influence of drying conditions on the effective diffusivity and activation energy during convective air and vacuum drying of pumpkin

The main purpose of the work is to investigate the efficiency of convective air and vacuum processing on pumpkin drying kinetics. The pumpkin samples were of two different geometrical shapes (cylinder and cube) and were dried in a laboratory scale hot air dryer using some specific parameters (constant air velocity of 1.0 m/s, three different temperatures 50, 60 and 70ºC suited to relative humidity (RH) values of 9.8, 6.5, and 5.4% respectively). The vacuum drying was led at constant pressures of 5 kPa and accordance temperatures of 50, 60 and 70ºC. Moisture transfer from pumpkin slices was described by applying Fick’s diffusion model. Temperature dependence of the effective diffusivity was described by the Arrhenius-type equation. Cylindrical samples have a slightly better behaviour compared to cubic samples, due to the disposition of the tissues, and the mass and thermic transfer possibilities. Analysing the results of both drying methods, it was deduced that the most efficient method is convective air drying at 70ºC.