lecithin

An example of a phosphatidylcholine, a type of phospholipid in lecithin. Red - choline and phosphate group; Black - glycerol; Green - unsaturated fatty acid; Blue - saturated fatty acid

Lecithin is a generic term to designate any group of yellow-brownish fatty substances occurring in animal and plant tissues composed of phosphoric acid, choline, fatty acids, glycerol, glycolipids, triglycerides, and phospholipids (e.g., phosphatidylcholine, phosphatidylethanolamine, and phosphatidylinositol).

Lecithin was first isolated in 1846 by the French chemist and pharmacist Theodore Gobley;^[1] in 1850 he named the phosphatidylcholine léchithine.^[2] 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;^[3] 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, chicken and sheep brain.

Lecithin can easily be extracted chemically (using hexane) or mechanically from readily available sources such as soy beans. 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 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

Phosphatidylcholine occurs in all cellular organisms, being one of the major components of the phospholipid portion of the cell membrane.

Production

Commercial lecithin, as used by food manufacturers, is a mixture of phospholipids in oil. The lecithin can be obtained by degumming the extracted oil of seeds. It is a mixture of various phospholipids, and the composition depends on the origin of the lecithin. A major source of lecithin is soybean oil. Because of the EU requirement to declare additions of allergens in foods, in addition to regulations regarding genetically modified crops, 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. They are often abbreviated to PC, PI, PE, and PA, respectively.

Hydrolysed lecithin

To modify the performance of lecithin to make it suitable for the product to which it is added, it may be hydrolysed enzymatically. In hydrolysed lecithins, a portion of the phospholipids have one fatty acid removed by phospholipase. Such phospholipids are called lysophospholipids. The most commonly used phospholipase is phospholipase A2, which removes the fatty acid at the C2 position of glycerol. Lecithins may also be modified by a process called fractionation. During this process, lecithin is mixed with an alcohol, usually ethanol. Some phospholipids, such as phosphatidylcholine, have good solubility in ethanol, whereas most other phospholipids do not dissolve well in ethanol. The ethanol is separated from the lecithin sludge, after which the ethanol is removed by evaporation to obtain a phosphatidylcholine-enriched lecithin fraction.

Properties and applications

Lecithin has emulsification and lubricant properties, and is a surfactant. It can be totally metabolized (see Inositol) by humans, so is well tolerated by humans and nontoxic when ingested; some emulsifiers can only be excreted via the kidneys.

Lecithin is used for applications in human food, animal feed, pharmaceutical, paint, and other industrial applications.

Applications listed by one manufacturer, in addition to food applications, include:^[4]

• In the pharmaceutical industry, it acts as a wetting, stabilizing agent and a choline enrichment carrier, helps in emulsifications and encapsulation, and is a good dispersing agent. It can be used in manufacture of intravenous fat infusions and for therapeutic use.
• In animal feed, it enriches fat and protein and improves pelletization.
• In the paint industry, it forms protective coatings for surfaces with painting and printing ink, has antioxidant properties, helps as a rust inhibitor, is a colour-intensifying agent, catalyst, conditioning aid modifier, and dispersing aid; it is a good stabilizing and suspending agent, emulsifier, and wetting agent, helps in maintaining uniform mixture of several pigments, helps in grinding of metal oxide pigments, is a spreading and mixing aid, prevents hard settling of pigments, eliminates foam in water-based paints, and helps in fast dispersion of latex-based paints.
• Lecithin can also be used as a release agent for plastics, an antisludge additive in motor lubricants, an antigumming agent in gasoline, and an emulsifier, spreading agent, and antioxidant in textile, rubber and other industries.

Use with food, and health effects

The nontoxicity of lecithin leads to its use with food, as an additive or in food preparation. It is used commercially in foods requiring a natural emulsifier or lubricant. In the food industry, it has multiple uses: In confectionery, it reduces viscosity, replaces more expensive ingredients, controls sugar crystallization and the flow properties of chocolate, helps in the homogeneous mixing of ingredients, improves shelf life for some products, and can be used as a coating. In emulsions and fat spreads, it stabilizes emulsions, reduces spattering during frying, improves texture of spreads and flavour release. In doughs and bakery, it reduces fat and egg requirements, helps even distribution of ingredients in dough, stabilizes fermentation, increases volume, protects yeast cells in dough when frozen, and acts as a releasing agent to prevent sticking and simplify cleaning. It improves wetting properties of hydrophilic powders (e.g., low-fat proteins) and lipophilic powders (e.g., cocoa powder), controls dust, and helps complete dispersion in water.^[4] It can be used as a component of cooking sprays to prevent sticking and as a releasing agent.

For example, lecithin is the emulsifier that keeps cocoa and cocoa butter in a candy bar from separating. In margarines, especially those containing high levels of fat (>75%), lecithin is added as an 'antispattering' agent for shallow frying.

It is approved by the United States Food and Drug Administration for human consumption with the status "generally recognized as safe." Lecithin is admitted by the EU as a food additive, designated by E number E322. Research studies show soy-derived lecithin has significant effects on lowering serum cholesterol and triglycerides, while increasing HDL ("good cholesterol") levels in the blood.^[5][6] However, studies on egg lecithin have been inconsistent and contradictory since the 1920s.^[7]

New studies suggest gut bacteria metabolites of choline promote atherosclerosis in mice through TMAO production and "augmented macrophage cholesterol accumulation and foam cell formation".^[8] Mice fed with egg-yolk derived lecithin developed arterial plaque in spite of no increase in cholesterol or triglyceride levels.^[9]

Compatibility with special diets

A proven benefit and suggested use for lecithin is for those taking niacin to treat high cholesterol. Niacin treatment can deplete choline, necessitating an increased amount of lecithin or choline in the diet.^{[10][11][12][13][14]} Egg-derived lecithin may be a concern for those following some specialized diets. Egg lecithin is not a concern for those on low-cholesterol diets, because the lecithin found in eggs markedly inhibits the absorption of the cholesterol contained in eggs.^[15] There is no general agreement among vegetarians concerning egg-derived lecithin; vegans and lactovegetarians would likely abstain from it.

Religious restrictions

Soy-derived lecithin is considered by some to be kitniyot and prohibited on Passover for Ashkenazi Jews when many grain-based foods are forbidden, but not at other times. This does not necessarily affect Sephardi Jews, who do not have the same restrictions on rice and kitniyot during Pesach/Passover.^[16]

Muslims are not forbidden to eat lecithin per se; however, since it may be derived from animal as well as plant sources, care must be taken to ensure this source is halal. Lecithin derived from plants and egg yolks is permissible, as is that derived from animals slaughtered according to the rules of dhabihah.^[17]

References

External links

• Introduction to Lecithin (University of Erlangen)
• FDA Industry guideline for soy lecithin labeling broken link
• Phosphatidylcholine info
• Use of lecithin for recurrent plugged ducts
• European Lecithin Manufacturers Association official website
• The International Lecithin & Phospholipid Society Website