Long-term Listeria monocytogenes proliferation control in milk by intermittently delivered pulsed electric fields, implications for food security in the low-income countries

Microbial density control is a major challenge for food preservation especially in the low-income countries, where 850 million undernourished people live. In this work, we report on non-thermal, chemical-free microbial cell density control by intermittently delivered pulsed electric fields (IDPEF). We show that IDPEF allows for precise control of L. monocytogenes density in contaminated milk, an essential product for small farmers in low-income countries. Using L. monocytogenes growth kinetics, we designed an IDPEF protocol that consists of 2 sequences of 10 square wave pulses, 50 μ s duration, 12.5 kV cm-1 electric field strength, delivered at 0.5 Hz and 1 min pause between the sequences applied every 1.5 hours. In a 12 hours experiment at 32 °C, L. monocytogenes density of untreated samples reached (9.1 ± 0.6) ⋅ 107 CFU ml-1 and (7.1 ± 0.3) ⋅ 108 CFU ml-1 for initial load of (1.4 ± 0.2) ⋅ 103 CFU ml-1 and (3.1 ± 0.3) ⋅ 106 CFU ml-1 respectively; the final density in the IDPEF treated samples, however, was 120 ± 44 CFU ml-1 and (1.1 ± 0.3) ⋅ 105 CFU ml-1. The energy required for IDPEF storage of milk in the low-income countries could be generated by a small-scale 2kW solar energy system operating 5.5 hours per day in combination with small-scale energy storage system. We believe that IDPEF storage technology can empower millions of small farmers in the low-income countries by providing them a simple and energy efficient technology for milk preservation.