Effect of ultrasound pre-treatment on microwave drying of okra

The experiment was conducted to study drying kinetics of ultrasound assisted, microwave drying of okra and its effect on colour change, texture and rehydration properties of okra. The samples were dried in a continuous microwave dryer at 540 W power level and at a belt speed of 5 mm s-1. It was observed that ultrasound as pre-treatment led to significant reduction in drying time of okra. Page model was found to be the best to explain the drying behaviour of okra with high R2, lowest RMSE and X2. Ultrasound retained the colour properties of okra. The lowest total colour difference was recorded in ultrasound treated60 minutes sample (18.11) followed by the control dried sample (17.58). The textural properties of the treatments of ultrasound treated – 60 minutes and ultrasound treated-vacuum packed -30 minutes samples had the values of hardness, gumminess and chewiness closer to fresh okra values. The highest coefficient of rehydration was recorded in ultrasound treated60 minutes samples. The vacuum pack did not show any effect on the rehydration ratio. The rehydration ratio increased with increase in time from 30 to 60 minutes. Key word: Ultrasound pre-treatment, microwave drying, okra, vacuum packing