Application of PCR-RFLP analysis on species identification of canned tuna

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.

Current State of Milk, Dairy Products, Meat and Meat Products, Eggs, Fish and Fishery Products Authentication and Chemometrics

Food fraud is a matter of major concern as many foods and beverages do not follow their labelling. Because of economic interests, as well as consumers' health protection, the related topics, food adulteration, counterfeiting, substitution and inaccurate labelling, have become top issues and priorities in food safety and quality. In addition, globalized and complex food supply chains have increased rapidly and contribute to a growing problem affecting local, regional and global food systems. Animal origin food products such as milk, dairy products, meat and meat products, eggs and fish and fishery products are included in the most commonly adulterated food items. In order to prevent unfair competition and protect the rights of consumers, it is vital to detect any kind of adulteration to them. Geographical origin, production methods and farming systems, species identification, processing treatments and the detection of adulterants are among the important authenticity problems for these foods. The existence of accurate and automated analytical techniques in combination with available chemometric tools provides reliable information about adulteration and fraud. Therefore, the purpose of this review is to present the advances made through recent studies in terms of the analytical techniques and chemometric approaches that have been developed to address the authenticity issues in animal origin food products.

Rapid discrimination of the native medicinal plant Adenostemma lavenia from its adulterants using PCR-RFLP

Background

In Taiwan, the aerial part of Adenostemma lavenia (Al) is used in the form of herbal tea or in a folk remedy primarily to mitigate inflammatory conditions in the lungs and liver. Due to the excellent health benefits of Al against inflammation, it has become increasingly crucial and in great demand during the COVID-19 pandemic. However, Al has been found to be adulterated with Wedelia biflora, Sigesbeckia orientalis, and/or Wedelia chinensis because of similarities in appearance and vernacular names.

Methods

This study aimed to develop a PCR-RFLP DNA molecular method for the authentication of Al. The restriction enzyme BsrI was used according to the sequencing and alignment results of PCR products in the ITS2 regions of Al and its adulterants. Gel electrophoresis resulted in the clear separation of Al and its adulterants into two distinct categories.

Results

In conclusion, the PCR-RFLP authentication method developed herein provides an easy, rapid, and accurate method to distinguish Al from its adulterants to assure user health and safety.

Multiplex PCR Assay for Simultaneous Identification of Five Types of Tuna (Katsuwonus pelamis, Thunnus alalonga, T. albacares, T. obesus and T. thynnus)

There is a need to identify the species of similar types of fish, especially those that are commercially sold. Particularly, the price of tuna varies depending on its type, which is difficult to determine as they are sold in cut or processed forms. This study developed a multiplex polymerase chain reaction (PCR) assay to identify the five most common tuna species: bigeye, skipjack, Atlantic bluefin, albacore, and yellowfin tunas. Newly designed species-specific primer sets for these five tuna species were created. Subsequently, the amplicon sizes obtained were 270, 238, 200, 178, and 127 base pairs for bigeye, skipjack, Atlantic bluefin, albacore, and yellowfin tunas, respectively. Each primer’s specificity was further tested using 15 other fish species, and no cross-reactivity was observed. To identify multiple targets in a single reaction, multiplex PCR was optimized to increase its resolution and accuracy. The detection levels of the multiplex PCR assay were confirmed to be 1 pg for all the five tunas. Additionally, it was successfully applied to 32 types of commercial tuna products. Therefore, this multiplex PCR assay could be an efficient identification method for various tuna species.

Identification of Selected Tuna Species in Commercial Products

This study was conducted to develop systems for the identification of four tuna species (skipjack tuna Katsuwonus pelamis, yellowfin tuna Thunnus albacares, bullet tuna Auxis sp. and Atlantic bonito Sarda sp). At first, raw samples of these species and a mix intended as internal control were prepared for the authentication of fish muscle tissue of the genus Thunnus sp., Auxis sp. and Sarda sp. DNA from raw muscle tissue, the mix and samples was extracted with the DNeasy mericon Food Kit (Qiagen GmbH, Hilden, Germany). The concentration and purity of DNA in raw samples were evaluated using a spectrophotometer. Primers and probe sequences were specifically designed to identify the selected species. In addition, primers and a probe for the endogenous 12S rRNA gene were designed to determine the presence of amplifiable fish (especially tuna) DNA in samples. Furthermore, the species specificity of the designed primers and probes was verified in DNA samples of various tuna and bonito species. Limit of detection for the selected species was calculated as well as the coefficient of determination R² and efficiency of real-time PCR testing was determined. To evaluate the developed real-time PCR methods, 70 commercial tuna products were analysed. The results show that mislabelling of fish products can still be encountered and, moreover, the presence of an additional species can be identified.

