A method for rapid identification of imported Atlantic salmon and domestic freshwater rainbow trout based on specific elements

Abstract

The present invention discloses a method for rapidly distinguishing imported Atlantic salmon, seawater rainbow trout, and domestic freshwater rainbow trout based on specific elements. The method involves taking a sample of the salmon or rainbow trout to be tested and measuring its boron and thallium content. If the thallium content is less than 1 μg / kg and the boron content is between 0.050 and 1.5 mg / kg, the sample is imported Atlantic salmon or seawater rainbow trout. If the thallium content is between 2 and 10 μg / kg, or the boron content is extremely low or undetectable, the sample is domestic freshwater rainbow trout. This method does not require the establishment of a database; it only requires measuring the thallium and boron content in the sample. The two element contents can be used to determine whether the sample is freshwater rainbow trout. The detection time is short, requiring only a few hours, and the misidentification of imported seawater farmed rainbow trout as freshwater rainbow trout is avoided.

Description

Technical Field

[0001] The invention belongs to the field of detection, and in particular relates to a method for quickly identifying imported Atlantic salmon and domestic freshwater rainbow trout based on specific elements. Background Art

[0002] In 2018, the China Aquatic Products Circulation and Processing Association, in collaboration with several companies, developed the "Raw Salmon" group standard, which defines salmon as a general term for salmonids, encompassing most species of salmonids, including Atlantic salmon, rainbow trout, coho salmon, and king salmon. This standard has garnered widespread public attention. The salmon sold in my country primarily consists of imported Atlantic salmon and domestically farmed rainbow trout (Oncorhynchus mykiss), known as "freshwater salmon." Salmon has small scales, few bones, an orange-red flesh, and a delicious texture. It is rich in unsaturated fatty acids, which can effectively lower blood lipids and cholesterol, and prevent cardiovascular disease. In recent years, with the improvement of living standards and changes in lifestyles among Chinese residents, the popularity of raw and semi-raw salmon has increased.

[0003] Atlantic salmon are primarily found in the waters where the Atlantic, Pacific, and Arctic Oceans meet. They are cold-water, highly migratory fish, primarily produced in high-latitude regions such as Canada, Norway, Japan, and Denmark. Norway boasts the largest salmon production. It is generally believed that salmon that inhabit colder ocean regions have a higher fat content, are more robust, and have a more flavorful texture. Therefore, the higher the latitude of the salmon's origin, the better its quality. Salmon from colder waters in Northern Europe, such as Norway and the Faroe Islands, fetches higher prices in the market, while salmon from other origins is less expensive.

[0004] Rainbow trout (Oncorhynchus mykiss), a member of the Salmonidae family (Salmonoidea), is known as the "rainbow trout." Its body is covered in small black spots and has a red band running down its sides, resembling a rainbow. It is a globally valuable, high-quality, cold-water aquaculture species. Freshwater aquaculture of rainbow trout first began in the United States, and in my country since 1959, it is now cultivated in over 20 provinces, municipalities, and autonomous regions, making it a widely cultivated cold-water fish in China. Salmon is a typical cold-water fish. Because my country lacks waters with suitable temperatures year-round for salmon and trout farming, domestic salmon is primarily farmed in mountain streams or large reservoirs. In 2017, my country's rainbow trout production reached 41,460 tons, a 17.79% increase over 2016, making it a key aquaculture species in the country. Triploid rainbow trout, in particular, are highly sought after by consumers due to their short breeding cycle, large size, and delicate texture.

[0005] Atlantic salmon is recognized as a world-renowned and prized fish; rainbow trout is one of the four premium freshwater aquaculture species recommended by the Food and Agriculture Organization of the United Nations and is consistently listed as a prized fish internationally. Both species possess high nutritional and economic value. The debate centers on the widespread belief among consumers and industry that freshwater-farmed rainbow trout carries a risk of parasitic infection when eaten raw, while marine-farmed Atlantic salmon carries a lower risk. Therefore, effectively distinguishing domestic freshwater-farmed rainbow trout from imported Atlantic salmon is crucial.

