Taste, acid umami

The existence of protein receptors in the tongues of mice and cows have been shown. Monosodium L-glutamate MSG [142-47-2] is utilized as a food flavor enhancer in various seasonings and processed foods. D-Glutamate is tasteless. L-Aspartic acid salt has a weaker taste of umami. Glycine and L-alanine are slightly sweet. The relationship between taste and amino acid stmcture has been discussed (222). 

Other components described in the literature which are able to enhance saltiness or umami taste are umami-tasting glutamate glycoconjugates (e.g. 18 or 19) [42], (S)-malic acid 1-0-D-glucopyranoside (morelid 20) [43], theogalline (21) [44], M-lactoyl ethanolamine (22) [45] and JV-gluconyl ethanolamines (23) [46], a-keto acids derived from amino acids (e.g. 24) [47] and some N-succinoyl derivatives of aspartic acid or glutamic acid (e.g. 25 and 26) [48]. 

The simplest tastant, the hydrogen ion, is perceived as sour. Other simple ions, particularly sodium ion, are perceived as salty. The taste called umami is evoked by the amino acid glutamate, often encountered as the flavor enhancer monosodium glutamate (MSG). In contrast, tastants perceived as bitter or sweet are extremely diverse. Many bitter compounds are alkaloids or other plant products of which many are toxic. However, they do not have any common structural elements or other common properties. Carbohydrates such as glucose and sucrose are perceived as sweet, as are other compounds including some simple peptide derivatives, such as aspartame, and even some proteins. 

Glutamate is an abundant amino acid that is present in protein-rich foods as well as in the widely used flavor enhancer monosodium glutamate. This amino acid has a taste, termed umami, that is distinct from the other four basic tastes. 

MSG stands for monosodium glutamate. It is a natural, but nonessential amino acid. It is used by food manufacturers as a flavor enhancer, and by itself has the taste of umami — the fifth taste sensation we mentioned in Macroscopic Properties The World We See. There have been countless studies on its safety to eat, and the data overwhelmingly supports MSG as being safe to consume even in absurdly large quantities. But don t try to disprove those studies—everything in moderation— your mother was right about that... 

In 1908, Dr. Kikunae Ikeda identified monosodium glutamate (MSG) as the compound imparting the taste of Umami to numerous foods. Umami is distinct from other tastes such as bitter, sour, salty and sweet. Ikeda and his colleagues began to industrially produce MSG by subjecting wheat protein gluten to acid hydrolysis. Ajinomoto Co. Inc. was the first company to produce MSG on an industrial scale. 

A persistent idea is that there is a very small number of flavor quaUties or characteristics, called primaries, each detected by a different kind of receptor site in the sensory organ. It is thought that each of these primary sites can be excited independently but that some chemicals can react with more than one site producing the perception of several flavor quaUties simultaneously (12). Sweet, sour, salty, bitter, and umami quaUties are generally accepted as five of the primaries for taste sucrose, hydrochloric acid, sodium chloride, quinine, and glutamate, respectively, are compounds that have these primary tastes. Sucrose is only sweet, quinine is only bitter, etc saccharin, however, is slightly bitter as well as sweet and its Stevens law exponent is 0.8, between that for purely sweet (1.5) and purely bitter (0.6) compounds (34). There is evidence that all compounds with the same primary taste characteristic have the same psychophysical exponent even though they may have different threshold values (24). The flavor of a complex food can be described as a combination of a smaller number of flavor primaries, each with an associated intensity. A flavor may be described as a vector in which the primaries make up the coordinates of the flavor space. 

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). 

Mushrooms have been investigated with especial reference to shiitake, Lentinus edodes, the flavorful fungus widely used in Chinese and Japanese dishes. While the umami taste is attributed to guanylic acid, lentinic acid 14 (Scheme 6) is converted to lenthionine, 1,2,3,5,6-pentathiacycloheptane 15, a compound with the characteristic shiitake flavor. This complex reaction requires a C-S lyase enzyme.30 Other important flavor compounds are 1,2,4,6-tetrathiacycloheptane 16 (Scheme 6) and 1,2,3,4,5,6-hexathiacycloheptane (not shown). 

The role of these tastes has been nicely summarized Taste is in charge of evaluating the nutritious content of food and preventing the ingestion of toxic substances. Sweet taste permits the identification of energy-rich nutrients, umami allows the recognition of amino acids, salt taste ensures the proper dietary electrolyte balance, and sour and bitter warn against the intake of potentially noxious and/or poisonous chemicals. ... 

Sodium Ion. The excessive intake of sodium ion coming from other than NaCl should be noticed, though reduced intake of NaCl is now a matter of great concern. Monosodium glutamate (MSG), for instance, is a subject of discussion. Since MSG effectively provides umami taste, it has been very popular as a Japanese seasoning. In the United States, MSG has currently been mark as a cause of "Chinese restaurant syndrome". In addition, beef, liver, blood and their processed foods contains a large amount of sodium ion. Sine sodium ion combines with aspartic acid and glutamic acid residues in protein, study of affinity of acidic amino acids to sodium ion has to be set out first. 

Sensory analysis of mixed solutions of MSG and each of four dipeptides was carried out (Table VI). The umami taste of MSG was not changed when it was mixed with peptides containing aspartic acid. On the other hand, Glu-Glu, produced the... 

Some peptides enjoy the property of masking the bitter taste of foods. Ohyama et al. (24) conducted sensory analyses using synthetic peptides and found that neutralized peptides consisting of aspartic acid and glutamic acid had a taste similar to that of monosodium glutamate. They termed this umami taste or relish. ... 

On the other hand, L-alanine, glycine and L-threonine taste mainly sweet [26]. Only for these amino acids, the potentials of channels 1 and 2 decreased. L-Glutamic acid and L-histidine monohydrochloride, which taste mainly sour, increased each of the potentials of channels 1-5 to almost the same degree. Only monosodium L-aspartate elicits mainly umami taste in humans among amino acids used here the response pattern was different from those of the other amino acids. 

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