The effect of different drying methods and conditions on the structure of carrot slices was observed under SEM. The SEM photos in the section of dried carrot slices showed distinct differences in the microstructure of carrot slices subjected to different methods (Fig. 4). In vacuum-dried samples (Fig. 4a and b), there are less open structures and pores as compared to USV dried samples (Fig. 4c and d), which indicates tissue shrinkage during vacuum drying. The less shrinkage in the USV dried samples may be accountable to the shorter drying time and some tissue expansion from internal water vapor. Furthermore, the structure is more porous in samples dried under higher temperature conditions during USV drying (Fig. 4d). SEM images of USV-dried carrot slices further confirmed the channeling effect caused by ultrasonic irradiation. Our results also agreed with the previous reports [22], [23] and [24]. The “sponge effect’’ generated by the ultrasonic waves propagating in solid materials often creates microscopic channels and facilitates the transformation of water [23], [24] and [25].