Issues in Contemporary Agriculture: Food

Microwave Pasteurization of In-Shell Eggs

Dr. Vijaya Raghavan, Department of Bioresource Engineering, McGill University

Measurement and Modeling of Dielectric Properties

The measurement of dielectric properties of the individual egg components were made and found that the egg white has a greater potential to convert microwave energy into heat than the yolk and linear regression models were developed based on the data collected to predict the dielectric properties of egg constituents at a given temperature and frequency. The egg shell and shell membrane were found to be almost transparent to the microwave radiation, thereby making microwave processing more ideal for in-shell egg pasteurization.

Modification of Microwave Thermal Processor and Preliminary Trials

Preliminary trials of heating in-shell eggs to the pasteurization temperatures in a single mode microwave cavity were conducted. Results indicated that with adequate microwave power modulation the yolk reached a higher temperature of 61ºC while simultaneously maintaining the albumen at 57 ºC which is exactly the requirement for pasteurization. Also a preliminary quality comparison of microwave and water bath heated egg white for in-shell pasteurization with the raw egg white for the heat induced changes with respect to physical properties like enthalpy of denaturation, viscosity, foam density, foam stability, turbidity and dielectric properties was performed and found that the heat induced quality deterioration in microwave heated in-shell eggs were much less than the water bath heated ones and were close to the quality of the raw egg white.

3-D Modeling and Simulation of In-Shell Egg Geometry & Microwave Cavity

A 3D computer modeling of the in-shell egg was being carried out and 3D Finite Difference Time Domain (FDTD) and 3D Finite Element (FEM) Models were developed. Simulations ran using the FEM precisely predicted the microwave heating process of in-shell eggs within the pasteurization temperature limits. The microwave cavity was fine tuned with appropriate adjustments for the proper focussing of microwaves for achieving uniform heating. This part of the study also resulted in the development of a generalised model for the finite element analysis of microwave heating of any biological commodity, provided the dielectric properties are known making it an excellent tool for further microwave research in any food and biological material.

Optimization through modeling and experimental trials

The effects of varying parameters (which affect the total heating time and uniformity) like power density, waveguide position and orientation (rotation) were investigated to find the optimum values for the same with uniformity being the factor representing effectiveness. The results obtained were optimized for maximum uniformity. Uniform heating implies no coagulated spots. The number and size (diameter) of the coagulated spots obtained were tabulated for each simulation trial and the combination of parameters for which there is no coagulation occurred with the fastest heating was considered to be the optimal set of parameters for microwave pasteurization.

Microbial validation of the microwave pasteurization process

While fine tuning and fabrication of an innovative slotted waveguide is still underway, the microbial validation of the process had just begun. The non pathogenic strain of E.coli with thermal destruction kinetics similar to that of Salmonella enteriditis will be used for this study.