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

Abstract

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.