Fish meat evaluation method

Abstract

The invention relates to the technical field of fish meat quality evaluation, in particular to a fish meat evaluation method, which comprises the following steps: appearance characteristic determination: determining the shape and chromaticity of fish meat; tactile feature determination: determining the texture, water-holding capacity and coarse components of the fish meat; gustation feature determination: determining the gustation features of the fish meat; determining smell characteristics: extracting volatile substances of the fish meat, performing chromatography-mass spectrometry analysis, then determining compounds, calculating an odor activity value OAV according to the content values of the compounds, calculating a relative contribution degree ROC according to the odor activity value, and taking the first several compounds with the highest ROC as characteristic data; the calculation formula of the odor activity value is OAV = compound concentration / odor threshold value of the compound; the calculation formula of the relative contribution degree is ROC (%) = OAVi / OAVt * 100%. According to the method, a relatively complete fish quality evaluation method is constructed, and the quality of the same kind of fishes from different sources can be accurately evaluated.

Description

Technical Field

[0001] This invention relates to the field of fish meat quality evaluation technology, specifically a method for evaluating fish meat. Background Technology

[0002] As one of the world's most important sources of protein, fish consumption demand continues to grow. In particular, driven by the concept of healthy eating, consumers are paying increasing attention to the nutritional value and safety of aquatic products. The refined evaluation of fish quality has become an important research topic in the fields of food science, aquatic product processing, and quality testing.

[0003] However, the evaluation of fish quality is complex and varied, and to date, no unified standard or method has been established. Currently, the evaluation system for fish quality mainly relies on discrete analysis of single-dimensional indicators, which is not comprehensive enough. Therefore, it is necessary to establish a more robust method for evaluating fish quality to achieve a more comprehensive description and analysis of fish quality. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a method for evaluating fish meat quality. This evaluation method integrates multiple dimensions, including appearance, touch, taste, and smell, constructing a relatively complete method for evaluating fish meat quality and enabling precise evaluation of the quality of the same species of fish from different sources.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] This invention provides a method for evaluating fish meat, comprising the following steps:

[0007] Appearance characteristics measurement: including measurement of fish flesh shape and color;

[0008] Tactile characteristic measurement: including the measurement of fish flesh texture, water holding capacity, and crude composition;

[0009] Taste characteristics determination: Determining the taste characteristics of fish meat;

[0010] Olfactory characteristic determination: Volatile substances were extracted from fish meat, and compounds were identified by chromatographic-mass spectrometry analysis. The odor activity value (OAV) was calculated based on the content value of the compound, and the relative contribution value (ROC) was calculated based on the odor activity value. The top few compounds with the highest ROC were used as characteristic data.

[0011] The formula for calculating the odor activity value is as follows:

[0012] OAV = compound concentration / odor threshold of the compound;

[0013] The formula for calculating the relative contribution is:

[0014] ROC(%) = OAV i / OAV t ×100%;

[0015] OAV i This indicates the content of a certain type of OAV. t This indicates all OAVs in the sample. i sum;

[0016] Fish meat samples were obtained, and various feature data were obtained through appearance feature measurement, tactile feature measurement, taste feature measurement, and olfactory feature measurement; principal component analysis was performed on the feature data to obtain evaluation results.

[0017] Preferably, the determination of fish meat morphology includes measuring the fish's body weight, body length, visceral weight, and liver weight, and calculating the liver-to-body ratio, visceral-to-body ratio, and fatness.

[0018] Preferably, the colorimetric determination includes dividing each side of the fish meat sample into 15cm sections. 2 The frequency of the three measurements was measured using a colorimeter, with each measurement taken at a different location, and the average value was calculated.

[0019] Preferably, the fish meat sample for colorimetric determination is the dorsal muscle of the fish.

[0020] Preferably, the determination of fish meat texture includes obtaining a cube-shaped fish meat sample, performing texture profile analysis on the fish meat sample using a physical property tester to obtain texture characteristics, the texture characteristics including at least one of hardness, viscosity, cohesion, elasticity, resilience and chewiness; and conducting a double compression test with a compression ratio of 30%, wherein the probe movement speed of the physical property tester is 1 mm / s and the interval between the two compressions is 2s.

[0021] Preferably, the determination of water-holding capacity includes: weighing the fish meat sample; wrapping the fish meat sample in filter paper and centrifuging it at room temperature with a centrifugal force of 3500-4500g for 8-15 minutes, the filter paper absorbing the juice of the fish meat sample and becoming wet filter paper, drying the wet filter paper at 70-80℃ to constant weight to obtain dried filter paper; weighing the initial weight of the filter paper, the weight of the wet filter paper, and the weight of the dried filter paper, and calculating the juice loss rate, water loss rate, and fat loss rate.

[0022] Preferably, the taste characteristic determination includes: the fish meat sample is limited to a specified part of the fish body, added to distilled water at a ratio of 0.3 g / mL and pulverized to obtain a slurry; the slurry is subjected to ultrasonic extraction to obtain an extract, for 10-15 min, with an ultrasonic frequency of 40-50 kHz and a temperature controlled at 4-5℃; the extract is centrifuged and filtered to obtain a supernatant, with a centrifugation speed of 10000 rpm, a time of 10-15 min, and a temperature controlled at 4-5℃, using a nylon filter membrane; the supernatant is measured using an electronic tongue device, wherein the test solutions for the electronic tongue device are: reference solution: 30 mM potassium chloride + 0.3 mM tartaric acid; negative electrode cleaning solution: 100 mM hydrochloric acid + 30% volume ethanol; positive electrode cleaning solution: 10 mM potassium hydroxide + 100 mM potassium chloride + 30% volume ethanol.

