Moisture Desorption Isotherms and Isosteric Heat of Sorption Characteristics of Malting Barley (hordeum Distichum L.)

 The equilibrium moisture content of malting barley grains (cv. Scarlett) was determined by gravimetric-static method in the range 20-50°C using saturated salt solutions (LiCl, MgCl2.6H2O, K2CO3, NaBr, NaNO2, KI, NaNO3, NaCl, (NH4)2SO4) to provide water activities for each temperature between 0.11 and 0.813. Desorption isotherms were obtained at 20, 30, 40, and 50°C. All the sorption curves were found to be Type II, increasing moisture content with the increase of water activity from approximately 5.5–7.45% d.b. (dry basis) for different temperatures when the water activity was 0.111. Different models (Modified Henderson, Modified Chung-Pfost, Modified Halsey, Modified Oswin and GAB) were fit to the data and it was found that the best results corresponded to the Modified Henderson equation. The isosteric sorption heat varied from 3479 kJ/kg (20oC) to 2393 kJ/kg (50oC) decreasing with increasing moisture content, thus indicating that reducing the moisture content increases the energy required to remove water. Keywords Equilibrium, isotherms, heat of sorption, malting barley, modeling.