Inhibition of Listeria monocytogenes in Cold-process (Smoked) Salmon by Sodium Nitrite and Packaging Method

The behavior of Listeria monocytogenes in relation to sodium nitrite (NaNO₂) in combination with sodium chloride (NaCl) was evaluated in cold-process (smoked) salmon during storage at 5 or 10°C in either oxygen-permeable film or vacuum-sealed impermeable film. Salmon slices containing either 3 or 5% water-phase NaCl, with or without 190-200 ppm of NaNO₂, were inoculated with 10 or 327 CFU/g (150 or 4.9 × 10³ CFU/15-g sample) of strain Scott A. The inhibitory contribution of NaNO₂ was relative to inoculum size, storage time and temperature, packaging method, and concentration of NaCl. There was less growth of L. monocytogenes in vacuum-packaged samples as compared to those packaged in oxygen-permeable film. The most inhibition was achieved in vacuum-packaged products stored at 5°C, where NaNO₂ in combination with 5% water-phase NaCl prevented any increase in a 10 CFU/g-inoculum during 34 d storage. At 10°C, inhibition was initially enhanced by NaNO₂, but by 32 d L. monocytogenes populations had increased from a 10 CFU/g-inoculum to the range of 10⁶ CFU/g in vacuum-packaged products and 10⁸ CFU/g in permeable-film packaged products, regardless of NaNO₂ or NaCl concentration. Growth of naturally occurring aerobic microorganisms was also inhibited by NaNO₂ but to a lesser degree than L. monocytogenes .