Inactivation of food-borne enteropathogenic bacteria and spoilage fungi using pulsed-light

The lethality of high-intensity pulsed-light emissions from low and high ul traviolet (UV) light sources on predetermined microbial populations has bee n investigated. Prior to treatment, the bacterial enteropathogens Bacillus cereus, Escherichia coli, and Salmonella enteritidis and the food-spoilage fungi Aspergillus niger and Fusarium culmorum were seeded separately onto t he surface of either tryptone soya yeast extract or malt extract agar plate s. Prescribed microbial population densities were applied to the test media and these samples were exposed to one of two light sources. These were low -pressure, Xenon filled, flash lamps that produced either high or low UV in tensities. They were operated in pulsed mode, being driven by a stacked Blu mlein cable generator. Microbial samples were treated by exposure to differ ent numbers of light pulses. The treated bacterial populations were reduced by similar to 8 log orders after 1000 light-pulses of the higher UV intens ity light and the fungal counts had a corresponding reduction of 4.5 log or ders. The fungus, Aspergillus niger, was shown to be significantly more res istant in spore form to the intense UV light compared with Fusarium culmoru m. This resistance has been attributed to the high level of UV absorbance a ssociated with the dark pigment present in A. niger. The pulsed light sourc e of lower UV intensity was shown to be significantly less effective in red ucing microbial populations.