Behavior of Listeria monocytogenes during processing and storage of experimentally contaminated hot-smoked trout.

Hot-smoked fish like smoked trout is quite frequently contaminated with Listeria monocytogenes. In order to estimate the potential health hazard for the consumer eating such products, the behavior of L. monocytogenes was studied during processing and storage of artificially-inoculated hot-smoked trout. Four trials were performed; in trials 1 and 3 a wild-type strain was used, while in trials 2 and 4 a serological reference strain, SLCC 2755, was used. In the first two trials, raw trout was surface inoculated with L. monocytogenes, marinated, hot-smoked (core temperature 65 degrees C during 20 min), and stored at 4 and 8-10 degrees C, respectively, for up to 20 days. At different times during processing and storage, samples were taken and, by means of a MPN-method, quantitatively analysed for L. monocytogenes. The initial Listeria levels in the trout were 10(6) MPN/g. Until smoking, the concentrations remained about the same. After the hot-smoking process and during storage, however, L. monocytogenes could no longer be detected. In trials 3 and 4, the trout were inoculated after hot-smoking at a final concentration of 4.5 x 10(1) MPN/g and 3.1 x 10(1) MPN/g, respectively. During storage at 4 degrees C, neither an increase nor a decrease of L. monocytogenes was observed. At 8-10 degrees C, however, a significant increase up to 10(7) MPN/g occurred. By hot-smoking, low level contaminations of raw fish with L. monocytogenes will easily be eliminated. Nevertheless, it is of great importance to prevent postprocessing contamination, because during storage at refrigeration temperatures growth of L. monocytogenes is possible.(ABSTRACT TRUNCATED AT 250 WORDS)