Gg. Birch et al., IMPORTANCE OF MOLAR VOLUMES AND RELATED PARAMETERS IN SWEET TASTE CHEMORECEPTION, Pure and applied chemistry, 69(4), 1997, pp. 685-692
A major new chemical approach to the study of sweet taste chemorecpeti
on now centres on the role of water. Interaction of sweet stimulus wit
h receptor requires a molecular ''fit'' which in turn demands specific
volume requirements of the stimulus in water and probably also in the
biophase. Apparent specific volume, rather than partial specific volu
me, defines taste quality at normal tasting concentrations and sweet t
aste quality is largely confined to the range 0.51-0.71 cm(3)g(-1) wit
h the ''ideal'' quality of sugar and sugar alcohol sweetness being abo
ut 0.60-0.64 cm(3)g(-1). Specific volumes define hydrostatic packing o
f sweet molecules among water molecules whereas the related intrinsic
viscosities define their hydrodynamic behaviour. Both are related to '
'characteristic volumes'' which are partial specific volumes at absolu
te zero. A further solution characteristic is the partial molar isentr
opic compressibility (K-2s) which defines the compactness of the hydra
tion layer around sweet molecules. This parameter is much more sensiti
ve to structural differences between sweeteners than is partial molar
volume and it best represents compatibility with water structure. The
K-2s of (D) under bar-galactose, for example, is -2.08x10(-3)cm(3)mol(
-1)bar(-1) while that of the conformationally analogous (D) under bar-
glucose is -1.76x10(-3)cm(3)mol(-1)bar(-1). (D) double under bar-galac
tose is therefore less compatible with water than (D) double under bar
-glucose and half as sweet. These studies will help to elucidate the m
echanistic differences between sweeteners and their mode of interactio
n with water and flavours in foods.