Taste intensity

Profiles of each basic taste intensity are expressed as follows ( + + +) strongest, (H—h) stronger, and (+) detectable. 

There are, however, a number of criticisms of these theories. Beidler argued that, as Renqvist had assumed that the magnitude of response is proportional to the amount of stimulant adsorbed per unit time, it is evident that, at equilibrium, the net velocity of adsorption is zero. It would follow that taste intensity should be zero, and the receptors completely adapted. However, Beidler showed that the receptors do not adapt completely, but reach a steady level of response that is consistent for the duration of stimulation. Therefore, he concluded that human taste-adaption is dominated by events in the central nervous system, and not by the peripheral receptor. The same facts also prove Lasarefl s assumption to be incorrect, as his experimental data also depended on a change in adaption that is not seen at the receptor level. 

Fig. 42.—Perceived Taste-intensity versus Time, for Type A and Type B Sweetener.[Type A, rapid taste onset and cut-of type B, slow taste-onset and persistent after-taste.]...

Basically, there are four major types of measures that are used in taste intensity measurements (a) threshold measures or estimates of the physical level at which the sensation of sweetness begins, (b) equal-sweetness matches between a sugar and other sweeteners, (c) category or rating scales, and (d) ratio scales. Each method has found its adherents and uses, and each possesses specific advantages and defects that indicate its use for one application, but contraindicate its use for another. These methods and their applications have been critically analyzed and reviewed, " " and it is, therefore, superfluous to deal with the topic here. 

Had= Hardness Spr.= Springiness Che= Chewiness Gum= Gumminess Coe= Cohesiveness HS= Sensory hardness SP= Spreadability Ac= Acid Sw= Sweet Fia= Fiavour Ti= Taste intensity OA= Overall acceptance. 

The best investigated odor-taste interactions occur in conditioned flavor aversions. Tastes that precede a delayed food-related illness are often avoided after only one experience. Odors are not avoided under similar conditions. However, if taste and odor are presented together before the malaise, animals will avoid odor when encountered later by itself. Taste affects odor, but not vice versa. If only the taste intensity is increased, both taste and odor aversion increase. Conversely, if only the odor stimulus is increased, only the odor aversion increases (Garcia etal, 1986). 

The current accepted theory suggests that a bitter compound and a sweet compound bind independently at specitic receptors. This situation will be referred to as "independent" in this report. The data to follow will demonstrate that a bitter compound and a sweet compound bind at the same receptor in a competitive manner. Therefore, this situation will be referred to as "competitive" in this report. Which theory was the functioning mechanism of taste reception should be determinable when one measured the taste intensities of mixed solutions of bitter and sweet tasting compounds. In this experiment the mechanism could be predicted to elicit a considerable difference in taste intensity and response that was varying based on the final concentration of each component. The "independent" receptor mechanism would be expected to yield data in which the intensities of bitter and sweet would be unaffected by mixing the two tastes, no matter what the concentration. On the other hand, with the "competitive" receptor mechanism one would expect both flavors to become altered, i.e., one stronger and the other weaker, as component concentrations varied the latter would occur because of competition of the substances for the same site. 

These peptides produced the same taste. The interesting point was that Asp-Asp, took the largest amount of sodium ion, produced the weakest taste. The taste intensity of Asp-Asp was about 1/4 of that of Asp-Glu which produced the strongest taste. These results showed that sodium ion intake capacity and taste intensity depend on amino acid sequence of acidic peptides. We have to carefully think about these facts when we construct the taste of foods and carry out sodium ion diet. 

Taste of amino acids was studied using the taste sensor [23]. Taste of amino acids has had the large attention so far because each of them elicits complicated mixed taste itself, e.g., L-valine produces sweet and bitter tastes at the same time. Thus, there exist detailed data on taste intensity and taste quality of various amino acids by sensory panel tests [26]. The response of the sensor to amino acids was compared with the results of the panel tests, and response potentials from the eight membranes were transformed into five basic tastes by multiple linear regression. This expression of five basic tastes reproduced human taste sensation very well. 

Several kinds of taste intensity scales have been established for the four tastes. Typical examples are the gust scale by Beebe-Center (31) and the T scale by Indow (32). In order to deal with the umami on the same basis with the four tastes, we newly established a new subjective taste intensity scale for umami as well as for the four tastes (9, 30). Six solutions for each of the five taste substances were prepared. The taste intensity of... 

The relationship between the concentration and the perceived taste intensity of MSG was logarithmically linear like those of the four common tastes, although the slope for MSG was somewhat less steep than the others. It means that Weber-Fechner s law holds for all of the five taste substances. The relation of the taste intensity (S) to the concentration (x) can be expressed by... 

