Protein-based multifunctional food preservative film as well as preparation method and application thereof

Abstract

The invention discloses a protein-based multifunctional food preservative film as well as a preparation method and application thereof, and belongs to the technical field of functional modification of natural polymer materials. The preparation method of the protein-based multifunctional food preservative film comprises the following steps: firstly, carrying out hydrolysis pretreatment on zein by utilizing the hydrolysis effect of protease, then grafting catechol into a protein structure by utilizing an acyl transfer reaction of TGase, and finally, carrying out functional grafting modification on the zein by utilizing chitosan by utilizing an oxidation reaction of laccase, so as to obtain the protein-based multifunctional food preservative film. The physical and mechanical properties, the stability and the antibacterial activity of the zein film are further improved, and the protein film is endowed with antioxidant activity, so that the protein-based multifunctional food preservative film material suitable for food preservation is prepared. When the protein-based multifunctional food fresh-keeping film is used for fruit fresh-keeping treatment, the shelf life is remarkably prolonged, and the protein-based multifunctional food fresh-keeping film has a good fresh-keeping effect.

Description

Technical Field

[0001] This invention relates to a protein-based multifunctional food preservation film, its preparation method, and its application, belonging to the field of functional modification technology of natural polymer materials. Background Technology

[0002] Zeadrin is a byproduct of corn starch processing, widely available and without toxic side effects. Although zeadrin lacks essential amino acids such as lysine and tryptophan, resulting in low biological value, its unique amino acid composition and hydrophobicity give it exceptional self-assembly properties compared to proteins from other sources. It is readily processed into regenerable materials such as membranes, fibers, and micro / nanoparticles, demonstrating enormous application potential in food packaging, tissue engineering, and textiles.

[0003] Membrane materials formed directly from zein are brittle, unstable, and have weak functionality, severely affecting their performance in food preservation. Currently, the mechanical strength and functionality of zein membranes can be improved through chemical cross-linking or blending with other functional compounds. However, the use of chemical cross-linking agents poses potential threats to the environment and human health, while physical blending results in poor interfacial compatibility between the modified material and the protein matrix, leading to insignificant enhancement of the membrane's macroscopic mechanical properties and stability.

[0004] Existing technologies leverage the unique structure of zein to improve the mechanical properties of zein membranes through graft modification. For example, Chinese patent CN119039628A discloses a biological method for preparing zein membranes. This method first uses the reducing agent L-cysteine ​​to reduce the disulfide bonds in zein, loosening the molecular structure and exposing more glutamine residues. Based on this, it utilizes glutamine transaminase to catalyze an acyl transfer reaction, introducing ε-polylysine, rich in primary amino groups, into the protein structure, thereby preparing a protein membrane with high physical and mechanical properties, water solubility stability, and high antibacterial activity. Although this method improves the mechanical properties of the protein membrane to some extent, it still suffers from low mechanical strength. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a protein-based multifunctional food preservation film, its preparation method, and its applications. Specifically, zein is first pretreated with protease to expose more glutamine groups. Then, using the acyl transfer reaction of transglutaminase (TGase), dopamine containing a catechol structure is grafted onto the zein, strengthening the phenolic hydroxyl structure in the protein. Finally, through the catalytic action of laccase, a highly reactive intermediate product is formed, which reacts with the functional polymer chitosan to crosslink, obtaining chitosan-modified zein. The preservation film formed from this chitosan-modified zein exhibits higher physical and mechanical properties and flexibility, higher stability and antibacterial and antioxidant activity, and better food preservation. This method uses a whole-enzymatic approach instead of a chemical method, is safe, non-toxic, and environmentally friendly, and has profound potential application value and practical significance.

