Turid Mørkøre

Feed ration prior to slaughter : a potential tool for managing product quality of Atlantic salmon (Salmo salar)

During a 110-day winter period, five duplicated groups of 50 Atlantic salmon (3.9 kg initial weight) were fed 0.0, 0.25, 0.5, 0.75 and 1.0 times maximum feed intake before slaughter with the purpose of studying body composition and quality related characteristics in raw and smoked salmon fillets. Final weights increased linearly with feed ration from 3.5 to 4.9 kg at ration 0.0 and 1.0, respectively. Decreasing feed ration resulted in a slimmer body shape (i.e., lower condition factor), increased carcass-yield and decreased fillet-yield, and decreased fillet fat content. Although fillet protein content was not significantly affected by ration level, the percent of water-soluble proteins in white muscle was increased by feed ration. Decreased content of free and increased content of protein-bound hydroxyproline in white muscle was found with increasing feed ration. White muscle pH, in post-rigor state, but not at slaughter, decreased with increasing ration level, reflecting in vivo glycogen and post-rigor lactate levels. After filleting, a significant increase of fillet gaping was found with increasing ration. Sensory analyses of smoked fillets revealed that fatness, juiciness and coarseness increased, whereas hardness decreased with increasing feed ration. Further, acidulous flavour and odour in smoked fillet increased significantly. Despite an increased astaxanthin content in raw fillet, the sensory scores for colour intensity decreased and whiteness increased with increasing feed ration. Consequently, reduced ration before slaughter can be a tool for improving slaughter-yield, reducing fat content and gaping in raw fillet, slightly improving colour intensity and changing textural properties of smoked fillet. The costs in terms of lost weight and less fillet-yield will, however, be substantial.

Relation of smoking parameters to the yield, colour and sensory quality of smoked Atlantic salmon (Salmo salar)

The relations between smoking parameters and the characteristics of salmon raw material were investigated with respect to yield, colour, flesh content of phenol and salt, and sensory properties. The fish studied were ocean ranched salmon harvested in Iceland in July 1998 and farmed salmon from Norway slaughtered in October 1998 and April 1999. Seven treatments were applied on fresh or frozen raw material combining dry or brine salting with cold smoking at 20 or 30°C. Electrostatic smoking was tested on dry-salted salmon fillets. The results show a lower yield after filleting and trimming with ocean ranched fish. Although freezing had little effect on yield, total loss was slightly greater, especially for fish with low fat content. Sensory differences were also apparent. The brine salting technique resulted in lower losses. Fish with higher fat content gave a better yield after processing, although careful control of the smoking procedure was required (especially at 30°C) to avoid a case-hardening effect. With brine salting, salt uptake was higher for smaller, leaner fish. The phenol content of flesh depended on the technique and/or smoking temperature used, regardless of the fish studied. However, for a smoking temperature of 30°C, the flesh of smaller, leaner fish showed a higher phenol level. Smoking conditions and preliminary treatment such as freezing produced similar differences in sensory characteristics, regardless of the fish studied, although smaller, leaner individuals appeared to be more sensitive to these processes.

Seasonal variations in growth, feed utilisation and product quality of farmed Atlantic salmon (Salmo salar) transferred to seawater as 0+smolts or 1+smolts

Abstract Seasonal variations in growth, feed utilisation, condition factor (CF), fillet fat content, colour, texture and gaping were studied in farmed Atlantic salmon transferred to seawater after 9 (0+salmon) or 16 months (1+salmon) in freshwater. The fish were weighed in bulk and sampled for quality assessment every second month over a 1-year period (July–July), and feed consumption was recorded daily. During the experiment, body weight increased from 0.20 to 3.37 kg in 1+salmon and from 0.43 to 5.10 kg in 0+salmon. The specific growth rate (SGR) decreased and feed conversion ratio (FCR) increased during late autumn and winter for both salmon groups, but the seasonal variations in SGR and FCR were largest in 1+salmon. The initial CF was 1.1 for both salmon groups. The CF of the 0+salmon stabilised at approximately 1.5 in November, whereas the CF of the 1+salmon averaged 1.5 in May. The fillet fat content increased from 3–4% to 17–19% during the experiment, and the most pronounced fat increase occurred from July–November (12–13% units) in both 0+ and 1+salmon. From November to July, the Roche Colour Card (RCC) score increased from 14.3 to 15.3 in 1+salmon and 15.6 in 0+salmon. Hardness, measured as breaking strength, was highest during the winter period. Breaking strength correlated negatively to SGR in both salmon groups, indicating that fast growth can promote flesh softening in salmon. The degree of fillet gaping was highest during spring and summer. To conclude, seasonal variations were observed in production efficiency and product quality in both salmon groups, but neither growth performance, feed utilisation nor product quality characteristics differed significantly between 0+salmon and 1+salmon when the data were corrected for weight differences.

