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

Twenty-three years of PCR-based seafood authentication assay development: What have we learned?

Seafood is a prime target for fraudulent activities due to the complexity of its supply chain, high demand, and difficult discrimination among species once morphological characteristics are removed. Instances of seafood fraud are expected to increase due to growing demand. This manuscript reviews the application of DNA-based methods for commercial fish authentication and identification from 2000 to 2023. It explores (1) the most common types of commercial fish used in assay development, (2) the type of method used, (3) the gene region most often targeted, (4) provides a case study of currently published assays or primer-probe pairs used for DNA amplification, for specificity, and (5) makes recommendations for ensuring standardized assay-based reporting for future studies. A total of 313 original assays for the detection and authentication of commercial fish species from 191 primary articles published over the last 23 years were examined. The most explored DNA-based method was real-time polymerase chain reaction (qPCR), followed by DNA sequencing. The most targeted gene regions were cytb (cytochrome b) and COI (cytochrome c oxidase 1). Tuna was the most targeted commercial fish species. A case study of published tuna assays (n = 19) targeting the cytb region found that most assays were not species-specific through in silico testing. This was conducted by examining the primer mismatch for each assay using multiple sequence alignment. Therefore, there is need for more standardized DNA-based assay reporting in the literature to ensure specificity, reproducibility, and reliability of results. Factors, such as cost, sensitivity, quality of the DNA, and species, should be considered when designing assays.

CRISPR/Cas12-based electrochemical biosensors for clinical diagnostic and food monitoring

Each organism has a unique sequence of nitrogenous bases in in the form of DNA or RNA which distinguish them from other organisms. This characteristic makes nucleic acid-based detection extremely selective and compare to other molecular techniques. In recent years, several nucleic acid-based detection technology methods have been developed, one of which is the electrochemical biosensor. Electrochemical biosensors are known to have high sensitivity and accuracy. In addition, the ease of miniaturization of this electrochemical technique has garnered interest from many researchers. On the other hand, the CRISPR/Cas12 method has been widely used in detecting nucleic acids due to its highly selective nature. The CRISPR/Cas12 method is also reported to increase the sensitivity of electrochemical biosensors through the utilization of modified electrodes. The electrodes can be modified according to detection needs so that the biosensor's performance can be improved. This review discusses the application of CRISPR/Cas12-based electrochemical biosensors, as well as various electrode modifications that have been successfully used to improve the performance of these biosensors in the clinical and food monitoring fields.

Is the metabarcoding ripe enough to be applied to the authentication of foodstuff of animal origin? A systematic review

Food authentication using molecular techniques is of great importance to fight food fraud. Metabarcoding, based on the next-generation sequencing (NGS) technologies, allowing large-scale taxonomic identification of complex samples via massive parallel sequencing of fragments (called DNA barcodes) simultaneously, has become increasingly popular in many scientific fields. A systematic review to answer the question "Is the metabarcoding ripe enough to be applied to the authentication of foodstuff of animal origin?" is presented. The inclusion criteria were focused on the selection of scientific papers (SPs) only applying metabarcoding to foodstuff of animal origin collected on the market. The 23 included SPs were first analyzed with respect to the metabarcoding phases: library preparation (target genes, primer pairs, and fragment length), sequencing (NGS platforms), and final data analysis (bioinformatic pipelines). Given the importance of primer selection, the taxonomic coverage of the used primers was also evaluated. In addition, the SPs were scored based on the use of quality control measures (procedural blanks, positive controls, replicates, curated databases, and thresholds to filter the data). A lack of standardized protocols, especially with respect to the target barcode/s and the universal primer/s, and the infrequent application of the quality control measures, leads to answer that metabarcoding is not ripe enough for authenticating foodstuff of animal origin. However, the observed trend of the SP quality improvement over the years is encouraging. Concluding, a proper protocol standardization would allow a wider use of metabarcoding by both official and private laboratories, enabling this method to become the primary for the authentication of foodstuffs of animal origin.