[0006] Both Atlantic salmon and rainbow trout are relatively large. With the advancement of fish processing machinery, slicing and splitting are more conducive to processing and circulation. Salmon on the market is mainly sold in the form of slices, segments or blocks. The appearance of Atlantic salmon and rainbow trout that have undergone primary processing is basically the same, and ordinary consumers can hardly distinguish them with the naked eye. Therefore, there may be cases where freshwater rainbow trout is impersonated as imported Atlantic salmon.

[0007] The identification of Atlantic salmon and rainbow trout is mostly carried out using molecular biology, spectroscopy, mass spectrometry and other technologies. Molecular biology techniques involve time-consuming and tedious steps such as deoxyribonucleic acid (DNA) extraction, polymerase chain reaction (PCR) amplification, and sequence analysis. In addition, some species are very closely related, with almost no nucleotide differences in their sequences, which increases the difficulty of identification. Multivariate analysis techniques such as spectroscopy and mass spectrometry can obtain principal component analysis score maps by performing dimensionality reduction analysis on large amounts of data to establish a standard library, and achieve identification of unknown samples through comparison. Existing literature searches have found that due to the difficulty in obtaining aquatic product samples of authentic species, the small sample size affects the accuracy of the method. In addition, the multivariate analysis techniques currently relied on for preprocessing spectral data involve first-order derivatives, second-order derivatives, mean centering, multivariate scatter correction, standard normal variate transformation and normalization, etc. The steps are relatively cumbersome, and professional metrology software and technology limit the application of this method in real life.

[0008] Furthermore, currently reported methods for distinguishing Atlantic salmon from rainbow trout fail to consider the rainbow trout's habitat. They simply distinguish between species, failing to address consumer concerns about freshwater rainbow trout, which may pose a parasite risk due to freshwater farming, making it unsuitable for raw consumption. Not all rainbow trout are unsuitable for raw consumption; in Japan, eating rainbow trout raw is quite common. Marine-farmed rainbow trout is also farmed abroad. According to reports, Norwegian marine-farmed rainbow trout and Atlantic salmon are raised under the same standards and grown in seawater, posing no risk of parasite infection when eaten raw. my country also imports marine-farmed rainbow trout annually, and the majority of its rainbow trout fry are imported from abroad. Molecular biology methods cannot effectively distinguish freshwater rainbow trout from imported marine-farmed rainbow trout, and currently reported methods do not address the effective differentiation of imported marine-farmed rainbow trout from domestically produced freshwater rainbow trout. Summary of the Invention

[0009] The invention aims to provide a method for quickly identifying imported Atlantic salmon and domestic freshwater rainbow trout based on specific elements.

[0010] The method of the present invention for rapidly identifying imported Atlantic salmon, seawater rainbow trout and domestic freshwater rainbow trout based on specific elements comprises the following steps: taking a salmon or rainbow trout sample to be tested, and determining the boron and thallium contents thereof; if the thallium content is both lower than 1 μg / kg and the boron content is between 0.050 and 1.5 mg / kg, the sample is imported Atlantic salmon or seawater rainbow trout; and if the thallium content is between 2 and 10 μg / kg and the boron content is extremely low or undetectable, the sample is domestic freshwater rainbow trout.

[0011] Preferably, the extremely low boron content is less than 0.040 mg / kg.

[0012] Preferably, the salmon or rainbow trout sample to be tested is muscle of the salmon or rainbow trout to be tested.

[0013] Preferably, the salmon or rainbow trout sample to be tested is the muscle of a whole salmon or rainbow trout to be tested.

[0014] Preferably, the imported Atlantic salmon is salmon or rainbow trout from Australia, the Faroe Islands, Canada, Norway or Chile.

[0015] Preferably, the domestic freshwater rainbow trout is rainbow trout farmed in freshwater in Qinghai or Hunan.

