Hydration number and water activity models for the sucrose-water system: a critical review

The nature of various molecular interactions occurring in the sucrose-water system and the structure of the aqueous solution are outlined briefly. The thermodynamic implications of these interactions are discussed, with special emphasis placed on the sucrose hydration number and the water activity coefficient. The existing "chemical" models of water activity, due to Scatchard (1921), Stokes and Robinson (1966), Schönert (1986), and Van Hook (1987), are evaluated in detail, including their predictive ability for dilute solutions and their limiting behavior in the region of high sucrose content. Some suggestions, based on the sucrose association mechanism, are made with regard to possible reformulations of the existing activity models that could result in a powerful thermodynamic model of the system.