Composite preservation method for black fish fillet

Abstract

The present invention provides a composite preservation method for black fish slices. The following steps are included: S1. After slaughtering the black fish, scales, viscera, head and tail are removed, the water is drained after washing with running water, and the black fish slices are cut into black fish slices. S2. Modified xanthan gum-carbon point nanoparticles are prepared. S3. Whey protein / gliadin / sodium hydroxymethylcellulose fresh-keeping solution modified by citral is prepared. S4. Whey protein / gliadin / sodium hydroxymethylcellulose / lemon sustained-release fresh-keeping solution loaded with modified xanthan gum-carbon point nanoparticles is prepared. S5. The black fish slices are immersed in the sustained-release fresh-keeping solution, dried, and vacuum-packed. The present invention uses whey protein / gliadin / sodium hydroxymethylcellulose / lemon sustained-release fresh-keeping solution loaded with modified xanthan gum-carbon point nanoparticles to preserve the black fish slices. The sustained-release fresh-keeping solution regulates the release of active substances in the modified xanthan gum-carbon point nanoparticles, improves the stability and moisture barrier of the fresh-keeping film, and the modified xanthan gum-carbon point nanoparticles further improve the antibacterial effect.

Description

Technical Field

[0001] The invention belongs to the technical field of food processing, and in particular relates to a composite fresh-keeping method for black fish fillets. Background Art

[0002] As people's living standards improve, the requirements for food quality and safety are getting higher and higher. Among meat products, fish is deeply loved by consumers because of its rich nutritional value and delicious taste. However, fish are susceptible to microbial contamination and oxidation during fishing, transportation, processing and storage, resulting in quality degradation and shortened shelf life. Therefore, it is of great significance to study effective fish preservation technology. This article mainly introduces the background of composite preservation technology of black fish fillets. Snakehead fish, also known as black snakehead, is widely distributed in my country and has high nutritional and economic value. Snakehead fish has tender meat, few bones, and high meat content. The protein content in its muscle is as high as 19.13%, which is higher than that of carp, grass carp and crucian carp. The fat content is only 0.88%. Snakehead fish is a high-quality high-protein, low-fat fish. Snakehead fish contains many types of amino acids in a reasonable proportion, which can make up for the deficiency of amino acids in people's daily diet and improve the body's utilization of protein. In addition, the umami amino acids in the muscles of snakehead fish, such as glutamic acid and aspartic acid, can not only participate in human metabolism, but also have a delicious taste, which can make the snakehead fish meat delicious. At present, the most common preservation technologies are physical preservation, chemical preservation, and biological preservation. Physical preservation can meet the requirements of large-scale commercial preservation, but in the actual storage and transportation process, the complex temperature changes and the impact of various environmental factors on the preservation effect must be fully considered. Chemical preservation technology has certain safety hazards to human health. Biological preservation technology can effectively reduce the corruption and quality loss of black fish, ensure the freshness, taste and nutritional content of black fish, and reduce the adverse impact on the environment. Summary of the invention

[0003] Technical problem to be solved: In view of the above technical problem, the purpose of the present invention is to provide a composite preservation method for black fish fillets, which comprises slaughtering fresh black fish, removing scales, viscera, head and tail, washing with running water and draining the water, cutting into black fish fillets, and then immersing the black fish fillets in a preservative liquid, drying and preserving them in a vacuum. The invention prepares a sustained-release fresh-keeping liquid loaded with carbon dot nanoparticles. The carbon dot nanoparticles are prepared from walnut carbon dot powder and modified xanthan gum, and the introduction of carbon dots enhances the antibacterial effect. Sodium hydroxymethylcellulose provides a good film-forming basis, and whey protein and gliadin are combined to form a stable network structure. The whey protein / gliadin / sodium hydroxymethylcellulose fresh-keeping liquid reduces oxidation reaction in black fish slices, adjusts the gas environment in the black fish slices, increases the barrier property of the film, and reduces the exchange between the fish slices and the external environment. After the whey protein / gliadin / sodium hydroxymethylcellulose fresh-keeping liquid is modified by citral, the cross-linking between the whey protein and gliadin is promoted, and the antibacterial effect of the fresh-keeping liquid is enhanced. The carbon dot nanoparticles are added into the whey protein / gliadin / sodium hydroxymethylcellulose fresh-keeping liquid modified by citral to prepare the sustained-release fresh-keeping liquid, and the release of active substances in the carbon dot nanoparticles is regulated, so as to improve the moisture resistance of the fresh-keeping liquid.