[0006] To achieve the above objectives, the following technical solution is provided:

[0007] The first objective of this invention is to provide a method for preparing a protein-based multifunctional food preservation film, the method comprising the following steps:

[0008] (1) Pretreatment of zein

[0009] Zeat protein was dissolved in an aqueous ethanol solution to obtain a zeat protein solution. The pH of the zeat protein solution was then adjusted, and a protease was added to react with it. After the reaction, the mixture was dialyzed and freeze-dried to obtain partially hydrolyzed zeat protein powder.

[0010] (2) Enzymatic cross-linking modification of zein by dopamine (DA)

[0011] The partially hydrolyzed zein powder obtained in step (1) was dissolved in an aqueous ethanol solution and the pH was adjusted to 6-7. Then, dopamine hydrochloride solution and TGase were added to react. After the reaction, the mixture was dialyzed and freeze-dried to obtain zein-DA protein powder.

[0012] (3) Chitosan-corn protease-induced grafting modification

[0013] The zein-DA protein powder obtained in step (2) was dissolved in an ethanol aqueous solution to prepare a zein-DA protein solution. Then chitosan, laccase and TEMPO were added to react. After the reaction was terminated, the precipitate was centrifuged, washed and freeze-dried to obtain grafted modified zein protein powder.

[0014] (4) Preparation of zein membrane

[0015] Dissolve the grafted modified zein powder prepared in step (3) in an ethanol aqueous solution, add glycerol, stir the solution thoroughly, remove bubbles by sonication to form a film-forming solution, pour it into a mold, and let it stand and dry until the solvent completely evaporates to obtain a protein-based multifunctional food preservation film.

[0016] In one embodiment, the ethanol aqueous solution in step (1) is an ethanol aqueous solution with a volume fraction of 70-80%, m / v, g / ml.

[0017] In one embodiment, the concentration of the zein solution in step (1) is 5-10 g / 100 mL.

[0018] In one embodiment, the pH value in step (1) is 8 to 9.

[0019] In one embodiment, the pH adjustment of the zein solution in step (1) is specifically performed using water and a buffer solution; the buffer solution is a tris-hydrochloric acid buffer; and the volume fraction of ethanol in the solution after pH adjustment is 5-10%.

[0020] In one embodiment, the protease in step (1) includes one or more of serine proteases, alkaline proteases, and trypsin.

[0021] In one embodiment, the amount of protease added in step (1) is 50 U to 100 U / mg protein.

[0022] In one embodiment, the reaction in step (1) is carried out at a temperature of 30–45°C for 2–5 hours.

[0023] In one embodiment, the ethanol aqueous solution in step (2) is an ethanol aqueous solution with a volume fraction of 70-80%, m / v, g / ml.

[0024] In one embodiment, step (2) involves adjusting the pH value using a phosphate buffer solution, resulting in an ethanol fraction of 5-10% in the solution after pH adjustment.

[0025] In one embodiment, the concentration of the dopamine hydrochloride solution in step (2) is 2-5 g / L.

[0026] In one embodiment, the amount of TGase added in step (2) is 80-100 U / g protein.

[0027] In one embodiment, the mass ratio of the partially hydrolyzed zein and dopamine hydrochloride in step (2) is 20-30:2-5.

[0028] In one embodiment, the reaction in step (2) is carried out in a constant temperature water bath at 40-45°C for 2-5 hours.

[0029] In one embodiment, the dialysis in step (2) is performed using acetic acid-acidified deionized water with a pH of 5 to 6.

[0030] In one embodiment, the ethanol aqueous solution in step (3) is an ethanol aqueous solution with a volume fraction of 70-80%, m / v, and g / ml.

[0031] In one embodiment, the zein-DA protein solution in step (3) needs to be diluted to 5-10% ethanol concentration before subsequent reactions.

[0032] In one embodiment, the concentration of the zein-DA protein solution in step (3) is 10-20 mg / mL.

[0033] In one embodiment, the amount of chitosan added in step (3) is 1 to 3 g / L.

[0034] In one embodiment, the laccase in step (3) has an enzyme activity of 50-100 U / g and is added in an amount of 5-10 U / g protein.

