Phospholipids
[Overview]
Phospholipids generally refer to various phosphorus-containing lipids, which are divided into phosphoglycerides and sphingolipids. Phosphoglycerides mainly include lecithin (phosphatidylcholine), cephalin (phosphatidylethanolamine), tyrosine phospholipids and inositol phospholipids. Its basic structure is that the two hydroxyl groups of the glycerol contained in glycerol phosphate are combined with fatty acids to form an ester, and the third hydroxyl group is esterified by phosphoric acid to generate phosphatidic acid, which is then combined with other alcoholic hydroxyl compounds to form different phospholipids. Phospholipids are the main components of biological membranes and have some other important physiological functions. For example, lecithin has anti-fatty liver effects, and cephalin may be the prosthetic group of prothrombin activator in platelets. Sphingomyelin, also known as sphingomyelin, is composed of neuraminol, fatty acids, phosphoric acid and choline and is mainly found in the brain and nervous tissue. Phospholipids are also involved in lipoprotein composition and cholesterol metabolism. Egg yolks, plant seeds and germs, and soybeans are rich in phospholipids. [1]
[Composition Overview]
So far, people have discovered that phospholipids are present in almost all cells of the body, and there are more phospholipids in important tissues of animals and plants. Animal phospholipids are mainly derived from egg yolk, milk, animal brain tissue, liver, kidney and muscle tissue. Plant phospholipids mainly exist in oil seeds, and most of them exist in the colloidal phase, and exist in a combined state with proteins, sugars, fatty acids, bacterial alcohols, vitamins and other substances. They are an important type of oil companion. During the oil production process, phospholipids are released with the oil. Soybean crude oil has the highest phospholipid content in crude oil, so soybean phospholipids are the most important source of plant phospholipids.
Phospholipids are a type of lipids containing phosphoric acid. The body mainly contains two types of phospholipids. The phospholipids composed of glycerol are called phosphoglycerides; the phospholipids composed of sphingosine are called sphingolipids. ). Its structural characteristics are: a hydrophilic head composed of substituent groups (ammonium-containing bases or alcohols) connected to phosphoric acid and a hydrophobic tail composed of fatty acid chains. In biological membranes, the hydrophilic heads of phospholipids are located on the surface of the membrane, while the hydrophobic tails are located on the inside of the membrane. Phospholipids are important amphiphilic substances, they are important components, emulsifiers and surfactants of biological membranes.
[Composition]
Phospholipid is composed of five elements: C, H, O, N, and P. It is an important component of biological membranes. Its characteristic is that it produces a mixture containing fatty acids and phosphoric acid after hydrolysis. According to the main chain structure of phospholipids, they are divided into phosphoglycerolipids and sphingomyelin.
1． The main chain of phosphoglycerides is glycerol-3-phosphate. The other two hydroxyl groups in the glycerol molecule are esterified by fatty acids. The phosphoglyceride group can be esterified by various small molecule compounds with different structures to form various phosphoglycerides. Glyceryl phosphate. Phosphatidylcholine (lecithin), phosphatidylethanolamine (cephalin), phosphatidylserine, phosphatidylglycerol, diphosphatidylglycerol (cardiolipin) and phosphatidylinositol are abundant in the body. Each phospholipid can There are several types depending on the composition of fatty acids.
It can be seen from the molecular structure that the central atom of the glycerol molecule is asymmetric and therefore has different three-dimensional configurations. Naturally occurring phosphoglycerides all have the same main chemical configuration. Following chemical convention, these molecules can be represented by two-dimensional projections. The configurations of D-form and L-form glyceraldehyde phosphate were determined based on their X-ray crystal diffraction results. Right-hand rotation is D-type, left-hand rotation is L-type. The stereochemical configuration and nomenclature of glyceryl phosphate were deduced from this.
2. Sphingomyelin is a phospholipid containing sphingosine or dihydrosphingosine. Its molecule does not contain glycerol. It is a molecule of fatty acid connected to the amino group of sphingosine through an amide bond. Sphingosine or dihydrosphingosine is an aminodiol with a long aliphatic chain. Sphingosine or dihydrosphingosine has a hydrophobic tail composed of a long-chain aliphatic hydrocarbon group and a polar head composed of two hydroxyl groups and an amino group.
