Specific volumes and sweet taste

Partial molar and specific volumes are now well-known parameters in assessing drug potency in general and have recently been explored in sweet taste chemoreception. At natural tasting concentrations the apparent specific volume seems to be the most useful index of taste with 0.51–0.71 cm 3 g −1 defining sweet taste quality. Most sugars are in the range 0.60–0.63 cm 3 g −1. Apparent specific volumes of sweet molecules correlate well with other volume parameters such as intrinsic viscosity, partial molar compressibility and theoretical molecular volume calculations. Fragments of sugar molecules contribute differently to overall volume. Lowering of molecular weight by removal of an oxygen atom or larger fragments from a sugar molecule may actually elevate specific volume by diminishing hydrogen bonding. The positional contributions of substituents around sugar rings to overall volume allow orientational comparisons to be made, and examples of these effects in multisapophoric molecules and L-sugars are illustrated. The interaction of a tastant molecule with water causes physical changes which may or may not give rise to a change in gustatory quality over the course of time. Detailed studies of specific volumes will therefore contribute to the understanding of the role of water in sweet taste chemoreception. However, differences in taste (if any) between enantiomers cannot be explained by differences in hydration.