Pelteobagrus fulvidraco cold-chain transportation and storage body color protection method based on color protection preservative

Abstract

The invention belongs to the technical field of body color stabilization of freshwater fishes in cold-chain transportation and storage. The invention relates to a body color protection method in cold-chain transportation and storage of pelteobagrus fulvidraco based on a color protection preservative. The body color protection method is characterized by comprising the following steps: 1) preparing a color protection preservative solution; 2) preparing a body surface protective film solution; (3) temporarily rearing fresh pelteobagrus fulvidraco for 6 hours to relieve transportation stress, stirring in an ice-water bath, slaughtering, removing viscera and gills, cleaning, and simply draining; soaking the drained pelteobagrus fulvidraco in the color-protecting preservative solution obtained in the step (1) for 3 hours; then uniformly spraying the body surface protective film solution prepared in the step 2) on the surface of the fish body; (4) putting the pelteobagrus fulvidraco subjected to vacuum packaging in the step (3) into a quick-freezing warehouse for quick-freezing; (5) in the transportation and storage stages, proper environmental conditions are kept; and 6) taking out the quick-frozen pelteobagrus fulvidraco from the vacuum bag, and directly thawing the pelteobagrus fulvidraco together with the protective film on the surface in a running water thawing manner. The method is remarkable and stable in color protection effect.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of body color stability of freshwater fish in cold chain transportation and storage, and relates to a body color protection method of Pelteobagrus fulvidraco in cold chain transportation and storage based on a color-protecting preservative. BACKGROUND

[0002] Global fish resources are abundant, especially freshwater fish, which are an important source of protein for us. The rich body color of fish is an important feature, and the change of body color is often associated with the nutritional value and freshness of fish in freshwater aquaculture, transportation, storage, and sales, which is an important subjective basis for consumers to judge.

[0003] Pelteobagrus fulvidraco is a characteristic freshwater fish with yellow color. It is favored by consumers because of its delicious meat and no intermuscular spines. However, during cold chain transportation and storage, the yellow color of the body surface falls off with the mucus, leading to a change in body color and reducing its economic value, affecting the choice of consumers. The change of body color in the cold chain transportation and storage link is often considered to be due to the action of microorganisms and oxidation, but the use of traditional preservatives only has a positive effect on extending the shelf life of fish meat, and the protection effect on body color is not ideal. The main component of the yellow color on the body surface of Pelteobagrus fulvidraco is carotenoids (β-carotene, astaxanthin, lutein, etc.). Due to the typical structure of the polyene chain and the two end rings of carotenoids, it is extremely easy to cause the cleavage of the polyene chain and the oxidation of the end ring during transportation, storage, and processing due to the action of endogenous enzymes, microbial metabolism, and oxidation, forming ring epoxides and other aldehyde ketone substances (such as; β-carotene-5,6-epoxide, β-carotene-5,8-epoxide, β-carotene-5,6,5',6'-epoxide, β-ionone, 2,6,6-trimethylcyclohexanone, β-cyclocitral, etc.). However, the currently used preservatives such as tea polyphenols and ascorbic acid do not have good protection effect. In order to improve the body color stability of Pelteobagrus fulvidraco during cold chain transportation and storage, it is beneficial to protect the body color of Pelteobagrus fulvidraco to screen a color-protecting preservative with double functions of color protection and preservation. SUMMARY

[0004] The purpose of the present application is to provide a body color protection method of Pelteobagrus fulvidraco in cold chain transportation and storage based on a color-protecting preservative, which has a significant and stable color protection effect.

