ARS | Publication request: Developing Postharvest Disinfestation Treatments of Legumes Using Radio Frequency Energy.

Submitted to: Biosystems Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 7, 2009
Publication Date: January 22, 2010
Repository URL: http://hdl.handle.net/10113/40358
Citation: Wang, S., Tiwari, G., Jiao, S., Johnson, J.A., Tang, J. 2010. Developing Postharvest Disinfestation Treatments of Legumes Using Radio Frequency Energy. Biosystems Engineering. 105:341-349.

Interpretive Summary: Chickpeas, green peas and lentils are three important legume crops in the US Pacific Northwest. Infestation by insect pests can be a major problem in the processing and marketing of these legumes. Currently, industry relies on fumigation with methyl bromide for postharvest insect control, however due to environmental concerns, most phytosanitary uses of methyl bromide have been phased out. Therefore, there is a need to develop practical alternatives such as heat treatments for control of insect pests in legumes. The goal of this study was to develop practical heat treatments for postharvest disinfestation of legumes using radio frequency (RF) energy. A pilot-scale 27 MHz, 6 kW RF unit was used to study heating uniformity and the resulting quality of RF treated chickpeas, green peas, and lentils. Only 5-7 min was needed to raise the central temperature of 3 kg legume samples to 60°C using RF energy, compared to more than 275 min when using forced hot air at 60°C. RF heating uniformity in product samples was improved by adding forced hot air, and movement along a conveyor belt. The final temperatures exceeded 55.8°C in the interior of the sample container and 57.3°C on the surface for all three legumes, resulting in good uniformity for the interior and surface temperatures. RF treatments combined with forced hot air at 60°C to maintain the target treatment temperature for 10 min followed by forced air cooling provided good product quality. No significant differences in weight loss, moisture content, color or germination were observed between RF treatments and unheated controls. RF treatments should provide a practical, effective and environmentally friendly method for disinfestation of postharvest legumes, thereby allowing processors to maintain access to critical export markets.

Technical Abstract: There is an urgent need to develop technically effective and environmentally sound phytosanitary and quarantine treatments for the legume industry to replace chemical fumigation. The goal of this study was to develop practical non-chemical treatments for postharvest disinfestation of legumes using radio frequency (RF) energy. A pilot-scale 27 MHz, 6 kW RF unit was used to investigate RF heating and consequent quality attributes in treated chickpea, green pea, and lentil samples. Only 5-7 min was needed to raise the central temperature of 3 kg legume samples to 60°C using RF energy, compared to more than 275 min when using forced hot air at 60°C. RF heating uniformity in product samples was improved by adding forced hot air, and back and forth movements on the conveyor at 0.56 m/min. The final temperatures exceeded 55.8°C in the interior of the sample container and 57.3°C on the surface for all three legumes, resulting in low uniformity index values of 0.014-0.016 (ratio of standard deviation to the average temperature) for the interior temperature distributions and 0.061-0.078 for surface temperature distributions. RF treatments combined with forced hot air at 60°C to maintain the target treatment temperature for 10 min followed by forced room air cooling through a 1 cm product layer provided good product quality. No significant differences in weight loss, moisture content, color or germination were observed between RF treatments and unheated controls.