Parameters for Control of Listeria monocytogenes in Smoked Fishery Products: Sodium Chloride and Packaging Method

The behavior of Listeria monocytogenes (10 Scott A cells per g) in cold-process (smoked) salmon containing 3, 5, or 6% water-phase NaCl was evaluated during 30 to 40 d storage at 5 or 10°C in either oxygen-permeable film or vacuum-sealed impermeable film. At 10°C, L. monocytogenes grew to 10⁶ to 10⁸ CFU/g by the second week, with no differences attributed to NaCl concentration except for an initial lag in the 6% NaCl samples. Vacuum packaging suppressed growth of L. monocytogenes by 10- to 100-fold in samples with 3 or 5% NaCl. Inhibition related to NaCl concentration was most apparent at 5°C and L. monocytogenes populations were held below 10² CFU/g by 6% NaCl. Growth of a 327 CFU/g inoculum was about 10-fold greater than a 10 CFU/g inoculum at 10°C and 100-fold greater at 5°C. Growth of two strains isolated from naturally contaminated, commercially prepared, cold-smoked fish did not differ from Scott A. The use of sugar in the product did not influence growth of L. monocytogenes. Maximum populations of aerobic microorganisms reached at 5 and 10°C were similar, although the rate of growth was somewhat delayed at 5°C, and some inhibition was shown by 5 and 6% NaCl and by vacuum packaging.