Pickering emulsion coating fresh-keeping material as well as preparation method and application thereof

Abstract

The invention relates to the technical field of chemical modification of organic polymer materials, in particular to a Pickering emulsion coating fresh-keeping material as well as a preparation method and application thereof. The preparation method comprises the following steps: mixing a polyphenol solution and a protein solution, adjusting the pH value of the mixed solution to be alkaline, and carrying out grafting reaction in air to obtain a protein-polyphenol covalent complex; mixing the plant essential oil and the protein-polyphenol covalent compound dispersion liquid, and emulsifying to obtain a Pickering crude emulsion; and mixing the crude Pickering emulsion, the polysaccharide dispersion liquid and a cross-linking agent, and emulsifying to obtain the Pickering emulsion. The Pickering emulsion coating fresh-keeping material is prepared from the emulsion, the coating forms a uniform thin film on the surfaces of fruits and vegetables, water loss is reduced, oxygen / microorganism contact is inhibited, enzymatic browning and respiratory metabolism are delayed, and the green packaging concept of no chemical residue and degradability is met.

Description

Technical Field

[0001] This invention relates to the field of chemical modification technology of organic polymer materials, and in particular to a Pickering emulsion coating preservation material, its preparation method and application. Background Technology

[0002] Film coating preservation is a method that uses bio-based polymers, such as polysaccharides (chitosan, cellulose, pectin, etc.) or proteins (gelatin, zein, collagen, etc.), to achieve preservation effects through their film-forming properties and bioactivity, including antibacterial and antioxidant activities, as well as reducing the respiration rate, enzyme activity, and metabolic rate of post-harvest fruits. Furthermore, due to the non-toxicity, biodegradability, and biocompatibility of bio-based polymers, and their ability to load bioactive substances (polyphenols, plant essential oils, etc.) to enhance film-forming properties, gas permeability, or improve antibacterial properties against pathogens, they have shown excellent performance in fruit and vegetable storage and preservation applications, and have become a current research hotspot.

[0003] Coating preservatives, applied by soaking or spraying, form a film on the surface of fruits and vegetables, reducing the contact area between the sample surface and air, decreasing enzymatic oxidation and browning, reducing the invasion of external bacteria, and maintaining freshness by controlling the respiration rate of fruits and vegetables. Coating preservatives also have multiple functions, including physical isolation, sterilization and bacteriostasis, regulation of fruit respiration, delaying aging, and maintaining fruit quality. Pickering emulsions, as a loading system stabilized by nanoparticles made from natural biopolymers, have good compatibility with film-forming matrices also composed of biopolymers. Furthermore, the formation of the Pickering emulsion system does not require the addition of additional chemical stabilizers, thus possessing both good stability and non-toxicity. Therefore, in the field of coating packaging, biopolymer-stabilized Pickering emulsions have the ability to improve film-forming performance when mixed with a film-forming matrix after loading bioactive substances. In the field of coating packaging, loading bioactive substances to enhance the performance of the matrix after film formation is a current research hotspot. For example, adding small molecule polyphenols can enhance the cross-linking between the film-forming matrix and improve the mechanical properties of the composite film; or loading plant essential oils can enhance the antibacterial and antioxidant properties of the composite film.

[0004] While existing technologies disclose several composite coating preservation materials prepared through compounding and mixing, these methods suffer from issues such as single coating components, poor mechanical properties, and instability. Furthermore, composite films constructed through simple mixing may lack stability. Additionally, the mechanical properties and antibacterial properties of existing composite coating preservation materials have not been significantly improved.

[0005] In today's era, with a clear focus on green environmental protection and a strong emphasis on sustainable development, replacing traditional petroleum-based materials with green, biodegradable, and bioactive packaging materials remains a key goal for researchers in the food packaging field. While various natural biopolymers have been developed as packaging materials for food preservation, current research indicates that single-component natural biopolymer matrices exhibit unsatisfactory film-forming performance, and their properties require further improvement for food preservation. Summary of the Invention

[0006] The purpose of this invention is to provide a Pickering emulsion coating preservation material, its preparation method and application, in order to solve the technical problems existing in the prior art.

[0007] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0008] This invention provides a method for preparing a Pickering emulsion, comprising the following steps:

[0009] (1) Mix the polyphenol solution and the protein solution, adjust the pH of the mixed solution to alkaline, and carry out the grafting reaction in the air to obtain a protein-polyphenol covalent complex.

[0010] (2) Mix the plant essential oil and the protein-polyphenol covalent complex dispersion and emulsify them to obtain Pickering crude emulsion;

[0011] (3) The Pickering crude emulsion, polysaccharide dispersion and crosslinking agent are mixed and emulsified to obtain the Pickering emulsion.

[0012] Optionally, the polyphenol solution is obtained by mixing polyphenols and a solvent; the polyphenols include one or more of chlorogenic acid, ferulic acid, gentic acid, vanillic acid, cinnamic acid, syringic acid, sinapic acid, p-coumaric acid, caffeic acid, protocatechuic acid, and gallic acid;

[0013] The concentration of the polyphenol solution is 2-5% (w / v);

[0014] The protein solution is obtained by mixing protein and solvent; the protein includes one or more of whey protein, egg white protein, soy protein isolate, pea protein, zein, β-lactoglobulin, wheat protein, lysozyme protein, α-lactoglobulin, soy globulin, mung bean globulin, rice bran protein, and β-casein;

[0015] The concentration of the protein solution is 2-5% (w / v); the pH of the protein solution is 9-12.

[0016] Optionally, the volume ratio of the polyphenol solution to the protein solution is 1 to 3:1;

[0017] In step (1), the pH of the mixed solution is adjusted to 9-12; the temperature of the grafting reaction is 20-30℃ and the time is 12-48h.

[0018] Optionally, the plant essential oils include one or more of the following: thyme essential oil, galangal essential oil, tea tree essential oil, lemon essential oil, lemongrass essential oil, oily skin essential oil, mustard essential oil, peppermint essential oil, cinnamon essential oil, clove essential oil, garlic essential oil, almond essential oil, eucalyptus essential oil, senna essential oil, and lavender essential oil.

[0019] The plant essential oil has a volume fraction of 60-80% in the Pickering crude emulsion.

[0020] Optionally, the protein-polyphenol covalent complex dispersion is obtained by mixing the protein-polyphenol covalent complex and a solvent; the concentration of the protein-polyphenol covalent complex dispersion is 1-3% (w / v);

[0021] In step (2), the emulsification speed is 10000-12000 r / min and the time is 3-8 min.

