Influence of drying process variables on the effective moisture diffusivity and activation energy of African oil bean seed

Abstract

This study evaluated the effects of drying temperature, slice thickness and pretreatment on the effective moisture diffusivity and activation energy of African oil bean seed in a hot-air convective oven dryer. Thin-layer drying of untreated, brine and sucrose pre-treated African oil bean seed slices was investigated under four oven temperatures (40, 50, 60, 70℃) and three slice thicknesses (2, 3, 5 mm) to determine the effective moisture diffusivity (Deff) and activation energy (Ea). Fick's second law of diffusion and the plot of ln(Deff) versus Ea were used to compute the moisture diffusivity and activation energy, respectively. The results showed that Deff for African oil bean seed is in the range of 0.637 × 10−10 to 13.870 × 10−10 m2s−1, whereas Ea ranged from 18.52 to 32.01 kJ mol−1. An increase in temperature, slice thickness and pre-treatment increased the diffusivity. Brine pretreatment was found to lower the activation energy of African oil bean seed whereas the reverse is the case for sucrose pretreatment. The moisture diffusivity is useful in understanding the rate of internal moisture movement during the processing and storage of African oil bean seed. The result of activation energy is important in selecting appropriate drying variables to ensure energy conservation during the drying of African oil bean seeds.