In this experiment, only the intensity of taste was rated and the quality of taste was disregarded. Consequently, the same value of S in the above mentioned equations represents the same intesnity of taste. Beebe-Center defined the unit of taste intensity as gust. One gust means the taste intensity of 1% sucrose solution. However, the gust scale is not always convenient because it does not define the upper limit of the scale. 

Figure 1. Relationship between taste intensity and concentration (9)...

MSG, when added to beef consomme, had no effect on the aroma. It increased the overall taste intensity, but its effects on the intensities of saltiness, sweetness, sourness, and bitterness were very small. Although the term "umami" was intentionally not used in the profile test, it may be easily supposed that the quality of the taste increased here is umami. 

MSG increases the total taste intensity of food. The quality of the taste brought about by MSG is different from the four tastes. 

Figure 3. Taste intensity and hydrophobicity of amino acid...

Figure 7. Homologous bitter compounds relationship between taste intensity and, the number of C-atoms in the side chain (9) R-CO-CH, (A) R-NH-CO-NHt (A) L-R-CH(NHi)-COOH O R -NH2 R-NH (O)...

The synergistic effect of umami substances is exceptional. The subjective taste intensity of a blend of monosodium glutamate and disodium 5 -inosinate was found to be 16 times stronger than that of the glutamate by itself at the same total concentration (Yamaguchi 1979). 

Determining the threshold value is difficult because subthreshold levels of one compound may affect the threshold levels of another. Also, the flavor quality of a compound may be different at threshold level and at suprathreshold levels. The total range of perception can be divided into units that represent the smallest additional amount that can be perceived. This amount is called just noticeable difference (JND). The whole intensity scale of odor perception covers about 25 JNDs this is similar to the number of JNDs that comprise the scale of taste intensity. Flavor thresholds for some compounds depend on the medium in which the compound is dispersed or dissolved. Patton (1964) found large differences in the threshold values of saturated fatty acids dissolved in water and in oil. 

Figure 3. The effects of Gymnema sylvestre on the taste intensity of sucrose. Reproduced with permission from Ref. 15. Copyright 1969, Rockefeller University Press.

L-Glu and Asp are sour stimuli in dissociated state, but their sodium salts dissociate on solution and elicit the umami taste. Free L-glutamate is contained in natvu al foods, as shown in Table 2 and contributes to the savory taste of foods as its sodium salt. Ibotenlc and tricholomlc acids (lA and TA) discovered in mushrooms are the derivatives of oxyglutamic acid and are also umami substances (, 5). The umami taste intensity of lA or TA is A to 25 times that of MSG. As these compounds are not amino acids commonly found in an animal system, they have not been used as seasoners. The umami taste or TA-5 -ribonucleotide mixture is much more Intense only MSG, lA or TA. Among 5 -ribonucleotides, 5 -guanylate have synergistic effects in a mixture with This phenomenon is called the synergistic effect of... 

The comparison of the amino acid sequence of the above-mentioned bitter peptides shows a large proportion of hydrophobic amino acids in each peptide. And the amino acid sequence of peptides also plays an important role in the intensity of the bitter taste. For example, the bitterness of Phe-Pro is more intense than that of Pro-Phe, and the bitterness of Gly-Phe-Pro is more intense than that of Phe-Pro-Gly (23). C-terminal groups of all bitter peptides in pepsin hydrolysates of the above-mentioned soy protein were characterized by the location of the Leu residue (14-17). The research on the relationship between the structure and bitter taste intensity of Arg-Gly-Pro-Pro-Phe-Ile-Val (BP-Ia) showed that Pro and Arg located on center and the N-terminal site, respectively, played an important role in the increment of bitter taste intensity besides the hydro-phobic amino acids located on C-terminal site (24-26). This may indicate that the peptide molecular structure formed by the arrangement of Arg, Pro and hydrophobic amino acid residues contributes to the bitter taste intensity of the peptide. 

Several dipeptides having L-Glu at N-terminus elicit the umami taste, though its umami taste intensity is much less than that of MSG. Aral et al. ( ) synthesized L-Glu-X (X= amino acid) and examined their taste in aqueous solution containing NaCl at pH 6. Glu-Asp, Glu-Thr, Glu-Ser and Glu-Glu were found to produce the umami taste. Ohyama et (30) showed that Asp-Leu and Glu-Leu were umami substances. In section "Sour Taste", the peptides containing Asp or/and Glu were shown to elicit a sour taste in water. However, several of their peptides besides Glu-Asp and Glu-Glu may also be umami stimuli in aqueous solutions containing NaCl at pH 6. 

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