Ultrasound-assisted intensification of a hybrid intermittent microwave - hot air drying process of potato: Quality aspects and energy consumption.

The objective of this study was to intensify combined intermittent microwave - low temperature (40 °C) hot air drying with ultrasound. The process variables were ultrasound time (40 kHz for 0, 10, 20 and 30 min), microwave power (360, 600 and 900 W), and microwave pulse ratio (1, 2, 3 and 4). Results showed that the highest reduction in moisture content was observed in the samples pretreated with ultrasound for 10 min and then dried at 900 W microwave with the pulse ratio of 4. As ultrasound time, microwave power and pulse ratio increased, significant increases were noticed in Deff by 4.89, 16.44 and 20.7%, respectively. Moreover, shrinkage was lower in the samples pretreated with lower ultrasound time and microwave pulse ratio. Besides, bulk density reduced when the microwave power was increased due to lower volume reduction. In addition, the highest increase in rehydration (32.23%) was observed in the samples dried using the high-power intermittent microwave. Finally, the highest significant reduction in specific energy consumption as a result of increased microwave power was 23.32%. In general, results of this study demonstrated that the ultrasound-intensified combined intermittent microwave - low temperature hot air drying may be a suitable alternative for industrial applications.