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United States Department of Agriculture

Agricultural Research Service

Research Project: BIOLOGICAL, BEHAVIORAL, AND PHYSICAL CONTROL AS ALTERNATIVES FOR STORED PRODUCT AND QUARANTINE PESTS OF FRESH/DRIED FRUITS AND NUTS

Location: Commodity Protection and Quality

Title: Industrial-scale radio frequency treatments for insect control in lentils

Authors
item Jiao, S -
item Wang, S -
item Johnson, Judy
item Tang, J -

Submitted to: Microwave International Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: April 3, 2011
Publication Date: June 8, 2011
Citation: Jiao, S., Wang, S., Johnson, J.A., Tang, J. 2011. Industrial-scale radio frequency treatments for insect control in lentils. Proceedings of 2011 IMPI 45th Annual Microwave Power Symposium, June 8-10, 2011, New Orleans, Lousianna. 49-54.

Interpretive Summary: Radio frequency heat treatments are being considered as a potential method to disinfest postharvest legumes. Once treatment protocols are determined, the method must be scaled up for industrial applications. A pilot-scale 27 MHz, 6 kW radio frequency unit combined with hot air was used to determine heating uniformity, validate complete mortality of the most heat resistant life stage (pupae) of cowpea weevils, and evaluate the product quality using seed color, moisture content, and germination. The radio frequency treatment protocol selected was 60°C for 10 min followed by forced ambient air cooling for 15 min. The optimal electrode gap was chosen based on the electric current and heating time. Heating uniformity was determined through the heating uniformity index, using temperature measurements of the sample surface by a thermal imaging camera and within the sample by thermocouples. Heating efficiency (%) was calculated as the ratio of the total energy absorbed by treated samples to the power input. The throughout (kg/h) of the treatment was estimated based on the conveyor belt speed (m/s) and the mass of samples per length of the belt (kg/m) for the given RF systems. The results showed that the heating uniformity in RF treated samples was acceptable after heating the samples to 60°C and holding them for 10 min in hot air. Complete insect mortality in RF treated lentils was achieved without damaging the product quality. 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.

Technical Abstract: Radio frequency (RF) treatments are considered as a potential postharvest technology for disinfesting legumes. After treatment protocols are validated to control postharvest insects without significant quality degradation, it is important to scale-up laboratory RF treatments to industrial applications. A pilot-scale 27 MHz, 6 kW RF unit with build-in hot air system was used to determine the heating uniformity based on hot air surface heating and conveyor belt movement, validate the insect mortality using the most heat resistant life stage (pupae) of cowpea weevils, and evaluate the product quality using seed color, moisture content, and germination. Since RF heating to 60°C with 10 min holding can achieve 100% insect mortality in lentils, this RF treatment protocol was applied with forced ambient air cooling for 15 min. The optimal electrode gap was chosen based on the electric current and heating time. Heating uniformity was determined through the temperature measurement on the sample surface by thermal imaging camera and inside the container by thermocouples using the heating uniformity index. The heating efficiency (%) was calculated as the ratio of the total energy absorbed by the unit samples to the power input. The throughput (kg/h) of the treatment was estimated based on the conveyor belt speed (m/s) and the mass of samples per length of the belt (kg/m) for the given RF systems. The results showed that the heating uniformity in RF treated samples was acceptable after heating the samples to 60°C and holding them for 10 min in hot air. The complete insect mortality in RF treated lentils was achieved without damaging the product quality. 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.

Last Modified: 9/10/2014
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