Sweeteners binding

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. " ... 

A sweetener must be soluble in water and the molecule must bind readily to a specific kind of receptor molecule at the surface of the tongue. The receptor is coupled to a G-protein, which dissociates when the sweetener binds to the receptor, activating a nearby enzyme, and triggering a sequence of events resulting in signals that are carried to and interpreted by the brain. The sweetness signal depends on this interaction between receptor and sweetener. The importance of molecular shape to sweemess is illustrated by the case of aspartame, as its stereo isomer, L-aspartyl-D-phenylalanine methyl ester, has a bitter, not a sweet, taste. 

Acid-modified starches are used in the manufacture of gum candies because they form hot concentrated pastes that form strong gels on cooling. ThermaUzed starches are used in foods to bind and carry flavors and colors. Sweetening agents (com symp, HFCS) are made from starch by enzymatic or acid treatment as previously noted. 

Fig. 9. Sweetener receptor binding sites postulated by Tinti and Nofre, where 5 is an anionic group, eg, CO 2y or CN a hydrogen bond donor...

Finally, some amphiphilic sweeteners, eg, aspartame, saccharin, and neohesperidin dihydrochalcone, have been shown to be capable of stimulating a purified G-protein direcdy in an in vitro assay (136). This suggests some sweeteners may be able to cross the plasma membrane and stimulate the G-protein without first binding to a receptor. This type of action could explain the relatively longer response times and the lingering of taste associated with many high potency sweeteners. 

Xylitol is used as a sweetener in many foods, including low-calorie candies, gums, and breath mints. It prevents bacteria from adhering to cells in the mouth and gums. It also binds to calcium and aids in remineralizing tooth enamel and bones. 

Fig. 12.—Location" of the Third Binding-site in Nitroanilines (X), Sugars (-y), and Dipeptide Sweeteners (S). [Distances given in pm.]...

The binding specificity of d-[ C]glucose by the taste-papillae membranes, compared to that of control membranes isolated from epithelial tissue, has been confirmed in two studies. One inherent problem in the approach is that the stimuli, primarily carbohydrate sweeteners, are not ideal model compounds to use, as they are not active at low concentrations and do not show sufficiently high binding-constants. The use of other stimulus compounds that are at least several hundred times sweeter than sucrose, such as saccharin, dihydrochalcone sweeteners, dipeptide sweeteners, stevioside, perillartine and other sweet oximes, the 2-substituted 5-nitroanilines, and... 

Fig. 9. Sweetener receptor binding sites postulated by Tinti and Nofre, where B is an anionic group, eg, CO 2, SO 3, or CN 4 AH, a hydrogen bond donor group, eg, NH or OH G, a hydrophobic, hydrocarbon group D, a hydrogen bond acceptor group, eg, CN, N02, or Cl Y, Ep and are hydrogen bond acceptors, eg, CO or halogen atoms and XH is a hydrogen bond donor group, eg, NH or OH (121).

Morini, G., Bassoli, A., Temussi, P.A. (2005) From small sweeteners to sweet proteins anatomy of the binding sites of the human... 

---