Procedures for the identification and detection of adulteration of fish and meat products

The addition or exchange of cheaper fish species instead of more expensive fish species is a known form of fraud in the food industry. This can take place accidentally due to the lack of expertise or act as a fraud. The interest in detecting animal species in meat products is based on religious demands (halal and kosher) as well as on product adulterations. Authentication of fish and meat products is critical in the food industry. Meat and fish adulteration, mainly for economic pursuit, is widespread and leads to serious public health risks, religious violations, and moral loss. Economically motivated adulteration of food is estimated to create damage of around € 8 to 12 billion per year. Rapid, effective, accurate, and reliable detection technologies are keys to effectively supervising meat and fish adulteration. Various analytical methods often based on protein or DNA measurements are utilized to identify fish and meat species. Although many strategies have been adopted to assure the authenticity of fish and meat and meat a fish products, such as the protected designation of origin, protected geographical indication, certificate of specific characteristics, and so on, the coverage is too small, and it is unrealistic to certify all meat products for protection from adulteration. Therefore, effective supervision is very important for ensuring the suitable development of the meat industry, and rapid, effective, accurate, and reliable detection technologies are fundamental technical support for this goal. Recently, several methods, including DNA analysis, protein analysis, and fat-based analysis, have been effectively employed for the identification of meat and fish species.

Character-based identification system of scombrids from Indian waters for authentication and conservation purposes

Scombrids are the important component of pelagic fishery resources which include 54 species under 15 genera commonly known as mackerels, bonitos, and tunas. Due to the high commercial value attained, there are real chances of fraudulent substitution by species of inferior value. DNA based species identification methods can be applied to detect product adulteration, as well as to better contribute to the conservation and management of these species by providing accurate species identification independently of the age of the individuals or the tissue processed. In this study, a total of 15 commercially important scombrid species from Indian waters were analyzed. Due to the inadequacy of mitochondrial COI barcoding gene in discriminating between some Thunnus species, cytochrome b sequences were used instead. For all the 15 species, we propose a DNA character-based keys which uses a diagnostic combination of nucleotides and respective probes, including the first character-based keys and probes to differentiate between Thunnus albacares and T. obsesus.

Methodology and application of PCR-RFLP for species identification in tuna sashimi

The Thunnini, or tuna, comprise many species with very different commercial values. The principal raw tuna product on the market is sashimi, for which the species used is difficult to identify through conventional morphological analysis. The present study amplified the cytochrome b gene (Cytb) of 4 major tuna species used for preparing sashimi-yellowfin tuna (Thunnus albacares), southern bluefin tuna (Thunnus maccoyii), bigeye tuna (Thunnus obesus), and Atlantic bluefin tuna (Thunnus thynnus)-and 4 species commonly mislabeled as components of tuna sashimi-albacore tuna (Thunnus alalunga), skipjack tuna (Katsuwonus pelamis), striped marlin (Tetrapturus audax), and swordfish (Xiphias gladius). Polymerase chain reaction (PCR) amplicons were digested with 5 restriction enzymes-Eco147 I, Hinf I, Mbo I, Xag I, and Hind II-to obtain characteristic restriction maps of the above-mentioned raw tuna species and the commonly mislabeled species. An identification method using PCR restriction fragment length polymorphism (PCR-RFLP) was established and validated using 39 commercial tuna sashimi samples, which verified that this method provides results consistent with those obtained by classical sequencing. PCR-RFLP has several advantages over classical sequencing, such as simplicity, speed and accuracy. This technique could support species identification for raw tuna and sashimi.

