Preparation method of plant polyphenol / cottonseed protein multifunctional film for food preservation

Abstract

The invention discloses a preparation method of a plant polyphenol / cottonseed protein multifunctional film for food preservation, and relates to the technical field of preparation of proteins, fiber compositions and preservative films. Comprising the following raw materials in parts by weight: 10-20 parts of plant polyphenol, 30-50 parts of cottonseed protein powder, 2-6 parts of a cross-linking agent, 5-10 parts of konjac glucomannan, 2-4 parts of carboxymethylcellulose, 0.2-3 parts of a plasticizer and 5-8 parts of nano silicon dioxide powder. The preservative film is prepared by modifying cottonseed protein with plant polyphenol, the plant polyphenol is modified on a cottonseed protein structure through a covalent grafting method, and a plasticizer is added to form a film at room temperature, so that the plant polyphenol / cottonseed protein preservative film is obtained. Abundant hydroxyl groups of plant polyphenols are utilized to improve the antibacterial property and oxidation resistance of the film and prolong the quality guarantee period of food, and the preservative film disclosed by the invention takes the plant polyphenols, cottonseed protein, konjac glucomannan, carboxymethyl cellulose and nano silicon dioxide powder as main raw materials, so that the preservative film has degradability.

Description

Technical Field

[0001] The invention belongs to the technical field of protein, fiber composition and fresh-keeping film preparation in the biological industry, and more specifically, the invention relates to a method for preparing a plant polyphenol / cottonseed protein multifunctional film for food preservation. Background Art

[0002] In the modern food industry, cling film is an important means to protect food quality and extend shelf life, and its performance and safety have always received widespread attention. Although traditional cling film materials, such as synthetic plastics such as polyethylene (PE) and polypropylene (PP), have good mechanical properties and processability, their non-degradability has caused long-term pressure on the environment, and these materials themselves do not have antibacterial or antioxidant functions, making it difficult to meet the growing demand for green and healthy consumption.

[0003] Therefore, developing a cling film material that is both environmentally friendly and functional has become a hot topic in current research. As an emerging biodegradable material, plant protein-based cling film has shown great application potential in the field of food packaging due to its good biocompatibility, degradability and adjustable functionality. Among them, cottonseed protein, as a widely available and low-cost agricultural by-product, has a high content of amino acids and modifiable functional groups that provide a material basis for the preparation of high-performance cling film.

[0004] However, the single cottonseed protein film still has deficiencies in mechanical strength, water resistance and functionality, which limits its widespread promotion in practical applications. In order to overcome these defects, researchers began to explore ways to improve its performance through chemical modification. Plant polyphenols, as a class of natural antioxidants widely present in nature, not only have abundant hydroxyl groups, which can give the material excellent antioxidant and antibacterial properties, but also can bind to protein molecules through covalent and non-covalent bonds to enhance the stability and functionality of the material. At present, there is still a lack of relevant research on the preparation of plastic wrap using a combination of plant polyphenols and cottonseed protein. Summary of the invention

[0005] An object of the present invention is to solve at least the above problems and / or disadvantages and to provide at least the advantages which will be described hereinafter.

[0006] In order to achieve these purposes and other advantages according to the present invention, a plant polyphenol / cottonseed protein multifunctional film for food preservation is provided, characterized in that it comprises the following raw materials in parts by weight: 10 to 20 parts of plant polyphenols, 30 to 50 parts of cottonseed protein powder, 2 to 6 parts of cross-linking agent, 5 to 10 parts of konjac glucomannan, 2 to 4 parts of carboxymethyl cellulose, 0.2 to 3 parts of plasticizer, and 5 to 8 parts of nano silicon dioxide powder.

[0007] Preferably, the plant polyphenol is one of tea polyphenol, apple polyphenol, grape polyphenol, resveratrol and bayberry tannin.

[0008] Preferably, the plasticizer is one of glycerol, sorbitol, epoxidized soybean oil, triester of citrate, and acetyl tributyl citrate.

[0009] Preferably, the cross-linking agent is glutaraldehyde or genipin.