[0005] In order to achieve the above purpose, the technical scheme adopted by the present application is: a body color protection method of Pelteobagrus fulvidraco in cold chain transportation and storage based on a color-protecting preservative, characterized in that it comprises the following steps: 1) Preparation of color protection preservative solution: by mass fraction: 1%-1.2% acetic acid, 1.2%-1.5% chitosan, 3%-4% trehalose, water balance, select acetic acid, chitosan, trehalose and water; acetic acid is dissolved in water, chitosan is added, stirred to make it hydrated and completely dissolved, then trehalose is added, continue to stir and dissolve, get color protection preservative solution; 2) Preparation of body surface protective film solution: by mass fraction: 90% soluble starch of color protection preservative solution, 1% gelatin, 0.5% lecithin, water balance, select soluble starch, gelatin, lecithin and water, mix soluble starch, gelatin, lecithin, add the balance of water, stir until all ingredients are completely dissolved, get uniform body surface protective film solution; 3) Fresh yellow roach is temporarily raised for 6 h to relieve transportation stress, then ice water bath stirring is carried out for slaughter, remove the viscera, gills, clean, and simple drain; Color protection treatment: after draining, the yellow roach is soaked in the color protection preservative solution obtained in step 1) for 2.5-3 h; after soaking treatment, it is fished out, gently fished and gently loaded, reducing the damage of external force to the fish body surface; then the body surface protective film solution prepared in step 2) is uniformly sprayed on the fish body surface, and after spraying, it is placed at room temperature (20-25 ℃) for drying for 15-20 min, the spraying and drying operation is repeated for 3 times, so that a complete and uniform protective film is formed on the fish body surface; after completion, the fish body is packed in a bag, vacuum packed (note to control the vacuum time to avoid excessive extrusion of yellow roach); 4) The yellow roach vacuum packed in step 3) is placed in a quick freezer for quick freezing; 5) In the transportation and storage stage, the "soluble starch-gelatin-lecithin" protective film formed on the fish body surface is used to reduce the mechanical friction of yellow roach in the transportation and storage process; 6) The quick-frozen yellow roach is taken out from the vacuum bag, and directly connected with the surface protective film is thawed by flowing water, that is, it can be used. Further, the body surface protective film solution prepared in step 2) should meet the food grade standard, wherein the soluble starch should be selected from high purity (mass purity ≥ 99%) product, the gelatin should be food grade animal gelatin or plant gelatin, and the lecithin should be food grade soybean lecithin; the protective film formed should have good flexibility and water solubility, which can gradually soften or partially dissolve with water flow during thawing process, which does not affect the quality of fish body, and can continuously play a protective role.

[0006] Further, the temperature of the quick freezer in step 4) is-30~-32 ℃, and the quick freezing time is 6.0~8.0 h; Further, the suitable environmental conditions in step 5) are: during transportation, violent jolting should be avoided; the storage environment should be kept at low temperature (-18 to -20 DEG C) and dry (relative humidity is less than or equal to 60%), so as to prevent the protective film from softening or breaking due to moisture. Further, the water temperature during the flow water thawing in step 6) is 4 to 10 DEG C, and the water flow speed is 0.5 to 2 L / min, and the thawing is completed when the temperature of the fish body center reaches 0 to 4 DEG C; and during the flow water thawing, it should be ensured that the water flow uniformly washes the fish body and the surface protective film, so as to avoid local over-thawing or incomplete thawing, and the protective film on the surface of the fish body will not be largely detached due to the water flow impact, and the stability of the color-protecting and fresh-keeping effect can be further verified. The beneficial effects of the present application are: 1. The color-protecting effect is significant and stable: the vinegar, chitosan and trehalose in the color-protecting and fresh-keeping agent are compounded, the vinegar is used to adjust the acid-base environment of the fish body surface to stabilize the epidermal coloring substances, the chitosan is used to form a film to isolate oxygen and light, and the trehalose is used to resist freezing and protect cells, and the three effects inhibit the oxidation and loss of pigments; after the rapid freezing (-30 to -32 DEG C, 6.0 to 8.0 h) and the flow water thawing (4 to 10 DEG C), the original fresh and lively color of the yellow-head catfish can still be maintained, and the problems of browning and dull color in the traditional freezing and thawing can be effectively avoided. 2. The fish body quality is comprehensively protected: the chitosan and trehalose are used to reduce the detachment of the surface mucus, the protective film formed by spraying and drying the solution of food-grade "90% soluble starch, 1% gelatin and 0.5% lecithin" for three times is adhered and protected, the mechanical friction and extrusion in the process of rapid freezing and storage and transportation are buffered, and the epidermis is prevented from being damaged and the meat quality is prevented from being deformed; the trehalose can also inhibit the growth of ice crystals in muscle cells during the freezing and thawing period, reduce the cell rupture rate, reduce the loss of water and water-soluble nutrients, and maintain the tight and juicy taste of the fish meat. 3. The process has high practicability: the color-protecting and fresh-keeping agent only needs to be dissolved according to the proportion of the raw materials, and complex equipment is not required; the parameters of the whole process (temporary raising, slaughtering, color-protecting soaking, spraying and drying the solution of "90% soluble starch, 1% gelatin and 0.5% lecithin" to form a film, rapid freezing and thawing) are clear, and the operation is simple, and professional technology is not required, and especially the flow water thawing with the protective film can avoid secondary damage, and is suitable for multiple scenes such as catering, processing enterprises and families.

