Moisture adsorption isotherms of guar (Cyamposis tetragonoloba) grain and guar gum splits

Moisture adsorption isotherms of guar grain and guar gum splits were determined at 10, 20, 30 and 40 °C and 23–96% relative humidities using gravimetric method. The sorption data were fitted to six well-known sorption isotherm models (modified Chung–Pfost, modified Halsey, modified Henderson, modified Oswin, Chen–Clayton, and GAB models) using non-linear least square method. The GAB model was found the most satisfactory for representation of the equilibrium moisture content data for guar grain and guar gum splits. The equilibrium moisture content of guar gum splits was found to be significantly higher (p < 0.05) than that of guar grain. The isosteric heat of sorption was determined from the equilibrium moisture adsorption data using Clausius–Clapeyron type equation. Exponential relationship described well the dependence of isosteric heat of sorption on the equilibrium moisture content. The enthalpy–entropy compensation theory applied to sorption isotherms indicated enthalpy controlled sorption process.