Taste substances

Generalizations. Several generalizations can be made regarding taste (16,26). A substance must be in water solution, eg, the Hquid bathing the tongue (sahva), to have taste. Water solubiUty is the first requirement of the taste stimulus (12). The typical stimuli are concentrated aqueous solution in contrast with the Hpid-soluble substances which act as stimuli for olfaction (22). Many taste substances are hydrophilic, nonvolatile molecules (15). Taste detection thresholds for lipophilic molecules tend to be lower than those of their hydrophilic counterparts (16). 

Organic aromatic molecules are usually sweet, bitter, a combination of these, or tasteless, probably owing to lack of water solubiUty. Most characteristic taste substances, especially salty and sweet, are nonvolatile compounds. Many different types of molecules produce the bitter taste, eg, divalent cations, alkaloids, some amino acids, and denatoirium (14,15). 

Primel, /. primrose, -kratzstoff, m. an unpleasant-tasting substance in primrose root. Primzahl,/. prime number,... 

When used in products not licensed for drinking, ethanol usually occurs in the form of denatured alcohol, or specially denatured alcohol—alcohol that has been rendered unfit for drinking. You will often see SD alcohol mentioned on a label, sometimes followed by a number and letter, such as 40-B. This is the designation given by the U.S. Bureau of Alcohol, Tobacco, and Firearms to the denaturing method used. For example, SD-40 is ethanol denatured by adding tiny amounts of the most bitter-tasting substance known denatonium benzoate. 

Denatonium benzoate is the bitterest-tasting substance known. It gets its name from denatured alcohol—alcohol that has been rendered unfit for drinking—and is often used in the denaturing process. Specially denatured alcohol 40, or SD-40, is ethanol that has been denatured by a tiny amount of denatonium benzoate. Denatonium benzoate is an ester of PABA, and is related to lidocaine, benzocaine, novocaine, and cocaine. 

Nontoxic chlorofluorocarbons, 24 188 Nontronite (iron smectite), 6 664, 696 structure and composition, 6 669 Nonuniqueness, 24 446 Nonvessel operating common carriers (NVOCC), 25 328 Nonvolatile compounds, as taste substances, 11 566 Nonvolatile food components,... 

A large number of sweet-tasting substances has been described in the scientific literature, most of them in the course of the last 20 to 30 years. The number of substances having an intense sweetness is by far higher than the number of products with a sweetening power similar to sucrose which could therefore be used as bulking sugar substitutes. Only a small number of these has found... 

Molecular cavities are of topical research interest because of their ability to enclose and bind guest molecules. They may serve as models for the study of binding sites between, e.g. drugs, odorant/taste substances, antigens, etc. and receptors. Cyclo-dextrins, as prime examples of host cavities, have found many useful applications. This is due to the guest molecules being bound within the cavity which changes properties such as solubility, volatility and reactivity. 

Differential sensory sensitivity. The insect s perception of plant odours differs essentially from their discrimination of non-volatile taste substances, as phytophagous insects may already perceive the odour at some distance from the plant. In adult phytophagous insects the antennae bear a large number of olfactory sensilla in order to detect the minute concentrations of the leaf odour components in the air downwind from a plant. The overall sensitivity of the antennal olfactory receptor system can be measured by making use of the electroantennogram technique (17). An electroantennogram (EAG) is the change in potential between the tip of an antenna and its base, in response to stimulation by an odour component. Such an EAG reflects the receptor potentials of the olfactory receptor cell population in the antenna. 

The wine yeast, Saccharomyces fermentati, is able to form a film or veil on the surface of dry white wines of about 15-16% alcohol. This yeast produces agreeable smelling and tasting substances which dissolve in the wine and give it the aroma and flavor characteristic of Spanish fino sherries. To provide itself with energy for growth while in the film form on the surface of the wine, the yeast utilizes some of the oxygen from the atmosphere above the wine in the partially filled butt or barrel to oxidize some of the ethyl alcohol from the wine. The ethyl alcohol of the wine is not completely metabolized to carbon dioxide and water, however, but is oxidized to acetaldehyde—probably the principal compound in the complex mixture responsible for the aroma of this type of appetizer wine. 

