Thermodynamic properties of moisture desorption of raw pinhao (Araucaria angustifolia seeds)

The seeds of Araucaria angustifolia, named pinhao, are consumed in the south and southeast of Brazil. They are big in size and have high nutritious value. The literature about technological aspects of pinhao is very scarce and there are no reports about moisture sorption models. In this work, moisture desorption isotherms of raw pinhao were determined at 15, 25, 30 and 40 degrees C. Results show that temperature has little effect on the sorption behaviour and the Chirife model was found to best represent the experimental data. The isosteric heat of sorption (differential enthalpy) was calculated through direct use of moisture desorption isotherm by applying the Clausius-Clapeyron equation. The differential enthalpy of desorption decreased with increasing moisture content. The enthalpy-entropy compensation theory was applied to desorption isotherms and plots of differential enthalpy vs. differential entropy for pinhao provided the isokinetic temperature, indicating an enthalpy-controlled desorption process.