Effect of water activity on glass transitions of date pastes

Water sorption isotherms of freeze dried and control (without freeze drying) date paste of cultivar Khalas were obtained at 20 °C using the static saturated salt solution method. The GAB equation fitted adequately for the whole range of water activity for both date paste samples. The monolayer moisture contents ranged between 0.102 and 0.12 for freeze dried and control samples respectively. The glass transition temperatures of saturated salt equilibrated paste samples were measured using a differential scanning calorimetry (DSC). Glass transition temperature of both samples decreased linearly with an increase in water activity. Water adsorption characteristics of freeze dried and control samples differed from each other and were supported by glass transition temperatures.