[0035] In one embodiment, the amount of TEMPO added in step (3) is 0.1 to 0.5 g / L.

[0036] In one embodiment, the reaction temperature in step (3) is 40-45°C and the reaction time is 3-7 hours.

[0037] In one embodiment, the centrifugation conditions in step (3) are 8000-10000 rpm for 5-10 min.

[0038] In one embodiment, the ethanol aqueous solution in step (4) is an ethanol aqueous solution with a volume fraction of 70-80%, m / v, g / ml.

[0039] In one embodiment, the amount of glycerol added in step (4) is 1-2%, m / v, g / ml.

[0040] In one embodiment, the mold in step (4) is a polytetrafluoroethylene mold.

[0041] The second objective of this invention is to provide a protein-based multifunctional food preservation film prepared by the method described above.

[0042] The third objective of this invention is to provide an application of the aforementioned protein-based multifunctional food preservation film in food preservation.

[0043] The fourth objective of this invention is to provide a method for improving the preservation performance of food, wherein the food is sealed and preserved using the aforementioned protein-based multifunctional food preservation film.

[0044] The fifth objective of this invention is to provide a method for improving the mechanical properties of protein-based multifunctional food preservation films, the method comprising the following steps:

[0045] (1) Pretreatment of zein

[0046] Zeat protein was dissolved in an aqueous ethanol solution to obtain a zeat protein solution. The pH of the zeat protein solution was then adjusted, and a protease was added to react with it. After the reaction, the mixture was dialyzed and freeze-dried to obtain partially hydrolyzed zeat protein powder.

[0047] (2) Enzymatic cross-linking modification of zein by dopamine (DA)

[0048] The partially hydrolyzed zein powder obtained in step (1) was dissolved in an aqueous ethanol solution and the pH was adjusted to 6-7. Then, dopamine hydrochloride solution and TGase solution were added to react. After the reaction, the mixture was dialyzed and freeze-dried to obtain zein-DA protein powder.

[0049] (3) Chitosan-corn protease-induced grafting modification

[0050] The zein-DA protein powder obtained in step (2) was dissolved in an ethanol aqueous solution to prepare a zein-DA protein solution. Then chitosan, laccase and TEMPO were added to react. After the reaction was terminated, the precipitate was centrifuged, washed and freeze-dried to obtain grafted modified zein protein powder.

[0051] (4) Preparation of zein membrane

[0052] Dissolve the grafted modified zein powder prepared in step (3) in an ethanol aqueous solution, add glycerol, stir the solution thoroughly, remove bubbles by sonication to form a film-forming solution, pour it into a mold, and let it stand and dry until the solvent completely evaporates to obtain a protein-based multifunctional food preservation film.

[0053] Beneficial effects:

[0054] (1) This invention first uses the hydrolysis of protease to pre-treat zein, then uses the acyl transfer reaction of TGase to incorporate catechol into the protein structure, and finally uses the oxidation reaction of laccase to functionalize and graft chitosan onto zein, thereby improving the physical and mechanical properties, stability and antibacterial activity of zein film and endowing the protein film with antioxidant activity, thus preparing a protein-based food preservation film material suitable for food preservation.

[0055] (2) Compared with traditional chemical and physical blending modifications, this invention has high modification efficiency, mild reaction conditions, and no environmental problems or toxic side effects caused by chemical reagents, making it highly practical.

[0056] (3) When the protein-based multifunctional food preservation film prepared by the present invention is used for fruit preservation, it significantly improves shelf life and has a good preservation effect. Detailed Implementation

[0057] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. The specific embodiments described below further illustrate the present invention.

[0058] The testing method involved in this invention:

[0059] 1. Mechanical property testing of zein membrane

[0060] The thickness of the membrane was randomly read at 6 points using a micrometer screw gauge as the average thickness of the membrane. The membrane was then cut into 50mm×10mm pieces for testing the tensile strength (Ts) and elongation at break (E) of the membrane. Three strips were taken from each membrane as parallel samples. The clamp running speed was 5mm / min.

