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Lecithin
An example of a phosphatidylcholine, a type of phospholipid in
lecithin.Lecithin is any of a group of yellow-brownish fatty substances
occurring in animal and 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.
It has low solubility in water. 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 is usually classified as amphoteric.
Lecithin is sold as a food supplement and for medical uses. In cooking,
it is sometimes used as an emulsifier.
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