Preparation method of multifunctional nano hydrogel and coating preservation method of multifunctional nano hydrogel

Abstract

The preparation method is characterized by comprising the following steps: dissolving zein in an ethanol water solution, adjusting the pH value of the solution, adding basil essential oil and / or oregano essential oil into the zein solution, uniformly mixing, and carrying out vacuum drying, so as to obtain the multifunctional nano hydrogel. A step of obtaining a zein-essential oil mixed solution; the zein-essential oil mixed solution is dropwise added into the carrageenan-sodium alginate mixed solution according to the volume ratio, stirring is carried out while dropwise adding is carried out, after even mixing is carried out, bubbles are removed through ultrasonic waves, standing is carried out, and the multifunctional nano hydrogel is obtained. Growth of microorganisms and fat oxidation in meat can be effectively inhibited, the spoilage process is delayed, meanwhile, the loss of heme iron is reduced by stabilizing a myoglobin structure, and the color stability of the meat is maintained.

Description

Technical Field

[0001] The present 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] Meats and meat products are extremely prone to microbial contamination and lipid oxidation during processing, storage, and circulation. Foodborne pathogenic bacteria represented by Escherichia coli, Salmonella, Listeria monocytogenes, and Bacillus cereus not only accelerate the spoilage process, leading to quality problems such as off-flavors and color deterioration in meat products, but also pose a serious threat to consumer health. Research shows that Bacillus cereus is one of the main pathogens of food poisoning globally, and the vomiting and diarrhea-type poisonings caused by it account for 5% - 20% of foodborne disease cases. In addition, the contamination rate of Bacillus cereus in meats is as high as 12% - 30%, and the annual growth rate of meat product recall events contaminated by this bacterium is 7.5%. Moreover, its spores are heat-resistant, and conventional sterilization methods are difficult to completely inactivate them. Therefore, developing a new type of antibacterial material that can effectively inhibit Bacillus cereus while also achieving a broad-spectrum inhibitory effect on other pathogenic bacteria is of great significance for ensuring meat product safety.

[0003] Existing antibacterial 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 antibacterial and anti-corruption problems in the storage, transportation, and circulation of meats and meat products by precisely regulating the synergistic effects of material molecular structures and functional components. Among many antibacterial packaging materials, antibacterial films are widely used due to their good barrier properties and mechanical strength. However, the film-forming process requires high-temperature drying, which may cause inactivation of heat-sensitive antibacterial components and affect their antibacterial effects and food preservation performance. In contrast, nano-coating can form a uniform coating through a simple dipping process without high-temperature drying, showing broad application prospects in the field of food preservation.

[0004] As a functional material with high water content, excellent biocompatibility and environmental friendliness, the unique three-dimensional network structure of nano-hydrogel can not only serve as an effective carrier for antibacterial agents to achieve the slow release and long-term effect of antibacterial components, but also optimize its mechanical properties and antibacterial effect by adjusting the material composition and structure. At present, nano-hydrogels are mostly prepared by ionic crosslinking or adding initiators. Carrageenan and sodium alginate are natural polysaccharides extracted from algae, which have good gelation and biocompatibility and are widely used in the field of food packaging. Zein, as a natural protein extracted from corn, has attracted much attention due to its unique hydrophobicity and film-forming property. Oregano essential oil is a volatile oil extracted from oregano, and its active substances such as γ-terpinene and myrcene have strong antibacterial properties and can effectively inhibit the growth of foodborne pathogenic bacteria. Basil essential oil is a natural essential oil extracted from basil, which is rich in active substances such as linalool and eucalyptol. At present, there is no relevant report on the preparation of nano-hydrogels by loading oregano essential oil and basil essential oil with carrageenan, sodium alginate and zein and their antibacterial, anti-corrosion 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 and a coating fresh-keeping method of a multifunctional nano-hydrogel with antibacterial and antioxidant functions, low-temperature film-forming adaptability and biodegradability. The hydrogel coating has excellent antibacterial ability against Bacillus cereus and other common spoilage bacteria, and the antibacterial rate against Bacillus cereus reaches 99.02%. It 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 as follows: A preparation method of a multifunctional nano-hydrogel, comprising the following steps: (1) Preparation of carrageenan-sodium alginate mixed solution: Dissolve carrageenan and sodium alginate in deionized water respectively, and then mix the carrageenan and sodium alginate solutions according to the volume ratio, and stir evenly to obtain a carrageenan-sodium alginate mixed solution; (2) Preparation of zein-essential oil mixed solution: Dissolve zein in an ethanol aqueous solution, adjust the pH value of the solution, and then add basil essential oil and / or oregano essential oil to the zein solution, and mix evenly to obtain a zein-essential oil mixed solution; (3) Preparation of nano-hydrogel: Dropwise add the zein-essential oil mixed solution obtained in step (2) into the carrageenan-sodium alginate mixed solution, stir while dropping, and after uniform mixing, remove the bubbles by ultrasonic treatment and let it stand to obtain a multifunctional nano-hydrogel.