Dual-output toehold-mediated strand displacement amplification for sensitive homogeneous electrochemical detection of specie-specific DNA sequences for species identification

The determination of specie-specific DNA sequences is a key factor for identification of animal species and detection of meat adulteration. Herein, a simple homogeneous electrochemical biosensor was developed for sensitive detection of specie-specific DNA sequences from meat products based on high efficient and specific dual-output toehold-mediated strand displacement (TMSD). After incubation with target DNA, large amount of methylene blue (electrochemical signal molecule) labeled probes (MB-P) were released from preformed DNA duplex structures by the process of dual-output TMSD amplification. The free MB-P could be further digested by Exonuclease I, and the enzymatic products contain little negative charge could diffuse to the surface of indium tin oxide electrode, generating significantly electrochemical signal. As a result, the designed biosensor showed a broad dynamic range from 0.01 pM to 100 pM, with a low detection limit of 8.2 fM, and ideal selectivity and reproducibility. Meanwhile, the approach exhibited acceptable accuracy for the detection of specie-specific DNA sequences, and possessed the potential application for the identification of animal species from meat products.

Exploring the possible reasons for fish fraud in China based on results from monitoring sardine products sold on Chinese markets using DNA barcoding and real time PCR

Sardine is the common name for several small-sized pelagic species from Clupeiformes, representing a resource of great importance in the global fishery. Great efforts have been made to utilise these species as dried, smoked, and restructured fish products. However, in most of these products, it is quite challenging to identify the individual species as the external features are lost during processing, paving the way for species mislabelling. In this study, DNA barcoding (max, using about 650 bp, described as FDB; mini, of about 192 bp, described as MDB) was used for species identification of 139 specimens taken from 48 sardine products (canned and dried seasoning) randomly collected from local markets in Nanjing, China. Moreover, species specific primers were designed for Sardina pilchardus, with the aim to screen the species of S. pilchardus in mixed products. Results highlighted a success rate of amplification from 38.1% for FDB to 97.9% for MDB. Only one sample failed the Sanger-sequencing, and species-specific real time PCR confirmed the existence of S. pilchardus in the product. A maximum species identity in the range of 98-100% was obtained for all readable sequences and 11 species/genera were identified, belonging to 5 orders (Scorpaeniformes, Perciformes, Clupeiformes, Aulopiformes, Scombriformes). Significant legislative and managerial shortcomings and incentives to facilitate the market access of certain species, together with public indifference, represent the main reasons for fish fraud in China.

Identification of tuna species Thunnus albacares and Katsuwonus pelamis in canned products by real-time PCR method

Tuna species are a popular food among consumers. They are mostly sold as heat-processed canned products on the market. Different quality and price of tuna species can lead the producer to the adulteration of food products. The main difficulties in developing a method for species identification in these fish is the high similarity of DNA sequences among close relative fish species. All complete mitochondrial DNA sequences of skipjack tuna (Katsuwonus pelamis) and yellowfin tuna (Thunnus albacares) were compared to all other mitochondrial DNA sequences of tuna fish deposited in the GenBank. The most variable regions within species were determined and primers and probes were designed in this region for the species-specific DNA amplification of skipjack tuna and yellowfin tuna. Moreover, to check the content of amplifiable DNA of fish (namely tuna) in the sample, primers and a probe of mitochondrial12SrRNAgene in the region of conservative sequence were designed. Real time PCR methods were verified by investigating 51 samples of canned tuna with the declared content of tuna species from the market; the species was confirmed in all tested samples. This method was designed to be suitable for the determination of DNA sequences especially in highly heat treated products.

Overview on Untargeted Methods to Combat Food Frauds: A Focus on Fishery Products

Authenticity and traceability of food products are of primary importance at all levels of the production process, from raw materials to finished products. Authentication is also a key aspect for accurate labeling of food, which is required to help consumers in selecting appropriate types of food products. With the aim of guaranteeing the authenticity of foods, various methodological approaches have been devised over the past years, mainly based on either targeted or untargeted analyses. In this review, a brief overview of current analytical methods tailored to authenticity studies, with special regard to fishery products, is provided. Focus is placed on untargeted methods that are attracting the interest of the analytical community thanks to their rapidity and high throughput; such methods enable a fast collection of “fingerprinting signals” referred to each authentic food, subsequently stored into large database for the construction of specific information repositories. In the present case, methods capable of detecting fish adulteration/substitution and involving sensory, physicochemical, DNA-based, chromatographic, and spectroscopic measurements, combined with chemometric tools, are illustrated and commented on.

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.

