Method for identifying salinity of living environment of grass carp through fish meat

Abstract

The method for identifying the salinity of the living environment of the grass carp through the fish meat comprises the following steps: firstly, quantitatively analyzing and detecting volatile components in back muscles of the grass carp; and then, according to a quantitative analysis detection result, identifying and judging the salinity of the living environment of the grass carp. By utilizing the method disclosed by the invention, the grass carp cultured in fresh water and the grass carp cultured in saline water with different salinity can be quickly and accurately identified.

Description

Technical Field

[0001] The invention relates to a method for identifying the salinity of a fish living environment, and in particular to a method for identifying the salinity of a grass carp living environment. Background Art

[0002] Grass carp is one of the four major carps in my country and an important economic fish in my country. Grass carp is a freshwater fish that usually grows in freshwater, but can also survive in an environment with a certain salinity. Salinity is one of the important environmental factors affecting the quality of aquatic organisms. It can improve the quality of aquatic organisms by changing the meat quality, free amino acids, unsaturated fatty acid content and volatile flavor substances of aquatic organisms.

[0003] At present, it takes a long time to identify saline grass carp using traditional nutritional methods, and there is no method that can quickly distinguish grass carp treated with brackish water from freshwater farmed grass carp. Summary of the invention

[0004] The technical problem to be solved by the present invention is to overcome the above-mentioned defects of the prior art and provide a method with simple operation method for identifying the salinity of the living environment of grass carp through fish meat.

[0005] The technical solution adopted by the present invention to solve its technical problem is: a method for identifying the salinity of the living environment of grass carp through fish meat, comprising the following steps: first, quantitatively analyzing and detecting the volatile components in the back muscle of grass carp; then, identifying the salinity of the living environment of grass carp based on the results of quantitative analysis.

[0006] By adopting the above technical solution, grass carp cultured in freshwater environment and grass carp cultured in saltwater environment with different salinity can be quickly and accurately identified.

[0007] Preferably, the volatile components in the fish meat used for identification are one or more of butyraldehyde, 2-methylbutyraldehyde, nonanal, hexanal-D, hexanal-M, 2-hexenal, 3-methylbutyraldehyde, isopentanol-D, isopentanol-M, n-hexanol-D, n-hexanol-M, 1-pentanol-D, 1-pentanol-M, methyl acetate, ethyl acetate-D, ethyl acetate-M, propyl butyrate, propyl acetate, 2-butanone-D, 2-butanone-M, 2,3-butanedione, 2,3-pentanedione, 2-pentanone-D, 2-pentanone-M, acetone, cyclohexanone, ammonia, and aniline-D. -M and -D represent the monomer and dimer of the substance, respectively.

[0008] More preferably, 2,3-pentanedione and nonanal are used as volatile components for identification.

[0009] By adopting the above technical solution, grass carp cultured in freshwater environment and grass carp cultured in saltwater environment with different salinity can be quickly and accurately identified.

[0010] Preferably, the volatile components in the dorsal muscle of grass carp are quantitatively analyzed and detected by gas chromatography-ion mobility spectrometry.

[0011] The pre-treatment of gas chromatography-ion mobility spectrometry detection is simple and the detection time is short. It can quickly identify high-quality saline grass carp through characteristic volatile flavor substance markers. After the test, the gas phase retention time of volatile compounds can be obtained, the retention index can be calculated, the ion migration time, migration rate and relative ion peak intensity can be collected, and the gas phase ion mobility chromatogram can be drawn to perform qualitative analysis on the volatile components. The analysis can be completed through the test instrument's built-in data processing function, or the data can be exported and analyzed by other methods. The spectrum can be viewed using LAV (Laboratory Analytical Viewer) and the substance can be qualitatively analyzed using GC-IMS Library Search.

[0012] By adopting the above technical solution, the identification accuracy is high.

[0013] Preferably, the sampling method for the quantitative analysis and detection is: cut a certain amount of grass carp back muscle into pieces, add it into a sealable container, seal it, and incubate it at 30-50°C for 20-40 minutes to allow the volatile gas in the fish meat to diffuse into the top space of the sealed container, and the obtained headspace gas is used as a sample for testing.

[0014] By adopting the above technical solution, the identification accuracy is higher.

[0015] Preferably, a series of grass carps with different living environment salinities and known living environment salinities are selected as a calibration set, the volatile components in the fish meat under different living environment salinities are tested, and a mathematical relationship between the living environment salinity and the volatile components is established as a standard for identifying the salinity of the living environment of grass carp.