[0007] Further, the preparation method of the carrageenan solution - sodium alginate mixed solution described in step (1) is specifically as follows: Add carrageenan powder to deionized water, stir at 60 - 80 °C for 1 - 2 h, adjust the pH value to 3.5 - 4.5 to obtain a carrageenan solution with a concentration of 5 - 10 mg / mL; dissolve sodium alginate in deionized water, continuously stir at 50 - 60 °C for 1.5 - 2.5 h, adjust the pH value to 3.5 - 4.5 to obtain a sodium alginate solution with a concentration of 10 - 30 mg / mL; mix the carrageenan solution and the sodium alginate solution in a volume ratio of (5 - 1):1, and stir evenly at 50 - 60 °C to obtain a carrageenan - sodium alginate mixed solution.

[0008] Further, in step (1), a 5 mg / mL carrageenan solution and a 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.

[0009] Further, the preparation method of the zein - essential oil mixed solution described in step (2) is specifically as follows: Dissolve zein in an ethanol aqueous solution of 60 - 80%, stir at room temperature for 20 - 40 min, and after it is fully dissolved, adjust the pH value of the solution to 3.5 - 4.5 to obtain a zein solution with a concentration of 20 mg / mL; add basil essential oil and / or oregano essential oil to the zein solution, and mix evenly to obtain a zein - essential oil mixed solution.

[0010] Further, the concentration of the essential oil in the zein - essential oil mixed solution is 50 mg / mL, and the mixing ratio of the basil essential oil to the oregano essential oil is 5:0, 4:1, 3:2, 1:1, 2:3, 1:4, and 0:5.

[0011] Further, the mixing ratio of the basil essential oil to the oregano essential oil is 1:4.

[0012] Further, the volume ratio of the carrageenan - sodium alginate mixed solution to the zein - essential oil mixed solution described in step (3) is 4:1 - 1:1; the ultrasonic power is 400 W, the time is 10 min, and after standing at 4 °C for 8 - 20 h, a multifunctional nanohydrogel is obtained.

[0013] The present invention also provides an application of the multifunctional nano-hydrogel obtained by the above preparation method in the preparation of a fresh-keeping coating for meat samples. The specific steps of the coating fresh-keeping method are as follows: completely immerse the meat product in the multifunctional nano-hydrogel solution that has not yet gelled, and keep it for 2-5 minutes to ensure that the solution fully wets the surface of the meat product; slowly lift the meat product from the solution and place it obliquely in a petri dish, and let it stand for 2 minutes to remove the excess solution; place the wetted meat product in a refrigerator at 4°C and let it stand for 8-16 hours so that the hydrogel solution gels on the surface of the meat product to form an antibacterial hydrogel coating.

[0014] Compared with the prior art, the advantages of the present invention are as follows: (1) The method for preparing the multifunctional nano-hydrogel provided by the present invention uses carrageenan, sodium alginate and zein as base materials, and combines basil essential oil and / or oregano essential oil as antibacterial agents, all based on natural ingredients without using any toxic reagents and chemical cross-linking agents. Compared with the existing film technology, the formation of the hydrogel does not require long-term drying, avoiding the influence of temperature on the active substances.

