CYANIDE REDUCTION PATTERN AND DRYING KINETICS OF CASSAVA (Mannihot esculenta) CHIPS USING A FLUIDIZED BED DRYER

Abstract

This research work investigated the cyanide reduction pattern and drying kinetics of cassava chips using fluidized bed dryer with a view to predicting the most suitable drying model for the drying pattern of cassava (TMS30572 and TMS98/0581) and also the best drying temperature and air velocity for reduction of hydrogen cyanide and minimization of nutrient loss. The experiment was carried out using a 4x4x2 factorial that is four air velocities, 2.03, 2.25, 2.45, and 2.75 m/s, four air temperatures, 40, 50, 60, and 70°C, and two varieties of cassava (TMS30572 and TMS98/0581) with three replications for each treatment with total of ninety-six samples using a fluidized bed dryer. Fresh cassava tubers (TMS30572 and TMS98/0581) used for the drying experiment were harvested from a farm along Polytechnic Road, Ado Ekiti, Ekiti State. The cassava was peeled, washed, drained and chipped using the manual slicer. A 100g of the wet chips was then subjected to drying using pre heated fluidized bed drier at a specific temperature (40oC, 50 oC, 60 oC, 70 oC) and varied air velocity (2.03, 2.25, 2.45, 2.75 m/s). The change in mass was recorded at constant time interval of 20 minutes until constant weight was recorded. The dried cassava chips were packaged and labeled. They were analyzed for hydrogen cyanide content using AOAC (1990) method. The variations in the cyanide concentrations from both varieties were significant at p<0.05. The average cyanide contents for the samples from dried TMS30572 chips ranged from 7.08±0.02 to 1.63±0.06, 6.75±0.05 to 1.07±0.01, 4.05±0.05 to 1.01±0.01, 2.53±0.01 to 1.01±0.02 at temperature of 40oC, 50, 60, 70 and varied air velocity (2.03, 2.25, 2.45, 2.75 m/s) respectively. TMS98/0581dried samples ranged from 7.44±0.01 to 3.06±0.01, 3.10±0.05 to 0.68±0.00, 0.63±0.05 to 0.59±0.05 and 0.58±0.05 to 0.45±0.05 for temperatures 40, 50, 60 and 70oC respectively and air velocity (2.03, 2.25, 2.45, 2.75 m/s). The cyanide content in the two varieties reduced in TMS30572 from 18.19±0.02 to 1.01mg/kg at air velocity of 2.75 m/s. Cyanide content reduced in TMS98/0581 from 18.43±0.01 to 0.45mg/kg at the peak air velocity of 2.75 m/s. For both varieties drying temperature of 60oC and air velocity of 2.75 m/s were found suitable. The mathematical modeling of the drying process of cassava chips in a laboratory fluidized bed dryer was also investigated. In order to select a suitable drying model for prediction of the drying kinetics of dried cassava chips, twelve different mathematical drying models were fitted to the experimental data of the moisture ratio against the time using nonlinear regression analysis by SigmaPlot 10.0 and Microsoft Excel (2010) computer program. The models were compared based on their coefficients of determination (R2), reduced chi-squares (χ2), root mean square errors (RMSE), and mean bias error (MBE) between the experimental and predicted moisture ratios. The Modified Henderson and Pabis model was found to be the best mathematical model for describing the drying kinetics of cassava chips from TMS30572 and TMS98/0581 respectively since it has the highest value for R2, least values for the χ2, RMSE and MBE.