What are phospholipids?

Phospholipids are lipids containing phosphoric acid and belong to complex lipids. Phospholipids are the main components of biological membranes, and are divided into two categories: glycerophospholipids and sphingomyelins, which are composed of glycerol and sphingosine, respectively. Phospholipids are amphiphilic molecules with a hydrophilic nitrogen- or phosphorus-containing head at one end and a long hydrophobic (lipophilic) hydrocarbon-based chain at the other. For this reason, the hydrophilic ends of phospholipid molecules are close to each other, and the hydrophobic ends are close to each other, and often together with other molecules such as proteins, glycolipids, and cholesterol, form a phospholipid bilayer, that is, the structure of the cell membrane.

Composition overview
So far, it has been found that phospholipids exist in almost all body cells, and there are more phospholipids in important tissues of animals and plants. Animal phospholipids mainly come from egg yolk, milk, animal brain tissue, liver, kidney and muscle tissue. Plant phospholipids mainly exist in oilseeds, and most of them exist in the colloid phase, and exist in a combined state with proteins, carbohydrates, fatty acids, bacteria alcohol, vitamins and other substances, and are an important class of lipid concomitants. In the process of oil making, phospholipids come out with the oil. The content of phospholipids in crude oil is the highest in soybean oil, so soybean lecithin is the most important source of vegetable phospholipids.

Phospholipids are a class of lipids containing phosphoric acid. There are two main types of phospholipids in the body. The phospholipids composed of glycerol are called phosphoglycerides; the phospholipids composed of sphingosine are called sphingolipids. Its structural characteristics are: a hydrophilic head (hydrophilic head) composed of substituent groups (containing ammonia bases or alcohols) linked by phosphoric acid and a hydrophobic tail (hydrophobic tail) composed of fatty acid chains. In biological membranes, the hydrophilic heads of phospholipids are located on the membrane surface, while the hydrophobic tails are located on the inside of the membrane. Phospholipids are important amphiphiles, they are important components of biological membranes, emulsifiers and surfactants.

Phospholipid (phospholipid) is composed of five elements, C, H, O, N, and P, and is an important part of biological membranes. According to the main chain structure of phospholipids, they are divided into phosphoglycerolipids and sphingomyelins.
1. The main chain of phosphoglycerides is glycerol-3-phosphate, the other two hydroxyl groups in the glycerol molecule are esterified by fatty acids, and the phosphate group can be esterified by various small molecular compounds with different structures to form various Phosphoglycerides. The most abundant in the body are phosphatidylcholine (lecithin), phosphatidylethanolamine (cephalin), phosphatidylserine, phosphatidylglycerol, diphosphatidylglycerol (cardiolipin) and phosphatidylinositol, etc. Each phospholipid can There are several types of fatty acids depending on the composition.
It can be known from the molecular structure that the central atom of the glycerol molecule is asymmetric, so it has different three-dimensional configurations. The naturally occurring phosphoglycerides all have the same host chemical configuration. Following chemical conventions, these molecules can be represented by two-dimensional projections. The configurations of D-type and L-type glyceraldehyde phosphate were determined according to the results of X-ray crystallography. Right-handed is D-shaped, and left-handed is L-shaped. The stereochemical configuration and nomenclature of phosphoglycerides are deduced from this.

2. Sphingomyelin (sphingomyelin) Sphingomyelin is a phospholipid containing sphingosine or dihydrosphingosine, its molecule does not contain glycerol, and is a molecule of fatty acid linked to the amino group of sphingosine by an amide bond. Sphingosine or dihydrosphingosine is an amino diol with a long aliphatic chain. Sphingosine or dihydrosphingosine has a hydrophobic tail composed of long-chain aliphatic hydrocarbon groups and a polar head composed of two hydroxyl groups and one amino group.
Sphingomyelin contains phosphoric acid, and its terminal hydrocarbyl substituent is phosphorylcholine ethanolamine. The most abundant sphingomyelin in the human body is sphingomyelin, which is composed of sphingosine, fatty acid and phosphorylcholine. Sphingomyelin is an important phospholipid constituting biofilms. It often coexists with lecithin on the outside of the cell membrane.

