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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 −1 or cm 2 and 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 ). Efficacy was diminished in substrates containing muscle or meat particles and 500 μg ml −1 Myr-Met only produced a transient bacteriostatic effect in pork muscle slurries. A concentration of 500 μg ml −1 Myr-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. |
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