Ultrasound pre-treatment enhances the carrot drying and rehydration.

The present work aimed to describe the mechanisms involved in the enhancement of the drying and rehydration process of carrot slices caused by the pre-treatment using the ultrasound technology. For that, carrot slices of 4mm of thickness were pre-treated for 30 and 60min using an ultrasonic bath (41W/L; 25kHz). The convective drying process was performed at 40 and 60°C with 2.0m/s of air velocity, while the rehydration process was performed at 25°C. The Henderson & Pabis model was used to describe the drying kinetics and the Peleg model to describe the rehydration process of the carrots slices. As a result, the drying and rehydration kinetics were described, at the different conditions of process, correlating the results with the main effects that the ultrasound cause as a pre-treatment (cell bloating and micro-channels) and the air-drying temperature. Depending on the length of the pre-treatment, the effects caused by the ultrasound in the following processes were different. In addition, it was corroborated that when the drying temperature is increased, less evidenced is the ultrasound effect. The ultrasound, when is applied for long times, enhanced the drying and further rehydration rate at low temperatures, due to the tissue damage. Moreover, vacuum-packed samples were pre-treated with ultrasound in order to exclude the water gain and to evaluate only the micro-channels formation effect. It was concluded that the ultrasound pre-treatment enhances the drying and rehydration processes; however, future optimization studies are recommended.