[0016] By adopting the above technical solution, the identification accuracy is higher.

[0017] Preferably, a two-dimensional fingerprint of salinity-volatile component signal intensity is established as a standard for identifying the salinity of the grass carp living environment. The Gallery Plot plug-in can be used to establish the fingerprint spectrum and intuitively and quantitatively compare the differences in volatile components in different samples. Other software with this function can also be used. It is also feasible to use other data processing methods.

[0018] By adopting the above technical solution, the identification result display is more intuitive.

[0019] Preferably, principal component analysis is performed on all detected volatile components, and the variation of the content of significantly different substances with salinity is selected as the standard for identifying the salinity of the living environment of grass carp. SIMCA software (Version 14.1, Umetrics AB, Malmo, Sweden) can be used to perform principal component analysis (PCA) on all volatile substances that have been identified. Other software with this function can also be used.

[0020] The retention time of 2,3-pentanedione is 176.5s, and the ion drift time is 1.227ms. It is suitable for further confirmation of freshwater farmed grass carp and saline grass carp in principal component analysis. When the peak intensity is lower than 167.07, it is freshwater farmed grass carp. When the peak volume is 339.98-434.20, it is saline grass carp treated with 7.5PSU. When the peak volume is 434.20-542.34, it is saline grass carp treated with 2.5PSU and 5PSU. When the peak volume is ≥542.34, it is saline grass carp treated with 10PSU. The retention time of nonanal is 774.43s, and the ion drift time is 1.481ms. It is suitable for further confirmation of the saline grass carp treated with 2.5PSU and 5PSU identified in the previous step. The peak volume of nonanal in freshwater cultured grass carp meat is 171.34, which is significantly decreased after 2.5PSU and 10PSU salinity treatments, to 114.28 and 97.99, respectively. There is no significant change after 5PSU and 7.5PSU salinity treatments, to 174.27 and 144.02, respectively. When the peak volume is ≤171.34, it is saline grass carp treated with 2.5PSU, and when the peak volume is ≥174.27, it is saline grass carp treated with 5PSU.

[0021] By adopting the above technical solution, volatile components suitable for identification can be screened out and the identification method can be simplified.

[0022] Preferably, a plurality of freshwater cultured grass carps are selected and respectively placed in saltwater with four salinity gradients of 2.5 PSU, 5 PSU, 7.5 PSU and 10 PSU to obtain a calibration set.

[0023] Grass carp has difficulty growing in an environment with salinity above 10 PSU, and identification is generally unnecessary in the case of higher salinity. By adopting the above technical solution, identification is highly accurate and efficient.

[0024] Preferably, when increasing the salinity of the grass carp's living environment, increase 2.5-5 PSU every day until the preset salinity is reached; after the living environment of all grass carp reaches the preset salinity, continue to raise them for 15-30 days.

[0025] By adopting the above technical solution, the identification accuracy is high and it is relatively efficient.

[0026] Preferably, the feeding conditions of grass carp are as follows: water temperature: 26.5-28.3°C; dissolved oxygen: 7.0-7.5 mg / L; pH value: 7.0-7.4; 20-50% of the water is replaced every day, and the salinity is stabilized at a preset level.

[0027] By adopting the above technical solution, the identification accuracy is high and it is relatively efficient.

[0028] Beneficial effects of the present invention:

[0029] (1) The method of the present invention is relatively simple to operate, has a short detection time, and has high application value;

[0030] (2) The present invention can be used to quickly and accurately distinguish between grass carp cultured in freshwater environments and grass carp cultured in saltwater of different salinities. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 These are gas phase ion migration chromatograms of grass carp samples cultured in saltwater environments with different salinities and grass carp samples cultured in freshwater environments.

[0032] Figure 2 These are the fingerprint spectra of grass carp samples cultured in saltwater environments with different salinities and grass carp samples cultured in freshwater environments.

[0033] Figure 3 This is the PCA analysis chart of grass carp samples cultured in saltwater environments with different salinities and grass carp samples cultured in freshwater environments.

[0034] Figure 4 These are texture index diagrams of grass carp samples cultured in saltwater environments with different salinities and grass carp samples cultured in freshwater environments. DETAILED DESCRIPTION

[0035] The present invention will be further described below in conjunction with the embodiments and drawings. In order to facilitate understanding of the present invention, the present invention will be described more comprehensively and meticulously in conjunction with the drawings and preferred embodiments of the specification, but the protection scope of the present invention is not limited to the following specific embodiments.