Gelatin controversies in food, pharmaceuticals, and personal care products: Authentication methods, current status, and future challenges

Gelatin is a highly purified animal protein of pig, cow, and fish origins and is extensively used in food, pharmaceuticals, and personal care products. However, the acceptability of gelatin products greatly depends on the animal sources of the gelatin. Porcine and bovine gelatins have attractive features but limited acceptance because of religious prohibitions and potential zoonotic threats, whereas fish gelatin is welcomed in all religions and cultures. Thus, source authentication is a must for gelatin products but it is greatly challenging due to the breakdown of both protein and DNA biomarkers in processed gelatins. Therefore, several methods have been proposed for gelatin identification, but a comprehensive and systematic document that includes all of the techniques does not exist. This up-to-date review addresses this research gap and presents, in an accessible format, the major gelatin source authentication techniques, which are primarily nucleic acid and protein based. Instead of presenting these methods in paragraph form which needs much attention in reading, the major methods are schematically depicted, and their comparative features are tabulated. Future technologies are forecasted, and challenges are outlined. Overall, this review paper has the merit to serve as a reference guide for the production and application of gelatin in academia and industry and will act as a platform for the development of improved methods for gelatin authentication.

A single enzyme PCR-RFLP protocol targeting 16S rRNA/tRNAval region to authenticate four commercially important shrimp species in India

Food authenticity is an issue of major concern for food authorities, as mislabeling represents one of the major commercial frauds. In this study, a novel PCR-RFLP protocol was developed as a tool to authenticate four shrimp products of commercial importance belonging to the family, Penaeidae, viz. Litopenaeus vannamei, Penaeus monodon, P. semisulcatus and Fenneropenaeus indicus. PCR amplification was performed targeting 16S rRNA/tRNA^val region having an amplicon size of 530bp using the specific primers for shrimps, 16S-Cru4/16S-Cru3. Subsequent restriction analysis with a single restriction enzyme, Tsp5091, yielded distinct RFLP pattern for each species of shrimps having fragment sizes below 150bp. The unique RFLP patterns were also obtained in processed shrimp products without any degradation or alteration in the major fragments. The method was also validated with commercial shrimp products. Thus, the developed protocol can be performed within 8h using a single enzyme to authenticate four shrimp products of commercial significance.

Development of a qPCR Method for the Identification and Quantification of Two Closely Related Tuna Species, Bigeye Tuna (Thunnus obesus) and Yellowfin Tuna (Thunnus albacares), in Canned Tuna

Bigeye tuna (Thunnus obesus) and yellowfin tuna (Thunnus albacares) are among the most widely used tuna species for canning purposes. Not only substitution but also mixing of tuna species is prohibited by the European regulation for canned tuna products. However, as juveniles of bigeye and yellowfin tunas are very difficult to distinguish, unintentional substitutions may occur during the canning process. In this study, two mitochondrial markers from NADH dehydrogenase subunit 2 and cytochrome c oxidase subunit II genes were used to identify bigeye tuna and yellowfin tuna, respectively, utilizing TaqMan qPCR methodology. Two different qPCR-based methods were developed to quantify the percentage of flesh of each species used for can processing. The first one was based on absolute quantification using standard curves realized with these two markers; the second one was founded on relative quantification with the universal 12S rRNA gene as the endogenous gene. On the basis of our results, we conclude that our methodology could be applied to authenticate these two closely related tuna species when used in a binary mix in tuna cans.

