Comparison of single and double-stage drying methods for processing tropical foods: a case study with banana and ginger

Abstract

In this study, the drying behaviours of banana and ginger under single-stage and double-stage hot-air convective drying were compared. Banana and ginger slices were blanched before drying at 40°C, 50°C or 60°C in the single-stage drying method. In the double-stage drying, samples were dried at 70°C during the first hour and then at 40°C, 50°C or 60°C till the end. Moisture content, colour and shrinkage were measured by standard methods. The drying data were fitted to six drying models using non-linear regression. A comparable drying rate of 0.0052 g water/g sample.min was recorded in banana dried at 60°C in both single- and double-stage methods. At 40°C and 50°C, however, drying rates were higher in double-stage than single-stage. For ginger, higher drying rates occurred at all temperatures in the single-stage compared to the double-stage mode. Midilli et al. and Page’s models best described the drying behavior of both banana and ginger under both drying modes. The moisture diffusivity ranged between 1.52 – 3.07 × 10-10 for banana and 1.27 – 2.54 × 10-10 for ginger. Considering the changes that occurred after drying, the single-stage method is more appropriate for drying these banana and ginger