Effects of handling stress and storage conditions on quality of farmed cod (Gadus morhua)
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- Institutt for marin teknikk 
Atlantic cod is a promising species for fish farming in Norway. In order to maintain a high fish quality and achieve higher fish quality, it is necessary toincrease the understanding of pre and post mortem biochemical processes in fish.The effects of pre slaughter handling stress on fish quality have been observed in many studies. Stress and storage temperature had effect on the color and texture of pre rigor filleted farmed cod. The main objectives of this study were to determine effects of handling stress and storage conditions on cod quality by a number of defined quality criteria, and determine activities of selected proteolytic enzymesthat are important for the quality properties. In the first experiment, done in 2008, cod were subjected to crowding stress by restricting the available water volume in combination with forced movement of the fish with continuous sea water supply for 1.5 hour. In experiment 2, done in 2009, making noise “sound effects” on the cover of the reservoir and increasing handling of the fish were applied with the aim of subjecting the fish to a more stressful event than the first experiment. Fish were slaughtered by stunning and bleeding, and then gutted and filleted. Both the control fish and the stressed fishfillets were stored in ice and in a cold room (+5 Cº) for 4 and 8 days in the first experiment. In the experiment 2, fillets were stored in ice for 5 days. Samples collection were done on the day of slaughter for protease activities analysis, stress parameters (plasma cortisol, lactate and glucose), muscle pH while on the day of storage, muscle pH was measured, sampling for quality parameters (water holdingcapacity, solubility properties of proteins) and proteases activities analysis were collected. Results showed that handling stress was confirmed by increase in plasma cortisol, lactate and glucose levels in blood, measured on the day of slaughter. Muscle pH measured on the day of slaughter was significantly higher in the stress fish than in the control fish and muscle pH declined during storage. In experiment 2, increased level of handling stress led to significantly higher WHC in the control fish than in the stress fish. Handling stress and time of storage had significantly negative effecton water-soluble proteins while the interaction of all factors had a negative significant effect on salt soluble proteins and extractable proteins. Handling stress and storage conditions did not have significant effects on general protease activity and amount of TCA soluble peptides. The amount of muscular water-soluble proteins in the enzyme extracts in the initial samples was significantly higher than amount of muscular water-soluble proteins in the enzyme extracts after storage. During storage, activity of cathepsin B- and B+L-like enzymes were relatively stable. Activity of collagenase-like enzymes was significantly reduced during storage while activity of cathepsin D/E varied during storage. Significant correlations between muscle pH, amount of muscular water-soluble proteins and specific proteases activities were found. No significant correlations between quality parameters (WHC, solubility properties of proteins, water content) and specific proteases activities were found, except for significant positive correlations between salt soluble, extractable proteins and activity of cathepsin D/E-like enzymes calculated per g wet weight. Results from sensory analysis in experiment 2 showed that there were significant differences in yellow color and hardness 1 between the control fish and the stressed fish fillets, and no significant differences were found in the other investigated parameters. The significant correlations among specific proteases activities indicated the contribution of specific proteases activities to muscle degradation during postmortem storage. The coming results on proteomic may explain if handling stress really affect on the muscle degradation and/or which types of proteins will be degraded.