Study of the convective drying of pumpkin (Cucurbita maxima)

The main goals of the present work are, on one hand to study the influence of drying operation in some chemical properties of pumpkin, and, on the other hand, to study the drying kinetics, by applying different kinetics models to the experimental drying data.In this way, pumpkin was dried by convection for different air temperatures, ranging between 30 °C and 70 °C. The chemical properties that were analysed in the fresh and dried pumpkin were: moisture content, total and reducing sugars, acidity, proteins, lipids, crude fibre and ash.The results enable concluding that the convective drying at the lowest temperature, 30 °C, induces reductions of 14% in proteins, 65% in total sugars and 36% in fibre. Furthermore, the drying temperature seems to have a negligible effect on the nutritional characteristics of the pumpkin, since the results for the drying at 30 °C are quite similar to those for the drying at 70 °C.With respect to the other subject analysed, the drying kinetics, the results show that the increase on the operating temperature strongly accelerates the drying process, so that the process at 30 °C takes 8 h while at 70 °C the drying is finished after only 2 h. The experimental data for moisture ratio was fitted to different models, and the best were Page and modified Page.

Research highlights▶ Increasing drying temperature greatly accelerates the process. ▶ The best kinetic models to fit the experimental data are Page and Modified Page. ▶ Macronutrients are very affected by air drying, independently of the temperature. ▶ In this work it was estimated that D0 = 0.028 m2/s and E = 33.74 kJ/mol.