Mechanism of microwave sterilization in the dry state

With an automated computerized temperature control and a specialized temperature measurement system, dry spores of Bacillus subtilis subsp. niger were treated with heat simultaneously in a convection dry-heat oven and a microwave oven. The temperature of the microwave oven was monitored such that the temperature profiles of the spore samples in both heat sources were nearly identical. Under these experimental conditions, we unequivocally demonstrated that the mechanism of sporicidal action of the microwaves was caused solely by thermal effects. Nonthermal effects were not significant in a dry microwave sterilization process. Both heating systems showed that a dwelling time of more than 45 min was required to sterilize 10(5) inoculated spores in dry glass vials at 137 degrees C. The D values of both heating systems were 88, 14, and 7 min at 117, 130, and 137 degrees C, respectively. The Z value was estimated to be 18 degrees C.

[1]  Om P. Gandhi,et al.  Effect of Millimeter-Wave Irradiation on Growth of Saccharomyces cerevisiae , 1986, IEEE Transactions on Biomedical Engineering.

[2]  L. Quesnel,et al.  Thermal activation and dry-heat inactivation of spores of Bacillus subtilis MD2 and Bacillus subtilis var. niger. , 1980, The Journal of applied bacteriology.

[3]  J. C. Lin,et al.  Health aspects of radio and microwave radiation. , 1979, Journal of environmental pathology and toxicology.

[4]  G R Vela,et al.  Mechanism of lethal action of 2,450-MHz radiation on microorganisms , 1979, Applied and environmental microbiology.

[5]  Chia-lun J. Hu,et al.  Model for Some Nonthermal Effects of Radio and Microwave Fields on Biological Membranes , 1977 .

[6]  J. Wayland,et al.  On the interdependence of thermal and electromagnetic effects in the response of Bacillus subtilis spores to microwave exposure. , 1977, Radiation research.

[7]  F. Cope.  Superconductivity--a possible mechanism for non-thermal biological effects of microwaves. , 1976, The Journal of microwave power.

[8]  G. Molin,et al.  Dry-heat inactivation of Bacillus subtilis var. niger spores with special reference to spore density. , 1976, Canadian journal of microbiology.

[9]  J. T. Peeler,et al.  Influence of spore moisture content on the dry-heat resistance of Bacillus subtilis var. niger. , 1968, Applied microbiology.

[10]  S. J. WEBB,et al.  Inhibition of Bacterial Cell Growth by 136 gc Microwaves , 1968, Nature.

[11]  K. Fox,et al.  Effect of temperature and gas velocity on dry-heat destruction rate of bacterial spores. , 1968, Applied microbiology.

[12]  S A Goldblith,et al.  Effect of Microwaves on Escherichia coli and Bacillus subtilis. , 1967, Applied microbiology.

[13]  S. Lohmann,et al.  Microwave sterilization of vials. , 1986, Journal of parenteral science and technology : a publication of the Parenteral Drug Association.

[14]  O. Makinson,et al.  Microwave sterilization. , 1986, Journal of the American Dental Association.

[15]  E. Taylor,et al.  Microwave sterilization of hydrophilic contact lenses. , 1986, American journal of ophthalmology.

[16]  D. Fung,et al.  Destruction of Escherichia coli and Salmonella typhimurium in Microwave-cooked Soups , 1975 .

[17]  S. F. Cleary,et al.  Biological effects of microwave and radiofrequency radiation , 1970 .

[18]  S. S. Stuchly,et al.  Dielectric Properties of Some Granular Solids Containing Water , 1970 .

[19]  L. Beuchat,et al.  Procedure for evaluating the effects of 2,450-megahertz microwaves upon Streptococcus faecalis and Saccharomyces cerevisiae. , 1969, Applied microbiology.

[20]  Carl M. Olsen,et al.  Some Biological Effects of Microwave Energy , 1966 .