Preparation method of a multifunctional nano-hydrogel and its coating fresh-keeping method

Abstract

The invention discloses a preparation method of a multifunctional nano-hydrogel and a coating and preservation method thereof. The method is characterized by comprising the steps of dissolving zein in an ethanol aqueous solution, adjusting the pH value of the solution, and then adding basil essential oil and / or oregano essential oil to the zein solution and mixing uniformly to obtain a zein-essential oil mixed solution; and adding the zein-essential oil mixed solution dropwise to a carrageenan-sodium alginate mixed solution according to a volume ratio, stirring while adding dropwise, removing bubbles by ultrasonication after uniform mixing, and allowing the mixture to stand to obtain the multifunctional nano-hydrogel. The method has the advantages of excellent antibacterial and antioxidant capabilities, can effectively inhibit the growth of microorganisms and fat oxidation in meat, delay the process of spoilage, and simultaneously reduce heme iron loss by stabilizing the myoglobin structure, thereby maintaining the color stability of the meat.

Description

Technical Field

[0001] The invention belongs to the technical field of hydrogel preservation, and in particular relates to a preparation method of a multifunctional nano hydrogel and a coating preservation method thereof. Background Art

[0002] Meat and meat products are highly susceptible to microbial contamination and fat oxidation during processing, storage, and distribution. Foodborne pathogens such as Escherichia coli, Salmonella, Listeria monocytogenes, and Bacillus cereus not only accelerate spoilage and cause quality issues such as off-flavor and color loss in meat, but also pose a serious threat to consumer health. Studies have shown that Bacillus cereus is one of the leading pathogens of food poisoning worldwide, causing vomiting and diarrheal poisoning in 5% to 20% of foodborne illness cases. Furthermore, Bacillus cereus contamination rates in meat are as high as 12% to 30%, and recalls of meat products contaminated by this bacterium are increasing at an annual rate of 7.5%. Furthermore, its spores are heat-resistant, making them difficult to completely inactivate using conventional sterilization methods. Therefore, the development of a novel antimicrobial material that effectively inhibits Bacillus cereus while also achieving broad-spectrum inhibition against other pathogens is crucial for ensuring meat safety.

[0003] Existing antimicrobial packaging materials mostly rely on petroleum-based raw materials. Although they can delay spoilage through physical barriers, their non-degradability limits the development of green food packaging, and their targeted inhibitory effect on Bacillus cereus is insufficient. In recent years, nano-coating technology has provided a new direction for solving the antimicrobial and anti-spoilage problems in the storage, transportation and circulation of meat and meat products by precisely regulating the synergistic effect of the molecular structure and functional components of the material. Among the many antimicrobial packaging materials, antimicrobial films are widely used due to their good barrier properties and mechanical strength. However, the film-forming process requires high-temperature drying, which may lead to the inactivation of heat-sensitive antimicrobial components, affecting their antimicrobial effect and food preservation properties. In contrast, nano-coating can form a uniform coating through a simple dipping process without the need for high-temperature drying, and shows broad application prospects in the field of food preservation.

[0004] Nanohydrogels, as functional materials with high water content, excellent biocompatibility, and environmental friendliness, possess a unique three-dimensional network structure that not only serves as an effective carrier for antimicrobial agents, achieving sustained release and long-lasting effects, but also optimizes their mechanical properties and antimicrobial efficacy by adjusting their composition and structure. Currently, nanohydrogels are mostly prepared through ionic crosslinking or the addition of initiators. Carrageenan and sodium alginate, natural polysaccharides extracted from algae, exhibit excellent gelation and biocompatibility and are widely used in food packaging. Zein, a natural protein extracted from corn, has attracted considerable attention for its unique hydrophobicity and film-forming properties. Oregano essential oil, a volatile oil extracted from oregano, contains active compounds such as γ-terpinene and myrcene, which possess strong antimicrobial properties and can effectively inhibit the growth of foodborne pathogens. Basil essential oil, a natural essential oil extracted from basil, is rich in active compounds such as linalool and eucalyptol. At present, there is no report on the preparation of nanohydrogels loaded with oregano essential oil and basil essential oil using carrageenan, sodium alginate and zein and their antibacterial, antiseptic and fresh-keeping effects on meat and meat products. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a preparation method of a multifunctional nanohydrogel having antibacterial and antioxidant functions, low-temperature film-forming adaptability and biodegradable properties, and a coating and preservation method thereof. The hydrogel coating has excellent antibacterial ability against Bacillus cereus and other common spoilage bacteria, with an inhibition rate against Bacillus cereus reaching 99.02%, which can improve the quality of meat products and extend the shelf life of meat products by 0.5 times.

