Lecithin
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219611245
2008-06-16T02:05:40Z
Canderson7
202193
rvv
''[[Image:Phosphatidylcholine.png|thumb|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]], [[glycolipid]]s, [[triglyceride]]s, and [[phospholipid]]s (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 language|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 biology==
[[Phosphatidylcholine]] occurs in all cellular organisms being one of the components of the phospholipid portion of the [[Cell_membrane | Cell Membrane]]
==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 "[[GRAS|Generally Recognized As Safe]]." Lecithin is an integral part of [[cell membrane]]s, and can be totally [[metabolism|metabolized]], so it is virtually non-[[toxic]] to humans. Other [[emulsifier]]s can only be excreted via the [[kidney]]s.
Lecithin is used commercially in substances requiring a natural [[emulsifier]] and/or [[lubricant]], from [[pharmaceuticals]] to protective coverings. For example, lecithin is the emulsifier that keeps [[cocoa]] and [[cocoa butter]] in a [[candy bar]] from separating.
There are studies that show soy-derived lecithin has significant effects on lowering [[cholesterol]] and [[triglyceride]], while increasing [[HDL]] ("good cholesterol") levels in the blood <ref>Iwata, T., Kimura, Y., Tsutsumi, K., Furukawa, Y. & Kimura, S. (1993).The effect of various phospholipids on plasma lipoproteins and liver lipids in hypercholesterolemic rats. <i>Journal of Nutritional Science and Vitaminology</i> <b>39</b>, 63-71.</ref><ref>Jimenez, M. A., Scarino, M. L., Vignolini, F. & Mengheri, E. (1990). Evidence that polyunsaturated lecithin induces a reduction in plasma cholesterol level and favorable changes in lipoprotein composition in hypercholesterolemic rats. <i> Journal of Nutrition</i> <b>120</b>, 659-667.</ref>.
Commercial lecithin, as used by food manufacturers, is a mixture of [[phospholipid]]s in [[Vegetable_fats_and_oils|oil]]. The lecithin is obtained by [[degumming]] the extracted oil of the seeds. The lecithin 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. To modify the performance of lecithin, i.e., 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 [[lyso-phospholipids]]. 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 an 'anti-spattering' agent for shallow [[frying]]. Lecithin is admitted by the EU as a [[food additive]], designated by [[E number]] E322.
Lecithins may also be modified by a process called [[fractionation]]. During this process, lecithin is mixed with an alcohol, usually ethanol. Some phospholipids have a good solubility in ethanol (e.g., phosphatidylcholine), 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.
=== Compatibility with special diets ===
Thus far, the only proven benefit and suggested use 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.
[[Egg (food)|Egg]]-derived lecithin may be a concern for those following some specialized [[Diet (nutrition)|diet]]s. Egg lecithin is not a concern for those on low-[[cholesterol]] diets, but, if not purified before being used as a food ingredient, it could significantly raise the overall cholesterol content of the food. Consumer Product companies should clearly indicate the source of lecithin to help consumers.
For observant [[Jew]]s under [[Kashrut]], it is considered ''[[pareve]]'', neutral, e.g., may be mixed with both meat and dairy.{{Fact|date=May 2008}} However, soy derived lecithin is considered by some to be [[kitniyot]] and prohibited on [[Passover]].{{Fact|date=May 2008}} For most [[Muslim]]s, lecithin or any other derivatives from plants, egg yolks or animals are allowed.{{Fact|date=May 2008}} There is no general agreement among [[vegetarian]]s concerning egg-derived lecithin, but since it is animal-derived, [[Jain]]s, strict [[vegetarian]]s, [[vegan]]s choose not to consume it.
== See also ==
* [[Biochemistry]]
* [[Choline]]
* [[Lipid]]
* [[Lipid bilayer]]
== References ==
<references/>
== External links ==
*[http://www2.chemie.uni-erlangen.de/services/dissonline/data/dissertation/Christoph_Wabel/html/Chapter1.html Introduction to Lecithin] ([[University of Erlangen]])
*[http://www.cfsan.fda.gov/~dms/soyguid.html FDA Industry guideline for soy lecithin labeling]
*[http://www.pdrhealth.com/drug_info/nmdrugprofiles/nutsupdrugs/pho_0288.shtml Phosphatidylcholine info]
*[http://www.kellymom.com/nutrition/vitamins/lecithin.html Use of lecithin for recurrent plugged ducts]
[[Category:Food emulsifiers]]
[[Category:Phospholipids]]
[[Category:Membrane biology]]
[[Category:Nootropics]]
[[Category:Soy products]]
[[Category:Surfactants]]
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