Thermal Stability of Encapsulated Listeria Bacteriophage and Its Efficacy Against Listeria monocytogenes in Ready-To-Eat Meats

Abstract

This research explored the potential application of encapsulated lytic Listeria phages as an additive in ready-to-eat meats prior to cooking to control L. monocytogenes. The objectives of this research were to: (a) evaluate the thermal stability of Listeria phage; (b) encapsulate Listeria phage to increase its thermal stability during thermal treatment; (c) investigate methods to apply phages in cooked meat product to control L. monocytogenes. The thermal stability of Listeria phages P100 and A511 at temperatures simulating typical preparation of RTE meats was evaluated. Substantial differences were found in thermal stability of the phages, with A511 showed a higher thermal stability than P100. However, P100 exhibited a greater ability to reconstitute during the cooling stage after the thermal treatment (80 °C) compared to A511. Heat treatment was accompanied by morphological changes to phage particles as revealed by transmission electron microscopy. Next, the bacteriophage was encapsulated in food-grade biopolymer matrices and their thermal stability evaluated. Through response surface analysis, the optimal polymer concentrations for achieving maximal thermal stability at 71 °C(30 s) was determined to be 2.91% (w/w) sodium alginate, 1.28% (w/w) gum Arabic, and 1.13% (w/w) gelatin. Encapsulating the phage with this formulation significantly (P<0.05) improved thermal stability of A511, showing the potential of this matrix to be used for protecting the phage during thermal processing. The efficacy of A511 bacteriophage added to cooked meat slurries was examined during refrigerated storage. Cooked meat slurries with phage A511 and L. monocytogenes inside or on the surface of the slurries were prepared. Phage A511 dispersed inside the meat together with L. monocytogenes did not significantly (P>0.05) affected pathogen counts. Conversely, applying the phages on the surface inactivated surface-inoculated L. monocytogenes. Overall, this study shows that significant (P<0.05) differences in thermal stability exist between P100 and A511 Listeria phages. Encapsulation of phages can significantly (P<0.05) enhance their thermal stability. Adding the bacteriophage as an additive into RTE meat products is not effective in inhibiting the growth of L. monocytogenes cells present within the meat matrices. However, phages applied to the surface are potent against the pathogens present on the surface of the product.