Rapid PCR-lateral flow assay for the onsite detection of Atlantic white shrimp

The Atlantic white shrimp (Litopenaeus setiferus) is of great economic importance to the United States and risk being substituted with imported species due to a shortage in domestic production. To improve the current methods used for the identification of the Atlantic white shrimp species, we designed and validated a robust multiplex PCR-lateral flow assay for the onsite identification of L. setiferus. The standardized assay was validated using a miniaturized, low-cost PCR instrument with 68 shrimp, prawn, and fish samples, spread over fourteen seafood species. L. setiferus was simultaneously amplified by the multiplex assay to give three visual bands, which distinguished it from other species having either one or two bands on the dipstick. The standardized assay showed 100% inclusivity for target L. setiferus samples, 100% exclusivity for non-target samples and can be completed in less than two hours. The assay standardized in this study can be used for onsite testing of L. setiferus samples at processing facilities, restaurants, and wholesalers' facilities.

Molecular Barcoding: A Tool to Guarantee Correct Seafood Labelling and Quality and Preserve the Conservation of Endangered Species

The recent increase in international fish trade leads to the need for improving the traceability of fishery products. In relation to this, consistent monitoring of the production chain focusing on technological developments, handling, processing and distribution via global networks is necessary. Molecular barcoding has therefore been suggested as the gold standard in seafood species traceability and labelling. This review describes the DNA barcoding methodology for preventing food fraud and adulteration in fish. In particular, attention has been focused on the application of molecular techniques to determine the identity and authenticity of fish products, to discriminate the presence of different species in processed seafood and to characterize raw materials undergoing food industry processes. In this regard, we herein present a large number of studies performed in different countries, showing the most reliable DNA barcodes for species identification based on both mitochondrial (COI, cytb, 16S rDNA and 12S rDNA) and nuclear genes. Results are discussed considering the advantages and disadvantages of the different techniques in relation to different scientific issues. Special regard has been dedicated to a dual approach referring to both the consumer's health and the conservation of threatened species, with a special focus on the feasibility of the different genetic and genomic approaches in relation to both scientific objectives and permissible costs to obtain reliable traceability.

High-Resolution Melting (HRM) Analysis for Rapid Molecular Identification of Sparidae Species in the Greek Fish Market

The red porgy (Pagrus pagrus) and the common dentex (Dentex dentex) are Sparidae species of high commercial value, traded in the Greek market. In some cases, fish species identification from Greek fisheries is difficult for the consumer due to the strong morphological similarities with their imported counterparts or closely related species such as Pagrus major, Pagrus caeroleustictus, Dentex gibbosus and Pagellus erythrinus, especially when specimens are frozen, filleted or cooked. Techniques based on DNA sequencing, such as COI barcoding, accurately identify species substitution incidents; however, they are time consuming and expensive. In this study, regions of mtDNA were analyzed with RFLPs, multiplex PCR and HRM in order to develop a rapid method for species identification within the Sparidae family. HRM analysis of a 113 bp region of cytb and/or a 156 bp region of 16s could discriminate raw or cooked samples of P. pagrus and D. dentex from the aforementioned closely related species and P. pagrus specimens sampled in the Mediterranean Sea when compared to those fished in the eastern Atlantic. HRM analysis exhibited high accuracy and repeatability, revealing incidents of mislabeling. Multiple samples can be analyzed within three hours, rendering this method a useful tool in fish fraud monitoring.