[0004] Technical solution: A composite preservation method for black fish fillets, comprising the following steps: S1. Kill fresh snakehead fish, remove scales, viscera, head and tail, rinse with running water, drain and cut into slices; S2. Using walnut kernel carbon dot powder and modified xanthan gum as raw materials, modified xanthan gum-carbon dot nanoparticles were prepared; S3. whey protein, gliadin, sodium hydroxymethyl cellulose as raw materials for preparing fresh-keeping solution and citral was used to modify the fresh-keeping solution to obtain a citral-modified composite fresh-keeping solution; S4. The modified xanthan gum - carbon dot nanoparticles were added to the citral-modified whey protein / gliadin / sodium hydroxymethylcellulose preservative solution and stirred for 30-40 min to obtain a sustained-release preservative solution loaded with modified xanthan gum - carbon dot nanoparticles; S5. Soak the black fish fillets in the slow-release preservative solution, dry them, and vacuum pack them. Furthermore, the specific preparation method of the modified xanthan gum-carbon dot nanoparticles in step S2, in parts by weight, comprises the following steps: S21. The walnut kernels were crushed and powdered, 1 part of the walnut kernel powder was put into a high pressure reactor, 9-12 parts of distilled water were added, and the mixture was heated in an oven at 200-220°C for 10-12 hours, and then the residue was removed by filtration. The filtrate was centrifuged and dialyzed in pure water with a dialysis membrane for 24-30 hours. The purified carbon dots were freeze-dried for 48-60 hours to obtain walnut kernel carbon dot powder; S22. 1 part of xanthan gum was dissolved in 15-20 parts of acetic acid solution having a volume fraction of 1%-2%, and stirred. H2O2 was added dropwise during the stirring process. The entire reaction was carried out in a water bath at 60-80°C. The reaction was stopped after 5-10 hours. The pH value of the reaction solution was adjusted to 7.0-8.0 using NaOH solution, and washed with anhydrous ethanol. After suction filtration and drying, modified xanthan gum was obtained; S23. Take 3-6 parts of modified xanthan gum and dissolve them in 100 parts of distilled water to obtain a modified xanthan gum solution, add the walnut carbon dot powder to the modified xanthan gum solution, and homogenize for 20-30 minutes to obtain a modified xanthan gum - carbon dot nanoparticle solution; S24. The modified xanthan gum-carbon dot nanoparticle solution is centrifuged, and the precipitate is freeze-dried to obtain modified xanthan gum-carbon dot nanoparticles. Further, the mass volume ratio of the walnut kernel carbon dot powder to the modified xanthan gum solution in step S23 is (2-5) g:100 mL. Further, the specific preparation method of the citral-modified composite fresh-keeping solution in step S3 comprises the following steps: S31. The whey protein was dissolved in distilled water, the gliadin was dissolved in 75-80% ethanol to obtain a 2% whey protein solution and a 2% gliadin solution, sodium hydroxymethyl cellulose was added to the whey protein / gliadin mixed solution and stirred to obtain whey protein / gliadin / sodium hydroxymethyl cellulose preservative solution; S32. Dissolve citral in 60-70% ethanol to obtain a 3%-5% citral solution, add the citral solution to the whey protein / gliadin / sodium hydroxymethylcellulose preservative solution, homogenize for 15-20 minutes, and vacuum degas for 6-10 hours to obtain a citral-modified composite preservative solution. Furthermore, in step S31, the whey protein solution and the gliadin solution are mixed in a volume ratio of (1-3):1, and the mass volume ratio of hydroxymethyl cellulose to the whey protein / gliadin mixed solution is (2-5) g:100 mL. Furthermore, in step S32, the volume ratio of the citral solution to the whey protein / gliadin / sodium hydroxymethylcellulose mixed solution is (1-3):10. Furthermore, in step S4, the mass volume ratio of the modified xanthan gum-carbon dot nanoparticles to the citral-modified whey protein / gliadin / sodium hydroxymethylcellulose preservative solution is (1-3) g:10 mL. Beneficial effects: 1. The present invention uses walnut kernels as raw materials to prepare carbon dot powder, modified xanthan gum, and then prepares modified xanthan gum-carbon dot nanoparticles with the modified xanthan gum. The carbon dots and the modified xanthan gum can be combined through non-covalent interactions to form a stable nanocomposite. The introduction of the carbon dots enhances the antibacterial effect. The modified xanthan gum can stabilize the carbon dot nanoparticles, enhance the dispersibility of the carbon dot powder in the nanoparticles, and improve the film-forming properties and antibacterial effect of the preservative solution. 2. The whey protein / gliadin / sodium hydroxymethylcellulose preservative solution prepared by the present invention can form a stable network structure by combining whey protein and gliadin, and both whey protein and gliadin contain certain antioxidant peptides, which can remove free radicals, reduce the oxidation reaction in the fish fillet, regulate the gas environment in the fish fillet, and reduce the oxygen content. Sodium hydroxymethylcellulose can provide a good film-forming basis, and the addition of whey protein and gliadin can reduce the air permeability of the film, increase the barrier property of the film, and reduce the exchange between the fish fillet and the external environment. 3. The present invention adds citral to the whey protein / gliadin / sodium hydroxymethylcellulose preservative solution, and the citral modifies the whey protein / gliadin / sodium hydroxymethylcellulose preservative solution. The citral can react with the amino acid residues of whey protein and gliadin to change the structure of the protein, improve the air permeability and barrier properties, promote the cross-linking between whey protein and gliadin, and enhance the antibacterial effect of the preservative solution. 