Effect of laser and environmental parameters on reducing microbial contamination of stainless steel surfaces with Nd:YAG laser irradiation.
OBJECTIVE
The effect of laser (pulse repetition frequency, pulse energy and exposure time) and environmental parameters (pH, NaCl concentration and wet or dry samples) of Nd:YAG laser decontamination of stainless steel inoculated with Escherichia coli, Staphylococcus aureus and Listeria monocytogenes was investigated.


RESULTS
Stainless steel discs were inoculated with the bacterial samples and exposed to laser energy densities to about 900 J cm(-2). These inactivation curves allowed selection of laser parameters for two-level multifactorial designed experiments, the results of which allowed comparisons to be made between effects of individual and combined parameters on the laser inactivation efficiency. Escherichia coli was inactivated most effectively as a wet film with L. monocytogenes and S. aureus showing similar response. For the multifactorial experiments all laser parameters were significant and were smallest for S. aureus as a wet film.


CONCLUSIONS
pH and NaCl concentration had little effect on the efficacy of laser inactivation but dry or wet states and all laser parameters were significant.


CONCLUSIONS
Such systems may prove to be applicable in industrial processes where stainless steel may be contaminated with acidic solutions or salt, e.g. in the food industry with laser inactivation seeming to be independent of these parameters. Parameters have been identified that allow optimization of the treatment process.
Watson
I A
IA
Department of Mechanical Engineering, Laser and Optical Systems Engineering Centre (LOSEC), University of Glasgow, Glasgow, UK. i.watson@mech.gla.ac.uk
Wang
R K
RK
Peden
I
I
Ward
G D
GD
Stewart-Tull
D E S
DE
Wardlaw
A C
AC
D000704:Analysis of Variance; D001419:Bacteria / Q000254:growth & development / Q000528:radiation effects*; D015169:Colony Count, Microbial / Q000379:methods; D003470:Culture Media; D003666:Decontamination / Q000379:methods*; D004777:Environment; D004866:Equipment Contamination / Q000517:prevention & control; D004926:Escherichia coli / Q000254:growth & development / Q000528:radiation effects; D006813:Humidity; D006863:Hydrogen-Ion Concentration; D007834:Lasers; D008089:Listeria monocytogenes / Q000254:growth & development / Q000528:radiation effects; D012965:Sodium Chloride / Q000032:analysis; D013193:Stainless Steel; D013211:Staphylococcus aureus / Q000254:growth & development / Q000528:radiation effects; D013997:Time Factors
D003470:Culture Media; D013193:Stainless Steel; D012965:Sodium Chloride