Radio Frequency-Vacuum Drying of Kiwifruits: Kinetics, Uniformity, and Product Quality

To overcome long drying time, low energy efficiency and poor product quality associated with conventional drying, a radio frequency (RF) vacuum technology is proposed for drying kiwifruit slices using a 27.12 MHz, 3 kW RF-vacuum drying system. The results demonstrated that the process variables, electrode gap, vacuum pressure, and sample thickness, had major effects on the RF-vacuum drying. The RF-vacuum drying was associated with internal heating and rapid drying resulting in 65% reduction of hot air drying (60 °C) time. Moreover, kiwifruits dehydrated by RF-vacuum drying were associated with better color stability, higher vitamin C retention, and higher rehydration capacity (p < 0.05) as compared with hot-air-dried samples. Based on acceptable drying rate, stable temperature and avoiding arcing, a RF-vacuum drying protocol with the electrode gap of 60 mm, vacuum pressure of 0.02 MPa, and sample thickness of 8 mm was identified. Despite some differences observed in individual fruit slices, the RF-vacuum drying technique achieved better and more uniform drying patterns among the samples. Overall, the RF-vacuum drying process may provide a more effective and practical method for high-quality dehydration of kiwifruits.