The hydroxyl groups on C1 and C2 of glycerol are esterified with fatty acid, the hydroxyl group on C3 is esterified with phosphoric acid, and the phosphoric acid is connected with a polar alcohol (X-OH), which constitutes glycerophospholipid. The non-polar tail of the molecule contains two long chains of fatty acids. The C1 on the carbon frame of glycerol is usually connected to a saturated fatty acid with 16 or 18 carbon atoms, and its C2 is often occupied by an unsaturated fatty acid with 16 to 20 carbon atoms. . Phosphoryl-X constitutes the polar head of glycerophospholipid, so glycerophospholipid can be classified according to the difference of polar head alcohol (X-OH). X=H constitutes the simplest glycerophospholipid, called phosphatidic acid, which is only present in small amounts in biological membranes. The glycerophospholipids normally present in biological membranes have polar heads. Examples of important glycerophospholipid polar head alcohols are:

Polar phospholipids naturally form lipid monolayers with a thickness of one lipid molecule on the surface of aqueous solutions, their hydrocarbon tails avoid water and face the atmosphere, while their hydrophilic polar heads point towards the polar aqueous phase. In aqueous systems, polar lipids naturally come together to form molecular clusters (with the non-polar tails facing inward) or extremely thin lipid bilayers to separate the two aqueous parts. The nonpolar tails of lipid bilayer lipid molecules stretch inwards to form a continuous inner hydrocarbon core, while the polar heads face outwards into the aqueous phase. Lipid bilayers are soft and easy to bend and flow, and are the basic structure of biological membranes. They account for 20-80% of the membrane weight depending on the type of membrane.
See Sphingolipids for the structure and properties of sphingomyelin.

research Development
Phospholipids were first discovered from the human brain by Uauquelin in 1812, isolated from egg yolks by Gobley in 1844, and named Lecithin (lecithin) according to the Greek lekithos (yolk) in 1850.
The commercial production of phospholipids has a history of more than 70 years. So far, the most abundant soybean phospholipids were found in Germany in 1930 and gradually realized commercial production. Since the 1970s, Europe and the United States and other countries have begun to use such health care products. In the United States, the total sales of lecithin health care products ranks third after multivitamins and vitamin E. According to statistics, the annual output of soybean lecithin in the world is about 140,000 tons. The United States and Western Europe account for 60% of the world’s total production of soybean lecithin, and the main manufacturers are the mainstream large companies in the United States and Germany.
Japan approved the use of soybean lecithin in 1961, and lecithin products companies have prospered. There are many varieties of soybean lecithin products on the market. Japanese nutritionist Hiromi Kobori in his book “Soybean Lipids” called phospholipids “the most popular in this century.” Great health food”.

1. According to the classification of phospholipid glycerol backbone
Phospholipids can be divided into glycerolphospholipids and sphingolipids according to the glycerol backbone. They are all polar lipids. Polar lipids consist of a polar part (called the polar head) and a non-polar part (called the apolar tail). Among them, glycerophospholipids can be classified into Phosphatidyl cholines (PC), Phosphatidyl ethanolamines (PE), Phosphatidyl serines (PS), Phosphatidyl serines (PS), Phosphatidyl serines (PS) Alcohol (Phosphatidyl inositols, PI), phosphatidyl glycerol (PG), glycerophosphatidic acid (phosphatidic acid, PA), etc.

Glycerophospholipids can be divided into many types due to different substituent groups, among which the important ones are:

①choline (choline) + phosphatidic acid ——→ phosphatidyl choline (phosphatidyl choline), also known as lecithin (lecithin)
②Ethanolamine (ethanolamine) + phosphatidic acid ——→phosphatidyl ethanolamine (phosphatidyl ethanolamine), also known as cephain
③ Serine (serine) + phosphatidic acid ——→ phosphatidyl serine (phosphatidyl serine)
④Glycerol (glycerol) + phosphatidic acid ——→ phosphatidyl glycerol (phosphatidyl glycerol)
⑤inositol (inositol) + phosphatidic acid ——→ phosphatidyl inositol (phosphatidyl inositol)
⑥Cardiolipin is composed of C1 and C3 of glycerol combined with two molecules of phosphatidic acid. It is an important component of mitochondrial inner membrane and bacterial membrane, and it is the only phospholipid molecule with antigenicity.
⑦In addition to the above 6 kinds, the fatty acyl group of glycerol at the first position in the glycerophospholipid molecule is replaced by a long-chain alcohol to form an ether, such as plasmalogen and platelet activating factor (PAF), which belong to glycerol. Phospholipids.