4. The present invention adds chitosan-carbon dot nanoparticles to a citral-modified whey protein / gliadin / sodium hydroxymethylcellulose preservative solution to prepare a sustained-release preservative film loaded with chitosan-carbon dot nanoparticles, thereby regulating the release of active substances in the chitosan-carbon dot nanoparticles and improving the stability and moisture barrier properties of the preservative film. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 It is a graph showing the change of total volatile basic nitrogen value of Example 11 and Comparative Examples 5-7; Figure 2 The total number of colonies in Example 11 and Comparative Examples 5-7 is shown in FIG. Figure 3 The graph showing the change in thiobarbituric acid value of Example 11 and Comparative Examples 5-7; Figure 4 It is a graph showing the whiteness variation of Example 11 and Comparative Examples 5-7; Figure 5 The water holding capacity change diagram of Example 11 and Comparative Examples 5-7. DETAILED DESCRIPTION The present invention proposes a composite preservation method for black fish fillets. In order to make the purpose, technical scheme and effect of the present invention clearer and more specific, the present invention will be further described in detail with reference to the embodiments below. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. Example 1 The preparation method of modified xanthan gum-carbon dot nanoparticles is as follows: S1. The walnut kernels were crushed and powdered. 1 g of walnut kernel powder was weighed and put into a high-pressure reactor. 9 mL of distilled water was added. The mixture was heated in an oven at 220 ° C for 12 h and then taken out. The residue was removed by filtration. The filtrate was centrifuged and dialyzed in pure water with a dialysis membrane for 30 h. The purified carbon dots were freeze-dried for 60 h to obtain walnut kernel carbon dot powder. S2. 1 g of xanthan gum was dissolved in 15 mL of 1% acetic acid solution, and the xanthan gum solution was stirred with an electric stirrer. H2O2 was added dropwise during the stirring process. The entire reaction was carried out in a 60°C water bath. The reaction was stopped after 10 h. The pH value of the reaction solution was adjusted to 7.0 using NaOH solution, and the solution was washed with anhydrous ethanol, filtered, and dried to obtain modified xanthan gum. S3. 3 g of modified xanthan gum was dissolved in 100 mL of distilled water to prepare a modified xanthan gum solution, and the walnut kernel carbon dot powder was added to the modified xanthan gum solution. The ratio of the walnut kernel carbon dot powder to the modified xanthan gum solution was 2 g: 100 mL. After homogenization for 20 min, a modified xanthan gum-carbon dot nanoparticle solution was obtained; S4. Centrifuge the modified xanthan gum-carbon dot nanoparticle solution, and freeze-dry the precipitate to obtain modified xanthan gum-carbon dot nanoparticles. Example 2 The preparation method of modified xanthan gum-carbon dot nanoparticles is as follows: S1. The walnut kernels were crushed and powdered. 1 g of walnut kernel powder was weighed and put into a high-pressure reactor. 9 mL of distilled water was added. The mixture was heated in an oven at 220 ° C for 12 h and then taken out. The residue was removed by filtration. The filtrate was centrifuged and dialyzed in pure water with a dialysis membrane for 30 h. The purified carbon dots were freeze-dried for 60 h to obtain walnut kernel carbon dot powder. S2. 1 g of xanthan gum was dissolved in 15 mL of 1% acetic acid solution, and the xanthan gum solution was stirred with an electric stirrer. H2O2 was added dropwise during the stirring process. The entire reaction was carried out in a 60°C water bath. The reaction was stopped after 10 h. The pH value of the reaction solution was adjusted to 7.0 using NaOH solution, and the solution was washed with anhydrous ethanol, filtered, and dried to obtain modified xanthan gum. S3. 3 g of modified xanthan gum was dissolved in 100 mL of distilled water to prepare a modified xanthan gum solution, and the walnut kernel carbon dot powder was added to the modified xanthan gum solution. The ratio of the walnut kernel carbon dot powder to the modified xanthan gum solution was 3 g: 100 mL. After homogenization for 20 min, a modified xanthan gum-carbon dot nanoparticle solution was obtained; S4. Centrifuge the modified xanthan gum-carbon dot nanoparticle solution, and freeze-dry the precipitate to obtain modified xanthan gum-carbon dot nanoparticles. Example 3 The preparation method of modified xanthan gum-carbon dot nanoparticles is as follows: S1. The walnut kernels were crushed and powdered. 1 g of walnut kernel powder was weighed and put into a high-pressure reactor. 9 mL of distilled water was added. The mixture was heated in an oven at 220 ° C for 12 h and then taken out. The residue was removed by filtration. The filtrate was centrifuged and dialyzed in pure water with a dialysis membrane for 30 h. The purified carbon dots were freeze-dried for 60 h to obtain walnut kernel carbon dot powder. S2. 1 g of xanthan gum was dissolved in 15 mL of 1% acetic acid solution, and the xanthan gum solution was stirred with an electric stirrer. H2O2 was added dropwise during the stirring process. The entire reaction was carried out in a 60°C water bath. The reaction was stopped after 10 h. The pH value of the reaction solution was adjusted to 7.0 using NaOH solution, and the solution was washed with anhydrous ethanol, filtered, and dried to obtain modified xanthan gum. S3. 