Impact of Process Parameters on Listeria innocua Inactivation Kinetics by Pulsed Light Technology

Abstract

The impact of several pulsed light (PL) processing parameters on microbial inactivation was evaluated in buffered water systems using Listeria innocua as test microorganism. Reduction in L. innocua population increased directly with pulse energy, pulse fluence and the number of light pulses, and inversely with the distance between samples and a xenon lamp. Overall, the higher the amount of light received by the target microorganism by both direct and reflected light, the larger the loss of cell counts. Total fluence striking on the samples per area unit was shown to be the most relevant process factor affecting L. innocua inactivation by PL. Microbial population decreased with total fluence, obtaining more than 7 log reductions after 0.4 J cm−2. The inactivation kinetics was clearly sigmoidal, showing an initial shoulder in the inactivation curve. No significant reduction (<1 log) in L. innocua counts was induced at fluences lower than 0.04 J cm−2. From this threshold total fluence, L. innocua inactivation increased exponentially to the maximum detectable level. Since total fluence is the most relevant process factor affecting microbial inactivation by PL, this parameter must be reported to describe PL processing conditions.