Lecithin is any of a group of yellow-brownish fatty substances occurring in animal an plant tissues, and in egg yolk, composed of phosphoric acid, choline, fatty acids, glycerol, glycolipids, triglycerides, and phospholipids (e.g., phosphatidylcholine, phosphatidylethanolamine, and phosphatidylinositol). However, lecithin is sometimes used as a synonym for pure phosphatidylcholine, a phospholipid that is the major component of its phosphatide fraction. It may be isolated either from egg yolk (in Greek lekithos—λέκιθος) or from soy beans, from which it is extracted chemically (using hexane) or mechanically.