Assessment of DNA quality in processed tuna muscle tissues

Authentication of tuna fish products is necessary to assure consumers of accurate labelling of food products. The quality of species specific DNA crucially affects the efficiency of amplification during the subsequent PCR. The problem in DNA detection in canned products lies in the possibility of the fragmentation of DNA during the processing technologies and the use of ingredients (oil, salt, spice), that may inhibit the PCR reaction. In this study three DNA extraction methods were compared: DNeasy Blood and Tissue Kit, DNeasy mericon Food Kit and Chemagic DNA tissue 10 Kit. The quantity and quality of DNA were evaluated by measuring DNA concentration and ratios A260/A280. Several parameters were estimated: the effect of whole and mechanically treated muscle, sterilization procedure used in canned process (high temperature in combination with high pressure) and addition of raw materials. The highest DNA concentrations were observed in non-processed muscle that is not influenced by the sterilization process. Canned whole muscle demonstrated lower DNA yield, and furthermore, the mechanical treatment (canned ground) resulted in lower values of DNA concentration that was registered by using all three types of DNA extraction kits. DNeasy mericon Food Kit produced DNA of higher concentration in non-processed sample, Chemagic DNA tissue 10 Kit delivered higher DNA yields than kits DNeasy Blood and Tissue Kit and DNeasy mericon Food Kit in canned samples, although the purity was lower, but still within the range 1.7 - 2.0. DNA was considered to be satisfactorily pure in all three types of samples and using all three types of DNA isolation. In case of the samples enriched of ingredients and treated with sterilization process as whole or ground muscle Chemagic DNA tissue 10 Kit produced in all samples (whole and ground muscle) the highest values of DNA concentration, but almost all values of A260/A280 were lower than 1.7. Therefore DNeasy mericon Food Kit appears to be a favorite one, in all samples with whole muscle gives higher values of DNA concentrations than DNeasy Blood and Tissue Kit. Addition of ingredients influenced the DNA yield in terms of decreasing in samples containing vinegar and lemon, but some of the ingredients resulted surprisingly in higher yield of DNA. This was not consistent in whole and ground muscle, and the differences were described also among particular kits. The impact of ingredients was not conclusively approved and their importance to the suitability of extracted DNA for PCR amplification is needed to be discussed in further analysis.

The differentiation of tuna (family: Scombridae) products through the PCR-based analysis of the cytochrome b gene and parvalbumin introns

BACKGROUND

In spite of the many studies performed over the years, there are still problems in the authentication of closely related tuna species, not only for canned fish but also for raw products. With the aim of providing screening methods to identify different tuna species and related scombrids, segments of mitochondrial cytochrome b (cyt b) and nuclear parvalbumin genes were amplified and sequenced or subjected to single-strand conformation polymorphism (SSCP) and restriction fragment length polymorphism (RFLP) analyses.

RESULTS

The nucleotide diagnostic sites in the cyt b gene of five tuna species from Indonesia were determined in this study and used to construct a phylogenetic tree. In addition, the suitability of the nuclear gene that encodes parvalbumin for the differentiation of tuna species was determined by SSCP and RFLP analyses of an intron segment. RFLP differentiated Thunnus albacares and from T. obesus, and fish species in the Thunnus genus could be distinguished from bullet tuna (Auxis rochei) by SSCP.

CONCLUSIONS

Parvalbumin-based polymerase chain reaction systems could serve as an additional tool in the detection and identification of tuna and other Scombridae fish species for routine seafood control. This reaction can be performed in addition to the cyt b analysis as previously described.

Identification of five highly priced tuna species by quantitative real-time polymerase chain reaction

Tunas are economically important fishery worldwide, and are often used for commercial processed production. For effective fishery management and protection of consumers' rights, it is important to develop a molecular method to identify species in canned tuna products rapidly and reliably. Here, we have developed a duplex quantitative real-time PCR (qPCR) for identification of five highly priced tuna species (Thunnus maccoyii, Thunnus obesus, Thunnus albacares, Thunnus alalunga and Katsuwonus pelamis) from processed as well as fresh fish. After amplification and sequencing of seven genetic markers commonly used for species identification, 16S rDNA and control region (CR) of mitochondrial DNA were selected as the reference gene markers for genus Thunnus and tuna species identification, respectively. Subsequently, a 73 bp fragment of 16S rDNA and 85-99 bp fragment of CR were simultaneously amplified from each target species by qPCR. The qPCR efficiency of each reaction was calculated according to the standard curves, and the method was validated by amplification DNA extracted from single or mixed tuna specimen. The developed duplex qPCR system was applied to authenticate species of 14 commercial tuna products successfully, which demonstrated it was really a useful and academic technique to identify highly priced tuna species.

Development of a multiplex PCR-ELISA method for the genetic authentication of Thunnus species and Katsuwonus pelamis in food products

In the present work a PCR-ELISA technique for the authentication of Thunnus species was developed. This method is composed by four systems that can be used in a hierarchical way allowing the identification of several scombroids species; or each individual system independently. The hierarchical strategy, proposes a first step, to assign one sample to the Thunnus genus. Next, if the result is positive, several tests can be applied to assign the sample to some particular species of the Thunnus genus. In the case that the result is negative (absence of Thunnus species), it is possible to verify if Katsuwonus pelamis is included in the sample. The method even allows the detection of mixtures of these species in relatively low amounts (up to 1%). Finally, this method was applied to 11 commercial samples to verify the labelling status of tuna products in the market, detecting that 18% were mislabelling.

