Thermodynamics of moisture sorption in melon seed and cassava

Experimental data on the sorption isotherms of melon seed and cassava were used to determine their thermodynamic functions (heat of vaporization, spreading pressure, net integral enthalpy and net integral entropy). The heat of vaporization of both products decreased with increase in moisture content and that of melon seed approached the latent heat of pure water at a moisture content of about 13% dry basis, while that of cassava approached it at a moisture content of about 36% dry basis. The spreading pressure of both products decreased with increase in temperature and increased with increase in water activity more markedly in the high range of water activity (a(w) > 0.6). The net integral enthalpy of melon seed decreased from a Value of 847 kJ/kg as the moisture content increased from 3.2% (db). The trend became asymptotic at a value of 161.7 kJ/kg as the moisture content of 10% (db) was approached. The net integral enthalpy of cassava increased with moisture content to a maximum value of 770 kJ/kg at 10.70% (db) moisture content, and declined. The net integral entropy of melon seed increased with moisture content while that of cassava decreased to a minimum of value at 12% (db) moisture content and increased. The differences in values and trend of the thermodynamic properties of melon seed and cassava were attributed to chemical adsorption, structural modification of the adsorbent, and presence of oil and more polar groups in melon seed and presence of starch in cassava. (C) 2002 Published by Elsevier Science Ltd.