[0036] The raw materials used in the embodiments of the present invention are all obtained through conventional commercial channels.

[0037] Example 1

[0038] In this embodiment, a method for identifying the salinity of the living environment of grass carp by using fish meat is provided. The sample obtaining method is as follows: the fish is anesthetized with the anesthetic MS-222 (100 mg / L), and then the white muscle on the left side of the back of the fish is minced and added to a headspace injection bottle, and incubated at 40° C. for 20 minutes to allow the volatile gas in the fish meat to diffuse into the top space of the container, and the obtained headspace gas is used as a sample for testing; the volatile components in the sample are quantitatively analyzed by gas chromatography-ion mobility spectrometry, and the salinity of the living environment of the grass carp is identified according to the test results.

[0039] The test conditions of gas chromatography-ion mobility spectrometry are as follows:

[0040] (1) Gas phase-ion mobility spectrometry unit

[0041] Analysis time: 20 min; chromatographic column type: MTX-5, 15 m, ID: 0.53 mm, film thickness 1 μm, chromatographic column temperature: 60°C; carrier gas / drift gas: high-purity nitrogen (purity ≥ 99.999%); IMS detector temperature 45°C.

[0042] (2) Automatic headspace injection conditions

[0043] Headspace incubation temperature: 40°C; incubation time: 20 min; injection volume: 500 μL, splitless mode; heating method: oscillating heating; injection needle temperature 85°C; incubation speed: 500 rpm.

[0044] (3) Gas chromatography conditions

[0045] Drift gas flow rate: 150 mL / min; chromatographic carrier gas flow rate program setting: 0-2 min, 2 mL / min; 2-10 min, increase from 2 mL / min to 10 mL / min; 10-20 min, increase from 10 mL / min to 100 mL / min.

[0046] The volatile components used for identification were: 2,3-pentanedione and nonanal.

[0047] 2,3-Pentanedione has a caramel flavor, with a retention time of 176.5s and an ion drift time of 1.227ms. Its peak intensity in freshwater cultured grass carp is 167.07, and after saline treatment, the peak volume of the substance increased significantly (p<0.05), reaching 434.20, 455.23, 339.98 and 542.34 respectively. This shows that the use of 2,3-pentanedione can clearly distinguish between freshwater grass carp and saline grass carp, and the peak intensity of the substance is the largest and the content is the highest in grass carp muscle treated with a salinity of 10PSU.

[0048] Nonanal mainly provides fat smell and is an important substance for evaluating the flavor of fish meat. The retention time of this substance is 774.43s and the ion drift time is 1.481ms. Its peak intensity in freshwater farmed grass carp meat is 171.34, but it decreases significantly after treatment with 2.5PSU and 10PSU salinity (p<0.05), which are 114.28 and 97.99, respectively. There is no significant change after treatment with 5PSU and 7.5PSU salinity (p>0.05), which are 174.27 and 144.02, respectively. This shows that the use of nonanal can clearly distinguish saline grass carp treated with 2.5PSU and 5PSU salinity.

[0049] The results of the test showed that the peak volume of 2,3-pentanedione in the grass carp meat of this example was 451.73, and the peak volume of nonanal was 183.26, indicating that the grass carp was cultured under a salinity of 5 PSU.

[0050] Example 2

[0051] 1. Experimental fish and protocol

[0052] Healthy grass carp (size 500±50g) were purchased from a farm in Hunan Province. After the fish were transported back, they were placed in a pond for temporary rearing for 1 week. During the temporary rearing period, commercial feed was fed twice a day, and the feeding amount was 3%-4% of the adult fish body weight. After the temporary rearing, 75 grass carps of the same size were selected and distributed into 15 (5 treatments × 3 replicates) 1000L fiberglass tanks (5 fish per tank). Five treatments: 0PSU (control group), 2.5PSU, 5PSU, 7.5PSU and 10PSU. The salinity of the water body was increased by adding sea salt to the tank, and the fish were slowly adapted to the salinity by increasing 2.5PSU every day. When the salinity set for each group was reached, the grass carp treatment began, and the treatment lasted for 16 days, during which the fish were fasted. The water quality indicators during the experiment were as follows: water temperature: 26.5-28.3℃; dissolved oxygen: 7.0-7.5mg / L; pH: 7.0-7.4. The water in the experimental system was replaced by 20% every day, and the salinity was stabilized at the experimental set level.