[0010] A method for preparing a plant polyphenol / cottonseed protein multifunctional film for food preservation comprises the following steps:

[0011] Step 1, heating deionized water to 40-60° C., dissolving plant polyphenols in the deionized water, and stirring to obtain a plant polyphenol solution; dissolving cottonseed protein powder in deionized water, and stirring to obtain a cottonseed protein powder solution;

[0012] Step 2, stirring the cottonseed protein powder solution at a certain speed, then adding a cross-linking agent drop by drop, and letting it stand after continuous stirring to obtain a cross-linked system; stirring the cross-linked system at a certain speed, adding a plant polyphenol solution drop by drop into the cross-linked system, and continuing to stir, heating to 60-80° C. and keeping warm for 1-2 hours after the addition is completed, stopping stirring, and cooling to obtain cottonseed protein modified with plant polyphenols;

[0013] Step 3, adding konjac glucomannan, carboxymethyl cellulose and nano-silicon dioxide into deionized water, and ultrasonically dispersing them to obtain a mixed suspension;

[0014] Step 4: Mix the mixed suspension with the cottonseed protein modified with polyphenols, add a plasticizer, and oscillate ultrasonically at 40 to 120 kHz for 1 to 3 hours, then stand and age for 12 to 24 hours to obtain a film-forming liquid; pour the film-forming liquid onto the surface of the glass plate, cast the film-forming liquid on the surface of the glass plate, use a scraper to scrape and smooth the film, and dry it at 30 to 55°C for 12 to 24 hours to obtain a plant polyphenol / cottonseed protein multifunctional film.

[0015] Preferably, in step 1, the mass volume ratio of plant polyphenols to deionized water is 1-2 g:20 mL; the mass volume ratio of cottonseed protein powder to deionized water is 3-5 g:50-100 mL.

[0016] Preferably, in the step 2, the stirring speed of the cross-linking system is 200-400 rpm, the stirring time is 40-60 min, and the standing time is 1-3 h; the stirring speed of dripping the plant polyphenol solution is 600-1200 rpm.

[0017] Preferably, in step 3, the mass volume ratio of konjac glucomannan to deionized water is 5-10 g:40-100 mL.

[0018] Preferably, in step 3, modified nano-silicon dioxide is used to replace nano-silicon dioxide, wherein the preparation method of modified nano-silicon dioxide comprises:

[0019] Nano silicon dioxide with a particle size distribution of 10 to 200 nm is selected and added to an ethanol solution, polyethylene glycol-200 is added as a dispersant, and ultrasonic dispersion is performed, the ultrasonic dispersion frequency is 20 to 40 kHz, and the ultrasonic dispersion time is 20 to 50 minutes; bis(dioctyloxypyrophosphate)ethylene titanate and 1,2-propylene glycol are added to the ethanol solution, ultrasonic dispersion is performed at 60 to 120 kHz for 10 to 30 minutes, and then the solution is allowed to stand for 1 to 5 hours, the temperature is raised to 50 to 80° C., the temperature is maintained for 5 to 15 minutes, the solution is cooled to room temperature, filtered, and dried to obtain modified nano silicon dioxide.

[0020] Preferably, the mass volume ratio of nano-silica, polyethylene glycol-200, bis(dioctyloxypyrophosphate)ethylene titanate, 1,2-propylene glycol and ethanol solution is 5-8g:0.2-0.5g:0.6-1g:0.2-1:50-250mL; and the concentration of the ethanol solution is 60-80wt%.

[0021] The present invention includes at least the following beneficial effects: the present invention discloses a method for preparing a plant polyphenol / cottonseed protein multifunctional film for food preservation, wherein cottonseed protein is modified with plant polyphenols to prepare a fresh-keeping film, plant polyphenols are modified on the cottonseed protein structure by a covalent grafting method, and a certain amount of plasticizer is added to form a film at room temperature to obtain a plant polyphenol / cottonseed protein fresh-keeping film. The rich hydroxyl groups of plant polyphenols are utilized to enhance the film's antibacterial and antioxidant properties and extend the shelf life of food. At the same time, since the fresh-keeping film of the present invention uses plant polyphenols, cottonseed protein, konjac glucomannan, carboxymethyl cellulose and nano-silicon dioxide powder as main raw materials, the fresh-keeping film has good degradability.

