Drying characteristics of six varieties of sweet potatoes in different dryers

In this work, which was designed for drying of agro-food products, six varieties of potatoes (Santana, Santea, Marfona, Diamant, Koncord, Renjer) were chosen as drying material. A pilot-scale tray dryer, with and without air circulation, and a fluidized bed dryer were used for performing drying experiments. The experiments were performed with and without blanching. The changes in structure and colour of six varieties of potatoes were studied. Temperature did not show significant effect on shrinkage, but blanching time and air circulation had significant effect on shrinkage as well as on the appearance of dried product. Less shrinkage occurred in Renjer and Diamant varieties at 80 degrees C in comparison with other varieties. Santana (at 80 degrees C), Santea (at 70 degrees C) and Renjer (at 80 degrees C) had better appearance and colour after free convection drying, whereas the appearance, colour and quality of Marfona variety was not acceptable at all. The quality and appearance of Marfona variety improved by using a tray dryer with air circulation. The quality and appearance of all varieties was very good in fluidized bed dryer. Blanching was effective in improving the colour of all dried varieties.