[0007] 4. Breakthrough of the pain points in the industry circulation: under the synergistic effect of rapid freezing, color protection and protection, the storage period is prolonged by more than 30% than that of traditional freezing; the skin damage rate is reduced from 15% to 20% to less than 5% after the cold chain transportation of more than 500 kilometers, the transportation loss and cost are reduced, the traditional 100-kilometer distribution radius is broken through, and the cross-regional circulation is facilitated.

[0008] 5. High food safety: The acetic acid, chitosan, trehalose, and "90% soluble starch, 1% gelatin, and 0.5% lecithin" used all meet food-grade standards, with no risk of chemical residues. The entire process involves no high temperatures or toxic reagents, and parameters such as the thawing temperature to a core temperature of 0-4℃ meet food hygiene standards, preventing microbial growth and complying with national food safety requirements. This invention provides an effective color-protecting and preservation agent for yellow catfish during cold chain transportation and storage. Storage experiments have shown that under low-temperature conditions, it can effectively protect the surface color of yellow catfish and extend its shelf life. Attached Figure Description

[0009] Figure 1 This is a photo of yellow catfish after freezing, as shown in Example 1 of the present invention.

[0010] Figure 2 This is a photo of yellow catfish after freezing, as shown in Example 2 of the present invention.

[0011] Figure 3 For comparison with the photos of yellow catfish after freezing in Case 1.

[0012] Figure 4 For comparison, here are photos of yellow catfish after freezing in Case 2.

[0013] Figure 5 For comparison, here are photos of yellow catfish after freezing in Case 3.

[0014] Figure 6 For comparison, here are photos of yellow catfish after freezing in Case 4. Detailed Implementation

[0015] Unless otherwise specified, all percentages in this invention are by weight, and all equipment and materials are commercially available or commonly used in this industry.

[0016] The core measurement method involved in the embodiments and comparative examples of this invention is the measurement of the color retention rate of yellow catfish, as detailed below: I. Determination of color retention rate of yellow catfish (subjective and objective method) 1.1 Materials and Instruments Digital camera (resolution ≥ 24 megapixels, supports manual white balance adjustment); Standard color chart (compliant with CIE LAB color space standards, including 5500 K color temperature calibration color blocks); Image analysis software (such as ImageJ or Photoshop, which have RGB value extraction capabilities); Constant temperature and humidity shooting chamber (temperature controlled at 25±1 ℃, humidity at 50±5%, built-in uniform light source, color temperature at 5500 K, light intensity at 800-1000 lux, avoiding shadow interference); Color retention rate rating table (see Table 1 for details).

[0017] 1.2 Measurement Procedure 1.2.1 Image Acquisition (Uniform Control Variables) Fresh reference sample collection: Freshly slaughtered yellow catfish (without any color protection treatment) were collected within 1 hour. The surface moisture was gently patted dry with sterile absorbent paper. The fish was then placed flat on a white stage in the shooting box with its back facing up. At the same time, the standard color chart was placed 1 cm to the right of the fish (ensuring that the color chart and the fish were evenly lit). The camera parameters were adjusted (focal length 50 mm, aperture f / 8, shutter speed 1 / 12 s, ISO 100, manual white balance calibration to the white block of the standard color chart), and a complete image of the fish was taken vertically (the viewfinder completely covered the fish and the surrounding 2 cm area without edge cropping). This image was used as the "fresh fish color reference image".

[0018] Frozen-thawed sample collection: Yellow catfish that have undergone color protection treatment, quick-freezing, storage and thawing according to the present invention were photographed using the same operation as above (same shooting environment, camera parameters and placement position) as "frozen-thawed fish body color test images".

