L-MONOSODIUM GLUTAMATE MSG

Monosodium L-glutamate [142-47-2] C HgNO Na H20 (mol wt 187.13) crystallizes from aqueous solution at room temperature as rhombic prisms. Its stmcture, as deterrnined by x-ray crystallography (6), indicates that the sodium ions are coordinated octahedraHy by four (3a and ly) carboxyl oxygen atoms and two water molecules as follows  

Commercially preferred crystals for use as flavor enhancement are obtained by crystallization in the presence of amino acids such as alanine (7). 

Crystalline MSG is less hygroscopic than sodium chloride. The critical humidities of MSG are 96.0, 94.8, and 90.0 at 20, 30, and 50°C, respectively. MSG loses its water of crystallization at 120°C intramolecular dehydration occurs at 155°C. The decomposition temperature is 225°C. 

The a-carbon of glutamic acid is chiral. A convenient and effective means to determine the chemical purity of MSG is measurement of its specific rotation. The specific optical rotation of a solution of 10 g MSG in 100 mL of 2 A/HQ is +25.16. Besides L-glutamic acid [56-86-0] D-glutamic acid [6893-26-1] and the racemic mixture, DL-glutamic acid [617-65-2] are known. Unique taste modifying characteristics are possessed only by the L-form. 

L-Glutamic acid does not racemize in neutral solution, even at 100°C. Deviation of pH from neutral to greater than 8.5 results in thermal racemization with loss of taste characteristics. Racemization in neutral solution occurs at 190 °C after formation of the lactam, 5-oxo-L-proline, pyroglutamic acid [98-79-3]. 

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In the food industries a number of amino acids have been widely used as flavor enhancers and flavor modifiers (see Flavors and spices). For example, monosodium L-glutamate is well-known as a meat flavor-enhancer and an enormous quantity of it is now used in various food appHcations (see Amino acids, L-MONOSODIUM glutamate (MSG)). Protein, hydroly2ed by acid or en2yme to be palatable, has been used for a long time in flavoring agents. 

Nucleotides - [AMINO AC IDS - L-MONOSODIUM GLUTAMATE (MSG)] (Vol 2) -as antibiotics [ANTIBIOTICS - NUCLEOSIDES AND NUCLEOTIDES] (Vol 3) -catabolism of [MINERALNUTRIENTS] (Vol 16) -electrodes for [BIOPOLYMERS - ANALYTICAL TECHNIQUES] (Vol 4) -phosphorus nmr [MAGNETIC SPIN RESONANCE] (Vol 15) -as radioactive tracers [RADIOACTIVETRACERS] (Vol 20)... 

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