Hydration properties and the role of water in taste modalities of sucrose, caffeine, and sucrose-caffeine mixtures.

Solution properties of sapid molecules are informative on their type of hydration (hydrophobic or hydrophilic) and on the extent of the hydration layer. Physicochemical properties (intrinsic viscosity and apparent specific volume) and nuclear magnetic resonance (NMR) relaxation rates R(1) and R(2) for pure sucrose, bitter molecule caffeine, and their mixture were found to be relevant in the interpretation of the effects of these solutes on water mobility. Likewise, surface tension, contact angles with a hydrophobic surface, and the adhesion forces to this type of surface of the aqueous solutions of sapid molecules were found to discriminate between their effects on water cohesion and also between their taste qualities. The interpretation of the two sets of independent experimental results, namely physicochemical and spectroscopic data, helps in the elucidation of the role of water in sweet and bitter taste chemoreception.