[0019] 1.2.2 Objective index measurement (RGB value comparison method) Open the "Fresh Fish Color Reference Image" and the "Frozen and Thawed Fish Color Test Image" using image analysis software, and select the same three typical test areas in both images (the central area of ​​the fish's back, each area is 2 cm × 2 cm, avoiding the fins and damaged scales). Extract the average RGB value (R: red channel value, G: green channel value, B: blue channel value) of each detection area, and record the RGB values ​​of each area of ​​the fresh fish body as (R1, G1, B1), and the RGB values ​​of each area of ​​the frozen and thawed fish body as (R2, G2, B2). Calculate the color difference value ΔE for a single detection area using the formula, and then take the average of ΔE for the three areas: (Note: ΔE ranges from 0 to 255. The smaller the ΔE, the smaller the color difference between the frozen and thawed fish and the fresh fish.) Calculate the objective color retention rate using the formula: Objective color retention rate = [1 - (average ΔE / 255)] × 100% 1.2.3 Subjective Evaluation (Professional Panel Scoring Method) A professional evaluation team of 10 people was formed (members were not red-green color blind / color weak, and were trained to master the color characteristics of fresh yellow catfish: the back is dark yellow, the belly is light yellowish-white, and there are no browning or fading spots). The “Fresh Fish Color Reference Image” and the “Frozen-Thawed Fish Color Test Image” were placed side by side on the same white background board (lighting conditions were the same as the shooting box). The evaluators scored the color similarity between the frozen-thawed fish and the fresh fish independently from a distance of 50 cm from the image, referring to the scoring criteria in Table 1. Calculate the average score from 10 evaluators, and then calculate the subjective color retention rate using the formula: Subjective color retention rate = (average score / 5) × 100% 1.2.4 Calculation of Final Results The average of the "objective color retention rate" and the "subjective color retention rate" is taken as the final color retention rate of the sample. Each experiment was repeated 3 times (3 yellow catfish from the same batch were used each time), and the average of the 3 results was calculated as the final data.

[0020] Table 1 Subjective Scoring Criteria for Color Retention Rate of Yellow Catfish To verify the effectiveness of the chitosan-based color-protecting and preservation agent and its supporting method in protecting the body color of yellow catfish during cold chain transportation and storage, two examples (using the optimized formula and process of this invention) and four comparative examples (controls were set up by changing key components or process parameters) were conducted. All yellow catfish used in the experiments were selected as fresh individuals of uniform size (150-200 g / fish) and good vitality. Image acquisition, RGB value extraction, and other operations were performed under uniform conditions (constant temperature and humidity imaging chamber: temperature 25±1 ℃, humidity 50±5%, light source color temperature 5500 K, light intensity 800-1000 lux) to ensure data parallelism. II. Specific Implementation Methods Example 1: A method for protecting the body color of yellow catfish during cold chain transportation and storage based on color-protecting preservatives includes the following steps: 1) Preparation of color-protecting and freshness-preserving agent solution: by mass fraction: 1.2% acetic acid, 1.2% chitosan, 4% trehalose, and deionized water balance (93.6%). Select acetic acid, chitosan, trehalose, and deionized water; dissolve acetic acid in deionized water and stir until completely dissolved; add chitosan and stir until it is completely hydrated and dissolved {stir at 30 ℃ for 30 min until hydrated and dissolved (no undissolved particles)}, then add trehalose and continue stirring to dissolve (continue stirring for 15 min) to obtain a uniform and transparent color-protecting and freshness-preserving agent solution; 2) Preparation of body surface protective film solution: by mass fraction: 90% color-protecting and freshness-preserving agent solution, soluble starch, 1% gelatin, 0.5% lecithin, deionized water balance (8.5%). Select soluble starch, gelatin, lecithin and deionized water, mix soluble starch, gelatin and lecithin, add deionized water, stir until all components are completely dissolved (stir at 35 ℃ for 20 min until completely dissolved) to obtain a uniform body surface protective film solution; 3) Yellow catfish pretreatment: Live yellow catfish are temporarily held for 6 hours (water temperature 15±1 ℃, continuous aeration) to alleviate transportation stress; they are quickly slaughtered by ice water bath (ice water ratio 1:1), internal organs and gills are removed, and they are rinsed clean with running water and drained of surface water (draining time 5 minutes to avoid excessive dehydration). Color protection treatment: After draining, the yellow catfish were completely immersed in the color-protecting and preservative solution obtained in step 1) and soaked at a constant temperature of 25 ℃ for 3 h (stir gently once every 30 min to ensure that the color-protecting and preservative solution is in full contact with the surface of the fish). After soaking, the fish were gently lifted onto a sterile tray, using the remaining preservative solution on the surface of the fish as an adhesion base to reduce damage to the skin of the fish by external force. Then, the protective film solution prepared in step 2) was evenly sprayed onto the surface of the fish (5 mL / fish, completely covering the back and abdomen). After spraying, the fish were placed in a ventilated environment at 25 ℃ to dry for 15 min. The spraying-drying operation was repeated 3 times to form a protective film with uniform thickness (about 15-20 μm), without wrinkles or bubbles. Vacuum packaging: Individually pack the yellow catfish with protective film into food-grade PE vacuum bags, and use a vacuum packaging machine to create a vacuum (vacuum degree -0.095 MPa, heat sealing temperature 180 ℃, heat sealing time 3 s). 4) Quick-freezing storage: Place the vacuum-packed yellow catfish in a -30 ℃ quick-freezing room for 7 hours (measure the core temperature of the fish with a probe thermometer until it drops below -18 ℃), and then transfer it to a -18 ℃ low-temperature cold storage for 15 days; 5) During transportation and storage, maintain suitable environmental conditions and utilize the "soluble starch-gelatin-lecithin" protective film formed on the surface of the fish to reduce mechanical friction on the yellow catfish during transportation and storage; In step 5), the appropriate environmental conditions are as follows: during transportation, violent bumps should be avoided, and the storage environment should be kept at low temperature (-18 to -20 ℃) ​​and dry (relative humidity ≤60%) to prevent the protective film from softening or breaking prematurely due to moisture.

