Reports

Shelf life tests on cod pieces: Effect of supercooling, pickling and gas packaging on quality changes and shelf life / Storage trials on cod loins: Effect of superchilling, brining and modified atmosphere packaging (MAP) on quality changes and sensory shelf-life

Published:

01/05/2007

Authors:

Hannes Magnússon, Hélène L. Lauzon, Kolbrún Sveinsdóttir, Ása Þorkelsdóttir, Birna Guðbjörnsdóttir, Emilia Martinsdóttir, Guðrún Ólafsdóttir, María Guðjónsdóttir, Sigurður Bogason, Sigurjón Arason

Supported by:

AVS Fisheries Research Fund, Technology Development Fund (Rannís)

contact

Kolbrún Sveinsdóttir

Project Manager

kolbrun.sveinsdottir@matis.is

Shelf life tests on cod pieces: Effect of supercooling, pickling and gas packaging on quality changes and shelf life / Storage trials on cod loins: Effect of superchilling, brining and modified atmosphere packaging (MAP) on quality changes and sensory shelf-life

The aim of these experiments was to evaluate the effect of supercooling, aerated packaging (MAP) and brine on quality changes and shelf life of cod pieces. The effects of gas packaging and different storage temperatures on the growth of several pathogens and pointing organisms were also investigated. The experiment was carried out in October 2006 at Samherji in Dalvík. After storage (0.6 and 2% salt), the fish was trimmed and the neck pieces were packed in standard 3 kg foam packs (air packs) and in air-conditioned packaging. The gas mixture was adjusted to 50% CO2, 5% O2 and 45% N2. Three pieces (350- 550g) were placed in each tray with a drying mat. After packing, the samples were placed in Matís freezer simulators set at 0 ° C, -2 ° C and -4 ° C. The samples were examined over a four-week storage period. Sensory evaluation, microbial counts and chemical measurements were used to assess quality changes and shelf life. Pickled (2% salt) fish were stored shorter than uncooked (0.6% salt). A comparison of the number of micro-organisms the day after packing showed that the pickled fish contained ten times more cold-resistant micro-organisms than the non-pickled ones. According to sensory evaluation, the shelf life of the pickled fish at -2 ° C was 12-15 days in both air- and gas-packed pieces. In the blunt fish, the effects of gas packaging and supercooling were evident. The shelf life of air-packed pieces was about 11 days at 0 ° C and 14-15 days at -2 ° C. The shelf life of gas-packed pieces, on the other hand, was about 15 days at 0 ° C and about 21 days at -2 ° C. Supercooling of fresh uncooked fish products in air-conditioned packaging can therefore significantly increase shelf life. Gas packing significantly reduced the growth rate of pathogens and microorganisms at low temperatures. Salmonella was most affected, then Escherichia coli and Listeria monocytogenes the least. Under air conditions, L. monocytogenes grew at -2 ° C, but E. coli began to multiply at 5 ° C and Salmonella at 10 ° C.

The aim of these experiments was to evaluate the effect of superchilling, modified atmosphere packaging (MAP) and brining on the quality changes and sensory shelf-life of cod loins. The effect of MAP and different storage temperatures on some pathogenic and indicator bacteria was also tested. These experiments were initiated in October 2006 at Samherji, Dalvík. After brining (0.6 and 2% salt) the fish fillets were trimmed, and loins packed on one hand in 3 kg styrofoam boxes (air) and on the other in MA. The gas mixture used was 50% CO2, 5% O2 and 45% N2. Three pieces (350-550 g) were placed in each tray with an absorbent mat. After packaging the samples were placed in 3 coolers at Matís which were adjusted to 0 ° C, -2 ° C and -4 ° C. Samples were examined over a four-week period. Sensory analysis, microbial counts and chemical measurements were used to determine the quality changes and shelf-life. Brined loins had a shorter shelf-life than unbrined (0.6% salt). Comparison on numbers of microorganisms the day after packaging revealed that the brined pieces contained ten times more microbes than the unbrined ones. According to sensory analysis the shelf-life of the brined loins at -2 ° C was 12-15 days for both air- and MA-packed fish. In the unbrined loins the effects of superchilling and MAP were obvious. The shelf-life of air-packed loins was about 11 days at 0 ° C and 14-15 days at -2 ° C. The shelf-life of MA-packed loins was about 15 days at 0 ° C but 21 days at -2 ° C. Superchilling of unbrined fish under MA can therefore increase the keeping quality considerably. MA packaging clearly decreased the growth rate of pathogenic and indicator bacteria at low storage temperatures. Most effects were seen with Salmonella, then Escherichia coli but least with Listeria monocytogenes. In fact, L. monocytogenes could grow at -2 ° C under aerobic conditions, while proliferation of E. coli was first observed at 5 ° C but 10 ° C for Salmonella.

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