Sphingomyelin contains phosphoric acid, and its terminal hydrocarbyl substituent is phosphocholine ethanolamine. The most abundant sphingomyelin in the human body is sphingomyelin, which is composed of sphingosine, fatty acids and phosphocholine. Sphingomyelin is an important phospholipid that constitutes biological membranes. It often coexists with lecithin on the outside of the cell membrane. [2]
[Structure]
The hydroxyl groups on C1 and C2 of glycerol are esterified by fatty acids, and the hydroxyl group on C3 is esterified by phosphoric acid. The phosphoric acid is connected to a polar alcohol (X—OH), which constitutes glycerophospholipid. The non-polar tail of the molecule contains two long chains of fatty acids. C1 on the glycerol carbon frame is often connected to a saturated fatty acid containing 16 or 18 carbon atoms, and its C2 is often occupied by an unsaturated fatty acid containing 16 to 20 carbon atoms. . Phosphoryl-X constitutes the polar head of glycerophospholipids, so glycerophospholipids can be classified according to the different polar head alcohols (X—OH). X=H constitutes the simplest glycerophospholipid, called phosphatidic acid, which is only found in small amounts in biological membranes. Glycerophospholipids commonly found in biological membranes have polar heads. Examples of important glycerophospholipid polar head alcohols are as follows:
Polar phospholipids naturally form a lipid monolayer with a thickness of one lipid molecule on the surface of the aqueous solution. Its hydrocarbon tail avoids water and faces the atmosphere, while the hydrophilic polar head
Toward the polar aqueous phase. In water systems, polar lipids naturally clump togetherFormation of molecular clusters (nonpolar tails facing in) or extremely thin lipid bilayers separates the two aqueous parts. The nonpolar tails of lipid molecules in a lipid bilayer extend inward to form a continuous internal hydrocarbon core, while the polar heads face outward into the aqueous phase. The lipid bilayer is soft, easy to bend and flow, and is the basic structure of biological membranes. Depending on the type of membrane, they account for 20 to 80% of the membrane weight.
For the structure and properties of sphingomyelin, see Sphingolipids. [2]
[Property]
Physical properties
It appears milky white, light yellow or brown depending on the degree of processing and bleaching. It is easily soluble in ether, benzene, chloroform, n-hexane, and insoluble in polar solvents such as acetone and water. It is an amphoteric surfactant with emulsifying properties.
Chemical properties
Can carry out hydrolysis reaction, acetylation, hydroxylation, acylation, sulfonation, saturation (oxidation to saturate phospholipids), activation (introduction of unsaturated groups) and other reactions.
[Function]
Phospholipids are lipid compounds containing phospholipid roots and are the basic substances of life. The cell membrane is composed of about 40% protein and about 50% lipids (mainly phospholipids). It is composed of lecithin, inositol phospholipid, cephalin, etc. These phospholipids play corresponding functions on various parts and organs of the human body. Phospholipids play a major role in activating cells, maintaining metabolism, basal metabolism and balanced secretion of hormones, and enhancing the body’s immunity and regeneration. [1] In addition, phospholipids can also promote red phosphorus flame retardant fat metabolism, prevent fatty liver, lower serum cholesterol, improve blood circulation, and prevent cardiovascular diseases.
Emulsification
Phospholipids can decompose excessive blood lipids and excessive cholesterol, clean blood vessels, and smooth blood circulation. They are recognized as “blood vessel scavengers.” Phospholipids can also emulsify neutral fat and cholesterol deposited in blood vessels into harmless particles, which can be dissolved in water and excreted from the body. At the same time, they can prevent excess fat from depositing on the blood vessel walls and relieve the pressure on the cardiovascular and cerebrovascular walls. One of the fundamental reasons why phospholipids can prevent and treat diseases of modern civilization is that they have a strong emulsifying effect.
Taking cardiovascular and cerebrovascular diseases as an example, excessive intake of meat in the daily diet causes cholesterol and lipids to be deposited on the blood vessel walls, leading to narrowing of blood vessel channels and triggering high blood pressure. When the blood lipids and fallen cholesterol in the blood meet the narrow position of the blood vessel, they are stuck and cannot pass through, causing blockage and forming an embolism. The powerful emulsification effect of phospholipids can emulsify the cholesterol and lipids deposited on the blood vessel walls in blood vessels, forming a milky white liquid that is excreted from the body.
The same applies to coronary heart disease and stones.
Proliferation
Human nerve cells and brain cells are covered by cell membranes composed of phospholipids. Insufficient phospholipids can cause damage to the membranes, resulting in mental retardation and mental stress. The acetyl group contained in the phospholipids enters the intercellular space and combines with choline to form acetylcholine. Acetylcholine is a signaling molecule that transmits information between various nerve cells and brain cells. It can speed up the transmission of information between nerve cells and brain cells, enhance memory, and prevent Alzheimer’s disease.
Activate cells
Phospholipids are an important part of the cell membrane and are responsible for the exchange of materials inside and outside the cell. If the phospholipids consumed by people every day are not replenished, the cells will be in a state of nutritional deficiency and lose their vitality.
The human liver can synthesize some phospholipids, but most of them are absorbed from the diet, especially after the age of 30 or 40. However, the activity of phospholipids is most effective at around 25 degrees Celsius. When the temperature exceeds 50 degrees Celsius, most of the phospholipid activity will be lost. Therefore, it is recommended that healthy people and sub-healthy people consume phospholipids as a way to maintain health.
[Application]
In the food industry, phospholipids are often used as emulsifiers to make oils soluble in water. The most common ones are lecithin, which is generally made from edible oil and used as a food additive in bread, solid chocolate foods, etc.
As an antioxidant, it can be used in pastries, candies and hydrogenated vegetable oils. It can be used in appropriate amounts according to production needs. It can also be used as an emulsifier. Used as food shortening.
References:
1. Editor-in-Chief: Wang Xiangpu, Wang Yingtong, Li Juesheng. Dictionary of Health Sciences. Qingdao: Qingdao Publishing House. 2000. Chapter 466…
2. Wang Xiangpu, Wang Yingtong, etc. Dictionary of Hygiene: Huaxia Publishing House, 1999
