Temperature dependence of water activity in aqueous solutions of sucrose

A comprehensive experimental data analysis was performed to evaluate the effect of temperature on the water activity coefficient and selected excess thermodynamic functions for aqueous solutions of sucrose. A four-suffix Margules equation with temperature-dependent parameters was used to fit thermodynamic data such as the vapor pressure, boiling point, osmotic coefficient, freezing point, sucrose solubility, heat of dilution and specific heat of solution. The proposed equation gives an adequate representation of the available literature data on sucrose solutions for temperatures from −15 to +150 °C and sucrose concentrations up to 98% wt. The isotherms of water activity coefficient exhibit a characteristic minimum at about 96% wt. sucrose which is then followed by a dramatic increase to values well exceeding 1, as it was suggested before by some theoretical models [Starzak, M., & Mathlouthi, M. (2002). Water activity in concentrated sucrose solutions and its consequences for the availability of water in the film of syrup surrounding the sugar crystal. Zuckerindustrie, 127, 175–185; Van Hook, A. (1987). The thermodynamic activity of concentrated sugar solutions. Zuckerindustrie, 112, 597–600]. The effect of temperature on water activity, almost negligible for dilute solutions, was found significant for very concentrated solutions (above 80% wt. sucrose). The new water activity equation should find numerous applications in the food technology and sugar industry.