THIN-LAYER DRYING CHARACTERISTICS OF CASTOR (RICINUS COMMUNIS) SEEDS

The thin-layer drying behavior of gray small size and white big size varieties of castor seeds dried at 40, 50, 60 and 70C in a laboratory model tray dryer fitted with a temperature control system was investigated. Temperature was found to affect the drying characteristics with samples dried at higher temperature attaining equilibrium moisture content faster. From the five thin-layer drying equations fitted to the drying data, the modified Page model gave the best fit with highest correlation coefficients of 0.999, 0.990–0.999 and the least root mean square error of 0.010–0.013, 0.011–0.038, respectively, for the two varieties. The effective diffusivity coefficient of moisture transfer varied, respectively, from 8.24 × 10−9–1.81 × 10−8m2/s and 3.72 × 10−8–7.62 × 10−8m2/s, which are within the range for food materials. The activation energies are, respectively, 21.47 kJ/mol and 18.03 kJ/mol. This indicates that the diffusion process requires lower energy hence ease of drying of the castor seeds. PRACTICAL APPLICATION Whole castor seed is extremely poisonous; however, it becomes fit for human consumption when properly processed. Drying is a fundamental unit operation in the processing of this seed which influences the physicochemical and quality characteristic of the product, hence an evaluation of the drying characteristics as a function of drying conditions could help in predicting suitable drying conditions for good quality products.