Developing a novel radio frequency dehydration process based on heating uniformity, drying characteristics, and product quality of white tea

Abstract

White tea is a beverage with high medicinal value and mellow flavor, produced through two sequential steps of withering and drying. Although hot air drying (HD) is currently the most common dehydration method for white tea, it is both time-consuming and energy-intensive, and with some adverse effects on the product quality. Therefore, this study compressed the withered white tea into cakes and employed the radio frequency (RF) technology for drying, while evaluating effects of electrode gap, sample diameter, sample thickness and placement spacing on RF heating characteristics. Then, based on the optimal processing parameters, the differences in drying characteristics and qualities of tea samples treated by RF drying (RFD), hot air-assisted RF drying (RFHD), and HD were compared. Results indicated that the RF heating rate and uniformity index decreased with the increasing electrode gap, sample diameter, and placement spacing, but raised with reducing sample thickness. Compared to HD, RFD and RFHD exhibited the higher drying rate, and the lower energy consumption. Furthermore, due to the uniform temperature distributions of samples, RFHD provided better color parameters, as well as higher levels of polyphenol, flavonoid, and antioxidant activity in the products compared to RFD. In summary, these findings demonstrated the unique advantages of RF technology in drying white tea and might provide the theoretical basis for further industrial applications.