Strains representing four common species of bacilli (bacteria) were used to monitor the survival of bacteria after microwave treatment at different power levels. Various conditions were designed to mimic different viscosities and water activity values (associated with food). The effects of materials used in the containers and of different incubation times were also investigated.
The findings showed that B. licheniformis spores had the highest microwave tolerance at a power level of 100% for different incubation times. B. coagulans spores showed the lowest microwave tolerance in salt solutions, and B. licheniformis spores were the most resistant in the tested salt solutions at different incubation times. An analysis of the effect of the viscosity revealed that the bacteria had the lowest microwave resistance in a medium containing <0.8% starch in solution. The microwave resistance levels of the bacteria were lower in glass containers than in polypropylene containers and aluminum foil-enclosed pouches. Of the four species, B. licheniformis had the highest microwave tolerance under all conditions.