Microwave Pasteurization of Shell Eggs---A Comprehensive Study.

摘要

Due to their rich nutritive value, eggs are potential hosts and carriers of pathogenic microbes like Salmonella enteritidis. Heat pasteurization is the best solution for controlling these pathogens, but affects the egg's vital functional properties due to protein denaturation. Therefore, microwave heating was considered for in-shell egg pasteurization.;Using the simulation results, process optimization was carried out to determine the most effective procedure and design for the process. Laboratory-scale experimental trials were conducted to test the validity and effectiveness of the optimized parameters. Operations under the optimal parameters set forth were found to be very efficient in terms of heating time and uniformity.;Based on the optimal parameters obtained by simulations, a slotted waveguide applicator for heating shell eggs was designed and built. The applicator consisted of a standard waveguide with an array of S--Parabolic slots. The issue of non-uniformity in microwave heating was overcome by optimizing the power density used for the process and by rotating the egg during the heating process. A power density of 1.5 W g-1 and an angular velocity of p6 rad s-1 were found to be optimal. The applicator enhanced both penetration and focus, as well as providing the necessary temperature gradient from the egg yolk to the shell for pasteurization.;The pasteurization process was validated by inoculating eggs with a microbial contaminant and pasteurizing them in the designed applicator. Heat-induced changes in the egg white's physical properties brought about by in-shell pasteurization by microwave or water bath heating of the egg white were assessed in comparison with the initial state of untreated raw egg white. Microwave-heated in-shell egg white showed minimal changes in all these properties.;Based on a few laboratory trials, finite difference time domain (FDTD) and finite element models (FEM) were developed to simulate the electric field and power distribution in the egg components (egg white and yolk), taking into consideration the complex shape, dielectric properties and heterogeneous composition of the in-shell egg.;A protocol for real-time inline pasteurization quality assessment of shell eggs by hyperspectral imaging (400-1700 nm) was developed by identifying 10 informative wavelengths and doing an unsupervised k-means classification of treated eggs.