Cold-smoked fish is not a cooked product. However, it is deemed ready for consumption because the combined action of salting, drying, and smoking seems to provide safety. The antimicrobial properties of smoking have been studied for many years, yet there is currently no consensus on the antimicrobial effect of smoke on fish. The presence of Listeria monocytogenes is a problem in smoked fish because of the ability of these products to support growth of this microbe and the recent documentation of outbreaks of Listeria in smoked fish from around the world. Listeria spp. can have severe economical consequences as it has previously shut down smoked fish processing plants in both the United States and Canada and is potentially lethal if ingested. Currently, the time and temperature used for smoking fish differ among processors and the optimal time and temperature for safety is unknown.
Researchers recently evaluated the difference in survival rates of Listeria innocua, used as a model organism for L. monocytogenes, on the surface of salmon fillets following cold smoking at varying time and temperature combinations. Three 500 g fillets were used for each time and temperature trial. A strain of L. innocua, isolated from crab, was used in the trials. Two milliliters of the culture, containing approximately 5 x [10.sup.8] CFU/mL, were spread on the surface of the fillets. The fillets were then smoked for a time ranging from 2 hours to 14 hours and with temperatures ranging from 18 [degrees] C to 30 [degrees] C.
The results showed that smoke temperature did not have a significant effect on reducing the counts of L. Innocua on the salmon tested. However, the smoking time did have a significant effect on reducing L. Innocua. The amount of smoke time was directly related to the amount of reduction in count. A 3-log cycle reduction in count of the microbe was seen with a smoking time of at least 12 hours. There were no significant reductions in L. innocua levels with regard to the pH, water activity, or salt concentration of the salmon fillets.
These findings do support the use of cold smoking as a means of controlling against L. monocytogenes contamination, provided that smoke is applied for an extended ([is greater than] 12 hour) length of time.
S. Sabanadesan, A. Lammerding, M. Griffiths, Survival of Listeria innocua in Salmon following Cold-Smoke Application, Journal of Food Protection 63:715-720 (June 2000). [Correspondence: Mansel W. Griffiths. Phone: 519-824-4120, ext. 2269. Fax: 519-824-6631. E-mail: mgriffit@uoguelph.ca.]
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