[0022] Nano silicon oxide is added to the plant polyphenol / cottonseed protein multifunctional film for food preservation prepared by the present invention, thereby improving the mechanical properties of the preservative film, increasing the elongation at break of the preservative film, and thus improving the durability of the preservative film;

[0023] At the same time, the invention uses polyethylene glycol-200 to disperse nano silicon dioxide, and uses bis(dioctyloxypyrophosphate)ethylene titanate to coat the nano silicon dioxide, so as to prepare modified nano silicon dioxide. In the preparation process, the nano silicon dioxide is first dispersed into a uniform dispersion system in an ethanol solution using polyethylene glycol-200, thereby reducing the agglomeration of the nano silicon dioxide; subsequently, when the bis(dioctyloxypyrophosphate)ethylene titanate is added, 1,2-propylene glycol is simultaneously added as a dispersant, and the nano silicon dioxide is dispersed in the modification process, thereby improving the The uniformity of the coating of nano-silica by bis(dioctyloxypyrophosphate)ethylene titanate is improved; the modified nano-silica with high dispersibility, low agglomeration and good compatibility with cottonseed protein powder, konjac glucomannan and carboxymethyl cellulose is prepared by the above preparation method; after the modified nano-silica is replaced by the modified nano-silica, the modified nano-silica has higher compatibility with the cottonseed protein powder, konjac glucomannan and carboxymethyl cellulose modified with plant polyphenols, and also has excellent fluidity and plasticity, thereby further improving the mechanical properties of the plastic wrap.

[0024] Other advantages, objectives and features of the present invention will be embodied in part through the following description, and in part will be understood by those skilled in the art through study and practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a scanning electron microscope image of the cottonseed protein powder used in Example 1. DETAILED DESCRIPTION

[0026] The present invention is further described in detail below in conjunction with the accompanying drawings so that those skilled in the art can implement the invention with reference to the description.

[0027] It should be understood that the terms such as “having”, “including” and “comprising” used herein do not exclude the existence or addition of one or more other elements or combinations thereof.

[0028] Example 1

[0029] This embodiment provides a method for preparing a plant polyphenol / cottonseed protein multifunctional film for food preservation, comprising the following steps:

[0030] Step 1: Heat 200 mL of deionized water to 40°C, dissolve 10 g of tea polyphenols in the deionized water, and stir to obtain a tea polyphenol solution; dissolve 30 g of cottonseed protein powder in 500 mL of deionized water, and stir to obtain a cottonseed protein powder solution; wherein the scanning electron microscope image of the cottonseed protein powder (CPI) used in this embodiment is as follows: Figure 1 As shown;

[0031] Step 2: Stir the cottonseed protein powder solution at a speed of 400 rpm, then drop 2 g of glutaraldehyde, continue stirring for 40 minutes and then stand for 3 hours to obtain a cross-linked system; stir the cross-linked system at a speed of 1200 rpm, drop the tea polyphenol solution into the cross-linked system, continue stirring, heat to 80° C. and keep warm for 2 hours after the addition is completed, stop stirring, and cool to obtain tea polyphenol-modified cottonseed protein;

[0032] Step 3: put 5g of konjac glucomannan, 2g of carboxymethyl cellulose, and 6g of nano-silicon dioxide into 100mL of deionized water, and disperse them by ultrasonication at a frequency of 60kHz and a time of 20min to obtain a mixed suspension;

[0033] Step 4: Mix the mixed suspension with polyphenol-modified cottonseed protein, add 1 g of glycerol, oscillate ultrasonically at 60 kHz for 2 hours, and then let it stand for 12 hours to obtain a film-forming liquid; pour the film-forming liquid onto the surface of the glass plate, cast the film-forming liquid on the surface of the glass plate to form a film, use a scraper to scrape and smooth the film, and dry it at 40°C for 12 hours to obtain a plant polyphenol / cottonseed protein multifunctional film.

[0034] Example 2

[0035] This embodiment provides a method for preparing a plant polyphenol / cottonseed protein multifunctional film for food preservation, comprising the following steps:

[0036] Step 1: Heat 200 mL of deionized water to 50° C., dissolve 15 g of apple polyphenol in the deionized water, and stir to obtain an apple polyphenol solution; dissolve 40 g of cottonseed protein powder in 600 mL of deionized water, and stir to obtain a cottonseed protein powder solution;

