Glutamic acid, characteristics

In Foods. Each amino acid has its characteristic taste of sweetness, sourness, saltiness, bitterness, or "umami" as shown in Table 13. Umami taste, which is typically represented by L-glutamic acid salt (and some 5 -nucleotide salts), makes food more palatable and is recognized as a basic taste, independent of the four other classical basic tastes of sweet, sour, salty, and bitter (221). 

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]. 

This polypeptide is structurally identical to ABA-type triblock copolymer with a central hydrophdic elastomeric end-block capped with two hydrophobic plastic end-blocks and exhibits amphiphilic characteristics. The end-blocks of the polymer were chosen in such a way that their LCST would reside at or near room temperature. Thus the polymer exhibits phase separation, which is analogue to conventional TPEs, and offers TPE gels under physiological relevant conditions [104]. Glutamic acid residue is placed periodically in the elastomeric mid-block to increase its affinity towards the aqueous... 

Positive ROA bands in the range 1297-1312 cm-1 are also characteristic of a-helix. These are observed at 1300 cm-1 in human serum albumin (Fig. 4) and at 1297 cm-1 in a-helical poly-L-lysine (Fig. 3). These additional bands appear to be associated with a-helix in a more hydrophobic environment (Barron etal., 2000). The striking absence of a positive ROA band in the range 1297-1312 cm-1 in a-helical poly-L-glutamic acid would then suggest that only the hydrated form of a-helix is present, possibly due to the shorter side chains relative to poly-L-lysine,... 

The adsorption of amino acids on rutile and hydroxyapatite exhibits some characteristics of specific adsorption. The results can be interpreted in terms of electrostatic models of adsorption, however, if reorientation of adsorbed molecules is taken into consideration. The electrokinetic behavior of hydroxyapatite in glutamic acid is complicated because of a chemical reaction, possibly involving calcium ions. The study shows that it is necessary to take into consideration the orientation of adsorbed molecules, particularly for zwitterionic surfactants. 

The main genera responsible for freshwater toxic blooms are Microcystis, Anabaena, Aphanizomenon and Oscillatoria. Toxins produced include 1. anatoxins, alkaloids and peptides of Anabaena 2. the peptide microcystin and related peptides of Microcystis 3. aphantoxins, compounds of Aphanizomenon with properties similar to some paralytic shellfish poisons. Properties of Oscillatoria toxin suggest they are peptides similar to those of Microcystis. Microcystis toxins are peptides (M.W. approx. 1200) which contain three invariant D-amino acids, alanine, erythro-3-methyl aspartic and glutamic acids, two variant L-amino acids, N-methyl dehydro alanine and a 3-amino acid. Individual toxic strains have one or more multiples of this peptide toxin. The one anatoxin characterized is a bicylic secondary amine called anatoxin-a (M.W. 165). The aphantoxin isolated in our laboratory contains two main toxic fractions. On TLC and HPLC the fractions have the same characteristics as saxitoxin and neosaxitoxin. 

Silk-fibroin is composed of practically only three amino acids, glycine, alanine and tyrosine, and is probably the simplest protein known. It resembles the fibroin of spider s silk very closely, but here the presence of so much glutamic acid is one of the characteristics. 

In a more recent study using circular dichroism, Pflumm and Beychok (313) have fitted the observed curve for RNase-A (see Figs. 11c and d) weighted mixtures of the characteristic bands for helix from poly-L-glutamic acid and / structure from poly-L-lysine. The data are compatible with 11.5% helix and 33% / conformation. Ribonuclease-S and RNase-A have almost identical CD spectra from 198 to 300 nm. The spectrum of S-protein is markedly different from the other two. 

Free amino acids are further catabolized into several volatile flavor compounds. However, the pathways involved are not fully known. A detailed summary of the various studies on the role of the catabolism of amino acids in cheese flavor development was published by Curtin and McSweeney (2004). Two major pathways have been suggested (1) aminotransferase or lyase activity and (2) deamination or decarboxylation. Aminotransferase activity results in the formation of a-ketoacids and glutamic acid. The a-ketoacids are further degraded to flavor compounds such as hydroxy acids, aldehydes, and carboxylic acids. a-Ketoacids from methionine, branched-chain amino acids (leucine, isoleucine, and valine), or aromatic amino acids (phenylalanine, tyrosine, and tryptophan) serve as the precursors to volatile flavor compounds (Yvon and Rijnen, 2001). Volatile sulfur compounds are primarily formed from methionine. Methanethiol, which at low concentrations, contributes to the characteristic flavor of Cheddar cheese, is formed from the catabolism of methionine (Curtin and McSweeney, 2004 Weimer et al., 1999). Furthermore, bacterial lyases also metabolize methionine to a-ketobutyrate, methanethiol, and ammonia (Tanaka et al., 1985). On catabolism by aminotransferase, aromatic amino acids yield volatile flavor compounds such as benzalde-hyde, phenylacetate, phenylethanol, phenyllactate, etc. Deamination reactions also result in a-ketoacids and ammonia, which add to the flavor of... 

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