Effect of ozone and ultraviolet light on Listeria monocytogenes populations in fresh and spent chill brines

Abstract

The efficacy of ozone and ultraviolet light (UV) treatment as hurdles against Listeria monocytogenes suspended in fresh (9% NaCl, 91.86% transmittance) and spent brines (20.5% NaCl, 0.01% transmittance) was evaluated. Brines were inoculated with a cocktail of L. monocytogenes-strains N1-227, N3-031, and R2-499. Ozonation was performed by sparging gaseous ozone into brine. This was followed by UV irradiation (253.7 nm) of the brine in sterile quartz cuvettes. Enumeration was performed by spread plating on modified Oxford medium and Trypticase Soy agar supplemented with yeast extract. In fresh brines containing L. monocytogenes, 10 min of ozonation lead to a 7.44 ± 0.13 log CFU/ml mean reduction and 10 min of UV radiation caused a 1.95 ± 0.41 log CFU/ml mean reduction. Sequential exposure of 10 min of ozonation and UV resulted in >9 log CFU/ml reduction in L. monocytogenes populations in fresh brine. Sixty minutes of ozonation of spent brines resulted in a 4.85 ± 0.61 log CFU/ml mean reduction of L. monocytogenes populations. Ten minutes of UV exposure in spent brines resulted in 0.49 ± 0.14 log CFU/ml mean reduction in L. monocytogenes. A sequential treatment of 60 min ozonation and 10 min UV resulted in an excess of 5 log CFU/ml reduction in L. monocytogenes cells in spent brine. Ozonation did not cause a significant increase in the transmittance of the spent brine to aid UV penetration but resulted in color change. Sequential treatments of Ozonation and UV maybe effective in reducing L. monocytogenes in chill brines.