Effects of ultrasound-assisted pretreatment combined with air impingement drying on drying kinetics, microstructure, crystallinity, color, total phenolic content (TPC), and antioxidant capacity of Chaenomeles sinensis slices were investigated in the current study. Experimental results showed that ultrasonic pretreatment significantly enhanced heat and mass transfer, reducing total drying time by 12.50% to 43.75% compared to untreated samples. Optical microscopy and scanning electron microscopy revealed that ultrasound disrupted cell walls, loosened tissue structure, and increased porosity, creating microchannels favorable for moisture diffusion. X-ray diffraction and color analysis indicated that moderate ultrasonic treatments improved crystallinity and reduced color degradation. Furthermore, increasing the ultrasonic time and power could greatly increase the TPC and FRAP values in fresh samples. The highest TPC, 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity, and ferric-ion reducing antioxidant power (FRAP) values in dried products were achieved with ultrasonic pretreatment at 160 W for 40 min, i.e., 8.71 mg/g, 6.14, and 23.18 mmol Trolox/g, respectively. These findings suggest that appropriate ultrasonic pretreatment facilitates the release and retention of bioactive compounds by altering the microstructure and crystallinity, as well as shortening drying duration. In summary, ultrasound-assisted air impingement drying is an effective approach to processing C . sinensis slices with the improvement of drying efficiency and physicochemical properties of products.
Wang et al. (Sun,) studied this question.