Robert S. Shallenberger

Molecular Theory of Sweet Taste

THE molecular feature common to the many different sweet tasting compounds has been sought for many years1. For the sugars, it was proposed2–5 that the sweet unit is the glycol group, and that intensity of sweetness varied inversely with the degree to which glycol OH groups appear to be intramolecularly hydrogen bonded. It is now apparent that vicinal OH groups in the glycol unit need to be approximately gauche, or in a staggered conformation. Vicinal OH groups which are in the anti conformation apparently are too far apart to cause sweet taste. Glycol OH groups which are eclipsed probably participate in an intramolecular hydrogen bond which competitively inhibits interaction of glycol with the receptor site. These steric features of sweet and non-sweet sugar glycol units are shown in perspective in Fig. 1. Glycol conformational parameters, and the gross conformation of pyranose and furanose rings, have been used to explain the varying sweetness of the sugars2–5.

Chemical Structure of Compounds and Their Sweet and Bitter Taste

In presenting the material in this chapter, four fundamental propositions are made. These are: (1) Sucrose (sugar) tastes sweet. (2) Quinine tastes bitter. (3) Sodium chloride tastes salty 1. (4) Hydrochloric acid tastes sour.

A lipophilic-hydrophobic attribute and component in the stereochemistry of sweetness

Abstract The bipartite AH,B concept of sweetness is extended to a tripartite AH,B,γ concept. This leads to the novel idea that intramolecular hydrogen bonding may, in some cases, enhance sweetness.

Relative stability of glucose and fructose at different acid pH

Abstract An empirical procedure is employed to assist in determining the relative stability of sugars at different pH. The procedure applies the most appropriate linear function for three arbitrary segments of the overall second order autocatalytic equation to sets of experimental data. As measured by the formation of 5-(hydroxymethyl)-2-furancarboxaldehyde (HMF) at 100°C, fructose is most stable between pH 4 and 6 and glucose between pH 2 and 6. However, fructose in its most stable environment is five times more reactive than glucose in its most stable environment.

Thermodynamics and kinetics of D-galactose tautomers during mutarotation

Abstract The tautomerism of D -galactose in water has been studied by using g.l.c. to separate per- O -trimethylsilyl derivatives of D -galactose tautomers formed during the mutarotation reaction. The initial, rapid stage of the biphasic mutarotation of α- D -galactopyranose is due to the formation of α- D -galactofuranose and β- D -galactofuranose. The slow phase is due to the formation of β- D -galactopyranose. The kinetic data of D -galactose tautomerism have been tabulated. The free-energy difference between pyranose tautomers (anomers) is primarily entropic. The free-energy difference between pyranose and furanose tautomers is distributed between relatively large and opposing enthalpic and entropic energies. It is concluded that the “transition state” for these tautomerization reactions is quite unlike the structure of any of the tautomers, and that, for the activation of a compound for tautomerization reactions, the same entropy and enthalpy exists for the formation both of furanoses and pyranoses.

Sweetness chemoreception theory and sweetness transduction.

This review summarizes the outcome of sweet taste chemoreception research over the last 30 years. Since the sweet taste receptor has yet to be isolated and identified, several models have been developed to account for sweetness and to explain how molecules are structured to elicit sweet taste chemoreception. The models proposed are classified as follows: category I: the receptor binding theories AH-B, AH-B-X; AH-B-γ; the multi-attachment theory; the α-helix protein theory; category II: the direct G-protein binding theory. All currently established hypotheses are discussed and their ability to account for the sweetness of a variety of structurally dissimilar compounds critically evaluated. After 30 years, the AH-B theory still appears to be the best explanation for the ligand binding chemistry that induces sweet taste response, and it is also consistent with prevailing sweet taste transduction hypotheses.

Autocatalytic mutarotation of D-glucose in pyridine

Abstract The mutarotation of α- and β- d -glucose in dry pyridine was followed gas chromatographically. Kinetic treatment of the data for a wide range of concentrations of D -glucose showed the reaction to be first-order in the starting anomer with a unimolecular dependence on the total concentration of D -glucose. Thus, rotation of D -glucose in dry pyridine appears to be autocatalytic, and a sterically acceptable mechanism for the reaction is a modification of the mechanism of Swain and Brown. Specific rotations of the D -glucopyranose anomers in dry pyridine were calculated to be +152° for α- D -glucopyranose and +11° for β- D -glucopyranose. At equilibrium, [α] spD  +72°, and the distribution of α- and β- D -glucopyranose is 43% and 57%, respectively.

The AH,B glycophore and general taste chemistry

Abstract When considered jointly, all tastes (sweet, salt, bitter, sour) are variations on a common electrostatic mechanism, and the primary distinction among them can be traced to the symmetrical nature of the interaction between the substance and the taste receptor. Sourness is a dissymmetric interaction between the hydronium ion (an acidophore) and the taste receptor, whereas saltiness is a concerted symmetrical electrostatic interaction betwen the Na + and Cl − ions (the halophore) and the receptor. Sweetness is elicited through a bilaterally symmetrical and concerted dipolar interaction between a glycophore and the receptor, while bitterness can be traced to either dissymmetric ionic or dipolar interactions between a picrophore and the receptor. As no products are ever formed, taste phenomena are collectively grouped as being due to electrostatic recognition interactions that can occur between a substance and the receptor without the need for chemical binding.

Laminaranase activity in the crystalline style of the surf clam (Spissula solidissima)

Isolierung und Charakterisierung eines Enzyms ausSpissula solidissima, welches die Fähigkeit besitzt, gewisse Polysaccharide spezifisch zu spalten.

Influence of acid and temperature on the rate of inversion of sucrose

Abstract The optical rotation, at acid pH, of inverted sucrose solutions was found to be independent of the type of acid. Since it was clear that, under these conditions, the anion had no influence on optical rotation, it was possible to devise a simple mathematical model to predict reaction velocity as measured by polarimetry.