Amino acids are a class of organic compounds that contain amino and carboxyl groups. They are the basic building blocks of biological macromolecules such as proteins and are essential substances for the formation of proteins required for animal nutrition. In amino acids, the hydrogen of the amino group can undergo substitution with other parts of the molecule to form an imine ring compound (imino acid). Among them, amino acids with amino and carboxyl groups bonded to the same carbon atom are called α-amino acids, and all amino acids that compose proteins are α-amino acids. Physically, amino acids are colorless crystals with melting points exceeding 200°C, which is much higher than that of ordinary organic compounds. α-Amino acids have four different tastes: sour, sweet, bitter, and umami. Glutamate monosodium and glycine are the most commonly used umami flavor enhancers. Amino acids are generally soluble in water, acid solutions, and alkaline solutions, but insoluble or slightly soluble in organic solvents such as ethanol or ether. In addition, amino acids have various functions in biological organisms. For example, tryptophan participates in the renewal of plasma proteins in animals, promotes the function of riboflavin, and aids in the synthesis of nicotinic acid and heme. Lysine can prevent bone loss, promote growth, and improve appetite and immunity. Threonine can adjust the amino acid balance in feed, promote growth, improve meat quality, and enhance the nutritional value of feed ingredients with low amino acid digestibility.

Amino acids are produced through a series of biochemical reactions. In microorganisms and plants, they can synthesize all amino acids within their bodies. However, animals cannot synthesize some amino acids within their bodies (known as essential amino acids). Essential amino acids are typically biosynthesized from intermediates of carbohydrate metabolism through multiple reactions (more than 6 steps). Non-essential amino acids require about 14 enzymes for synthesis, while essential amino acids require more, with approximately 60 enzymes participating in their synthesis. Additionally, there are several synthetic methods for amino acids, including: Strecker synthesis: This method uses acetaldehyde, ammonia, and HCN to react and form α-aminonitrile, which is then hydrolyzed to obtain α-amino acids. With modifications by Zelinsk, ammonium chloride and potassium cyanide can be used to replace hydrogen cyanide and ammonia, avoiding the direct use of these hazardous chemicals. Erlenmeyer synthesis: Also known as the Erlenmeyer-Plöchl synthesis, this method involves reacting α-acylaminoacetic acid with acetic acid or acetic anhydride and sodium acetate (or potassium carbonate) to form an azlactone intermediate. The intermediate then undergoes condensation with aldehydes under alkaline conditions, followed by reduction and hydrolysis to obtain α-amino acids. Malonic ester synthesis: The reactivity of the methylene group in malonic esters allows them to be used for the synthesis of α-amino acids.

There are 20 amino acids, of which 9 are considered essential because the body cannot produce them and they must be obtained through diet. The other 11 amino acids are non-essential because the body can synthesize them from other compounds. Synthesis of Proteins: Amino acids are the basic units that make up proteins. Proteins are necessary for growth, repair, and maintenance of body tissues, such as skin, hair, nails, muscles, and organs. Immune Function: Amino acids help in the production of antibodies, which are proteins that help fight infections and diseases. Energy Production: Although amino acids are primarily used for protein synthesis, they can also be converted into energy, especially during intense physical activity or when carbohydrate sources are limited. Hormone and Enzyme Production: Amino acids are involved in the production of hormones and enzymes, which play essential roles in regulating body processes. Brain Function: Amino acids are important for brain health and function. Some amino acids, such as tryptophan, are precursors for neurotransmitters that regulate mood, sleep, and appetite. Maintaining Nitrogen Balance: Amino acids help maintain nitrogen balance in the body, which is important for proper growth and development.

Nutritional additives: Amino acids are essential nutrients for the human body. There are 20 amino acids required by the human body, of which 9 are considered essential amino acids that must be obtained through food. Adding amino acids to foods can increase their protein content, enhancing the intake of essential amino acids and providing the body with necessary nutrients. Common amino acid additives include lysine, tryptophan, and phenylalanine. Flavor enhancers: Amino acids have specific tastes and aromas that can enhance the flavor and taste of foods. Some amino acids, such as glutamic acid and aspartic acid, have umami properties and can be used as organic flavor enhancers to increase the savory taste of foods. Amino acids can also enhance the sweetness, saltiness, and sourness of foods, improving their palatability. Improving texture and shelf life: Amino acids can also be used to improve the texture and shelf life of foods. For example, lysine is widely used in meat products to enhance their water retention and elasticity, improving the texture. Amino acids can also help prevent food spoilage and eliminate unpleasant odors. Functional foods: Amino acids can also be used as ingredients in functional foods, with various functions such as regulating human metabolism, enhancing immunity, and reducing cholesterol. With the increasing demand for global food safety and nutritional health, the market demand for food-grade amino acids is constantly increasing.