Dehydration and Rehydration Characterization of Yam (Dioscorea Rotundata) Tuber Slices Dehydrated Using a Refractance Windowtm Dryer

Abstract

The effect of slice thickness on the dehydration and rehydration characteristics of yam was studied in a Refractance Window TM (RW) type dryer constructed from a laboratory water bath. Yam slices 1.5, 3.0 and 4.5 mm thick were dried in a laboratory scale RW dryer where the water in the bath was maintained at temperature of 80 °C. The initial moisture content of the yam samples was 69% on a wet basis (wb). The drying process was carried out until the final moisture content of the product was below 10% (wb). The experimental data indicate that the drying time decreases rapidly as the yam slices decrease; the 1.5 mm, 3.0 mm and 4.5 mm thick yam slices, dried to below 10% within 40 minutes, 80 minutes and 120 minutes respectively. The experimental data indicated that the drying kinetics for the yam slices fitted the Haghi and Ghanadzadeh thin-layer drying model with a regression coefficient exceeding 99.9 % for the 1.5, 3.0 and 4.5 mm thick slices. The rehydration ratio increased to a steady value of about 1.91 when soaked in water for about 180 minutes.