[0037] Step 2: Stir the cottonseed protein powder solution at a speed of 400 rpm, then drop 4 g of glutaraldehyde, continue stirring for 50 minutes and then stand for 3 hours to obtain a cross-linked system; stir the cross-linked system at a speed of 1200 rpm, drop the apple polyphenol solution into the cross-linked system, continue stirring, heat to 80° C. and keep warm for 2 hours after the addition is completed, stop stirring, and cool to obtain cottonseed protein modified with apple polyphenol;

[0038] Step 3: put 8g of konjac glucomannan, 3g of carboxymethyl cellulose, and 6g of nano-silicon dioxide into 100mL of deionized water, and disperse them by ultrasonication at a frequency of 60kHz and a time of 20min to obtain a mixed suspension;

[0039] Step 4: Mix the mixed suspension with the cottonseed protein modified with polyphenols, add 1.2 g of sorbitol, oscillate at 80 kHz ultrasound for 3 hours, and then let it stand for 12 hours to obtain a film-forming liquid; pour the film-forming liquid onto the surface of the glass plate, cast the film-forming liquid on the surface of the glass plate to form a film, use a scraper to scrape and smooth the film, and dry it at 45°C for 12 hours to obtain a plant polyphenol / cottonseed protein multifunctional film.

[0040] Example 3

[0041] This embodiment provides a method for preparing a plant polyphenol / cottonseed protein multifunctional film for food preservation, comprising the following steps:

[0042] Step 1: Heat 200 mL of deionized water to 60° C., dissolve 20 g of resveratrol in the deionized water, and stir to obtain a resveratrol solution; dissolve 50 g of cottonseed protein powder in 1000 mL of deionized water, and stir to obtain a cottonseed protein powder solution;

[0043] Step 2: Stir the cottonseed protein powder solution at a speed of 400 rpm, then drop 6 g of glutaraldehyde, continue stirring for 60 minutes and let stand for 3 hours to obtain a cross-linked system; stir the cross-linked system at a speed of 1200 rpm, drop the resveratrol solution into the cross-linked system, continue stirring, heat to 80° C. and keep warm for 2 hours after the addition is completed, stop stirring, and cool to obtain resveratrol-modified cottonseed protein;

[0044] Step 3: put 10g of konjac glucomannan, 4g of carboxymethyl cellulose and 8g of nano-silicon dioxide into 100mL of deionized water, and disperse them by ultrasonication at a frequency of 60kHz and a time of 20min to obtain a mixed suspension;

[0045] Step 4: Mix the mixed suspension with polyphenol-modified cottonseed protein, add 1.5 g of epoxidized soybean oil, oscillate at 80 kHz ultrasonically for 3 hours, and then let it stand for 12 hours to obtain a film-forming liquid; pour the film-forming liquid onto the surface of the glass plate, cast the film-forming liquid on the surface of the glass plate, use a scraper to scrape and smooth the film, and dry it at 55°C for 12 hours to obtain a plant polyphenol / cottonseed protein multifunctional film.

[0046] Example 4

[0047] This embodiment provides a method for preparing a plant polyphenol / cottonseed protein multifunctional film for food preservation. The difference from Example 1 is that modified nano-silicon dioxide is used to replace the nano-silicon dioxide in step three, and the process parameters of the remaining steps are the same as those in Example 1; wherein the preparation method of modified nano-silicon dioxide is:

[0048] 50 g of nano silicon dioxide with a particle size distribution of 10 to 200 nm was selected and added to 500 mL of a 60 wt% ethanol solution, and 2 g of polyethylene glycol-200 was added as a dispersant, and ultrasonic dispersion was performed, the ultrasonic dispersion frequency was 40 kHz, and the ultrasonic dispersion time was 50 min; 6 g of bis(dioctyloxypyrophosphate)ethylene titanate and 2 g of 1,2-propylene glycol were added to the ethanol solution, ultrasonic dispersion was performed at 120 kHz for 20 min, and then the mixture was allowed to stand for 5 h, the mixture was heated to 80° C. and kept warm for 10 min, cooled to room temperature, filtered, and dried to obtain modified nano silicon dioxide.