[0006] The technical solution adopted by the present invention to solve the above technical problems is: a method for preparing a multifunctional nano-hydrogel, comprising the following steps:

[0007] (1) Preparation of carrageenan-sodium alginate mixed solution: dissolve carrageenan and sodium alginate in deionized water respectively, then mix the carrageenan and sodium alginate solutions according to volume ratio and stir evenly to obtain a carrageenan-sodium alginate mixed solution;

[0008] (2) Preparation of a zein-essential oil mixed solution: dissolving zein in an ethanol-water solution, adjusting the pH value of the solution, and then adding basil essential oil and / or oregano essential oil to the zein solution and mixing them uniformly to obtain a zein-essential oil mixed solution;

[0009] (3) Preparation of nanohydrogel: The zein-essential oil mixed solution obtained in step (2) is added dropwise to the carrageenan-sodium alginate mixed solution while stirring. After uniform mixing, the mixture is ultrasonically removed to remove bubbles and allowed to stand to obtain a multifunctional nanohydrogel.

[0010] Furthermore, the preparation method of the carrageenan solution-sodium alginate mixed solution described in step (1) is specifically as follows: adding carrageenan powder to deionized water, stirring at 60-80°C for 1-2 hours, adjusting the pH value to 3.5-4.5, and obtaining a carrageenan solution with a concentration of 5-10 mg / mL; dissolving sodium alginate in deionized water, continuously stirring at 50-60°C for 1.5-2.5 hours, adjusting the pH value to 3.5-4.5, and obtaining a sodium alginate solution with a concentration of 10-30 mg / mL; mixing the carrageenan solution and the sodium alginate solution in a volume ratio of (5-1):1, and stirring evenly at 50-60°C to obtain a carrageenan-sodium alginate mixed solution.

[0011] Furthermore, in step (1), 5 mg / mL carrageenan solution and 20 mg / mL sodium alginate solution are mixed at a volume ratio of 4:1, and stirred at 50-60° C. to obtain a carrageenan-sodium alginate mixed solution.

[0012] Furthermore, the preparation method of the zein-essential oil mixed solution described in step (2) is specifically as follows: dissolving zein in a 60-80% ethanol aqueous solution, stirring at room temperature for 20-40 minutes to fully dissolve it, and adjusting the pH value of the solution to 3.5-4.5 to obtain a zein solution with a concentration of 20 mg / mL; adding basil essential oil and / or oregano essential oil to the zein solution, and mixing to obtain the zein-essential oil mixed solution.

[0013] Furthermore, the concentration of essential oil in the zein-essential oil mixed solution is 50 mg / mL, and the mixing ratios of the basil essential oil and the oregano essential oil are 5:0, 4:1, 3:2, 1:1, 2:3, 1:4 and 0:5.

[0014] Furthermore, the mixing ratio of the basil essential oil to the oregano essential oil is 1:4.

[0015] Furthermore, the volume ratio of the carrageenan-sodium alginate mixed solution described in step (3) to the zein-essential oil mixed solution is 4:1-1:1; the ultrasonic power is 400 W, the time is 10 min, and the multifunctional nano-hydrogel is obtained after standing at 4° C. for 8-20 h.

[0016] The present invention also provides the application of the multifunctional nanohydrogel obtained by the above preparation method in preparing a fresh-keeping coating for meat samples. The specific steps of the coating preservation method are as follows: completely immerse the meat in the multifunctional nanohydrogel solution that has not yet gelled for 2-5 minutes to ensure that the solution fully infiltrates the surface of the meat; slowly lift the meat from the solution and place it tilted in a culture dish, let it stand for 2 minutes, and remove excess solution; place the immersed meat in a 4°C refrigerator and let it stand for 8-16 hours to allow the hydrogel solution to gel on the surface of the meat to form a layer of antibacterial hydrogel coating.

[0017] Compared with the prior art, the advantages of the present invention are:

[0018] (1) The present invention provides a method for preparing a multifunctional nanohydrogel using carrageenan, sodium alginate, and zein as base materials, combined with basil essential oil and / or oregano essential oil as antimicrobial agents. The method is based entirely on natural ingredients and does not use any toxic reagents or chemical cross-linking agents. Compared with existing thin film technologies, the hydrogel formation does not require long drying times, thus avoiding the effects of temperature on the active substances.