[0015] (2) The present invention entraps hydrophobic oregano essential oil and basil essential oil by the anti-solvent method of zein to form a nano-hydrogel, effectively preventing the volatilization and oxidation of the essential oils, realizing the slow release and long-term effect of the antibacterial components, and significantly improving 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 the two are mixed, they have a synergistic effect, which can effectively inhibit the growth of Bacillus cereus, and at the same time have broad-spectrum antibacterial properties against common foodborne pathogenic bacteria such as Escherichia coli, Salmonella and Listeria monocytogenes, delaying the oxidative deterioration of meat products, which is of great significance for extending the product shelf life and ensuring food safety.

[0016] (3) The preparation process of the nano-hydrogel of the present invention is simple, and a uniform antibacterial coating can be formed on the surface of the meat product through a simple dipping process, and it is applicable to the fresh-keeping of various meat products. At the same time, it can also effectively prevent the oxidation of myoglobin and maintain the color stability of the meat product.

[0017] In summary, for the preparation of a multifunctional nano-hydrogel and its coating preservation method of the present invention, carrageenan and sodium alginate solutions are mixed. Meanwhile, taking advantage of the hydrophobic property of zein, the anti-solvent method is used to encapsulate plant-derived antibacterial agents, basil essential oil and oregano essential oil, at the nanoscale. A composite hydrogel system with multiple functions is formed through the cross-linking of polysaccharides and proteins. The cross-linking of zein with carrageenan and sodium alginate can 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 and improve antibacterial ability in multiple dimensions. The prepared multifunctional nano-hydrogel can achieve targeted inhibition of Bacillus cereus, as well as Escherichia coli, Salmonella, and Listeria monocytogenes, and can be applied to the preservation of various meat products, inhibit the oxidation of myoglobin and lipid peroxidation reactions, extend the shelf life of meat products and maintain color stability, and has characteristics such as biocompatibility, strong degradability, and ecological friendliness, providing an innovative solution for the development of green preservation technologies for meat products. Description of the Drawings

[0018] Figure 1 For the change in the diameter of the inhibition zone in Comparative Examples 4 - 8; Figure 2 For the change in the antibacterial rate of different test groups; Figure 3 For the change in the DPPH and ABTS antioxidant capacities of different test groups; Figure 4 For the change in the particle size of the hydrogel in different test groups; Figure 5 For the microstructural diagrams of different test groups. Detailed Embodiments

[0019] The following further describes the present invention in detail with reference to the embodiments of the drawings.

[0020] Specific Example 1: By observing the gelation ability and state of the hydrogel, it was found that when the concentration of carrageenan was 10 mg / mL, the solution solidified too quickly at room temperature, affecting the uniformity of subsequent material addition; after reducing it to 5 mg / mL, the carrageenan solution could smoothly form a gel. When the concentration of sodium alginate was 30 mg / mL, the solution was too viscous to be mixed 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, since the concentration of carrageenan was too low to gel, only viscous liquids could be formed; when adjusted to 4:1, the mixed solution could 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, finally, a 5 mg / mL carrageenan solution and a 20 mg / mL sodium alginate solution were mixed at a volume ratio of 4:1 for subsequent research.

[0021] Preparation method of nano hydrogel with the ratio of basil essential oil to oregano essential oil being 5:0, the specific steps are as follows: Step 1: Preparation of carrageenan-sodium alginate mixed solution: Add carrageenan powder to deionized water, stir at 70 °C for 1 h to obtain a carrageenan solution with a concentration of 5 mg / mL. Dissolve sodium alginate in deionized water, continuously stir at 55 °C for 2 h to obtain a sodium alginate solution with a concentration of 20 mg / mL. Use food-grade hydrochloric acid and food-grade sodium hydroxide solutions with a concentration of 0.2 mol / mL to adjust the pH values of the carrageenan and sodium alginate solutions to 4.0 respectively. Mix the carrageenan and sodium alginate solutions in a volume ratio of 4:1, and stir evenly at 55 °C to obtain a carrageenan-sodium alginate mixed solution; Step 2: Preparation of zein-essential oil mixed solution: Dissolve zein in 70% ethanol aqueous solution, stir at room temperature for 30 min to make it fully dissolve. Use hydrochloric acid and sodium hydroxide solutions with a concentration of 0.2 mol / mL to adjust the pH value of the solution to 4.0 to obtain a zein solution with a concentration of 20 mg / mL. Add basil essential oil to the zein solution, and mix evenly to obtain a zein-basil essential oil mixed solution. The concentration of basil essential oil in the zein-basil essential oil mixed solution is 50 mg / mL; Step 3: Preparation of nano hydrogel: Gradually add the zein-basil essential oil mixed solution obtained in step (2) dropwise to the carrageenan-sodium alginate mixed solution in a volume ratio of 1:4, stir while dropping, and after uniform mixing, ultrasonicate at 400 W for 10 min to remove bubbles. Let it stand at 4 °C for 16 h to obtain a multifunctional nano hydrogel loaded with basil essential oil. Finally, the concentration of basil essential oil in the gel is 10 mg / mL, and the concentration of oregano essential oil is 0.

