Studies on microwave assisted hot air drying characteristics and rehydration of Bitter gourd (Momordica charantia L.)

Abstract

Fresh bitter gourd was procured from the local market were subjected to microwave and microwave assisted hot air drying. During microwave drying, power levels were kept as 160, 320 and 480W. Samples were dried in hot air dryer at 60•C and 1m/s air velocity. The drying time ranged between 25 to 40 minutes for all power levels. The drying time for unblanched sample was 25% less than the blanched sample. Drying rate of bitter gourd increased with increase in power from 160 W to 480 W. In hot air drying of bitter gourd drying was faster for the blanched samples. In microwave assisted hot air drying, a sudden increase in drying rate was observed when samples partially dried in hot air dryer were subjected to microwave drying. The microwave dried bitter gourd slices exhibit lower rehydration capacity than the other two drying methods because of case hardening which does not allow further absorption of moisture from the sample. Of all the experimental drying methods, the rehydration capacity of the sample dried in microwave assisted hot air drying method had the highest value. The rehydration capacity was more for blanched sample (666.67%) as compared to unblanched sample (352.27%) during microwave assisted hot air drying at 160 W.