Drying and Quality Characteristics of Whole Jujubes Subjected to Air Assisted Radio Frequency Heating

Abstract

Highlights The effect of air temperature and electrode gap (EG) on RF drying efficiency was evaluated. Drying rate (Dr), the mathematical modeling of drying curves, heating uniformity, effective moisture diffusivity coefficient (Deff), and quality parameters after drying were analyzed. Drying rate was accelerated by reducing EG or increasing air temperature under EG RF drying. The trend of heating uniformity was the same as that of Deff value. The evaluated quality parameters of treated whole jujubes showed that 40°C air assisted 17 cm EG RF drying had the best quality. Abstract. This study aims to investigate the drying and quality characteristics of whole jujubes heated by air assisted radio frequency (RF) energy. The effect of air temperature and electrode gap (EG) on RF drying efficiency was evaluated. The drying rate (Dr), the mathematical modeling of drying curves, heating uniformity, effective moisture diffusivity coefficient (Deff), and quality parameters after drying were analyzed. The results showed that under the conditions of 30°C air temperature or 17 cm EG RF drying, Dr was accelerated by reducing EG from 18 cm to 16 cm or increasing air temperature from 20°C to 40°C. The Midilli model had the best fitting to drying curves under 30°C RF treatments with 16 cm, 17 cm, and 18 cm EG, and 40°C RF heating with 17 cm EG conditions. But the Logarithmic model was better for 20°C air assisted 17 cm EG RF heating due to the largest R2 with lowest RMSE. The largest Deff value was shown at 40°C air assisted 17 cm EG RF drying, followed by 30°C air assisted 16 cm, 17 cm, and 18 cm EG RF heating, and 20°C air assisted 17 cm EG RF drying. The trend of heating uniformity was the same as that of the Deff value. The evaluated quality parameters of treated whole jujubes showed that 40°C air assisted 17 cm EG RF drying had the best quality. Therefore, 40°C air assisted 17 cm EG RF heating was chosen for drying jujubes due to its faster drying rate and better quality. Keywords: Air temperature, Drying characteristics, Jujube; Quality, Radio frequency heating.