[0023] Preferably, in the olfactory characteristic determination process, the process of extracting volatile substances from fish meat is as follows: the fish meat sample is placed in a headspace vial, an internal standard and a salt solution are added, and then heated for extraction. After extraction, the headspace microextraction needle is inserted into the headspace vial for continued heating, and finally, analysis is performed.

[0024] Preferably, the chromatographic conditions are as follows: column temperature: initial temperature 40℃, hold for 2 min, increase to 150℃ at 8℃ / min, hold for 3 min, then increase to 200℃ at 5℃ / min, hold for 5 min, increase to 280℃ at 15℃ / min, hold for 2 min; injection port temperature: 250℃; transfer line temperature: 280℃; carrier gas flow rate: 1.0 mL / min.

[0025] Preferably, the mass spectrometry conditions are: ion source temperature: 230℃, quadrupole temperature: 150℃, mass spectrometry: EI source, mode: full scan 40-600m / z.

[0026] Preferably, the odor-active substance corresponding to the odor activity value is selected from any one or more of 3-undecanoate, naphthalene, myristal, trans-4-decanal, trans-2-octenal, lauraldehyde, nonanal, decanal, hexadecaldehyde, tridecanal, pentadecaldehyde, dimethyl tetrasulfide, octanol, 1-nonanol, n-hexanol, and 1-octen-3-ol.

[0027] Preferably, the fish meat is selected from any one or more of wild fish meat, feed-fed fish meat, and fish raised in water.

[0028] The beneficial effects of this invention are:

[0029] This invention constructs a relatively complete method for evaluating fish meat quality from multiple dimensions, including appearance, touch, taste, and smell. This avoids the one-sided results obtained from single-perspective evaluation methods and simplifies the description of the olfactory characteristics of fish meat samples through the ROC index. This evaluation method has high accuracy and can effectively distinguish the quality evaluation of the same species of fish from different sources, providing a basis for fish meat quality control and improvement. Attached Figure Description

[0030] Figure 1 The crude component index of fish meat;

[0031] Figure 2 The water-holding capacity of fish meat;

[0032] Figure 3 To detect the taste characteristics of fish meat based on electronic tongue technology;

[0033] Figure 4 A distribution map of volatile odor compounds in fish meat;

[0034] Figure 5 This is a graph showing the content of volatile odor compounds in fish meat.

[0035] Figure 6 Principal component analysis (PCA) was performed to evaluate the appearance, tactile sensation, taste, and olfactory characteristics of fish meat. Detailed Implementation

[0036] To enable those skilled in the art to better understand the technical solution of the invention, the invention will be further described in detail below with reference to specific embodiments.

[0037] To avoid the one-sidedness caused by evaluating fish quality with a single indicator, this invention provides a method for comprehensively evaluating fish quality, which integrates multiple dimensions such as appearance, touch, taste, and smell, and realizes accurate evaluation of the quality of the same species of fish from different sources.

[0038] The evaluation method of the present invention includes the following steps:

[0039] Appearance characteristics measurement: including measurement of fish flesh shape and color;

[0040] Tactile characteristic measurement: including the measurement of fish flesh texture, water holding capacity, and crude composition;

[0041] Taste characteristics determination: Determining the taste characteristics of fish meat;

[0042] Olfactory characteristic determination: Volatile substances were extracted from fish meat, and compounds were identified through chromatographic-mass spectrometry analysis. The odor activity value (OAV) was calculated based on the content of these compounds. The relative contribution (ROC) was calculated based on the OAV, and the compounds with the highest ROC were selected as characteristic data. The formula for calculating the odor activity value is as follows:

[0043] OAV = compound concentration / odor threshold of the compound;

[0044] The formula for calculating the relative contribution is: ROC(%) = OAV i / OAV t ×100%;

[0045] OAV i This indicates the content of a certain type of OAV. t This indicates all OAVs in the sample. i sum;

[0046] Fish meat samples were obtained, and various characteristic data were obtained through the aforementioned appearance characteristic measurement, tactile characteristic measurement, taste characteristic measurement, and olfactory characteristic measurement.

[0047] Principal component analysis is performed on the feature data to obtain the evaluation results.

[0048] The detection target of this invention can be any one or more of wild fish meat, feed-raised fish meat, and pond-raised fish meat. In an embodiment of this invention, the fish species is grass carp. Wild grass carp are caught from wild waterways; pond-raised grass carp are "slimmed-down grass carp," commercial grass carp that have been raised in clean water for a period of time; and feed-raised grass carp are grass carp raised on artificial feed in ordinary ponds.

[0049] In the process of determining the appearance characteristics of the fish in this invention, the determination of the fish meat morphology includes measuring the fish's body weight, body length, visceral weight, and liver weight, and calculating the liver-to-body ratio, visceral-to-body ratio, and fatness. Based on the calculation results, the proportion of edible portion of the fish meat can be determined, and different proportions can distinguish fish meat from different sources.

[0050] The color measurement described in this invention includes dividing each surface of the fish meat sample into 15cm sections. 2 The measurement was performed three times using a colorimeter, with each measurement taken at a different location. The average value was then calculated, effectively reducing measurement errors and improving the accuracy and representativeness of the data. Based on the different colors, fish from different sources can be further distinguished. For example, grass carp with a whiter, cleaner color has higher market acceptance, reflecting better quality.

[0051] The fish meat sample used for colorimetric determination in this invention is the dorsal muscle of fish. The dorsal muscle of fish has a uniform muscle structure and stable pigment distribution, which can accurately reflect the typical flesh color and freshness changes of the fish species; at the same time, this part is least affected by external damage and fat interference, and can avoid the influence of abnormal areas such as blood-stained meat.

