Water Activity Prediction and Moisture Sorption Isotherms

The role of water in food stability can be described to a significant extent by the potential of water to contribute to both physical and chemical deteriorative reactions through its ability to dissolve reactants, mobilize them, and participate in the reactions as well. Water sorption isotherms illustrate the steady-state amount of water held (i.e. WHC) by the food solids as a function of a w or storage % RH at constant temperature The shape of the moisture sorption isotherms are characterized by the states of the system constituents. This chapter discusses several prediction models, both for water activity for moisture sorption isotherms, based on a broad perspective using fundamental concepts. In addition to empirical and theoretical models provided, there are various commercially available computer programs designed to predict a w for different food systems.