Reduction of Listeria monocytogenes on Beef Franks Utilizing Targeted Directional Microwave Technology

Introduction: Listeria monocytogenes is one of the leading causes of death in the U.S. among foodborne bacterial pathogens with infections linked to consumption of contaminated food, raw and even post-packaged meat products.  Targeted directional microwave (TDM) technology is a novel non-traditional sterilization method that uses microwave frequencies to kill microorganisms in a short amount of time and is proven effectively in inactivation of Salmonella in shell eggs and inhibition of mold in white enriched bread.

Purpose: The objective of this research is to determine the ability of the TDM to reduce L. monocytogenes on inoculated beef franks in package.

Methods: Beef franks were surface-inoculated with four-strain L. monocytogenes at 10³ CFU/g and cooled down in cold temperature storage (4°C).  In duplicate, the samples in packages were subjected to seven treatments using the TDM to vary levels of microwave power and microwave application time while monitoring product temperature change.  After treatment, serial dilutions were performed and plated on modified oxford agar followed by incubation at 35°C for 24 hours.

Results: When compared to the control sample, there were significant reductions (P < 0.05) of L. monocytogenes on beef franks in packages after treatments with varying TDM parameters controlling energy, exposure time and temperature.  Four out of seven treatments had reductions of 1.35 to 2.86 log CFU/g.  Only samples from one of the treatments had an internal temperature above the thermal kill temperature (71.1°C) of L. monocytogenes.

Significance: The data from this experiment suggest that TDM technology is an effective intervention against L. monocytogenes on beef franks in packages providing 1 to just less than 3 log CFU/g reduction.