Part of our work aims at studying the modifications that proteins suffer in foods and use them as markers to estimate the origin and history of the product. Proteomics is a powerful approach to do this: comparison of the two-dimensional (2-D) maps of the intact and treated samples would permit to identify marker spots so that in the future it may be possible to estimate the treatment a foodstuff has suffered by examining its 2-D protein map or just the selected markers. This work summarizes some of our previous studies showing the application of proteomics to the (i) identification of species and muscle tissues, (ii) characterization of post-mortem changes in arctic and tropical species, and (iii) study of the effect of some additives during the processing of fish muscle.
Raw, cooked, fried, smoked and gravad (brine-cured) products were analyzed by Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) of proteins and by randomly amplified polymorphic DNA (RAPD) in order to identify the species used in their manufacture. The discriminatory power of SDS-PAGE was dependent primarily on the composition and secondarily on the size of the gels: the Laemmli buffer system with 15% acrylamide and 0.087% piperazine diacrylamide separating gels resolved more discriminant protein bands than any of the commercial gels tested. Some of the processing conditions induced alterations in the protein patterns that made identification dubious. Differentiation even between closely related species was easier by RAPD than by SDS-PAGE. Neither the processing conditions nor the tissue from which the DNA was extracted had a significant effect on the RAPD profiles. For identifications based on SDS-PAGE, one should use an optimized gel composition and separate the sample under analysis in the same gel as the references. For RAPD-based identifications, the unknown sample should be amplified together with reference samples and separated in the same gel.
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