Sweetness and bitterness

When food contains both sweet and bitter substances, the temporal pattern of reception, ie, the order in which sweet and bitter tastes are perceived, affects the total quaUtative evaluation. This temporal effect is caused by the physical location of taste buds. The buds responding to sweet are located on the surface and the tip of the tongue, the bitter in grooves toward the rear. Therefore, the two types of taste buds can be activated sequentially. 

For oximes, the relationship between the sweet and bitter tastes and their structures was systematically studied by Acton and coworkers. By modifying the terpene moiety and keeping the oxime group intact, it was... 

Fig. 32.—Fixation of Sweet and Bitter Compounds (Amino Acids) in Rectangular Coor-dinates. ...

Fig. 34a.—Schematic Representation of the Structural Parameters for Sweet and Bitter Taste. [nj/e and n /e represent the systems of the stimulant and the receptor respectively.]...

That the sweet and bitter responses are intimately associated is clear from the results of gustatory studies of all of the conformationally defined sugars and of other organic compounds. If a carbohydrate has any taste at all, this is invariably sweet, bitter-sweet, or bitter. Chemical modification may alter the taste of a sweet compound so that the product is bitter-sweet or bitter, and it is now generally agreed that the two basic tastes may each be a feature of a single compound. It appears, therefore, that the interactions of these polyfunctional stimulants involve two different sets of receptor sites, representing sweet and bitter modalities. ... 

After the saliva has carried the tastants into the taste bud, they interact with the taste receptors on the surface of the cells, or with ion channels, which are pore-like proteins. Salty and sour tastants act through ion channels, and sweet and bitter sensations are mediated by surface receptors. The different taste submodalities rely on specific mechanisms Na+ flux through Na+... 

Saponins have been variously attributed with a diverse range of properties, some of which include both beneficial and detrimental effects on human health, piscidical, insecticidal and molluscicidal activity, allelopathic action, antinutri-tional effects, sweetness and bitterness, and as phytoprotectants that defend plants against attack by microbes and herbivores [2-11]. A more detailed understanding of the biochemical pathways and enzymes involved in saponin... 

The experimental data suggest that sweetness and bitterness are recognized at the same receptor. Furthermore, the receptor discriminates between bitter and sweet tastes based upon differences in functional unit combination. A new taste receptor model is proposed and presented. 

Fig. 3. The Model of Sweetness and Bitterness Production at the Taste Receptor...

Taste Behavior in Mixed Sweet and Bitter Solutions. 

Theoretical sensory sweetness and bitterness scores for the two theories are described below for mixed solutions of sweet and sour. This exercise considers the case of a mixture of 20 mM D-phenylalanine (D-PA) and 60 mM L-phenylalanine (L-PA). Individually each of these solutions yield a sensory score of 5.0, i.e. the sweetness of 30 mM D-PA is 5 and the bitterness score of 60 mM L-PA is 5. Theoretically, if both compounds bind independendy at different taste receptors, the sweetness and bitterness should each be 5. On the oAer hand, if both compound bind at the same taste receptor in a competitive manner, die sweetness and bitterness scores should decrcase. In regards to the latter, the sweet and bitter compound were mixed in a ration of 1 3 (20 mM to 60 mM) which yields a probability of fitting a taste receptor of l-in-4 for sweet and 3-in-4 for bitter. If these probabilities are multiplied by the original concentrations, i.e. 20 mM and 60 mM, the products would be in the expected concentration of 5 mM (1/4 of 20mM) and 45 mM (3/4 of 60mM). The sweetness of a 5 mM solution and the bitterness of a 45 mM solution corresponds to a sensory score of 2 and 3, respectively, and represent the expected sensory score for the competitive hypothesis. 

Results from sensory evaluation of mixed solution are seen in Table IV. The data list the theoretical response for both the independent and competitive receptor hypothesis as well as the actual sensory score. The actual sensory scores were found to agree fairly well with the competitive model. The minor dissimilarity between the actual and theoretical is due to the inability of individual to taste bitterness in solutions that are extremely sweet, i.e., there is some masking of overall sensory perception which is concentration dependent. The data, therefore, clearly indicate that sweetness and bitterness act in a competitive manner and should be considered to compete for the binding sites at the same receptor. 

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. 

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. 

Bums, D. J. W. and Noble, A. C. (1985). Evaluation of the separate contribution of viscosity and sweetness of sucrose to perceived viscosity, sweetness and bitterness of vermouth.. Text. Stud. 16, 365-381. 

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