Relationships between hydration number, water activity and density of aqueous sugar solutions

Abstract Hydration numbers ( n h ) of simple sugars have been investigated for decades using thermodynamic, spectroscopic as well as molecular modelling techniques. Results were shown to depend on the technique employed. The most reliable values only concern the first hydration shell assuming a maximum oxygen–oxygen distance below 2.8 A. As concentration increases, sugar–sugar interactions become preponderant and n h decreases. Assuming that no long range structuring effect is exerted by the solute on water, it is possible to estimate the volume occupied by each of hydration water (with nearly 9% volume contraction) and bulk water from density measurements. Likewise, the volume occupied by non-hydrated sugar molecules in the aqueous medium allows finding for sugar density in the aqueous medium a value comparable to that of solid crystalline form. On the other hand, using the literature values of aqueous sugar solution densities, it was possible to calculate the hydration numbers at different temperatures and concentrations. These values of n h show a noticeable decrease as temperature is raised and concentration increased. Decrease in n h can be explained assuming a partial occupation of potential hydration sites (OHs) because of differences in H-bonds lifetimes on the one hand and molecular folding around glycosidic bond on the other. Calculation of water activity coefficients ( f w ) based on n h values was made for sucrose solutions. Results show the same trend as found previously [Starzak, M., & Mathlouthi, M. (2006). Temperature dependence of water activity in aqueous solutions of sucrose. Food Chemistry, 96 , 346–370] for sucrose, i.e. a decrease of f w with increasing molar concentration. Temperature effect on water activity coefficients and hydration numbers is also determined. It shows a decrease in hydration number as temperature is increased. In this paper, empirical relations are proposed to calculate water activity coefficients and hydration numbers at different concentrations and temperatures by use of accurate density values. These models were first applied to sucrose, the most documented sugar and applied to disaccharides (maltose, trehalose) and monosaccharides (glucose, fructose).

[1]  M. Rueegg,et al.  はちみつと関連糖液の水分活性 | 文献情報 | J-GLOBAL 科学技術総合リンクセンター , 1981 .

[2]  C. Bressan,et al.  Thermodynamic activity of water and sucrose and the stability of crystalline sugar , 1994 .

[3]  L. Hough,et al.  Intensification of sweetness , 1978 .

[4]  M. Mathlouthi,et al.  Laser-raman study of solute-solvent interactions in aqueous solutions of d-fructose, d-glucose, and sucrose , 1980 .

[5]  C. Dussap,et al.  Excess properties and solid-liquid equilibria for aqueous solutions of sugars using a UNIQUAC model , 1994 .

[6]  W Wang,et al.  Instability, stabilization, and formulation of liquid protein pharmaceuticals. , 1999, International journal of pharmaceutics.

[7]  S. Immel,et al.  Molecular modeling of saccharides, 7. The conformation of sucrose in water: A molecular dynamics approach† , 1995 .

[8]  R. Robinson,et al.  Interactions in Aqueous Nonelectrolyte Solutions. I. Solute-Solvent Equilibria , 1966 .

[9]  H. Høiland,et al.  STEREOCHEMICAL ASPECTS OF HYDRATION OF CARBOHYDRATES IN AQUEOUS-SOLUTIONS .3. DENSITY AND ULTRASOUND MEASUREMENTS , 1991 .

[10]  M. Elias,et al.  Trehalose + water fragile system: properties and glass transition , 1999 .

[11]  M. Starzak,et al.  Hydration Number and Water Activity Models for the Sucrose-Water System: A Critical Review , 2000, Critical reviews in food science and nutrition.

[12]  How homogeneous are the trehalose, maltose, and sucrose water solutions? An insight from molecular dynamics simulations. , 2005, The journal of physical chemistry. B.

[13]  M. Bruhns,et al.  Sugar technologists manual: Chemical and physical data for sugar manufacturers and users. , 1995 .

[14]  M. Mathlouthi.  X-ray diffraction study of the molecular association in aqueous solutions of d-fructose, d-glucose, and sucrose , 1981 .

[15]  T. Bounahmidi,et al.  Measurement and modeling of atmospheric pressure vapor-liquid equilibrium data for binary, ternary and quaternary mixtures of sucrose, glucose, fructose and water components. , 1994 .

[16]  A. E. Oliver,et al.  The trehalose myth revisited: introduction to a symposium on stabilization of cells in the dry state. , 2001, Cryobiology.

[17]  Maciej Starzak,et al.  Temperature dependence of water activity in aqueous solutions of sucrose , 2006 .

[18]  The vapour pressure of water as a function of solute concentration above aqueous solutions of fructose, sucrose, raffinose, erythritol, xylitol, and sorbitol , 2002 .

[19]  J. S. Rowlinson,et al.  The thermodynamic properties of aqueous solutions of glucose , 1955 .

[20]  G. Scatchard.  THE HYDRATION OF SUCROSE IN WATER SOLUTION AS CALCULATED FROM VAPOR-PRESSURE MEASUREMENTS. , 1921 .

[21]  E. A. Brignole,et al.  Phase equilibria in sugar solutions using the A-UNIFAC model , 2003 .

[22]  Francescaromana Maradei,et al.  Measurement and Modeling , 2008 .

[23]  Aage Fredenslund,et al.  A modified UNIFAC group-contribution model for prediction of phase equilibria and heats of mixing , 1987 .