3 g of modified xanthan gum was dissolved in 100 mL of distilled water to prepare a modified xanthan gum solution, and the walnut kernel carbon dot powder was added to the modified xanthan gum solution. The ratio of the walnut kernel carbon dot powder to the modified xanthan gum solution was 4 g: 100 mL. After homogenization for 20 min, a modified xanthan gum-carbon dot nanoparticle solution was obtained; S4. Centrifuge the modified xanthan gum-carbon dot nanoparticle solution, and freeze-dry the precipitate to obtain modified xanthan gum-carbon dot nanoparticles. Example 4 The preparation method of modified xanthan gum-carbon dot nanoparticles is as follows: S1. The walnut kernels were crushed and powdered. 1 g of walnut kernel powder was weighed and put into a high-pressure reactor. 9 mL of distilled water was added. The mixture was heated in an oven at 220 ° C for 12 h and then taken out. The residue was removed by filtration. The filtrate was centrifuged and dialyzed in pure water with a dialysis membrane for 30 h. The purified carbon dots were freeze-dried for 60 h to obtain walnut kernel carbon dot powder. S2. 1 g of xanthan gum was dissolved in 15 mL of 1% acetic acid solution, and the xanthan gum solution was stirred with an electric stirrer. H2O2 was added dropwise during the stirring process. The entire reaction was carried out in a 60°C water bath. The reaction was stopped after 10 h. The pH value of the reaction solution was adjusted to 7.0 using NaOH solution, and the solution was washed with anhydrous ethanol, filtered, and dried to obtain modified xanthan gum. S3. 3 g of modified xanthan gum was dissolved in 100 mL of distilled water to prepare a modified xanthan gum solution, and the walnut kernel carbon dot powder was added to the modified xanthan gum solution. The ratio of the walnut kernel carbon dot powder to the modified xanthan gum solution was 5 g: 100 mL. After homogenization for 20 min, a modified xanthan gum-carbon dot nanoparticle solution was obtained; S4. Centrifuge the modified xanthan gum-carbon dot nanoparticle solution, and freeze-dry the precipitate to obtain modified xanthan gum-carbon dot nanoparticles. Comparative Example 1 The difference between this comparative example and Example 2 is that an unmodified xanthan gum solution is used. The preparation method of xanthan gum-carbon dot nanoparticles is as follows: S1. The walnut kernels were crushed and powdered. 1 g of walnut kernel powder was weighed and put into a high-pressure reactor. 9 mL of distilled water was added. The mixture was heated in an oven at 220 ° C for 12 h and then taken out. The residue was removed by filtration. The filtrate was centrifuged and dialyzed in pure water with a dialysis membrane for 30 h. The purified carbon dots were freeze-dried for 60 h to obtain walnut kernel carbon dot powder. S2. 3 g of xanthan gum was dissolved in 100 mL of distilled water to prepare a xanthan gum solution, and the walnut kernel carbon dot powder was added to the xanthan gum solution. The ratio of the walnut kernel carbon dot powder to the xanthan gum solution was 3 g:100 mL. After homogenization for 20 min, a xanthan gum-carbon dot nanoparticle solution was obtained; S4. The xanthan gum-carbon dot nanoparticle solution is centrifuged, and the precipitate is freeze-dried to obtain xanthan gum-carbon dot nanoparticles. Performance Testing (1) Particle size measurement Disperse an appropriate amount of sample in distilled water, place it in an electrochemical working cell, and measure the average particle size of the sample. Table 1 Average particle size of Examples 1-4 and Comparative Example 1 It can be seen from Table 1 that the particle size of Example 2 is the smallest, and the particle size of Comparative Example 1 is the largest, indicating that the modified xanthan gum will reduce the particle size of the nanoparticles. As the ratio of carbon dot powder to modified xanthan gum solution increases, the particle size of the nanoparticles increases. This may be because the particle size of the carbon dot powder itself is relatively large, and the carbon dots and modified xanthan gum are combined through non-covalent interactions to promote the formation of nanoparticles. Example 5 The preparation method of the citral-modified composite fresh-keeping liquid is as follows: S1. Dissolve whey protein in distilled water to obtain a 2% whey protein solution; dissolve gliadin in 75% ethanol to obtain a 2% gliadin solution, stir 2.4 g of sodium hydroxymethyl cellulose, 60 mL of whey protein solution and 60 mL of gliadin solution to obtain whey protein / gliadin / sodium hydroxymethyl cellulose preservative solution; S2. Dissolve citral in 60% ethanol to obtain a 3% citral solution, add 10 mL of the citral solution to 120 mL of whey protein / gliadin / sodium hydroxymethylcellulose preservative solution, homogenize for 20 minutes, and vacuum degas for 10 hours to obtain a citral-modified composite preservative solution. Example 6 The preparation method of the citral-modified composite fresh-keeping liquid is as follows: S1. Dissolve whey protein in distilled water to obtain a 2% whey protein solution; dissolve gliadin in 75% ethanol to obtain a 2% gliadin solution, stir 2.4 g of sodium hydroxymethyl cellulose, 80 mL of whey protein solution and 40 mL of gliadin solution to obtain whey protein / gliadin / sodium hydroxymethyl cellulose preservative solution; S2. Dissolve citral in 60% ethanol to obtain a 3% citral solution, add 12 mL of the citral solution to 120 mL of whey protein / gliadin / sodium hydroxymethylcellulose preservative solution, homogenize for 20 minutes, and vacuum degas for 10 hours to obtain a citral-modified composite preservative solution. Example 7 The