[0019] (2) The present invention uses the anti-solvent method of zein to embed hydrophobic oregano essential oil and basil essential oil to form a nano-hydrogel, which effectively prevents the volatilization and oxidation of the essential oils, achieves the sustained release and long-lasting effect of the antibacterial components, and significantly improves the stability of the antibacterial agent. Active substances such as γ-terpinene and myrcene in oregano essential oil and linalool and eucalyptol in basil essential oil have antibacterial and antioxidant activities. When mixed, the two have a synergistic effect and can effectively inhibit the growth of Bacillus cereus. At the same time, they have broad-spectrum antibacterial properties against common foodborne pathogens such as Escherichia coli, Salmonella and Listeria monocytogenes, delaying the oxidative deterioration of meat products, which is of great significance for extending the shelf life of products and ensuring food safety.

[0020] (3) The nano-hydrogel of the present invention has a simple preparation process. A uniform antibacterial coating can be formed on the surface of meat through a simple dipping process. It is suitable for preserving a variety of meat products. It can also effectively prevent the oxidation of myoglobin and maintain the color stability of meat.

[0021] In summary, the present invention provides a method for preparing a multifunctional nano-hydrogel and coating and preserving the same. Carrageenan and sodium alginate solutions are mixed, and the hydrophobic properties of zein are utilized. The plant-derived antibacterial agents basil essential oil and oregano essential oil are nano-encapsulated by the anti-solvent method. A composite hydrogel system with multiple functions is formed by cross-linking polysaccharides and proteins. Zein, carrageenan, and sodium alginate are cross-linked to form a more stable composite hydrogel network, further enhancing the stability of the antibacterial agent. The synergistic effect of these two essential oils can not only inhibit spoilage factors in multiple dimensions and improve antibacterial ability. The prepared multifunctional nano-hydrogel can achieve targeted inhibition of Bacillus cereus, as well as Escherichia coli, Salmonella, and Listeria monocytogenes. It can be used to preserve a variety of meat products, inhibit myoglobin oxidation and fat peroxidation reactions, extend the shelf life of meat products, and maintain color stability. It has the characteristics of biocompatibility, strong degradability, and eco-friendliness, providing an innovative solution for the development of green preservation technology for meat products. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The diameter change of the inhibition zone of comparative examples 4-8;

[0023] Figure 2 The changes in the inhibition rate of different test groups;

[0024] Figure 3 The changes of DPPH and ABTS antioxidant capacity in different experimental groups;

[0025] Figure 4 The changes in hydrogel particle size in different experimental groups;

[0026] Figure 5 Microstructure diagrams of different experimental groups. DETAILED DESCRIPTION

[0027] The present invention will be described in further detail below with reference to the accompanying drawings and embodiments.

[0028] Specific Example 1: By observing the gelation ability and state of the hydrogel, it was found that when the carrageenan concentration was 10 mg / mL, the solution solidified too quickly at room temperature, affecting the uniformity of subsequent material addition; when it was reduced to 5 mg / mL, the carrageenan solution was able to form a gel smoothly. When the sodium alginate concentration was 30 mg / mL, the solution was too viscous to mix evenly, and 20 mg / mL was selected as the appropriate concentration. When the volume ratio of carrageenan to sodium alginate was 3:1, 2:1, and 1:1, gelation could not be achieved due to the low concentration of carrageenan, and only a viscous liquid could be formed; when adjusted to 4:1, the mixed solution was able to gel and form a solid hydrogel; when the volume ratio of carrageenan to sodium alginate was 5:1, the gelation speed was too fast. Therefore, a solution of mixing 5 mg / mL carrageenan solution with 20 mg / mL sodium alginate solution in a 4:1 volume ratio was finally adopted for subsequent research.

[0029] Example 1, a method for preparing a nano-hydrogel having a ratio of basil essential oil to oregano essential oil of 5:0, comprising the following steps:

[0030] Step 1, preparing a carrageenan-sodium alginate mixed solution: adding carrageenan powder to deionized water, stirring at 70° C. for 1 hour to obtain a carrageenan solution with a concentration of 5 mg / mL; dissolving sodium alginate in deionized water, and continuously stirring at 55° C. for 2 hours to obtain a sodium alginate solution with a concentration of 20 mg / mL; adjusting the pH values of the carrageenan and sodium alginate solutions to 4.0 using 0.2 mol / mL food-grade hydrochloric acid and food-grade sodium hydroxide solution, respectively; mixing the carrageenan and sodium alginate solutions in a volume ratio of 4:1, and stirring uniformly at 55° C. to obtain a carrageenan-sodium alginate mixed solution;

