Comparison of pulsed light inactivation kinetics and modeling of Escherichia coli (ATCC-29055), Clostridium sporogenes (ATCC-7955) and Geobacillus stearothermophilus (ATCC-10149)

Pulsed light (PL) inactivation kinetics of Escherichia coli K-12, Clostridium sporogenes and Geobacillus stearothermophilus were evaluated under different treatment conditions. The PL system was factory set to operate at three pulses per second with a pulse width of 360 μs exposing samples placed on one of the 9 trays on a rack. Two PL parameters were evaluated in the study: number of pulses (a time factor) and the tray position (a spatial distance factor) both influencing the amount of light energy absorbed. As expected, the level of microbial inactivation increased with an increase in the number of pulses (from 1 to 15) and decreased with an increase in the Spatial distance (Tray # 1 to 9) away from the light source. Both the number of pulses and spatial distance as well as their interactions were found to have a significant effect (P < 0.05) on the extent of microbial inactivation. Vegetative cells of E. coli were most sensitive to PL treatment with a maximum 5 logarithmic reductions on Tray 1 after a 12-pulse treatment (4 s). G. stearothermophilus was more resistant to PL than C. sporogenes. Overall, the PL treatments (12–15 pulses) achieved a minimum four logarithmic reductions in the populations of all three microorganisms on the top tray at doses still below 12 J/cm(2), the FDA-approved limit.