[0022] Example 2: This example uses the same method as Example 1, the difference is that: the addition ratio of basil essential oil to oregano essential oil is 0:5. Finally, the concentration of oregano essential oil in the gel is 10 mg / mL, and the concentration of basil essential oil is 0.

[0023] Example 3: This example uses the same method as Example 1, the difference is that: the mixing ratio of basil essential oil to oregano essential oil is 1:4. Finally, the total concentration of essential oil in the gel is 10 mg / mL, among which the concentration of basil essential oil is 2 mg / mL, and the concentration of oregano essential oil is 8 mg / mL.

[0024] Comparative Example 1: Carrageenan solution with a concentration of 5 mg / mL.

[0025] Comparative Example 2: A carrageenan solution with a concentration of 5 mg / mL and an alginate solution with a concentration of 20 mg / mL were mixed at 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-alginate hybrid hydrogel.

[0026] Comparative Example 3: A zein solution with a concentration of 20 mg / mL.

[0027] Comparative Example 4: Basil essential oil and oregano essential oil were mixed at 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. Among them, the concentration of basil essential oil was 8 mg / mL, and the concentration of oregano essential oil was 2 mg / mL.

[0028] Comparative Example 5: Basil essential oil and oregano essential oil were mixed at 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. Among them, the concentration of basil essential oil was 6 mg / mL, and the concentration of oregano essential oil was 4 mg / mL.

[0029] Comparative Example 6: Basil essential oil and oregano essential oil were mixed at 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. Among them, the concentration of basil essential oil was 5 mg / mL, and the concentration of oregano essential oil was 5 mg / mL.

[0030] Comparative Example 7: Basil essential oil and oregano essential oil were mixed at 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. Among them, the concentration of basil essential oil was 4 mg / mL, and the concentration of oregano essential oil was 6 mg / mL.

[0031] Comparative Example 8: Basil essential oil and oregano essential oil were mixed at 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. Among them, the concentration of basil essential oil was 2 mg / mL, and the concentration of oregano essential oil was 8 mg / mL.

[0032] II. Analysis of experimental results of the multifunctional hydrogel: The effects of different substances and antibacterial agents on the gel properties and antibacterial properties were described according to the examples and comparative examples prepared in the above specific examples. The hydrogels obtained in the above examples and comparative examples were tested.

[0033] 1. Effect of the compounding ratio of basil essential oil and oregano essential oil on antibacterial activity: The antibacterial ability of Comparative Examples 4-8 against Escherichia coli, Salmonella, Bacillus cereus, and Listeria monocytogenes was analyzed through the inhibition zone experiment. As Figure 1As 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 the strongest when the mixing ratio of basil essential oil to oregano essential oil is 1:4.

[0034] 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, and Listeria monocytogenes was cultured in BHI broth to form a bacterial suspension with a concentration of 1×10 8 CFU / mL. Subsequently, 100 μL of the bacterial suspension was evenly spread on a solid agar plate. Corresponding holes were punched with a puncher, and Comparative Examples 1-2 and Examples 1-3 were added to the holes. Subsequently, the solid plate was incubated upside down at 37 °C for 12 h, and the antibacterial ability of the antibacterial solution was evaluated by the diameter of the inhibition zone. The results are shown in Table 1.

