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 co ld-process (smoked) salmon during storage at 5 or 10 degrees C in eith er oxygen-permeable film or vacuum-sealed impermeable film. Salmon sli ces containing either 3 or 5% waterphase NaCl, with or without 190-200 ppm of NaNO2, were inoculated with 10 or 327 CFU/g (150 or 4.9 x 10(3 ) CFU/15-g sample) of strain Scott A. The inhibitory contribution of N aNO2 was relative to inoculum size, storage time and temperature, pack aging method, and concentration of NaCl. There was less growth of L. m onocytogenes in vacuum-packaged samples as compared to those packaged in oxygen-permeable film. The most inhibition was achieved in vacuum-p ackaged products stored at 5 degrees C, where NaNO2 in combination wit h 5% water-phase NaCl prevented any increase in a 10 CFU/g-inoculum du ring 34 d storage. At 10 degrees 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 10(6) CFU/g in vacuum-packaged pro ducts and 10(8) 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.