| Pulsed Light technology utilizes high powered pulses of broad spectrum light to reduce microorganisms on food and food contact surfaces. While previous research has shown Pulsed Light to be effective at reducing various microorganisms on a variety of substrates, a better understanding of inactivation kinetics, pairing Pulsed Light with other antimicrobial treatments, and the cellular effect of Pulsed Light treatment will provide better insight into potential opportunities for future use of this technology. Inactivation of Listeria innocua in liquid suspensions and on the surface of stainless steel showed pronounced tailing. The utilization of the Weibull model accurately predicted inactivation in clear liquids but overestimated Pulsed Light's effectiveness on stainless steel surfaces where complex surface properties as well as inoculum size were of significant influence. The combination of Pulsed Light with the antimicrobial nisin was able to reach reductions of 4 to 5 log CFU/sausage of Listeria on the surface of sausages, extending storage from 8 day for individual treatments to 28 to 48 days suggesting that Pulsed Light in combination with additional antimicrobials can effectively reduce surface contamination of ready-to-eat foods. To evaluate the potential for repeated Pulsed Light exposure to lead to changes in growth and resistance behavior of survivors, L. monocytogenes, L. innocua , and E. coli were exposed to both low (1.1 J/cm 2) and high (10.1 J/cm2) levels of Pulsed Light and survivors were recovered and subsequently treated for 10 cycles of exposure and recovery. Isolates of all three organisms did not show changes in growth kinetics or resistance after multiple exposures when compared to untreated cells at either low or high fluence levels. Reduction levels of 3--4 and 5--6 log CFU/ml were obtained after exposure to 1.1 and 10.1 J/cm 2, respectively, for the untreated control and the repeatedly treated and recovered isolates. Whole genome microarray analysis showed increased transcription levels for stress related proteins, motility, and transcriptional regulators following both Pulsed Light and UV light. Removing the UV spectrum of Pulsed Light lead to no differences between treated and untreated samples and showed a downregulation in motility and cell membrane associated genes as well as no increases in stress response genes following exposure, suggesting that the mechanism of inactivation is related to the UV portion of Pulsed Light and the visible and NIR spectrum do not play a role in cell inactivation. |
