Published in Applied Research
Moderate intensity Pulsed Electric Fields as alternative mild preservation technology for fruit juice

Researchers from Wageningen University (Netherlands) have studied moderate intensity Pulsed Electric Fields (PEF) for microbial inactivation as an alternative to high intensity PEF or to classical thermal pasteurization. The results have been published in the International Journal of Food Microbiology, 298, 63-73, 2019.

The process is characterized by the application of electric pulses, allowing an increase of the product temperature by the ohmic heat generated by the pulses. A systematic evaluation of the effect of parameters electric field strength (E) and pulse width (tau) on the inactivation of Escherichia coli, Listeria monocytogenes, Lactobacillus plantarum, Salmonella Senftenberg and Saccharomyces cerevisiae in orange juice was carried out in a continuous flow system. A wide range of conditions was evaluated, and both E and tau were shown to be important in the efficacy to inactivate micro-organisms. Remarkably, PEF conditions at E=2.7kV/cm and tau=15-1000mus showed to be more effective in microbial inactivation than at E=10kV/cm and tau=2mus. Inactivation kinetics of the tested PEF conditions were compared to an equivalent thermal process to disentangle non-thermal effects (electroporation) from thermal effects responsible for the microbial inactivation. At standard high intensity PEF treatment a non-thermal inactivation at E=20kV/cm and tau=2mus pulses was observed and attributed to electroporation. Non-thermal effects could also be resolved with moderate intensity PEF at E=2.7kV/cm and pulse width between tau=15-1000mus. Microbial inactivation at these moderate intensity PEF conditions was studied in more detail at different pH and medium conductivity for E. coli and L. monocytogenes in watermelon juice and coconut water. Under moderate intensity PEF conditions the effectiveness of treatment was independent of pH for all evaluated matrices in the pH range of 3.8-6.0, whereas under high intensity PEF conditions the pH of the product is a critical factor for microbial inactivation. This suggests that the inactivation proceeds through a different mechanism at moderate intensity PEF, and speculations for this mechanism are presented. In conclusion, moderate intensity PEF conditions at E=2.7kV/cm and pulse width of 15-1000mus has potential for industrial processing for the preservation of fruit juices and pH neutral liquid food products.

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