91C-4 |
Process protocols based on radio frequency energy to control insect pests in in-shell walnuts |
S. WANG1, J. Tang1, J. A. Johnson2, E. Mitcham3, and J. Bower3. (1) Biological Systems Engineering, Washington State University, 213 LJ Smith Hall, Pullman, WA 99164-6120, (2) Horticultural Crops Research Laboratory, USDA-ARS, 9611 S. Riverbend, Parlier, CA 93648, (3) Department of Pomology, University of California, 1045 Wickson Hall, Davis, CA 95616-8683 Currently, in-shell walnuts destined for export are disinfested of codling moth, Indianmeal moth and navel orangeworm using methyl bromide fumigation. Restrictions on methyl bromide use have increased interest in developing alternative quarantine treatments. Our objective was to determine the most tolerant life stage, to develop a practical process protocol to control the targeted insects using RF energy with hot air and to study the impact of these treatment protocols on walnut quality. The heat resistance of insects was determined using a heating block system. RF energy was used as the main source of heating in the treatment protocol. To reduce temperature drop during the holding period and to improve the surface heating of in-shell walnuts, heated air was also used in combination with RF energy. Our results showed that navel orangeworms were the most heat resistant of the target pests, and that the fifth-instars were the most heat resistant life stage of this pest. Practical process protocols were developed to control the targeted insects using a 27 MHz pilot scale RF system. RF heating to 55°C with hot air holding for at least 5 min resulted in 100% mortality of the fifth instar navel orangeworms. 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.
Handout (.doc format, 77.5 kb)
Session 91C, Food Engineering: Food process engineering
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