The influence of pulse duration of monopolar and bipolar profile pulsed electric fields on the inactivation of obesumbacterium proteus-a spoilage microorganism

In recent years a number of new applications have emerged where pulsed power is being used in the treatment of waste and effluent, foodstuffs, and beverages. One of these emerging applications is pulsed electric field (PEF) inactivation of microorganisms in liquid media. Inactivation is achieved by the generation of electric field of the order of 30 kV/cm across liquids that are contaminated with microorganisms. Contaminants could be pathogenic microorganisms such as E. coli, Salmonella and Listeria monocytogenes, or spoilage microorganisms such as Zygosaccharomyces bailii, Lactobacillus brevis and Obesumbacterium proteus. The application of PEF induces a relatively large transmembrane potential that can lead to electroporation and consequently cell death. There are a number of ways in which PEF can be applied, including oscillatory, double exponential, and square wave pulse. Of these, the square wave pulse is considered to be the most efficient form of PEF delivery. It has been reported that the bipolar square wave pulse, involving polarity reversal half way through the pulse, provides superior inactivation when compared to monopolar pulse. However, results from the authors have shown that this is not always the case and that monopolar PEF is at least as effective for bacterial inactivation under the conditions investigated J. R. Beveridge et al. (2003). Further results will be presented on the effect of changing the pulse duration of the monopolar and bipolar pulse, using total pulse durations of 1,2,3 and 4 μs. These results, obtained from an improved system, will demonstrate how the relative effectiveness for inactivation is a function of pulse duration: showing the effectiveness converging as pulse length increases. These comparative experiments are conducted with complete control of the fluid temperature, which is maintained below 30°C.