The thin layer drying characteristics of blanch-assisted water yam slices were investigated with respect to its un-blanched water yam slices in a convective hot air oven. The yam slices (diameter 4 cm; thickness 0.8 cm) were dried at temperatures 50, 60 and 70 °C, respectively with a constant air velocity of 0.13 m/s. The drying data obtained were fitted into six existing drying models: Page, Newton, Midilli, Henderson and Pabis, Logarithmic and Diffusion model. Non-linear regression analysis was used to determine the model parameters; the coefficient of determination (R2) and standard error of estimates (SEE) in order to determine the model best fit. The study showed that the drying process occurred in the falling rate drying period. The blanch-assisted slices had a faster drying rate than the un-blanched yam slices. Among the models, the diffusion model gave the overall best fit for the drying data obtained. The effective moisture diffusivity ranged from 3.18×10-8 to 4.47×10-8 m2/s for the blanch-assisted slices and from 4.73×10-8 to 7.33×10-8 m2/s for the un-blanched slices. The activation energies of the blanch-assisted and un-blanched yam slices were 15.5 kJ/mol and 20.1 kJ/mol, respectively. These processing conditions obtained for water yam flour would be suitable for its process design and control thereby enhancing its utilization and overall acceptability.

The study assessed the sorption isotherm characteristics of water yam flour. This was in the view to predict the stability of the water yam flour under different humid conditions. The sorption isotherm of water yam flour obtained from blanched and un-blanched water yam cubes was determined by the static gravimetric method using sulphuric acid solution at 25, 35 and 45°C in the water activity range of 0.09-0.96.The un-blanched samples had higher equilibrium moisture content values than the blanched samples at the same water activity level and same temperature for both the adsorption and desorption processes. They also exhibited hysteresis loop over considerable levels of water activity. GAB model gave the overall best description to the sorption characteristics of the water yam flour out of the five sorption models fitted to the experimental data. The isosteric heat of adsorption and desorption decreases with increasing temperature. The study would be useful in the design and selection of adequate packaging materials and establishment of preferred humidity level during storage.