Article: Lecithin

Phosphatidylcholine, a phospholipid in lecithin.

Lecithin is mostly a mixture of glycolipids, triglycerides, and phospholipids (eg Phosphatidylcholine, Phosphatidylethanolamine, and Phosphatidylinositol). However, in biochemistry Lecithin is usually used as a synonym for pure phosphatidylcholine, a phospholipid which is the major component of a phosphatide fraction which may be isolated from either egg yolk (in Greek lekithos - λεκιθος) or soy beans from which it is mechanically or chemically extracted using hexane.

Lecithin is commercially available in high purity as a food supplement and for medical uses.

In biology

Nervous and circulatory lecithin is produced by the liver if the diet is adequate. It is needed by every cell in the body and is a key building block of cell membranes; without it, they would harden. Lecithin protects cells from oxidation and largely comprises the protective sheaths surrounding the brain.

As a food additive

Lecithin is regarded as a well tolerated and non-toxic surfactant. It is approved by the United States Food and Drug Administration for human consumption with the status "Generally Recognised As Safe". Lecithin is an integral part of cell membranes, and can be totally metabolized, so it is virtually non-toxic to humans. Other emulsifiers can only be excreted via the kidneys.

Lecithin is used commercially for anything requiring a natural emulsifier and/or lubricant, from pharmaceuticals to protective coverings. For example, lecithin is the emulsifier that keeps chocolate and cocoa butter in a candy bar from separating.

Various studies (Brook et al. 1986, Spilburg et al. 2003) indicate that soy-derived lecithin may positively affect cholesterol and triglyceride levels in the blood.

Commercial lecithin, as used by food manufacturers, is a mixture of phospholipids in oil. The lecithin is obtained by degumming crude oil. The lecithin is a mixture of various phospholipids, and the compositions depends on the origin of the lecithin. A major source of lecithin is soybean oil. Due to the EU-requirement to declare the addition of allergens in foods a gradual shift to other sources of lecithin, e.g., sunflower oil, is taking place.

The main phospholipids in lecithin from soya and sunflower are phosphatidyl choline, phosphatidyl inositol, phosphatidyl ethanolamine and phosphatidic acid. To modify the performance of lecithins, i.e., to make it suitable for the product to which it is added, it may be hydrolysed enzymatically. In hydrolysed lecithins, 20–25% of the phospholipids have one fatty acid removed by phospholipase. The most commonly used phospholipase is phospholipase A2, which removes the fatty acid at the sn-2 position.

In margarines, especially those containing high levels of fat (>75%), lecithin is added as 'anti-spattering' agent: it helps in suppressing spattering during shallow frying. Lecithin is admitted by the EU as a food additive and is designated by E number E322.

Compatibility with specialised diets

Egg-derived lecithin may be a concern for those following certain specialised diets. Under kashrut it is considered pareve (neutral, e.g., may be mixed with both meat and dairy), but under sharia it is restricted. There is no general agreement among vegetarians concerning egg-derived lecithin, but vegans especially would try to avoid consuming it. Egg lecithin itself is not a concern for those on a low cholesterol diet, but if not purified before being used as a food ingredient, it could contribute significantly to the overall cholesterol content of the food.

See also

• Biochemistry
• Choline
• Lipid
• Lipid bilayer