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An investigation into the methods of identifying species of canned fish.

Obiettivo

The aim is to enable the enforcement of regulations on the naming of species of tuna and bonito. The aim of the research will be to develop a methodology for separating, analysing and quantifying species specific components of the canned flesh for the procedure to be used for the unequivocal identification of the species.
The project has investigated alternative approaches to solubilising and analysing species specific protein fragments of canned tuna and bonito including possible procedures for optimising the cyanogen bromide method (which leaves proteins selectively at methionine residues) so that these closely related species could be differentiated. Alternative approaches based on possible species differences in the fatty acid composition of the phospholipids were also investigated as well as possible isolation of undergraded deoxyribonucleic acid (DNA) which could be used in species differentiation by applying the relevant DNA analytical technologies. The major part of the study was concerned with investigation into possible methods of releasing from the heat denatured canned flesh, protein residues or fragments which, when separated by electrophoretic or chromatographic techniques showed species related differences in the respective separation profiles.

The established procedure of solubilising heat denatured canned flesh using cyanogen bromide in 70% formic acid was modified at the digestion step, but it was not possible to obtain further differentiation of the tuna and bonito species examined by either conventional isoelectric focusing (IEF) or alternative chromatographic techniques. The cyanogen bromide peptides were analyzed by a number of chromatographic techniques and the separation profiles obtained by ultraviolet (UV) monitoring of the eluates were too variable between replicates of the same species to enable them to be considered for species differentiation.

Alternative methods of partially hydrolysing the heat denatured proteins were investigated. These included N-bromosucinimide, and limited proteolytic digestion by the enzymes, pepsin and trypsin. In all cases poor resolution of the peptides was obtained on IEF. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) has application to species identification but, as it is influenced considerably by the degree of heating, it should be considered more as a complementary technique to the cyanogen bromide procedure for samples exposed to mild heating conditions. For other commercial species of canned fish examined, IEF of the cyanogen bromide peptides and gradient SDS-PAGE are equally effective in differentiating species such as herring (Clupea harengus) and sild (Spattus sprattus) and sardine (Sardina pilchardus) and anchovy (Engraulis encrasicolus).

Preliminary studies suggest that new approaches using DNA analysis and the ratio of fatty acids C20:4 and C20:5 in the triglyceride and phospholipids of the tuna and bonito species should be investigated further.
The initial phase of the work will be preparation of samples of canned flesh from 7 commercially important species of tuna and bonito.

Phase 2 will be an assessment of the potential of different methods of solubilizing heat denatured fish flesh to give species specific residues and of the methodology selected, optimization of the analytical conditions with selected species of tuna and bonito.

Phase 3 will be validation of the methodology to commercially important species of canned tunas and bonitos in Europe.

Phase 4 will be validation of the methodology to species subjected to different degrees of heat processing.

Phase 5 will be the application of other commercial species such as sardine or anchovies and salmon.

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Meccanismo di finanziamento

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Coordinatore

Ministry of Agriculture, Fisheries and Food (MAFF)
Contributo UE
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Indirizzo
135 Abbey Road
AB9 8DG Aberdeen
Regno Unito

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Partecipanti (1)