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.

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Textural properties of raw Atlantic salmon (Salmo salar) fillets from different origin were studied on different locations of the fillets. Three instrumental methods were applied for evaluation of textural properties. Two methods were based on puncture tests, using flat-ended cylinder or spherical probes measuring the hardness of the fillet. The third method was based on cutting the fillet with a blade and measuring the shear force. Hardness and shear force increased from head to tail, and the location below the dorsal fin was found to be most reliable. The shear force method was found to be more sensitive than the puncture methods and best suited for practical application.

Salmonid fish require long-chain n-3 fatty acids in their diet. The digestibility of different chemical forms of fish oil fatty acids, fed as triacylglycerols, free fatty acids or ethyl esters, was examined in 300 g farmed Atlantic salmon (Salmo salar) using cholestane as an indicator of fat absorption in lieu of the chromium oxide (Cr2O3) which is commonly used as a marker in digestibility studies. It was established that the two digestibility markers gave similar results. Conveniently, cholestane does not require a separate analysis if fatty acids are to be determined by appropriate gas-liquid chromatography. The long-chain polyunsaturated fatty acids were particularly well absorbed, the apparent digestibility being 90-98% when feeding triacylglycerols or free fatty acids. However, the digestibility of monounsaturated fatty acids (75-94%) was lower, and lower still for saturated fatty acids (50-80%). Ethyl esters of fatty acids were significantly less well absorbed (P less than 0.05) than were the corresponding fatty acids in free acid or triacylglycerol form. Irrespective of dietary fat type, only free fatty acids were identified in feces, indicating total hydrolysis of triacylglycerols and ethyl esters.