Moisture Sorption Isotherms, Thermodynamic Properties, and Glass Transition of Pears and Apples

Moisture sorption isotherms of apples and pears were determined at 30, 45, and 60 degrees C and water activity (a(w)) range of 0.04-0.83 using a standard static gravimetric method. The sorption isotherms of both fruits decreased with increasing temperature and exhibited type III behavior according to Brunauer-Emmett-Teller (BET) classification. The moisture desorption data fitted well with the Peleg model (0.997 <= r <= 0.999, 0.009 <= SE <= 0.071, and 4.840 <= p <= 13.779). The glass transition temperature (T-g) of both fruits decreased linearly with the increase in water activity (a(w)). The variation in glass transition temperature versus water activity (T-g similar to a(w)) and glass transition temperature versus solid fraction of pears and apples (T-g similar to W-s) were adequately predicted by Khalloufi et al.'s model (0.998 <= r <= 0.999 and 0.007 <= SE <= 4.088) and the Gordon and Taylor model (0.879 <= r <= 0.979 and 9.798 <= SE <= 18.507). The thermal transition and desorption isotherms data were used to establish state diagrams of pear and apple and evaluate suitable fruits storage conditions.