Taste-response

The speed with which taste stimulation occurs, coupled with the fact that stimulation with toxic substances does no damage to the receptors, led Beidler to suggest that taste stimulus need not enter the interior of the taste cell in order to initiate excitation. Because a taste cell has been shown to be sensitive to a number of taste qualities, and to a large number of chemical stimuli, he and his coworkers concluded that a number of different sites of adsorption must exist on the surface of the cell. Therefore, they assumed that taste response results from adsorption of chemical stimuli to the surface of the receptor at given receptor sites. This adsorption is described by a monomolecular reaction similar to that assumed by Renqvist, Lasareff, and Hahn, but with a difference. From the fact that each type of chemical-stimulus compound has a unique level of saturation of the taste receptor, it was concluded that the magnitude of the response is dependent on the initial reaction with the receptor, and not on other, subsequent receptor-reactions that are common to all types of receptor stimulation. Therefore, it was assumed that the magnitude of neural response is directly proportional to the number of sites filled, the maximum response occurring when all of the sites are filled. Beidler derived a fundamental... 

That the initial event of taste stimulation takes place on the cell surface of the taste receptor is now universally accepted. In addition, accumulated evidence strongly suggests that taste-bud stimulation is extracellular in nature. For example, (1) the sweet-taste response is both rapid and reversible, (2) the intensely sweet proteins monellin" and thaumatin could not possibly penetrate the cell, because of their size, and (3) miraculin, the taste-modifying glycoprotein, having a molecular weight of 44,000 would also be too large to penetrate the taste cell. ... 

However, the model is defined such that the terms ir, a, fi, and a may all be measures of different types of receptor-sweetener binding. These all reflect the probability of that event s occurring, while, at the same time, the probability of the sweetener s reaching its receptor, and that of the receptor complex s undergoing the response-eliciting reaction, may both be unity The sole criterion for the sweet-taste response would thus require the formation of the proper sweetener-receptor complex. The validity of such a hypothesis has yet to be proved. " ... 

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

It is noted that, as is shown in Figure 15, the chemicals with different taste-responses show markedly different effects on the dynamic behavior of the phospholipid film. Detail discussion on the chemical response in relation to the mechanism of taste sensation has already been given in a series of studies from our research group [3,42,43]. 

Figure 3. Positioning of /3-d-glucose over the proposed taste receptor site to initiate sweet taste response...

Monosodium glutamate lor many years has been the best known and most widely used of the flavor enhancers. MSG is normally effective in terms ol a relatively few pans per thousand, but far less powerful than the newer flavor potentiators. Like enhancers, potentiators do not add any taste of their own to food substances, but intensify the taste response to the flavorings already present in the food. Because a potentiator is more powerful, smaller quantities of the substances are required than in the Case of the enhancers. Generally, the available potentiators are from about 15 to nearly 100 times more effective than tile enhancer. 

POTENTIATOR. A term used in the flavor and food industries to characterize a substance that intensifies the taste of a food product to a far greater extent than does an enhancer. The most important of these are the 5 -nucleotides. They are approved by the FDA. Their effective concentration is measured in parts per billion, whereas that of an enhancer such as MSG is m parts per thousand. The effect is thought to be due to synergism, Potentiators do not add any taste of their own, but intensify7 the taste response to substances already present in the food. 

Chalcones and Pihydrochalcones. Chalcones and dihydro-chalcones are Intensely sweet compounds (39) that are effective in raising the threshold at which the bitterness of naringin and limonin is perceived (46). As illustrated in Figure 5, chalcones are easily formed fromTlavanone glycosides by the addition of alkali and dihydrochalcones are formed from hydrogenated chalcones. Like the flavanone neohesperidosides, the chalcones and dihydrochalcones vary in the intensity of their taste response. 

Folmer-Andersen, J. F., Kitamura, M., Anslyn, E. V., Pattern-based discrimination of enantiomeric and structurally similar amino acids An optical mimic of the mammalian taste response. J. Am. Chem. Soc. 2006,128, 5652-5653. 

Valenticic, T., Wegert, S., and Caprio, J., Learned olfactory discrimination versus innate taste responses to amino acids in channel catfish (Ictalurus punctatus), Physiol. Behav., 55, 865, 1994. 

Polyols. Linear polyols containing two carbon to seven carbon atoms all evoked neural responses. Two important results were observed (Figure 8)s (1) The effectiveness (CR q.) of the polyols increased as the chain length increased up to five carbon atoms (2) In contrast to monosaccharides, the configurations of linear polyol may not play a role in the taste response. This is indicated by the identical responses to the four pentitols D-arabinitol, L-arabinitol, D-ribitol, or D-xylitol. 

Figure 7. (A) Comparison of integrated chorda tympani nerve responses to methyl a-n-glucopyranoside (0)N — 15, methyl a-D-xylopyranoside (A) N — 5, and methyl 2-deoxy-a-D-arabino-hexopy-ranoside ( ) N = 5 solutions flowed over the tongue. Bars represent 95% confidence intervals. (B) Taste responses to methul a-D-glucopyranoside (0) N — 15, methyl a-v-mannopyranoside (O) N = 6, ana methyl a-D-galactopyranoside (A) N = 5. Responses relative to sucrose response of 100% (13).

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