preparation method of the citral-modified composite fresh-keeping liquid is as follows: S1. The whey protein was dissolved in distilled water to obtain a 2% whey protein solution; the gliadin was dissolved in 75% ethanol to obtain a 2% gliadin solution, 2.4g sodium hydroxymethylcellulose, 90mL whey protein solution and 30mL gliadin solution were stirred to obtain whey protein / gliadin / sodium hydroxymethylcellulose preservative solution; S2. Dissolve citral in 60% ethanol to obtain a 3% citral solution, add 12 mL of the citral solution to 120 mL of whey protein / gliadin / sodium hydroxymethylcellulose preservative solution, homogenize for 20 minutes, and vacuum degas for 10 hours to obtain a citral-modified composite preservative solution. Comparative Example 2 The difference between this comparative example and Example 6 is that the preservative solution is not modified with citral. The preparation method of whey protein / gliadin / sodium hydroxymethylcellulose preservative solution is as follows: S1. Dissolving whey protein in distilled water to prepare a 2% whey protein solution; dissolving gliadin in 75% ethanol to prepare a 2% gliadin solution; S2. 2.4g sodium hydroxymethylcellulose, 80mL whey protein solution and 40mL gliadin solution were stirred to obtain whey protein / gliadin / sodium hydroxymethylcellulose preservative solution; Performance Testing (1) Determination of particle size Zeta potential and nanoparticle size analyzer were used to detect the particle size of the preservation solution. Each analytical sample was tested in triplicate and the results were averaged. (2) Determination of DPPH free radical scavenging rate Prepare DPPH anhydrous ethanol solution, take 3 mL into a test tube, add 1 mL of preservative solution and mix well, place at room temperature and away from light for 30 minutes, and then measure the absorbance value A at a wavelength of 517 nm. i; Mix 3 mL of anhydrous ethanol and 1 mL of preservative solution and place in the dark at room temperature for 30 min. Measure the absorbance A at a wavelength of 517 nm. j ; Replace the preservative solution with anhydrous ethanol, add 3mL DPPH anhydrous ethanol to determine the absorbance value A0, and average it for 3 parallel runs in each group. The calculation formula for DPPH free radical scavenging rate is as follows: (3) Determination of ABTS free radical scavenging rate Prepare a mixture of ABTS and potassium persulfate, let it stand overnight (14h) at room temperature in the dark to prepare ABTS free radical storage solution, dilute it with 75% ethanol when using it, and use it as the final application solution when the absorbance is 0.70 (±0.05) at 734nm. Mix the preservation solution and ABTS application solution at a ratio of 1:39, place it in an ELISA reader at room temperature in the dark for 6min, and then measure its absorbance at 734nm, and use distilled water instead of the sample solution as a blank control. Each group is repeated three times and the average is calculated. ABTS free radical scavenging rate (%) = (A 空白 -A 保鲜液 )÷A 空白 ×100% Table 2 Average particle size and antioxidant activity of Examples 5-7 and Comparative Example 2 As can be seen from Table 2, the ratio of whey protein to gliadin affects the particle size and antioxidant activity of the fresh-keeping solution. Example 6 has the highest antioxidant activity. This may be because citral can react with the amino acid residues of whey protein and gliadin to change the structure of the protein, improve the air permeability and barrier properties, and promote the cross-linking between whey protein and gliadin, thereby improving the antioxidant activity. Therefore, the following examples use the method of Example 6 to prepare the fresh-keeping solution. Example 8 The preparation method of the sustained-release preservative solution loaded with modified xanthan gum-carbon dot nanoparticles is as follows: add 1 g of the modified xanthan gum-carbon dot nanoparticles prepared in Example 2 to 10 mL of the citral-modified whey protein / gliadin / sodium hydroxymethylcellulose preservative solution prepared in Example 6, and stir for 40 minutes to obtain a sustained-release preservative solution loaded with modified xanthan gum-carbon dot nanoparticles. Example 9 The preparation method of the sustained-release preservative solution loaded with modified xanthan gum-carbon dot nanoparticles is as follows: add 2 g of the modified xanthan gum-carbon dot nanoparticles prepared in Example 2 to 10 mL of the citral-modified whey protein / gliadin / sodium hydroxymethylcellulose preservative solution prepared in Example 6, stir for 40 minutes, and obtain a sustained-release preservative solution loaded with modified xanthan gum-carbon dot nanoparticles. Example 10 The preparation method of the sustained-release preservative solution loaded with modified xanthan gum-carbon dot nanoparticles is as follows: add 3 g of the modified xanthan gum-carbon dot nanoparticles prepared in Example 2 to 10 mL of the citral-modified whey protein / gliadin / sodium hydroxymethylcellulose preservative solution prepared in Example 6, and stir for 40 minutes to obtain a sustained-release preservative solution loaded with modified xanthan gum-carbon dot nanoparticles. Comparative Example 3 The difference between this comparative example and Example 9 is that the sustained-release fresh-keeping liquid is loaded with the xanthan gum-carbon dot nanoparticles prepared in Comparative Example 1. The preparation method of the sustained-release fresh-keeping liquid loaded with xanthan gum-carbon dot nanoparticles is as follows: 2 g of the xanthan gum-carbon dot nanoparticles prepared in Comparative Example 1 is added to 10 mL of the citral-modified whey protein / gliadin / sodium hydroxymethylcellulose