Developing a radio frequency dehydration technology for white tea: Heating uniformity, drying characteristics, and product quality

White tea, valued for its therapeutic properties and distinctive sensory profile, undergoes withering and dehydration. While conventional hot-air drying (HD) remains prevalent, its prolonged duration, high energy demands, and detrimental impact on final quality necessitate improved methods. This study presents radio frequency (RF) drying for the withered white tea cakes based on a 27.12 MHz, 6 kW pilot-scale free-running oscillator RF unit, systematically evaluating the influence of the electrode gap, the diameter of tea cake, and the thickness of tea cake, with the placement spacing, on thermal uniformity and heating efficiency. Subsequently, the drying characteristics, energy efficiency, and critical quality attributes of RF drying (RFD), hot-air-assisted RF drying (RFHD), and HD were compared under optimized RF parameters. These findings demonstrate that an increased electrode gap, larger tea cake diameter, and wider placement spacing reduced RF heating rates and uniformity, whereas a reduced thickness enhanced both. RFD (120 min) and RFHD (80 min) significantly accelerated dehydration relative to HD (190 min). Furthermore, RFHD consumed approximately 40% less energy than HD, and provided a better uniformity index (0.098) compared to RFD (0.170). Additionally, RFHD surpassed RFD in preserving color integrity and retaining higher concentrations of polyphenols (97.54 mg GAE/g d.b. for RFHD and 89.23 mg GAE/g d.b. for RFD) and flavonoids (12.34 mg RE/g d.b. for RFHD and 11.73 mg RE/g d.b. for RFD), attributable to its more uniform temperature distribution in the RF field. These results reveal the distinctive merits of RFHD for white tea processing and establish a foundation for the relevant industrial implementation.