[0053] 2. Sample collection

[0054] After 16 days of treatment, 2 fish were randomly selected from each fish tank for sampling. The fish were anesthetized with the anesthetic MS-222 (100 mg / L), and then the white muscle on the left side of the back of the fish was minced and added to the headspace injection bottle. It was incubated at 40°C for 20 minutes to allow the volatile gas in the fish meat to diffuse into the top space of the container. The obtained headspace gas was used as the sample for testing; the volatile components in the sample were quantitatively analyzed by gas chromatography-ion mobility spectrometry, and the salinity of the grass carp's living environment was identified based on the test results.

[0055] 3. Gas chromatography-ion mobility spectrometry analysis

[0056] (1) Gas phase-ion mobility spectrometry unit

[0057] Analysis time: 20 min; chromatographic column type: MTX-5, 15 m, ID: 0.53 mm, film thickness 1 μm, chromatographic column temperature: 60°C; carrier gas / drift gas: high-purity nitrogen (purity ≥ 99.999%); IMS detector temperature 45°C.

[0058] (2) Automatic headspace injection conditions

[0059] Headspace incubation temperature: 40°C; incubation time: 20 min; injection volume: 500 μL, splitless mode; heating method: oscillating heating; injection needle temperature 85°C; incubation speed: 500 rpm.

[0060] (3) Gas chromatography conditions

[0061] Drift gas flow rate: 150 mL / min; chromatographic carrier gas flow rate program setting: 0-2 min, 2 mL / min; 2-10 min, increase from 2 mL / min to 10 mL / min; 10-20 min, increase from 10 mL / min to 100 mL / min.

[0062] 4. Data processing

[0063] The experimental data were analyzed by one-way analysis of variance using SPSS 26.0 statistical software, and p < 0.05 indicated a significant difference.

[0064] 5. Results and Analysis

[0065] (1) Using the GCxIMS LibrarySearch software, the built-in application software NISTT gas phase retention index data and IMS migration time database were used to perform qualitative analysis on volatile substances and draw gas phase ion mobility chromatography spectra ( Figure 1 ). In the figure, one point represents a substance, the horizontal axis represents the ion migration time (ms, normalized), the vertical axis represents the gas chromatography retention time (s), the background of the whole figure is blue, the red vertical line at the horizontal axis 1.0 is the RIP peak (reaction ion peak, normalized), each point on both sides of the RIP peak represents a volatile organic compound, the color represents the concentration of the substance, white represents a lower concentration, red represents a higher concentration, and the darker the color, the greater the concentration.

[0066] (2) Using the GalleryPlot plug-in, all volatile component signal peaks in saline grass carp samples with different salinities and freshwater cultured grass carp samples were extracted according to the peak intensity signal or color difference of the characteristic substances to form a fingerprint spectrum ( Figure 2 ), intuitively and quantitatively compare the differences in volatile organic compounds between different samples. Figure 2The darker the color, the higher the content of the volatile component. If it is a number, it means that the substance has not been qualitatively identified. The relative contents of the detected substances vary between different groups. For example, methyl acetate, ethyl acetate, butyraldehyde, 2-hexanal, 2-butanone, 2,3-butanedione, 2-pentanone, acetone and 2-methylbutyraldehyde have the highest concentrations in the Control group samples, isopentanol, propyl butyrate, cyclohexanone and aniline have the highest concentrations in the 2.5PSU group samples, nonanal, hexanol, hexanal, pentanol, ethanol and propyl acetate have the same concentrations in the 5PSU and 7.5PSU group samples, which are all higher than those in other sample groups, and 3-methylbutyraldehyde, ammonia and 2,3-pentanedione have the highest concentrations in the 10PSU group samples.