Sphingolipids are characterized in that they do not contain glycerol and contain sphingosine, which can be divided into two types according to the difference of the substituent group X:

①X is phosphorylcholine called sphingomyelin (sphingmyelin)
②X is a sugar group called glycosphingolipid (glycosphingolipid)
2. According to the classification of amino acids
According to the different amino alcohols, it can be divided into the following categories:
①Phosphatidylcholine (lecithin) (PC), HO—CH2CH2N+ (CH3)3 (choline), distribution: in the brain, semen, adrenal glands, red blood cells, egg yolk (8-10%) of plants such as soybeans and animals . Function: Control liver lipid metabolism and prevent the formation of fatty liver.
②Phosphatidylethanolamine (cephalin) (PE), HO—CH2CH2—N+H3 (ethanolamine), involved in blood coagulation.
③Phosphatidylserine (PS), HO—CH2CH—COO- (serine), N+H3, Note: (1)—(3) X are amino alcohols.
④ Phosphatidylinositol (PI)
⑤ Phosphatidylglycerol (PG)
⑥Diphosphatidylglycerol (cardiolipin)

physical properties
It is milky white, light yellow or brown depending on the degree of processing and bleaching, easily soluble in ether, benzene, chloroform, n-hexane, but insoluble in polar solvents such as acetone and water. It is an amphoteric surfactant with emulsifying properties.

Chemical properties
Hydrolysis, acetylation, hydroxylation, acylation, sulfonation, saturation (oxidation to saturate phospholipids), activation (introduction of unsaturated groups) and other reactions can be carried out.

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% lipid (mainly phospholipid). It is composed of lecithin, inositol phospholipids, cephalin and so on. These phospholipids play corresponding functions to various parts and organs of the human body. Phospholipids play an important role in activating cells, maintaining metabolism, basal metabolism and balanced secretion of hormones, and enhancing the body’s immunity and regeneration. In addition, phospholipids can also promote fat metabolism, prevent fatty liver, lower serum cholesterol, improve blood circulation, and prevent cardiovascular disease.

Phospholipids can decompose excessive blood lipids and excessive cholesterol, clean blood vessels, and make blood vessels circulate smoothly. They are recognized as “vascular scavengers”. Phospholipids can also emulsify neutral fat and cholesterol deposited in blood vessels into particles that are harmless to the human body, dissolve in water and excreted from the body, prevent excess fat from depositing on the blood vessel wall, 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, resulting in narrowing of blood vessel passages and causing high blood pressure. When the blood lipid block and the shed cholesterol block in the blood meet the narrow position of the blood vessel, they are stuck and cannot pass through, causing a blockage and forming an embolism. The powerful emulsifying effect of phospholipids can emulsify the cholesterol and lipids deposited on the blood vessel walls in the blood vessels, forming milky white liquids and expelling them from the body.
Coronary heart disease and stones are the same.

Human nerve cells and brain cells are covered by a cell membrane composed of phospholipids. Insufficient phospholipids will cause damage to the membrane, resulting in mental decline and mental stress. The acetyl groups contained in phospholipids enter the intercellular space and combine with choline to form acetylcholine. Acetylcholine is a signal 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.
activated cells
Phospholipids are an important part of cell membranes and are responsible for the exchange of substances inside and outside cells. If the phospholipids consumed by people every day are not replenished, the cells will be in a state of nutrient deficiency and lose their vitality.
The human liver can synthesize some phospholipids, but most of them are taken 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 activity of phospholipids will be lost. Therefore, it is recommended that healthy people and sub-healthy people consume phospholipids as a way of health care.

After removing most of the lecithin from soybean lecithin, it is extracted and separated with an organic solvent, then emulsified and spray-dried.
Add 3% water to soybean crude oil, stir well at 60-80℃ for 30min, the phospholipids are hydrated into gelatinous precipitates, and hydrated phospholipids are obtained by continuous centrifugation. %) decolorization; then drying under reduced pressure at 80-100° C. and 2.67-8.00 kPa to obtain a liquid phospholipid with a content of 60%-70%.
Dissolve the oil and fatty acid in the phospholipids with 3-5 times of acetone at 50°C, after centrifugation, repeat the treatment twice, and finally dry under reduced pressure at 60°C to obtain phospholipid powder with a content of more than 95%.

In the food industry, phospholipids are often used as emulsifiers to make oils soluble in water. The common one is lecithin, which is generally made from edible oil and used as a food additive for bread, solid chocolate food, etc.

As an antioxidant, it can be used in cakes, candies and hydrogenated vegetable oils. It can be used in moderation according to production needs, and can also be used as an emulsifier.
Used as food shortening.

food source
Phospholipids are present in all animal and plant cells. In plants, it is mainly distributed in seeds, nuts and grains. Egg yolks and soybeans are rich in phospholipids. Other plants such as corn, cottonseed, rapeseed, peanut, and sunflower seed contain a certain amount of phospholipids. Many studies have reported that it is relatively rare as a by-product because the content is relatively low and the scale of oil processing is not as good as that of soybeans.