Abstract

Pulsed high voltage discharges have been recently developed as sterilization method to replace the traditional thermal processes for the sterilization of liquid foods such as milk. The gas-liquid hybrid discharge (HD) reactor consists ofplexiglas cylinder containing the liquid of high voltage electrode above liquid’s surface and grounded electrode submerged in the liquid. The HD could produce both arc discharge in gas and liquid phases. The high energy plasma arc produces a pressure shock wave, which kills the targeted micro organisms by causing physical damage to their cellular matrix either by the sudden recoil of the cell or by the micro-eddies created on the internal cell structure. Bacterio assay, has shown that the number survivor micro organisms after treatment by 13.5 msec pulse discharge N = 0.388 x 10⁹ CFU/ml versus the initial number of viable micro organisms  in the control sample before treatment (N_O) = 1.456 x 10⁹ CFU/ml which translates to log reduction of about 0.57. The applied electric field strength (of about 2.5 MV/m ) has more pronounced effect on inactivation the microorganisms than the length of the treatment time. The decimal reduction time or time required for a 1-log cycle reduction in the microbial population is about 24 msec. Bacterol analysis, has shown that the Proteus mirabilis and Enterobactericloacae (enterobacteriaceae) that were appearing in the control sample before treatment, were disappeared from treated sample.

Key words: Pulse discharge, sterilization, hybrid discharge, thermal processes, shock wave.