Umami

Monosodium glutamate (MSG) and the 5 -nucleotides are generally recognized as the primary food components that provide the umami sensation [105,106]. MSG is readily measured by ion chromatography or reverse phase HPLC [103]. The 5 -nucleotides are most commonly determined by HPLC as well [107,108] but other methods have found use, e.g., derivative spectrophotometry [108]. 

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The aroma of fmit, the taste of candy, and the texture of bread are examples of flavor perception. In each case, physical and chemical stmctures ia these foods stimulate receptors ia the nose and mouth. Impulses from these receptors are then processed iato perceptions of flavor by the brain. Attention, emotion, memory, cognition, and other brain functions combine with these perceptions to cause behavior, eg, a sense of pleasure, a memory, an idea, a fantasy, a purchase. These are psychological processes and as such have all the complexities of the human mind. Flavor characterization attempts to define what causes flavor and to determine if human response to flavor can be predicted. The ways ia which simple flavor active substances, flavorants, produce perceptions are described both ia terms of the physiology, ie, transduction, and psychophysics, ie, dose-response relationships, of flavor (1,2). Progress has been made ia understanding how perceptions of simple flavorants are processed iato hedonic behavior, ie, degree of liking, or concept formation, eg, crispy or umami (savory) (3,4). However, it is unclear how complex mixtures of flavorants are perceived or what behavior they cause. Flavor characterization involves the chemical measurement of iadividual flavorants and the use of sensory tests to determine their impact on behavior. 

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). 

L-Amino acid Threshold value, mg/dL Sweet Sour Bitter Salty 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). 

Y. Kawamura and M. R. Kara, Umami M Basic Taste, Marcel Dekker, New York, 1987. 

The intensity of "umami" increases linearly with a logarithmic increase in the concentration of MSG. The synergistic effect of MSG with 5 -ribonucleotides is expressed by the following relation... 

Sake is a subtle drink. It is sometimes described as having umami, or criticized for its lack of umami. Umami, which some characterize as a flavor, like sweetness or sourness, is a quality of palatability and the degree to which something satisfies the palate. A Zen archer s version of hitting the spot. ... 

Sensory receptors expressed in particular in taste receptor cells of the taste buds that sense the five basic tastes salt, sour, sweet, bitter and umami (glutamate taste). Sodium type ion channels sense salty taste whereas sour taste is transduced by potassium type ion channels. The underlying cause of sweet, bitter, and umami tastes is the selective activation of different groups of G protein coupled receptors that discriminate between sweet, bitter, and umami tasting molecules. 

The human tongue is sensitive to five flavors salty, sweet, bitter, sour, and umami, the taste of MSG. 

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). 

Sweet, bitter and umami taste involve receptor-coupled second-messenger pathways that are differentially expressed across the gustatory epithelium 827... 

Multiple senses, including taste, contribute to our total perception of food. Our perception of the flavor of food is a complex experience based upon multiple senses taste per se, which includes sweet, sour, salty and bitter olfaction, which includes aromas touch, also termed mouth feel , that is, texture and fat content and thermoreception and nociception caused by pungent spices and irritants. Taste proper is commonly divided into four categories of primary stimuli sweet, sour, salty and bitter. One other primary taste quality, termed umami (the taste of L-glutamate), is still somewhat controversial. Mixtures of these primaries can mimic the tastes of more complex foods. 

In many cells, phosphoinositide signaling leads to an elevation in intracellular calcium levels through the release of calcium from intracellular stores in response to IP3-dependent gating of channels in the endoplasmic epithelium (Ch. 20). It is not known if IP3 plays a critical role in TRC transduction, but such a role would be consistent with recent findings that a Ca2+-activated cation channel, TRPM5, is essential for normal sweet, bitter and umami taste function [49,66-69],... 

Zhang, Y. et al. Coding of sweet, bitter, and umami tastes different receptor cells sharing similar signaling pathways. Cell 112 293-301,2003. 

He, W. et al. Umami taste responses are mediated by alpha-transducin and alpha-gustducin. /. Neurosci. 24 7674—7680, 2004. 

Damak, S. et al. Detection of sweet and umami taste in the absence of taste receptor Tlr3. Science 301 850-853, 2003. 

Ultraviolet sunscreen agents, salicylic acid esters as, 22 12, 16 Umami receptor, 24 248 Umami sensation, 11 523, 565 Umber... 

Selecting an approach Off-flavors are typically due to volatile compounds present at extremely low levels. (Flavor is sensed more by the olfactory system than the tongue, which senses only 5 flavors, sweet, sour, bitter, salty, and umami). GC is ideal for detecting low levels of volatile components. In this case, headspace GC will allow you to treat the plastic directly. Since the off-flavor is suspected to be derived from the polypropylene packaging material, you decide to compare different samples ( good vs. bad ) of the material using headspace GC with both a flame ionization detector (FID) and a sniff port. These chromatograms are shown in Fig. 21.9. 

RoUs ET, Critchley HD, Browning A, Hernadi I (1998) The neurophysiology of taste and olfaction in primates, and umami flavor. Ann N Y Acad Sci 855 426 37 Rose JE, Behm EM, Westman EC, Mathew RJ, London ED, Hawk TC, Turkington TG, Coleman RE (2003) PET studies of the influences of nicotine on neural systems in cigarette smokers. Am J Psychiatry 160 323-333... 

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. ... 

There are five primary taste sensations salty, sour, sweet, bitter, and umami (or savory). The receptors for these tastes are encoded in a few dozen genes in the human genome. These are expressed in taste buds. 

Straszewski L, Li X, Xu H, Durick K, Zoller M, Adler E, Human receptors for sweet and umami taste, Proc NatlAcd Sci USA 99 4692 696, 2002. 

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