Combinations of selected non-thermal technologies and antimicrobials for microbial inactivation in a buffer system

Inactivation of Escherichia coli and Listeria innocua by combinations of High Intensity Light Pulses (HILP), Ultrasound (US) and Pulsed Electric Fields (PEF) and sub-lethal concentrations of nisin (2.5 mg/L) or lactic acid (500 mg/L) was investigated in two different buffer systems (pH 4 for E. coli and pH 7 for L. innocua). Individually, HILP (3.3 J/cm2), US (126 s residence time, 500 W, 40 °C) and PEF (24 kV/cm, 18 Hz and 1 μs of pulse width) did not induce a microbial reduction of greater than 2.7 or 3.6 log units, for L. innocua and E. coli, respectively. Combined treatment using HILP + PEF sufficiently inactivated E. coli without antimicrobial addition. The addition of either antimicrobial enhanced the effect of US + PEF for both E. coli and L. innocua. The addition of lactic acid enhanced the effect of HILP + US. For L. innocua the addition of nisin enhanced the effect of HILP + PEF. This confirms the potential of selected non-thermal technologies for microbial inactivation when combined with antimicrobials.Industrial relevanceThe application of sublethal non-thermal processing and GRAS antimicrobial hurdle combinations has the potential to allow for the production of safe, stable products while also maintaining the desired organoleptic characteristics of a minimally processed product. An initial step to assessing the suitability of non thermal treatments is to evaluate their efficacy in model solutions prior to their study in food systems.

► We examined combinations non-thermal technologies for microbial inactivation.
► When applied alone non-thermal technologies gave insufficient microbial kill.
► Combinations of non-thermal technologies generally improved microbial kill.
► Addition of antimicrobials enhanced the effect of combined non-thermal technologies.