[0049] Example 5

[0050] This embodiment provides a method for preparing a plant polyphenol / cottonseed protein multifunctional film for food preservation. The difference from Example 1 is that modified nano-silicon dioxide is used to replace the nano-silicon dioxide in step three, and the process parameters of the remaining steps are the same as those in Example 1; wherein the preparation method of modified nano-silicon dioxide is:

[0051] 80g of nano-silica with a particle size distribution of 10 to 200nm was selected and added to an ethanol solution, and 4g of polyethylene glycol-200 was added as a dispersant, and ultrasonic dispersion was performed, the ultrasonic dispersion frequency was 40kHz, and the ultrasonic dispersion time was 30min; 8g of bis(dioctyloxypyrophosphate)ethylene titanate and 3g of 1,2-propylene glycol were added to the ethanol solution, and ultrasonic dispersion was performed at 120kHz for 30min, and then the solution was allowed to stand for 5h, the temperature was raised to 80°C, and the temperature was kept for 10min, the solution was cooled to room temperature, filtered, and dried to obtain modified nano-silica.

[0052] Comparative Example 1

[0053] This embodiment provides a method for preparing a plant polyphenol / cottonseed protein multifunctional film for food preservation. Compared with Example 1, the difference is that no nano-silicon dioxide is added to the plant polyphenol / cottonseed protein multifunctional film for food preservation, and the process parameters of the remaining steps are the same as those in Example 1.

[0054] Comparative Example 2

[0055] The present embodiment provides a method for preparing a plant polyphenol / cottonseed protein multifunctional film for food preservation. Compared with Example 1, the tea polyphenol modification of cottonseed protein in step 2 is not performed, and the tea polyphenol solution obtained in step 1, the cottonseed protein powder solution and the same amount of konjac glucomannan, carboxymethyl cellulose and nano-silicon dioxide as in Example 1 are directly put into deionized water, ultrasonically dispersed to obtain a mixed suspension, and then 1 g of glycerol is added, ultrasonically oscillated at 60 kHz for 2 hours, and then aged for 12 hours to obtain a film-forming liquid; the film-forming liquid is poured onto the surface of a glass plate, the film-forming liquid is cast onto the surface of the glass plate to form a film, the film is scraped and smoothed with a scraper, and dried at 40°C for 12 hours to obtain a plant polyphenol / cottonseed protein multifunctional film.

[0056] Comparative Example 3

[0057] This comparative example provides a method for preparing a food preservative film, the steps comprising:

[0058] Step 1, dissolving 30 g of cottonseed protein powder in 500 mL of deionized water, and stirring to obtain a cottonseed protein powder solution;

[0059] Step 3: put 15g konjac glucomannan, 2g carboxymethyl cellulose and 6g nano-silicon dioxide into 100mL deionized water, and disperse them by ultrasonication at a frequency of 60kHz and a time of 20min to obtain a mixed suspension;

[0060] Step 4: Mix the mixed suspension with the cottonseed protein powder solution modified with polyphenols, add 1 g of glycerol, oscillate ultrasonically at 60 kHz for 2 hours, and then let it stand for 12 hours to obtain a film-forming liquid; pour the film-forming liquid onto the surface of the glass plate, cast the film-forming liquid on the surface of the glass plate, use a scraper to scrape and smooth the film, and dry it at 40°C for 12 hours to obtain a plant polyphenol / cottonseed protein multifunctional film.

[0061] According to the method of GB / T 1040.3-2006, the tensile strength and elongation at break of the plant polyphenol / cottonseed protein multifunctional films for food preservation prepared in Examples 1 to 5 and Comparative Examples 1 to 2 were measured respectively, and the following table was obtained:

[0062] Table 1 Mechanical properties of membrane samples Performance Test Table

[0063] Tensile strength(MPa) Elongation at break (%) Example 1 10.83 282.31 Example 2 9.95 280.26 Example 3 10.20 279.65 Example 4 13.74 359.27 Example 5 13.52 348.32 Comparative Example 1 7.26 95.14 Comparative Example 2 8.45 102.09

[0064] As can be seen from the above table, the plant polyphenol / cottonseed protein multifunctional films for food preservation prepared in Examples 1 to 5 all have excellent tensile strength, and the tensile strength and elongation at break of Examples 4 and 5 are further improved compared with Examples 1 to 3, and the tensile strength of the samples of Examples 4 and 5 reaches the standard of PE cling film in GB / T 10457-2021. At the same time, the elongation at break of the samples prepared in Examples 1 to 5 is significantly better than that of Comparative Examples 1 and 2, and the elongation at break of the samples prepared in Examples 4 and 5 is further improved, indicating that the plant polyphenol / cottonseed protein multifunctional film for food preservation prepared by the present invention can meet the requirements of daily food preservation.

