Modeling Dehydration and Rehydration of Instant Rice Subjected to Combined Microwave-Hot-Air Drying

Instant rice with twin-screw extruder was subjected to convective hot-air,microwave and combined microwave-hot-air dehydration.The combination of three microwave power(210,300,560 W) and three air temperature(70,80,90 ℃) were investigated to find the drying kinetics,rehydration kinetics and colour change.Combined microwave and hot-air drying could decreased the drying time required when compared to drying with either hot-air or microwave energy alone.Predictive models were developed to describe dehydration and rehydration kinetics.Dehydration rate,rehydration rate and total colour change of rehydrated product generally increased with microwave level and air temperature.The combination of MW=300 W and T=80 ℃ was the optimal dry-process in terms of drying time,rehydration time and colour.