[0052] The method for determining fish meat texture according to this invention includes obtaining a cube-shaped fish meat sample, performing texture profile analysis on the fish meat sample using a physical property testing instrument to obtain texture characteristics, which include at least one of hardness, viscosity, cohesion, elasticity, resilience, and chewiness; and conducting a double compression test with a compression ratio of 30%, in which the probe movement speed of the physical property testing instrument is 1 mm / s, and the interval between the two compressions is 2 s. Studies have found that wild fish meat can be distinguished based on differences in muscle elasticity. This method for determining fish meat texture, through a standardized double compression test, can objectively quantify various texture characteristics of fish meat, and compared with traditional subjective evaluation methods, it has the advantages of good repeatability, reliable data, and simple operation.

[0053] Water-holding capacity refers to the ability of muscle to retain its own water and absorb external water. Higher water-holding capacity results in a slower rate of muscle protein degradation, leading to "delicious and juicy" muscle. Conversely, lower water-holding capacity indicates greater water loss, resulting in the loss of flavor compounds and other nutrients, and a significant decrease in muscle processing characteristics. Different sources of fish can be distinguished based on their water-holding capacity. The water-holding capacity determination method of this invention includes: weighing a fish sample; wrapping the fish sample in filter paper and centrifuging it at room temperature at a centrifugal force of 3500–4500 g for 8–15 minutes, causing the filter paper to absorb the juices from the fish sample and become wet; drying the wet filter paper at 70–80°C to constant weight to obtain dried filter paper; weighing the initial weight of the filter paper, the weight of the wet filter paper, and the weight of the dried filter paper, and calculating the juice loss rate, water loss rate, and fat loss rate. The centrifugation parameters (3500-4500g, 8-15min) can efficiently separate the outflowing juice, simulate the juice loss during processing and storage, and ensure the accuracy of the measurement. Drying at 70-80℃ can quickly remove moisture and avoid fat oxidation, ensuring the accuracy of subsequent calculations of water loss rate and fat loss rate, thereby scientifically characterizing the water-holding capacity of fish meat.

[0054] The taste characteristic determination method of this invention includes: the fish meat sample is limited to a specified part of the fish body, added to distilled water at a ratio of 0.3 g / mL and pulverized to obtain a slurry; the slurry is subjected to ultrasonic extraction to obtain an extract, for 10-15 min, with an ultrasonic frequency of 40-50 kHz and a temperature controlled at 4-5°C; the extract is centrifuged and filtered to obtain a supernatant, with a centrifugation speed of 10000 rpm for 10-15 min and a temperature controlled at 4-5°C, using a nylon filter membrane; the supernatant is measured using an electronic tongue device. Low-temperature ultrasonic extraction can effectively destroy cell membrane structure, efficiently release flavor substances, improve extraction efficiency, and inhibit the degradation of heat-sensitive components and enzyme activity, while preserving the original flavor; high-speed low-temperature centrifugation combined with nylon membrane filtration can thoroughly remove proteins and impurities, obtaining a clear supernatant and avoiding interference with the electronic tongue sensor response. The entire process significantly improves extraction efficiency and measurement accuracy, ensuring that the electronic tongue data truly reflects the taste of the fish meat.

[0055] The electronic tongue device uses an artificial lipid membrane sensor with wide-range selectivity to simulate the taste perception mechanism of living organisms. It evaluates five basic tastes (sour, sweet, bitter, salty, and umami) and astringency by detecting changes in membrane potential caused by electrostatic or hydrophobic interactions between various taste substances and the artificial lipid membrane. The electronic tongue described in this invention includes, but is not limited to, the detection of umami, saltiness, sourness, bitterness, astringency, umami richness, bitter aftertaste, and astringent aftertaste. Based on the measurement results, products with richer taste characteristics can be selected.

[0056] The selection of test solutions for electronic tongue devices is crucial, directly determining the effectiveness, accuracy, repeatability, and reliability of the tests. To ensure the accuracy of the measurement results, the test solutions for the electronic tongue device described in this invention are as follows: Reference solution: 30mM potassium chloride + 0.3mM tartaric acid (this is the "zero point" or "baseline" for electronic tongue measurements, and the flavor signals of all samples are generated relative to it); Negative electrode cleaning solution: 100mM hydrochloric acid + 30% volumetric ethanol (used for cleaning and regenerating the working electrode); Positive electrode cleaning solution: 10mM potassium hydroxide + 100mM potassium chloride + 30% volumetric ethanol (used for cleaning and regenerating the reference electrode). The addition of tartaric acid specifically targets the core flavor of fish—umami—enabling the equipment to sensitively capture subtle differences in umami substances. This effectively distinguishes fish of different species, origins, and freshness levels. The powerful cleaning combination of HCl and ethanol completely solves the problem of protein and fat contamination of the sensor in fish, significantly reducing signal drift and memory effects, ensuring the comparability of results from multiple measurements and samples. KCl provides a stable ionic standard, while a special cleaning solution (KOH + KCl + ethanol) for the reference electrode ensures the stability of the measurement "reference ruler" itself, making all measured flavor signals authentic and reliable. The precise combination of these components guarantees accurate and stable fish flavor analysis.

[0057] The olfactory characteristic determination process described in this invention involves extracting volatile substances from fish meat as follows: The fish meat sample is placed in a headspace vial, an internal standard and salt solution are added, and then heated for extraction. After extraction, the headspace microextraction needle is inserted into the headspace vial for continued heating, followed by analysis. This method aims to capture and amplify extremely trace but crucial volatile flavor signals in fish meat as realistically, comprehensively, and reproducibly as possible. By using gentle headspace heating instead of solvent extraction, the process of human nose olfaction is better simulated, capturing the truly "volatile" odors. The introduction of the internal standard method acts as a "quality controller" for the entire process, ensuring the reliability and quantification of data across different batches and instruments, which is crucial for studying flavor changes during storage. Salting out and heating significantly increase headspace concentration, allowing the extraction head to efficiently enrich these substances, enabling the detection of even key flavor compounds at extremely low concentrations (ppb or even ppt levels).

