The genus Carnobacterium contains nine species, but only C. divergens and C. maltaromaticum are frequently isolated from natural environments and foods. They are tolerant to freezing/thawing and high pressure and able to grow at low temperatures, anaerobically and with increased CO2 concentrations. They metabolize arginine and various carbohydrates, including chitin, and this may improve their survival in the environment. Carnobacterium divergens and C. maltaromaticum have been extensively studied as protective cultures in order to inhibit growth of Listeria monocytogenes in fish and meat products. Several carnobacterial bacteriocins are known, and parameters that affect their production have been described. Currently, however, no isolates are commercially applied as protective cultures. Carnobacteria can spoil chilled foods, but spoilage activity shows intraspecies and interspecies variation. The responsible spoilage metabolites are not well characterized, but branched alcohols and aldehydes play a partial role. Their production of tyramine in foods is critical for susceptible individuals, but carnobacteria are not otherwise human pathogens. Carnobacterium maltaromaticum can be a fish pathogen, although carnobacteria are also suggested as probiotic cultures for use in aquaculture. Representative genome sequences are not yet available, but would be valuable to answer questions associated with fundamental and applied aspects of this important genus.

The importance of carnobacteria as spoilage microorganisms or potential protective cultures in food is not resolved, and little is known about their metabolism during growth in specific products. This study used chromatographic techniques including GC-MS and HPLC to evaluate the spoilage metabolism of Carnobacterium divergens, Carnobacterium maltaromaticum, and Carnobacterium mobile. Metabolic activity was studied in cooked and peeled modified atmosphere packed (MAP) shrimp at 5 degrees C as carnobacteria has been anticipated to contribute to spoilage of shrimp products. C. divergens and C. maltaromaticum caused sensory spoilage of shrimps and generated ammonia, tyramine, and various alcohols, aldehydes, and ketones. The effects of Carnobacterium species on the growth and metabolism of Brochothrix thermosphacta were also evaluated, but metabiosis between the two groups of bacteria was not observed. C. mobile and a specific cluster of C. maltaromaticum isolates (cluster L) did not cause sensory spoilage of shrimp.

Aims: To evaluate the microbial spoilage, formation of biogenic amines and shelf life of chilled fresh and frozen/thawed salmon packed in a modified atmosphere and stored at 2°C. Methods and Results: The dominating microflora, formation of biogenic amines and shelf life were studied in two series of storage trials with naturally contaminated fresh and thawed modified atmosphere-packed (MAP) salmon at 2°C. Photobacterium phosphoreum dominated the spoilage microflora of fresh MAP salmon at more than 10 6 cfu g )1 and the activity of this specific spoilage organism (SSO) limited the shelf life of the product to ca 14 and 21 d in the two experiments. Despite the high levels of P. phosphoreum, less than 20 mg kg )1 histamine was observed in fresh MAP salmon prior to sensory spoilage. Freezing eliminated P. phosphoreum and extended the shelf life of MAP salmon at 2°C by 1-2 weeks. Carnobacterium piscicola dominated the spoilage microflora of thawed MAP salmon and probably produced the ca 40 mg kg )1 tyramine detected in this product at the end of its shelf life.Conclusions: Photobacterium phosphoreum dominated the spoilage microflora of fresh MAP salmon but produced only small amounts of biogenic amines in this product. The elimination of P. phosphoreum by freezing allowed this bacteria to be identified as the SSO in fresh MAP salmon. Significance and Impact of the Study: The identification of P. phosphoreum as the SSO in fresh MAP salmon facilitates the development of methods to determine and predict the shelf life of this product, as previously shown with fresh MAP cod.

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