[0031] Step 2, preparation of zein-essential oil mixed solution: zein is dissolved in 70% ethanol aqueous solution, stirred at room temperature for 30 minutes to fully dissolve it, and the pH value of the solution is adjusted to 4.0 using 0.2 mol / mL hydrochloric acid and sodium hydroxide solution to obtain a zein solution with a concentration of 20 mg / mL. Basil essential oil is added to the zein solution and mixed to obtain a zein-basil essential oil mixed solution, wherein the concentration of basil essential oil in the zein-basil essential oil mixed solution is 50 mg / mL;

[0032] Step 3, Preparation of Nanohydrogel: The zein-basil essential oil mixed solution obtained in step (2) was added dropwise to the carrageenan-sodium alginate mixed solution at a volume ratio of 1:4, with stirring. After uniform mixing, the solution was ultrasonicated at 400W for 10 minutes to remove bubbles. The solution was allowed to stand at 4°C for 16 hours to obtain a multifunctional nanohydrogel loaded with basil essential oil. Finally, the concentration of basil essential oil in the gel was 10 mg / mL, and the concentration of oregano essential oil was 0.

[0033] Example 2: This example uses the same method as Example 1, except that the addition ratio of basil essential oil to oregano essential oil is 0:5. Ultimately, the concentration of oregano essential oil in the gel is 10 mg / mL, and the concentration of basil essential oil is 0.

[0034] Example 3. This example uses the same method as Example 1, except that the mixing ratio of basil essential oil to oregano essential oil is 1:4. Ultimately, the total concentration of essential oils in the gel is 10 mg / mL, of which the concentration of basil essential oil is 2 mg / mL and the concentration of oregano essential oil is 8 mg / mL.

[0035] Comparative Example 1: Carrageenan solution with a concentration of 5 mg / mL.

[0036] Comparative Example 2: A carrageenan solution with a concentration of 5 mg / mL and a sodium alginate solution with a concentration of 20 mg / mL were mixed in a volume ratio of 4:1, the pH value of the solution was adjusted to 4.0, ultrasonicated at 400 W for 10 min, and allowed to stand at 4°C for 16 h to obtain a carrageenan-sodium alginate mixed hydrogel.

[0037] Comparative Example 3: a zein solution having a concentration of 20 mg / mL.

[0038] Comparative Example 4: Basil essential oil and oregano essential oil were mixed in a ratio of 4:1 and dissolved in deionized water to prepare a composite essential oil solution with a total concentration of 10 mg / mL, wherein the concentration of basil essential oil was 8 mg / mL and the concentration of oregano essential oil was 2 mg / mL.

[0039] Comparative Example 5: Basil essential oil and oregano essential oil were mixed in a ratio of 3:2 and dissolved in deionized water to prepare a composite essential oil solution with a total concentration of 10 mg / mL, wherein the concentration of basil essential oil was 6 mg / mL and the concentration of oregano essential oil was 4 mg / mL.

[0040] Comparative Example 6: Basil essential oil and oregano essential oil were mixed in a ratio of 1:1 and dissolved in deionized water to prepare a composite essential oil solution with a total concentration of 10 mg / mL, wherein the concentration of basil essential oil was 5 mg / mL and the concentration of oregano essential oil was 5 mg / mL.

[0041] Comparative Example 7: Basil essential oil and oregano essential oil were mixed in a ratio of 2:3 and dissolved in deionized water to prepare a composite essential oil solution with a total concentration of 10 mg / mL, wherein the concentration of basil essential oil was 4 mg / mL and the concentration of oregano essential oil was 6 mg / mL.

[0042] Comparative Example 8: Basil essential oil and oregano essential oil were mixed in a ratio of 1:4 and dissolved in deionized water to prepare a composite essential oil solution with a total concentration of 10 mg / mL, wherein the concentration of basil essential oil was 2 mg / mL and the concentration of oregano essential oil was 8 mg / mL.

[0043] II. Analysis of Experimental Results of Multifunctional Hydrogels: The effects of different substances and antimicrobial agents on gel properties and antimicrobial properties were described based on the examples and comparative examples prepared in the above specific embodiments. The hydrogels obtained in the above examples and comparative examples were tested.

[0044] 1. Effect of the ratio of basil essential oil to oregano essential oil on antibacterial activity: The antibacterial activity of comparative examples 4-8 against Escherichia coli, Salmonella, Bacillus cereus and Listeria monocytogenes was analyzed by inhibition zone test. Figure 1 As shown, compared with Comparative Examples 4-7, Comparative Example 8 has the largest inhibition zone diameters against Escherichia coli, Salmonella, Bacillus cereus and Listeria monocytogenes, which are 14.31 mm, 15.19 mm, 18.36 mm and 16.89 mm, respectively, indicating that the antibacterial effect is strongest when the mixing ratio of basil essential oil to oregano essential oil is 1:4.

