Bitter-sweet molecules

Fig. 36.—Binding of a Bitter-sweet Molecule to a Sweet Receptor- and a Bitter Receptor-site.

Fig. 38.— Polarization of Bitter-Sweet Molecules on Taste Receptors. ...

This being the case, a purely sweet molecule may be expected to interact with structurally suitable features distributed over the areas SB and SB (see Fig. 35,ii) interactions in the area of overlap SB do not produce a secondary bitter note, but are essential for the generation of the sweet taste. A bitter taste can be produced only when suitable features in the area of the overlap and in the whole of the bitter area (SB) interact, as in Fig. 35,iii (pure bitter). Fig. 35,iv (bitter-sweet), and Fig. 35,v (sweet with a secondary bitter taste). Therefore, as long as the interactions are distributed over the whole area representing a modality, that modality will be identified by higher centers, provided that its intensity is not subliminal. If interactions are distributed over a part of a modal area (see Fig. 35,vi), identification of the modality will not result, so that no response will be produced. Interactions in the bitter or in the sweet area have a low efficiency, or they may be effective but involve only a small fraction of the sites. This can only affect the intensity of the generated response. 

Fig. 37.—Binding of One Molecule of a Bitter-sweet Compound to (i) a Sweet Receptor, and of a Second Molecule of the Same Compound to (ii) a Bitter Receptor.

Monosubstituted ureas are usually sweet although some are tasteless. Urea itself is Bitter. Symmetrical molecules are often Bitter... 

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). 

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 taste properties of the di-O-methylhexopyranosyl derivatives, like those of the corresponding deoxy sugars, are never sweet, and always bitter. As with the deoxy sugars, this is possibly the result of increased lipophilicity of the molecule. In sucrose, however, the presence of two methyl groups on the D-glucopyranosyl or the D-fructofuranosyl group does not seem to cause any marked bitterness (see Table XVIII). 

---