[0061] 2. Stability test of zein membrane

[0062] The concentration of protein membrane dissolved in water over time was determined using ultraviolet spectrophotometry. 80 mg of protein membrane was weighed and placed in a 6 mol / L urea solution, incubated in a 25°C water bath, and centrifuged for 2 hours. The supernatant was then collected, and its absorbance at 280 nm was measured to calculate the degree of protein dissolution. A standard curve was prepared using bovine serum albumin as the standard protein.

[0063] 3. Antibacterial rate test of zein membrane

[0064] According to GB / T 20944.3-2008, the antibacterial test was conducted using the shaking method, and the antibacterial activity of the protein membrane against Gram-negative Escherichia coli strain (E. coli, ATCC-25922) and Gram-positive Staphylococcus aureus strain (S. aureus, ATCC-6538) was evaluated using the inhibition zone method and colony counting method. The inhibition rate was calculated using the colony counting method.

[0065] 4. Antioxidant properties test of zein membrane

[0066] Antioxidant activity was assessed using relative free radical scavenging rate. A 0.2 mmol / L DPPH-ethanol solution was prepared and stirred completely in the dark. Modified protein membrane samples were cut to 2.5 cm × 2.5 cm sizes. 6 mL of DPPH-ethanol solution was added to the membrane and mixed thoroughly. After standing in the dark for 30 min, the absorbance at 517 nm was measured using an unmodified zein membrane as a blank sample. Relative DPPH free radical scavenging rate was used to assess antioxidant activity.

[0067] The division rate is calculated according to formula (1):

[0068] ADPPH = (A0-A1) / A0 × 100% (1)

[0069] In the formula: ADPPH is the free radical scavenging rate (%); A1 is the sample absorbance; A0 is the blank absorbance.

[0070] 5. Water vapor transmission rate (WVP) test of zein membrane

[0071] A protein membrane was placed on top of a centrifuge tube containing anhydrous calcium chloride (0% relative humidity), and then the tube was placed in a constant temperature and humidity incubator (20°C, 65%). The mass of the centrifuge tube was weighed every 12 hours, and WVP (g / (mm² / hPa)) was calculated using the following formula. - 1):

[0072]

[0073] Where W is the added weight (g), d is the average membrane thickness (mm), Δt is the measurement interval (h), and A is the effective coverage area of ​​the membrane (mm²). 2 ), where ΔP is the water vapor pressure difference (Pa) across the membrane.

[0074] 6. Test on the preservation effect of zein film on fruit

[0075] Select blueberries with similar color, uniform size, and no obvious surface damage. After washing with deionized water, the blueberries are randomly divided into four groups. Untreated blueberries are selected as the control, and the other three groups are sealed and preserved with zein membrane. The changes in the appearance of the blueberries and the weight loss rate of the blueberries are recorded daily.

[0076] 7. Blueberry freshness test

[0077] Blueberries were sealed and preserved using a protein membrane, and their weight loss and appearance changes were recorded daily.

[0078] The raw materials involved in the embodiments and comparative examples of this invention are as follows:

[0079] Gliadin: Corn gliadin, with a protein content of 99%;

[0080] Dopamine: 98% purity;

[0081] TGase: 100 U / g;

[0082] Chitosan: Deacetylation degree ≥95%, viscosity 100~200mpa.s;

[0083] Serine protease: 200,000 U / mg;

[0084] Laccase: 50 U / g.

