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

Abstract

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 0157: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 ms). 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 ms. While results showed that as few as 64 light pulses of 1 ms duration were required to reduce E. coli 0157: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 ³ 0·01). Cell populations of E. coli 0157:H7 and Listeria were reduced by as much as 6 and 7 log 10 orders at the upper exposure level of 512 ms, respectively. Survival data revealed that E. coli 0157:H7 was less resistant to the lethal effects of radiation (P ³ 0·01). These studies have shown that pulsed light emissions can significantly reduce populations of E. coli 0157:H7 and L. monocytogenes on exposed surfaces with exposure times which are 4-6 orders of magnitude lower than those required using continuous u.v. light sources.

Pulsed Light Treatments for Food Preservation. A Review

“…The efficiency of PL on inactivating bacteria, mold spores, and viruses is well documented (MacGregor et al 1997;Rowan et al 1999;Anderson et al 2000;Roberts and Hope 2003). The effects of PL on microorganisms in vitro are shown in Table 1.…”

“…Photoreactivation in flashed cells was evident after PL treatment (Gómez-López et al 2005a), the rate of this photoreactivation after a PL treatment was slower than after a continuous UV treatment (Otaki et al 2003). In fact, some authors have taken the precaution of wrapping the Petri dishes in aluminum foil to avoid photoreactivation after PL treatments (MacGregor et al 1997;Rowan et al 1999;Anderson et al 2000).…”

The role of pulsed light spectral distribution in the inactivation of Escherichia coli and Listeria innocua on fresh-cut mushrooms

“…Several studies have shown the ability of PL to inactivate Salmonella spp., Escherichia coli, E. coli O157:H7, Listeria monocytogenes and Listeria innocua in some products (Bialka & Demirci, 2008;Ozer & Demirci, 2006;Palgan et al, 2011;Sauer & Moraru, 2009;Uesugi & Moraru, 2009). The variability of results (2e8 log reductions) is most likely due to the different target microorganisms, the intensity of the treatment, and the properties of the substrates (MacGregor et al, 1998;Paskeviciute, Buchove, & Luksience, 2010;Sharma & Demirci, 2003;Woodling & Moraru, 2005).…”

Bacterial inactivation using pulsed light

“…The differences between the materials used and experimental conditions under which different studies were performed have given rise to variable results which render any comparison difficult. Data in the literature confirm the effects of light pulse treatment on agar surfaces (MACGREGOR et al, 1998;ROWAN et al, 1999;KRISHNAMURTHY et al, 2004). KRISHNAMURTHY and co-workers (2004) observed a 7.5 log reduction of Staphylococcus aureus in agar-seeded cells treated for 5 s or longer by pulsed UV light at an energy of 5.6 J cm -2 .…”