Anlaug Ådland Hansen

Quality changes of prerigor filleted Atlantic salmon (Salmo salar L.) packaged in modified atmosphere using CO2 emitter, traditional MAP, and vacuum.

Pieces of prerigor salmon fillets were packaged in modified atmosphere (60% CO(2) and 40% N(2)) and in vacuum. The MA packages had a gas to product volume ratio (g/p ratio) of 3/1 (traditional MAP) and 1/1 (packaged with a CO(2) emitter). All the samples were stored at 1.2 degrees C for 25 d. The MA packages had lower bacterial growth during storage compared to vacuum packages. The analyses of 16S rRNA at day 22 indicated a similar bacterial diversity, independent of packaging methods, dominated by Photobacterium phosphoreum. The results therefore suggest that CO(2) inhibited total bacterial count, including, P. phosphoreum. Negative odors and liquid losses were detected earlier for the vacuum-packaged samples (8 d) compared to the MA samples (15 d) and higher levels were detected at the end of the storage period. The breaking strength (firmness) tended to be lower for the MA packaged samples compared with the vacuum samples after 15 d of storage, whereas the redness (a* value) and the yellowness (b* value) were significantly higher for the MA samples. In conclusion, MA packaging preserved the quality better during storage than vacuum packaging. MA packaging with a CO(2) emitter and reduced g/p ratio gave similar or better results compared with traditional MAP, thus CO(2) emitters are well suited for reduction of volume of MA packaged farmed salmon fillet pieces.

The effect of crowding stress on bacterial growth and sensory properties of chilled Atlantic salmon fillets.

UNLABELLED Atlantic salmon were subjected to minimal preslaughter crowding stress (Control), short-term crowding for 20 min (SS-group), or long-term crowding for 24 h (LS-group). The fish were filleted prerigor, cut into 270 g pieces, and packaged in modified atmosphere (60% CO₂ and 40% N₂). Fillet quality analyses were determined during 22 d of storage at 0.3 °C. Bacterial growth and unpleasant sensory properties increased earlier in the LS-group. The negative effects of long-term preslaughter stress were more pronounced for raw than cooked samples, and more pronounced for odor than flavor. Sequence analyses of bacterial DNA at the end of storage revealed that 100% of the bacteria were comprised by Photobacterium phosphoreum of the SS- and LS-group, whereas the Control group also contained 21% of Carnobacterium maltaromaticum (lactic acid bacteria, LAB). Counting of LAB, using Man-Rogosa-Sharke agar, similarly showed higher numbers of the Control group after 15 d of storage. A total bacterial count of log 6 CFU/g was observed after 15 d of storage of the LS-group, which was 3 and 7 d earlier compared with the Control and SS-group, respectively. Fillet color, texture, and liquid losses were not negatively affected by preslaughter crowding stress. From the sensory and bacterial analyses, it is concluded that long-term crowding stress accelerates bacterial growth and development of unpleasant sensory properties, hence reduces the shelf life of prerigor modified atmosphere packaged (MAP) salmon. PRACTICAL APPLICATION Stressful handling of Atlantic salmon before slaughter resulted in faster reduction of fresh taste and smell, faster bacterial growth, and hence shorter shelf life. The deteriorative effects were more pronounced of raw compared to cooked salmon. Therefore, salmon should be handled carefully in connection with slaughter to avoid impaired welfare and fillet quality, in particularly for fish that is consumed raw, such as sushi.

Contamination of salmon fillets and processing plants with spoilage bacteria.

The processing environment of salmon processing plants represents a potential major source of bacteria causing spoilage of fresh salmon. In this study, we have identified major contamination routes of important spoilage associated species within the genera Pseudomonas, Shewanella and Photobacterium in pre-rigor processing of salmon. Bacterial counts and culture-independent 16S rRNA gene analysis on salmon fillet from seven processing plants showed higher levels of Pseudomonas spp. and Shewanella spp. in industrially processed fillets compared to salmon processed under strict hygienic conditions. Higher levels of Pseudomonas spp. and Shewanella spp. were found on fillets produced early on the production day compared to later processed fillets. The levels of Photobacterium spp. were not dependent on the processing method or time of processing. In follow-up studies of two plants, bacterial isolates (n=2101) from the in-plant processing environments (sanitized equipment/machines and seawater) and from salmon collected at different sites in the production were identified by partial 16S rRNA gene sequencing. Pseudomonas spp. dominated in equipment/machines after sanitation with 72 and 91% of samples from the two plants being Pseudomonas-positive. The phylogenetic analyses, based on partial 16S rRNA gene sequencing, showed 48 unique sequence profiles of Pseudomonas of which two were dominant. Only six profiles were found on both machines and in fillets in both plants. Shewanella spp. were found on machines after sanitation in the slaughter department while Photobacterium spp. were not detected after sanitation in any parts of the plants. Shewanella spp. and Photobacterium spp. were found on salmon in the slaughter departments. Shewanella was frequently present in seawater tanks used for bleeding/short term storage. In conclusion, this study provides new knowledge on the processing environment as a source of contamination of salmon fillets with Pseudomonas spp. and Shewanella spp., while Photobacterium spp. most likely originate from the live fish and seawater. The study show that strict hygiene during processing is a prerequisite for optimal shelf life of salmon fillets and that about 90% reductions in the initial levels of bacteria on salmon fillets can be obtained using optimal hygienic conditions.