Inhibition of Brochothrix thermosphacta in broths and pork by myristoyl-L-methionine Original Research Article

The antibacterial properties of myristoyl-L-methionine (Myr-Met) were examined in commercial broths (APT, cooked meat medium), aqueous extracts of pork muscle, pork muscle slurries and at the surface of pork muscle discs inoculated with Brochothrix thermosphacta. Broths and muscle substrates were inoculated with B. thermosphacta to give an initial concentration of about 4 log cfu ml−1or cm2and bacterial growth in the presence or absence of Myr-Met was determined by plate counts during 9 days of aerobic incubation at 4°C. In an aqueous muscle extract and APT broth Myr-Met was bactericidal at concentrations of 5 and 50 μg ml−1, respectively, reducing B. thermosphacta to below recoverable levels (<1 log cfu ml−1). Efficacy was diminished in substrates containing muscle or meat particles and 500 μg ml−1Myr-Met only produced a transient bacteriostatic effect in pork muscle slurries. A concentration of 500 μg ml−1Myr-Met was without effect upon the growth of B. thermosphacta in a commercial cooked meat medium or on the surface of inoculated pork muscle discs. To produce a significant inhibition of B. thermosphacta growth on pork muscle tissue it was necessary to increase the concentration of Myr-Met to 5000 μg ml−1, using the sodium salt of Myr-Met to permit solublization. A mechanism to prevent Myr-Met inactivation in meat is necessary if Myr-Met is to be of practical value as a preservative.