Nitrogen Factors for Atlantic Salmon, Salmo salar, farmed in Scotland and in Norway and for the derived ingredient, “Salmon Frame Mince”, in Fish Products.
Peter Colwell, Stephen L. R. Ellison, Michael J. Walker, Selvarani Elahi, Duncan Thorburn Burns and Kirstin Gray
Pre-packed named fish products are required to be labelled with a declaration of the amount of named fish present as a percentage of the final weight of the product, (quantitative ingredient declaration, QUID). The basis of independent analytical assessment of QUID claims for fish is comparison of the fish-specific nitrogen content of a particular food sample with the known species nitrogen content, the “nitrogen factor”. The only extant species nitrogen content datum for Atlantic salmon, Salmo salar, is that reported in 1973 and it has been claimed that this nitrogen factor is not representative of modern farmed Atlantic salmon. In addition, there is no published nitrogen factor for the commercial ingredient derived by machine recovery in minced form of the residual salmon flesh remaining on the salmon “frames" after removal of the fillets. Pursuant to his statutory duties, the Government Chemist instigated at the request of both trade and enforcement interests, a review of the appropriate nitrogen factors for farmed Atlantic salmon and salmon frame mince. We present data confirming that the 1973 nitrogen factor is not appropriate for farmed Atlantic salmon and suggest that the estimation of salmon content should be based on nitrogen factors expressed on a fat-free basis. Dumas nitrogen factors on a fat-free basis for various cuts of Norwegian and Scottish farmed salmon are given (Table 7) and a general Dumas factor, on a fat-free basis of 3.80 (3.75 Kjeldahl) is suggested. For salmon frame mince a general factor, on a fat-free basis, of 2.85 (2.81 Kjeldahl) is suggested.
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