Prediction of water activity of osmotic solutions

Models to correlate and predict water activity in aqueous solutions of sing le and multiple solutes, including electrolytes, relevant for osmotic proce ssing of foods are reviewed. During the last decade a significant number of theoretical thermodynamic models that are applicable to these systems have been developed and published. Though their use is still limited, their per formance is in general very good, similar to the best traditional empirical equations. Their predictive character together with built-in capabilities to work at different temperatures and in some cases pressure suggests that an increased effort to their wide use should take place. It was found that predictions of water activity in aqueous solutions may easily be made with average relative deviations of less than 2%; this value is of the same orde r or in some cases less than the typical error of current instrumentation a vailable to measure water activity. (C) 2001 Elsevier Science Ltd. All righ ts reserved.