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Microwave-Convective Drying Characteristics of Okra

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan www.asabe.org

Citation:  2010 Pittsburgh, Pennsylvania, June 20 - June 23, 2010  1008690.(doi:10.13031/2013.29702)
Authors:   Deepak Kumar, Suresh Prasad
Keywords:   Microwave convective drying, okra, drying rate, effective moisture diffusivity

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 70C) 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 17.594x10-10 to 89.837 x 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.

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