Identification of Fish Species and Targeted Genetic Modifications Based on DNA Analysis: State of the Art

Food adulteration is one of the most serious problems regarding food safety and quality worldwide. Besides misleading consumers, it poses a considerable health risk associated with the potential non-labeled allergen content. Fish and fish products are one of the most expensive and widely traded commodities, which predisposes them to being adulterated. Among all fraud types, replacing high-quality or rare fish with a less valuable species predominates. Because fish differ in their allergen content, specifically the main one, parvalbumin, their replacement can endanger consumers. This underlines the need for reliable, robust control systems for fish species identification. Various methods may be used for the aforementioned purpose. DNA-based methods are favored due to the characteristics of the target molecule, DNA, which is heat resistant, and the fact that through its sequencing, several other traits, including the recognition of genetic modifications, can be determined. Thus, they are considered to be powerful tools for identifying cases of food fraud. In this review, the major DNA-based methods applicable for fish meat and product authentication and their commercial applications are discussed, the possibilities of detecting genetic modifications in fish are evaluated, and future trends are highlighted, emphasizing the need for comprehensive and regularly updated online database resources.

DNA barcoding reveals fraud in commercial common snook (Centropomus undecimalis) products in Santa Marta, Colombia

The common snook Centropomus undecimalis is one of the main commercial fish species in the Caribbean region, including Colombia, where its populations have drastically decreased due to overfishing and environmental degradation. Thus, there is a market imbalance between the availability of snook products and their demand by consumers, which creates an opening for fraudulent actions such as species substitutions. Legislation in Colombia (and most Caribbean countries) lacks effective tools for the easy and rapid detection of frauds. Furthermore, there are very few studies published in scientific journals addressing this issue, of which none include C. undecimalis as the target species. Therefore, in order to investigate the existence of mislabeling in common snook products in Santa Marta, the present study analysed 44 frozen snook fillets from the five commercial brands available in the city. Moreover, 15 fresh snook fillets from six of the main fish markets were also analysed. To discover the frequency of possible frauds in labeling, samplings were carried out in July, September and November of 2019. Sample analyses involved the identification of each fillet at species level through molecular barcodes (16S-rRNA and COI), whose sequences were verified using BLAST and BOLD, and corroborated by a phylogenetic analysis. As a result, an astonishing 98% of the supermarkets fillets were found to be fraudulent, contrasting with a single case registered in the fish shop samples. The species used to substitute snook include the Pacific bearded brotula Brotula clarkae (38 samples), the Nile perch Lates niloticus (4 samples) and the acoupa weakfish Cynoscion acoupa (1 sample). Based on these results, there is a high rate of fraudulent labeling in the marketing of common snook in the city of Santa Marta, which calls for urgent actions to be taken by the corresponding authorities.

Identification and Authentication of Commercial Mi-iuy Croaker (Miichthys miiuy) Products by Two PCR-Based Methods

ABSTRACT

Mi-iuy croaker (Miichthys miiuy) is one of the most important ingredients of Korean cuisine and, thus, has a high economic value. However, the similar morphological traits among croaker fish belonging to family Sciaenidae are often exploited for seafood fraud. In this study, an M. miiuy-specific primer set was designed and further improved by the development of a rapid and cost-effective duplex PCR method. The specificity of M. miiuy-specific duplex PCR was tested using 22 seafood species, and no cross-reactivity was observed. The sensitivity of the PCR assay was found to be 0.1 ng/μL. For the first time, labeling compliance of 43 commercial mi-iuy croaker products was verified using both full DNA barcoding and M. miiuy-specific duplex PCR methods. For species identification, BOLDSYSTEMS and GenBank database were screened with the consensus sequences of each PCR product as a query. This identification result was further confirmed using the M. miiuy-specific duplex PCR method. The findings of this study revealed that principal species substituted were law croaker (Pseudotolithus senegallus, n = 4), bigeye croaker (Micropogonias megalops, n = 3), whitemouth croaker (Micropogonias furnieri, n = 1), and tigertoothed croaker (Otolithes ruber, n = 1). A significant percentage (21%) of mislabeling was present in commercial mi-iuy products sold on the South Korean market.