[0035] Table 1 Inhibition zones of different examples and comparative examples against different bacteria

[0036] 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 are shown in Table 1. As can be seen from Table 1, after the antibacterial agent was loaded into the gel, the inhibition zone diameters of Examples 1-3 against the four bacteria increased significantly. Compared with Examples 1 and 2, Example 3 has the largest inhibition zone diameters against Escherichia coli, Salmonella, Bacillus cereus, and Listeria monocytogenes. Especially for Example 3, it shows the most excellent antibacterial ability against Bacillus cereus, with an inhibition zone diameter of 20.90 mm, which is increased by 84.63% and 11.65% compared with Examples 1 and 2 respectively. In addition, the inhibition zone diameter of Example 3 against Bacillus cereus is increased by 21.51%, 7.62%, and 6.2% compared with Escherichia coli, Salmonella, and Listeria monocytogenes respectively. These results indicate that Example 3 has an excellent inhibitory effect on Bacillus cereus, and the synergistic effect of the two essential oils improves the antibacterial ability of the nano-hydrogel. At the same time, Example 3 also exhibits broad-spectrum antibacterial properties and has inhibitory ability against Escherichia coli, Salmonella, and Listeria monocytogenes. In addition, compared with Comparative Example 8, the inhibition zone diameters of Example 3 against Escherichia coli, Salmonella, Bacillus cereus, and Listeria monocytogenes are increased, indicating that the three-dimensional network structure of the nano-hydrogel can effectively improve the slow-release efficiency of the active ingredients, thereby significantly enhancing the antibacterial efficacy.

[0037] 3. Antibacterial rate analysis of hydrogels in different test groups: Escherichia coli, Salmonella, Bacillus cereus, and Listeria monocytogenes were cultured in broth until the concentration of the bacterial suspension reached 1×10 8 CFU / mL. Comparative examples 1-2 and examples 1-3 were added to the bacterial suspension and co-cultured at 37°C for 8 h. After incubation, the broth was serially diluted, and 100 μL of the diluted culture solution was spread onto solid plates. Finally, the plates were incubated upside down at 37°C for 24 h for colony counting. The results are as Figure 2 shown.

[0038] As Figure 2 can be seen, the antibacterial rates of examples 1-3 with added essential oils against Escherichia coli, Salmonella, Bacillus cereus, and Listeria monocytogenes were 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 inhibitory rate against Bacillus cereus, with an inhibitory rate of 99.02%. In addition, the inhibitory rates of example 3 against Escherichia coli, Salmonella, and Listeria monocytogenes were also significantly higher than those of examples 1 and 2. These results indicate that the combined addition of basil essential oil and oregano essential oil to the nanohydrogel plays a synergistic role and enhances the antibacterial ability of the hydrogel system.

[0039] 4. Antioxidant capacity analysis of hydrogels in different test groups: The antioxidant capacities of comparative examples 1-2 and examples 1-3 were determined using the DPPH and ABTS 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, thoroughly mixed, and reacted in the dark for 30 min. The absorbance was measured at a wavelength of 517 nm to calculate the DPPH radical scavenging rate; the hydrogels of comparative examples 1-2 and examples 1-3 were mixed with the ABTS solution, shaken well, and reacted in the dark for 10 min. The absorbance was measured at a wavelength of 734 nm to calculate the ABTS radical scavenging rate. The results are as Figure 3 shown.

[0040] As Figure 3 can be seen, carrageenan and sodium alginate themselves have certain antioxidant capacities, but the antioxidant effects are weak. Compared to comparative examples 1 and 2, the DPPH and ABTS radical scavenging rates of the hydrogels of examples 1-3 were significantly increased. Among them, example 3 showed the highest scavenging rates in both radical scavenging experiments, which were 95.83% and 88.07% respectively. Compared with example 2, its DPPH radical scavenging rate increased by 19.5%, and the ABTS radical scavenging rate increased by 7.8%. This shows that after the antibacterial agents are loaded onto the gel, the two essential oils act synergistically, thus showing excellent antioxidant capacity.

[0041] 5. Particle size analysis of hydrogels in different experimental groups: Dilute Comparative Examples 1-3 and Examples 1-3 tenfold with deionized water and measure the particle size using a particle size analyzer. The results are as Figure 4 shown.

