Sanitization of food-grade materials: Combined effect of an enzymatic product and two chemical sanitizers on Listeria monocytogenes biofilms.

In industrial practice, different food-grade materials could be subjected to contamination by microorganisms that are responsible for the spoilage of foods. The chemical sanitizers used to inactivate microbes on the food-grade surfaces have proved effective on vegetative cells, but may not be successful on biofilms, thus encouraging food companies to search alternative ways to eradicate these microbes. For this reason, in this work, two commercially available chemicals based on quaternary ammonium salts (QAC) and alcohols were tested alone or in combination with an enzymatic product against seven-day-old biofilms of three Listeria monocytogenes strains on stainless steel (SS) or poly-tetra-fluoro-ethylene (PTFE). When the sanitizers were applied without any pre-treatment, with the QAC, no survivors were detected after 10 minutes at a concentration of 0.75-1.0% on SS; on PTFE, it was necessary to increase the concentration to 1.0% to obtain a total inactivation of the sessile cells for all the tested strains. The use of the alcoholic product enabled us to obtain total inactivation of the sessile cells at a concentration of 50% for contact times greater than 2.5-5 minutes on SS; on the contrary, on PTFE, it was necessary to use the undiluted sanitizer for 10 minutes for all the tested strains. When the enzymatic solution was used as a pre-treatment, the achieved logarithmic reductions were significantly higher than the ones obtained when using the sanitizing products alone: In half of the cases, this combination enabled us to obtain a total inactivation on the biofilm-forming cells.