Influence of drying process variables on hot air convection drying characteristics of pale flesh white skin sweet potatoes (Ipomoea batatas)

Drying of spherical sweet potatoes (Ipomoea batatas) with pale flesh and white skin (a newly introduced variety grown in Burkina Faso) was carried out at air temperatures of 50°C, 60°C, 70°C and 80°C using 2 and 3 cm diameter samples to study the influence of process variables including air temperature and sample diameter on drying characteristics. The results of the analyzed drying data indicated that moisture content was influenced by sample diameters and hot air-drying temperatures. Increasing air temperature and sample diameter resulted in reduced drying time for temperature influence and increased drying time for diameter influence. Effective moisture diffusivity decreased relatively with increasing moisture ratio value at all hot air temperatures. A polynomial of degree five was derived to correlate the effective moisture diffusivity with the moisture ratios of sweet potato spheres. The average effective moisture diffusivity increased as the air temperature and the diameter of the spherical sweet potato samples increased. The air temperature dependence of the average effective moisture diffusivity values was described by an Arrhenius-type equation. This dependence allowed the determination of the activation energy values of the spherical sweet potato. The activation energy values increased by 30.50 and 27.71 kJ/mol when the sample diameters varied from 2 to 3 cm.