Novel Ultrasonic Pretreatment for Improving Drying Performance and Physicochemical Properties of Slices During Radio Frequency Vacuum Drying.

To enhance the physicochemical quality, drying efficiency, and nutrient retention of dried products, this study investigated the effects of ultrasonic pretreatment on the radio frequency vacuum (RFV) drying characteristics, microstructure, and retention of natural active substances in slices. The ultrasonic time, power, and frequency were considered as experimental factors. The results showed that, compared with conventional RFV drying, ultrasonic pretreatment reduced the drying time of slices by 20-60 min. The Weibull model accurately described the moisture ratio changes under different pretreatment conditions (R > 0.9984, χ < 2.381 × 10). The optimal retention of polysaccharides, total phenols, total flavonoids, and antioxidants was achieved under pretreatment conditions of 30 min of ultrasonic time, 180 W of ultrasonic power, and 40 kHz of ultrasonic frequency. Furthermore, ultrasonic pretreatment preserved the internal cellular structure of slices, maintaining intact tissue cells and well-defined microchannels. However, a slight reduction in sample color was observed following ultrasound application. In conclusion, ultrasonic pretreatment significantly improved the RFV drying process for slices by enhancing drying efficiency, preserving active ingredients, and optimizing the physicochemical quality of the dried product. This study provides novel insights and methods for optimizing the drying process of , offering a foundation for further research and industrial applications.