[0022] Optionally, the polysaccharide dispersion is obtained by mixing polysaccharides and solvents; the polysaccharides include one or more of carboxymethyl chitosan, carboxymethyl cellulose, cellulose nanocrystals, carboxylated cellulose nanocrystals, gum arabic, pectin, xanthan gum, and carrageenan.

[0023] The concentration of the polysaccharide dispersion is 1-5% (w / v);

[0024] The volume ratio of the polysaccharide dispersion to the protein-polyphenol covalent complex dispersion is 1:1 to 5;

[0025] The crosslinking agent includes one or more of genipin, citric acid, itaconic acid, catechol, and caffeic acid-dopamine complex;

[0026] The mass of the cross-linking agent is 0.01% to 1% of the total mass of the polysaccharide and protein-polyphenol covalent complex;

[0027] In step (3), the emulsification speed is 10000-12000 r / min and the time is 3-8 min.

[0028] The present invention also provides a Pickering emulsion prepared by the above-described preparation method.

[0029] The present invention also provides a Pickering emulsion coating preservation material, comprising the above-mentioned Pickering emulsion, and further comprising a film-forming substance, a dispersant, a plasticizer, nano-reinforcing particles and a binder.

[0030] The present invention also provides a method for preparing the above-mentioned Pickering emulsion coating preservation material, characterized by comprising the following steps:

[0031] (1) Mix the film-forming substance, dispersant and plasticizer to obtain the film-forming base liquid;

[0032] (2) The Pickering emulsion, film-forming base liquid, nano-reinforcing particles and binder are mixed, sheared and then degassed to obtain a composite coating preservation material.

[0033] This invention also provides the application of the above-mentioned Pickering emulsion coating preservation material in the preservation of fruits and vegetables.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] 1. This invention prepares protein-polyphenol covalent complexes through free radical-mediated grafting reactions, solving the problems of strong hydrophilicity and weak emulsifying ability of natural proteins. Its amphiphilic structure can be efficiently adsorbed at the oil-water interface to form stable Pickering emulsions.

[0036] 2. This invention introduces polysaccharide-synergistic emulsion stabilization. Through the dual effects of "protein-polyphenol covalent interface adsorption + polysaccharide spatial network support", the stability of the emulsion is significantly improved (the oil phase volume fraction can reach 60-80%), overcoming the phase separation defects of traditional simple mixing systems.

[0037] 3. The protein-polyphenol covalent prepared by this invention not only serves as an emulsion stabilizer, but its polyphenol groups also impart antioxidant and antibacterial activities, forming a synergistic effect with the broad-spectrum antibacterial properties of plant essential oils, thus achieving the dual functions of "stabilizing carrier + enhancing activity".

[0038] 4. The composite coating of the present invention significantly improves the mechanical and barrier properties of the film through the "physical cross-linking" of Pickering emulsion particles and the introduction of nano-reinforcing particles, thus solving the problems of "poor mechanical properties and easy damage" of existing coatings.

[0039] 5. This invention utilizes the intermolecular interactions (hydrogen bonds, hydrophobic interactions) between polysaccharides and protein-polyphenol covalents to enhance the network density of the membrane matrix, reduce phase separation in simple mixed systems, and improve the long-term stability of the coating. Furthermore, the coating forms a uniform film on the surface of fruits and vegetables, reducing moisture loss, inhibiting oxygen / microbial contact, and delaying enzymatic browning and respiratory metabolism.

[0040] 6. This invention uses bio-based raw materials (natural proteins / polyphenols / polysaccharides) throughout the entire process, avoiding the addition of chemical stabilizers, and conforms to the green packaging concept of "no chemical residue and degradable" (GRAS certified raw materials). Attached Figure Description

[0041] Figure 1 The infrared spectra of different substances in Example 1 are whey protein (WPI), gallic acid (GA), and whey protein-gallic acid covalent complex (WPI-GA).

[0042] Figure 2 The XRD pattern shows the secondary structure of the protein before and after modification in Example 1, including whey protein (WPI) and whey protein-gallic acid covalent complex (WPI-GA).

[0043] Figure 3 Particle size distribution, zeta potential, and laser confocal microscopy image of Pickering emulsion of cinnamon essential oil stabilized by carboxymethyl chitosan synergistic with WPI-GA complex prepared in Example 1;

[0044] Figure 4 To evaluate the preservation effect of the Pickering emulsion film preservative material prepared in Example 1 on bananas. CK was the blank control group, MXA was the imazalil coating treatment group, and RYM was the Pickering emulsion film preservative material coating treatment group.

[0045] Figure 5 A comparison chart showing the storage stability of Pickering emulsions prepared in Comparative Example 1 and Example 1;

[0046] Figure 6 The graph shows the effect of adding nano-reinforcing particles (TiO2) on the mechanical properties of the coating in Example 1.

[0047] Figure 7 The diagram shows the effect of adding nano-reinforcing particles (TiO2) on the coating barrier (OP and WVP) in Example 1. Detailed Implementation

[0048] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0049] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0050] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0051] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be obvious to those skilled in the art. This application specification and embodiments are merely exemplary.

[0052] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0053] All raw materials used in this invention can be obtained commercially or prepared using existing technologies.

[0054] Unless otherwise specified, "room temperature" in this invention refers to 25±2℃.

[0055] This invention provides a method for preparing a Pickering emulsion, comprising the following steps:

[0056] (1) Mix the polyphenol solution and the protein solution, adjust the pH of the mixed solution to alkaline, and carry out the grafting reaction in the air to obtain a protein-polyphenol covalent complex.

[0057] (2) Mix the plant essential oil and the protein-polyphenol covalent complex dispersion and emulsify them to obtain Pickering crude emulsion;

[0058] (3) The Pickering crude emulsion, polysaccharide dispersion and crosslinking agent are mixed and emulsified to obtain the Pickering emulsion.

[0059] Step (1) involves first mixing polyphenols and solvent to obtain a polyphenol solution; then dispersing the protein in the solvent, adjusting the pH of the protein dispersion to above the isoelectric point using an alkaline solution, and stirring to dissolve and obtain a protein solution.

[0060] Then, the polyphenol solution and protein solution were stirred and mixed, and the pH of the mixed solution was adjusted to alkaline. The mixed system was then completely exposed to the air environment, and the grafting reaction was carried out through free radical mediated reaction. The reaction was carried out under open conditions to remove unreacted polyphenols. At the same time, the pH value of the reaction system was kept stable at 9-12 during the preparation process. The solution after the reaction was dialyzed and dried to obtain the protein-polyphenol covalent complex.

