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.

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.

A novel packaging method with a dissolving CO(2) headspace combined with organic acids prolongs the shelf life of fresh salmon.

The aim of this study was to evaluate a novel packaging method for fresh fish and to determine its effect on the bacterial growth in fresh salmon. Fresh salmon was packed with a small amount of 100% CO(2) (gas/product ratio 0.2/1.0 v/v) and a brine solution containing various combinations of citric acid (3% w/w, pH 5), acetic acid (1% w/w, pH 5) and cinnamaldehyde (200 microg/ml). Total bacterial counts, counts of sulphur reducing bacteria, lactic acid bacteria and Enterobacteriaceae as well as the bacterial composition in the product after storage were determined. The combination of CO(2) and organic acids completely inhibited bacterial growth during 14 days of storage at 4 degrees C both in inoculation experiments and in experiments on salmon with natural background flora. CO(2), acetic acid and citric acid alone each inhibited the growth of total bacterial counts, lactic acid bacteria, sulphur reducing bacteria and Enterobacteriaceae, but effects were enhanced in combinations. The addition of cinnamaldehyde did not influence bacterial growth. Analysis of the bacterial flora of salmon inoculated with different spoilage bacteria showed that Photobacterium phosphoreum and Carnobacterium maltaromaticum remained the dominating species after inoculation while Yersinia aldovae, Aeromonas salmonicida and Shewanella putrefaciens were outcompeted by other species. In addition, lactic acid bacteria from the natural background flora grew to high numbers. Combinations of CO(2) and acetic acid reduced the relative abundance of P. phosphoreum. All CO(2) dissolved in the product, thereby creating a product with the outer appearance of a vacuum package. Further work is needed to determine consumer acceptability of acid concentrations and to implement the packaging method for industrial purposes. However, implication of this packaging method in the industry may lead to a new packaging technology, combining the advantages of vacuum packaging (low space requirement) and modified atmosphere packaging (antimicrobial effect of CO(2)).