[0016] This study, leveraging the differences between marine and freshwater aquaculture environments, collected nearly 400 batches of Atlantic salmon samples from five major importing production areas (Australia, the Faroe Islands, Canada, Norway, and Chile). The study identified characteristic differential elements between marine-farmed Atlantic salmon and Chinese freshwater-farmed rainbow trout. The study established a method that accurately distinguishes domestic freshwater rainbow trout from imported Atlantic salmon based solely on the differences in the concentrations of two characteristic elements, thallium and boron, between freshwater rainbow trout and imported Atlantic salmon, without requiring the use of chemometric methods to establish a model or spectral library. This method can also clearly distinguish domestic freshwater rainbow trout from imported rainbow trout. This method will provide the necessary technical support for government agencies to strengthen salmon market supervision and combat the counterfeiting of domestic rainbow trout as imported Atlantic salmon. It also addresses the consumer concern of distinguishing freshwater rainbow trout from imported Atlantic salmon and imported marine-farmed rainbow trout. DETAILED DESCRIPTION

[0017] The present invention is further described in detail below with reference to specific examples. These examples are intended only to illustrate the present invention and are not intended to limit the scope of the present invention. The experimental methods used in the following examples are conventional methods unless otherwise specified; the materials and reagents used are commercially available unless otherwise specified.

[0018] Example 1: Method for Rapidly Identifying Imported Atlantic Salmon and Domestic Freshwater Rainbow Trout Based on Thallium and Boron Content

[0019] 1. Selection of specific differentiating elements

[0020] Boron and its compounds play a vital role in industrial and agricultural production, as well as in the growth and reproduction of plants and animals. However, excessive boron intake can cause nausea, headaches, diarrhea, kidney damage, and even circulatory failure leading to death. Boron in seawater exists primarily as boric acid, with an average concentration of 5.0 mg / L. Freshwater boron levels are typically lower, generally less than 0.5 mg / L. Rainbow trout farming requires demanding conditions and is typically carried out in high-quality cold water. Qinghai Province, located in the heart of the Qinghai-Tibet Plateau, boasts abundant cold water resources, clean water, and excellent water quality, making it one of my country's primary rainbow trout production areas. Therefore, it is speculated that boron may be a differentiating element between Atlantic salmon (which has a higher boron content) farmed in marine waters and rainbow trout farmed in freshwater. Furthermore, differences in pollutant levels between marine and freshwater salmon can also occur due to differences in water quality, feed, and hygiene. Testing of imported Atlantic salmon and freshwater rainbow trout for boron, as well as lead, cadmium, nickel, chromium, and thallium, revealed thallium as a characteristic differentiating element between the two species.

[0021] 2. Identification method

[0022] The thallium and boron contents in approximately 400 batches of imported salmon were tested with reference to the first method of GB 5009.268-2016. GBW10050 (GSB-28) prawns were used as quality control samples. Other quality control samples of biological component analysis standard substances with fixed boron and thallium values ​​in aquatic matrices can also be selected. The boron content range of the quality control samples is 0.05-5 mg / kg, and the thallium content range is 0.2-20 μg / kg. The concentration range of the standard curve and the type of internal standard can be dynamically adjusted according to the sample content. The method quantitative limit does not exceed 0.02 mg / kg for boron and 0.0003 mg / kg for thallium. The test results of the quality control samples are within the range specified in the certificate, and the precision meets the GB

[0023] 5009.268-2016 Method 1 precision requirements.

[0024] The Atlantic salmon samples used in the experiment were imported from Guangzhou Airport between 2018 and 2022. The importing companies were all reputable and registered with customs authorities, ensuring the authenticity of the sample sources. The imported Atlantic salmon were imported whole, and muscle samples were used for testing. A total of 380 Atlantic salmon samples were collected from my country's five major importing regions (Australia, the Faroe Islands, Canada, Norway, and Chile). This large sample size ensured that the measured analyte levels in the samples were fully representative. The number of Atlantic salmon imported from each region was as follows: 135 from Norway, 95 from Chile, 85 from the Faroe Islands, 40 from Australia, 15 from Canada, 8 from the United Kingdom, and 2 from Iceland. The sources and quantities of imported Atlantic salmon are shown in Table 1. Forty rainbow trout samples were used for the study: five were purchased whole from the Longyangxia Reservoir in Qinghai, China, purchased from Huangsha Aquatic Products, five from a production base in Hunan, and 30 from the Longyangxia Rainbow Trout flagship store on JD.com.

