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ARS Home » Pacific West Area » Parlier, California » San Joaquin Valley Agricultural Sciences Center » Commodity Protection and Quality Research » Research » Publications at this Location » Publication #250279
Title: Radio frequency treatments for insect disinfestation of dried legumes

Author
item Johnson, Judy
item WANG, SHAOJIN - Washington State University
item TANG, JUMING - Washington State University

Submitted to: Stored Products Protection International Working Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 2/15/2010
Publication Date: 2/15/2010
Citation: Johnson, J.A., Wang, S., Tang, J. 2010. Radio frequency treatments for insect disinfestation of dried legumes. Stored Products Protection International Working Conference Proceedings, June 27 - July 2, 2010, Estoril, Portugal. p. 688-694.

Interpretive Summary: Chickpeas, green peas and lentils are three important rotational legumes in the western United States. Infestation by postharvest insect pests can be a major problem in the processing and marketing of dried legumes. Two of the most important postharvest insects in stored legumes is the cowpea weevil and the Indianmeal moth. Legumes infested with cowpea weevils and other internal feeders are not often easily detected by external inspection, causing regulatory agencies and importers in many countries to establish phytosanitary protocols, often including postharvest disinfestation treatments. Historically, the legume industry has relied on chemical fumigation (methyl bromide or phosphine) for postharvest insect control. However, regulatory actions have curtailed the use of methyl bromide and there are concerns over the development of insect resistance to phosphine, prompting dried pulse processors to search for alternative disinfestation methods. Heat treatment methods using hot air have been considered, but conventional hot air heating methods require extended treatment times and may cause deleterious effects to product quality. Radio frequency energy offers the possibility of rapidly increasing temperatures within bulk materials by directly interacting with the product to generate heat volumetrically. To determine the potential of RF treatments to control insect pests in dried pulse products, the heat tolerance of the cowpea weevil was evaluated and compared to the tolerance of previously studied insects, and the dielectric properties of both the insect and the products were compared. The most heat tolerant stage of the weevil was found to be the pupal stage, with adults being the most susceptible. Cowpea weevil pupae were fairly heat tolerant; to obtain rapid mortality (exposure < 10min) temperatures of 56- 58°C were needed. Dielectric loss factors for both adult and larval cowpea weevil was higher than those for legumes, suggesting that cowpea weevils would heat at a faster rate than the product. Previous studies showed that suitable heating uniformity during RF treatments was obtained through the addition of hot air (60°C) and conveyor belt movement. These studies showed that chickpeas, green peas and lentils were able to tolerate RF treatments of 60°C for 10 minutes without adverse effects on quality, suggesting that practical large scale RF treatments to disinfest pulses may be possible.

Technical Abstract: Dried pulses (chickpeas, green peas or lentils) are valuable export commodities in the US Pacific Northwest. A major problem in the marketing of these products is infestation by insect pests. Typically, chemical fumigants are used to disinfest product, but regulatory issues, insect resistance, environmental concerns and the increase of the organic market have forced the industry to explore non-chemical alternatives. One possible alternative is the use of radio frequency (RF) energy to rapidly heat product to insecticidal levels. To determine the potential of RF treatments to control insect pests in dried pulse products, the heat tolerance of the cowpea weevil (Callosobruchus maculatus F.) was evaluated and compared to the tolerance of previously studied insects, and the dielectric properties of both the insect and the products were compared. The most heat tolerant stage of the weevil was found to be the pupal stage, with adults being the most susceptible. Cowpea weevil pupae were fairly heat tolerant; to obtain rapid mortality (exposure < 10min) temperatures of 56- 58°C were needed. At frequencies commonly used by industry for RF heating, dielectric loss factors for both adult and larval cowpea weevil was higher than those for legumes, suggesting that cowpea weevils would heat at a faster rate than the product. Previous studies showed that suitable heating uniformity during RF treatments was obtained through the addition of hot air (60°C) and conveyor belt movement. These studies showed that chickpeas, green peas and lentils were able to tolerate RF treatments of 60°C for 10 minutes without adverse effects on quality. The results suggest that practical large scale RF treatments to disinfest pulses may be possible.