Industrial-scale radio frequency treatments for insect control in lentils

Abstract

Radio frequency (RF) treatments are considered to be a potential postharvest technology for disinfesting legumes of internal seed pests such as the cowpea weevil. After treatment protocols are shown to control postharvest insects without significant quality degradation, it is important to scale-up laboratory RF treatments to industrial level applications. A 27.12 MHz, 6 kW RF unit with a built-in forced hot air system was used to conduct industrial scale-up studies. A treatment protocol was designed to provide 100% cowpea weevil mortality combined RF with forced hot air to heat product to 60 °C for 10 min, followed by forced ambient air cooling for 20 min. An electrode gap (14.0 cm) was chosen based on the electric current and heating time, and conveyor belt speed was set to 7.5 m/h. Heating uniformity was evaluated by measuring post-treatment surface temperatures with a thermal image camera and interior temperatures with thermocouples. Changes in moisture content, color and germination were used to evaluate treatment effects on product quality. Finally, the RF system heating efficiency and throughput were calculated. Results showed that heating uniformity and quality of lentils in continuous RF treatment with hot air and movement were acceptable, the average heating efficiency of the RF system was 76.5% and throughput was 208.7 kg/h. The average energy efficiency and throughput of the RF system provided sufficient data to develop an industrial-scale RF process as an alternative to chemical fumigation.