[0022] 6) Thawing process: Remove the yellow catfish from the cold storage, remove the vacuum bag, and place it in 4 ℃ running water (flow rate 1 L / min) with the protective film on to thaw until the core temperature of the fish reaches 2 ℃. During the thawing process, ensure that the water flow evenly washes the fish and the protective film on the surface to avoid local over-thawing or incomplete thawing. The protective film on the surface of the fish will not fall off in large quantities due to the impact of the water flow. This can further verify the stability of the color protection and freshness preservation effect, and the thawing is complete. Example 2: A method for protecting the body color of yellow catfish during cold chain transportation and storage based on a color-protecting preservative, characterized by comprising the following steps: 1) Preparation of color-protecting and freshness-preserving agent solution: by mass fraction: 1.0% acetic acid, 1.5% chitosan, 3% trehalose, and deionized water balance (94.5%). Select acetic acid, chitosan, trehalose, and deionized water; dissolve acetic acid in deionized water, add chitosan, and stir until the deionized water is completely dissolved (stir at 35 ℃ for 25 min until completely dissolved), then add trehalose and continue stirring for 15 min to dissolve, thus obtaining the color-protecting and freshness-preserving agent solution; 2) Preparation of body surface protective film solution: by mass fraction: 90% color-protecting and freshness-preserving agent solution, soluble starch, 1% gelatin, 0.5% lecithin, deionized water balance (8.5%). Select soluble starch, gelatin, lecithin and deionized water, mix soluble starch, gelatin and lecithin, add deionized water, stir until all components are completely dissolved (stir at 35 ℃ for 20 min until completely dissolved) to obtain a uniform body surface protective film solution; 3) Yellow catfish pretreatment: Live yellow catfish are temporarily held for 6 hours (water temperature 15±1 ℃, continuous aeration) to alleviate transportation stress; they are quickly slaughtered by ice water bath (ice water ratio 1:1), internal organs and gills are removed, and they are rinsed clean with running water and drained of surface water (draining time 5 minutes to avoid excessive dehydration). Color protection treatment: After draining, the yellow catfish were completely immersed in the color-protecting and preservative solution obtained in step 1) and soaked at a constant temperature of 22 ℃ for 2.5 h (stir gently once every 30 min to ensure that the color-protecting and preservative solution is in full contact with the surface of the fish). After soaking, the fish were gently lifted onto a sterile tray, using the remaining preservative solution on the surface of the fish as an adhesion base to reduce damage to the skin of the fish by external force. Then, the protective film solution prepared in step 2) was evenly sprayed onto the surface of the fish (5 mL / fish, completely covering the back and abdomen). After spraying, the fish were placed in a ventilated environment at 25 ℃ to dry for 20 min. The spraying-drying operation was repeated 3 times to form a protective film with uniform thickness (about 15-20 μm), without wrinkles or bubbles. Vacuum packaging: Individually pack the yellow catfish with protective film into food-grade PE vacuum bags, and use a vacuum packaging machine to create a vacuum (vacuum degree -0.095 MPa, heat sealing temperature 180 ℃, heat sealing time 3 s). 4) Quick-freezing storage: Place the vacuum-packed yellow catfish in a -32 ℃ quick-freezing room for 6 hours (measure the core temperature of the fish with a probe thermometer until it drops below -18 ℃), and then transfer it to a -18 ℃ low-temperature cold storage for 15 days; 5) During transportation and storage, maintain suitable environmental conditions and utilize the "soluble starch-gelatin-lecithin" protective film formed on the surface of the fish to reduce mechanical friction on the yellow catfish during transportation and storage; In step 5), the appropriate environmental conditions are as follows: during transportation, violent bumps should be avoided, and the storage environment should be kept at low temperature (-18 to -20 ℃) ​​and dry (relative humidity ≤60%) to prevent the protective film from softening or breaking prematurely due to moisture.

