DETERMINATION OF THE MOISTURE-SORPTION ISOTHERMS AND ISOSTERIC HEAT OF HENNA LEAVES

Equilibrium moisture desorption and adsorption isotherms of Lawsonia inermis L. (commonly known as henna)
leaves at temperatures of 30, 40 and 50^o C with a water activity ranging from 0.057 to 0.898 were obtained by the
gravimetric-static method. It was established that when the temperature of these leaves increases, their moisture content increases too with a hysteresis effect. The experimental data on the sorption of the indicated leaves were compared with the corresponding calculation data obtained with the use of the GAB, modifi ed BET, Henderson–Thompson, modifi ed Halsey, modifi ed Oswin, and Peleg models. Evaluation of these models on the basis of statistical processing of the data obtained with them, including the calculus of the standard error and the correlation
coeffi cient, has shown that the GAB and Peleg models represent sorption curves more adequately. The net isosteric
heats of desorption and adsorption of henna leaves were determined by the sorption isotherms constructed using the
Clausius–Clapeyron equation. An expression for predicting these thermodynamic properties of plants is proposed.
   
Author:  S. Bennaceur, B. Draoui, B. Touati, A. Benseddik, A. Saad, and L. Bennamoun
Keywords:  henna leaves, equilibrium moisture sorption, isosteric heat of sorption, sorption isotherms
Page:  52