Prediction of water activity in sugar solutions using models of group contribution and equation of state

Data of water activity in sugar solutions (of sucrose, glucose, fructose, a nd maltose) were obtained experimentally utilizing a dew point device (Aqua -Lab CX-2) at temperatures of 25, 30, and 35 degrees C, and atmospheric pre ssure. 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 wa s obtained for the temperatures tested by fitting the UNIFAC and ASOG model s to the experimental data; equations of state were used to determine binar y interaction parameters for water-sucrose, water-glucose, water-fructose, and water-maltose. Water activity was predicted for a quaternary mixture (s ucrose, 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 gr oup contribution methods, the deviations were 0.48% for the ASOG and 0.52% for the UNIFAC.