[0061] In this invention, the polyphenols include one or more of chlorogenic acid, ferulic acid, gentic acid, vanillic acid, cinnamic acid, syringic acid, sinapic acid, p-coumaric acid, caffeic acid, protocatechuic acid and gallic acid, preferably ferulic acid or gallic acid;

[0062] The solvent includes one or more of water, methanol, ethanol, acetone, isopropanol, chloroform, ethyl acetate, tetrahydrofuran, and N,N-dimethylformamide, preferably a mixture of water and ethanol, with a volume ratio of water to ethanol of 10-7:0-3, preferably 10:0.

[0063] The concentration of the polyphenol solution is 2-5% (w / v), preferably 3-4% (w / v), where w / v refers to the percentage concentration of polyphenol by mass relative to solvent volume in the polyphenol solution, expressed in g / mL.

[0064] The protein includes one or more of whey protein, ovalbumin, soy protein isolate, pea protein, zein, β-lactoglobulin, wheat protein, lysozyme protein, α-lactoglobulin, soy globulin, mung bean globulin, rice bran protein, and β-casein, preferably whey protein, ovalbumin, or zein;

[0065] The solvent includes one or more of water, methanol, ethanol, acetone, isopropanol, chloroform, ethyl acetate, tetrahydrofuran, and N,N-dimethylformamide, preferably a mixture of water and ethanol, with a volume ratio of water to ethanol of 10-7:0-3, preferably 10:0.

[0066] The alkaline solution includes NaOH aqueous solution and KOH aqueous solution, preferably NaOH aqueous solution; the concentration of the alkaline solution is 1-10 mol / L, preferably 2-8 mol / L, more preferably 3-6 mol / L, and even more preferably 4-5 mol / L.

[0067] The concentration of the protein solution is 2-5% (w / v), preferably 3-4% (w / v), where w / v refers to the percentage concentration of protein by mass relative to solvent volume, expressed in g / mL; the pH of the protein solution is 9-12, preferably 10-11.

[0068] In this invention, the volume ratio of the polyphenol solution to the protein solution is 1 to 3:1, preferably 1.5 to 2.5:1, and more preferably 2:1;

[0069] In step (1), the pH of the mixed solution is adjusted to 9-12, preferably 10-11; the temperature of the grafting reaction is 20-30℃, preferably 22-28℃, more preferably 25-26℃, and the time is 12-48h, preferably 15-45h, more preferably 20-40h, and even more preferably 25-30h.

[0070] In this invention, the dialysis specifically involves placing the reacted solution in an 8-14 kDa dialysis bag and dialyzing for 24-48 hours; the drying is freeze-drying.

[0071] Step (2) involves dispersing the protein-polyphenol covalent complex in a solvent to obtain a protein-polyphenol covalent complex dispersion, which is used as the aqueous phase; then, the plant essential oil is used as the oil phase, and shear emulsification is performed while the oil phase is dripped into the aqueous phase to obtain a crude emulsion of the plant essential oil Pickering emulsion.

[0072] In this invention, the plant essential oil includes at least one of thyme essential oil, galangal essential oil, tea tree essential oil, lemon essential oil, lemongrass essential oil, oily skin essential oil, mustard essential oil, peppermint essential oil, cinnamon essential oil, clove essential oil, garlic essential oil, almond essential oil, eucalyptus essential oil, sage essential oil, and lavender essential oil, preferably clove essential oil or cinnamon essential oil;

[0073] The volume fraction of the plant essential oil in the Pickering crude emulsion is 60-80%, preferably 65-75%, and more preferably 70-72%.

[0074] In this invention, the protein-polyphenol covalent complex dispersion is obtained by mixing the protein-polyphenol covalent complex and a solvent; the concentration of the protein-polyphenol covalent complex dispersion is 1-3% (w / v), preferably 2% (w / v), where w / v refers to the percentage concentration of the mass of the protein-polyphenol covalent complex in the protein-polyphenol covalent complex solution relative to the volume of the solvent, expressed in g / mL;

[0075] In step (2), the emulsification speed is 10000-12000 r / min, preferably 10500-11500 r / min, more preferably 11000-11200 r / min, and the time is 3-8 min, preferably 4-7 min, more preferably 5-6 min.

[0076] Step (3) involves adding the polysaccharide dispersion dropwise to the Pickering emulsion, adding a crosslinking agent, and then performing shear emulsification and ultrasonic treatment to obtain a polysaccharide-protein-polyphenol covalent complex stabilized plant essential oil Pickering emulsion.

[0077] In this invention, the polysaccharide dispersion is obtained by mixing polysaccharide and solvent; the polysaccharide includes one or more of carboxymethyl chitosan, carboxymethyl cellulose, cellulose nanocrystals, carboxylated cellulose nanocrystals, gum arabic, pectin, xanthan gum and carrageenan, preferably carboxymethyl chitosan, carboxymethyl cellulose or cellulose nanocrystals; the solvent is acetic acid solution or water.

[0078] The concentration of the polysaccharide dispersion is 1-5% (w / v), preferably 2-4% (w / v), and more preferably 3% (w / v), where w / v refers to the percentage concentration of the polysaccharide by mass relative to the volume of the solvent in the polysaccharide dispersion, expressed in g / mL.

[0079] The volume ratio of the polysaccharide dispersion to the protein-polyphenol covalent complex dispersion is 1:1 to 5, preferably 1:2 to 4, and more preferably 1:3;

[0080] The crosslinking agent includes one or more of genipin, citric acid, itaconic acid, catechol, and caffeic acid-dopamine complex, preferably genipin, citric acid, or itaconic acid;

[0081] The mass of the crosslinking agent is 0.01-1% of the total mass of the polysaccharide and protein-polyphenol covalent complex, preferably 0.05-0.8%, more preferably 0.1-0.5%, and even more preferably 0.3-0.4%.

[0082] In step (3), the emulsification speed is 10000-12000 r / min, preferably 10500-11500 r / min, more preferably 11000-11200 r / min, and the time is 3-8 min, preferably 4-7 min, more preferably 5-6 min.

[0083] The present invention also provides a Pickering emulsion prepared by the above-described preparation method.

[0084] The present invention also provides a Pickering emulsion coating preservation material, comprising the above-mentioned Pickering emulsion, and further comprising a film-forming substance, a dispersant, a plasticizer, nano-reinforcing particles and a binder.

[0085] In this invention, the film-forming substance includes at least one of soluble starch, cellulose, polyvinyl alcohol, zein, chitosan, chitosan derivatives, cyclodextrin, gelatin, konjac glucomannan, and pullulan; wherein the chitosan derivative includes carboxymethyl chitosan, quaternary ammonium salt chitosan, or quaternary phosphorus salt chitosan.

[0086] The dispersant includes at least one of water, ethanol, or an aqueous solution of acetic acid;

[0087] The plasticizer includes at least one of ethylene glycol, glycerol, sorbitol, polyethylene glycol with a molecular weight of less than 5000, ethylenediamine, and triethanolamine.

