Radio frequency disinfestation treatments for dried fruit: Model development and validation Bandar Alfaifi a,b , Juming Tang a,⇑ , Yang Jiao a , Shaojin Wang c , Barbara Rasco d , Shunshan Jiao a , Shyam Sablani a a Department of Biological Systems Engineering, Washington State University, Pullman, WA 99164-6120, USA b Agricultural Engineering Department, King Saud University, P.O. Box 2460, Riyadh 11451, Saudi Arabia c College of Mechanical and Electronic Engineering, Northwest A&F University, Yangling, Shaanxi 712100, China d School of Food Science, Washington State University, Pullman, WA 99164-6376, USA article info Article history: Received 14 March 2013 Received in revised form 18 June 2013 Accepted 15 July 2013 Available online 23 July 2013 Keywords: RF heating Heating uniformity Computer simulation Dielectric properties Dried fruits abstract Non-uniform heating is one of the most important challenges during the development of radio frequency (RF) heat treatments for pest control and other applications. A computer simulation model using finite element-based commercial software, COMSOL, was developed to investigate the heating uniformity of raisins packed in a rectangular plastic container (25.5  15.0  10.0 cm 3 ) and treated in a 6 kW, 27.12 MHz RF system. The developed model was then experimentally validated. Simulated and experi- mental temperature distributions in raisins after RF heating were compared in three different horizontal layers (top, middle, and bottom) within the container. Simulated and experimental average and standard deviation of the temperature values were highest in the middle layer, followed by the top and bottom layers. A sensitivity study indicated that the heating uniformity of the samples was most affected by the density of the raisins followed by the top electrode voltage, the dielectric properties, the thermal con- ductivity and the heat transfer coefficient. Corners and edges were heated more than the centers in each layer of the RF treated raisins. The model developed here can be used for future investigations to improve the heating uniformity for insect disinfection of dried fruit and other similar applications. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction Insect infestation is one of the most important sanitary or quar- antine considerations limiting domestic and international trade of dried fruits including raisins, dates, apricots, figs, and prunes. Post- harvest control of insects that attack dried fruits such as: Indian- meal moth (Plodia interpunctella), navel orangeworm (Amyelois transitella), raisin moth (Cadra figulilella), fig moth (Ephestia cautel- la), driedfruit beetle (Carpophilus hemipterus), and sawtoothed grain beetle (Oryzaephilus surinamensis) is essential if quarantine regulations required in many countries (Johnson et al., 2009) are to be met. On the other hand, total postharvest product losses from insect infestation are conservatively estimated to be between 10% and 40% worldwide through direct damage; contamination with fecal matter, webbing and insect parts (Pimentel and Raman, 2002). Insect infestation promotes increased mold growth, toxin production, and product degradation. Traditionally, chemical fumi- gation has been the most widely used treatment for insect control due to its efficacy and relatively low cost (Barreveld, 1993). However, environmental and public health concerns about the hazards of chemical fumigation have increased the demand for non-chemical pest control methods for dried fruits. The interest in non-chemical methods for insect disinfestations in agricultural commodities has grown in recent years due to in- creased food and environmental safety requirements. One alterna- tive to chemical fumigation is radio frequency (RF) treatment, which has been shown to be lethal to insects at low intensity (Wang et al., 2007b). RF dielectric heating employs electromag- netic waves of 13.56, 27.12, and 40.68 MHz for industrial applica- tions (Metaxas, 1996). However, major challenges with adopting RF heating in the food industry are non-uniform heating and run- away heating, which cause overheating in corners, edges, and cen- ter parts, especially in foods of intermediate and high water content (Fu, 2004). Temperature variations among and within pro- cessed agricultural commodities reduce the efficiency of a treat- ment and may cause severe thermal damage to its quality and adversely affect product safety. During RF processing, several inter- acting factors influence heating uniformity (Wang et al., 2005). These factors include the design of RF heating systems (e.g. the electrode shape and power output), packaging geometries, dielec- tric, thermal and physical properties of the treated materials, 0260-8774/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jfoodeng.2013.07.015 ⇑ Corresponding author. Address: 213 LJ Smith Hall, Pullman, WA 99164-6120, USA. Tel.: +1 509 335 2140; fax: +1 509 335 2722. E-mail address: jtang@wsu.edu (J. Tang). Journal of Food Engineering 120 (2014) 268–276 Contents lists available at ScienceDirect Journal of Food Engineering journal homepage: www.elsevier.com/locate/jfoodeng