[0065] By detecting the membrane samples for DPPH free radicals, ABTS + The free radical scavenging rate was used to verify the antioxidant activity of the plant polyphenol / cottonseed protein multifunctional film used for food preservation.

[0066] Weigh 0.05 g of the plant polyphenol / cottonseed protein multifunctional film for food preservation prepared in Examples 1 to 5 and 0.05 g of the preservative film sample prepared in Comparative Example 3, and respectively place them in 10 mL of deionized water for oscillation and dissolution, and then centrifuge at 10000 rpm for 5 min to obtain the supernatant for later use;

[0067] The experimental method for determining the DPPH free radical scavenging rate is as follows:

[0068] Take 2 mL of the supernatant and mix them evenly with 2.5 mL of 0.1 mmol DPPH methanol solution, react for 30 min in a dark environment, and measure the absorbance of the mixed solution at 517 nm. The calculation formula for DPPH free radical scavenging rate is:

[0069] RDPPH(%)=(A T -A S ) / A O ×100%

[0070] Where: A T A is the absorbance of DPPH methanol solution and 2 mL methanol solution at 517 nm; S A is the absorbance of DPPH methanol solution and 2 mL sample solution; O It is the absorbance of DPPH methanol solution and 2mL deionized water.

[0071] ABTS + The experimental method for determining the free radical scavenging rate is as follows:

[0072] Take 2 mL of supernatant and 2.5 mL of ABTS + / PBS solution (absorbance is 0.700±0.025) was mixed evenly, reacted for 30 minutes under light-proof conditions, and its absorbance was measured at 734nm. The calculation formula for ABTS+ free radical scavenging rate is:

[0073] RABTS + (%) = (A2-A1) / A0×100%

[0074] Where: A2 is ABTS at 734nm + / PBS solution and PBS solution absorbance; A1 is ABTS at 734nm + / The absorbance of PBS solution and sample solution; A0 is the absorbance of ABTS at 734nm + / The absorbance of PBS solution and 2.5mL deionized water

[0075] Through the measurement experiment, the following table is obtained:

[0076] Table 2 Scavenging rate of membrane samples for DPPH free radicals

[0077] DPPH free radical scavenging rate (%) <![CDATA[ABTS + Free radical scavenging rate (%)]]> Example 1 90.33 92.56 Example 2 90.65 93.60 Example 3 92.16 90.29 Example 4 92.04 93.82 Example 5 92.27 91.19 Comparative Example 3 20.41 18.07

[0078] As can be seen from the table above, Examples 1 to 5 all used cottonseed protein modified with plant polyphenols, and the prepared membrane samples had a positive effect on DPPH free radical scavenging rate and ABTS + The free radical scavenging rates were all over 90%, much higher than that of Comparative Example 3, indicating that the plant polyphenol / cottonseed protein multifunctional films for food preservation prepared in Examples 1 and 5 have excellent antioxidant properties.

[0079] The number of devices and processing scales described here are used to simplify the description of the present invention. Applications, modifications and variations of the present invention will be obvious to those skilled in the art.

[0080] Although the embodiments of the present invention have been disclosed as above, they are not limited to the applications listed in the specification and the implementation modes, and they can be fully applied to various fields suitable for the present invention. For those familiar with the art, additional modifications can be easily implemented. Therefore, without departing from the general concept defined by the claims and the scope of equivalents, the present invention is not limited to the specific details and the illustrations shown and described herein.

Claims

1. A plant polyphenol / cottonseed protein multifunctional film for food preservation, characterized in that: The invention comprises the following raw materials in parts by weight: 10 to 20 parts of plant polyphenols, 30 to 50 parts of cottonseed protein powder, 2 to 6 parts of cross-linking agent, 5 to 10 parts of konjac glucomannan, 2 to 4 parts of carboxymethyl cellulose, 0.2 to 3 parts of plasticizer and 5 to 8 parts of nano silicon dioxide powder.

2. The plant polyphenol / cottonseed protein multifunctional film for food preservation according to claim 1, characterized in that: The plant polyphenol is one of tea polyphenol, apple polyphenol, grape polyphenol, resveratrol and bayberry tannin.

