Remove L. monocytogenes biofilms using ultrasound and ozone.

The removal of biofilms is an important aspect of any sanitation program. Biofilms may harbor pathogens and act as a source of post-processing contamination. One pathogen that is ubiquitous throughout the industry is L. monocytogenes.

Due to their resistance to sanitizers and mechanical brushing, biofilms may best be removed by combining different techniques. The combination of power ultrasound and ozone has shown promise for eliminating biofilms of L. monocytogenes. The objective of scientists at the University of Illinois was to determine the ability of power ultrasound and ozonation, used individually and in tandem, to remove L. monocytogenes biofilms from stainless steel chips. The researchers indicate that a combination of both may be an effective treatment for removing biofilm from stainless steel food contact surfaces.

In tests, the scientists inoculated stainless steel chips with L. monocytogenes. Tryptic soy broth was applied to the chips after they were rinsed with a potassium phosphate buffer (PPB, pH 7.0). Power ultrasound at 20 kHz, 100% amplitude and 120 W was applied for 30 sec or 60 sec to a biofilm chip while it was submerged in 250 ml of sterile PPB. Ozone also was cycled through the 250 ml of PPB containing the biofilm chip for 30 sec or 60 sec at concentrations of 0.25 ppm, 0.5 ppm or 1.0 ppm. Power ultrasound and ozonation were also used in tandem for testing their combined effect.

Both treatments separately resulted in a significant reduction in recoverable microbial cells. Power ultrasound was the most effective treatment, yielding a 3.8 [log.sub.10] CFU per ml reduction after 60 sec. For the ozone combined with the ultrasound treatment, reductions were significantly higher than with either treatment independently. There were no recoverable cells after 60 sec of a combined treatment when an ozone concentration of 0.5 ppm was used. This treatment yielded a reduction of 7.31 [log.sub.10] CFU per ml. The research in this area is continuing. Further information. Scott Martin, Department of Food Science and Human Nutrition, University of Illinois, Urbana-Champaign, 1207 W. Gregory Dr., 486 Animal Sciences Laboratory, MC-630, Urbana, IL 61801; phone: [phone]; fax: [phone]; email: [e-mail].