[0067] (3) The identified substance information is shown in Table 1 and Table 2. There are 30 characteristic volatile components in the saline grass carp samples and freshwater cultured grass carp samples of different salinities, including 7 aldehydes, 8 ketones, 7 alcohols, 5 esters and 4 other types of substances. Aldehydes are mainly produced by lipid oxidation, and their odor threshold is low, which has an important impact on the odor of fish. The aldehydes identified in this example include butyraldehyde, 2-hexenal, 2-methylbutyraldehyde, nonanal, hexanal monomers and dimers, and 3-methylbutyraldehyde. Hexanal is a peroxide of n-6PUFA, which provides fish and other aquatic products with a grassy and fatty taste. In this example, the content of hexanal monomers and dimers in the 5PSU and 7.5PSU groups was significantly higher than that in the control group (p<0.05), while there was no significant change in the 2.5PSU and 10PSU groups (p>0.05). Nonanal has a grassy and fatty aroma, and can emit a strong aroma that masks other odors even at low concentrations. In this study, compared with the control group, the nonanal content in the 5PSU and 7.5PSU groups did not change significantly (p>0.05), while the nonanal content in the 2.5PSU and 10PSU groups was significantly reduced (p<0.05). These results show that grass carp suitable for salinization treatment (5-7.5PSU) has a superior aroma in terms of aldehydes, which can improve the flavor quality of grass carp. The ketones identified in this example include 2-butanone dimers and monomers, 2,3-butanedione, 2,3-pentanedione, and 2-pentanedione dimers and monomers. 2,3-Pentanedione has a caramel flavor. In this study, its content increased significantly after salinization treatment (p<0.05), and the content was the highest in the 10PSU group. 2-Butanone has an unpleasant odor similar to solvents and plastics. In this example, the 2-butanone content of each salinity treatment group was significantly lower than that of the control group (p<0.05). The results show that saline treatment can reduce the content of ketone volatile substances such as 2-butanone that are harmful to the human body, and increase the content of fish-specific flavor substances such as 2,3-pentanedione, thereby improving the flavor of grass carp. The alcohols identified in this embodiment include isopentanol dimers and monomers, n-hexanol dimers and monomers, 1-pentanol dimers and monomers and ethanol. N-hexanol emits the aroma of grass. In this study, compared with the control group, the content of n-hexanol monomers and dimers in the 7.5PSU group increased significantly (p<0.05). Most esters are mainly formed by the esterification reaction of organic acids and alcohols, have sweet fruit flavors, have relatively high odor thresholds, and have little effect on flavor. The esters identified in this study include methyl acetate, ethyl acetate dimers and monomers, propyl butyrate and propyl acetate, most of which have the highest content in the control group.

[0068] Summary

[0069] As mentioned above, proper salinization treatment (5-7.5 PSU) can reduce the content of undesirable flavor substances such as 2-butanone, and increase the content of beneficial flavor substances such as 2,3-butanedione, n-hexanol, hexanal, etc., thereby improving the flavor of grass carp.

[0070] (4) Principal component analysis (PCA): PCA analysis of all volatile flavor substances in saline grass carp samples with different salinities and freshwater farmed grass carp samples was performed using SIMCA software. The results are as follows: Figure 3 The PCA analysis results showed that the contribution values ​​of the two principal components were 49.1% and 27.4%, respectively, indicating that the volatile flavor compounds in the grass carp muscle of the four salinity treatment groups were significantly different from those of the control group, among which the 2.5PSU group and the 10PSU group were more similar, and the 5PSU group and the 7.5PSU group were more similar.

[0071] (5) Establishment of detection method for saline grass carp:

[0072] According to the difference in the peak intensity signal of the substance and the retention time and migration time corresponding to the substance, two significantly different substances that can significantly distinguish the salinized grass carp of different salinities are selected from the characteristic area of ​​the fingerprint spectrum to make a detailed distinction between different salinities, and combined with principal component analysis to achieve accurate and rapid distinction of salinized grass carp of different salinities. The specific analysis is as follows:

[0073] 2,3-Pentanedione has a caramel flavor, with a retention time of 176.5s and an ion drift time of 1.227ms. Its peak intensity in freshwater cultured grass carp is 167.07, and after saline treatment, the peak volume of the substance increased significantly (p<0.05), reaching 434.20, 455.23, 339.98 and 542.34 respectively. This shows that the use of 2,3-pentanedione can clearly distinguish between freshwater grass carp and saline grass carp, and the peak intensity of the substance is the largest and the content is the highest in grass carp muscle treated with a salinity of 10PSU.

[0074] Nonanal mainly provides fat smell and is an important substance for evaluating the flavor of fish meat. The retention time of this substance is 774.43s and the ion drift time is 1.481ms. Its peak intensity in freshwater farmed grass carp meat is 171.34, but it decreases significantly after treatment with 2.5PSU and 10PSU salinity (p<0.05), which are 114.28 and 97.99, respectively. There is no significant change after treatment with 5 and 7.5PSU salinity (p>0.05), which are 174.27 and 144.02, respectively. It shows that the use of nonanal can clearly distinguish the saline grass carp treated with 2.5PSU and 5PSU salinity, as shown in Table 1 and Table 2.

[0075] (6) The texture parameters of grass carp samples from saltwater and freshwater cultured grass carp samples with different salinities are as follows Figure 4The results showed that after salinization, the hardness and chewiness of grass carp muscles increased significantly (p<0.05). According to literature reports, people prefer grass carp with harder meat, so salinity treatment can improve the quality of grass carp by increasing the hardness and chewiness of grass carp muscles.

