Effect of sublethal temperatures on pulsed light inactivation of bacteria

• PL inactivation independent of temperature for L. innocua, E. coli and P. fluorescens within 5 °C to 40 °C in a clear liquid
• A modest synergistic effect between PL and temperature was observed for L. innocua at 50 °C.
• The Weibull model can accurately predict inactivation kinetics.

This study investigated the effect of sublethal temperatures on the efficacy of pulsed light (PL) treatment for the inactivation of Listeria innocua, Escherichia coli ATCC 25922, and Pseudomonas fluorescens. A thin layer of clear, liquid phosphate buffer inoculated with one of the challenge organisms, at a concentration of about 108 CFU/mL, was equilibrated to a temperature ranging from 5 °C to 50 °C and then treated with PL, at doses between 1.02 and 12.29 J/cm2. All treatments were performed in triplicate. In the temperature range of 5 °C to 40 °C, the average maximum reductions for L. innocua, E. coli, P. fluorescens were 6.27 ± 0.23 log CFU, 6.66 ± 0.36 log CFU, and 6.15 ± 0.19 log CFU, respectively. Temperature did not affect PL inactivation of E. coli or P. fluorescens, but a modest synergistic effect between PL and temperature was observed for L. innocua treated above 40 °C.Industrial relevanceThis study suggests that PL inactivation of bacteria is independent of temperature in the sublethal range 5 °C to 40 °C. The practical benefit of this finding is that PL treatments can be conducted in a wide range of environmental temperatures, without any change in the outcome of the treatment.