Amino acids are colorless crystals with a melting point of more than 200℃, much higher than that of ordinary organic compounds. α -amino acids have sour, sweet, bitter and fresh taste. Monosodium glutamate and glycine are the most used umami flavoring ingredients. Amino acids are generally soluble in water, acid and alkali solutions, insoluble or slightly soluble in organic solvents such as ethanol or ether. The solubility of amino acids in water varies greatly. For example, tyrosine has the lowest solubility. At 25℃, only 0.045g of tyrosine dissolved in 100g of water, but the solubility of tyrosine is greater in hot water. Lysine and arginine often exist in the form of hydrochloride, because they are easily soluble in water and difficult to crystallize due to deliquescence
(1) Color and color: all kinds of common amino acids are easy to become colorless crystals, and the crystal shape varies with the structure of amino acids. For example, L-glutamic acid is a quadrangular column crystal, and D-glutamic acid is a diamond flake crystal.
(2) Melting point: the melting point of amino acid crystallization is high, generally at 200 ~ 300℃, and many amino acids will decompose into amine and CO2 when reaching or approaching the melting point.
(3) Solubility: Most amino acids are soluble in water. The solubility of different amino acids in water is different, such as lysine, arginine, proline solubility is larger, tyrosine, cysteine, histidine solubility is very small. Various amino acids are soluble in strong bases and acids. But amino acids are insoluble or slightly soluble in ethanol.
(4) Taste sensation: Amino acids and their derivatives have certain taste sensation, such as sour, sweet, bitter and salty. The kinds of taste are related to the kinds and stereoscopic structure of amino acids. Generally speaking, d-type amino acids have sweet taste, and their sweet taste intensity is higher than the corresponding L-type amino acids.
(5) UV absorption characteristics: all kinds of common amino acids have no absorption ability to visible light. But tyrosine, tryptophan and phenylalanine have obvious light absorption in uv region. These three amino acids are found in most proteins, especially tyrosine. Therefore, the uv absorption characteristics at 280nm can be used to quantitatively detect protein content.
An important optical property of amino acids is their absorption of light. All 20 kinds of PR-Aa have light absorption in visible region, and all have light absorption in far ULTRAVIOLET region (<220nm). Only three kinds of AA have light absorption ability in ultraviolet region (near ultraviolet region) (220nm ~ 300nm). These three kinds of amino acids are phenylalanine, tyrosine and tryptophan, because their R group contains benzene ring conjugated double bond system.
The maximum light absorption of phenylalanine AA is 259nm, the maximum light absorption of tyroaa is 278nm, and the maximum light absorption of chroma AA is 279nm. Protein generally contains these three AA residues, so its maximum light absorption is about 280nm wavelength, so it can be used to easily determine the content of protein. Spectrophotometric determination of protein content is based on lambert-Beer law. The absorbance value of protein solution at 280nm is proportional to its concentration.
Amino acids, basic amino,acidic carboxyl Shaanxi Kepler Biotech Co.,Ltd , https://www.keplerherb.com
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