Prediction of Water Activity in Sugar Solutions Using Models of Group Contribution and Equation of State.

Abstract

Data of water activity in sugar solutions (of sucrose, glucose, fructose, and maltose) were obtained experimentally utilizing a dew point device (Aqua-Lab CX-2) at temperatures of 25, 30, and 35°C, and atmospheric pressure. The thermodynamic models of group contribution (UNIFAC, ASOG) and of equations of state (EOS PR/Classic; EOS PR/SV) were used for modeling and predicting water activity in these solutions. A single set of parameters was obtained for the temperatures tested by fitting the UNIFAC and ASOG models to the experimental data; equations of state were used to determine binary interaction parameters for water-sucrose, water-glucose, water-fructose, and water-maltose. Water activity was predicted for a quaternary mixture (sucrose, glucose, fructose and water), with average relative deviations of 0.5% and 1.3% for the EOS PR/SV and EOS PR/Classic, respectively. For the group contribution methods, the deviations were 0.48% for the ASOG and 0.52% for the UNIFAC.