MOISTURE ADSORPTION ISOTHERMS AND THERMODYNAMIC PROPERTIES OF AURICULARIA AURICULA

Moisture adsorption isotherms of Auricularia auricula were determined using the gravimetric static method at 15-35C and within the range of 0.1-0.9 water activity. The adsorption data were fitted into eight isotherm models. The best fit of experimental data was obtained with GAB model in the range of temperatures and water activities investigated. The moisture adsorption isotherms obtained were type II sigmoid shape. The thermodynamic properties such as net isosteric heat, differential entropy and spreading pressure were also determined from moisture adsorption isotherm data of A. auricula. The net isosteric heat of adsorption and differential entropy decreased with increasing moisture contents. From the values obtained for net isosteric heat and differential entropy, it was verified that the enthalpy-entropy compensation theory could be applied, the process being carried out by enthalpy (T beta > T-hm). The spreading pressure increased with increasing water activity, and decreased with increasing temperature.