[0058] In the determination of olfactory characteristics, the selection of chromatographic and mass spectrometric conditions is the core technology of the entire process. They directly determine the resolution, sensitivity, accuracy, and reliability of the analysis, and ultimately profoundly affect the validity of the OAV and ROC calculation results. The core objective of chromatographic conditions is to achieve complete separation of dozens or even hundreds of volatile compounds in the fish headspace sample on the chromatographic column in the shortest possible time. Separation is a prerequisite for qualitative and quantitative analysis. The chromatographic conditions described in this invention are as follows: Column temperature: Initial temperature 40℃, held for 2 min (a low initial temperature is beneficial for the focusing and separation of low-boiling-point compounds. If the initial temperature is too high, these compounds will elute together instantly, making separation impossible, resulting in overlapping chromatographic peaks, inaccurate quantification, and severely distorting their contribution to flavor (OAV)). Then, increase the temperature to 150℃ at 8℃ / min and hold for 3 min (the eluent at this stage is mainly medium-boiling-point compounds, which is the region where flavor substances are most concentrated (such as most esters, terpenes, and some aldehydes and ketones). A moderate heating rate can improve analytical efficiency while ensuring resolution). Next, increase the temperature to 200℃ at 5℃ / min and hold for 5 min (reducing the heating rate is to improve resolution. At this point, the eluent may be compounds with higher boiling points and more similar structures (such as some sesquiterpenes and aromatic compounds). Slightly slowing down the rate gives the column more time to focus the chromatographic peaks). (They are separated), the temperature is increased to 280℃ at 15℃ / min and held for 2min (rapid heating is to "wash" out high-boiling-point substances. Some wax esters and long-chain fatty acids in fish meat have very high boiling points. They do not contribute much to the flavor but can contaminate the chromatographic column. Rapidly heating to a high temperature and quickly washing them out can shorten the analysis time, protect the chromatographic column, and prepare for the analysis of the next sample); Inlet temperature: 250℃ (to ensure that all compounds adsorbed on the extraction head, including high-boiling-point substances, can be completely desorbed instantly and enter the chromatographic column with a narrow bandwidth. This is a prerequisite for obtaining sharp peak shape and high resolution); Transfer line temperature: 280℃ (to ensure that all compounds flowing out of the chromatographic column remain in a gaseous state before reaching the mass spectrometer and are not lost due to condensation during transport); Carrier gas flow rate: 1.0mL / min (to achieve a good balance between resolution and analysis speed).

[0059] The mass spectrometry conditions described in this invention are as follows: Ion source temperature: 230℃ (the compound molecules are ionized by electron bombardment (EI) at this temperature. This temperature prevents the compound from condensing in the ion source, ensuring accurate quantification, which is the basis for accurate OAV calculation), Quadrupole temperature: 150℃ (used to screen ions with different mass-to-charge ratios (m / z). Heating is used to remove any possible residual contaminants, keep the mass analyzer clean, ensure the accuracy and stability of the mass scan, and avoid generating interference signals), Mass spectrometry: EI source (provides highly reproducible and rich fragment ion information. The generated fragment ion peaks have "fingerprint" characteristics and can be compared with standard mass spectrometry libraries (such as the NIST library) to reliably identify compounds), Mode: Full scan 40-600 m / z (fully captures the complex flavor profile of fish).

[0060] The chromatographic and mass spectrometric conditions of this invention fully consider the requirements for the separation, identification, and quantification of complex volatile flavor compounds in fish. Any operation that deviates from these conditions may introduce errors, causing the final calculated odor activity value (OAV) and relative contribution (ROC) to fail to truly reflect the objective olfactory characteristics of fish, thus rendering the entire advanced data analysis meaningless.

[0061] The ROC values ​​of each volatile odor active substance were ranked from high to low. The top few substances with the highest ROC values ​​were summed. The odor description of the OAV corresponding to the sum of ROC values ​​≥ 80% was used as the evaluation result of the overall odor characteristics of the sample.

[0062] In embodiments of the present invention, the odor-active substance corresponding to the odor activity value is selected from any one or more of 3-undecanoate, naphthalene, myristal, trans-4-decanal, trans-2-octenal, lauraldehyde, nonanal, decanal, hexadecaldehyde, tridecanal, pentadecaldehyde, dimethyl tetrasulfide, octanol, 1-nonanol, n-hexanol, and 1-octen-3-ol.

[0063] The above is a detailed description of the technical solution of the present invention. The following are specific embodiments.

[0064] Example 1

[0065] 1. Selection of fish meat samples

[0066] Thirty grass carp from different sources were randomly selected (ten wild grass carp, ten feed grass carp, and ten suspended grass carp; the wild grass carp were caught from wild waterways, the suspended grass carp were "slimmed grass carp" that had been raised in clean water for a period of time, and the feed grass carp were grass carp raised in ordinary ponds with artificial feed).

[0067] 2. Appearance characteristics measurement

[0068] Test method:

[0069] (1) Morphology

[0070] Measure the fish's body weight and length, and dissect it to separate the internal organs and liver, weighing them to calculate morphological indicators.

[0071] Fish body weight measurement method: Weigh the fish to be measured using an electronic balance with an accuracy of 0.01g and record its weight value in grams (g). Before measurement, ensure that the surface moisture of the fish has been dried.

