Survivability of Inoculated Versus Naturally Grown Bacteria in Apple Juice Under Pulsed Electric Fields

Abstract

In this paper, the effect of different pulse and system parameters on the killing efficiency of pulsed electric field (PEF) treatment is investigated. Both Escherichia coli and naturally grown bacteria inoculated in apple juice were treated. Results showed that an electric field higher than 4 kV/mm is required to enhance the killing efficiency using PEF and achieve sufficient log reductions in the microbial numbers. The maximum temperature rise during pulse application was found to be around 35°C above ambient with the treated medium temperature reaching 41°C, and it is observed that this rise in medium temperature has synergistic effect and has resulted in high inactivation. As the temperature rise can be limited to a value below the pasteurization temperature, the synergistic effect can be highly beneficial. While a high killing rate was achieved for inoculated bacteria (up to 6-log reduction), less than 2-log reduction was achieved for naturally grown bacteria in apple juice under similar test conditions.