Evaluation of the role of Carnobacterium piscicola in spoilage of vacuum- and modified-atmosphere-packed cold-smoked salmon stored at 5 degrees C.
The microflora on spoiled cold-smoked salmon often consists of a mixture of lactic acid bacteria (LAB) and Gram-negative bacteria. To elucidate the role of the different groups, a storage trial was carried out in which nisin and CO2 were used for the selective inhibition of the two bacterial groups. The shelf-life of vacuum-packed cold-smoked salmon, recorded by sensory evaluation, was four weeks at 5 degrees C and the microflora was composed of LAB (10(6)-10(7) cfu/g) with an associate Gram-negative flora in varying levels (10(5)-10(7) cfu/g). The addition of nisin and/or a CO2-atmosphere increased the shelf-life to five or six weeks and limited the level of LAB to about 10(4)-10(6), 10(3)-10(6) and 10(2)-10(4) cfu/g, respectively. CO2-atmosphere +/- nisin inhibited the growth of Gram-negative bacteria, whereas nisin had no effect on these in vacuum packages. The Gram-negative flora on vacuum-packed salmon was dominated by a Vibrio sp., resembling V. marinus, Enterobacteriaceae (Enterobacter agglomerans, Serratia liquefaciens and Rahnella aquatilis) and occasionally Aeromonas hydrophila. Irrespective of the addition of nisin and/or CO2-atmosphere, the LAB microflora was dominated by Carnobacterium piscicola, which was found to account for 87% of the 255 LAB isolates characterized. Whole-cell-protein patterns analysed by SDS-PAGE confirmed the Carnobacterium species identification. The spoilage potential of C. piscicola isolates was further studied by inoculation of approx. 10(6) cfu/g in cold-smoked salmon stored at 5 degrees C. The salmon did not spoil within 4 weeks of storage in vacuum- or CO2-atmosphere, and it is concluded that despite high levels (> 10(7) cfu/g) of C. piscicola, sensory rejection was caused by autolytic changes. This was supported by the development of soft texture and sour, rancid and bitter off-flavours at the point of spoilage, irrespective of the length of shelf-life and low or high total counts of LAB and Gram-negative bacteria.
Paludan-Müller
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Danish Institute for Fisheries Research, Department of Seafood Research, Danish Technical University, Lyngby, Denmark. cpm@ffl.min.dk
Dalgaard
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Huss
H H
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Gram
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D000818:Animals; D001426:Bacterial Proteins / Q000032:analysis; D002245:Carbon Dioxide; D003080:Cold Temperature; D015169:Colony Count, Microbial; D004591:Electrophoresis, Polyacrylamide Gel; D005069:Evaluation Studies as Topic; D005396:Fish Products / Q000382:microbiology*; D005516:Food Microbiology; D018857:Food Packaging / Q000379:methods*; D005519:Food Preservation / Q000379:methods / Q000592:standards; D005520:Food Preservatives / Q000494:pharmacology; D006090:Gram-Negative Bacteria / Q000145:classification / Q000187:drug effects / Q000254:growth & development; D006094:Gram-Positive Bacteria / Q000145:classification* / Q000187:drug effects / Q000254:growth & development; D006863:Hydrogen-Ion Concentration; D008744:Methylamines / Q000032:analysis; D009561:Nisin / Q000494:pharmacology; D009584:Nitrogen / Q000032:analysis; D009812:Odorants; D012474:Salmon / Q000382:microbiology*; D012965:Sodium Chloride / Q000032:analysis; D014618:Vacuum
D001426:Bacterial Proteins; D005520:Food Preservatives; D008744:Methylamines; D009561:Nisin; D002245:Carbon Dioxide; D012965:Sodium Chloride; C005855:trimethyloxamine; C023336:trimethylamine; D009584:Nitrogen