EFFECT OF OSMOTIC DEHYDRATION ON THE DRYING KINETICS OF YELLOW CASSAVA ROOT (MANIHOT ESCULENTA CRANTZ)

Abstract

The effect of osmotic dehydration on the drying kinetics of yellow cassava (Manihot esculenta Crantz) was evaluated. Cassava chips of average diameter and thickness of 29.59 mm and 5.64 mm, respectively were immersed in varying concentration of NaCl (10, 20, 30 % w/v) at different temperature (30, 60, 70^oC) and different process time (30, 60, 90 min). The pretreated chips were then dried in an oven dryer at temperature of 105^oC. The optimization of the processing parameters (concentration, temperature and time) was carried out for maximum water loss and weight reduction and minimum solid gain using response surface methodology. The optimized results were 51.40 ^oC for temperature, 16.70% for concentration and 90 minutes for time to give the values of water loss, solid gain and weight reduction as 11.88 (g/100g fresh sample), 2.72 (g/100g fresh sample) and 9.16 (g/100g fresh sample), respectively. The thin layer drying kinetics of both the osmodehydrated and untreated (control) yellow cassava root also were investigated by using an oven dryer operated at 105^oC. The results showed that the drying time for the osmodehydrated sample was shorter than that of the untreated sample. The experimental drying data were fitted to five well known drying models: the Page, Wang, and Singh, Two-term exponential, Newton and Logarithmic models. Among the five models considered, the Logarithmic model was found to best describe the drying kinetics of both the treated and untreated yellow cassava chips. This work shows that pretreating yellow cassava with osmotic dehydration can enhance the drying rate of the product.