[0045] 2. Analysis of the antibacterial ability of hydrogels in different test groups: Escherichia coli, Salmonella, Bacillus cereus and Listeria monocytogenes were used to evaluate the antibacterial activity of the gel. Escherichia coli, Salmonella and Bacillus cereus were cultured in LB broth, while Listeria monocytogenes was cultured in BHI broth to form a concentration of 1×10 8 CFU / mL of bacterial suspension. Subsequently, 100 μL of the bacterial suspension was evenly applied to a solid agar plate. Corresponding wells were punched using a hole punch, and Comparative Examples 1-2 and Examples 1-3 were added to the wells. The solid plate was then incubated upside down at 37°C for 12 hours, and the antibacterial activity of the antibacterial solution was evaluated by the diameter of the inhibition zone. The results are shown in Table 1.

[0046] Table 1 Inhibition zones of different examples and comparative examples for different bacteria

[0047]

[0048] Table 1 shows the changes in the inhibition zones of different hydrogels (Comparative Examples 1-2 and Examples 1-3) against Escherichia coli, Salmonella, Bacillus cereus, and Listeria monocytogenes. As shown in Table 1, after the antimicrobial agent was loaded into the gel, the diameters of the inhibition zones against the four bacteria in Examples 1-3 increased significantly. Compared to Examples 1 and 2, Example 3 exhibited the largest inhibition zone diameters against E. coli, Salmonella, Bacillus cereus, and Listeria monocytogenes. In particular, Example 3 exhibited the strongest antibacterial activity against B. cereus, with an inhibition zone diameter of 20.90 mm, representing increases of 84.63% and 11.65% compared to Examples 1 and 2, respectively. Furthermore, the inhibition zone diameters of Example 3 against B. cereus increased by 21.51%, 7.62%, and 6.2% compared to E. coli, Salmonella, and Listeria monocytogenes, respectively. These results demonstrate that Example 3 exhibits excellent inhibitory effects against Bacillus cereus, with the two essential oils synergistically enhancing the antibacterial capacity of the nanohydrogel. Furthermore, Example 3 exhibits broad-spectrum antibacterial activity, inhibiting Escherichia coli, Salmonella, and Listeria monocytogenes. Furthermore, compared to Comparative Example 8, Example 3 exhibited increased inhibition zone diameters against Escherichia coli, Salmonella, Bacillus cereus, and Listeria monocytogenes, demonstrating that the three-dimensional network structure of the nanohydrogel effectively enhances the sustained release efficiency of the active ingredient, thereby significantly enhancing antibacterial efficacy.

[0049] 3. Analysis of the antibacterial rate of hydrogels in different test groups: Escherichia coli, Salmonella, Bacillus cereus and Listeria monocytogenes were cultured in broth until the concentration of bacterial suspension was 1×10 8 CFU / mL. Comparative Examples 1-2 and Examples 1-3 were added to the bacterial suspension and incubated at 37°C for 8 hours. After the incubation, the broth was diluted in a gradient manner and 100 μL of the diluted culture solution was spread on a solid plate. Finally, the culture was inverted and incubated at 37°C for 24 hours, and the colonies were counted. The results are shown in Figure 2. Figure 2 shown.

[0050] Depend on Figure 2 It can be seen that the inhibition rates of Examples 1-3 with the addition of essential oils on Escherichia coli, Salmonella, Bacillus cereus, and Listeria monocytogenes are significantly increased compared to Comparative Examples 1 and 2. Examples 1, 2, and 3 all showed the strongest inhibitory effect on Bacillus cereus. Among all the examples, Example 3 showed the maximum inhibition rate on Bacillus cereus, with an inhibition rate of 99.02%. In addition, the inhibition rate of Example 3 on Escherichia coli, Salmonella, and Listeria monocytogenes was also significantly higher than that of Examples 1 and 2. These results indicate that the basil essential oil and oregano essential oil exerted a synergistic effect after being added to the nano-hydrogel, enhancing the antibacterial ability of the hydrogel system.

[0051] 4. Analysis of the antioxidant capacity of hydrogels in different test groups: The antioxidant capacity of Comparative Examples 1-2 and Examples 1-3 was determined using the DPPH and ABTS free radical scavenging rate methods. A 0.1 mM DPPH solution was prepared, and the hydrogels of Comparative Examples 1-2 and Examples 1-3 were mixed with the DPPH solution, mixed thoroughly, and reacted in the dark for 30 minutes. The absorbance was measured at a wavelength of 517 nm to calculate the DPPH free radical scavenging rate; the hydrogels of Comparative Examples 1-2 and Examples 1-3 were mixed with the ABTS solution, shaken thoroughly, reacted in the dark for 10 minutes, and the absorbance was measured at a wavelength of 734 nm to calculate the ABTS free radical scavenging rate. The results are as follows: Figure 3 shown.