HIGHLIGHTS

Canning Processes Reduce the DNA-Based Traceability of Commercial Tropical Tunas

Canned tuna is one of the most widely traded seafood products internationally and is of growing demand. There is an increasing concern over the vulnerability of canned tuna supply chains to species mislabelling and fraud. Extensive processing conditions in canning operations can lead to the degradation and fragmentation of DNA, complicating product traceability. We here employed a forensically validated DNA barcoding tool (cytochrome b partial sequences) to assess the effects of canning processes on DNA degradation and the identification of four tropical tuna species (yellowfin, bigeye, skipjack and longtail tuna) collected on a global scale, along their commercial chains. Each species was studied under five different canning processes i.e., freezing, defrosting, cooking, and canning in oil and brine, in order to investigate how these affect DNA-based species identification and traceability. The highest percentage of nucleotide substitutions were observed after brine-canning operations and were greatest for yellowfin and skipjack tuna. Overall, we found that DNA degradation significantly increased along the tuna canning process for most specimens. Consequently, most of the specimens canned in oil or brine were misidentified due to the high rate of nucleotide substitution in diagnostic sequences.

How Fishy Is Your Fish? Authentication, Provenance and Traceability in Fish and Seafood by Means of Vibrational Spectroscopy

Food authenticity, traceability and provenance are emerging issues of major concern for consumers, industries and regulatory bodies worldwide. In addition, both food safety and security are an intrinsic component of food quality where the above issues are key in modern traceability and management systems. It has been reported that substitution of a high-quality species by less expensive ones might be a frequent practice in seafood products such as fish and shellfish. In this type of products, the source (e.g., origin) and identification of the species are complex. Although different countries have implemented strict regulations and labelling protocols, these issues still are of concern. This article briefly reviews some of the most recent applications of vibrational spectroscopy (near and mid infrared, Raman) combined with chemometrics to target some of these issues in the seafood and fish industries.

What is in commercial cat and dog food? The case for mercury and ingredient testing

Commercial pet foods should be safe for long-term feeding. However, recent recalls and lawsuits have eroded public trust in pet food companies and products. Recent studies have identified high concentrations of mercury, a potent neurotoxin, in pet food products. Here we posit that pet food products require independent testing to verify safety and compliance with developed Food and Drug Administration and Association of American Feed Control Officials standards, and initiate a discussion as to why including quantification of mercury and methylmercury, as well as the identification of adulteration, are important to such testing protocols. The outcomes of these discussions will be multi-faceted: initiating the impetus to investigate the quality and label accuracy of pet foods; ensuring product safety; promoting transparency within the pet food industry; informing veterinary practices regarding pet food recommendations; providing data for evidence-based policy and regulatory enforcement; and working toward fulfilling the National Research Council's call for research that identifies levels of contaminants in animal feeds and residues in human foods.

DNA Barcoding Revealed Mislabeling and Potential Health Concerns with Roasted Fish Products Sold across China

HIGHLIGHTS

75.5% of products were identified as species outside the expected family. Six products were identified as containing multiple species from distinct families. Species from distinct families were verified in products of same brand for six groups. Identification of potentially toxic pufferfish species highlighted health concerns.

Comparison of real-time PCR methods for quantification of European hake (Merluccius merluccius) in processed food samples

The quantification of species in commercial products is limited by analytical shortcomings, as most of them provide semiquantitative results. An exception is real-time PCR, which can provide quantitative results using hybridization probes. In the present work, this technique has been applied to the absolute, absolute-relative and relative quantification of the most valued hake species in European markets, Merluccius merluccius (European Hake). The best quantification results for this species in binary mixtures with non-target species (Merluccius capensis) and using a species-specific real-time PCR MMER_VIC system was achieved using a relative quantification approach (MLL as reference system). Absolute quantification using the MLL nuclear system has been demonstrated as appropriate for the quantification of the Merluccius genus in food model samples. This study reveals the impact of different reference systems (MLL and HAKE) in the absolute-relative and relative quantification approaches, showing that the nuclear MLL system performed better than the mitochondrial HAKE system.

