Capture-based aquaculture of Atlantic cod (Gadus morhua L.) in Greenland – Sustainable distribution of superchilled, frozen and refreshed products

Jonas Steenholdt Sørensen*

*Corresponding author for this work

Research output: Book/ReportPh.D. thesis

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Abstract

Atlantic cod (Gadus morhua L.) has for centuries been an important species for the Greenlandic fisheries, and traditionally the value-added process has contributed to a large numbers of local jobs. In the period following the last major cod fisheries around 1990 in Greenlandic waters, the value-added processing was reduced and almost exclusively focused on headed and gutted whole cod, which were frozen in blocks and shipped to China for further processing. This was a consequence of cheaper labour in China and low sales prices for cod products in the primary markets in Europe. To optimise product quality and restore local workplaces, Royal Greenland has chosen to rethink the entire catch and value-added processing for cod in Greenland. This has been done with some inspiration from the salmon farming industry in Norway. The new process is referred to as Nutaaq® ("the new" in Greenlandic) and can best be described as capture-based aquaculture, where the cod are caught in the Greenlandic fjords, transferred to net cages where they are stored for two to four weeks without feeding. After this starvation period, the cod are transported by well boats to a processing plant, where the cod are slaughtered, filleted and either frozen or distributed fresh. The purpose of this PhD project has been to investigate whether the new production method for cod in Greenland can contribute to increased food quality, longer shelf-life and reduced food waste and losses? The significance of the changed production method was investigated in a study where the difference between traditionally caught and processed cod was compared with capture-based aquaculture produced cod during a frozen storage at -20 ° C. Further, the effect of frozen storage at -20, -40, and -80 °C was investigated for cod produced using capture-based aquaculture. After a freezing period of three, six, nine and twelve months, respectively, cod fillets from each of the two production methods were examined using hyperspectral images to determine colour and blood concentration, texture measurement, water holding capacity, salt soluble protein, and sensory profiling. Two other studies focused on shelf-life of fresh and thawed cod, respectively. The fresh cod was stored under four different storage conditions: (i) iced and packed in atmospheric air, (ii) superchilled and packed in atmospheric air, (ii) iced in modified atmospheric packing (MAP with 40 % CO2 and 60 % N2), and (iv) superchilled in MAP. The thawed cod was stored in ice (+0.4 °C), at +1.4 °C and +3 °C in atmospheric air as well as iced and at +3 °C in MAP. The shelf-life was determined by sensory evaluation and compared with the chemical and microbiological changes during storage. After frozen storage at -20 ° C for three months, the cod caught and processed using capture-based aquaculture had firmer texture compared to conventionally captured and processed cod. In addition to a better texture, the bleeding was more efficient as it was ensured that all the cod were decapitated in a rested state. For CBA slaughter and processing could be better controlled as live cod was available and pumped into the plant according to the available working capacity. In addition, the factory used for CBA had the possibility to better rinse the cod after decapitation before the bleeding process due to better spacing. As a result of this, the total number of bacteria, and in particular the number of H2S-producing bacteria, was significantly reduced compared to cod bled with gill cuts. Shipping of fresh, capture-based aquaculture cod from Greenland for the European market requires a long shelf-life, as transport is primarily by container ship, which often has a transit time of 8-12 days. Storing the iced cod in air gave a sensory shelf-life of 15 days and, when replacing the air with MAP, the shelf-life was extended to 22 days. Superchilling of -1.7 °C further increased the shelf-life, and after 32 days of storage, there was no evidence of sensory spoilage of the fish stored in air or MAP. The combination of superchilling and MAP resulted in a low bacteria concentration of 3.9 log CFU/g. Common to all treatments in the study was that time for sensory spoilage correlated with the time to reach a pH value above 7.0, a TVBN concentration of more than 35 mg-N/100g of fish and a TMA concentration of more than 20 mg-N/100 g fish. For superchilled cod fillets stored in air, a bacteria concentration above 7.0 log CFU/g was observed towards the end of the storage trial, but without the cod fillets being sensory spoiled. In order to elucidate how there could be a high concentration of bacteria without the cod being spoiled, the correlation between the growth of Photobacterium spp., Shewanella spp., Pseudomonas spp. and TVBN formation was studied as an indicator of the spoilage activity. This showed that the spoilage activity was significantly higher in Photobacterium spp. than for the other two genera and that high concentrations of Pseudomonas spp. of 7.0 log CFU/g producing very little TVBN. The formation of TVBN in the fresh cod fillets was solely formed by Photobacterium spp. and P. carnosum was identified as the specific spoilage organism for chilled cod from Greenland stored both aerobically and in MAP. The shelf-life of the frozen cod from capture-based aquaculture depended on the temperature. By lowering the temperature from -20 °C to -40 °C, the high-quality life was extended from 4-6 months to more than 12 months. The shelf-life was determined as the time until the water holding capacity was lower than 65 % and the percentage of the salt-soluble proteins at the same time was less than 70 %. The maximum shelf-life was extended from 7-10 months at -20 °C to a minimum of 12 months by lowering the temperature to -40 °C. The maximum shelf-life was indicated when the levels were <60% for both water holding capacity and salt soluble proteins. A significant sensory difference was observed between capture-based aquaculture produced cod and the conventionally produced cod when storing the cod for 12 months at -20 °C. The difference was particularly evident when assessing the texture as well as the metal taste for the cooked cod, and at the same time, a softer texture was observed in the raw fillet. The shelf-life of thawed fillets was investigated for cod from capture-based aquaculture production and previously stored at -20 °C for five months. Keeping the cod in in ice and storing in air resulted in sensory shelf-life of 19 days and compared to the fresh cod, the pH level and bacterial count were higher at the time of sensory spoilage. When replacing air with MAP, the shelf-life was significantly extended, and after 32 days of storage the cod was not spoiled at +0.4 or +2.9 ° C. In contrast to cod from several other countries the thawed MAP cod from capture-based aquaculture in Greenland had a low drip loss of <3.6 %. The research-based results from this PhD project have led Royal Greenland, at the processing plant in Cuxhaven, Germany, to market a new product, "Chilled selection", based on frozen and thawed, capture-based aquaculture iced cod sold with a 10-day shelf-life. The commercial shelf-life of frozen cod has been further been reduced to better match the results obtained from this PhD project. The implementation of the finding from this PhD project and the choice of optimal distribution and sales channels can help reduce food loss in the retail and consumer stages of the food supply chain. Simulations based on data collected from European retailers showed that by switching from fresh MAP cod to thawed and iced cod packed in air, the food loss would be reduced by up to 80 %. Important future perspectives include studies to elucidated whether the fishery season has an impact on texture of cod fillets and whether the texture obtained is due to the CBA production form or genetic differences between cod from Greenland and other regions including Iceland and Norway. A better understanding of the texture of the raw material at different season may illuminate the impact of this texture on the frozen shelf-life of the cod. With the frozen raw material, there is a risk of contraction due to thawed rigor mortis; such an event could reduced the fillet sensory quality. Therefore, it would be interesting to understand the optimum thawing procedure, thereby ensuring the most optimal treatment for Royal Greenland's new cod product.
Original languageEnglish
Place of PublicationKgs. Lyngby
PublisherTechnical University of Denmark
Number of pages156
Publication statusPublished - 2020

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