[0085] Example 1

[0086] A method for preparing a protein-based multifunctional food preservation film includes the following steps:

[0087] (1) Protease pretreatment of zein

[0088] A certain amount of zein powder was weighed and dissolved in a 70% (v / v) ethanol aqueous solution. After sonication for 5 min, the solution was magnetically stirred at room temperature to obtain a clear yellow zein solution with a zein concentration of 5 g / 100 mL. Then, 10.0 mL of deionized water and 10.0 mL of Tris-hydrochloric acid buffer (ethanol concentration diluted to 10%, pH of protein solution adjusted to 8) were added sequentially. Serine protease (50 U / mg protein) was added, and the solution was kept at 30 °C for 2 h. The reaction solution was then dialyzed in deionized water for 48 h and then lyophilized to obtain partially hydrolyzed zein powder.

[0089] (2) Enzymatic cross-linking modification of zein by dopamine (DA)

[0090] Weigh 0.30 g of partially hydrolyzed zein powder and dissolve it completely in 10 mL of 70% (v / v) ethanol aqueous solution. Then slowly pour it into 40 mL of phosphate buffer (pH 6), add 10 mL of 4 g / L dopamine hydrochloride solution, and then add TGase (enzyme activity of 80 U / g protein). Stir thoroughly and place the solution in a 40°C constant temperature water bath for 4 h. After the reaction is completed, dialyze the reaction solution in acidified deionized water (acetic acid, pH 5) for 48 h, and then freeze dry to obtain zein-DA protein powder.

[0091] (3) Chitosan-corn protease-induced grafting modification

[0092] 0.100 g of zein-DA protein powder was dissolved in 5 ml of 70% ethanol aqueous solution. After sonication for 5 min, the solution was magnetically stirred at room temperature to obtain a clear yellow protein solution. The solution was diluted with acetate-sodium acetate buffer to a 10% ethanol content. 0.5 g / L chitosan, 5 U / g protein laccase, and 0.5 g / L TEMPO were added. The solution was reacted at 40 °C for 7 hours. The reaction was terminated by water bathing the protein solution in boiling water for 5 min. After cooling, the solution was centrifuged at 8000 rpm for 10 min to remove the supernatant. 50 mL of pH 4.5 acetate-sodium acetate buffer was added to the precipitate. After thorough sonication, the solution was centrifuged at 8000 rpm for 10 min to remove unreacted chitosan. This washing process was repeated 3 times. The precipitate was then freeze-dried to obtain grafted modified zein protein powder.

[0093] (4) Preparation of zein membrane

[0094] Weigh 0.5g of grafted modified zein powder and dissolve it in 10ml of 80% acetic acid solution. Add 1% glycerol and stir at room temperature until fully dissolved. Then sonicate for 5min to remove air bubbles. Slowly pour the solution into a 5×7cm polytetrafluoroethylene mold and let it stand in a 40℃ oven until the solvent has completely evaporated. After equilibration at 20℃ and 65% constant temperature and humidity, the protein-based multifunctional food preservation film is obtained.

[0095] Example 2

[0096] A method for preparing a protein-based multifunctional food preservation film includes the following steps:

[0097] (1) Protease pretreatment of zein

[0098] A certain amount of zein powder was weighed and dissolved in a 70% (v / v) ethanol aqueous solution. After sonication for 5 min, the solution was magnetically stirred at room temperature to obtain a clear yellow zein solution with a zein concentration of 5 g / 100 mL. Then, 10.0 mL of deionized water and 10.0 mL of Tris-hydrochloric acid buffer (ethanol concentration diluted to 10%, pH of the protein solution adjusted to 8) were added sequentially. Serine protease (100 g protein) was added, and the solution was kept at 45 °C for 5 h. The reaction solution was then dialyzed in deionized water for 48 h and then lyophilized to obtain partially hydrolyzed zein powder.

