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Journal of Food Engineering 108 (2012) 183–193

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Journal of Food Engineering
journal homepage: www.elsevier.com/locate/jfoodeng

Radio-frequency heating of heterogeneous food – Meat lasagna
Jian Wang a Kunchalee Luechapattanaporn ,
a b

a,b

,Yifen Wang

a,c

, Juming Tang a,

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Department of Biological Systems Engineering, Washington State University, Pullman, WA 99164-6120, USA PepsiCo Asia Pacific R&D, 17th fl Emporium Tower, 622 Sukhumvit Rd., Wattana, Bangkok 10110, Thailand c Department of Biosystems Engineering, Auburn University, AL 36849, USA

article info
Article history: Received 16 January 2011 Received in revisedform 19 April 2011 Accepted 20 May 2011 Available online 12 June 2011 Keywords: Dielectric properties Radio-frequency heating Thermal processing Heterogeneous food Computer simulation

a b s t r a c t
This research studied feasibility of using radio-frequency (RF) energy to thermally process highly heterogeneous foods in large containers as shelf-stable products. Meat lasagna was selected asthe food for the study. Dielectric properties of beef, mozzarella cheese, noodles, and sauce were determined between 1 and 1800 MHz and from 20 to 121 C.  A 6-kW 27-MHz RF system was used to sterilize packaged meat lasagna in large polymeric containers (295 253 42 mm) during which the temperature of different components were monitored. Computer simulations were also conducted to evaluate theinfluence of the dielectric properties of each food component on the electric field distribution and heating pattern during RF heating. The measurements indicated small temperature differences in beef meatballs, mozzarella cheese and sauce when they were properly distributed between layers of noodles. Simulation results suggested that in spite of large differences in electric field intensities indifferent food components, adequate heat transfer reduced differential heating. Thus, RF heating can be used to process pre-packaged heterogeneous foods and retain product quality.  2011 Elsevier Ltd. All rights reserved.

1. Introduction Conventional thermal processes for solid and semi-solid foods in large containers, such as size 10 cans (159 mm diameter, 178 mm height) for food services or 6lb capacity (295 mm length, 254 mm width and 42 mm depth) trays for US military group meal rations, often lead to severe overheating at the periphery of the foods by the time the package interior reaches the desired sterility for heat resistant food pathogens. Dielectric heating by microwave or radio-frequency (RF) energy shortens thermal processes because heat is generated by direct interactionbetween electromagnetic energy and the foods within food packages. The free-space wavelength in the RF range (e.g., 13.56, 27.12 and 40.68 MHz) is 20–360 times longer than that of commonly used microwave frequencies (e.g., 915 and 2450 MHz), allowing RF energy to penetrate foods more deeply than microwave energy. Thermal processing with RF heating is, therefore, suitable for large food trays (Wang et al., 2003c ). Indeed, our previous inoculated pack studies (Luechapattanaporn et al., 2004, 2005) demonstrated that RF energy has adequate penetrations to inactivate heat resistant bacteria spores in food prepackaged in 6-lb capacity polymeric trays. We have also demonstrated with a pilot-scale RF sterilization unit that the total time for RF processing of foods in 6-lb capacity trays wasreduced to
⇑Corresponding author. Tel.: +1 509 335 2140; fax: +1 509 335 2722.
E-mail address: jtang@wsu.edu(J. Tang). 0260-8774/$ - see front matter  2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.jfoodeng.2011.05.031

one-third the time required in conventional canning processes to achieve approximately the same level of thermal sterility for bacterial spores ( Wang et al., 2003c;...