Hydration properties of Na, K, Mg gluconates and gluconate/sucrose mixtures and their possible taste effect

Density and ultrasonic velocity were measured in aqueous solutions of sodiu m, potassium and magnesium gluconate as a function of increasing concentrat ion. Apparent molar volume (AMV), apparent specific volume (ASV), isentropi c apparent molar (IAMC) compressibility and hydration numbers were calculat ed from the experimental data. The results show that AMV and ASV increase a s the concentration of gluconates is increased. This is interpreted on the basis of molecular interaction between solute and solvent molecules. These measurements were repeated by adding Na, K and Mg gluconates to 10 and 20% sucrose solution with the aim of understanding the influence of gluconates on water association in sucrose solutions. The results show that the values of IAMC decrease as the concentration is increased. Moreover, Mg gluconate shows more negative IAMC than Na and K gluconates. The observed results ar e explained on the basis of the hydration of gluconates in the sucrose-wate r system. NMR relaxation rates (R-1 and R-2) show an increase as the concen tration of the gluconate is increased. On the other hand, the results of Na , K and Mg gluconate in 10 and 20% sucrose solutions demonstrated that the effect of Mg gluconate enhances the hydration properties of sucrose water m ixtures more than Na and K gluconate. The overall results show the importan ce of water interactions with sapid molecules and this can lead to a better understanding of their tastes. (C) 2000 Elsevier Science Ltd. All rights r eserved.