DNA-Based Methods for the Identification of Commercial Fish and Seafood Species

Selected tandem mass spectrometry ion monitoring for the fast identification of seafood species

Selected tandem mass spectrometry (MS/MS) ion monitoring (SMIM) is the most suitable scanning mode to detect known peptides in complex samples when an ion-trap mass spectrometer is the instrument used for the analysis. In this mode, the MS detector is programmed to perform continuous MS/MS scans on one or more selected precursors, either during a selected time interval, or along the whole chromatographic run. MS/MS spectra are recorded, so virtual multiple reaction monitoring chromatogram traces for the different fragment ions can be plotted. In this work, a shotgun proteomics approach was applied to the detection of previously characterized species-specific peptides from different seafood species. The proposed methodology makes use of high intensity focused ultrasound-assisted trypsin digestion for ultra fast sample preparation, peptide separation and identification by reverse phase capillary LC coupled to an ion-trap working in the SMIM scanning mode. This methodology was applied to the differential classification of seven commercial, closely related, species of Decapoda shrimps proving to be an excellent tool for seafood product authentication, which may be used by fisheries and manufacturers to provide a fast and effective identification of the specimens, guaranteeing the quality and safety of foodstuffs to consumers.

Interlaboratory evaluation of a real-time multiplex polymerase chain reaction method for identification of salmon and trout species in commercial products

This interlaboratory study evaluated a real-time multiplex polymerase chain reaction (PCR) method for identification of salmon and trout species in a range of commercial products in North America. Eighty salmon and trout products were tested with this method by three independent laboratories. Samples were collected in the United States and Canada, and only the collecting institution was aware of the species declaration. Following analysis with real-time PCR, all three laboratories were able to identify species in 79 of the 80 products, with 100% agreement on species assignment. A low level of fraud was detected, with only four products (5%) found to be substituted or mixtures of two species. The results for two of the fraudulent products were confirmed with alternate methods, but the other two products were heavily processed and could not be verified with methods other than real-time PCR. Overall, the results of this study show the usefulness and versatility of this real-time PCR method for the identification of commercial salmon and trout species.

Advances in DNA-based techniques for the detection of seafood species substitution on the commercial market

Increased worldwide trade and processing of seafood has increased the potential for species substitution on the commercial market. To detect and prevent species substitution, several deoxyribonucleic acid (DNA)-based methods have been developed that can be used to identify species in a variety of food types. For large-scale applications, such as regulatory screening, these methods must be rapid, cost-effective, reliable, and have high potential for automation. This review highlights recent technological advances in DNA-based identification methods, with a focus on seafood species identification in automated, high-throughput settings. Advances in DNA isolation methods include silica-based columns for use in high-throughput operations and magnetic bead particles for increased and targeted recovery of DNA. The three most widely used methods for seafood species identification (polymerase chain reaction [PCR] sequencing, PCR-restriction fragment length polymorphism, and species-specific PCR) will be discussed, with a focus on the incorporation of technologies such as rapid PCR cycling, microfluidic chips, and real-time PCR. Emerging methods, including DNA microarrays and next-generation sequencing will also be explored for their potential to identify seafood species on a large scale. Overall, many of the technological advances discussed here offer complementary properties that will enable species identification in a variety of settings and with a range of products.

High level of mislabeling in Spanish and Greek hake markets suggests the fraudulent introduction of African species

DNA analysis of hake products commercialized in southern European (Spanish and Greek) market chains have demonstrated more than 30% mislabeling, on the basis of species substitution. Tails and fillets were more mislabeled than other products, such as slices and whole pieces. African species were substitute species for products labeled as American and European species, and we suggest it is a case of deliberate economically profitable mislabeling because real market prices of European and American hake products are higher than those of African in Spanish market chains. The presented results suggest fraud detection that disadvantages African producers. Government-mandated genetic surveys of commercial hakes and the use of subsequent statements of fair trade on labels of seafood products could help to reduce fraud levels in a global market of increasingly conscious consumers sensitive to ethical issues.

Evolutionary relatedness of mackerels of the genus Scomber based on complete mitochondrial genomes: strong support to the recognition of Atlantic Scomber colias and Pacific Scomber japonicus as distinct species

Mackerels of the genus Scomber are commercially important species, but their taxonomic status is still controversial. Although previous phylogenetic data support the recognition of Atlantic Scomber colias and Pacific Scomber japonicus as separate species, it is only based on the analysis of partial mitochondrial and nuclear DNA sequences. In an attempt to shed light on this relevant issue, we have determined the complete mitochondrial DNA sequence of S. colias, S. japonicus, and Scomber australasicus. The total length of the mitogenomes was 16,568 bp for S. colias and 16,570 bp for both S. japonicus and S. australasicus. All mitogenomes had a gene content (13 protein-coding, 2 rRNAs, and 22 tRNAs) and organization similar to that observed in Scomber scombrus and most other vertebrates. The major noncoding region (control region) ranged between 865 and 866 bp in length and showed the typical conserved blocks. Phylogenetic analyses revealed a monophyletic origin of Scomber species with regard to other scombrid fish. The major finding of this study is that S. colias and S. japonicus were significantly grouped in distinct lineages within Scomber cluster, which phylogenetically constitutes evidence that they may be considered as separate species. Additionally, molecular data here presented provide a useful tool for evolutionary as well as population genetic studies.

Arginine kinase peptide mass fingerprinting as a proteomic approach for species identification and taxonomic analysis of commercially relevant shrimp species

A proteomic approach aimed at species identification and taxonomic analysis of shrimp species of commercial interest is presented. Six different species belonging to the order Decapoda were considered. Preliminary, two-dimensional gel electrophoresis (2-DE) analysis of the sarcoplasmic proteome revealed interspecific variability in the isoelectric point (pI) of arginine kinase. For this reason, arginine kinase spot was selected as a potential molecular marker and subjected to tryptic digestion followed by matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) peptide mass fingerprinting (PMF) analysis. Arginine kinase PMF allowed the differentiation of the six species studied. Four samples of commercial origin obtained in local markets were analyzed to validate the methodology. The PMF cluster analysis also provided information about the phylogenetic relationships in these species. The application of this methodology may be of interest for the differentiation and taxonomic analysis of shrimp species complementing DNA-based phylogenetic studies.

Identification of European Hake species (Merluccius merluccius) using real-time PCR

A rapid and precise method for identifying European hake (Merluccius merluccius) based on TaqMan technology is presented. The method can be applied to fresh, frozen, and processed fish products to detect the fraudulent or unintentional mislabeling of this species. Specific primers and a minor groove binding (MGB) TaqMan probe were designed for this purpose based on partial sequences of the mitochondrial DNA control region. Combinations of primers and probe concentrations that gave the lowest Ct value and the highest final fluorescence value were selected to carry out efficiency, specificity, and cross-reactivity assays. The method was successfully tested on 31 commercial hake samples. A Ct value of about 16 was obtained when Merluccius merluccius was present; however, the fluorescence signal was not detected most of the time (Ct value 40) or presented significantly higher Ct values (38.2 +/- 0.96) for the nonhake species.