Moisture Sorption Behavior and Effects of Temperature, Slice Thickness, and Loading Density on Drying Kinetics of a Local Sweet Potato Cultivar Grown in Bangladesh

Abstract

This study is aimed at investigating the moisture sorption behavior and thin-layer drying kinetics of local sweet potato sada (LSPS) variety slices. The sweet potato tubers were sliced at 3, 5, and 7 mm and dried at temperatures of 45, 55, and 62°C at a constant air velocity of 0.6 m/sec in a laboratory-scale cabinet dryer. The BET (Brunauer, Emmet, and Teller) and GAB (Guggenheim-Anderson-De Bore) models were applied to fit the sorption data. Fick’s diffusion equation was used to calculate the drying rate constant and effective moisture diffusivity. Our current result reveals that LSPS exhibited an isotherm with a sigmoid (type II) shape, and the GAB model was more goodness of fit than the BET model to clarify the adsorption isotherm of LSPS. The drying time increased with increasing slice thickness but reduced with increasing drying temperature. The drying rate constant for thin-layer drying decreased with an increase in slice thickness but increased with increasing drying temperature. The loading density with two different shapes (French cut and cube cut) also affected the drying rate constant, which decreased with the increase in loading density. Using statistical parameters, five thin-layer drying models were applied to fit the drying data. The findings indicated that the logarithmic model for 45-55°C and the Page model for 62°C were the most suitable models for explaining the drying behavior of LSPS slices. The effective moisture diffusivity increased with increasing slice thickness and drying temperature, ranging from $7.10\times {10}^{-11}$ to $1.55\times {10}^{-10}$  m2/s over the temperature range studied. The activation energy also increased with increasing slice thickness, and the values were 5.55 and 7.39 kJ/mol for 3 and 5 mm slices, respectively. The findings suggested that slice thickness, drying temperature, and sample loading density on cabinet dryer trays affect the drying kinetics of sweet potato slices.