[0088] The nano-reinforcing particles include at least one of nanocellulose, TiO2, nanoSiO2, nanoCaCO3, nanoZnO, nanoMgO, nanoAu, and nanoAg.

[0089] The binder includes at least one of cyclodextrin, oxidized starch, cationic starch, etherified starch, esterified starch, wheat protein, corn protein, gelatin, carrageenan, and gellan gum.

[0090] The present invention also provides a method for preparing the above-mentioned Pickering emulsion coating preservation material, characterized by comprising the following steps:

[0091] (1) Mix the film-forming substance, dispersant and plasticizer, stir evenly and then prepare the film-forming base liquid;

[0092] (2) The Pickering emulsion, film-forming base liquid, nano-reinforcing particles and binder are mixed, sheared and then degassed to obtain a composite coating preservation material.

[0093] Step (1) involves first mixing the film-forming substance and the dispersant to obtain a film-forming dispersion, then mixing the film-forming substance dispersion and the plasticizer, stirring evenly, and finally preparing a film-forming base liquid.

[0094] In this invention, the concentration of the film-forming substance in the dispersant is 1-3% (w / v), preferably 2% (w / v), where w / v refers to the percentage concentration of the mass of the film-forming substance in the dispersion of the film-forming substance relative to the volume of the dispersant, in g / mL.

[0095] The plasticizer is 20-50% of the dry weight of the film-forming substance, preferably 25-45%, and more preferably 30-40%.

[0096] The concentration of the film-forming base liquid is 1-5% (w / v), preferably 2-4% (w / v), and more preferably 3% (w / v). w / v refers to the percentage concentration of the mass of the film-forming substance and plasticizer to the volume of the dispersant in the film-forming base liquid, in g / mL.

[0097] The volume ratio of the Pickering emulsion to the film-forming base liquid is 1-6:4-9, for example, it can be 1:9, 6:4, etc.

[0098] The amount of the nano-reinforcing particles added is 1-10% of the dry weight of the film-forming material, preferably 2-8%, and more preferably 5-6%.

[0099] The mass of the adhesive is 0.5-5% of the dry weight of the film-forming substance, preferably 1-4%, and more preferably 2-3%.

[0100] In this invention, the shearing speed is 10000-12000 r / min, preferably 10500-11500 r / min, more preferably 11000-11200 r / min, and the time is 3-8 min, preferably 4-7 min, more preferably 5-6 min.

[0101] In this invention, the degassing is performed in a vacuum environment for 15 to 30 minutes.

[0102] This invention also provides the application of the above-mentioned Pickering emulsion coating preservation material in the preservation of fruits and vegetables.

[0103] In this invention, the application method is to dilute the composite coating preservation material 100 to 800 times, spray or coat it on fruits and vegetables, and then air dry it; wherein the fruits and vegetables include mango, pineapple, banana, dragon fruit, lychee, longan, eggplant, cucumber, green pepper, tomato, potato, etc.

[0104] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0105] Example 1

[0106] (1) Preparation of whey protein (WPI)-gallic acid covalent complex (WPI-GA)

[0107] Weigh a certain amount of WPI and disperse it in distilled water. Use 1 mmol / L NaOH to adjust the pH of the WPI dispersion to 12.0. Stir to completely dissolve it and prepare a 2% (w / v) WPI stock solution.

[0108] Weigh out a certain amount of gallic acid (GA) and dissolve it in distilled water to prepare a GA stock solution with a concentration of 0.4% (w / v).

[0109] Then, the GA stock solution was slowly added to an equal volume of WPI stock solution (volume ratio 1:1) under stirring, and the pH of the mixture was adjusted back to 12.0. The mixture was then completely exposed to air and reacted at room temperature under open conditions for 24 hours, while maintaining the pH of the reaction system at 12.0 throughout the preparation process. Finally, the reacted solution was dialyzed in an 8–14 kDa dialysis bag for 48 hours to remove unreacted GA. After freeze-drying, the WPI-GA complex was obtained.

[0110] (2) Preparation of WPI-GA complex stabilized cinnamon oil Pickering emulsion

[0111] A certain amount of freeze-dried WPI-GA complex was weighed and dispersed in distilled water to prepare a 1.5% (w / v) dispersion as the aqueous phase. Then, cinnamon essential oil (oil phase) was slowly dripped into the aqueous phase while homogenizing it for 3 minutes at 12000 r / min using a high-speed shear mill to form a Pickering emulsion of WPI-GA complex-stabilized cinnamon essential oil.

[0112] (3) Preparation of Pickering emulsion stabilized by carboxymethyl chitosan and WPI-GA

[0113] A certain amount of carboxymethyl chitosan was weighed and dispersed in deionized water to prepare a 1% (w / v) carboxymethyl chitosan solution. This solution was then added dropwise to the Pickering emulsion, along with genipin (0.01% of the total mass of carboxymethyl chitosan and WPI-GA). The mixture was homogenized for 5 minutes at 10,000 r / min using a high-speed shear mill to form a Pickering emulsion in which carboxymethyl chitosan (CMCS) and the WPI-GA complex stabilized cinnamon essential oil. The final volume concentration of cinnamon essential oil was 60% (v / v).

[0114] (4) Preparation of Pickering emulsion film preservation material

[0115] A certain amount of chitosan (CS) was weighed and dissolved in an aqueous solution of acetic acid to prepare a 1% (w / v) chitosan solution. 30% (based on the dry weight of CS) of glycerol was added, and the mixture was stirred until homogeneous to prepare a 1% (w / v) CS film-forming base solution. 10.0 mL of the Pickering emulsion from step (3) was taken and mixed with 90 mL of the CS film-forming base solution. 10% nano-TiO2 and 5% carrageenan were added based on the dry weight of the film-forming material, i.e., CS. The mixture was then homogenized at 10000 r / min for 3 min using a high-speed shear press, and then degassed in a vacuum environment for 30 min to form an emulsion active film-forming solution. The Pickering emulsion film preservation material was thus obtained.

[0116] (5) Pickering emulsion film preservation material for postharvest preservation of bananas

[0117] Select bananas that are of similar size, color, and ripeness and free from pests, diseases, and mechanical damage. Soak them in a 0.05% (v / v) sodium hypochlorite solution for 3 minutes to disinfect them, then wash them with distilled water. After air-drying them, divide the bananas into three groups.

[0118] Control group (CK): No treatment was given.

[0119] Imazalil coating group (MXA): Immerse bananas in 500ppm imazalil solution for 3 minutes, then remove and air dry.

[0120] Pickering emulsion film preservation material coating group (RYM): Dilute the Pickering emulsion film preservation material in step (4) by 100 times, then immerse the banana in the emulsion film forming solution for 3 minutes, and take it out to air dry naturally.

