Study type: Medical/biological study (experimental study)

Effect of microwave radiation on Bacillus subtilis spores med./bio.

Published in: J Appl Microbiol 2004; 97 (6): 1220-1227

Aim of study (acc. to author)

To compare the killing efficacy and the effects exerted by conventional heating and microwaves on structural and molecular components of Bacillus subtilis spores.

Background/further details

The spore damage was investigated by electron microscopy and by measuring the amount of dipicolinic acid released by treated spores.



Exposure Parameters
Exposure 1: 2.45 GHz
Modulation type: CW
Exposure duration: 2, 4, 6, 8, 10, 14 and 20 min

Exposure 1

Main characteristics
Frequency 2.45 GHz
  • guided field
Exposure duration 2, 4, 6, 8, 10, 14 and 20 min
Additional info Reference article: Metaxas, A.C. and Meredith, R.J. (1993) Multimode oven applicators. In Industrial Microwave Heating ed. Peregrinus, P. pp. 130-150. London, UK: Institute of Electrical & Electronics Engineer.
Modulation type CW
Exposure setup
Exposure source
Additional info A rectangular waveguide (7.2 x 3.4 cm) was connected to another identical adapter through a brass waveguide straight section. Two empty borosilicate glass spheres (4 mm outer diameter) were introduced into the test tubes and held to the bottom by a coiled, thin walled teflon tube (0.9 mm diameter x 50 mm). For comparison purpose, test tubes filled with water were placed in a commercial multimode oven (34.5 x 34 x 23 cm internal capacity) with a nominal working power of 750 W at 2.45 GHz. The samples immersed into the boiling water were heated for the same time intervals as the samples in the waveguide.
Measurand Value Type Method Mass Remarks
power 80 W - unspecified - input power to the waveguide
electric field strength 36 V/cm - unspecified - ± 5 V/cm

Exposed system:

Methods Endpoint/measurement parameters/methodology

Investigated system:
Time of investigation:
  • after exposure

Main outcome of study (acc. to author)

Microwaves are as effective as conductive heating in killing the spores, but the microwave electric field induces changes in the structural and/or molecular components of spores that differ from those attributable only to heat.

Study character:

Study funded by