Behavior and modelling of humidity isotherms of Erythroxylum minutifolium Griseb leaves

The knowledge of the relationship between the equilibrium moisture content and the water activity is very important in order to describe the drying process and the effect of humidity on safe storage. In this work the water sorption isotherms of the Erythroxylum minutifolium Griseb leaves at 30 and 40°C were determined over relative humidity ranging from 55 to 85%. The sorption capacity of natural product increased with the increase of water activity. The moisture sorption isotherms showed that the equilibrium moisture decreases with increase of temperature. Six models were used to fit the experimental curves of equilibrium humidity. The parameters of each equation were determined by non-linear regression analysis. The isosteric heat of moisture sorption was calculated using the Claussius-Clapeyron equation.