Effect of ultrasonic power on moisture migration and microstructure of contact ultrasound enhanced far-infrared radiation drying on taro slices

To clarify the moisture migration and microstructure of taro in contact ultrasound enhanced far-infrared radiation drying (CUFRD), low-field nuclear magnetic resonance (NMR), scanning electron microscopy (SEM), paraffin sectioning and microscopic observation techniques were applied to explore the changes of the drying curves, water status, microstructure, porosity, microscopic images and distribution curves of cell microstructure parameters of taro under different ultrasound powers of 0, 40, and 80 W. The results showed that applying contact ultrasound (CU) during drying was beneficial to accelerating the dehydration process and improving the porosity of taro slice. With the augment of CU power, the drying times of taro reduced by 16.67% to 25.00%, and the effective water diffusion coefficient was improved by 14.72% to 31.38%. In addition, the application of CU resulted in an increase firstly and then decrease in the cross-sectional area and perimeter distribution curves of taro cells and a widening of the peak shape of the distribution curve of taro cell roundness. In conclusion, CU application could cause faster internal moisture migration, and higher CU power had more obvious effect on microstructure and cell morphological parameters of taro during CUFRD.