Abstract

The present study was based on the investigations to determine whether the bactericidal effect of microwave radiations on bacteria was either thermal or due to microwaves. It was also investigated which bacterial sp is more sensitive to microwave. Five bacterial species, Proteus vulgaris PP25D, Staphylococcus aureus bgh010, Bacillu subtilis ase98, Escherchia coli TRE04 andCorynebacterium spN33 were exposed to microwave radiation. These cultures were selected as test organisms due to their importance in food industry as human pathogens. Bacterial suspensions were exposed to microwave radiations (2450 MHz and 800W) for 60, 120 and 180 s to study the effect of heat generated by microwaves. The second experiment was designed to study the effect of microwaves only by maintaining temperature below 40°C. The degree of inactivation at uncontrolled and controlled temperature was compared quantitavely. The viable counts of all cell suspensions were found to reduce greatly with an increase in microwave heating time and temperature. B. subtilis ase98 showed highest reduction at uncontrolled temperature. No significant reduction of cell density was observed in either cell suspension. The effect of microwave radiations was also studied in terms of morphological changes. No detectable change was observed in cell shape and morphology of colonies except S. aureus bgh010. Results indicated that the effect of microwave radiations on bacteria was purely thermal and no detectable change occurred in non-thermal treatment. B. subtilis ase98 were the most sensitive species for microwave radiations. B. subtilis ase98can be used as an indicator bacterium to assess microwaves for sterilization.

Key words: Microwave radiation, thermal and non thermal effect, sensitive bacterial sp..