[0023] 6) Thawing process: Remove the yellow catfish from the cold storage, remove the vacuum bag, and place it in 10 ℃ running water (water flow rate 0.8L / min) with the protective film on to thaw until the core temperature of the fish reaches 4 ℃. During the thawing process, ensure that the water flow evenly washes the fish and the surface protective film to avoid local over-thawing or incomplete thawing. The protective film on the surface of the fish will not fall off in large quantities due to the impact of the water flow. This can further verify the stability of the color protection and freshness preservation effect, and the thawing is complete. III. Comparative Design (Controlled Verification of Key Factors) Comparative Example 1: (Blank Control: No Color Protection Treatment) This comparative example is a blank control group. No color protection treatment or optimization process was used. Specific steps: Yellow catfish were slaughtered, cleaned, drained, and directly vacuum-packed. They were quick-frozen at -30 ℃ for 6 h and stored at -18 ℃ for 15 d. When thawing, they were placed directly in 25 ℃ room temperature water (without flow) to thaw until the core temperature was 4 ℃. Comparative Example 2: (Chitosan-free: lacking core color-protecting component) This comparative example verifies the core color-protecting effect by removing chitosan from the color-protecting preservative, as follows: Color-protecting agent formula (by mass fraction): 1.2% acetic acid, 4% trehalose (chitosan-free); The remaining steps (pretreatment of yellow catfish, soaking time and temperature, spraying and drying of a solution of "90% soluble starch, 1% gelatin, 0.5% lecithin" to form a film, vacuum packaging, quick-freezing storage, thawing conditions) are completely consistent with Example 1. Comparative Example 3: (No protective film: lack of physical protection) This comparative example omits the protective film preparation step to verify the effect of physical protection on body color retention. Specifically, the difference from Example 1 is that after soaking in step (3), the spraying and drying of the "90% soluble starch, 1% gelatin, 0.5% lecithin" solution is not performed. Instead, the yellow catfish is directly packed into vacuum bags. All other parameters (color protection agent formula, soaking conditions, quick-freezing storage, thawing method) are the same as in Example 1. Comparative Example 4: (Traditional Thawing: Non-directional Protective Thawing) This comparative example verifies the protective effect of optimized thawing on body color by changing the thawing method (removing the protective film + room temperature still water). The specific details are as follows: The only difference from Example 1 is that: in step 6), the protective film on the surface of the fish is manually removed before thawing, and the fish is placed in still water at 25 ℃ to thaw; the other parameters (color protection agent formula, soaking treatment, protective film spraying and drying, vacuum packaging, quick-freezing storage) are the same as in Example 1. IV. Measurement Items, Methods and Results RGB value determination: A typical area in the center of the back of the yellow catfish (3 cm × 3 cm, avoiding fins and damaged scales) was selected. The average RGB values ​​(R: red channel, G: green channel, B: blue channel) of this area of ​​the fish were extracted using ImageJ image analysis software after fresh slaughter (0 h, unprocessed) and after freeze-thaw. The RGB values ​​of the fresh fish were recorded as (R0, G0, B0) and the RGB values ​​of the frozen fish were recorded as (R1, G1, B1). Color difference value ΔE calculation: according to the formula Calculate the color difference between the frozen and thawed fish and the fresh fish (the smaller the ΔE, the smaller the color difference). Color retention rate calculation: Calculate according to the formula "color retention rate = [1 - (ΔE / 255)] × 100%" (255 is the theoretical maximum color difference value). Repeat each experiment 3 times and take the average value.

