Thermodynamic properties, sorption isotherms and glass transition temperature of cape gooseberry (Physalis peruviana L.)

Adsorption and desorption isotherms of fresh and dried Cape gooseberry (Physalis peruviana L.) were determined at three temperatures (20, 40 and 60 ^oC) using a gravimetric technique. The data obtained were fitted to several models including Guggenheim-Anderson-De Boer (GAB), Brunauer-Emmett-Teller (BET), Henderson, Caurie, Smith, Oswin, Halsey and Iglesias-Chirife. A non-linear least square regression analysis was used to evaluate the models. The Iglesias-Chirife model fitted best the experimental data. Isosteric heat of sorption was also determined from the equilibrium sorption data using the Clausius-Clapeyron equation and was found to decrease exponentially with increasing moisture content. The enthalpy-entropy compensation theory was applied to the sorption isotherms and indicated an enthalpy-controlled sorption process. Glass transition temperature (Tg) of Cape gooseberry was also determined by differential scanning calorimetry and modelled as a function of moisture content with the Gordon-Taylor, the Roos and the Khalloufi models, which proved to be excellent tools for predicting glass transition of Cape gooseberry.