Inhibition of Clostridium botulinum Types A and E Toxin Formation by Sodium Nitrite and Sodium Chloride in Hot-Process (Smoked) Salmon

Abstract

Sodium nitrite and NaCl were evaluated as inhibitors of outgrowth and toxin production by Clostridium botulinum types A and E in abuse-stored (25°C) hot-process salmon. Salmon steaks were brined in NaCl or NaCl plus NaNO2 and inoculated intramuscularly with spores. Steaks were then heated in a simulated hot-smoke process to internal temperatures of 62.8 to 76.7°C (145 to 170°F) for the final 30 min of a 3- to 4-h process, packaged in oxygen-impermeable film and stored at 25°C. During 7 days of storage, toxin production in steaks inoculated with 102 spores per g was inhibited by more than 3.8% water-phase NaCl for type E and 6.1% for type A. Presence of nitrite substantially reduced the salt level required to prevent toxin production. When steaks had more than 100 ppm NaNO2, only 2.5% NaCl inhibited type E toxin production; 150 ppm NaNO2 and 3.5% NaCl inhibited production of type A toxin. When storage time was lengthened to 14 days or the spore inoculum increased to 104 spores per g, more salt and nitrite were required for inhibition. Residual nitrite in samples stored under refrigeration (3.3°C) did not change during 22 days of storage. Under abuse temperature (25°C), residual nitrite decreased to less than 6 ppm by the 14th day in all samples tested regardless of the original nitrite concentration.