4. Conclusions
Dehydration and rehydration kinetics of instant rice were influenced by drying method, microwave power and air temperature. Generalised empirical models were proposed to describe the dehydration and rehydration kinetics. Both the dehydration and rehydration rate constant increased linearly with air temperature and microwave power, and the models built predicted the dehydration and rehydration processes reasonably well. Application of microwave energy during hot air drying of instant rice was beneficial in terms of reducing the processing times required. Samples subjected to combined convective–microwave drying could be dried in approximately 25% of the time required by air-dried or microwave dried samples, and rehydrated approximately 3-folds faster than air-dried samples. Increasing microwave power accelerated the dehydration kinetics, but had an adverse effect on the rehydrated sample’s colour. Total colour change of the rehydrated samples generally increased with increasing levels of microwave power and air temperature. Combination of microwave and convective drying at microwave power of 300 W, and air temperature of 80◦C, resulted in a rehydratedproduct with optimal quality within the range of experimental conditions studied.