[0052] Depend on Figure 3 It can be seen that carrageenan and sodium alginate themselves have certain antioxidant capacity, but the antioxidant effect is relatively weak. Compared with Comparative Examples 1 and 2, the hydrogels of Examples 1-3 have significantly improved DPPH and ABTS free radical scavenging rates. Among them, Example 3 showed the highest scavenging rates in both free radical scavenging experiments, at 95.83% and 88.07%, respectively. Compared with Example 2, its DPPH free radical scavenging rate increased by 19.5%, and its ABTS free radical scavenging rate increased by 7.8%, indicating that after the antibacterial agent is loaded on the gel, the two essential oils work synergistically, thereby showing excellent antioxidant capacity.

[0053] 5. Particle size analysis of hydrogels in different test groups: Comparative Examples 1-3 and Examples 1-3 were diluted ten times with deionized water and the particle size was measured using a particle size analyzer. Figure 4 shown.

[0054] Depend on Figure 4 It can be seen that the particle size of Comparative Example 2 is the largest, at 1602.33 nm; the particle size of Comparative Example 3 is the smallest, at 86.22 nm. Compared with Comparative Examples 1 and 2, the particle sizes of Examples 1-3 are significantly reduced, indicating that zein can effectively encapsulate essential oils to form nanoparticles. Among Examples 1-3, the particle size of Example 1 is the highest at 659.13 nm. Compared with Example 1, the particle size of Example 3 is significantly reduced, indicating that basil essential oil and oregano essential oil play a synergistic role, contributing to the formation of smaller particle sizes. The formation of nanoparticles helps to improve the strength and stability of the gel, while the smaller particle size can improve the biocompatibility and drug release performance of the hydrogel.

[0055] 6. Morphological analysis of hydrogels in different test groups: The microstructures of comparative examples 1-2 and examples 1-3 were observed by scanning electron microscopy. The examples and comparative examples were freeze-dried for 48 hours, and then gold was sprayed on the surface of the hydrogels. The results were scanned at an accelerating voltage of 15 kV. Figure 5 shown.

[0056] Depend on Figure 5 It can be seen that the surfaces of Comparative Examples 1 and 2 are in the form of a film, and the cross-section presents a disordered sheet structure, and no three-dimensional network structure unique to hydrogel is formed, indicating that Comparative Examples 1 and 2 have simple structures and a low degree of intermolecular cross-linking. Compared to Comparative Examples 1 and 2, Examples 1-3 in which zein is added form a more complex cross-linked network, indicating that the protein may interact with the polysaccharide molecules, contribute to the construction of a three-dimensional network, and increase the mechanical strength and stability of the material. Compared to Examples 1 and 2, the surface pores of Example 3 are reduced, forming a more dense network structure with smaller pores, indicating that the co-addition of the two essential oils promotes the cross-linking of the hydrogel, better resists external stress, and provides better support and sustained release.

[0057] 3. Application of coating and preservation of multifunctional nano-hydrogel.

[0058] 1. Effect of Hydrogel Coating on TVB-N, TBARS, and TVC of Fresh Chicken: Fresh chicken was immersed in the nanohydrogel solution of Example 3 for 3 minutes. The meat sample was slowly lifted from the solution and placed at an angle in a Petri dish. The sample was allowed to stand for 2 minutes, and the excess solution was removed. The sample was then placed in a 4°C refrigerator for 8 hours to allow the hydrogel coating to form on the surface. The sample was then stored at 4°C for 16 days. Changes in TVB-N, TBARS, and TVC in each group were observed every 4 days. The results are shown in Table 2. The CK group contained fresh chicken samples that were not treated with hydrogel.

[0059] Table 2 Effects of hydrogel coating in Example 3 on TVB-N, TBARS and TVC of chilled chicken

[0060]

