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United States Department of Agriculture

Agricultural Research Service

Title: Process protocols based on radio frequency energy to control field and storage pests in in-shell walnuts

Authors
item Wang, Shaojin - WASHINGTON UNIV.
item Tang, Juming - WASHINGTON UNIV.
item Johnson, Judy
item Mitcham, Elizabeth - U.C. DAVIS
item Hansen, James D
item Cavalieri, Ralph - U.C. DAVIS
item Bower, Jenny - U.C. DAVIS
item Biasi, Bill - U.C. DAVIS

Submitted to: Postharvest Biology and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 4, 2002
Publication Date: May 20, 2002
Citation: Wang, S., Tang, J., Johnson, J.A., Mitcham, E., Hansen, J., Cavalieri, R.P., Bower, J., Biasi, B. 2002. Process protocols based on radio frequency energy to control field and storage pests in in-shell walnuts. Postharvest Biology and Technology. 26:265-273. http://handle.nal.usda.gov/10113/14073.

Interpretive Summary: Fumigation is a common method to disinfest nut commodities of postharvest insect pests, and is an important tool to meet phytosanitary requirements for exported products. Increasing restrictions on methyl bromide use will likely increase the cost of the fumigant, as well as reduce its availability. Consequently, there is interest in developing alternative, non-chemical treatments to control insect pests in walnuts while retaining acceptable product quality. Radio frequency and microwave treatments have potential as alternative disinfestation treatments as well as for rapid product drying, because treatment energy interacts directly with products to provide rapid heating. A practical treatment protocol was developed to control insect pests in in-shell walnuts using a 27 MHz pilot scale radio frequency system. Because preliminary studies showed that navel orangeworm fifth-instar larvae were the most heat tolerant life stage and pest of postharvest walnuts, these were selected as the targeted insect for subsequent treatments. Radio frequency heating to 55°C and holding in hot air for 5 min resulted in 100% mortality of the fifth instar navel orangeworm. Walnut rancidity, sensory qualities and shell characteristics were not affected by the treatments. The process slightly reduced the moisture content of the walnut kernels, which could prove an additional benefit by providing even nut moisture content and reducing the growth of microorganisms. If this method can be economically integrated into the handling process, it should have excellent potential as a disinfestation method for in-shell walnuts.

Technical Abstract: A practical process protocol was developed to control insect pests in in-shell walnuts using a 27 MHz pilot scale radio frequency (RF) system. Fifth-instars, that had been determined to be the most heat resistant life stage for navel orangeworm (Amyelois transitella [Walker]) using a heating block system, were selected as the targeted insect in the protocol development. RF heating to 55°C and holding in hot air for at least 5 min resulted in 100% mortality of the fifth instar navel orangeworm. Rancidity, sensory qualities and shell characteristics were not affected by the treatments. The process slightly reduced the moisture content of the walnut kernels, which could prove an additional benefit by providing even nut moisture content and reducing the growth of microorganisms. If this method can be economically integrated into the handling process, it should have excellent potential as a disinfestation method for in-shell walnuts.

Last Modified: 11/22/2014
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