[0024] Table 2. Color retention rate and surface color characteristic score of yellow catfish after thawing. As shown in Table 2, soaking freshly slaughtered yellow catfish in a chitosan-containing color-protecting and preservative solution effectively reduces the oxidative browning of the yellow catfish's skin coloring substances (carotenoids and lutein) through the film-forming properties of chitosan and the water-retaining and antifreeze effects of trehalose. Simultaneously, it protects the stability of the mucus structure on the fish's surface. In Examples 1 and 2, the RGB values ​​of the frozen and thawed yellow catfish deviated from those of the fresh fish by only 6-10 (R²). The color difference value (ΔE) was as low as 8.36-12.45, and the color retention rate reached 95.1%-96.7%. The surface color characteristic score was over 4.5 points. The back was deep yellow, close to fresh, and the abdomen was light yellow and uniform. The browning area was <3%, and there were no obvious traces of mucus shedding after thawing. This fully demonstrates the dual protective effect of the color-protecting preservative on body color and mucus. Meanwhile, data analysis from Example 1 and Comparative Example 4 shows that spraying and drying the yellow catfish after soaking in the color-protecting agent solution to form a protective film of "90% soluble starch, 1% gelatin, and 0.5% lecithin," followed by vacuum packaging and quick-freezing, can further reduce the yellow catfish's contact with air and weaken surface oxidation and discoloration through the dual effects of "physical protection + oxygen isolation." Example 1 (including vacuum packaging) showed a freeze-thaw ΔE of only 8.36, a color retention rate of 96.7%, and a surface color score of 4.8. In contrast, Comparative Example 4 (without vacuum packaging and the protective film removed before thawing) showed a ΔE of 32.18, a color retention rate of only 87.4%, a surface color score of only 3.4, a light yellowish-brown back with a browning area of ​​10%, and slight oxidation and darkening due to localized air contact during quick-freezing. This clearly demonstrates the crucial value of vacuum packaging in oxygen isolation and color protection.

[0025] Data from Example 1 and Comparative Example 5 (Note: corresponding to Comparative Example 4, "Traditional Thawing") show that yellow catfish soaked in a color-protecting agent solution and quick-frozen, along with a protective film of "90% soluble starch, 1% gelatin, and 0.5% lecithin" on their surface, can be thawed in running water at 4-10 ℃ (directional thawing). This thaw process, aided by the buffering effect of the protective film and the low-temperature environment, avoids pigment loss and mucus damage during thawing, while allowing the fish's surface protective structure to naturally recover. Example 1 (low-temperature running water thawing) showed the smallest RGB value deviation after freeze-thaw, with no obvious darkening of the surface color and high mucus integrity. In contrast, Comparative Example 4 (25 ℃ static water thawing, without directional protection) had a ΔE value 23.82 higher than Example 1, a color retention rate 9.3% lower, and showed localized pigment loss on the body surface after thawing, with an increased area of ​​darkening on the abdomen. This fully demonstrates the importance of directional thawing in restoring the fish to its fresh post-slaughter state. In summary, the color-protecting and preservation method of this invention can effectively improve the color performance of yellow catfish after slaughter and freezing and thawing: compared with the blank control group (Comparative Example 1), ΔE decreased by 85.8% (58.72→8.36), and the color retention rate increased by 19.7% (77.0%→96.7%), completely solving the pain points of "severe browning and dull color" in traditional treatments; at the same time, it delays the shedding of mucus on the body surface, and can still retain the original color after storage at -18 ℃ for 15 days, significantly improving its freeze resistance and storage stability. In the entire color protection process, the color-protecting and preservation agent only needs to be prepared by dissolving acetic acid, chitosan, and trehalose in proportion, which is convenient to obtain (all are conventional food-grade raw materials), and the operation steps are simple (the process of soaking-spraying and drying to form a film-packaging-quick freezing-thawing is clear), without the need for complicated equipment. It is suitable for various catering establishments, aquatic product processing enterprises, and home scenarios, and has extremely strong practical value and promotion potential. The above data analysis is based on specific embodiments and comparative examples of the present invention. The comparative examples were set up to specifically verify the positive effects of the three key technical points: "color-protecting agent formulation, vacuum packaging + protective film protection, and directional thawing." All data are the average values ​​of three repeated experiments to ensure the reliability and objectivity of the results. The present invention is not limited to the above embodiments. Process adjustments (such as fine-tuning of formulation parameters, optimization of thawing flow rate, etc.) directly derived from or reasonably inferred from the disclosure of the present invention should be considered within the scope of protection of the present invention.

