Light inactivation of food-related pathogenic bacteria using a pulsed power source

The effects of high intensity light emissions, produced by a novel pulsed power energization technique (PPET), on the survival of bacterial populations of verocytotoxigenic Escherichia coli (serotype O157:H7) and Listeria monocytogenes (serotype 4b) were investigated. Using this PPET approach, many megawatts (MW) of peak electrical power were dissipated in the light source in an extremely short energization time (about 1 mu s). The light source was subjected to electric field levels greater than could be achieved under conventional continuous operation, which led to a greater production of the shorter bacteriocidal wavelengths of light. In the exposure experiments, pre-determined bacterial populations were spread onto the surface of Trypone Soya Yeast Extract Agar and were then treated to a series of light pulses (spectral range of 200-530 nm) with an exposure time ranging from 1 to 512 mu s. While results showed that as few as 64 light pulses of 1 mu s duration were required to reduce E. coli O157:H7 populations by 99.9% and Listeria populations by 99%, the greater the number of light pulses the larger the reduction in cell numbers (P < 0.01). Cell populations off. coli O157:H7 and Listeria were reduced by as much as 6 and 7 log(10) orders at the upper exposure level of 512 mu s, respectively. Survival data revealed that E. coli O157:H7 was less resistant to the lethal effects of radiation (P < 0.01). These studies have shown that pulsed light emissions can significantly reduce populations of E. coli O157:H7 and L. manocytogenes on exposed surfaces with exposure times which are 4-6 orders of magnitude lower than those required using continuous u.v. light sources.