[0072] Method for measuring fish body length: Place the fish body flat on a measuring plate, allowing it to stretch naturally. Use a ruler with an accuracy of 0.1 cm to measure the distance from the snout to the base of the tail fin. Record this distance as the body length in centimeters (cm).

[0073] Method for measuring the weight of internal organs: Use a dissecting knife to cut along the midline of the fish's abdomen from below the gill cover to the anus, carefully open the abdominal cavity, and completely remove all the internal organs (including intestines, stomach, spleen, kidneys, gonads, etc.). Use an electronic balance with an accuracy of 0.01g to weigh the total weight of the internal organs, in grams (g).

[0074] Liver weight measurement method: The liver is separated from the above-mentioned internal organs and weighed separately using an electronic balance with an accuracy of 0.01g. The unit is grams (g).

[0075] The hepatosomatic index (HSI), visceral index (VSI), and condition factor (CF) of fish are calculated using the following formulas:

[0076] Liver body ratio (HSI, %) = 100 × W h / W;(1)

[0077] Visceral body ratio (VSI, %) = 100 × W v / W; (2)

[0078] Conditionness (CF, g / cm³) 3 ) = W / L 3 (3)

[0079] In the above formula, W represents body weight (g); W h For liver weight (g); W v 1 is the weight of internal organs (g); L is the body length (cm).

[0080] (2) Fish meat color

[0081] After dissecting the fish, one side of the dorsal muscle was quickly harvested, and the color index of the fish meat was measured using a portable colorimeter (Konica Minolta, CM-2600d). The color index was determined for each 15cm section of the flesh. 2Repeat the measurement three times at different locations, and finally take the average value.

[0082] Test results:

[0083] The test results for the shape and color of the fish meat are shown in Table 1.

[0084] Table 1 Morphological indicators and muscle color of grass carp from different sources

[0085]

[0086]

[0087] Note: L*, a*, and b* represent brightness, red-green value, and yellow-blue value, respectively.

[0088] As shown in Table 1, morphologically, compared with feed-fed grass carp, the liver-to-body ratio and viscera-to-body ratio of wild grass carp were significantly lower (P<0.05), while the liver-to-body ratio, viscera-to-body ratio, and condition factor of wild grass carp were significantly lower (P<0.05). These results indicate that the edible portion of wild grass carp and wild grass carp is higher than that of feed-fed grass carp. In terms of flesh color, compared with feed-fed grass carp, the muscle brightness and whiteness values ​​of wild grass carp were significantly higher, and the yellow-blue tint of the muscle was significantly lower (P<0.05), exhibiting a whiter flesh color; while wild grass carp further improved the muscle brightness and whiteness on the basis of wild grass carp (P<0.05), thus presenting a whiter flesh color that is more popular with consumers.

[0089] 3. Tactile Feature Measurement

[0090] Test method:

[0091] (1) Texture of fish meat

[0092] Square muscle samples measuring 2cm × 2cm × 1cm were cut from fresh fish meat. A TA.XT plus physical property testing instrument (Stable Micro System, UK) was used, employing a flat-bottomed cylindrical probe P / 36R (diameter: 36mm) and a 50kg weighing sensor for texture profile analysis (TPA). The compression ratio was set to 30%, and the probe movement speed was 1mm / s during the experiment, with a 2s interval between compressions. TPA analysis yielded texture characteristics such as muscle hardness, viscosity, cohesion, elasticity, resilience, and chewiness.

[0093] Hardness: The maximum force (N) required to reach maximum deformation during the first compression process;

[0094] Viscosity: The area (N·S) of the negative force region generated by the sample adhering to the probe surface during the probe's ascent after the first compression;

[0095] Cohesion: The ratio of the energy of the second compressive deformation to the energy of the first compressive deformation;

[0096] Elasticity: The ratio (mm) of the sample's recovery height to the compression deformation height before the second compression begins;

[0097] Resilience: A measure of a sample’s ability to recover after a second compression, calculated as the ratio of the energy recovered from deformation after the second compression to the energy of deformation after the second compression;

[0098] Chewability: Hardness × Cohesion × Elasticity, representing the energy required to chew fish meat to a state suitable for swallowing.

[0099] (2) Water-holding capacity of fish

[0100] The water-holding capacity of fish meat was determined using the loss-in-weight method. The specific method is as follows: Weigh approximately 1g of square muscle pieces, wrap the fish meat in filter paper (V1), place it in a centrifuge tube, and centrifuge at room temperature (4000g, 10min). The filter paper absorbs the juice from the fish meat sample and becomes wet. Weigh the wet filter paper (V2), and then place the filter paper in an oven (75℃) to dry until a constant weight (V3). Calculate the water-holding capacity using the formula below.

[0101] Juice loss rate (%) = 100 × (V2 - V1) × S -1 (4)

[0102] Water loss rate (%) = 100 × (V2 - V3) × S -1 (5)

[0103] Fat loss rate (%) = 100 × (V3 - V1) × S -1 (6)

[0104] In the above formula, S is the weight of the muscle mass (g); V1 is the weight of the dry filter paper (g); V2 is the weight of the wet filter paper (g); and V3 is the weight of the filter paper after constant weight (g).

[0105] (3) Composition of crude components in fish meat

[0106] The determination of muscle moisture, crude protein, crude fat and ash content was carried out in accordance with the methods described in GB 5009.3-2016, GB5009.5-2016, GB 5009.6-2016 and GB 5009.4-2016, respectively.

[0107] Test results:

[0108] The test results for the texture indicators of the fish meat are shown in Table 2. The test results for crude component and water-holding capacity are shown in Table 3. Figure 1 and Figure 2 .

