Study of the microbial ecology of cold-smoked salmon during storage at 8°C

Microbiological, chemical and sensory changes in cold-smoked salmon were studied during 5 weeks of vacuum storage at 8°C. The aerobic 20°C viable count reached its maximum level after 6 days (3×106 cfu g−1) however, the shelf-life of the product was estimated to be 2 or 3 weeks by the panellists, confirming that there is no correlation between those two factors. Acid, pungent, sour and rancid odours and flavours and pasty texture were the main spoilage characteristics. Trimethylamine did not play a major role in the spoilage mechanisms as only small amounts were produced. Two-hundred and seventy strains were collected over the storage period, purified and characterized. During the first 2 weeks, Gram-negative bacteria were dominant, mainly represented by S. putrefaciens immediately after the smoking process and then P. phosphoreum. Aeromonas spp. were present throughout the storage but in smaller amounts. Gram-negative bacteria then progressively decreased while Gram-positive bacteria, dominated by lactic acid bacteria (LAB), became by far the most common variety found. Carnobacterium piscicola was widely represented (97/155 LAB isolates). A diversification was observed at the end of the storage, with the appearance of L. farciminis, L. sake and L. alimentarius. Occurrence of yeasts and moulds was quite rare. Spoilage potential of the strains was tested on a sterile smoked salmon extract juice. Shewanella putrefaciens, Aeromonas spp. and Brachothrix spp. produced strong off-odours while most of the LAB and P. phosphoreum seemed not to be involved in spoilage.