Abstract
The moisture sorption isotherms of potato were determined using a gravimetric static method at 30, 45 and 60 °C, and over a range of relative humidities. The isotherms exhibited Type II behaviour, with the sorption capacity decreased with increasing temperature. The Guggenheim–Anderson–de Boer (GAB) and Halsey models were found to adequately describe the sorption characteristics. Calculation of the thermodynamic properties (differential enthalpy, integral enthalpy, differential entropy and integral entrophy) was further used to provide an understanding of the properties of water and energy requirements associated with the sorption behaviour. Isosteric heats (differential enthalpies) were calculated through direct use of moisture isotherms by applying the Clausisus–Clapeyron equation. The differential enthalpy and entropy decreased with increasing moisture content and were adequately characterised by a power law model. A plot of differential heat versus entropy satisfied the enthalpy–entropy compensation theory. The spreading pressures (adsorption and desorption) increased with increasing water activity, and decreased with increasing temperature. The net integral enthalpy increased with moisture content to a maximum value (around the monolayer moisture content) and then decreased. In a reverse manner, the net integral entropy decreased with moisture content to a minimum value and then increased.
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