[0109] Table 2 Muscle Texture Indicators

[0110]

[0111] As shown in Table 2, in terms of muscle texture, the muscle elasticity of wild grass carp was significantly lower than that of grass carp raised in water and grass carp fed with feed (P<0.05), while there were no significant differences in other indicators (P>0.05).

[0112] Depend on Figure 1 The crude component indicators show that wild grass carp muscle has the highest moisture content, significantly higher than the other two grass carp species (P<0.05), while there is no significant difference in moisture content between the muscle of *Hydrocotyledon bream* and *Farmed grass carp* (P>0.05). *Hydrocotyledon bream* muscle has the highest crude protein content, significantly higher than wild grass carp (P<0.05), but no significant difference compared to *Farmed grass carp* (P>0.05). Wild grass carp muscle has the lowest crude fat content, significantly lower than the other two grass carp species (P<0.05). There is no significant difference in ash content among the three types of grass carp muscle (P>0.05).

[0113] This invention measures three indicators—juice loss rate, fat loss rate, and water loss rate—to collectively characterize muscle water-holding capacity. Figure 2 It can be seen that the muscle juice loss rate, water loss rate, and fat loss rate of the wild grass carp were significantly lower than those of the feed grass carp (P<0.05). Among the three types of grass carp, the wild grass carp had the lowest muscle fat loss rate, followed by the wild grass carp, while the feed grass carp had the highest muscle fat loss rate, which was significantly higher than the other two types of grass carp (P<0.05).

[0114] 4. Taste characteristics determination

[0115] (1) Sample pretreatment

[0116] Fish muscle was collected and added to distilled water at a ratio of 0.3 g / mL, then pulverized to obtain a slurry. The slurry was subjected to ultrasonic extraction to obtain an extract for 10–15 min at a frequency of 40–50 kHz and a temperature of 4–5 °C. The extract was centrifuged and filtered to obtain a supernatant at 10,000 rpm for 10–15 min at a temperature of 4–5 °C using a nylon membrane. The supernatant was used for testing.

[0117] To reduce errors caused by individual fish, the muscle of every two fish was mixed into one test sample.

[0118] (2) Main instruments and equipment and reagents

[0119] An electronic tongue device is used to evaluate five basic tastes (sour, sweet, bitter, salty, and umami) and astringency.

[0120] Test solution:

[0121] Reference solution (reference saliva): 30 mM potassium chloride + 0.3 mM tartaric acid;

[0122] Negative electrode cleaning solution: 100mM hydrochloric acid + 30% ethanol (by volume);

[0123] Positive electrode cleaning solution: 10mM potassium hydroxide + 100mM potassium chloride + 30% ethanol (by volume);

[0124] Data Processing: All data are relative output values ​​based on artificial saliva (reference solution). The electronic tongue test simulates the state of the human mouth when only saliva is present. Using the output of the reference solution as zero, except for sour and salty tastes, the tastelessness point for other indicators is 0. This invention uses taste items with a tastelessness point greater than 0 as the evaluation criteria. Since the reference solution is prepared from potassium chloride and tartaric acid, it contains small amounts of acid and salt; the tastelessness points for sour and salty tastes are -13 and -6, respectively.

[0125] Test results: The taste characteristics of fish meat are shown in [the following text is incomplete and requires further context]. Figure 3 .

[0126] Figure 3 The results of electronic tongue radar maps of the muscle tissue of three types of grass carp are presented. Indicators above the "tasteless" point are perceptible tastes, such as saltiness, richness (umami aftertaste), umami, and bitterness (perceptible only in wild grass carp). Indicators below the "tasteless" point are imperceptible, such as sweetness, sourness, bitter aftertaste, astringency, and astringent aftertaste. The greatest difference among the three types of grass carp is in saltiness, with wild grass carp having the highest saltiness value, followed by water-fed grass carp, and finally feed-fed grass carp. Richness also shows a similar trend to saltiness, but the difference is not as pronounced. Wild grass carp has the highest umami and richness indicators, followed by water-fed grass carp, and feed-fed grass carp has the lowest. Only wild grass carp muscle has a bitterness value above the "tasteless" point; the bitterness values ​​of feed-fed and water-fed grass carp muscle are imperceptible.

[0127] 5. Olfactory characteristics measurement

[0128] Test method:

[0129] (1) Extraction of volatile substances

[0130] Weigh an appropriate amount of the mixed fish meat sample (2-4g) that has been minced at low temperature and place it in a 20ml headspace vial. Add the internal standard 2,4,6-trimethylpyridine to make its concentration for the microextraction process 5mg / L. Add 5mL of saturated sodium chloride solution and heat at 78℃ for 48 minutes. After extraction, insert the headspace microextraction needle into the headspace vial and continue heating for 30 minutes. Then, desorb at 250℃ for 5 minutes.

[0131] (2) Chromatography-mass spectrometry analysis

[0132] The chromatographic column was an HP-5MS (30m × 0.25mm × 0.25μm). The chromatographic separation conditions were as follows: column temperature: initial temperature 40℃, hold for 2 min, increase to 150℃ at 8℃ / min, hold for 3 min, then increase to 200℃ at 5℃ / min, hold for 5 min, increase to 280℃ at 15℃ / min, hold for 2 min; injection port temperature: 250℃; transfer line temperature: 280℃; carrier gas flow rate: 1.0mL / min; split ratio: splitless; mass spectrometry conditions: ion source temperature: 230℃, quadrupole temperature: 150℃, mass spectrometry: EI source, mode: full scan 40-600m / z.