[0061] As shown in Table 2, the TVB-N values of Example 3 and the CK group increased with the increase of storage time. During the 16-day storage process, the TVB-N value of the CK group increased from 3.66 mg / 100g to 23.57 mg / 100g, and the TVB-N value of Example 3 increased from 3.42 mg / 100g to 14.42 mg / 100g. Compared with the CK group, the TVB-N value of Example 3 decreased by 38.82%. Excessive lipid oxidation usually has an adverse effect on the flavor and quality of meat. The TBARS value of the CK group increased from the initial value of 0.17 mg / 100g to 0.57 mg / 100g on the 16th day, while on the 16th day, the TBARS value of Example 3 was 26.3% lower than that of the control group, indicating that the nanohydrogel coating can effectively inhibit the lipid oxidation of chicken. The TVC of fresh chicken increased to varying degrees with storage time. Chicken treated with Example 3 had significantly lower TVC values than the CK group, indicating that the nanohydrogel effectively inhibited the growth of spoilage bacteria and extended the shelf life of the meat. Fresh meat is considered to have begun to spoil when the TVB-N value exceeds 15 mg / 100 g, the TBARS value exceeds 0.2 mg / 100 g, and the TVC value exceeds 51 g CFU / g. Therefore, the storage life of fresh chicken coated with the nanohydrogel was extended by 50% compared to the CK group.

[0062] 2. Effect of Hydrogel Coating on TVB-N, TBARS, and TVC of Air-Dried Goose Meat: Air-dried goose meat was immersed in the nanohydrogel solution of Example 3 for 3 minutes. The meat sample was slowly lifted from the solution and placed at an angle in a Petri dish. The sample was allowed to stand for 2 minutes, and the excess solution was removed. The sample was then placed in a 4°C refrigerator for 8 hours to allow the hydrogel coating to form on the surface. The sample was then stored at 4°C for 16 days. Changes in TVB-N, TBARS, and TVC in each group were observed every 4 days. The results are shown in Table 3. The CK group contained air-dried goose meat samples that were not treated with hydrogel.

[0063] Table 3 Effect of hydrogel coating on TVB-N, TBARS and TVC of air-dried goose meat in Example 3

[0064]

[0065] The same is true for the application of nano-hydrogel to air-dried goose meat. As the storage time increases, the TVB-N, TBARS and TVC values of the CK group and Example 3 continue to increase, and the TVB-N, TBARS and TVC values of the goose meat treated in Example 3 are always lower than those of the CK group. On the 16th day, the TVB-N, TBARS and TVC values of the experimental group were reduced by 23.07%, 72.45% and 12.94% respectively compared with the CK group, extending the shelf life of the air-dried goose meat by 0.5 times. These results show that the nano-hydrogel coating effectively alleviates the degradation of protein, fat oxidation and microbial growth in the meat, thereby preventing the spoilage of meat and extending its shelf life.

[0066] 3. Fresh chicken was stored at 4°C for 16 days. The lightness (L), redness (a), and yellowness (b) values of the fresh chicken were measured every four days. Meat samples not treated with hydrogel served as a control group. The results are shown in Table 4.

[0067] Table 4 Effect of hydrogel coating in Example 3 on color change of chilled fresh chicken

[0068]

[0069] As shown in Table 4, the L values of the CK group and the treatment group of Example 3 gradually decreased with the extension of storage time. On the 16th day, the L value of the experimental group was 55.37, which was significantly higher than that of the CK group ( p <0.05). Similar to the change trend of L value, the a value of the CK group and the experimental group decreased with the increase of storage time. On the 16th day, the a value of the experimental group was -1.51, which was significantly higher than that of the CK group and increased by 33.77% compared with the CK group. The b value of the experimental group and the control group increased with the increase of storage time. The b value of the CK group increased from 8.73 to 17.92, while that of the experimental group increased from 8.69 to 13.52. The upward trend was slower than that of the control group, indicating that the hydrogel coating can maintain the color stability of fresh chilled chicken.

[0070] Effect of Hydrogel Coating on the Color Change of Air-Dried Goose Meat: Air-dried goose meat was stored at 4°C for 16 days. The L, a, and b values of the air-dried goose meat were measured every four days. Meat samples without hydrogel treatment served as a control group. The results are shown in Table 5.

[0071] Table 5 Effect of hydrogel coating in Example 3 on the color change of air-dried goose meat

[0072]

[0073] The results in Table 5 show that compared with the untreated group (CK), the nano-hydrogel coating of Example 3 significantly delayed the color deterioration of air-dried goose meat during storage at 4°C. During the 16-day storage period, the L value of the CK group decreased from 48.68 to 38.92, while the experimental group only decreased from 48.38 to 41.63. From the 8th day on, the L value of the experimental group was significantly higher than that of the control group ( p <0.05), indicating that the hydrogel effectively maintained the surface brightness of the meat by inhibiting oxidative browning and microbial metabolism. The redness of meat, a key indicator of meat color, decreased with increasing storage time of air-dried goose meat in both the CK and experimental groups, with the rate of decline in the experimental group slowing by 38% compared to the control group, indicating that the antioxidant components in the nanohydrogel delayed myoglobin oxidation. The b values of both the experimental and control groups increased with increasing storage time, but the upward trend in the experimental group was slower than that in the control group, indicating that the hydrogel coating mitigated the yellowing of the meat by blocking oxygen and inhibiting fat oxidation. These results demonstrate that the hydrogel coating, through its synergistic antioxidant and antimicrobial effects, not only extends the shelf life of meat but also maintains the color stability of air-dried goose meat.