Effects of -1.5 °C Super-chilling on quality of Atlantic salmon (Salmo salar) pre-rigor Fillets : Cathepsin activity, muscle histology, texture and liquid leakage

The aim of this study was to evaluate the impact of super-chilling on the quality of Atlantic salmon (Salmo salar) pre-rigor fillets. The fillets were kept for 45min in a super-chilling tunnel at -25°C with an air speed in the tunnel at 2.5m/s, to reach a fillet core temperature of -1.5°C, prior to ice storage in a cold room for 4 weeks. Super-chilling seemed to form intra- and extracellular ice crystals in the upper layer of the fillets and prevent myofibre contraction. Lysosome breakages followed by release of cathepsin B and L during storage and myofibre-myofibre detachments were accelerated in the super-chilled fillets. Super-chilling resulted in higher liquid leakage and increased myofibre breakages in the fillets, while texture values of fillets measured instrumentally were not affected by super-chilling one week after treatment. Optimisation of the super-chilling technique is needed to avoid the formation of ice crystals, which may cause irreversible destruction of the myofibres, in order to obtain high quality products.

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.

Relevance of calpain and calpastatin activity for texture in super-chilled and ice-stored Atlantic salmon (Salmo salar L.) fillets

The aim of the present experiment was to measure the protease activities in ice-stored and super-chilled Atlantic salmon (Salmo salar) fillets, and the effect on texture. Pre-rigour fillets of Atlantic salmon were either super-chilled to a core temperature of -1.5°C or directly chilled on ice prior to 144h of ice storage. A significantly higher calpain activity was detected in the super-chilled fillets at 6h post-treatment compared to the ice-stored fillets and followed by a significant decrease below its initial level, while the calpastatin activity was significantly lower for the super-chilled fillets at all time points. The cathepsin B+L and B activities increased significantly with time post-treatment; however, no significant differences were observed at any time points between the two treatments. For the ice stored fillets, the cathepsin L activity decreased significantly from 6 to 24h post-treatment and thereafter increased significantly to 144h post-treatment. There was also a significantly lower cathepsin L activity in the super-chilled fillets at 0h post-treatment. No significant difference in breaking force was detected; however, a significant difference in maximum compression (Fmax) was detected at 24h post-treatment with lower Fmax in the super-chilled fillets. This experiment showed that super-chilling had a significant effect on the protease activities and the ATP degradation in salmon fillets. The observed difference in Fmax may be a result of these observed differences, and may indicate a softening of the super-chilled salmon muscle at 24h post-treatment.

Metabolism, health and fillet nutritional quality in Atlantic salmon (Salmo salar) fed diets containing n-3-rich microalgae.

Microalgae, as primary producers of EPA and DHA, are among the most prominent alternative sources to fish oil for n-3 long-chain PUFA in animal and human nutrition. The present study aimed to assess technical, nutritional and fish health aspects of producing n-3-rich Atlantic salmon (Salmo salar) fish fillets by dietary supplementation of increasing levels of a DHA-producing Schizochytrium sp. and reduced or without use of supplemental fish oil. Atlantic salmon smolt were fed diets with graded levels of microalgae for 12 weeks, during which all fish showed high feed intake rates with postprandial plasma leptin levels inversely correlating with final mean fish body weights. Fish performance was optimal in all experimental treatments (thermal growth coefficient about 4·0 and feed conversion ratio 0·8–0·9), protein digestibility was equal in all diets, whereas dietary lipid digestibility inversely correlated with the dietary levels of the SFA 16 : 0. Fillet quality was good and similar to the control in all treatments in terms of n-3 long-chain PUFA content, gaping, texture and liquid losses during thawing. Histological fluorescence staining and immunofluorescence analysis of salmon intestines (midgut: base of intestine and villi) revealed significant effects on slime, goblet cell production and inducible nitric oxide synthase (iNOS) activity with increasing levels of dietary Schizochytrium sp. supplementation. Microarray analysis did not reveal any signs of toxicity, stress, inflammation or any other negative effects from Schizochytrium sp. supplementation in diets for Atlantic salmon.