[0133] (3) Compound identification

[0134] The mass spectra of the compounds were compared with the NIST20 database. The retention index (RI) was calculated using the modified Kováts method. The compounds were identified by comparing standard mass spectra with the RI. Substances with a matching degree greater than or equal to 70% were screened to obtain the number of volatile compounds under each extraction condition. The relative content of each volatile component to the internal standard was calculated using the following formula:

[0135] Content of unknown substance (ng / g) = Peak area of ​​unknown substance ion / Peak area of ​​internal standard × Content of internal standard substance × 1000 (7)

[0136] (4) Identification of odor-active substances

[0137] Using the relative internal standard concentrations of each volatile compound, the odor activity value (OAV) is calculated according to the following formula:

[0138] OAV = Compound concentration (ng / g) / Odor threshold of the compound (ng / g) (8)

[0139] Based on OAV ≥ 1, odor-active substances were screened out, namely those compounds that actually contribute to the overall odor of grass carp meat. However, odor-active substances are often not just one or two, but multiple substances, and different substances exhibit different odors. If the odor of all substances with OAV is used to describe the overall odor characteristics of the sample, it often becomes very complex and difficult to understand. Therefore, we introduce a concept—Relative Contribution (ROC).

[0140] ROC(%) = OAV i / OAV t ×100%(9)

[0141] In the above formula, OAV i This indicates the content of a certain type of OAV. t This indicates all OAVs in the sample. i sum.

[0142] The ROC values ​​of each volatile odor active substance were ranked from high to low. The top few substances with the highest ROC values ​​were summed. The odor description of the OAV corresponding to the sum of ROC values ​​≥ 80% was used as the evaluation result of the overall odor characteristics of the sample.

[0143] Test results:

[0144] The distribution, content, active volatile odor compounds, and relative contribution of volatile odor substances in fish meat are shown in the following figures. Figure 4 , Figure 5 And Table 4.

[0145] Table 4. Results of Volatile Odor-Active Substances and Their Relative Contributions in Fish Meat

[0146]

[0147] Note: In the table above, ND indicates that the substance was not detected, and therefore there is no OAV value.

[0148] Volatile compounds detected in the muscle of three grass carp species were classified into eight categories: aldehydes, esters, ketones, hydrocarbons, alcohols, aromatic compounds, heterocyclic compounds, and nitrogen- and sulfur-containing compounds. Radar chart analysis was performed to assess the distribution of each compound type and its concentration (see [link to analysis]). Figure 4 , Figure 5 ). Figure 4 This is the result of classifying volatile odor compounds detected in the muscles of three types of grass carp. The numbers represent the number of substances. It can be seen that the feed grass carp has more types of hydrocarbons and aldehydes, with 10 types in each. The draught grass carp has the most aldehydes, with 11 types. The main volatile odor compounds in wild grass carp are hydrocarbons and aldehydes, but there are very few types, with only 4 types in each. Figure 5 It can be seen that grass carp fed with feed have the highest content of hydrocarbons and aldehydes, grass carp raised in water have a relatively high content of aldehydes, but less than grass carp fed with feed, and wild grass carp have the lowest content of compounds.

[0149] As can be seen from the above, wild grass carp meat has fewer types and lower content of volatile odor compounds, with aldehydes and hydrocarbons being the main volatile odor substances; the content of volatile odor compounds in water-fed grass carp is between that of wild grass carp and water-fed grass carp, with aldehydes and alcohols being the main volatile odor substances; and feed grass carp has the highest content and the most types of volatile odor compounds, with aldehydes and hydrocarbons being the main volatile odor substances.

[0150] Calculations of the content of odor active substances (OAVs) in grass carp meat samples revealed a total of 16 OAVs in the muscle of grass carp from three sources: 4 OAVs were detected in wild grass carp meat, 15 OAVs were detected in grass carp meat raised in water, and 12 OAVs were detected in grass carp fed with feed. The ROC calculation results showed that hexadecaldehyde, nonanal, and pentadecaldehyde contributed over 99% to the overall aroma of wild grass carp meat, reflecting relatively complete odor information. Based on the odor characteristics of these three compounds, the aroma of wild grass carp meat can be described as sweet apricot and nutty, accompanied by a small amount of fishy smell and a small amount of smoky smell. For grass carp raised in water, nonanal, dimethyl tetrasulfide, and 1-octen-3-ol contributed over 80% to the overall aroma, reflecting relatively complete odor information. Based on the odor characteristics of these three compounds, the aroma of grass carp raised in water can be described as a complex aroma with a small amount of fishy smell mixed with a small amount of garlic and raw fish smell, accompanied by a small amount of earthy smell. For grass carp raised in feed, nonanal and dimethyl tetrasulfide contributed over 80% to the overall aroma, reflecting relatively complete odor information. Based on the odor characteristics of these two compounds, the aroma of grass carp raised in feed can be described as a very strong garlic and raw fish smell accompanied by a high concentration of fishy smell.

[0151] 6. Principal component analysis based on appearance, touch, taste, and smell characteristics.

[0152] Principal component analysis (PCA) was performed based on the appearance, touch, taste, and smell-related indicators detected in the fish meat. PCA was used to simplify the feature data, transforming it to a new coordinate system such that the first largest variance of any data projection lies on the first coordinate (called the first principal component), and the second largest variance lies on the second coordinate (the second principal component). See [link to PCA]. Figure 6 The numbers 1 and 3 represent different types of grass carp. 1-1 represents the first wild grass carp sample, 1-2 the second, and so on. 2 represents grass carp raised in water, 2-1 the first sample, 2-2 the second, and so on. 3 represents forage grass carp, 3-1 the first sample, 2-2 the second, and so on. It can be seen that, on the Y-axis, all five forage grass carp samples are on the right side of the Y-axis, while all five wild grass carp samples are clustered on the left side, indicating a significant difference between the two types of grass carp along the Y-axis. On the X-axis, all five forage grass carp samples are above the X-axis, while both wild and forage grass carp samples are below the X-axis. These results show that the three different sources of the same species of fish can be clearly distinguished, indicating that evaluating fish meat quality based on these characteristics can effectively differentiate samples of the same species from three different sources, demonstrating the high accuracy of the evaluation method.

