What Are Phospholipids?
Overview
what are phospholipids (phosphatides)Phospholipids were first identified in the human brain by Uauquelin in 1812 and isolated from egg yolks by Gobley in 1844. In 1850, Gobley named them lecithin, derived from the Greek word “lekithos,” meaning yolk.
The commercial production of phospholipids began over 70 years ago. In 1930, researchers in Germany identified abundant soybean phospholipids, leading to commercial production. By the 1970s, countries like the U.S. and those in Europe started using them in healthcare products. In the U.S., lecithin sales rank third behind multivitamins and vitamin E. Globally, annual soybean lecithin output is around 140,000 tons, with the U.S. and Western Europe accounting for 60% of production. Major manufacturers are large companies in the U.S. and Germany.
Japan approved soybean lecithin in 1961, sparking a boom in lecithin products. Today, various soybean lecithin types are available. Japanese nutritionist Hiromi Kobori described phospholipids as “the most popular health food of this century” in his book, “Soybean Lipids.”
Phospholipids are crucial for biological membranes. They have a hydrophilic “head” that attracts water and two hydrophobic “tails” that repel it. This structure allows them to form bilayers, creating protective barriers around cells and organizing internal components.
As amphiphilic molecules, phospholipids feature a nitrogen- or phosphorus-containing head and a long hydrophobic hydrocarbon chain. This configuration leads to the aggregation of hydrophilic heads and the alignment of hydrophobic tails, resulting in bilayer formation. Together with proteins, glycolipids, and cholesterol, these bilayers constitute the basic architecture of cell membranes.
Sources of Phospholipids
Phospholipids are present in all animal and plant cells. In plants, they are predominantly found in seeds, nuts, and grains. Key dietary sources of phospholipids include:
- Egg yolks: Rich in phosphatidylcholine, essential for brain health.
- Soybeans: A significant source of phospholipids used in various food products.
- Sunflower seeds: Contain a variety of phospholipids beneficial for heart health.
- Peanuts and nuts: Provide healthy fats and 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 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.
Structure of Phospholipids
Phospholipids are essential components of biological membranes. They consist of a glycerol backbone with specific modifications. The hydroxyl groups on C1 and C2 of glycerol are esterified with fatty acids, while C3 is linked to phosphoric acid. This phosphoric acid connects to a polar alcohol (X-OH), forming glycerophospholipids with a non
-polar tail made of two long fatty acid chains.
Typically, C1 links to a saturated fatty acid of 16 or 18 carbon atoms, while C2 connects to an unsaturated fatty acid of 16 to 20 carbon atoms. The structure allows for the classification of phospholipids based on the polar head group. For instance, when X is hydrogen, it forms phosphatidic acid, which is present in small amounts in biological membranes.
In aqueous solutions, phospholipids form lipid monolayers. Hydrophobic tails face away from water, while hydrophilic heads point toward it. This arrangement creates structures with non-polar tails inward and polar heads outward, resulting in thin lipid bilayers. These bilayers are fundamental to biological membranes, providing flexibility and making up 20-80% of membrane weight, depending on the type.
Phospholipids fall into two main categories: phosphoglycerolipids and sphingomyelins. Phosphoglycerolipids include common types like phosphatidylcholine (lecithin), phosphatidylethanolamine (cephalin), phosphatidylserine, phosphatidylglycerol, cardiolipin, and phosphatidylinositol.
Sphingomyelin, in contrast, lacks glycerol. It contains sphingosine or dihydrosphingosine, with a fatty acid linked to the amino group of sphingosine via an amide bond. Sphingomyelin has a hydrophobic tail made of long-chain hydrocarbons and a polar head with hydroxyl groups and an amino group. The most abundant sphingomyelin in the human body is composed of sphingosine, fatty acid, and phosphorylcholine, playing a vital role in cell membranes.
Phospholipids Classification
Phospholipids are vital components of biological membranes. They are classified primarily based on their backbone structure and the amino alcohols they contain. These molecules consist of a polar head and a non-polar tail, categorizing them as polar lipids. The two main types are glycerophospholipids and sphingolipids.
1. Classification by Glycerol Backbone
- Glycerophospholipids: These phospholipids contain a glycerol backbone and can be further divided based on their substituent groups:
- Phosphatidylcholines (PC): Made from choline and phosphatidic acid, these are commonly known as lecithin. They are essential for liver lipid metabolism and help prevent fatty liver formation.
- Phosphatidylethanolamines (PE): Comprised of ethanolamine and phosphatidic acid, these phospholipids play a key role in blood coagulation.
- Phosphatidylserines (PS): Formed from serine and phosphatidic acid, they are important for cell signaling.
- Phosphatidylinositols (PI): Derived from inositol and phosphatidic acid, these phospholipids are involved in signaling pathways.
- Phosphatidylglycerols (PG): Created from glycerol and phosphatidic acid, they support membrane structure and function.
