Moisture sorption behaviour and thermodynamic properties of adsorbed water of Jerusalem artichoke (Helianthus tuberosus L.) powder

Moisture sorption isotherms of Jerusalem artichoke (Helianthus tuberosus L.) powders were determined at 20, 30, and 40°C by the static gravimetric method over water activity (aw) in the range of 0.11 and 0.85. The sorption isotherms exhibited type III behaviour according to Brunner-Emmett-Teller (BET) classification. Seven sorption isotherm models were fitted to the experimental data, and the Guggenheim-Anderson-de Boer (GAB) model was selected to evaluate the thermodynamic properties to determine the characteristics of adsorbed water and energy requirements associated with the sorption process. The monolayer moisture contents of the sorption process were 8.08, 7.09, and 5.06 g/100 g dried solids at 20, 30 and 40°C, respectively. Both the net isosteric heat of sorption and differential entropy increased with the increase of moisture content, below the monolayer moisture content above which both registered a sharp decline. The maximum isosteric heat of sorption and differential entropy for these powders were 17.91 kJ/mol and 47.15 J/(mol K), respectively. The application of enthalpy-entropy compensation theory showed that the moisture sorption mechanism was controlled by enthalpy, and it was a non-spontaneous process. The values of specific surface areas available for sorption at 20, 30, and 40°C were 286.50, 251.43 and 179.48 m2/g, respectively. These results can be used to design efficient dehydration and storage conditions for Jerusalem artichoke powders, and to predict their storage stability.