[0153] The above are merely preferred embodiments of the present invention. It should be noted that the above preferred embodiments should not be considered as limitations on the present invention, and the scope of protection of the present invention should be determined by the scope defined in the claims. For those skilled in the art, several improvements and modifications can be made without departing from the spirit and scope of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for evaluating fish meat, characterized in that, Includes the following steps: Appearance characteristics measurement: including measurement of fish flesh shape and color; Tactile characteristic measurement: including the measurement of fish flesh texture, water holding capacity, and crude composition; Taste characteristics determination: Determining the taste characteristics of fish meat; Olfactory characteristic determination: Volatile substances were extracted from fish meat and analyzed by chromatography-mass spectrometry to identify compounds. The odor activity value (OAV) was calculated based on the concentration of these compounds. The relative contribution (ROC) was calculated based on the OAV, and the compounds with the highest ROC values ​​were selected as characteristic data. The formula for calculating the odor activity value is: OAV = Compound concentration / Odor threshold of the compound; the formula for calculating the relative contribution is: ROC(%) = OAV i / OAV t ×100%; OAV i This indicates the content of a certain type of OAV. t This indicates all OAVs in the sample. i sum; Fish meat samples were obtained, and various characteristic data were obtained through the aforementioned appearance characteristic measurement, tactile characteristic measurement, taste characteristic measurement, and olfactory characteristic measurement. Principal component analysis is performed on the feature data to obtain the evaluation results.

2. The fish meat evaluation method according to claim 1, characterized in that, The determination of fish morphology includes measuring the fish's body weight, body length, visceral weight, and liver weight, and calculating the liver-to-body ratio, visceral-to-body ratio, and fatness.

3. The fish meat evaluation method according to claim 1, characterized in that, The colorimetric determination includes dividing each side of the fish meat sample into 15cm sections. 2 The frequency of the three measurements was measured using a colorimeter, with each measurement taken at a different location, and the average value was calculated.

4. The fish meat evaluation method according to claim 1, characterized in that, The determination of water-holding capacity includes: weighing the fish sample; wrapping the fish sample in filter paper and centrifuging it at room temperature with a centrifugal force of 3500-4500g for 8-15 minutes, during which the filter paper absorbs the juice from the fish sample and becomes wet filter paper; drying the wet filter paper at 70-80℃ to constant weight to obtain dried filter paper; weighing the initial weight of the filter paper, the weight of the wet filter paper, and the weight of the dried filter paper, and calculating the juice loss rate, water loss rate, and fat loss rate.

5. The fish meat evaluation method according to claim 1, characterized in that, The determination of fish meat texture includes obtaining a cube-shaped fish meat sample, performing texture profile analysis on the fish meat sample using a physical property tester to obtain texture characteristics, the texture characteristics including at least one of hardness, viscosity, cohesion, elasticity, resilience and chewiness; and conducting a double compression test with a compression ratio of 30%, in which the probe movement speed of the physical property tester is 1 mm / s and the interval between the two compressions is 2 s.

6. The fish meat evaluation method according to claim 1, characterized in that, The taste characteristic determination includes: the fish meat sample is limited to a specified part of the fish body, added to distilled water at a ratio of 0.3 g / mL and pulverized to obtain a slurry; the slurry is subjected to ultrasonic extraction to obtain an extract, for 10-15 min, with an ultrasonic frequency of 40-50 kHz and a temperature controlled at 4-5℃; the extract is centrifuged and filtered to obtain a supernatant, with a centrifugation speed of 10000 rpm, a time of 10-15 min, and a temperature controlled at 4-5℃, using a nylon filter membrane; the supernatant is measured using an electronic tongue device, the test solutions of which are: reference solution: 30 mM potassium chloride + 0.3 mM tartaric acid; negative electrode cleaning solution: 100 mM hydrochloric acid + 30% volume ethanol; positive electrode cleaning solution: 10 mM potassium hydroxide + 100 mM potassium chloride + 30% volume ethanol.

7. The fish meat evaluation method according to claim 1, characterized in that, The process of extracting volatile substances from fish meat during the olfactory feature determination is as follows: the fish meat sample is placed in a headspace vial, an internal standard and a salt solution are added, and then the sample is heated for extraction. After extraction, the headspace microextraction needle is inserted into the headspace vial for continued heating, and finally the sample is analyzed.

8. The fish meat evaluation method according to claim 1, characterized in that, The chromatographic conditions were as follows: column temperature: initial temperature 40℃, hold for 2 min, increase to 150℃ at 8℃ / min, hold for 3 min, then increase to 200℃ at 5℃ / min, hold for 5 min, then increase to 280℃ at 15℃ / min, hold for 2 min; injection port temperature: 250℃; transfer line temperature: 280℃; carrier gas flow rate: 1.0 mL / min.

9. The fish meat evaluation method according to claim 1, characterized in that, The odor-active substance corresponding to the odor activity value is selected from any one or more of 3-undecanone, naphthalene, myristal, trans-4-decanal, trans-2-octenal, lauraldehyde, nonanal, decanal, hexadecaldehyde, tridecanal, pentadecaldehyde, dimethyl tetrasulfide, octanol, 1-nonanol, n-hexanol, and 1-octen-3-ol.

10. The method for evaluating fish meat according to any one of claims 1 to 9, characterized in that, The fish meat is selected from any one or more of the following: wild fish meat, feed-fed fish meat, and fish raised in water.

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