Microwave pasteurization and sterilization of food products

Microwaves can directly interact with foods in packages to generate heat. It is, therefore, possible to develop high-temperature-short-time pasteurization and sterilization processes to improve product quality. Several technical hurdles, however, need to be overcome before microwave processes can be used in commercial applications. These hurdles include system development to provide predictable, uniform heating and effective methods to evaluate and validate microwave-based processes. In this study, we investigated various methods to improve the uniformity in microwave heating and evaluated the quality of food products pasteurized or sterilized using microwave energy.; Asparagus spears are sensitive to thermal treatments. Lengthy pasteurization at elevated temperatures may cause severe thermal degradation. Prior to the pasteurization studies of asparagus (Chapter 3), kinetic models were first developed in chapter 2 to describe the textural changes of green asparagus during heating in the temperature range applicable for pasteurization (70°C and 98°C). Thermal softening of asparagus followed a first order kinetic reaction. The kinetics data obtained from Chapter 2 were then used for designing the high-temperature-short-time pasteurization processes for picked asparagus (Chapter 3). Pasteurization of pickled asparagus using 915 MHz microwaves with shielding technique resulted in a uniform heat distribution. As a result of the rapid heating, microwave pasteurization markedly reduced thermal degradation of asparagus.; An essential step in designing an effective thermal process is to determine the efficacy of the least heated locations in food packages. In conventional processes, this location is well defined and single point temperature measurement is adequate. For microwave sterilization, limited point temperature measurements may not be sufficient. The intrinsic Chemical Marker method developed at the US Army Natick Soldier Center can be used as a non-invasive technique to map heating uniformity within foods systems at sterilization temperatures. The kinetics of 4-hydroxy-5-methy-3(2H) (M-2) formation in a model food system (20% whey protein gel) was determined for studying cumulative time-temperature effects in high-temperature-short-time processes (Chapter 4). M-2 formation followed a first order kinetics and the rate constant temperature dependence was described using an Arrhenius model. This study provides essential kinetic information to enable us to use chemical marker (M-2) in determining time-temperature effect in a model food system during microwave sterilization.; Chapter 5 focuses on the investigation of the heating uniformity of model food in pouches and trays in pilot scale 915 MHz and 2450 MHz microwave systems with and without water immersion techniques. Relatively uniform marker yields were achieved in the whey protein gels heated in 915 MHz and 2450 MHz microwave systems with the water immersion technique. This study provides sound evidence that immersing the food packages in water during microwave heating can reduce edge and corner overheating.; Following the uniformity studies of microwaves using model food systems, a study was conducted to evaluate the heating characteristics and quality attributes in macaroni and cheese and in scrambled eggs using 915 MHz microwaves in comparison with conventional heating retort methods (Chapter 6). Chemical marker analysis revealed that 915 MHz microwave heating provided relatively uniform heating the food products. Color measurements suggested that microwave heating reduced color degradation through relatively brief heat exposure, compared to conventional methods.