Combined radio frequency heating and pulsed vacuum technology to enhance drying characteristics and heat-mass transfer in peanut pod drying

This study aims to develop an innovative radio frequency pulsed vacuum drying (RFPVD) technology to improve the drying efficiency of peanut pods. Compared to hot air drying (HAD), RFPVD significantly enhanced the heating rate of peanut pods from 0.31 to 1.98 °C/min, while also rapidly compensating for heat loss due to pulsating pressure and moisture evaporation throughout the drying process. The Midilli model exhibited the highest goodness of fit in modeling the RFPVD process of peanut pods. The larger values of n and b in Midilli model indicated that the RFPVD generated a substantial driving force for the moisture migration of peanut pods. These phenomena depend on the isotropic temperature and humidity gradients synergistically created by RF volumetric heating and pulsed vacuum, as visualized in the heat-mass transfer simulation results. Compared with HAD, the RFPVD significantly boosted the drying efficiency due to larger porosity (48.28 %–55.74 %) in shells and more pore structures in kernels. Due to the excellent shortening of drying time and oxygen contact time by RFPVD, peanut proteins and fatty acids were retained in higher quantities. Although the increased drying temperature and longer atmospheric pressure holding time resulted in an increasing acid value and produced lesser fluctuations in the peroxide value, both met the edible oil standard. This study explored the unique RFPVD characteristics and heat mass transfer behavior of peanut pods, which presented a novel technique for drying in-shell materials.