The goal of this five year research program is to address key scientific and technical issues in developing microwave and RF sterilization and pasteurization processes. For microwave heating, we will continue to improve computer simulation models, gain better understanding of kinetics in quality changes, and develop chemical markers for pasteurization applications. We also will study interactions between food packages with food materials and provide scientific data on memo-migrations from microwavable food packages. <P> For RF heating, we will focus on developing pasteurization technology for pathogen control in bulk dry materials. Specifically, we will accomplish the following tasks: <P> 1. Study interactions between electromagnetic energy at MW and RF frequencies and selected food materials by measuring dielectric properties of foods as a function of food composition in sterilization and pasteurization. These data will be used in computer simulation models for studying heating patterns.<P> 2. Enhance the capacity and reliability of computer based predictive tools for microwave and RF heating processes, using the Finite Difference Time-Domain (FDTD) and Finite Element Time Domain (FETD) Methods; develop user friendly interfaces that allow general applications in food companies and research communities.<P> 3. Develop effective chemical marker systems applicable to short-time microwave pasteurization applications at temperatures between 65 and 100oC. <P> 4. Develop pilot scale microwave pasteurization system that allows flexibility to validate different designs of applicators for optimal heating uniformity in single meal size packaged foods with efficient coupling of microwave power. This effort will be supported with computer simulation models. <P> 5. Study the influence of novel MW and RF processes on retention of nutrients and micro-nutrients of foods, and their impact on food attributes that influence consumer acceptance.<P> 6. Study influence of microwave heating on performance of food packages.
Non-Technical Summary: <BR>Microwave (MW) and radio frequency (RF) energy used in novel thermal processes for prepackaged foods offers several major advantages over traditional methods in commercial food production, including short processing times, reduced waste, higher product quality, and cleaner work environment. The goal of this project is to expand our knowledge and strengthen the scientific base for better design and control MW or RF processes/systems to achieve the best results for in-package food pasteurization and sterilization applications in support of industrial adaptation of the new technologies. In RF heating, we will focus future activities on developing novel RF pasteurization to address regulatory and industrial concerns over food safety caused by contaminated dry products (e.g., baby formula, peanut butters, almonds, and hazelnuts, to name a few). <P> Approach: <BR> PROCEDURE 1. Dielectric properties of foods and packaging materials will be measured over moisture and salt content ranges relevant to commercial food production applications. For RF pasteurization, we will include low moisture and intermediate moisture contents (3-20 %) that are particularly important in thermal pasteurization of dry foods. An open-end coaxial probe with HP 8752C Vector Network Analyzer (Hewllet-Packard, Santa Rosa, CA 95403) will be used at microwave frequencies between 300 MHz to 3,000 MHz and with HP 4291B RF Impedance/Material Analyzer at RF frequencies between 1 and 300 MHz. Temperature will be controlled by a water bath. 2. We will use QuickWave-3D (QWED, Inc., Warsaw Poland) in studies of microwave heating processes. We will evaluate how process parameters, applicators and food composition affect microwave field distribution in packaged foods to guide the development of microwave based thermal processes. On RF heating, we develop Finite Elelements simulation models to design RF applicators for uniform heating. The computer models will be validated with Infrared temperature imaging systems as per Tiwari et al. (2011a and b). 3. Current chemical marker M-2 in whey protein gels is formed through Mailard reaction between reducing sugars and amines. But for pasteurization processes in which foods are typically heated to between 65-100oC, whey protein gels are not suited. We will explore different gel systems, including gellan and egg white which set at lower temperatures, for this application. A critical element of this study is to develop and identify a chemical reaction in those gel systems that lead to color changes at pasteurization temperatures where the intensity of the color change correlates with the level of pasteurization of targeted food pathogens. 4. We will develop a 915 MHz small pilot-scale unit with flexibility for a wide range of pilot testing for pasteurization applications. The system will be equipped with directional couplers to measure delivery of MW power to the single-mode cavity and a three-stub tuner to achieve maximum power delivery. The system will be used for: 1) studying MW cavity configurations/food package geometry that will provide the desired heating uniformity; 2) collecting preliminary data to select approximate ranges of process parameters for in-package pasteurization processes; and 3) conducting preliminary tests for pasteurization and sterilization, before full scale test runs. 5. MW sterilization and pasteurization processes for pre-packaged single meals typically take about 3 min heating to a target temperature and about 3 min holding before cooling. Quality kinetics studies will be conducted to assess appearance, texture, and color changes, using protocols we have developed for heat sterilized and pasteurized foods (Kong et al. 2007 & 2008). 6. The structural, thermal and gas barrier properties of the packaging materials will be evaluated. Packaging will be assessed by means of differential scanning calorimetry, dynamic mechanical analysis, X-ray diffraction, transmission electron microscopy, tensile tests, and oxygen and water vapor transmission analyses (Dhawan et al., 2010).