fresh-keeping liquid prepared in Example 6, and stirred for 40 minutes to obtain a sustained-release fresh-keeping liquid loaded with modified xanthan gum-carbon dot nanoparticles. Comparative Example 4 The difference between this comparative example and Example 9 is that the sustained-release fresh-keeping liquid is the whey protein / gliadin / sodium hydroxymethylcellulose fresh-keeping liquid prepared in Comparative Example 2. The preparation method of the sustained-release fresh-keeping solution loaded with modified xanthan gum-carbon dot nanoparticles is as follows: add 2 g of the modified xanthan gum-carbon dot nanoparticles prepared in Example 2 to 10 mL of the whey protein / gliadin / sodium hydroxymethylcellulose fresh-keeping solution prepared in Comparative Example 2, and stir for 40 minutes to obtain a sustained-release fresh-keeping solution loaded with modified xanthan gum-carbon dot nanoparticles. Performance Testing The determination methods of particle size, DPPH free radical scavenging rate, and ABTS free radical scavenging rate are the same as above. (1) Determination of embedding rate The preservation solution was taken into an ultrafiltration centrifuge tube and centrifuged at 12000r / min for 30min. The unencapsulated nanoparticles were centrifuged out of the external centrifuge tube. The retained nanoparticles were taken and crushed by adding an equal volume of HCl solution. The nanoparticles were fixed to a 10mL volumetric flask with 95% ethanol solution. A blank control was prepared by the same method with the preservation solution without nanoparticles. The absorbance was measured at a wavelength of 275nm. The embedding rate was calculated as follows: Embedding rate (%) = (m1-m2) / m1×100% Wherein, m1 is the total mass of preservative solution added / g; m2 is the mass of free nanoparticles / g. Table 2 Average particle size, embedding rate and antioxidant activity of Examples 8-10 and Comparative Examples 3-4 As can be seen from Table 2, Example 9 has the strongest antioxidant activity and the highest embedding rate. The ratio of modified xanthan gum-carbon dot nanoparticles to citral-modified whey protein / gliadin / sodium hydroxymethylcellulose fresh-keeping solution will affect the embedding rate and antioxidant activity. Modified xanthan gum can stabilize carbon dot nanoparticles, enhance the dispersibility of carbon dot powder in nanoparticles, and better exert the antioxidant activity of nanoparticles. In addition, the whey protein / gliadin / sodium hydroxymethylcellulose fresh-keeping solution is modified with citral to promote the cross-linking between whey protein and gliadin, change the structure of the protein, and thus improve the antioxidant activity and particle size of the fresh-keeping solution. Therefore, the following examples use the method of Example 9 to prepare the fresh-keeping solution. [Example 11 A composite fresh-keeping method for black fish fillet is as follows: S1. Kill fresh snakehead fish, remove scales, viscera, head and tail, rinse with running water, drain and cut into slices; S2. Soak the black fish fillet in the sustained-release preservative solution loaded with modified xanthan gum-carbon dot nanoparticles prepared in Example 9, dry it, and vacuum pack it. Comparative Example 5 The difference between this comparative example and Example 11 is that the sustained-release fresh-keeping liquid loaded with xanthan gum-carbon dot nanoparticles prepared in Comparative Example 3 is used. A composite fresh-keeping method for black fish fillet is as follows: S1. Kill fresh snakehead fish, remove scales, viscera, head and tail, rinse with running water, drain and cut into slices; S2. The black fish fillets are immersed in the sustained-release preservative solution loaded with xanthan gum-carbon dot nanoparticles prepared in Comparative Example 3, dried, and vacuum-packed. Comparative Example 6 The difference between this comparative example and Example 11 is that the sustained-release fresh-keeping liquid loaded with modified xanthan gum-carbon dot nanoparticles prepared in Comparative Example 4 is used. A composite fresh-keeping method for black fish fillet is as follows: S1. Kill fresh snakehead fish, remove scales, viscera, head and tail, rinse with running water, drain and cut into slices; S2. The black fish fillets are immersed in the sustained-release preservative solution loaded with modified xanthan gum-carbon dot nanoparticles prepared in Comparative Example 4, dried, and vacuum-packed. Comparative Example 7 The difference between this comparative example and Example 11 is that there are no modified xanthan gum-carbon dot nanoparticles in the preservative solution. A composite fresh-keeping method for black fish fillet is as follows: S1. Kill fresh snakehead fish, remove scales, viscera, head and tail, rinse with running water, drain and cut into slices; S2. The black fish fillet is immersed in the citral-modified whey protein / gliadin / sodium hydroxymethylcellulose preservative solution prepared in Example 6, dried, and vacuum-packed. Performance Testing Example 11 and Comparative Examples 5-7 were placed in a refrigerator at 4°C for 12 days, and the fish fillets were taken out every 3 days to measure the total volatile basic nitrogen (TVB-N), total bacterial count (APC), thiobarbituric acid (TBA), color, and water holding capacity. (1) Determination of total volatile basic nitrogen (TVB-N) value Weigh 3g of black fish fillet and mince it, add perchloric acid solution at 1:9 (w / v), homogenize, centrifuge, and filter. Take 5mL of filtrate and use Kjeldahl nitrogen analyzer to determine the TVB-N content of fish meat every day, and measure three times for each group to get the average. (2) Determination of the total bacterial count (APC) The