Thermodynamic Properties of Water on Rice as Calculated from Reversible and Irreversible Isotherms

Moisture sorption isotherms (MSI) of dehydrated rice obtained at 10°, 20°, and 30° for two successive adsorption and desorption cycles were used to compute thermodynamic functions of water on rice. Uncompensated heats declined with increasing temperature, from 41 J/g dry matter at 10°C to 5.6 J/g dry matter at 30°C. No hysteresis was observed in cycle 2 isotherms at any temperature, indicating thermodynamic reversibility. The cycle 2 MSI were generally in between the adsorption and desorption branches of the cycle 1 MSI. Behavior of the thermodynamic quantities calculated from cycle 2 MSI was qualitatively similar to those calculated from the cycle 1 adsorption MSI, though their magnitudes differed. Some implications of these results are discussed.