[0076] The above implementation examples are only used to illustrate the present invention. The implementation of each step can be varied. All equivalent changes and improvements based on the method of the present invention should not be excluded from the protection scope of the present invention.

[0077] Table 1. Qualitative analysis of volatile components of grass carp samples: retention index, retention time, drift time

[0078]

[0079]

[0080] Note: -M and -D represent the monomer and dimer of the substance respectively.

[0081] Table 2. Qualitative analysis of volatile components in grass carp samples: Peak volume

[0082]

[0083]

[0084] Note: If the superscript letters in each row are the same, it means there is no significant difference (p>0.05), if the superscript letters are different, it means there is a significant difference (p<0.05). -M and -D represent the monomer and dimer of the substance, respectively.

Claims

1. A method for identifying the salinity of the living environment of grass carp through fish meat, characterized in that: The following steps are involved: Firstly, the volatile components in the dorsal muscle of grass carp were quantitatively analyzed and detected; Then, based on the results of quantitative analysis, the salinity of the grass carp's living environment was identified.

2. The method for identifying the salinity of the living environment of grass carp through fish meat according to claim 1, characterized in that: The volatile components are: one or more of butyraldehyde, 2-methylbutyraldehyde, nonanal, hexanal-D, hexanal-M, 2-hexenal, 3-methylbutyraldehyde, isopentanol-D, isopentanol-M, n-hexanol-D, n-hexanol-M, 1-pentanol-D, 1-pentanol-M, methyl acetate, ethyl acetate-D, ethyl acetate-M, propyl butyrate, propyl acetate, 2-butanone-D, 2-butanone-M, 2,3-butanedione, 2,3-pentanedione, 2-pentanone-D, 2-pentanone-M, acetone, cyclohexanone, ammonia, and aniline-D.

3. The method for identifying the salinity of the living environment of grass carp through fish meat according to claim 1 or 2, characterized in that: Gas chromatography-ion mobility spectrometry was used to quantitatively analyze the volatile components in the dorsal muscle of grass carp.

4. The method for identifying the salinity of the living environment of grass carp through fish meat according to any one of claims 1 to 3, characterized in that: The sampling method for quantitative analysis and detection is: a quantitative amount of grass carp back muscle is cut into pieces, added into a sealable container, sealed, incubated at 30-50° C. for 20-40 minutes, so that the volatile gas in the fish meat diffuses into the top space of the sealed container, and the obtained headspace gas is used as a sample for quantitative analysis and detection.

5. The method for identifying the salinity of the living environment of grass carp through fish meat according to any one of claims 1 to 4, characterized in that: A series of grass carp with different living environment salinities and known living environment salinities were selected as the calibration set, and the volatile components in fish meat under different living environment salinities were quantitatively analyzed and detected. A mathematical relationship between the living environment salinity and the volatile components was established as a standard for identifying the living environment salinity of grass carp.

6. The method for identifying the salinity of the living environment of grass carp through fish meat according to any one of claims 1 to 5, characterized in that: A two-dimensional fingerprint of salinity-volatile component signal intensity was established as a standard for identifying the salinity of the grass carp's living environment.

7. The method for identifying the salinity of the living environment of grass carp by using fish meat according to any one of claims 1 to 6, characterized in that: Principal component analysis was performed on all the volatile components detected, and the changes in the contents of significantly different substances with salinity were selected as the standard for identifying the salinity of the grass carp's living environment.

8. The method for identifying the salinity of the living environment of grass carp by using fish meat according to any one of claims 5 to 7, characterized in that: A number of freshwater cultured grass carps were selected and placed in saltwater with four salinity gradients of 2.5 PSU, 5 PSU, 7.5 PSU and 10 PSU to obtain a calibration set.

9. The method for identifying the salinity of the living environment of grass carp through fish meat according to claim 8, characterized in that: When increasing the salinity of the grass carp's living environment, increase 2.5-5 PSU every day until the preset salinity is reached; after the living environment of all grass carp reaches the preset salinity, continue to raise them for 15-30 days.

10. The method for identifying the salinity of the living environment of grass carp through fish meat according to claim 8 or 9, characterized in that: The rearing conditions for grass carp are: water temperature: 26.5~28.3℃; dissolved oxygen: 7.0~7.5 mg / L; pH value: 7.0~7.4; replace 20-50% of the water every day and stabilize the salinity at a preset level.

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