In biological taste reception, taste substances are received by the biological membrane of gustatory cells in taste buds on tongue (Figure 1). Then the information on taste substances is transduced into an electric signal, which is... 

Development of this sensor was based on a concept very different from that of conventional chemical sensors, which selectively detect specific chemical substances such as glucose or urea. However, taste cannot be measured in those terms even if all the chemical substances contained in foodstuffs are measured. Humans do not distinguish each chemical substance, but express the taste in itself the relationship between chemical substances and taste is not clear. It is also not practical to arrange so many chemical sensors with respect to the number of chemical substances, which amounts to over 1000 in one kind of foodstuff. Moreover, there exist interactions between taste substances, such as the synergistic effect or the suppression effect. A taste sensor should measure these effects the intention is not to measure the amount of each chemical substance but to measure the taste itself, and to express it quantitatively. The recently developed sensor satisfies this request. In fact, this sensor could detect the interactions between saltiness and sourness. 

We here mention the principle of the taste sensor and applications to aqueous solution constructed of five basic taste substances and several foodstuffs such as beer, coffee and tomatoes. Quantification of the taste is possible using such a taste sensor, and hence we can discuss the taste objectively. 

One method to realize the taste sensor may be the utilization of similar materials to biological systems as the transducer. The biological membrane is composed of proteins and lipids. Proteins are main receptors of taste substances. Especially for sour, salty, or bitter substances, the lipid-membrane part is also suggested to be the receptor site [6]. In biological taste reception, taste stimulus changes the receptor potentials of taste cells, which have various characteristics in reception [7,8]. Then the pattern constructed of receptor potentials is translated into the excitation pattern in taste neurons (across-fiber-pattem theory). 

In the present study, therefore, lipid membranes were used as transducers of taste information. Artificial lipid materials, such as dioleyl phosphate (DOPH) or dioctadecyl-dimethyl-ammonium, were used to construct a lipid membrane and responses of electrical potential and resistance of the membranes were measured [9-15]. It was confirmed that the lipid membranes could discriminate five primary taste substances. Moreover, they could detect the interactions between taste substances observed in biological systems. The response properties were different in different types of lipids. If a hydrophobic part of a lipid was different, taste substances which can be detected were different. These facts indicate that the taste sensor can be realized by the use of various kinds of lipid membranes as transducers. 

It was the first finding that the lipid membrane can respond to five taste substances. However, the sensing reproducibility was not good, because the standard deviations were about 10%. Therefore, it is not easy to distinguish between quinine and HC1. 

Figure 2. Responses of the DOPH adsorbed membrane to five basic taste substances. The membrane potential is taken as relative.

The DOPH membrane and the ammonium salt membrane responded to taste substances in different ways. The above results suggest that taste substances can be perceived satisfactorily using various kinds of lipid materials. Furthermore, we must improve the sensing reproducibility. As a second step, we have developed a multichannel lipid membrane taste sensor. Taste substances can be discriminated by the output pattern from several lipid membranes. 

Although the above lipid membranes had the ability to sense the taste by responding to many taste substances, information was insufficient to recognize quality of the taste. This weakness was overcome by means of a multichannel sensor, where transducers were composed of lipid membranes immobilized with a polymer [16-23]. We investigated responses of the sensors to various taste solutions. The electrode showed five different response patterns to five primary tastes with small experimental deviations. The patterns looked alike when the applied substance elicited the same taste in humans. 

Figure 7. Electrical potential profile near the membrane surface. The surface potential is mainly changed by taste substances.

Typical five primary taste substances, HC1 (sour), NaCl (salty), quinine-HCl (bitter), sucrose (sweet) and MSG (umami) were studied [16]. In general, the response of each lipid membrane was nonspecific to various taste substances. 