Establishment of mink heart identification method based on mitochondrial cytochrome b gene and development of its detection kit

In this study, the mink heart mitochondrial DNA was used as the target gene to design the specific primers of mink heart mtDNA Cytb, the extraction and detection reagents of mink heart DNA were developed using DNA fingerprinting technique, and the specificity, reproducibility, and stability of the reagents were investigated. Molecular cloning and sequencing technique were used to clone the standard substance of mink heart DNA detection, then a DNA fingerprint detection method of mink heart and the quality standard for mink heart were established, and a DNA detection kit of mink heart was developed. The results showed that the structure of DNA extracted from mink heart by self-developed reagents was complete, and both the concentration and purity of DNA were high. A specific amplification band of the original mink samples was found at 337 bp. The sequence of mink heart DNA was consistent with that of mink heart mtDNA specific fingerprint region. The mink heart DNA fingerprint identification method established, in this study, is accurate and reliable, and the procedure of the developed DNA kit is easy, the results obtained using this kit is stable and the method is suitable for popularization and application.

Quantitative analysis of Alaska pollock in seafood products by droplet digital PCR

A highly accurate quantitative method, based on the new technique, droplet digital PCR (ddPCR), was applied to determine the content of Alaska pollock (Gadus chalcogrammus) in seafood products. Using this method, we found a linear relationship among raw sample weight, DNA concentration and DNA copy number. We also established a formula to calculate the raw sample weight, based on the number of DNA copies. To confirm the accuracy and applicability of this method, mixed samples of known composition were analyzed. Results from this study indicated that the ddPCR method described is suitable for quantifying Alaska pollock in seafood products and has the potential applied to a variety of tasks in food quality certification.

Molecular authentication of Pargo fillets Lutjanus purpureus (Perciformes: Lutjanidae) by DNA barcoding reveals commercial fraud

ABSTRACT The Caribbean Red Snapper (Pargo) Lutjanus purpureus is the most economically important snapper in Brazil, which is sold, among other forms, as frozen fillets. During the process of transformation into fillets there is the removal of the distinctive morphological traits, being able to favor the substitution by less valued species. In addition, there is no national legislation requiring the insertion of the specific name on the product label. However, according to a Normative Instruction (IN N ° 29/2015 MAPA) that correlates the common and specific names of the products destined to the national trade, in Brazil only L. purpureus and L. campechanus can be denominated “Pargo”. Thus, the DNA barcode tool was used to identify the fillets sold in north of Brazil, labeled “Pargo”, with the aid of sequences from the public and control databases. The results showed that among 142 fillets examined, 78% was identified as L. purpureus and 22% as Rhomboplites aurorubens, a snapper with low commercial value in the country, revealing commercial fraud. The molecular identification method successfully used in this study to authenticate fillets snappers may also be used by surveillance authorities in the quality control of processed fish products, towards ensuring consumer rights.

Application of molecular tools to elucidate the microbiota of seafood

The aim of this review is to present the methodologies currently applied to identify microbiota and pathogens transmitted to humans through seafood consumption, focusing on molecular techniques and pointing out their importance, advantages, disadvantages and applicability. Knowledge of available techniques allows researchers to identify which technique best fits their expectations. With such discernment, it will be possible to infer which disadvantages will be present and, therefore, not interfering with the final result. Two methodologies can be employed for this purpose, dependent and independent cultures. However, the dependent culture has certain limitations that can be solved through the independent cultivation techniques, such as PCR, PFGE and NGS, especially through the sequencing of the 16S rRNA region, providing a complete view of microbial diversity. These have revolutionized microbiological knowledge, mainly because they allow for the identification of uncultivable micro-organisms, which represent a substantial portion of total micro-organisms, making it possible to elucidate not yet described taxa which may display pathogenic potential, besides quantifying microbial communities, microbiota genetics, translated proteins and produced metabolites. In addition, transcriptomic and metabolomic techniques also allow for the evaluation of possible impacts that microbial communities may create in their environment, as well as the determination of potential pathogenicity to humans.