[0121] The bananas treated in the above three groups were stored in a constant temperature and humidity chamber at 25°C and 75% relative humidity.

[0122] Example 2

[0123] (1) Preparation of zein-gallic acid covalent complex (zein-GA)

[0124] Weigh a certain amount of zein and disperse it in distilled water. Adjust the pH of the zein dispersion to 12.0 using 1 mmol / L NaOH. Stir until completely dissolved to prepare a 2% (w / v) zein stock solution.

[0125] Weigh out a certain amount of gallic acid (GA) and dissolve it in distilled water to prepare a GA stock solution with a concentration of 0.4% (w / v).

[0126] Then, the GA stock solution was slowly added to an equal volume of zein stock solution (volume ratio 1:1) under stirring. The pH of the mixture was then adjusted back to 12.0, and the mixture was completely exposed to air. The reaction was carried out at room temperature under open conditions for 24 hours, while maintaining the pH of the reaction system at 12.0 throughout the preparation process. Finally, the reacted solution was dialyzed in an 8–14 kDa dialysis bag for 48 hours to remove unreacted GA. After freeze-drying, the zein-GA complex was obtained.

[0127] (2) Preparation of zein-GA stabilized Pickering emulsion

[0128] A certain amount of freeze-dried zein-GA powder was weighed and dispersed in distilled water to prepare a dispersion with a concentration of 1.5% (w / v) as the aqueous phase. Then, cinnamon essential oil (oil phase) was slowly dripped into the aqueous phase while homogenizing it at a speed of 12000 r / min for 3 min using a high-speed shear machine to form a Pickering emulsion of zein-GA complex to stabilize cinnamon essential oil.

[0129] (3) Preparation of Pickering emulsion stabilized by carboxymethyl cellulose and zein-GA

[0130] A certain amount of carboxymethyl cellulose was weighed and dispersed in deionized water to prepare a 1% (w / v) carboxymethyl cellulose solution. This solution was then added dropwise to the Pickering emulsion and itaconic acid (1% of the total mass of carboxymethyl cellulose and zein-GA) was added. The mixture was homogenized for 5 minutes at 10,000 r / min using a high-speed shear mill to form a Pickering emulsion in which carboxymethyl cellulose and zein-GA complex stabilize cinnamon essential oil. The final volume concentration of cinnamon essential oil was 60% (v / v).

[0131] (4) Preparation of Pickering emulsion film preservation material

[0132] A certain amount of pullulan (PUL) was weighed and dissolved in water to prepare a 5% (w / v) pullulan solution. 20% (based on the dry weight of PUL) of potassium sorbate was added, and the solution was stirred until homogeneous to prepare a 5% (w / v) PUL film-forming base solution. 60.0 mL of the Pickering emulsion from step (3) was taken and mixed with 40 mL of the PUL film-forming base solution. 1% nano-SiO2 and 1% gellan gum (based on the dry weight of the film-forming material, PUL) were added. The mixture was then homogenized for 3 min at 10000 r / min using a high-speed shear press, followed by degassing in a vacuum environment for 30 min to form an emulsion active film-forming solution. The Pickering emulsion film preservation material was thus obtained.

[0133] (5) Pickering emulsion film preservation material for postharvest preservation of bananas

[0134] Select bananas that are of similar size, color, and ripeness and free from pests, diseases, and mechanical damage. Soak them in a 0.05% (v / v) sodium hypochlorite solution for 3 minutes to disinfect them, then wash them with distilled water and let them air dry. Divide the mangoes into three groups.

[0135] Control group (CK): No treatment was given.

[0136] Imazalil coating group (MXA): Immerse bananas in 500ppm imazalil solution for 3 minutes, then remove and air dry.

[0137] Pickering emulsion film preservation material coating group (RYM): Dilute the Pickering emulsion film preservation material in step (4) by 100 times, then immerse the banana in the emulsion film forming solution for 3 minutes, and take it out to air dry naturally.

[0138] The bananas treated in the above three groups were stored in a constant temperature and humidity chamber at 25°C and 75% relative humidity.

[0139] Example 3

[0140] (1) Preparation of ovalbumin (OVA)-ferulic acid covalent complex (OVA-FA)

[0141] Weigh a certain amount of OVA and disperse it in distilled water. Use 1 mmol / L NaOH to adjust the pH of the OVA dispersion to 12.0. Stir to completely dissolve it and prepare a 2% (w / v) OVA stock solution.

[0142] Weigh a certain amount of ferulic acid (FA) and dissolve it in distilled water to prepare a FA stock solution with a concentration of 0.4% (w / v).

[0143] Then, the FA stock solution was slowly added to an equal volume of OVA stock solution (volume ratio 1:1) under stirring, and the pH of the mixture was adjusted back to 12.0. The mixture was then completely exposed to air and reacted at room temperature under open conditions for 24 hours, while maintaining the pH of the reaction system at 12.0 throughout the preparation process. Finally, the reacted solution was dialyzed in an 8–14 kDa dialysis bag for 48 hours to remove unreacted FA. After freeze-drying, the OVA-FA complex was obtained.

[0144] (2) Preparation of OVA-FA stabilized Pickering emulsion

[0145] A certain amount of freeze-dried OVA-FA powder was weighed and dispersed in distilled water to prepare a dispersion with a concentration of 1.5% (w / v) as the aqueous phase. Then, clove essential oil (oil phase) was slowly added dropwise to the aqueous phase while homogenizing at 12000 r / min for 3 min using a high-speed shear mill to form a Pickering emulsion of clove essential oil stabilized by the OVA-FA complex.

[0146] (3) Preparation of Pickering emulsion stabilized by carboxymethyl cellulose and OVA-FA

[0147] A certain amount of cellulose nanocrystals was weighed and dispersed in deionized water to prepare a 1% (w / v) cellulose nanocrystal solution. This solution was then added dropwise to the Pickering emulsion and citric acid (0.5% of the total mass of cellulose nanocrystals and OVA-FA) was added. The mixture was homogenized for 3 minutes at 12000 r / min using a high-speed shear mill to form a Pickering emulsion in which carboxymethyl cellulose and the OVA-FA complex stabilized clove essential oil. The final volume concentration of clove essential oil was 60% (v / v).

