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United States Department of Agriculture

Agricultural Research Service

Title: Industrial-scale radio frequency treatments for insect control in walnuts I. Heating uniformity and energy efficiency

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 I. Heating uniformity and energy efficiency. 45(2007): 240-246. Postharvest Biology and Technology. http://handle.nal.usda.gov/10113/14095.

Interpretive Summary: Restrictions on the use of MeBr fumigation have forced the multi-billion dollar U.S. nut industries to seek alternatives for control of postharvest insect pests. Because the future of alternative chemical fumigants is uncertain and public concern over residues in treated products is increasing, non-chemical control methods are of particular interest. Laboratory-scale studies have described radio frequency (RF) as a new means to rapidly heat walnuts to control postharvest insects without significant quality degradation. When transferring laboratory research results to industrial-scale applications, heating uniformity is one of the most important considerations. Improving heating uniformity of in-shell walnuts is essential to ensure insect control without quality degradation. The effect of walnut size, orientation, and location on RF heating uniformity may be reduced by a thorough mixing of the nuts between RF exposures. In studies using an industrial-scale RF system, non-uniform vertical temperature distributions were measured in the RF unit, indicating that mixing and circulated hot air were needed to obtain the required treatment uniformity. Using a uniformity index derived experimentally for the RF unit, we showed that a single mixing of the walnuts was sufficient to optimize heating uniformity. The average energy efficiency of two RF units in series was estimated to be 79.5% when heating walnuts at 1561.7 kg/h. This study provided the basis for subsequent evaluations of treatment efficacy and product quality needed to develop an industrial-scale RF process to control insect pests in walnuts.

Technical Abstract: Conducting industrial-scale confirmatory treatments is the final step in developing commercially and environmentally sound insect control technologies for in-shell walnuts using radio frequency (RF) energy as an alternative to chemical fumigation. Improving heating uniformity of in-shell walnuts in the industrial process is essential to ensure insect control without quality degradation. An industrial-scale 27 MHz, 25 kW RF system was used to determine the heating uniformity of in-shell walnuts. Non-uniform vertical temperature distributions were measured in the RF unit, indicating that mixing and circulated hot air were needed to obtain the required treatment uniformity. Using a uniformity index derived experimentally for the RF unit, we showed that a single mixing of the walnuts was required to optimize heating uniformity. The predicted standard deviation of walnut surface temperatures was verified experimentally. The average energy efficiency of two RF units in series was estimated to be 79.5% when heating walnuts at 1561.7 kg/h. This study provided the basis for subsequent evaluations of treatment efficacy and product quality needed to develop an industrial-scale RF process to control insect pests in walnuts.

Last Modified: 10/24/2014
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