Study of the Moisture Sorption Isotherms and Isosteric Heat of Sorption of the Medicinal Plant Launeae Nudicaulis from Algerian Sahara

The aim of this work is to determine the sorption isotherms of Launeae nudicaulis, a medicinal plant growing in south-west of Algeria. The equilibrium moisture content was measured, using the static gravimetric method, with the water activity from 6.3 to 89.8% at 30 and 40 degrees C. It was shown that at higher water activities the moisture content increases sharply with the temperature, resulting in crossing of the isotherm curves. Four models were applied for analyzing experimental data (namely, the Peleg, GAB, Henderson-Thompson, and the BET modified ones). The desorption and adsorption data showed the best correlation with the Peleg model. The isosteric sorption heat of water was determined from the equilibrium data at different temperatures. This heat was shown to decrease as the moisture content increases and to be a polynomial function of the moisture content.