[0148] (4) Preparation of Pickering emulsion film preservation material

[0149] A certain amount of pullulan (PUL) was weighed and dissolved in water to prepare a 5% (w / v) pullulan solution. 20% (based on the dry weight of PUL) of potassium sorbate was added, and the solution was stirred until homogeneous to prepare a 5% (w / v) PUL film-forming base solution. 60.0 mL of the Pickering emulsion from step (3) was taken and mixed with 40 mL of the PUL film-forming base solution. 1% nano-SiO2 and 1% gellan gum (based on the dry weight of the film-forming material, PUL) were added. The mixture was then homogenized for 3 min at 10000 r / min using a high-speed shear press, followed by degassing in a vacuum environment for 30 min to form an emulsion active film-forming solution. The Pickering emulsion film preservation material was thus obtained.

[0150] (5) Pickering emulsion film preservation material for postharvest preservation of bananas

[0151] Select bananas that are of similar size, color, and ripeness and free from pests, diseases, and mechanical damage. Soak them in a 0.05% (v / v) sodium hypochlorite solution for 3 minutes to disinfect them, then wash them with distilled water. After air-drying them, divide the bananas into three groups.

[0152] Control group (CK): No treatment was given.

[0153] Imazalil coating group (MXA): Immerse bananas in 500ppm imazalil solution for 3 minutes, then remove and air dry.

[0154] Pickering emulsion film preservation material coating group (RYM): Dilute the Pickering emulsion film preservation material in step (4) by 100 times, then immerse the banana in the emulsion film forming solution for 3 minutes, and take it out to air dry naturally.

[0155] The bananas treated in the above three groups were stored in a constant temperature and humidity chamber at 25°C and 75% relative humidity.

[0156] Comparative Example 1

[0157] (1) Preparation of whey protein (WPI)-gallic acid covalent complex (WPI-GA)

[0158] Weigh a certain amount of WPI and disperse it in distilled water. Use 1 mmol / L NaOH to adjust the pH of the WPI dispersion to 12.0. Stir to completely dissolve it and prepare a 2% (w / v) WPI stock solution.

[0159] Weigh out a certain amount of gallic acid (GA) and dissolve it in distilled water to prepare a GA stock solution with a concentration of 0.4% (w / v).

[0160] Then, the GA stock solution was slowly added to an equal volume of WPI stock solution (volume ratio 1:1) under stirring, and the pH of the mixture was adjusted back to 12.0. The mixture was then completely exposed to air and reacted at room temperature under open conditions for 24 hours, while maintaining the pH of the reaction system at 12.0 throughout the preparation process. Finally, the reacted solution was dialyzed in an 8–14 kDa dialysis bag for 48 hours to remove unreacted GA. After freeze-drying, the WPI-GA complex was obtained.

[0161] (2) Preparation of WPI-GA complex stabilized cinnamon oil Pickering emulsion

[0162] A certain amount of freeze-dried WPI-GA complex was weighed and dispersed in distilled water to prepare a 1.5% (w / v) dispersion as the aqueous phase. Then, cinnamon essential oil (oil phase) was slowly dripped into the aqueous phase while homogenizing it for 3 minutes at 12000 r / min using a high-speed shear mill to form a Pickering emulsion of WPI-GA complex-stabilized cinnamon essential oil.

[0163] (3) Preparation of Pickering emulsion film preservation material

[0164] A certain amount of chitosan (CS) was dissolved in an aqueous solution of acetic acid to prepare a 1% (w / v) chitosan solution. 30% (based on the dry weight of CS) of glycerol was added, and the solution was stirred until homogeneous to prepare a 1.5% (w / v) CS film-forming base solution. 10.0 mL of the Pickering emulsion from step (2) was taken and mixed with 90 mL of the CS film-forming base solution. 10% nano-TiO2 and 5% carrageenan were added based on the dry weight of the film-forming material, i.e., CS. The mixture was then homogenized at 10000 r / min for 3 min using a high-speed shear mill, followed by degassing in a vacuum environment for 30 min to form an emulsion active film-forming solution. The Pickering emulsion film preservation material was thus obtained.

[0165] The test results for Example 1 are as follows:

[0166] 1. The structural functional groups of different substances in Example 1 were analyzed by infrared spectroscopy using a German Tensor27 Fourier transform infrared spectroscopy (FT-IR), including whey protein (WPI), gallic acid (GA), and whey protein-gallic acid covalent complex (WPI-GA).

[0167] FTIR spectroscopy can reflect information about the characteristic functional groups of a substance, and in infrared spectral data, the amide I band (1600 cm⁻¹) is dominated by C=O stretching. -1 -1700cm -1 The amide II band (1500 cm) is dominated by CN stretching vibration and NH bending vibration. -1 -1560cm -1 FTIR, commonly used to analyze changes in protein structure (Glassford et al. 2013), can therefore be used to reveal the interactions between proteins and polyphenol molecules and to understand the effect of polyphenol covalent bonding on protein structure. Figure 1 As shown, whey protein (WPI) concentrations at 3281, 2920, 1740, 1636, and 1524 cm⁻¹ were... -1 The maximum absorption peaks are located at [value missing] cm⁻¹, and are associated with OH stretching vibration, amide I band, and amide II band, respectively. When whey protein (WPI) covalently binds to gallic acid (GA), its amide I and amide II bands shift to 1723 cm⁻¹. -1 1627cm -1 1538cm -1 The varying degrees of red shift or blue shift mentioned above indicate that the covalent bonding between WPI and GA causes changes in the secondary structure of WPI. The changes in the amide I and amide II bands may be due to the newly formed CN bonds between WPI and GA.

[0168] 2. The secondary structures of the protein in Example 1 before and after modification were analyzed by using a JASCO J-1500 circular dichroism chromatograph (CD) from Japan, including whey protein (WPI) primary whey protein-gallic acid covalent complex (WPI-GA).

[0169] The specific steps are as follows: Prepare a 0.2-0.3 mg / ml protein sample, and choose a highly transparent phosphate buffer (5 mM, pH 7.4) as the buffer system. Wavelength range: 190-260 nm; optical path: 0.1 cm or 0.2 cm (shorter optical path reduces buffer absorption); scan speed: 50 nm / min.

[0170] To further investigate the intermolecular interactions of the whey protein-gallic acid covalent complex (WPI-GA), circular dichroism spectroscopy was used to analyze the changes in its secondary structure before and after the covalent binding of WPI and GA. Figure 2As shown, whey protein (WPI) is predominantly composed of α-lactalbumin (α-La). It exhibits significant negative peaks (α-helices) at 208 nm and 222 nm, while showing a weak β-sheet signal peak at 216 nm. Gallic acid covalently cross-links with the lysine ε-amino group, cysteine ​​thiol group, or tyrosine phenolic hydroxyl group of whey protein via phenolic hydroxyl groups, forming a Schiff base or Michael addition product, the whey protein-gallic acid covalent complex (WPI-GA). Its secondary structure undergoes changes: β-sheet reduction: covalent binding may disrupt the β-sheet structure of β-lactoglobulin, leading to a weakening of the negative peak at 216 nm. α-helices and random coils increase: as the protein structure unfolds, the signals of α-helices (negative peak at 208 nm) and random coils (broad peak at 202 nm) are enhanced. These studies indicate that the β-sheet of the whey protein-gallic acid covalent complex (WPI-GA) is transformed into a random coil.

