Synergistic effect of a combination of ultraviolet–C irradiation and sodium hypochlorite to reduce Listeria monocytogenes biofilms on stainless steel and eggshell surfaces

• Synergism was observed after UV/NaOCl against L. monocytogenes biofilm on stainless.
• Synergism was observed after UV/NaOCl against L. monocytogenes biofilm on eggshell.
• The color of eggshell did not change after UV/NaOCl.

The present study demonstrates the synergistic effect of treatment with a combination of ultraviolet (UV)C (300, 600, 1200, and 1800 mWs/cm2) irradiation and sodium hypochlorite (NaOCl) (50, 100, 150, and 200 ppm) on Listeria monocytogenes ATCC 19113 biofilms formed on stainless steel and eggshell surfaces. The synergistic effect was not dependent on the dose of UV–C irradiation or the concentration of NaOCl. Synergistic reductions of biofilms after UV–C/NaOCl treatment on stainless steel and eggshells were 0.95–3.68 log CFU/cm2 and –0.22 to 1.02 log CFU/cm2, respectively. The largest synergistic reductions of biofilms were 3.68 log CFU/cm2 using 1800 mWs/cm2 UV–C and 200 ppm NaOCl on stainless steel, and 1.02 CFU/cm2 using 600 mWs/cm2 UV–C and 50 ppm NaOCl on eggshells. The Hunter colors of L*, a*, and b* were not significantly (P > 0.05) changed on eggshell surfaces treated with all single and combined treatments. The results in this study indicate that the combination treatment of 1800 mWs/cm2 UV–C/200 ppm NaOCl could be feasible for use on stainless steel surfaces in industrial kitchens, facilities, and restaurants. In addition, the combination of 600 mWs/cm2 UV–C/500 ppm NaOCl could possibly be used in egg production, processing, and distribution processes to enhance food safety without causing changes to the eggshell surface color.