Toxin and species identification of toxic octopus implicated into food poisoning in Taiwan

A food poisoning incident due to ingestion of unknown octopus occurred in Taipei in December, 2010. The serum and urine from victims (male 38 and 43 years old) were collected, determined the toxicity, and identified tetrodotoxin (TTX) by high-performance liquid chromatography with tandem mass spectrometry (LC-MS/MS). It was found that only urine contained the trace of TTX. Then, two retained specimen (one without blue ring in the skin and another with small blue ring in the skin) were collected from victims and examined for the toxicity and toxin. Meanwhile, 6 specimens of octopus without blue ring in the skin and 4 specimens of octopus with blue ring in the skin were re-collected from the market. Both retained octopus samples were found to contain TTX. However, re-collected market's octopus without blue ring in the skin did not show to contain TTX the and was identified as Octopus aegina by using the analysis of cytochrome b gene (Cyt b) and cytochrome c oxidase subunit I gene (COI). Only octopus with blue ring in the skin contained TTX and was identified as Hapalochlaena fasciata by using the analysis of Cyt b and COI. Therefore, this octopus food poisoning was caused by toxic octopus H. fasciata and the causative agent was TTX.

PCR-RFLP identification of four Chinese soft-shelled turtle Pelodiscus sinensis strains using mitochondrial genes

A PCR-RFLP method to confirm the identification of four Pelodiscus sinensis strains (Taihu Lake strain, Taiwan strain, Yellow River strain and Japanese strain) was developed and evaluated. In this study, we sequenced and analyzed the partial sequences of mitochondrial NADH4, COX I and NADH5-NADH6 genes of 60 individuals from the four P. sinensis strains. Bgl I, Hpa II and Cla I were selected for cutting NADH4, COX I and NADH5-NADH6 PCR products, respectively, and each strain has its unique restriction band patterns. The result showed that all the 140 samples tested can be correctly identified based on the combination of the three digested fragments pattern. This study provides an effective method to distinguish the four main strains of P. sinensis.

Biogenic amine content, histamine-forming bacteria, and adulteration of pork in tuna sausage products

Twenty-five tuna sausage products were purchased from retail markets in Taiwan. The rates of occurrence of biogenic amines, histamine-forming bacteria, and adulteration by pork and poultry were determined. The average content of various biogenic amines in all tested samples was less than 2.0 mg/100 g (<0.05 to 1.85 mg/100 g). Thirteen histamine-producing bacterial strains isolated from tested samples produced 12.1 to 1,261 ppm of histamine in Trypticase soy broth supplemented with 1.0% L-histidine. Among them, Raoultella ornithinolytica (one strain), Enterobacter aerogenes (one strain), and Staphylococcus pasteuri (two strains) were identified as prolific histamine formers. PCR assay revealed that the adulteration rates were 80% (20 of 25) and 4% (1 of 25) for pork and poultry, respectively, in tuna sausage. The fish species in the tuna sausage samples were identified as Thunnus albacares for 22 samples (88%), Thunnus alalunga for 1 sample (4%), and Thunnus thynnus for 1 sample (4%), whereas the remaining sample was identified as Makaira nigricans (blue marlin).

Liquid chromatography-tandem mass spectrometry determination of the toxicity and identification of fish species in a suspected tetrodotoxin fish poisoning

Suspected tetrodotoxin (TTX) poisoning was associated with eating unknown fish in April 2009 in Taiwan. After ingestion of the fish, symptoms of the victim included perioral paresthesia, nausea, vomiting, ataxia, weakness of all limbs, respiration failure, and death within several hours. The toxicity in the remaining fish was determined, with the mice exhibiting symptoms of neurotoxin poisoning. The implicated fish and deceased victim tissues were analyzed for TTX by liquid chromatography-tandem mass spectrometry. The urine, bile, cerebrospinal fluid (spinal cord), pleural effusion, and pericardial effusion of the victim contained TTX. In addition, the partial cytochrome b gene of the implicated fish was determined by PCR. The DNA sequence in the partial 465-bp cytochrome b gene identified the implicated fish as Chelonodon patoca (puffer fish). These results indicate that people should avoid eating unknown fish species from fish markets where harvested fish may include toxic 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.