Reports

Guidelines for precooling of fresh fish during processing and choice of packaging with respect to temperature control in cold chains

Published:

01/12/2010

Authors:

Kristín Líf Valtýsdóttir, Björn Margeirsson, Sigurjón Arason, Hélène L. Lauzon, Emilía Martinsdóttir

Supported by:

AVS Fund of Ministry of Fisheries in Iceland (R-037 08), Technology Development Fund at the Icelandic Center for Research (081304508), University of Iceland Research Fund and EU (contract FP6-016333-2)

Contact

Sigurjón Arason

Chief Engineer

sigurjon.arason@matis.is

Guidelines for precooling of fresh fish during processing and choice of packaging with respect to temperature control in cold chains

The purpose of the guidelines is to assist in the choice between different methods of pre-cooling fresh fish products as well as to assist in the selection of packages with regard to the heat load that the product experiences on its way from producer to buyer. The following pre-cooling methods are discussed: liquid cooling, sludge cooling and skin cooling (CBC, touch and blow cooling). The treatment of products during processing and the effect of different refrigerants on temperature control, quality and shelf life of fillets before packaging the product are also discussed. The guidelines take into account the processing of lean whitefish, such as cod and haddock. The results of research show that a well-designed pre-cooling before packing can result in a shelf life of 3 - 5 days longer due to no pre-cooling before packing. Inadequate fluid exchange during hydraulic cooling with associated cross-contamination can, however, negate the positive effect of pre-cooling. Icelandic fresh fish producers mainly use expanded polystyrene (EPS) and corrugated plastic (CP) boxes for the export of fresh fillets and fillet pieces. Therefore, only the aforementioned packaging types are discussed here. The conclusion is that if the temperature control is inadequate and the temperature fluctuations are high, it is desirable to use foam plastic boxes that provide better thermal insulation than corrugated plastic boxes.

The aim of the guidelines is to provide and assist with choice of different precooling techniques for fresh fish fillets as well as assist with choice of packaging with respect to thermal abuse, which the product experiences during transport and storage from processor to customer. The following precooling techniques are discussed; liquid cooling (LC), slurry ice cooling (SIC) and combined blast and contact cooling (CBCC). In addition, the following is discussed; handling during processing and the effect of applying different cooling media before packaging on temperature control, quality and shelf life of fresh fillets. The guidelines are designed with lean white fish muscle in mind, such as cod and haddock. The results reveal that efficient precooling before packaging can prolong shelf life up to 3 to 5 days compared to no precooling before packaging. If the liquid exchange in the liquid cooler's circulation system is insufficient, cross-contamination can diminish the positive effects of precooling. Icelandic fresh fish processors mainly use expanded polystyrene (EPS) and corrugated plastic (CP) boxes for export of fresh fish fillets. The guidelines are therefore only focused on the above-mentioned packaging types. The conclusion is that if temperature control is unsatisfactory and temperature fluctuations are great, then expanded polystyrene boxes are the preferred alternative because they provide better insulation.

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Reports

The effect of different precooling media during processing and cooling techniques during packaging of cod (Gadus morhua) fillets

Published:

01/04/2010

Authors:

Björn Margeirsson, Hannes Magnússon, Kolbrún Sveinsdóttir, Kristín Líf Valtýsdóttir, Eyjólfur Reynisson, Sigurjón Arason

Supported by:

AVS Fund of Ministry of Fisheries in Iceland, The Technology Development Fund at the Icelandic Center for Research, University of Iceland Research Fund

Contact

Kolbrún Sveinsdóttir

Project Manager

kolbrun.sveinsdottir@matis.is

The effect of different precooling media during processing and cooling techniques during packaging of cod (Gadus morhua) fillets

The purpose of the experiments was to investigate the effect of different refrigerants in pre-cooling before packaging on temperature control, quality and shelf life of cod fillets. The following refrigerants were examined and compared with no special pre-packing pre-packing:

  1. brine with a low salt content, 2) ice cream with a low salt content.

In addition, the effects of using ice mats and dry ice on the storage of the wrecks were investigated. Temperature changes were monitored by temperature sensors at all levels. Samples were quality assessed by sensory evaluation, microbial and chemical measurements for up to 13 days from processing and packaging (16 days from fishing). The fillets were stored in supercooled conditions (below 0 ° C) for most of the storage time. Lower temperatures of slurry ice than brine led to lower fillet temperatures during packing, and the temperature of the liquid brine was found to rise rapidly during processing. Different treatment resulted in a comparable freshness period according to sensory evaluation. However, the use of a liquid brine during pre-packaging pre-packing proved to lead to a shorter shelf life of 1-2 days compared to no pre-cooling or pre-cooling with slush ice. The reasons for this can be traced to the fact that the brine contained a considerable amount of microorganisms, including H2S-producing bacteria which are active producers of trimethylamine (TMA). Comparison of liquid-cooled fillets showed that the use of dry ice prolonged shelf life by 1 day compared to ice mats. The results of microbial and chemical measurements were consistent with these results.

The aim of the experiment was to investigate effects of two cooling media during precooling at processing on temperature control, quality and storage life of cod fillets. The two cooling media compared to no special precooling during processing (NC) were: 1) liquid brine (LC) and 2) slurry ice (SIC). In addition, the influence of using either dry ice or ice packs during storage was studied. The samples were kept at superchilled conditions during most of the trial. The environmental and product temperature history of each group was studied using temperature monitors. The samples were analyzed with sensory evaluation, microbial and chemical methods for up to sixteen days from catch (thirteen days from processing). Lower temperature of the slurry ice than the liquid brine resulted in lower fillet temperature at packaging and the liquid brine temperature increased rapidly during a processing break, which seems to be a weakness of the liquid brine tank. Results from sensory, microbial and chemical analysis all showed that immersing the skinless cod fillets in liquid cooling brine prior to packaging resulted in one to two days reduction of shelf life in comparison with fillets that were not immersed in liquid brine (no cooling) or in slurry ice. This could be attributed to the fact that the cooling brine carried considerable amounts of microbes including H2Sproducing bacteria which are active producers of trimethylamine (TMA). Comparison of the groups receiving liquid cooling showed that dry ice appeared to extend the shelf life of one day as compared to ice packs. The length of the freshness period was, however, similar in all experimental groups according to sensory evaluation. These results were confirmed by total volatile bases (TVB-N) and TMA analysis and microbial counts.

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