Microorganism Inactivation by Nanosecond Pulsed Electric Fields: Full-wave Analysis and Experiment Phumin Kirawanich 1 + , P. Satusap 2 , Visith Chavasit 2 and Naz E. Islam 3 1 Electrical Engineering Department, Mahidol University, Salaya, Nakhon Pathom, Thailand 73170 2 Institute of Nutrition, Mahidol University, Salaya, Nakhon Pathom, Thailand 73170 3 Electrical and Computer Engineering, University of Missouri, Columbia, Missouri, USA 65203 Abstract. This paper describes the application of nanosecond pulsed electric fields on microorganism inactivation of food products. Inside custom-designed chamber, liquid and semi-solid samples were subjected to ultrashort high-intensity electrical pulses with a maximum energy input of 75 kJ.kg -1 . An efficient treatment environment provided by the chamber was preliminarily confirmed through simulated field distributions and specific absorption rates for its field homogeneity and high energy absorption. Observations through statistical analyses showed that nanosecond pulsed electric fields caused as high as 5-log reduction of the total microbial population in liquid medium (P < 0.05). An effective microbial destruction and a minimal rise in temperature together provide this treatment an alternative food pasteurization method. Keywords: nanosecond pulsed electric field treatment; energy dosimetry; total microbial count 1. Introduction An increasing interest and preference of consumers towards health-concerned nutrition and fresh-like taste of food have led producers to develop preservation technologies preventing the growth of food pathogens responsible of undesired food degradation without having negotiation the initial qualities of food. The most preferred technique is a treatment at temperatures less than those of typical heat pasteurization. The original nutritional and sensory qualities of food, accordingly, are slightly disturbed by heating effects while extending the shelf life of food products is plausible. The development of a widely available, highly effective, less thermal technique that provides a relatively high level of preservation is of great interest. Application of pulsed electric field (PEF) has been found as a new treatment for food preservation where short electrical pulses are applied momentarily to samples through conductive electrodes in direct contact with samples. Major portion of research efforts on PEF has been focusing on a reduction of microbial fractions in liquid food [1]-[3] or semi-solid food [4]-[7]. This process causes structural damage to microbial membranes at less significant energy levels when compared to typical heating process. As part of the response to an increasing voltage across samples, the resultant transmembrane potential causes the cell membrane to lose its impermeability beyond the critical value, owing to the pore formation induced on the membrane surface leading to the disintegration of the cell membranes [8]-[9]. Studied factors include differences among microorganisms, bacterial growth phase, food pH, food ionic strength, food conductivity, and food water activity. In addition, an effectiveness of PEF on microorganism inactivation has been extensively studied over the past decade through a number of influencing parameters, including electric field strength and pulse profiles, i.e., polarity, duration, repetitiveness, and rise time [10]. Of all pulse profiles, + Corresponding author. Tel.: +662-839-2138 ext. 6501; fax: +662-839-2138 ext. 6529 E-mail address: egphumin@mahidol.ac.th 6 2011 International Conference on Food Engineering and Biotechnology IPCBEE vol.9 (2011) © (2011)IACSIT Press, Singapoore