total number of bacteria in black fish fillets was determined every 3 days according to the GB / T4789.2-2008 method. Three parallel tests were performed in each group, and the results were averaged. (3) Determination of thiobarbituric acid (TBA) value The thiobarbituric acid test method was used for determination. The minced fish meat was added with trichloroacetic acid containing 0.1% EDTA and then homogenized and centrifuged. The ratio of fish meat to trichloroacetic acid was 1g:5mL, and then filtered with double-layer filter paper. The supernatant was taken, 0.02M TBA solution was added, reacted in a boiling water bath for 40 minutes, then taken out and cooled for 1 hour, chloroform was added, shaken and allowed to stand for stratification, and the supernatant was taken to measure the absorbance at wavelengths of 532mm and 600nm and record the data. The volume ratio of the supernatant, TBA solution, and chloroform solution was 1:1:1, and distilled water was used instead of the sample as the blank value. The results were expressed as milligrams of malondialdehyde (MDA) contained in every 100g of black fish, which was mg MDA / (100g black fish). Three parallel tests were performed in each group, and the results were averaged. The TBA value calculation formula is as follows, where m is the mass of black fish. TBA (mg / 100g) = (A 532 -A 600 ) / 155×72.6×0.05×100 (4) Determination of color A colorimeter was used for color difference analysis. The CIE-LAB system was used to measure the L* (lightness index), a* (redness), and b* (yellowness) of black fish. Whiteness was used to represent the color change of hairtail. The calculation formula for whiteness is as follows: (5) Determination of water holding capacity Take the hairtail meat and mince it and dissolve it in a centrifuge tube in a water bath for 20 minutes, then centrifuge it at 1500r / min for 3 minutes, filter the water and weigh it, measure three parallels in each group, and average the results. The water holding capacity formula is as follows, where the water content is 75.03%: Depend on Figure 1 It can be seen that with the increase of storage days, the value of total volatile basic nitrogen has been rising. This is because volatile basic nitrogen is one of the main products of fish product spoilage. The protein in the fish product is decomposed by microorganisms to produce ammonia, amines and other substances. The total volatile basic nitrogen value of Example 11 is lower than that of Comparative Examples 5-7, indicating that Example 11 has a better antibacterial effect. from Figure 2 It can be seen that with the extension of storage time, the total colony count of black fish fillets shows an upward trend. Example 11 can effectively inhibit the growth of colonies. This is because the modified xanthan gum can stabilize the carbon dot nanoparticles, and the introduction of carbon dots enhances the antibacterial effect. Citral can react with the amino acid residues of whey protein and gliadin, change the structure of the protein, and promote the cross-linking between whey protein and gliadin, thereby enhancing the antibacterial effect of the preservative solution. from Figure 3 It can be seen that with the extension of storage time, the thiobarbituric acid value of black fish fillet shows an upward trend. This is because the unsaturated fatty acids in the black fish are easily oxidized and hydrolyzed into aldehyde products such as malondialdehyde. The thiobarbituric acid value of Example 11 is the lowest, which may be due to the strong barrier properties of the citral / whey protein / gliadin / sodium hydroxymethylcellulose sustained-release preservative solution loaded with modified xanthan gum-carbon dot nanoparticles. from Figure 4 It can be seen that the whiteness value of the black fish fillet gradually decreases with the extension of the storage time. This is because the bacteria decompose the myoglobin and lipid oxidation in the black fish, thereby causing the change in the whiteness value of the black fish. Example 11 can effectively delay the change in the whiteness value of the black fish fillet. This may be because the citral / whey protein / gliadin / sodium hydroxymethylcellulose sustained-release preservative solution loaded with modified xanthan gum-carbon dot nanoparticles has strong moisture resistance and antibacterial properties. from Figure 5 It can be seen that with the extension of storage time, the water holding capacity of black fish fillet shows a downward trend. This is because the growth and reproduction of microorganisms lead to the denaturation of fish protein, the muscle tissue of the fish begins to gradually soften and is destroyed by bacteria, and the water holding capacity decreases more and more. Example 11 can effectively delay the change of the water holding capacity of black fish. The sustained-release cling film loaded with chitosan-carbon dot nanoparticles regulates the release of active substances in the chitosan-carbon dot nanoparticles, improves the stability and moisture barrier of the cling film, and is beneficial to inhibiting the reduction of the water holding capacity of black fish fillet. The above is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any technician familiar with the art can make many possible changes and modifications to the technical solution of the present invention by using the above disclosed methods and technical contents without departing from the spirit and technical solution of the present invention, or modify it into an equivalent embodiment of equivalent changes. Therefore, any simple modification, equivalent replacement, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention still falls within the scope of protection of the technical solution of the present invention.