[0042] As Figure 4 can be seen, 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 Example 1 and Comparative Example 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 smaller particle sizes can improve the biocompatibility and drug release performance of the hydrogel.

[0043] 6. Morphology analysis of hydrogels in different experimental 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 h, then gold was sprayed on the surface of the hydrogels, and scanned at an accelerating voltage of 15 kV. The results are as Figure 5 shown.

[0044] As Figure 5 can be seen, the surfaces of Comparative Examples 1 and 2 are in a film form, and the cross-section shows a disordered flaky structure, without forming the unique three-dimensional network structure of hydrogels, indicating that Comparative Examples 1 and 2 have a simple structure and a low degree of intermolecular crosslinking. Compared with Comparative Examples 1 and 2, Examples 1-3 with added zein form a more complex crosslinked network, indicating that the protein may interact with polysaccharide molecules, contributing to the construction of a three-dimensional network and increasing the mechanical strength and stability of the material. Compared with Examples 1 and 2, the surface pores of Example 3 are reduced, forming a denser network structure with smaller pores, indicating that the co-addition of the two essential oils promotes the crosslinking of the hydrogel, better resists external stress, and provides better support and sustained release effects.

[0045] III. Coating preservation application of multifunctional nano-hydrogels.

[0046] 1. Effects of hydrogel coating on TVB-N, TBARS and TVC of chilled chicken: Immerse chilled chicken in the nano-hydrogel solution of Example 3 for 3 min, slowly lift the meat sample from the solution and place it obliquely in a petri dish, let it stand for 2 min, remove the excess solution, and let it stand in a 4 °C refrigerator for 8 h to form a hydrogel coating on the surface of the meat sample. Then store it at 4 °C for 16 days, and observe the changes in TVB-N, TBARS and TVC of each group every 4 days. The results are shown in Table 2. The CK group is a chilled chicken sample without hydrogel treatment.

[0047] Table 2 Effects of the hydrogel coating in Example 3 on TVB-N, TBARS, and TVC of chilled fresh chicken

[0048] As can be seen from Table 2, the TVB-N values of both the Example 3 group and the CK group increased with the increase in storage time. During the 16-day storage process, the TVB-N value of the CK group increased from 3.66 mg / 100 g to 23.57 mg / 100 g, and the TVB-N value of Example 3 increased from 3.42 mg / 100 g to 14.42 mg / 100 g. 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 / 100 g to 0.57 mg / 100 g 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 nano-hydrogel coating can effectively inhibit the lipid oxidation of chicken. The TVC of chilled fresh chicken showed varying degrees of increase with the extension of storage time. The TVC value of the chicken treated with Example 3 was significantly lower than that of the CK group, indicating that the nano-hydrogel effectively inhibited the growth of spoilage bacteria and extended the storage period of the meat. When the TVB-N value is higher than 15 mg / 100 g, the TBARS is greater than 0.2 mg / 100 g, and the TVC value is greater than 5 lg CFU / g, fresh meat is considered to start spoiling. Therefore, the storage period of the chilled fresh chicken coated with nano-hydrogel was extended by 50% compared with the CK group.

[0049] 2. Effects of the hydrogel coating on TVB-N, TBARS, and TVC of air-dried goose meat: The air-dried goose meat was immersed in the nano-hydrogel solution of Example 3 for 3 min, and the meat sample was slowly lifted from the solution and placed obliquely in a petri dish, left standing for 2 min, and the excess solution was removed. The meat sample was left standing in a 4°C refrigerator for 8 h to form a hydrogel coating on the surface of the meat, and then stored at 4°C for 16 days. The changes in TVB-N, TBARS, and TVC of each group were observed every 4 days, and the results are shown in Table 3. The CK group was the air-dried goose meat sample without hydrogel treatment.

[0050] Table 3 Effects of the hydrogel coating in Example 3 on TVB-N, TBARS, and TVC of air-dried goose meat

[0051] The application of nano-hydrogel to air-dried goose meat is also applicable. With the increase of storage time, the TVB-N, TBARS and TVC values of the CK group and Example 3 continuously increase, and the TVB-N, TBARS values 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 values and TVC values of the experimental group are reduced by 23.07%, 72.45% and 12.94% respectively compared with the CK group, and the shelf life of air-dried goose meat is extended by 0.5 times. These results indicate that nano-hydrogel coating effectively alleviates the degradation of proteins, oxidation of fats and growth of microorganisms in meat, thereby preventing meat spoilage and extending its shelf life.

