Effectiveness of combined Pulsed Electric Field (PEF) and Manothermosonication (MTS) for the control of Listeria innocua in a smoothie type beverage

The combination of novel, non-thermal technologies for preservation purposes is a recent trend in food processing research. The objectives of the current study were (i) to optimise PEF or MTS treatment conditions which would achieve a maximum reduction of up to 3 log cycles of Listeria innocua in a milk based smoothie, when these technologies were applied individually, and (ii) to investigate possible additive or synergistic effects of the combined technologies. Microbiological analysis was performed by inoculating the smoothie with L. innocua and enumerating populations pre- and post-processing. All technologies applied within combinations significantly reduced L. innocua in the smoothie, when compared to untreated controls (p <= 0.0001). The sequence in which the MTS and PEF were applied was found to have a significant impact on the level of microbial reduction achieved (p <= 0.05). The sequence of MTS followed by PEF was the most effective in inactivating L innocua achieving a mean reduction of 5.6 log cfu/ml, thereby exceeding the 5 log cycles minimum requirement specified by the United States Food and Drug Administration (US FDA). Significantly (p <= 0.05) lower reductions of 4.2 log cfu/ml were achieved when the PEF + MTS sequence combination was applied. The combination of MTS + PEF achieved inactivation comparable to thermally treated samples (p > 0.05). This study has shown the combination MTS + PEF is a promising hurdle preservation approach to control undesirable microorganisms in milk based smoothie beverages. (C) 2011 Elsevier Ltd. All rights reserved.