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Comparison of methods of differentiating between fresh and frozen-thawed fish or fillets
Duflos, G.; Le Fur, B.; Mulak, V.; Becel, P.; Malle, P. (2002). Comparison of methods of differentiating between fresh and frozen-thawed fish or fillets. J. Sci. Food Agric. 82(12): 1341-1345
In: Journal of the Science of Food and Agriculture. Wiley: London. ISSN 0022-5142, more
Peer reviewed article  

Available in  Authors 

Keywords
    Fish; Fish fillets; Freezing storage; Thawing; Marine

Authors  Top 
  • Duflos, G.
  • Le Fur, B.
  • Mulak, V.
  • Becel, P.
  • Malle, P.

Abstract
    Freezing is an efficient way of storing fish. Objectively though, it is very hard to determine whether a fish has been previously frozen. Following an appraisal of various methods, we selected a physical determination (torrymeter), a physiological examination (eye lens) and three enzymatic assays (-glucosidase, -N-acetylglucosaminidase and -hydroxyacyl-CoA-dehydrogenase) and applied them to three species: plaice (Pleuronectes platessa), whiting (Merlangus merlangus) and mackerel (Scomber scombrus). We also compared the results obtained following slow and rapid freezing and investigated how spoilage affects the torrymeter measurements and -glucosidase assay values. For whole fish the physical method using the torrymeter is a reliable indicator. For fish fillets we recommend the enzymatic method using the -glucosidase assay, which should be accompanied by measurement of the freshness to avoid confusing a frozen-thawed fish and a fish in an advanced stage of spoilage. The values noted for fresh and thawed whiting and plaice indicated cut-off values of 0.15 for whiting and 0.5 for plaice, above which it can be asserted that the sample had been frozen.

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