The pattern of each taste substance is different, and hence each taste substance can be easily discriminated The reproducibility is very high, because the standard deviations are smaller than 1 % or so. The taste sensor shows similar response patterns to the same group of taste. As examples of sour substances, HC1, citric acid and acetic acid show similar response patterns. Bitter substances such as quinine, MgS04 and phenylthiourea show similar patterns. 

We attempted to make an artificial taste solution, which shows a similar taste to some commercial aqueous drinks, by combination of basic taste substances by comparing electrical potential patterns of the taste sensor [22],... 

As the basic taste substances, HC1, NaCl, sucrose and quinine were chosen for sourness, saltiness, sweetness and bitterness, respectively. Four different concentrations were prepared for each of these substances 1, 3, 10, 30 mM for HC1 30, 100, 300, 1000 mM for NaCl and sucrose 0.03, 0.1, 0.3, 1 mM for quinine. The lowest concentrations correspond nearly to the thresholds to be detected by humans. We prepared 44(=256) mixed solutions with different compositions by combination of these four types of basic solutions. 

The above-mentioned 256 mixed solutions were measured with the multichannel taste sensor. Therefore, data on the output electrical potential pattern were taken for the 256 solutions. While the data on each channel output were dispersed discretely in the four-dimensional space constructed from four different concentrations, we approximated them by a quadratic function of the concentrations. As a result, eight quadratic functions were obtained. The data can be regarded as expressed by a set of eight different functions (corresponding to 8 channels) of concentrations of four taste substances. 

The best combination of the concentrations for basic taste substances was obtained 2 mM HC1, 50 mM NaCl, 0.2 mM quinine and 100 mM sucrose. As can be seen from Figure 10, the pattern for the mixed solution is surely closer to that of the drink A compared to another drink. The sensory evaluation by... 

As is well known, the r scale is effective to express the taste strength [1, 2]. The concentration of each taste substance can be transformed into the taste strength. While tartaric acid is used in the r scale, we can safely consider that HC1 has the strength two times as large as tartaric acid. The above mixed solution is thus composed of 4.04 sourness, 2.03 saltiness, 5.01 bitterness and 2.24 sweetness in terms of the r scale. Therefore, drink A has the above taste strength. 

For quantification of the taste of tomatoes, the taste sensor was applied to commercial canned tomato juice, to which four basic taste substances had been added. Data were analyzed by means of principal component analysis. The taste of several brands of tomatoes was expressed in terms of four basic taste qualities by projecting the data obtained from these tomatoes onto the principal axes. This expression agreed with the human taste sensation. 

Basic taste substances had been added to standard tomato juice. We used NaCl for saltiness, citric acid for sourness, MSG for umami and glucose for sweetness. No taste substance for bitterness was added because tomatoes taste... 

Figure 16 shows examples of the response pattern for one sample each of five brands of tomatoes. Different brands of tomatoes were distinguished by the shapes of the output electrical potential patterns. Therefore, tomatoes of the same brand can be considered to have a taste with similar proportions the difference in taste among tomatoes of the same brand may be due, mainly, to the difference in magnitude of taste, because the output electrical potential changed linearly with the concentrations of taste substances in a narrow range [18, 21]. 

The sensor could detect minute differences of taste between NaCl, KC1, KBr, NaBr, NH4C1, LiCl and KI [19]. In fact, the response patterns are different, as can be seen from Figure 8. It implies that such taste substances as KBr, NaBr and KI do not show pure saltiness elicited by NaCl. Therefore, the sensor can detect large differences between five basic taste qualities, and furthermore can distinguish between these small differences of similar taste quality. 

We tried three methods to quantify the taste of the foodstuffs. The first method is to compare output patterns between test solution and the mixed solutions by performing many measurements of various mixed solutions (Figure 10) [22], The taste of commercial aqueous drink was reproduced by blending four basic taste substances (HC1, NaCl, quinine, sucrose) so that the response pattern could get closest to that of an aqueous drink. With this attempt, the best combination of the concentrations of basic taste substances was obtained 2 mM HC1, 50 mM NaCl, 0.2 mM quinine and 100 mM sucrose. This mixed solution produced almost the same taste as the aqueous drink. 

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