Sorption isotherms of turnip top leaves and stems in the temperature range from 298 to 328 K Original Research Article

Data for desorption and adsorption isotherms at 298, 313 and 328 K of both fresh and vacuum dehydrated turnip tops were experimentally obtained and compared. Analysis of the isotherms for leaves and stems showed no significant differences. Sorption isotherms at 298 K can be classified as Type II and at higher temperatures as Type III. The experimental data were fitted by the Peleg model with satisfactory results. The desorption isotherms of leaves clearly showed the influence of temperature, decreasing the moisture content at a fixed water activity value with higher temperatures. With the other isotherms, the effect of the temperature was less important. The presence of hysteresis cycles was detected at 298.1 K, but at the higher temperatures the hysteresis cycles were not practically significant (for both stems and leaves). The isosteric heat of sorption was evaluated, being higher for desorption processes and at lower moisture contents and temperatures.