Reduction of Foodborne Pathogens
Methods Evaluation for Reduction of Foodborne Pathogens in Biofilm and RTE Meat
Center for Food Safety
Listeria monocytogenes can survive as a form of biofilms for a long time in food processing facilities. It will continue to be introduced into the environment in which ready-to-eat foods are exposed for further processing and packaging. Two studies were performed to reduce potential RTE meat contamination and to control biofilm formation. Two different bacteriocins, i.e., L50B, and an L50A-like bacteriocin, designated as Dur 152A from E. durans 152 were thoroughly characterized. Then, partially purified and evaluated for inhibitory activity to L. monocytogenes in deli ham. Results demonstrated that the peptone-negative control group, L. monocytogenes grew to greater than 9.5 log10 CFU/g within 7 weeks at 8? and 21 days at 15?, whereas none of E. durans 152 bacteriocin-treated ham samples reached this level of listeria growth.
The efficacy of phenyllactic acid (PLA) to inactivate Listeria monocytogenes planktonic cells and biofilms was determined and compared with the killing effects of lactic acid (LA), and levulinic acid (LVA) with sodium dodecyl sulfate (SDS). The results indicated that phenyllactic acid reduced the population of L. monocytogenes by 7 log CFU/ml within 1 min. The biofilms assays demonstrated that L. monocytogenes biofilms could be inactivated to different degrees by these treatments. These finding revealed that new bacteriocins could be used as a food additive to increase the safety of RTE meat from the contamination of L. monocytogenes and phenyllactic acid could be used as a sanitizer for control of biofilm in food processing facility.
Listeria monocytogenes is a nonfastidious, widely occurring foodborne pathogen that is a major challenge to the food industry. Investigation indicates up to 35% of samples from retail deli environments are positive for L. monocytogenes. Recent USDA-FSIS data indicate that approximately 10% of samples collected from grocery delis nationwide are positive for L. monocytogenes. Development of effective methods for their control is needed to solve these problems for food industry.
We did two projects to solve these problems. The first project is to characterize Enterococcus durans 152 bacteriocins by genetic approach and their inhibition of Listeria monocytogenes in ham. The second project is to evaluate the effect of phenyllactic acid as a sanitizing agent for inactivation of Listeria monocytogenes in biofilms at different maturities.
From the first project, we demonstrated that at 400 AU/ml, the bacteriocins prevented growth of listeria in deli ham for at least 10 weeks at 8? and at least 30 days at 15?. For comparison, 500 ppm Nisin controlled listeria growth for up to 6 weeks at 8? and up to 18 days at 15?. These findings reveal the potential for the bacteriocins of E. durans 152 to serve as anti-listerial agents in deli meat (Du, L., F. Liu, T. Zhao, P. Zhao, and M. P. Doyle. 2017. Characterization of Enterococcus durans 152 bacteriocins and their inhibition of Listeria monocytogenes in ham. Food Microbiology 68:97-103). From the second project, we demonstrated that the killing effect of phenyllactic acid was increased as exposure time and concentrations were raised. These results revealed that the bacterial cells in these biofilms were more difficult to inactivate as biofilm maturity increased (Liu, F. L. Du, T. Zhao, P. Zhao, and M. P. Doyle. 2017. Effects of phenyllactic acid as sanitizing agents for inactivation of Listeria monocytogenes biofilms. Food Control 78:72-78).
Our results revealed that the new bacteriocins we characterized could significantly increase the food safety against the contamination of L. monocytogenes in RTE meats. Phenyllactic acid can be used as a sanitizing agent for inactivation of L. monocytogenes biofilms that often occurred in food processing facilities.