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Static application of chemicals best for cleaning biofilms.

Preventing contamination of ready-to-eat meat products infected by L. monocytogenes continues to present a challenge to the industry. The pathogen is able to enter a processing plant along with raw product, equipment or personnel, and then it can grow on wet surfaces within a biofilm.

This biofilm contains product residues and microbial polymers that protect the embedded pathogen from being disinfected. Biofilms that form in meat processing facilities are particularly difficult to control because they usually contain fats and proteins that impede the effectiveness of any cleaners and sanitizers that you may use.

Using cleaning and sanitizing agents is difficult because we must not produce aerosols that in themselves could spread the pathogens throughout the facility. One solution is to apply these agents under static conditions without using water sprays or hand scrubbing. The agents could be applied as foams or viscous liquids and then rinsed off the surface of equipment.

Scientists at the University of Georgia evaluated the efficacy of cleaning and sanitizing agents applied to biofilms under static conditions. They evaluated alkaline and neutral pH cleaning compounds, sodium hypochlorite and a variety of other agents. They tested the chemicals against biofilms that contained chicken protein, chicken fat and L. monocytogenes on a stainless steel surface.

Cleaning agents were evaluated for their ability to remove poultry soil and biofilm material; and sanitizing agents for their ability to inactivate Listeria before and after cleaning agents were applied in the presence and absence of chicken protein and fat. Researchers prepared biofilms by growing L. monocytogenes on stainless steel and coating them with chicken serum albumin and rendered chicken fat. An alkaline cleaning agent removed 99% of fat and 93% of protein within a 30-minute exposure.

A neutral pH cleaning agent was just as effective at removing fat, but it removed only 77% of protein. The alkaline agent also effectively removed L. monocytogenes biofilm coated with protein, decreasing cell numbers on the surface after a 10-minute exposure.

Acidified sodium chlorite and a peracetic acid-octanoic acid mixture were the most effective sanitizers at killing L. monocytogenes in biofilm coated with fat and protein. Both achieved more than a 5-log reduction in numbers within 1 minute. Using an alkaline cleaner for 10 minutes followed by acidifed sodium chlorite for 30 minutes reduced populations of the bacteria to nearly undetectable levels.

Further information. Michael Doyle, Center for Food Safety, University of Georgia, Griffin Campus, Griffin, GA 30223; phone: 770-228-7284; fax: 770-229-3216; email:
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Publication:Microbial Update International
Date:Feb 1, 2003
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