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United States Department of Agriculture

Agricultural Research Service

Title: Industrial-scale radio frequency treatments for insect control in walnuts II. Insect mortality and product quality

Authors
item Wang, Shaojin - WASHINGTON STATE UNIV
item Monzon, Maria - UC DAVIS
item Johnson, Judy
item Mitcham, Elizabeth - UC DAVIS
item Tang, Juming - WASHINGTON STATE UNIV

Submitted to: Postharvest Biology and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 14, 2006
Publication Date: August 1, 2007
Citation: Wang, S., Monzon, M., Johnson, J.A., Mitcham, E.J., Tang, J. 2007. Industrial-scale radio frequency treatments for insect control in walnuts II. Insect mortality and product quality. Postharvest Biology and Technology. 45(2007):247-253. http://handle.nal.usda.gov/10113/14096.

Interpretive Summary: Heating with radio frequency (RF) energy has been proposed as a potential alternative to chemical fumigation for postharvest control of insects infesting agricultural products such as in-shell walnuts. Earlier work studied heating uniformity of walnuts in a 25 kW industrial-scale RF system in an attempt to scale-up treatment protocols developed from laboratory tests. To further evaluate the 25 kW RF system, it is necessary to determine its efficacy in disinfesting walnuts of insect pests and to evaluate the effect of the treatments on walnut quality. The RF treatment caused 100% mortality of fifth-instar navel orangeworm larvae, the most heat tolerant target pest, in both unwashed and air dried walnuts, and was effective over a relatively wide range of walnut moisture contents. Walnut quality was not affected by the RF treatments; kernel color, peroxide values and fatty acid values of treated walnuts were similar to untreated controls after 20 days at 35°C, simulating 2 years of storage under commercial conditions at 4°C. The RF treatment slightly reduced the moisture content of the walnuts, especially the shells. The RF treatment developed in this study should also control codling moth, Indianmeal moth and red flour beetle in in-shell walnuts. This treatment will provide an effective and environmentally friendly phytosanitary treatment technology for the walnut industry.

Technical Abstract: This paper reports on the 2nd part of a scaling-up study investigating the technical feasibility of using radio frequency (RF) energy in commercial postharvest insect control in in-shell walnuts as an alternative to chemical fumigation. A large scale treatment for conveyorized walnuts was designed based on a 25 kW 27 MHz RF system to achieve an average walnut surface temperature of 60°C, and minimum temperature of 52°C, for 5 min. The treatment caused 100% mortality of fifth-instar navel orangeworm larvae, the most heat tolerant target pest, in both unwashed and air dried walnuts, and was effective over a relatively wide range of walnut moisture contents (3-7.5%). Walnut quality was not affected by the RF treatments; kernel color, peroxide values and fatty acid values of treated walnuts were similar to untreated controls after 20 days at 35°C simulating 2 years of storage under commercial conditions at 4°C. The RF treatment slightly reduced the moisture content of the walnuts, especially the shells. The RF treatment developed in this study should also control codling moth, Indianmeal moth and red flour beetle in in-shell walnuts. This treatment will provide an effective and environmentally friendly phytosanitary treatment technology for the walnut industry.

Last Modified: 7/24/2014
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