Effects of power ultrasound enhancement on infrared drying of carrot slices: Moisture migration and quality characterizations

To investigate the intensive effect of contacting ultrasound applied in infrared (IR) drying, a self-designed ultrasound-assisted IR (US-IR) dryer was developed, the water diffusion kinetics of carrot slices during hybrid US-IR drying was studied and the quality properties of dried products were evaluated. Results showed that the drying rates and rehydration ratios were significantly enhanced when the ultrasound was applied. Compared to pure IR dying, the drying durations shortened by 21%, 17%, and 11% for US-IR drying at 900, 1200, and 1500 W, respectively. The intensive effect of ultrasound increased the water activity when the moisture content of carrot slices decreased from 4.23 to 0.11 g water/g dry solids. The Deff values of US-IR dried samples were in the range of 8.09–26.98 × 10−10 m2/s, which were higher than the IR dried samples (6.34–22.92 × 10−10 m2/s). The micrographs showed the applied ultrasound created more porous structures to allow water migration from the inside of carrot tissue to the outside. Besides, ultrasound could be helpful to mitigate the formed dense layer on the surface of carrot slices during drying at high IR power.