51A-20

S. M. Vitt and B. H. HIMELBLOOM, Fishery Industrial Technology Center, University of Alaska Fairbanks, 118 Trident Way, Kodiak, AK 99615-7401.

Listeria monocytogenes is a food safety threat due to human illnesses and deaths from consuming contaminated ready-to-eat foods. Since L. monocytogenes can be found in ready-to-eat smoked seafood, new techniques are needed to provide safer products.

We investigated liquid smoke as an inhibitor against Listeria in a laboratory broth and in cold-smoked salmon fillets.

Five commercial liquid smokes were tested against L. monocytogenes and L. innocua. Cultures were grown overnight in brain heart infusion (BHI) at 35°C and inocula were added to BHI tubes containing 0.1-0.5% liquid smoke (final concentration). Optical densities at 600 nm were compared for bacteriocidal activity. For brined salmon fillets, 25% liquid smoke was sprayed on or the fillets were dipped in liquid smoke (20-100%) for 0.25-5 minutes. An inoculum (0.5 ml) of L. innocua was spread on fillets and dried in a smokehouse, without wood smoke, at 21°C for 16 hours. Samples were serially diluted, spread-plated on modified Oxford medium, incubated for 24-48 hours at 35°C and colonies with black halos were counted. Color was determined using a Minolta color meter. Salt, moisture and pH were determined using standard methods.

Only CharSol Supreme, at final concentrations ³ 0.4% in BHI, was inhibitory to both Listeria species. A 5-minute dip in 60% liquid smoke reduced L. innocua 3-4 logs after drying the fillets. Treated fillets had 10% lower L* values (darker) than the controls after drying. Fillet pH decreased from 6.3 to 5.3 when dipped in 100% CharSol Supreme. Moisture content did not differ between treated fillets and the controls whereas the control fillets were slightly saltier. Liquid smoke, 60-100%, resulted in 2-log reductions in L. innocua during fillet drying.

Liquid smoke should be considered a natural and practical bacteriocide against Listeria in cold-smoked salmon.