Postharvest treatments with radio frequency for 10 and 20 kg batches of black beans (Phaseolus vulgaris L.)

Radio frequency (RF) heating has been considered an alternative to conventional postharvest disinfestation methods in stored agricultural products. RF treatments at pilot scale (12 kW, 27.12 MHz) were applied in black beans (batches of 10 and 20 kg), until reach the target temperature for weevil mortality (50 °C). Temperature was held by 1 min, and then beans were cooled by forced air. During the protocol, the temperatures were followed by thermal images. For the 10 kg batch, the average heating time was 2.72 min, while for the 20 kg batch, only 1.29 min were required to reach the target temperature of 50 °C. This reduction in heating time is due to dielectric heating provides rapid and volumetric heating. Average cooling time was 14.75 and 26.75 min for batches of 10 and 20 kg respectively. The heating uniformity index values (λ) were close to zero (0.025 for 10 kg batch and 0.023 for 20 kg), indicating even heating. Water absorption capacity, density and viability of beans were not affected by the RF treatments (P > 0.05). Due to volumetric heating, better results were obtained for 20 kg batch, demonstrating the feasibility of RF technology for disinfestation purposes in relatively large batches of black beans.