Control of Listeria monocytogenes in salmon; antimicrobial effect of salting, smoking and specific smoke compounds

Abstract

Salmon fillets were either salted only, salted and conventionally smoked in a kiln or salted and dried in the kiln without smoke. The processed fillets were experimentally inoculated with Listeria monocytogenes (102-3/g), vacuum packed and the growth monitored during storage at 4°C over a 30-day period. There was no significant growth in the smoked samples, whereas the number of bacteria increased by between 2 and 5 log cycles in the salted-only samples. In samples salted and dried over the time of conventional smoking, the growth was delayed until the second week of storage after which it increased by 2 log cycles. Commercially available phenol components from wood smoke were mixed in concentrations found in smoked products. These mixtures plus formaldehyde were tested for their antimicrobial properties against L. monocytogenes in tryptone soya broth (TSB) with added salt at a concentration similar to that in smoked salmon (60 g/kg). A range of TSB based phenolic plus formaldehyde growth substrates, each inoculated with 102 L. monocytogenes/g, were tested over a 25 day period at 8°C. A 50 μg/ml formaldehyde concentration inhibited the growth of L. monocytogenes for 2 weeks after which growth started. The phenols did not have any synergistic effect with salt or formaldehyde against L. monocytogenes. ©1998 Academic Press Limited.