Moisture sorption isotherms and thermodynamic properties of sorbed water of chironji (Buchanania lanzan Spreng.) kernels at different storage conditions

摘要

Moisture sorption isotherms of chironji kernels were determined at 25, 35 and 45 degrees C over a water activity range of 0.11-0.93. Three sorption models i.e., Guggenheim-Anderson-de Boer (GAB), Brunauer-Emmett-Teller (BET) and Caurie were evaluated to find out their fitness to the sorption data. Thermodynamic properties of sorbed water were analyzed over the selected range of water activity and temperature. The result showed that the sorption isotherms reflected Type II BET sorption characteristics with a clear hysteresis at the temperatures. Of the three models, GAB and Caurie models were found superior predicting the sorption of chironji kernels over the entire range of water activity values. The monolayer moisture content values calculated by the best-fitted GAB and Caurie model for adsorption were 9.86 and 6.31%, 8.023 and 6.18%, 6.90 and 5.97% (db) and for desorption were 6.53 and 6.01%, 5.85 and 5.68%, 4.21 and 5.60% (db), respectively at 25, 35 and 45 degrees C. The value of isosteric heat decreased with increasing moisture content and approached the latent heat of pure water. Sorption entropy increased with increasing moisture content and decreased gradually with increase in moisture content. The spreading pressures, for both adsorption and desorption, increased with increasing water activity at the three selected temperatures.