Thermodynamic analysis of experimental sorption isotherms of loquat and quince fruits

Sorption isotherms of loquat and quince fruits were determined by static gravimetric method at different temperatures, in the range from 20 to 65 °C. The curves obtained can be considered as type II at 20 °C and type III at higher temperatures according to the Brunauer–Emmett–Teller (BET) classification. Equilibrium moisture content data were correlated by different mathematical models usually applied to foodstuffs (GAB, Peleg and Halsey). The best fit of the experimental data was obtained with Peleg and GAB models. Experimental data were analysed by a thermodynamic approach to obtain such properties as net isosteric heat, net equilibrium heat, differential and integral entropy that provide a deeper understanding of the properties of water and energy requirements associated with sorption process. Particularly, for loquat and quince fruits, the differential enthalpy and entropy decreased with increasing moisture content and satisfied the compensation theory. The net integral enthalpy show maximum values (32, 26, 24 kJ/mol for loquat pulp, loquat seeds and quince, respectively) and the net integral entropy has the opposite behaviour with minimum values (−90.8, −70.8, −68.1 J/mol K for loquat pulp, loquat seeds and quince, respectively) at specified moisture contents.