3. The plant polyphenol / cottonseed protein multifunctional film for food preservation according to claim 1, characterized in that: The plasticizer is one of glycerol, sorbitol, epoxy soybean oil, triester of citrate, and acetyl tributyl citrate.

4. The plant polyphenol / cottonseed protein multifunctional film for food preservation according to claim 1, characterized in that: The cross-linking agent is glutaraldehyde or genipin.

5. A method for preparing a plant polyphenol / cottonseed protein multifunctional film for food preservation as claimed in any one of claims 1 to 4, characterized in that: The following steps are involved: Step 1, heating deionized water to 40-60° C., dissolving plant polyphenols in the deionized water, and stirring to obtain a plant polyphenol solution; dissolving cottonseed protein powder in deionized water, and stirring to obtain a cottonseed protein powder solution; Step 2, stirring the cottonseed protein powder solution at a certain speed, then adding a cross-linking agent drop by drop, and letting it stand after continuous stirring to obtain a cross-linked system; stirring the cross-linked system at a certain speed, adding a plant polyphenol solution drop by drop into the cross-linked system, and continuing to stir, heating to 60-80° C. and keeping warm for 1-2 hours after the addition is completed, stopping stirring, and cooling to obtain cottonseed protein modified with plant polyphenols; Step 3, adding konjac glucomannan, carboxymethyl cellulose and nano-silicon dioxide into deionized water, and ultrasonically dispersing them to obtain a mixed suspension; Step 4: Mix the mixed suspension with the cottonseed protein modified with polyphenols, add a plasticizer, and oscillate ultrasonically at 40 to 120 kHz for 1 to 3 hours, then stand and age for 12 to 24 hours to obtain a film-forming liquid; pour the film-forming liquid onto the surface of the glass plate, cast the film-forming liquid on the surface of the glass plate, use a scraper to scrape and smooth the film, and dry it at 30 to 55°C for 12 to 24 hours to obtain a plant polyphenol / cottonseed protein multifunctional film.

6. The method for preparing the plant polyphenol / cottonseed protein multifunctional film for food preservation according to claim 5, characterized in that: In the step 1, the mass volume ratio of plant polyphenols to deionized water is 1-2 g:20 mL; the mass volume ratio of cottonseed protein powder to deionized water is 3-5 g:50-100 mL.

7. The method for preparing the plant polyphenol / cottonseed protein multifunctional film for food preservation according to claim 5, characterized in that: In the step 2, the stirring speed of the cross-linking system is 200-400 rpm, the stirring time is 40-60 min, and the standing time is 1-3 h; the stirring speed of dripping the plant polyphenol solution is 600-1200 rpm.

8. The method for preparing the plant polyphenol / cottonseed protein multifunctional film for food preservation according to claim 5, characterized in that: In the step 3, the mass volume ratio of konjac glucomannan to deionized water is 5-10 g:40-100 mL.

9. The method for preparing the plant polyphenol / cottonseed protein multifunctional film for food preservation according to claim 5, characterized in that: In the step 3, modified nano-silicon dioxide is used to replace nano-silicon dioxide, wherein the preparation method of modified nano-silicon dioxide comprises: Nano silicon dioxide with a particle size distribution of 10 to 200 nm is selected and added to an ethanol solution, polyethylene glycol-200 is added as a dispersant, and ultrasonic dispersion is performed, the ultrasonic dispersion frequency is 20 to 40 kHz, and the ultrasonic dispersion time is 20 to 50 minutes; bis(dioctyloxypyrophosphate)ethylene titanate and 1,2-propylene glycol are added to the ethanol solution, ultrasonic dispersion is performed at 60 to 120 kHz for 10 to 30 minutes, and then the solution is allowed to stand for 1 to 5 hours, the temperature is raised to 50 to 80° C., the temperature is maintained for 5 to 15 minutes, the solution is cooled to room temperature, filtered, and dried to obtain modified nano silicon dioxide.

10. The method for preparing the plant polyphenol / cottonseed protein multifunctional film for food preservation according to claim 9, characterized in that: The mass volume ratio of nano silicon dioxide, polyethylene glycol-200, bis(dioctyloxypyrophosphate)ethylene titanate, 1,2-propylene glycol and ethanol solution is 5-8g:0.2-0.5g:0.6-1g:0.2-1:50-250mL; the concentration of the ethanol solution is 60-80wt%.

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