[0025] Table 1 Sources and quantities of collected imported Atlantic salmon

[0026]

[0027] Assuming that the method's precision, limit of quantification, and quality control sample values ​​met the aforementioned requirements, thallium and boron were measured in 380 batches of imported Atlantic salmon. The boron and boron contents of domestic freshwater rainbow trout were also measured. Table 2 shows the boron and boron contents of Atlantic salmon and freshwater rainbow trout from various production areas. As shown in Table 2, thallium levels in imported Atlantic salmon were all below 1 μg / kg, while those in freshwater rainbow trout ranged from 2 to 10 μg / kg. This difference in thallium levels may be related to differences in feed and water quality during the two aquaculture environments. The difference in boron levels may be due to the fact that imported Atlantic salmon are aquacultured in seawater, where boron content ranges from 4 to 6 mg / L, with an average boron content of approximately 5.0 mg / L. This results in relatively high boron content in marine aquaculture products. Boron contents in the 380 batches of imported Atlantic salmon ranged from 0.050 to 1.5 mg / kg. Boron levels in my country's freshwater are relatively low, generally below the 0.5 mg / L limit for boron in drinking water, as stipulated in the National Health Standard GB5749-2006. Therefore, boron levels in farmed freshwater rainbow trout are also relatively low. Testing revealed that boron was not detected in samples prepared from purchased whole freshwater rainbow trout. However, boron levels in Longyangxia rainbow trout chunks purchased from JD.com's flagship store ranged from 0.030 to 0.040 mg / kg, likely due to cross-contamination from the environment and utensils used during filleting. As shown in Table 2, thallium and boron levels in samples can be used to distinguish domestic rainbow trout from imported Atlantic salmon.

[0028] Table 2 Boron and thallium content in Atlantic salmon samples from different regions (μg / kg)

[0029]

[0030]

[0031] 3. Verify the accuracy of the identification method using blind samples

[0032] Forty-four samples of imported Atlantic salmon were collected from airport customs, including 22 from Norway, 16 from Chile, 3 from Canada, 2 from the Faroe Islands, and 1 from Australia. Ten rainbow trout fillets were purchased from the Qinghai Longyangxia Rainbow Trout flagship store on JD.com. The boron and silicon content of these 54 samples is shown in Table 3. As shown in Table 3, the boron and thallium content in the samples can accurately distinguish freshwater rainbow trout from imported Atlantic salmon with 100% accuracy.

[0033] Table 3 Boron and thallium contents in imported Atlantic salmon and freshwater rainbow trout samples (blind samples) (μg / kg)

[0034]

[0035] 4. Identification of freshwater rainbow trout and imported rainbow trout

[0036] Three Norwegian rainbow trout samples imported from the airport customs were collected, and the boron content of the samples was detected to be 255±158μg / kg, and the thallium content was 0.315±0.198μg / kg, which were inconsistent with the boron and silicon contents of freshwater rainbow trout and could be accurately distinguished from freshwater rainbow trout.

[0037] 5. Advantages of this method

[0038] This method does not require the establishment of a database. It only needs to measure the content of thallium and boron in the sample. The content of the two elements can be used to determine whether the sample is freshwater rainbow trout. The detection time is short and the judgment can be made in a few hours. At the same time, imported seawater farmed rainbow trout will not be mistakenly identified as freshwater rainbow trout.

Claims

1. A method for rapidly identifying imported Atlantic salmon, seawater rainbow trout and domestic freshwater rainbow trout based on specific elements, characterized in that: Take samples of the salmon or rainbow trout to be tested and determine the boron and thallium content. If the thallium content is lower than 1μg / kg and the boron content is between 0.050 and 1.5mg / kg, it is imported Atlantic salmon or seawater rainbow trout. If the thallium content is between 2 and 10μg / kg and the boron content is lower than 0.040mg / kg, it is domestic freshwater rainbow trout.

2. The method according to claim 1, characterized in that The salmon or rainbow trout sample to be tested is the muscle of the salmon or rainbow trout to be tested.

3. The method according to claim 1, characterized in that The salmon or rainbow trout sample to be tested is the muscle of a whole salmon or rainbow trout to be tested.

4. The method according to claim 1, wherein The imported Atlantic salmon are salmon from Australia, Faroe Islands, Canada, Norway and Chile.

5. The method according to claim 1, wherein The domestic freshwater rainbow trout is the rainbow trout raised in freshwater in Qinghai or Hunan.

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