[0099] (2) Enzymatic cross-linking modification of zein by dopamine (DA)

[0100] Weigh 0.30 g of partially hydrolyzed zein powder and dissolve it completely in 10 mL of 70% (v / v) ethanol aqueous solution. Then slowly pour it into 40 mL of phosphate buffer (pH 6), add 10 mL of 4 g / L dopamine hydrochloride solution, and then add TGase (enzyme activity of 80 U / g protein). Stir thoroughly and place the solution in a 40°C constant temperature water bath for 4 h. After the reaction is completed, dialyze the reaction solution in acidified deionized water (acetic acid, pH 5) for 48 h, and then freeze dry to obtain zein-DA protein powder.

[0101] (3) Chitosan-corn protease-induced grafting modification

[0102] 0.100 g of zein-DA protein powder was dissolved in 5 ml of 70% ethanol aqueous solution. After sonication for 5 min, the solution was magnetically stirred at room temperature to obtain a clear yellow protein solution. The solution was diluted with acetate-sodium acetate buffer to a 10% ethanol content. 1 g / L chitosan, 10 U / g protein laccase, and 0.5 g / L TEMPO were added. The solution was reacted at 40 °C for 7 hours. The reaction was terminated by water bathing the protein solution in boiling water for 5 min. After cooling, the solution was centrifuged at 8000 rpm for 10 min to remove the supernatant. 50 mL of pH 4.5 acetate-sodium acetate buffer was added to the precipitate. After thorough sonication, the solution was centrifuged at 8000 rpm for 10 min to remove unreacted chitosan. This washing process was repeated 3 times. The precipitate was then lyophilized to obtain grafted modified zein protein powder.

[0103] (4) Preparation of zein membrane

[0104] Weigh 0.5g of grafted modified zein powder and dissolve it in 10ml of 80% acetic acid solution. Add 1% glycerol and stir at room temperature until fully dissolved. Then sonicate for 5min to remove air bubbles. Slowly pour the solution into a 5×7cm polytetrafluoroethylene mold and let it stand in a 40℃ oven until the solvent has completely evaporated. After equilibration at 20℃ and 65% constant temperature and humidity, the protein-based multifunctional food preservation film is obtained.

[0105] Comparative Example 1: Gliadin without any treatment

[0106] Weigh 0.5g of zein powder and dissolve it in 10ml of 80% acetic acid solution. Add 1% glycerol and stir at room temperature until fully dissolved. Sonicate for 5 minutes to remove air bubbles. Then slowly pour the solution into a 5×7cm polytetrafluoroethylene mold and let it stand in a 40℃ oven until the solvent has completely evaporated. After equilibration at 20℃ and 65% constant temperature and humidity, protein-based food preservation film is obtained.

[0107] Comparative Example 2 without protease pretreatment

[0108] The only difference from Example 1 is that step (1) serine protease treatment is omitted, and zein is directly processed. All other parameters and conditions are the same as in Example 1.

[0109] Comparative Example 3 without dopamine modification

[0110] The only difference from Example 1 is that step (2) is omitted, while the other parameters and conditions are the same as in Example 1.

[0111] Comparative Example 4: A mixture of zein and chitosan

[0112] Take 0.5g of zein and 0.1g of chitosan, dissolve them in 10ml of 80% acetic acid solution, add 1% glycerol, stir at room temperature until fully dissolved, sonicate for 5min to remove air bubbles, then slowly pour into a 5×7cm polytetrafluoroethylene mold, let stand in a 40℃ oven until the solvent completely evaporates, and then equilibrate under constant temperature and humidity conditions of 20℃ and 65% to obtain protein-based food preservation film.

[0113] Results Analysis

[0114] The zein films obtained in Examples 1 and 2 and Comparative Examples 1, 2, 3, and 4 were tested for mechanical properties, stability, antibacterial properties, moisture permeability, and blueberry preservation. The test results are shown in Table 1.

[0115] Table 1. Properties of Zein Film

[0116]

[0117]

[0118] The embodiments provided above are not intended to limit the scope of the invention, nor are the described steps intended to limit the order of execution. Any obvious modifications made to the invention by those skilled in the art based on existing common knowledge also fall within the scope of protection defined by the claims.

