Photodynamic inactivation of foodborne and food spoilage bacteria by curcumin

•Bacterial viability was reduced after exposure to curcumin at 75 μM and LED light doses of 139 J/cm2, 278 J/cm2 and 417 J/cm2.•Aeromonas hydrophila displayed more sensibility to the treatment than other Gram negative bacteria.•Pseudomonas aeruginosa was the most resistant to photodynamic inactivation mediated by curcumin.

The present study evaluated the efficacy of photodynamic inactivation (PDI) of foodborne and spoilage bacteria using curcumin and a blue light emitting diode (LED). Curcumin at 75 μM was used to photo-irradiate Staphylococcus aureus ATCC 25923, Aeromonas hydrophila ATCC 7966, Salmonella Typhimurium ATCC 14028, Escherichia coli ATCC 25922 and Pseudomonas aeruginosa ATCC 27853 at light doses of 139 J/cm2, 278 J/cm2 and 417 J/cm2. The cytotoxicity of curcumin in VERO cells was evaluated in similar conditions to bacterial photoinactivation assay, and the percentage of cell destruction was ≅ 13 ± 0.05%, for all light doses. Curcumin-mediated PDI of S. aureus induced a significant reduction of approximately 3.50 log CFU/ml at 139 J/cm2 and 278 J/cm2. Full inactivation was observed at 417 J/cm2. Among Gram negative bacteria, P. aeruginosa was the least susceptible to PDI, which counts were not significantly reduced. A significant reduction in E. coli counts was observed at 278 J/cm2, and no viable cells were detected after light exposure at 417 J/cm2. When photo-irradiated with curcumin at 278 J/cm2 and 417 J/cm2, A. hydrophila was completely eradicated, while a significant decrease (3.33log CFU/ml) was observed in bacterial counts at 139 J/cm2. Curcumin in combination with a blue LED is a potential candidate for PDI against Gram positive and Gram negative bacteria.