Use of UNIFAC in the prediction of water activity values of aqueous polyol solutions

The water activity (a(w)) values of two commonly used aqueous polyol solutions (xylitol and sorbitol) in the confectionery industry were estimated at 25C by using the UNIFAC (universal functional group activity coefficient) model in the a(w) range 0.50-0.99. The comparison between the experimental and estimated a(w) values at the high a(w) region (a(w) > 0.96) revealed very good agreement. However, the predicted values by the UNIFAC model did not fit well to the experimental data at a(w) < 0.96, indicating that the UNIFAC method needed to be modified. The agreement between the experimental and predicted values was considerably improved at a(w) < 0.96 when the modified UNIFAC model was used.