uses ), Bernard F. Szuha, Pub: The American Oil Chemist's Society, ISBN 0-935315-27-6, Chapter 7, page 109. (Google Books)〕 Lecithins are usually phospholipids, composed of phosphoric acid with choline, glycerol or other fatty acids usually glycolipids or triglyceride. Glycerophospholipids in lecithin include phosphatidylcholine, phosphatidylethanolamine, phosphatidylinositol, phosphatidylserine, and phosphatidic acid.〔(Food Additives Databook ) Page 367 and on (Google Books)〕 Lecithin was first isolated in 1846 by the French chemist and pharmacist Theodore Gobley. In 1850, he named the phosphatidylcholine ''lécithine''. Gobley originally isolated lecithin from egg yolk—λέκιθος ''lekithos'' is "egg yolk" in Ancient Greek—and established the complete chemical formula of phosphatidylcholine in 1874; in between, he had demonstrated the presence of lecithin in a variety of biological matters, including venous blood, bile, human brain tissue, fish eggs, fish roe, and chicken and sheep brain. Lecithin can easily be extracted chemically using any non-polar solvent such as hexane, ethanol, acetone, petroleum ether, benzene, etc., or extraction can be done mechanically. It is usually available from sources such as soybeans, eggs, milk, marine sources, rapeseed, cottonseed, and sunflower. It has low solubility in water, but is an excellent emulsifier. In aqueous solution, its phospholipids can form either liposomes, bilayer sheets, micelles, or lamellar structures, depending on hydration and temperature. This results in a type of surfactant that usually is classified as amphipathic. Lecithin is sold as a food supplement and for medical uses. In cooking, it is sometimes used as an emulsifier and to prevent sticking, for example in nonstick cooking spray. ==Biology== Lecithin, as a food additive, is also a dietary source of several active compounds: Choline and its metabolites are needed for several physiological purposes, including cell membrane signaling and cholinergic neurotransmission, although its exact function has not been determined, and the involvement of choline in long-term health and development of clinical disorders, such as cardiovascular diseases, cognitive decline in aging and regulation of blood lipid levels, has not been well defined, and remains under research in 2015. While lecithin is also a rich source of a variety of types of dietary fats, the small amounts of lecithin typically used for food additive purposes mean it is not a significant source of fats. Lecithin is a source for methyl groups via its metabolite, trimethylglycine (betaine) although this is mostly consumed from plants (and is abundant in sugar beets for example).〔(Advanced Nutrition and Human Metabolism ), Sareen S. Groper and Jack L. Smith, Wadsworth pub., 2005, ISBN 9781133104056, p. 348 (Google Books)〕 Phosphatidylcholine occurs in all cellular organisms, being one of the major components of the phospholipid portion of the cell membrane.〔(choline )〕 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「lecithin」の詳細全文を読む スポンサード リンク
|