Adsorption-desorption isotherms and heat of sorption of prickly pear fruit (Opuntia ficus indica)

The equilibrium moisture contents were determined for prickly pear fruit using the gravimetric static method at t = 30, 40 and 50 degreesC over a range of relative humidities from 0.05 to 0.9. The sorption curves of prickly pear fruit decreased with increase in temperature at constant relative humidity. The hysteresis effect was observed. The GAB, modified Halsey, modified Chung-Pfost, modified Oswin and modified Henderson models were tested to fit the experimental data. The GAB model was found to be the most suitable for describing the sorption curves. The monolayer moisture content values for the sorption at different temperatures are calculated using a modified BET equation. The isosteric heats of desorption and adsorption of water were determined from the equilibrium data at different temperatures. (C) 2003 Elsevier Ltd. All rights reserved.