[0074] The above description is not intended to limit the present invention, and the present invention is not limited to the above examples. Any changes, modifications, additions or substitutions made by persons of ordinary skill in the art within the spirit and scope of the present invention shall also fall within the scope of protection of the present invention.

Claims

1. A method for preparing a multifunctional nanohydrogel, characterized in that The following steps are involved: (1) Preparation of carrageenan-sodium alginate mixed solution: dissolve carrageenan and sodium alginate in deionized water respectively, then mix the carrageenan and sodium alginate solutions according to volume ratio and stir evenly to obtain a carrageenan-sodium alginate mixed solution; (2) Preparation of a zein-essential oil mixed solution: dissolving zein in an ethanol-water solution, adjusting the pH value of the solution, and then adding basil essential oil and oregano essential oil to the zein solution and mixing them evenly to obtain a zein-essential oil mixed solution; (3) Preparation of nanohydrogel: The zein-essential oil mixed solution obtained in step (2) is added dropwise to the carrageenan-sodium alginate mixed solution while stirring. After uniform mixing, the mixture is ultrasonically removed to remove bubbles and allowed to stand to obtain a multifunctional nanohydrogel.

2. The method for preparing a multifunctional nano-hydrogel according to claim 1, characterized in that The preparation method of the carrageenan solution-sodium alginate mixed solution described in step (1) is specifically as follows: adding carrageenan powder to deionized water, stirring at 60-80°C for 1-2 hours, adjusting the pH value to 3.5-4.5, and obtaining a carrageenan solution with a concentration of 5-10 mg / mL; dissolving sodium alginate in deionized water, continuously stirring at 50-60°C for 1.5-2.5 hours, adjusting the pH value to 3.5-4.5, and obtaining a sodium alginate solution with a concentration of 10-30 mg / mL; mixing the carrageenan solution and the sodium alginate solution in a volume ratio of (5-1):1, and stirring evenly at 50-60°C to obtain a carrageenan-sodium alginate mixed solution.

3. The method for preparing a multifunctional nano-hydrogel according to claim 2, characterized in that In step (1), 5 mg / mL carrageenan solution and 20 mg / mL sodium alginate solution are mixed in a volume ratio of 4:1, and stirred evenly at 50-60° C. to obtain a carrageenan-sodium alginate mixed solution.

4. The method for preparing a multifunctional nano-hydrogel according to claim 1, characterized in that The preparation method of the zein-essential oil mixed solution described in step (2) is specifically as follows: dissolving zein in a 60-80% ethanol aqueous solution, stirring at room temperature for 20-40 minutes to fully dissolve it, and adjusting the pH value of the solution to 3.5-4.5 to obtain a zein solution with a concentration of 20 mg / mL; adding basil essential oil and oregano essential oil to the zein solution, and mixing them to obtain the zein-essential oil mixed solution.

5. The method for preparing a multifunctional nano-hydrogel according to claim 4, characterized in that: The concentration of essential oil in the zein-essential oil mixed solution is 50 mg / mL, and the mixing ratios of the basil essential oil and the oregano essential oil are 4:1, 3:2, 1:1, 2:3 and 1:

4.

6. The method for preparing a multifunctional nano-hydrogel according to claim 5, characterized in that: The mixing ratio of the basil essential oil and the oregano essential oil is 1:

4.

7. The method for preparing a multifunctional nano-hydrogel according to claim 1, characterized in that: The volume ratio of the carrageenan-sodium alginate mixed solution described in step (3) to the zein-essential oil mixed solution is 4:1-1:1; the ultrasonic power is 400 W, the time is 10 min, and the multifunctional nano-hydrogel is obtained after standing at 4°C for 8-20 h.

8. Use of the multifunctional nano-hydrogel obtained by the preparation method according to any one of claims 1 to 7 in preparing a fresh-keeping coating for meat samples, characterized in that The specific steps of the coating preservation method are as follows: completely immerse the meat in the non-gelled multifunctional nano-hydrogel solution for 2-5 minutes; slowly lift the meat from the solution and place it tilted in a culture dish, let it stand for 2 minutes, and remove excess solution; place the soaked meat in a 4°C refrigerator and let it stand for 8-16 hours. The hydrogel solution will gel on the surface of the meat to form a layer of antibacterial hydrogel coating.

Images