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The effect of pretreatment and drying temperature on the drying kinetics and quality of cocoyam was investigated in this study. The best model to predict the drying kinetics was also determined. Cocoyam slices were pretreated by water blanching (WB) and soaking in sodium metabisulphite (SM) and dried in a hot air oven at temperatures of 50, 60 and 70 °C while untreated samples were sun dried. Seventhin layer drying models (Exponential, Generalized Exponential, Page, Logarithmic, Parabolic, Wang and Singh and Two-term) were fitted to the experimental data and selection was done basedon model with highest correlationcoefficient (R(2)), and lowest reduced chi-square (χ (2)), sum square error (SSE) and root mean square error (RMSE) respectively. The Logarithmic and Parabolic model was found to best describe the oven and sun drying of cocoyam respectively. The vitamin C and beta-carotene value of the dried cocoyam slices, which varied from 0.0038 to 0.0075 and 4.1 to 5.888 mg/100 g respectivelygenerally decreased with an increase in drying temperature.

The thin layer drying behaviour of ginger slices in a laboratory dryer was examined. The slices of 5 mm, 10 mm and 15 mm thicknesses were dried using heated ambient air at temperatures from 40 to 70 ºC and air velocity of 1.5 m/s. The effects of drying air temperature and slice thickness on the drying characteristics, drying time and energy requirement of drying process was determined. The results have shown that an increase in the drying air temperature causes shorter drying times. Thinner slices also causes a shorter drying time. The effective moisture diffusivity values increased from 3.36814 × 10 -10 m 2 /s to 5.82524 × 10 -9 m 2 /s while the activation energy values for different slice thickness of ginger varied from 196.15 to 198.79 kJ/mol. The total needed energy varied from 735.3 to 868.5 kWh while the value of specific energy requirement varied from 3676.6 to 4342.4 kWh/kg respectively.

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