- Cardiolipin: This phospholipid consists of two molecules of phosphatidic acid linked to a glycerol backbone. It is crucial for mitochondrial membranes and has antigenic properties.
- Plasmalogens and Platelet-Activating Factor (PAF): These are formed when a long-chain alcohol replaces the fatty acyl group at the first position in glycerophospholipids.
- Sphingolipids: In contrast to glycerophospholipids, sphingolipids do not contain glycerol. Instead, they consist of sphingosine and can be classified based on their substituent group (X):
- If X is a phosphorylcholine, the sphingolipid is known as sphingomyelin.
- If X is a sugar group, it is called a glycosphingolipid.
2. Classification by Amino Acids
Phospholipids can also be classified by the amino alcohols they contain:
- Phosphatidylcholine (PC): This contains choline (HO—CH₂CH₂N⁺(CH₃)₃). It is found in the brain, semen, adrenal glands, and red blood cells. Soybeans contribute about 8-10% of egg yolk.
- Phosphatidylethanolamine (PE): This phospholipid contains ethanolamine (HO—CH₂CH₂—N⁺H₃) and is involved in various biological processes.
- Phosphatidylserine (PS): This contains serine (HO—CH₂CH—COO⁻) and plays a key role in cell signaling.
- Phosphatidylinositol (PI): This phospholipid is critical for cell signaling pathways.
- Phosphatidylglycerol (PG): It contributes to membrane structure and function.
- Diphosphatidylglycerol (Cardiolipin): This phospholipid is essential for mitochondrial function and membrane integrity.
In summary, phospholipids are crucial for maintaining cellular structure and facilitating communication. Their classification helps us understand their roles in health and disease.
Phospholipids Nature
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
You can perform hydrolysis, acetylation, hydroxylation, acylation, sulfonation, saturation (oxidation to saturate phospholipids), activation (introduction of unsaturated groups), and other reactions with phospholipids.
Phospholipids 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% 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.
Emulsification
Phospholipids play a crucial role in managing excessive blood lipids and cholesterol. They act as “vascular scavengers,” cleaning blood vessels and promoting smooth circulation. By emulsifying neutral fat and cholesterol deposits in blood vessels, phospholipids convert them into harmless particles that dissolve in water and are excreted from the body. This process prevents excess fat from accumulating on blood vessel walls and reduces pressure on cardiovascular and cerebrovascular walls. Their strong emulsifying effect is fundamental in preventing and treating modern diseases.
For instance, a high intake of meat can lead to cholesterol and lipid buildup on blood vessel walls, narrowing the passages and causing high blood pressure. When blood lipid blocks and shed cholesterol meet at narrow points in the vessels, they can become stuck, leading to blockages and embolisms. The emulsifying power of phospholipids helps break down these deposits into milky white liquids, allowing them to be expelled from the body. This mechanism is also relevant for conditions like coronary heart disease and gallstones.
Proliferation
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 play a crucial role in cell membranes, facilitating the exchange of substances between the inside and outside of cells. If people do not replenish the phospholipids they consume daily, their cells can become nutrient-deficient and lose vitality.
While the human liver can synthesize some phospholipids, most come from the diet, particularly after age 30 or 40. It’s important to note that phospholipid activity peaks at around 25 degrees Celsius. When temperatures exceed 50 degrees Celsius, most of their activity diminishes. Therefore, it’s advisable for both healthy individuals and those with suboptimal health to consume phospholipids as part of their wellness regimen.
Manufacturing Process
To manufacture the product, first remove most of the lecithin from soybean lecithin. Extract and separate it using an organic solvent, then emulsify and spray-dry the mixture.
Next, add 3% water to soybean crude oil and stir the mixture well at 60-80°C for 30 minutes. This process hydrates the phospholipids, forming gelatinous precipitates. Obtain the hydrated phospholipids by continuous centrifugation and perform decolorization. Afterward, dry the mixture under reduced pressure at 80-100°C and 2.67-8.00 kPa to achieve a liquid phospholipid with a content of 60-70%.
Finally, dissolve the oil and fatty acid in phospholipids using 3-5 times the amount of acetone at 50°C. After centrifugation, repeat this treatment twice. Dry the final product under reduced pressure at 60°C to obtain phospholipid powder with a content of over 95%.
Application of Phospholipids in the Food Industry
In the food industry, phospholipids serve crucial roles as emulsifiers, allowing oils to blend seamlessly with water. One of the most common phospholipids used is lecithin, typically derived from edible oils. Lecithin acts as a food additive in products like bread, solid chocolate, and various confections, enhancing texture and stability.
As an antioxidant, phospholipids also contribute to extending the shelf life of food products. They find applications in cakes, candies, and hydrogenated vegetable oils, helping to preserve flavor and prevent spoilage. Manufacturers can use phospholipids in moderation based on production needs, and they often serve dual purposes as emulsifiers and food shortening.