[0171] 3. The particle size distribution and zeta potential of the emulsion were determined using the Nanotrac Wave II. Before measurement, the emulsion sample was diluted 10-fold with distilled water. The microstructure of the emulsion was observed using a laser confocal microscope (CLSM).

[0172] The specific steps are as follows: The sample was stained with a 1:1 volume ratio of Nile Red (0.1%, w / v) and Nile Blue (0.1%, w / v). Under light-protected conditions, 10 μL of the emulsion and 10 μL of the mixed dye were respectively added to a glass slide, mixed thoroughly, and covered with a coverslip. The emulsion images were observed at excitation wavelengths of 488 nm and 633 nm.

[0173] Figure 3 The image shows the particle size distribution, zeta potential, and laser confocal microscopy image of the Pickering emulsion of cinnamon essential oil stabilized by the carboxymethyl chitosan (CMCS) synergistic WPI-GA complex prepared in Example 1. The particle size distribution and zeta potential of the Pickering emulsion are important parameters for assessing its stability. Figure 3 As shown in (A), the average droplet diameter of the emulsion is 10.01±1.05 μm, and the main particle size distribution is basically unimodal, indicating that its droplet size distribution is relatively uniform. In addition, the potential value of the emulsion is -37.05±1.33 mV, and related studies indicate that when the absolute value of the Pickering emulsion potential is greater than 30 mV, it is considered a stable system. Figure 3(B) shows laser confocal microscopy images of the cinnamon essential oil Pickering emulsion at different excitation wavelengths. The green area represents the oil phase, the red area represents the cinnamon essential oil, and the green area represents the carboxymethyl chitosan (CMCS) synergistic WPI-GA complex. As shown in the figure, the cinnamon essential oil dispersed in the aqueous phase is encapsulated by the CMCS / WPI-GA complex, indicating that the CMCS / WPI-GA complex can adsorb between the oil and water phases to maintain the stability of the Pickering emulsion system. In conclusion, the CMCS / WPI-GA complex has the potential to serve as a stable carrier for cinnamon essential oil in the food packaging field.

[0174] Figure 4 To evaluate the preservation effect of the Pickering emulsion film preservative material prepared in Example 1 on bananas. CK was the blank control group (CK), MXA was the imazalil coating treatment group, and RYM was the Pickering emulsion film preservative material coating treatment group. The appearance images of bananas from different coating treatment groups stored at 25°C and 75% relative humidity for 25 days are shown below. Figure 4As shown. At 0 days: all three groups of bananas were bright green with no obvious differences, indicating a consistent initial state. At 10 days: all three groups of bananas remained green with no obvious black spots or signs of rot, indicating that all three treatment methods effectively maintained the appearance of the bananas in the early stages of storage. At 15 days: the bananas in the CK and MXA groups began to darken slightly, while the bananas in the RYM group remained a bright green, with the RYM group showing slightly better preservation. At 20 days: the bananas in the CK group turned significantly yellow with some brown spots; the bananas in the MXA group also turned significantly yellow with a few black spots; the bananas in the RYM group only turned slightly yellow with almost no black spots, demonstrating a significant effect in delaying yellowing and spotting. At 25 days: the bananas in the CK group turned severely yellow with numerous black spots, showing obvious signs of rot; the bananas in the MXA group also turned severely yellow with many black spots; although the bananas in the RYM group also turned yellow, the number and area of ​​black spots were significantly less than the previous two groups. The Essential Oil Emulsion Film (RYM) treatment group showed the best preservation effect, significantly delaying the yellowing process of bananas and demonstrating outstanding performance in inhibiting black spots and rot. The Essential Oil Emulsion Film (RYM) forms a continuous, uniform film on the banana surface, acting like a "protective coat" to effectively prevent water evaporation from the banana's interior to the external environment, maintaining the turgor pressure and water content of the banana cells, preserving its freshness and plumpness, and delaying aging and shriveling caused by water loss. In addition, this film can, to some extent, limit oxygen intake and carbon dioxide expulsion, reducing the banana's respiration rate. Postharvest respiration in bananas consumes their stored nutrients, and appropriately inhibiting respiration can reduce nutrient consumption, delaying fruit ripening and aging. Simultaneously, cinnamaldehyde in cinnamon essential oil can disrupt the cell membrane structure of microorganisms, interfering with their cellular metabolic processes, and has a significant inhibitory effect on bacteria (such as Escherichia coli and Bacillus subtilis) and fungi (such as anthracnose and Fusarium) that cause banana rot, reducing rot caused by microbial infection. Furthermore, the essential oil emulsion film acts as a carrier, enabling the slow and continuous release of essential oils. During banana storage, essential oils are continuously released onto the banana surface and surrounding environment over time, maintaining antibacterial activity for an extended period and continuously resisting microbial invasion. Plant essential oils can effectively eliminate free radicals generated within banana tissues. Free radicals attack intracellular biomolecules such as lipids, proteins, and nucleic acids, triggering oxidative stress and causing browning and aging in bananas. The physical barrier, antibacterial, and antioxidant effects of the essential oil emulsion film work synergistically to delay banana ripening and aging, resulting in an overall preservation effect superior to single-function preservation methods.

[0175] Figure 5The figure shows a comparison of the storage stability of the Pickering emulsions prepared in Comparative Example 1 and Example 1. As can be seen from the figure, Comparative Example 1 (WPI-GA stable emulsion) began to separate into layers (sediment at the bottom, clear at the top) after 7 days, and the separation intensified after 14 days (obvious emulsion separation), indicating that the droplets coalesced / flocculated, the phase separation was severe, and the stability was poor. The emulsion separation index of Comparative Example 1 was ≈15% after 7 days, and it rose sharply to 70%+ after 14 days. It remained at 80% after 30 days, indicating that the emulsion separated rapidly (droplets separated, forming an interface) and the stability was extremely poor. In contrast, Example 1 (carboxymethyl chitosan + WPI-GA stable emulsion) showed that the emulsion was uniform within 60 days with no obvious phase separation, showing excellent storage stability. The emulsion separation index of Example 1 was 0 within 60 days, with no emulsion separation and uniformly dispersed droplets, showing excellent stability. This is due to the synergistic effect of carboxymethyl chitosan. (1) Steric hindrance: The carboxymethyl chitosan molecular chains form a three-dimensional barrier on the surface of the droplets, which hinders the collision of droplets. (2) Charge repulsion: The electrostatic repulsion between carboxymethyl chitosan (negatively charged) and WPI-GA (after charge adjustment) enhances droplet dispersion. (3) Interfacial film enhancement: Carboxymethyl and WPI-GA form a composite film through hydrogen bonding and hydrophobic interactions, improving film strength and resisting storage disturbances. In summary, the synergistic effect of carboxymethyl chitosan and WPI-GA, through steric hindrance, charge repulsion, and interfacial film enhancement, ensures that the emulsion does not separate within 60 days, exhibiting stability far exceeding that of the single WPI-GA system (Comparative Example 1). This strategy provides a new method for the design of essential oil emulsion stabilizers, especially suitable for systems with high stability requirements (such as food preservation and functional emulsions).

