| The goal of this research is to develop radio frequency (RF) treatments for pest control in dried fruits. The dielectric properties of five dried fruits were determined at RF and microwave (MW) frequencies and temperatures to determine if differential heating might be possible. Results showed that RF treatment is feasible for insect disinfection due to the higher penetration depth (22.9-103.7 cm) in dried fruits at 27 and 40 MHz when compared to that (1.3-4 cm) at MW 915 and 1800 MHz.;A computer model that solves Maxwell's electromagnetic and Fourier's heat transfer equations was developed using finite element-based commercial software, COMSOL, to investigate temperature distributions in three horizontal layers: the top, middle, and bottom layers, of raisins packed in rectangular containers (25.5 × 15.0 × 10.0 m3) during RF heating. Simulated and experimental results showed overheating at the edges and corners of the samples. Temperatures in the middle layer were higher compared to the top and bottom layers.;The simulation model was further used to investigate the effect of sample shape, electrode configuration, and a combination treatment of RF with forced air at 60 °C on the heating uniformity of raisins. An RF treatment protocol to control insect in raisins was developed based upon the appropriate electrode configuration and treatment condition with forced air at 60 °C. The heating uniformity was improved throughout the bulk samples in containers with shapes that have less sharp edges and corners. The process time required to disinfest the raisins (3 kg bulk packaged) was reduced from 361 min using forced air at 60 °C to 21.5 min using RF-forced air at 60 °C. The quality of the RF-forced air treated samples showed slight differences when compared to the control, while significant changes in moisture and color occurred for raisins treated with forced air (60 °C) alone. This research provides a better understanding of the behavior of lower moisture fruits during RF heating and new information on how product and electrode configurations affect heating uniformity. These models can be used to design RF treatment systems for insect disinfection treatment and for scaling up of pilot RF processes. |
