Inactivation of Listeria monocytogenes on hot-smoked salmon by the interaction of heat and smoke or liquid smoke

L. monocytogenes was inoculated onto the surface of brined salmon steaks and heat processed in a commercial smokehouse to simulate a hot process for preparing smoked fish. The minimum temperature required for inactivation of L. monocytogenes was 153 degrees F (67.2 degrees C) when generated smoke was applied throughout the entire process. When generated smoke was added only during the last half of the process, L. monocyrogenes was recovered from steaks heated to temperatures as high as 176 degrees C (80.0 degrees C). When smoke was not applied during the process, L. monocytogenes survived on steaks heated to internal temperatures between 131 degrees and 181 degrees F(55.0 to 82.8 degrees C) but was not isolated from steaks heated above 181 degrees F (82.8 degrees C). When liquid smoke CharSol C-10 was applied as a full-strength (100%) dip before processing, L. monocytogenes was inactivated in samples processed at temperatures as low as 138 degrees F (58.9 degrees C). When liquid smoke 10-Poly or CharSol C-10 was applied at a concentration of 50%, the lethal temperature was increased to the range of 145 to 150 degrees F(62.8 to 65.6 degrees C). With further dilution of C-10 to 25% and 10% the inactivation temperatures increased to 156 degrees F (68.9 degrees C) and 163 degrees F (72.8 degrees C). A full-strength dip of CharOil, the oil-soluble fraction of CharSol C-10, was less effective, and L. monocytogenes survived in salmon steaks processed to an internal temperature of 166 degrees F (74.4 degrees C), the highest temperature tested with this liquid smoke. This study provides evidence that heat alone is not reliable for inactivation of L. monocytogenes during the hot-smoking process. The proper stage and duration of smoke application or proper composition and concentration of liquid smoke in combination with heat are critical for inactivation of the organism.