Water Activity and Its Prediction: A Review

Water activity is a very useful parameter in food preservation. Raoult's law gave a first base in the case of ideal solutions. In 1966, Norrish presented a thermodynamically based equation to predict activity coefficients in confectionery syrups. Later, the Gibbs-Duhem equation was used to produce series of predictive models starting with Ross in 1975. Some apparent refinements have been proposed since then by Caurie, followed by Lilley and Sutton. In this work an analysis of different approaches are discussed with their limits. New directions are also suggested for either a more numerical approach to solve directly the Gibbs-Duhem equation, or a more empirical one, based on the zonotopes.