DRYING OF BANANA SLICES UNDER VACUUM-INFRARED HEATING SYSTEM

Abstract

A combined vacuum-infrared (IR) drying system was tested for drying bananas slices as heat-sensitive material. Thirty two experimental runs were performed at the following conditions: drying vacuum of 0.2, 0.4, 0.6 and 0.8 bar; controlled temperatures at banana surfaces of 60, 70, 80 and 90°C; thickness of banana slices of 1mm and 5 mm. Three different thin layer drying models (Lewis’s; Henderson and Pabis’s; Logarithmic model) were examined to assess the most proper drying model for simulating and describing the drying behavior of banana slices under the studied experimental parameters. Physical quality of banana slices was evaluated in terms of color, rehydration ratio, shrinkage, crispness and hardness. The results showed that the changes of slices surface temperature have more significant effect on drying time than changes of drying vacuum and slices thickness. The Logarithmic model is recommended for describing the drying behavior and predicting the change of moisture ratio of banana slices in comparison with the other studied drying models. The combined vacuum –infrared drying method at drying vacuum of 0.8 bar, slices surface temperature of 80 °C and slices thickness of 1mm are considered the most proper drying parameters for banana slices under the studied drying system.