| The principal objective of this investigation was to assess the merit of microwave heating as an alternative to traditional thermal processing techniques for microbial inactivation. A side by side comparison between microwave and conventional heating was carried out on an isothermal basis. The role of the solutes in the suspending medium on lethality to microorganism was monitored. Ionizing solutes were found to enhance microbial inactivation through improved conductivity and ionic polarization. Non-ionizing solutes that contribute to the stabilization of the water structure contribute to distortion polarization which enhances the system lossiness. It was also found that a certain level of starch in water (up to 18.5%) greatly enhances the water's dielectric loss factor. Lipids present in the heating medium offered protection to microorganisms in the conventional heating mode, and added lethality in microwave heating. Regarding the medium's pH, only extreme values on either side of neutrality caused higher lethality to bacteria during microwave heating.;Physically, microwave heating resulted in the rupture of the cell wall and subsequently high intracellular components leakage. Results also indicate that only microwave heating caused destruction of the 23S RNA, while the 16S RNA was equally destroyed by other heating modes.;The effect of microwave sublethal heating on the membrane lipids of S. aureus was equal to that of conventional heating on the extent of acylglycerols hydrolysis. However, microwave heating resulted in a decrease in the amount of unsaturated and the anteiso fatty acids. Also, the level of trans fatty acids increased.;In general, microwave heating has a greater bio-negative effect on microorganisms, however due to the dependency of dielectric heating on the dielectric properties of the suspending medium and characteristics of the microorganism being irradiated, varying degrees of inactivations may result for each system.;Investigating the kinetics of thermal inactivation of Bacillus subtilis and Bacillus stearothermophilus spores during microwave heating indicated that it follows first order kinetics and that the process was slightly more temperature dependent than conventional thermal inactivation. Another study employed transmission electron microscopy, sucrose gradient centrifugation, and gas liquid chromatography to study the effect of microwave sublethal injury on the morphology, RNAs, and membrane lipids of Staphylococcus aureus respectively. |
