A predictive model for heat inactivation of Listeria monocytogenes biofilm on stainless steel

Heat treatment of potential biofilm-forming sites is sometimes used for control of Listeria monocytogenes in food processing plants. However, little information is available on the heat treatment required to kill L. monocytogenes present in biofilms. The purpose of this study was to develop a predictive model for the heat inactivation of L. monocytogenes in monoculture biofilms (strains Scott A and 3990) and in biofilms with competing bacteria (Pseudomonas sp. and Pantoea agglomerans) formed on stainless steel in the presence of food-derived soil. Biofilms were produced on stainless steel coupons with diluted tryptic soy broth incubated for 48 h at 25degreesC. Duplicate biofilm samples were heat treated for 1, 3, 5, and 15 min at 70, 72, 75, 77, and 80degreesC and tested for survivors using enrichment culture. The experiment was repeated six times. A predictive model was developed using logistic regression analysis of the fraction negative data. Plots showing the probability of L. monocytogenes inactivation in biofilms after heat treatment were generated from the predictive equation. The predictive model revealed that hot water sanitation of stainless steel can be effective for inactivating L. monocytogenes in a biofilm on stainless steel if time and temperature are controlled. For example, to obtain a 75% probability of total inactivation of L. monocytogenes 3990 biofilm, a heat treatment of 80degreesC for 11.7 min is required. The model provides processors with a risk management tool that provides predicted probabilities of L. monocytogenes inactivation and allows a choice of three heat resistance assumptions. The predictive model was validated using a five-strain cocktail of L. monocytogenes in the presence of food soil.