Power density control in microwave assisted air drying to improve quality of food

•A microwave/hot air drying system with the ability of automatic power control was developed for food drying.•The power control throughout the process helped to monitor thermal runaway in the product.•Power control allowed the improvement of product quality.•The strategy of microwave/hot air drying with power control would lead to a better retention of lycopene in tomato. Currently, the new trend is the development of microwave hot air drying control in order to solve the problem of hot spots on the product. So in this study, a microwave/hot air drying system with the ability of automatic power density control was developed for tomato drying. Three power densities (3, 5 and 7W/g) at 40°C air temperature were applied and the output, reflected microwave power and the mass of the sample were registered online. Two different drying strategies were implemented. The first consisted of a microwave drying without specific power control. The second one introduced power control. A feedback control based on specific power related to the actual sample mass resulted in the best power control and the improvement of product quality compared to the dry sample without power control.