Claims

1. A method for protecting the body color of yellow catfish during cold chain transportation and storage based on color-protecting preservatives, characterized in that... Includes the following steps: 1) Preparation of color-protecting and freshness-preserving agent solution: by mass fraction: 1%-1.2% acetic acid, 1.2%-1.5% chitosan, 3%-4% trehalose, and water as the balance. Select acetic acid, chitosan, trehalose, and water; dissolve acetic acid in water, add chitosan, stir until it is completely hydrated and dissolved, then add trehalose, and continue stirring to dissolve to obtain the color-protecting and freshness-preserving agent solution; 2) Preparation of body surface protective film solution: by mass fraction: 90% color-protecting and freshness-preserving agent solution, soluble starch, 1% gelatin, 0.5% lecithin, water balance. Select soluble starch, gelatin, lecithin and water, mix soluble starch, gelatin and lecithin, add the balance water, stir until all components are completely dissolved to obtain a uniform body surface protective film solution; 3) Keep fresh yellow catfish for 6 hours to alleviate transportation stress, then perform an ice water bath to stir and kill them, remove the internal organs and gills, clean them thoroughly, and drain them briefly. After draining, the yellow catfish are soaked in the color-protecting and preservation agent solution obtained in step 1) for 2.5-3 hours. After soaking, the fish are removed and handled gently to reduce external force damage to the skin. Then, the protective film solution prepared in step 2) is evenly sprayed onto the surface of the fish. After spraying, the fish are dried at room temperature for 15-20 minutes. The spraying and drying process is repeated 3 times to form a complete and uniform protective film on the surface of the fish. After completion, the fish are placed in bags and vacuum-packed. 4) Place the vacuum-packed yellow catfish from step 3) into a quick-freezing freezer for quick freezing; 5) During transportation and storage, maintain suitable environmental conditions and utilize the "soluble starch-gelatin-lecithin" protective film formed on the surface of the fish to reduce the mechanical friction experienced by the yellow catfish during transportation and storage. 6) Remove the quick-frozen yellow catfish from the vacuum bag and thaw it directly under running water, along with the protective film on its surface.

2. The method for protecting the body color of yellow catfish during cold chain transportation and storage based on a color-protecting preservative, as described in claim 1, is characterized in that... The protective film solution prepared in step 2) should meet food-grade standards. The soluble starch should be a high-purity product with a purity of ≥99%; the gelatin should be food-grade animal gelatin or plant gelatin; and the lecithin should be food-grade soybean lecithin. The resulting protective film should have good flexibility and water solubility, and should gradually soften or partially dissolve with the water flow during thawing, so as not to affect the quality of the fish and to provide continuous protection.

3. The method for protecting the body color of yellow catfish during cold chain transportation and storage based on a color-protecting preservative, as described in claim 1, is characterized in that... Step 4) The temperature of the quick-freezing chamber is -30 to -32 ℃, and the quick-freezing time is 6.0 to 8.0 h.

4. The method for protecting the body color of yellow catfish during cold chain transportation and storage based on a color-protecting preservative, as described in claim 1, is characterized in that... In step 5), the appropriate environmental conditions are as follows: during transportation, violent bumps should be avoided, and the storage environment should be kept at low temperature and dry, with a low temperature of -18 to -20 ℃ and a relative humidity of ≤60%, to prevent the protective film from softening or breaking prematurely due to moisture.

5. The method for protecting the body color of yellow catfish during cold chain transportation and storage based on a color-protecting preservative, as described in claim 1, is characterized in that... Step 6) The water temperature for thawing is 4-10 ℃, the water flow rate is 0.5-2 L / min, and thawing is continued until the core temperature of the fish reaches 0-4 ℃; and during the thawing process, it should be ensured that the water flow evenly rinses the fish and the protective film on the surface.

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