LECITHIN: STRUCTURE AND FUNCTIONS - BIOLOGY - 2025

The lecithin is a complex mixture of glycerophospholipids can be obtained from microbial sources, animal or plant and containing varying amounts of triglycerides, fatty acids, sterols, glycolipids and sphingolipids.

This term is usually used to refer to a mixture of lipid compounds obtained from the "degumming" process (removal of oil-insoluble phospholipids during fat refining) of crude vegetable oils.

Soy lecithin (Source: Helge Höpfner via Wikimedia Commons)

However, some texts define "lecithin" as a phospholipid that enriches the crude oils extracted from soybeans (phosphatidylcholine, specifically); while others claim that it is mainly a complex mixture of lipids such as phosphatidylcholine, phosphatidylethanolamine and phosphatidylinositol.

It is found in virtually all living cells, where it fulfills various types of biological functions, especially as a component of the lipid bilayers that make up biological membranes, where its derivatives can function as second messengers, precursors of other molecules, etc.

Lecithins are particularly abundant in seeds, nuts, eggs and cereals, with vegetables being the main source of obtaining them for industrial purposes, mainly for the production of food, drugs, cosmetics, among others.

Structure of lecithin

Commercially found lecithin usually comes from some plant source and consists of a mixture of approximately 17 different compounds, including carbohydrates, phytosterols, phytoglycolipids, pigments, triglycerides, etc.

The three main phospholipids that make up the mixture are phosphatidylcholine (19-21%), phosphatidylinositol (20-21%) and phosphatidylethanolamine (8-20%).

As phospholipids, these three molecules are composed of a glycerol “backbone” to which two fatty acid chains of variable length (usually between 14 and 18 carbon atoms) are esterified in positions 1 and 2, and whose third atom of Carbon is attached to a phosphate molecule to which different groups are attached.

General structure of phosphatidylcholine (Source: NEUROtiker via Wikimedia Commons)

The identity of the molecule that binds to the phosphated portion of diacylglycerol is what defines the identity of each phospholipid in question. Choline, ethanolamine, and inositol are the "substituent" groups for phosphatidylcholine, phosphatidylethanolamine, and phosphatidylinositol, respectively.

Other molecules such as biotin, folic acid, thiamine, riboflavin, pantothenic acid, pyridoxine, niacin and tocopherol are found in a much smaller proportion than the aforementioned phospholipids.

Protein

In addition to the lipid and non-lipid components that make up lecithin, some authors have found that these preparations obtained from the processing of vegetable oils can also have a low protein content.

Related studies indicate that the analyzed protein fractions of lecithins from different sources are enriched with globulin-type proteins, to which the allergenic effect that soy can have, for example, in many consumers is attributed.

Lecithins from other sources

Depending on the organism under consideration, lecithins can vary somewhat in their composition. While plant lecithins are rich in phosphatidylcholine, phosphatidylethanolamine, and phosphatidylinositol, animal lecithins, for example, are also rich in phosphatidylserine and sphingomyelin, but lack phosphatidylinositol.

Bacteria and other microbes also possess lecithins and these are very similar in composition to those of plant cells, that is, they are rich in phosphatidylethanolamine and phosphatidylcholine, although they can also have phosphatidylserine or sphingomyelin, as in animals.

Features

Lecithin has many biological functions as part of living cells. In addition, it is commercially exploited from many points of view, being particularly useful in the production of food, cosmetics and drugs.

Biological functions

One of the main functions outlined of this mixture of compounds for the human body is to supply the needs of choline, which is a necessary cofactor for the production of the neurotransmitter acetylcholine, which participates in muscle contraction.

Lecithin is also a rich source of fatty acids from the omega-3 group, which are usually deficient in the diet of most people and of which their intake is recommended.

Another interesting function of this complex mixture of molecules is that of its emulsifying capacity in the digestive system, a characteristic that has been commercially exploited for the emulsification and stabilization of different preparations.

Lecithins, along with cholesterol, bile acids, and bilirubin, are one of the main components of the bile produced by the liver in mammals. It has been determined that lecithins can form mixed micelles with cholesterol molecules and that they participate in intestinal fat emulsion.

As much of the composition of lecithin is represented by phospholipids, another of its biological functions has to do with the production of second messengers that participate in different cellular signaling cascades.

Industrial and / or commercial functions

They are usually consumed as nutritional supplements, although some drugs administered during the treatment of Alzheimer's and other pathologies such as diseases of the bladder, liver, depression, anxiety and high cholesterol, also have lecithin among their active compounds.

They function as "anti-dust" agents by reducing static electricity by "wetting" the dust particles. In some culinary preparations, lecithins function as "retarders" of fat nucleation or agglomeration, which is important for reducing the "grainy" texture of certain preparations.

As discussed, lecithins are famous for their ability to act as emulsifying agents, since they promote the stable formation of water-in-oil or oil-in-water emulsions, reducing the surface tension between immiscible liquids (which cannot be mixed)..

Additionally, lecithins are used in the mixing of ingredients for their ability to decrease the time and increase the mixing efficiency, in addition to providing lubrication and reduction of the viscosity in the contact surfaces between “incompatible” solids.

As it is mainly a mixture of fatty substances, lecithins work perfectly for greasing hot or cold metal surfaces for cooking food. They also reduce the "sticking" process between frozen food products and can be helpful when cleaning hot surfaces.

In this sense, said compound is also used to prevent the adhesion of products that would normally be difficult to separate from each other, such as confectionery (sweets) or cheese slices.

Summary of main applications

Some authors present a list where the applications of this mixture of substances are considerably summarized, which looks more or less as follows:

- Anticorrosive

- Antioxidants

- Biodegradable additives

- Anti-splash

- Altipust

- Biologically active agents

- Color intensifiers

- Surfactants or emulsifiers

- Lubricants

- Liposome encapsulating agents

- Wetting agents

- Nutritional supplements

- Stabilizers

- Water repellants

- Viscosity modifiers.

References

1. Dworken, HJ (1984). Gastroenterology: Edited by Gary Gitnick, MD 425 pp. John Wiley & Sons, Inc., New York, New York, 1983. Gastroenterology, 86 (2), 374.
2. Martín-Hernández, C., Bénet, S., & Marvin-Guy, LF (2005). Characterization and quantification of proteins in lecithins. Journal of agricultural and food chemistry, 53 (22), 8607-8613.
3. Rincón-León, F. Functional foods. Encyclopedia of Food Science and Nutrition, Vol. 1.
4. Scholfield, CR (1981). Composition of soybean lecithin. Journal of the American Oil Chemists' Society, 58 (10), 889-892.
5. Szuhaj, BF (2016). Phospholipids: Properties and Occurrence.