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 (2.5mg/L) or lactic acid (500mg/L) was investigated in two different buffer systems (pH 4 for E. coli and pH 7 for L. innocua). Individually, HILP (3.3J/cm ²), US (126s residence time, 500W, 40°C) and PEF (24kV/cm, 18Hz and 1μs 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 relevance: The 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.