Gene Expression Profiling of Soft and Firm Atlantic Salmon Fillet

Texture of salmon fillets is an important quality trait for consumer acceptance as well as for the suitability for processing. In the present work we measured fillet firmness in a population of farmed Atlantic salmon with known pedigree and investigated the relationship between this trait and gene expression. Transcriptomic analyses performed with a 21 K oligonucleotide microarray revealed strong correlations between firmness and a large number of genes. Highly similar expression profiles were observed in several functional groups. Positive regression was found between firmness and genes encoding proteasome components (41 genes) and mitochondrial proteins (129 genes), proteins involved in stress responses (12 genes), and lipid metabolism (30 genes). Coefficients of determination (R2) were in the range of 0.64–0.74. A weaker though highly significant negative regression was seen in sugar metabolism (26 genes, R2 = 0.66) and myofiber proteins (42 genes, R2 = 0.54). Among individual genes that showed a strong association with firmness, there were extracellular matrix proteins (negative correlation), immune genes, and intracellular proteases (positive correlation). Several genes can be regarded as candidate markers of flesh quality (coiled-coil transcriptional coactivator b, AMP deaminase 3, and oligopeptide transporter 15) though their functional roles are unclear. To conclude, fillet firmness of Atlantic salmon depends largely on metabolic properties of the skeletal muscle; where aerobic metabolism using lipids as fuel, and the rapid removal of damaged proteins, appear to play a major role.

Pigment-producing granulomatous myopathy in Atlantic salmon: a novel inflammatory response.

Melanin comprises a complex group of pigmented polymers whose primary function is ascribed to dermal solar protection, but may also have an interesting role in innate immunity. In ectothermic vertebrates, melanogenesis is reported in leukocyte populations, but it is not known if this occurs in connection with inflammatory reactions. Melanin accumulations in ectopic locations, in particular muscle, represent a serious quality problem in salmon production. Here, we investigated such changes for the expression of dopachrome tautomerase and tyrosinase as well as some important immune genes and pathogens. Furthermore, the nature of the pathological changes was addressed by morphological methods. Gene transcripts encoding key enzymes in melanogenesis, suggesting a de novo melanin synthesis in pigmented muscle, were found. MHC class II transcripts were up-regulated and there was no indication of bacterial or viral infection. The histological examination revealed granulomatous inflammation with distribution of MHC class II positive cells and T cells, analogous to the pattern found in mammals. Importantly, in contrast to mammals pigmented cells were contributing in the inflammation. We demonstrate that melanin production occurs in granulomatous inflammation in salmon, revealing a close and hitherto unreported link between the pigmentary and immune systems.

Berry marinades enhance oxidative stability of herring fillets.

Marinating herring fillets in a 50 g/L powder of elderberry, cranberry, or black currant inhibited the oxidation of lipids and proteins and also the degradation of tocopherol. Cranberry and black currant appeared to be more efficient than elderberry in inhibiting the degradation of tocopherol and the formation of ammonium. Elderberry marinades provided the most significant color changes. The injection of fillets with a 5% salt solution resulted in significantly increased levels of carbonyls, ammonium, and biogenic amines, whereas formation of the volatile lipid compounds propanal, hexanal, 2-penten-1-ol, and 1-penten-3-ol was lowest in fillets marinated in black currant following injection of the salt solution. All marinade treatments resulted in a significantly decreased liquid holding ability, coinciding with a lower muscle pH. It is concluded that marinating herring fillets in solutions containing berry powder can enhance the quality and shelf life of the fillets and simultaneously provide the fillets with natural antioxidants beneficial for consumers.