Evaluation of the mass and moisture transport parameters of thin-layer drying of pale-fleshed, white-skinned spherical sweet potato (Ipomoea batatas)

In this study, the evaluation of mass and moisture transport parameters of hot air drying of pale-fleshed, white-skinned spherical sweet potatoes (a newly introduced variety cultivated in Burkina Faso) was investigated at air temperatures of 50, 60, 70 and 80°C for 2 and 3 cm diameter samples using an oven dryer. With the measurement data, the objective of this paper is to evaluate the transport parameters (lag factor, drying constants, moisture diffusivities and moisture transfer coefficient) of spherical sweet potatoes during hot air convective drying. Drying data analyzed were obtained in the period of falling drying rate.  The moisture ratio and drying rate were influenced by the drying temperature and sample diameter. Concerning the mass moisture transport parameters results, the drying coefficient of sweet potato varied from 5.190×10^-7 s^-1 to 1.950×10^-6 s^-1 under our air-drying conditions. The lag factor of sweet potatoes varied from 1.043 to 1.083. The moisture Biot number values for sweet potatoes were in the range of 0.1232 - 0.2462. The effective moisture diffusivity for spherical sweet potatoes varied in range from 4.040×10^-10 to 2.615×10^-9 m2/s, for our drying conditions. The convective mass transfer coefficient values for spherical sweet potato samples were obtained to be in the range of 7.490×10^-8 – 7.844×10^-7 m/s. The activation energy for moisture diffusion was 48.349 and 45.838 kJ/mol, respectively for samples with diameters of 2 and 3 cm. The activation energy for convective mass transfer was 66.474 and 62.151 kJ/mol for sweet potato samples with diameters of 2 and 3 cm, respectively.