Mass transfer coefficients for the drying of pumpkin (Curcubita moschata) and dried product quality.

The aim of this work was to determine the mass transfer properties of pumpkin (Cucurbita moschata) exposed to air drying. The drying temperatures tested ranged between 30ºC and 70ºC, and the kinetic behaviour was studied in this temperature band. The samples were analyzed in terms of moisture content, acidity, proteins, lipids and crude fiber, both in the fresh state and after drying. From the chemical analyses made it was possible to conclude that drying induces some reductions in acidity, lipids, fibers and proteins. As to the influence of the drying temperature on the process, it was observed that a temperature rise from 30 ºC to 70 ºC led to a 70 % saving in drying time. The results obtained by fitting the experimental data to the kinetic models tested allowed concluding that the best model for the present case is Henderson-Pabis, and the worst is Vega-Lemus. Furthermore, in this work it was possible to determine the values of the diffusion coefficient at an infinite temperature, De0, and activation energy for moisture diffusion, Ed, which were, respectively, 0.0039 m2/s and 32.26 kJ/mol. Similarly the values of the Arrhenius constant and the activation energy for convective mass transfer, respectively hm0 and Ec, were also calculated, being the first 3.798x108 m/s and the later 86.25 kJ/mol. These results indicate that the activation energy for convective mass transfer is higher than that for mass diffusion