Photodynamic inactivation using water dispersible curcumin as a photosensitizer to inactivate Salmonella on poultry carcasses and Listeria monocytogenes on stainless steel food contact surfaces

Alternatives to the use of chemical antimicrobials to treat meat and poultry carcasses during processing and food processing environments are of interest to consumers globally. The influence of bacterial cell concentration, membrane permeabilizing agents, and effect on macromolecules of the photosensitizer curcumin (PSC) on Salmonella inactivation in a medium model and on chicken skin and the inactivation of Listeria monocytogenes biofilms on stainless steel were determined. The addition of 30 mg/mL CaCl₂ or higher significantly reduced the level of Salmonella compared to PSC treatment alone in a liquid media system. Combining CaCl₂ with PSC had no effect in enhancing the inactivation of Salmonella on chicken skin. Salmonella cell density had no effect on PSC treatment alone, but PSC in combination with CaCl₂ was more effective when the Salmonella population was 5 to 7 log CFU/mL compared to >7 log CFU/mL. The increased photoinactivation activity associated with the addition of CaCl₂ was due to an increase in membrane permeability and cellular uptake of PSC. PSC-mediated photoinactivation resulted in bacterial DNA disruption. Exposure of biofilm on stainless steel to PSC achieved >3.0 log CFU/cm² reduction in L. monocytogenes. This study highlights the importance of evaluating photodynamic inactivation systems in vitro, on food, and food contact surfaces, and the potential use of water dispersible curcumin to control foodborne pathogens on product and in the food processing environment.