Effects of pulsed electric fields and mild thermal treatment on antimicrobial efficacy of nisin-loaded pectin nanoparticles for food preservation

Abstract

Pulsed electric field (PEF) treatment is a common and primarily non-thermal sterilization technique that is used in food processing, which can be improved when combined with food-compatible antimicrobial agents such as nisin. In this work, we have combined the nisin-loaded nanoparticles with mild thermal treatment (40 °C, 2 min) and pulsed electric fields (30 kV/cm; 200 ns – 500 μs protocols, 17.5–87.6 kJ/L) for potentiation of the anti- microbial effects against S. typhimurium and L. innocua. It was demonstrated that PEF treatment efficacy does not linearly depend on the energy delivered to the cells, which highlights the differences in polarization between the two bacteria in sub-microsecond range. The mild thermal treatment improved the efficacy of nisin nanoparticles and allowed to inactivate both bacteria in stationary growth phase, while limit the energy density of PEF in 50–90 kJ/L range. The synergistic effect of PEF and nisin-loaded pectin nanoparticles improved the sensitivity of gram-negative bacteria to nisin.