Claims

1. A composite preservation method for black fish fillets, characterized in that: The following steps are involved: S1. Kill fresh snakehead fish, remove scales, viscera, head and tail, rinse with running water, drain and cut into slices; S2. Using walnut kernel carbon dot powder and modified xanthan gum as raw materials, modified xanthan gum-carbon dot nanoparticles were prepared; S3. whey protein, gliadin, sodium hydroxymethyl cellulose as raw materials for preparing fresh-keeping solution and citral was used to modify the fresh-keeping solution to obtain a citral-modified composite fresh-keeping solution; S4. The modified xanthan gum - carbon dot nanoparticles were added to the citral-modified whey protein / gliadin / sodium hydroxymethylcellulose preservative solution and stirred for 30-40 min to obtain a sustained-release preservative solution loaded with modified xanthan gum - carbon dot nanoparticles; S5. Soak the black fish fillets in the slow-release preservative solution, dry them, and vacuum pack them.

2. The composite fresh-keeping method for black fish fillet according to claim 1, characterized in that: The specific preparation method of the modified xanthan gum-carbon dot nanoparticles in step S2, in parts by weight, comprises the following steps: S21. The walnut kernels were crushed and powdered, 1 part of the walnut kernel powder was put into a high pressure reactor, 9-12 parts of distilled water were added, and the mixture was heated in an oven at 200-220°C for 10-12 hours, and then the residue was removed by filtration. The filtrate was centrifuged and dialyzed in pure water with a dialysis membrane for 24-30 hours. The purified carbon dots were freeze-dried for 48-60 hours to obtain walnut kernel carbon dot powder; S22. 1 part of xanthan gum was dissolved in 15-20 parts of acetic acid solution having a volume fraction of 1%-2%, and stirred. H2O2 was added dropwise during the stirring process. The entire reaction was carried out in a water bath at 60-80°C. The reaction was stopped after 5-10 hours. The pH value of the reaction solution was adjusted to 7.0-8.0 using NaOH solution, and washed with anhydrous ethanol. After suction filtration and drying, modified xanthan gum was obtained; S23. Take 3-6 parts of modified xanthan gum and dissolve them in 100 parts of distilled water to obtain a modified xanthan gum solution, add the walnut carbon dot powder to the modified xanthan gum solution, and homogenize for 20-30 minutes to obtain a modified xanthan gum - carbon dot nanoparticle solution; S24. Centrifuge the modified xanthan gum-carbon dot nanoparticle solution, and freeze-dry the precipitate to obtain modified xanthan gum-carbon dot nanoparticles.

3. The composite preservation method of black fish fillet according to claim 2, characterized in that: The mass volume ratio of the walnut kernel carbon dot powder to the modified xanthan gum solution in step S23 is (2-5) g:100 mL.

4. The composite fresh-keeping method for black fish fillet according to claim 1, characterized in that: The specific preparation method of the citral-modified composite fresh-keeping liquid in step S3 comprises the following steps: S31. The whey protein was dissolved in distilled water, the gliadin was dissolved in 75-80% ethanol to obtain a 2% whey protein solution and a 2% gliadin solution, sodium hydroxymethyl cellulose was added to the whey protein / gliadin mixed solution and stirred to obtain whey protein / gliadin / sodium hydroxymethyl cellulose preservative solution; S32. Dissolve citral in 60-70% ethanol to obtain a 3%-5% citral solution, add the citral solution to the whey protein / gliadin / sodium hydroxymethylcellulose preservative solution, homogenize for 15-20 minutes, and vacuum degas for 6-10 hours to obtain a citral-modified composite preservative solution.

5. The composite fresh-keeping method for black fish fillet according to claim 4, characterized in that: In step S31, the whey protein solution and the gliadin solution are mixed in a volume ratio of (1-3):1, and the mass volume ratio of hydroxymethyl cellulose to the whey protein / gliadin mixed solution is (2-5) g:100 mL.

6. The composite fresh-keeping method for black fish fillet according to claim 4, characterized in that: In step S32, the volume ratio of the citral solution to the whey protein / gliadin / sodium hydroxymethylcellulose mixed solution is (1-3):

10.

7. The composite preservation method of black fish fillet according to claim 1, characterized in that: In the step S4, the mass volume ratio of the modified xanthan gum-carbon dot nanoparticles to the citral-modified whey protein / gliadin / sodium hydroxymethylcellulose preservative solution is (1-3) g:10 mL.

Images