[0176] Figure 6 The effect of different amounts of nanomaterials (TiO2) added to the Pickering emulsion coating preservative material prepared in Example 1 on the mechanical properties of the composite film. Figure 6 As can be seen, the tensile strength of the coating material without added nano-reinforcing particles (TiO2) (0% TiO2) is 13.4 MPa, and the elongation at break is 26.11%. After adding 1% TiO2, the tensile strength of the composite film is 24.43 MPa, and the elongation at break is 49.22%. After adding 5% TiO2, the tensile strength of the composite film is 31.67 MPa, and the elongation at break is 75.84%. These results demonstrate that by adding a specific proportion of nano-reinforcing ions, the mechanical properties (tensile strength and elongation at break) of the composite film can be significantly improved, thus better ensuring the durability of the antibacterial and preservative effects of the coating.

[0177] Figure 7 The effect of different amounts of nanomaterials (TiO2) added to the Pickering emulsion coating preservative material prepared in Example 1 on the barrier properties (oxygen permeability OP and water vapor permeability WVP) of the composite membrane. Figure 7As can be seen, the oxygen permeability (OP) and water vapor permeability (WVP) of the composite film gradually decrease with the increase of nano-reinforcing particles (TiO2), indicating that the barrier performance of the composite film is significantly improved after the addition of nano-reinforcing particles (TiO2). This is mainly because the spatial structure of the composite film is more compact after the addition of nano-reinforcing particles (TiO2), which can provide an effective spatial shielding function, prevent the entry of O2 and H2O, reduce the respiration intensity of the fruit, and further extend the preservation time.

[0178] The Pickering emulsions prepared in Examples 2 and 3 also showed good stability, with homogeneity and no obvious phase separation within 60 days, demonstrating excellent storage stability. The Pickering emulsion film can delay the ripening and senescence of bananas, maintain the freshness of bananas well within 25 days, and the emulsion film also showed better mechanical properties.

[0179] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a Pickering emulsion, characterized in that, Includes the following steps: (1) Mix the polyphenol solution and the protein solution, adjust the pH of the mixed solution to alkaline, and carry out the grafting reaction in the air to obtain a protein-polyphenol covalent complex. (2) Mix the plant essential oil and the protein-polyphenol covalent complex dispersion and emulsify them to obtain Pickering crude emulsion; (3) The Pickering crude emulsion, polysaccharide dispersion and crosslinking agent are mixed and emulsified to obtain the Pickering emulsion.

2. The preparation method according to claim 1, characterized in that, The polyphenol solution is obtained by mixing polyphenols and a solvent; the polyphenols include one or more of chlorogenic acid, ferulic acid, gentic acid, vanillic acid, cinnamic acid, syringic acid, sinapic acid, p-coumaric acid, caffeic acid, protocatechuic acid and gallic acid; The concentration of the polyphenol solution is 2-5% (w / v); The protein solution is obtained by mixing protein and solvent; the protein includes one or more of whey protein, egg white protein, soy protein isolate, pea protein, zein, β-lactoglobulin, wheat protein, lysozyme protein, α-lactoglobulin, soy globulin, mung bean globulin, rice bran protein, and β-casein; The concentration of the protein solution is 2-5% (w / v); the pH of the protein solution is 9-12.

3. The preparation method according to claim 1, characterized in that, The volume ratio of the polyphenol solution to the protein solution is 1 to 3:1; In step (1), the pH of the mixed solution is adjusted to 9-12; the temperature of the grafting reaction is 20-30℃ and the time is 12-48h.

4. The preparation method according to claim 1, characterized in that, The plant essential oils include one or more of the following: thyme essential oil, galangal essential oil, tea tree essential oil, lemon essential oil, lemongrass essential oil, oily skin essential oil, mustard essential oil, peppermint essential oil, cinnamon essential oil, clove essential oil, garlic essential oil, almond essential oil, eucalyptus essential oil, senna essential oil, and lavender essential oil. The plant essential oil has a volume fraction of 60-80% in the Pickering crude emulsion.

5. The preparation method according to claim 1, characterized in that, The protein-polyphenol covalent complex dispersion is obtained by mixing the protein-polyphenol covalent complex and a solvent; the concentration of the protein-polyphenol covalent complex dispersion is 1-3% (w / v); In step (2), the emulsification speed is 10000-12000 r / min and the time is 3-8 min.

6. The preparation method according to claim 1, characterized in that, The polysaccharide dispersion is obtained by mixing polysaccharides and solvents; the polysaccharides include one or more of carboxymethyl chitosan, carboxymethyl cellulose, cellulose nanocrystals, carboxylated cellulose nanocrystals, gum arabic, pectin, xanthan gum, and carrageenan; The concentration of the polysaccharide dispersion is 1-5% (w / v); The volume ratio of the polysaccharide dispersion to the protein-polyphenol covalent complex dispersion is 1:1 to 5; The crosslinking agent includes one or more of genipin, citric acid, itaconic acid, catechol, and caffeic acid-dopamine complex; The mass of the cross-linking agent is 0.01% to 1% of the total mass of the polysaccharide and protein-polyphenol covalent complex; In step (3), the emulsification speed is 10000-12000 r / min and the time is 3-8 min.

7. The Pickering emulsion prepared by the preparation method according to any one of claims 1 to 6.

8. A Pickering emulsion coating preservative material, characterized in that, The Pickering emulsion of claim 7 further includes film-forming substances, dispersants, plasticizers, nano-reinforcing particles, and binders.

9. The method for preparing the Pickering emulsion coating preservative material according to claim 8, characterized in that, Includes the following steps: (1) Mix the film-forming substance, dispersant and plasticizer to obtain the film-forming base liquid; (2) The Pickering emulsion, film-forming base liquid, nano-reinforcing particles and binder are mixed, sheared and then degassed to obtain a composite coating preservation material.

10. The application of the Pickering emulsion coating preservative material according to claim 9 in the preservation of fruits and vegetables.

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