A rapid real-time PCR method to differentiate between mottled skate (Beringraja pulchra) and other skate and ray species

Skates and rays are commercially important fish in South Korea, and among them, Beringraja pulchra has the highest economic value. However, the similar morphological traits among skates and rays are often exploited for seafood fraud. Here, we designed both Beringraja pulchra-specific and skate-universal primer sets, capable of detecting short sequences in the cytochrome oxidase subunit I gene, and developed highly sensitive and reliable quantitative real-time PCR (qPCR) assays to differentiate between Beringraja pulchra and other skate and ray species. AΔCq method based on differences in the amplification efficiency was developed, validated, and then used to confirm the presence of Beringraja pulchra in twenty-six commercial skate products. The averageΔCq value obtained for other skate species (18.94 ± 3.46) was significantly higher than that of Beringraja pulchra (1.18 ± 0.15). For on-site applications, we developed an ultra-fast qPCR assay, allowing for completion of the entire analytical procedure within 30 min.

Modern analytical methods for the detection of food fraud and adulteration by food category

This review provides current information on the analytical methods used to identify food adulteration in the six most adulterated food categories: animal origin and seafood, oils and fats, beverages, spices and sweet foods (e.g. honey), grain-based food, and others (organic food and dietary supplements). The analytical techniques (both conventional and emerging) used to identify adulteration in these six food categories involve sensory, physicochemical, DNA-based, chromatographic and spectroscopic methods, and have been combined with chemometrics, making these techniques more convenient and effective for the analysis of a broad variety of food products. Despite recent advances, the need remains for suitably sensitive and widely applicable methodologies that encompass all the various aspects of food adulteration. © 2017 Society of Chemical Industry.

Species identification of bivalve molluscs by pyrosequencing

BACKGROUND

The increase in seafood consumption and the presence of different species of bivalves on the global markets has given rise to several commercial frauds based on species substitution. To prevent and detect wilful or unintentional frauds, reliable and rapid techniques are required to identify seafood species in different products. In the present work, a pyrosequencing-based technology has been used for the molecular identification of bivalve species.

RESULTS

Processed and unprocessed samples of 15 species belonging to the bivalve families Pectinidae, Mytilidae, Donacidae, Ostreidae, Pharide and Veneridae were analysed and correctly identified by the developed pyrosequencing-based method according to the homology between query sequences of the 16S ribosomal RNA (16S rRNA) and cytochrome c oxidase I (COI) genes and their correspondent reference libraries. This technique exhibits great potential in automated and high-throughput processing systems, allowing the simultaneous analysis of 96 samples in shorter execution and turnaround times.

CONCLUSIONS

The correct identification of all the species shows how useful this technique may prove to differentiate species from different products, providing an alternative, simple, rapid and economical tool to detect seafood substitution frauds. © 2016 Society of Chemical Industry.

Assessment of the labelling accuracy of spanish semipreserved anchovies products by FINS (forensically informative nucleotide sequencing)

Anchovies have been traditionally captured and processed for human consumption for millennia. In the case of Spain, ripened and salted anchovies are a delicacy, which, in some cases, can reach high commercial values. Although there have been a number of studies presenting DNA methodologies for the identification of anchovies, this is one of the first studies investigating the level of mislabelling in this kind of products in Europe. Sixty-three commercial semipreserved anchovy products were collected in different types of food markets in four Spanish cities to check labelling accuracy. Species determination in these commercial products was performed by sequencing two different cyt-b mitochondrial DNA fragments. Results revealed mislabelling levels higher than 15%, what authors consider relatively high considering the importance of the product. The most frequent substitute species was the Argentine anchovy, Engraulis anchoita, which can be interpreted as an economic fraud.