Inactivation of pathogenic and spoilage microorganisms in a test liquid using pulsed electric fields

Experiments have been carried out to investigate the effect of pulsed electric fields (PEF's) on the inactivation of microbial populations suspended in liquids using nonflowing and continuous flowing test chambers. Electric fields of similar to 30 kV/cm, and a pulse duration of 500 ns, were generated from a coaxial cable Blumlein pulse forming network (PFN) and applied to a parallel plate, circular electrode test configuration. Sample microorganisms were grown under standardized conditions and were introduced into test liquids in order to produce known population densities within the treatment cell. The organisms investigated include the mold Aspergillus niger, the yeast Saccharomyces cerevisiae, and the bacterial pathogens Bacillus cereus, Staphylococcus aureus, and Pseudomonas aeruginosa. The PEF studies were undertaken at a sample temperature range of 25 degrees C-30 degrees C, and the effect of the number of pulses on the test microbial population was studied. The results of this investigation showed that the greater the number of pulses applied, the larger the corresponding reduction in microbial cells/spores obtained. With the exception of dormant fungal spores, all of the test organisms were reduced by similar to 3 to 4 log orders after 3000 pulses. The number of B, cereus cells was reduced by similar to 7.5 log orders after 15 000 pulses, of which 10 000 pulses were applied in a flowing system followed by 5000 pulses in a static system.