Claims

1. A method for preparing a protein-based multifunctional food preservation film, characterized in that, The method includes the following steps: (1) Pretreatment of zein Zeat protein was dissolved in an aqueous ethanol solution to obtain a zeat protein solution. The pH of the zeat protein solution was then adjusted, and a protease was added to react with it. After the reaction, the mixture was dialyzed and freeze-dried to obtain partially hydrolyzed zeat protein powder. (2) Enzymatic cross-linking modification of zein by dopamine (DA) The partially hydrolyzed zein powder obtained in step (1) was dissolved in an aqueous ethanol solution and the pH was adjusted to 6-7. Then, dopamine hydrochloride solution and TGase solution were added to react. After the reaction, the mixture was dialyzed and freeze-dried to obtain zein-DA protein powder. (3) Chitosan-corn protease-induced grafting modification The zein-DA protein powder obtained in step (2) was dissolved in an ethanol aqueous solution to prepare a zein-DA protein solution. Then chitosan, laccase and TEMPO were added to react. After the reaction was terminated, the precipitate was centrifuged, washed and freeze-dried to obtain grafted modified zein protein powder. (4) Preparation of zein membrane Dissolve the grafted modified zein powder prepared in step (3) in an ethanol aqueous solution, add glycerol, stir the solution thoroughly, remove bubbles by sonication to form a film-forming solution, pour it into a mold, and let it stand and dry until the solvent completely evaporates to obtain a protein-based multifunctional food preservation film.

2. The method according to claim 1, characterized in that, The concentration of the zein solution in step (1) is 5-10 g / 100 mL.

3. The method according to claim 1, characterized in that, The amount of protease added in step (1) is 50U to 100U / mg protein.

4. The method according to claim 1, characterized in that, The concentration of the dopamine hydrochloride solution in step (2) is 2-5 g / L.

5. The method according to claim 1, characterized in that, In step (2), the amount of TGase added is 80-100 U / g protein.

6. The method according to claim 1, characterized in that, The amount of chitosan added in step (3) is 1-3 g / L.

7. The protein-based multifunctional food preservation film prepared by the method according to any one of claims 1 to 6.

8. The application of the protein-based multifunctional food preservation film according to claim 7 in food preservation.

9. A method for improving the preservation performance of food, characterized in that, The method involves sealing and preserving fresh food using the protein-based multifunctional food preservation film as described in claim 7.

10. A method for improving the mechanical properties of protein-based multifunctional food preservation film, characterized in that, The method includes the following steps: (1) Pretreatment of zein Zeat protein was dissolved in an aqueous ethanol solution to obtain a zeat protein solution. The pH of the zeat protein solution was then adjusted, and a protease was added to react with it. After the reaction, the mixture was dialyzed and freeze-dried to obtain partially hydrolyzed zeat protein powder. (2) Enzymatic cross-linking modification of zein by dopamine (DA) The partially hydrolyzed zein powder obtained in step (1) was dissolved in an aqueous ethanol solution and the pH was adjusted to 6-7. Then, dopamine hydrochloride solution and TGase solution were added to react. After the reaction, the mixture was dialyzed and freeze-dried to obtain zein-DA protein powder. (3) Chitosan-corn protease-induced grafting modification The zein-DA protein powder obtained in step (2) was dissolved in an ethanol aqueous solution to prepare a zein-DA protein solution. Then chitosan, laccase and TEMPO were added to react. After the reaction was terminated, the precipitate was centrifuged, washed and freeze-dried to obtain grafted modified zein protein powder. (4) Preparation of zein membrane Dissolve the grafted modified zein powder prepared in step (3) in an ethanol aqueous solution, add glycerol, stir the solution thoroughly, remove bubbles by sonication to form a film-forming solution, pour it into a mold, and let it stand and dry until the solvent completely evaporates to obtain a protein-based multifunctional food preservation film.

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