[0052] 3. Store the chilled fresh chicken at 4 °C for 16 days, and measure the lightness (L), redness (a) and yellowness (b) values of the chilled fresh chicken every 4 days. The meat samples untreated with hydrogel are used as the control group, and the results are shown in Table 4.

[0053] Table 4 Effects of the hydrogel coating in Example 3 on the color change of chilled fresh chicken

[0054] As can be seen from the results in Table 4, with the extension of storage time, the L values of the CK group and the treatment group in Example 3 gradually decrease. The L value of the experimental group on the 16th day is 55.37, which is significantly higher than that of the CK group ( p <0.05). Similar to the changing trend of the L value, the a values of the CK group and the experimental group decrease with the increase of storage time. The a value of the experimental group on the 16th day is -1.51, which is significantly higher than that of the CK group and is increased by 33.77% compared with the CK group; the b values of the experimental group and the control group increase with the increase of storage time. The b value of the CK group increases from 8.73 to 17.92, while that of the experimental group increases from 8.69 to 13.52, and its upward trend slows down compared with the control group, indicating that the hydrogel coating can maintain the color stability of chilled fresh chicken.

[0055] 4. Effects of hydrogel coating on the color change of air-dried goose meat: Store the air-dried goose meat at 4 °C for 16 days, and measure the L, a, b values of the air-dried goose meat every 4 days. The meat samples untreated with hydrogel are used as the control group, and the results are shown in Table 5.

[0056] Table 5 Effects of the hydrogel coating in Example 3 on the color change of air-dried goose meat

[0057] As can be seen from the results in Table 5, compared with the untreated group (CK), the nano-hydrogel coating in 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 that of the experimental group only decreased from 48.38 to 41.63, and since the 8th day, 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 the meat is the key to evaluating the meat color. As the storage time of the air-dried goose meat increased, the a values of both the CK group and the experimental group showed a downward trend, and the decrease amplitude of the experimental group was 38% slower than that of the control group, indicating that the antioxidant components in the nano-hydrogel delayed the oxidation of myoglobin; the b values of both the experimental group and the control group increased with the increase of the storage time of the air-dried goose meat, but the upward trend of the b value of the experimental group was slower than that of the control group, indicating that the hydrogel coating alleviated the yellowing of the meat color by blocking oxygen and inhibiting fat oxidation. These results show that the hydrogel coating can not only extend the shelf life of meat products, but also maintain the color stability of air-dried goose meat through the synergistic effect of antioxidant and antibacterial.

[0058] The above description is not a limitation of the present invention, nor is the present invention limited to the above examples. Changes, modifications, additions or substitutions made by those of ordinary skill in the art within the scope of the essence of the present invention shall also fall within the protection scope of the present invention.

Claims

1. A method for preparing a multifunctional nanohydrogel, characterized in that The following steps are involved: (1) Preparation of a carrageenan-sodium alginate mixed solution: dissolving carrageenan and sodium alginate in deionized water respectively, then mixing the carrageenan and sodium alginate solutions according to a volume ratio, and stirring to obtain a carrageenan-sodium alginate mixed solution; (2) Preparation of a zein-essential oil mixed solution: 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 well 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, and the mixture is stirred while being added. After uniform mixing, the mixture is subjected to ultrasonication 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 / or oregano essential oil to the zein solution, and mixing to obtain a 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 5:0, 4:1, 3:2, 1:1, 2:3, 1:4 and 0:

5.

6. The method for preparing a multifunctional nano-hydrogel according to claim 5, characterized in that: The mixing ratio of the basil essential oil to 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 to the zein-essential oil mixed solution in step (3) 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. An application 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 for 2 minutes to remove excess solution; place the soaked meat in a 4°C refrigerator for 8-16 hours to allow the hydrogel solution to gel on the surface of the meat to form an antibacterial hydrogel coating.

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