Determination and correlation of the water activity of unsaturated, supersaturated and saturated trehalose solutions

The water activity (aw) of unsaturated and supersaturated trehalose solutions (and some sucrose solutions) was determined using a dew point hygrometer, and correlated using an equation originally proposed by Norrish [1966. An equation for the activity coefficients and equilibrium relative humidities of water in confectionery syrups. Journal of Food Technology, 1,25] for predicting water activity in binary non-electrolyte solutions. The aw lowering behaviour of trehalose was found to be almost identical to that of sucrose solutions at same concentrations; however, due to the lower solubility of trehalose the aw of their saturated solutions is higher than that of sucrose ones. The aw of saturated trehalose solutions at 20, 25, 30, 35 and 40 °C was also determined and found to be between 0.953 and 0.928. These values agreed well with predictions made using aw data for trehalose solutions calculated at the solubility concentration at the various temperatures.