Water activity and its prediction: A review

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