Use of Bacteriophage as an Additive during the Preparation of Ready-to-Eat Meat Products to Control Listeria monocytogenes

Introduction: Bacteriophages have been approved for use as a processing aid to be applied on the surface of RTE meat products prior to packaging. However, it is currently not clear if mixing bacteriophage within the meat, as an additive before thermal processing of RTE meats, would affect the anti-Listeria activity.

Purpose: The purpose of this study was to evaluate the efficacy of Listeria phage A511 when used as an additive before cooking, to RTE meat products, to control L. monocytogenes.

Methods: Model RTE thin meat products were prepared with common levels of sodium polyphosphate and salt, as well as phage at 10⁸ PFU/g. Samples (10 g of meat slurry) were cooked to 71°C for 30 s, cooled, and then inoculated with 10³ CFU L. monocytogenes/g . Samples were stored at 4°C and enumerated for bacteriophage and L. monocytogenesat predetermined time intervals, over a 28-day period, in triplicate.

Results: Phage numbers significantly (P<0.05) decreased during cooking by approximately 1.5 log PFU/g. Neither salt (2 and 3%) nor sodium polyphosphate (0.5 and 1%) had a significant (P>0.05) effect on phage stability. No significant difference (P>0.05) in L. monocytogenes numbers was observed between bacteriophage-treated samples and untreated controls, suggesting that bacteriophage used as an additive does not inhibit the growth of L. monocytogenes. This is probably due to immobilization of bacteriophages in meat matrix.

Significance: Results from this study suggest that the use of bacteriophage as an additive in RTE meat products before thermal processing is not effective in inhibiting the growth of L. monocytogenes.