Microwave-convective drying characteristics of okra

Okra (Abelmoschus esculentus), also known as ladyfinger, is an important vegetable of subtropical Asia. Because of its high moisture content, okra is susceptible to rapid deterioration. The present study was conducted to investigate the potential of microwaves (MW) combined with hot air for drying of okra. Okra was dried from initial moisture content of about 89% (wet basis) to a safe level of about 0.1 g water/ g dry matter under different combinations of air velocity (1, 2 m/s), hot air temperature (40, 50, 60 and 70°C) and microwave power levels (0.5, 1, 1.5, 2 and 2.5 W/g). Drying time in microwave-convective drying decreased by many folds as compare to that of hot-air drying. Drying time was found decreasing with increase in either air temperature or microwave power level. However, effect of air temperature was more significant at lower microwave power levels. High air velocities prolonged the drying process due to its cooling effect on surface of the product. Most of the drying took place in falling rate period. The values of average effective moisture diffusivity ranged from 17.594×10^-10 to 89.837 × 10^-10 m²/s for microwave-convective drying. Empirical Page model gave the excellent fit for the drying data under all drying conditions with R² (correlation coefficient) values in the range of 0.988-0.999.