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

Abstract

The application discloses a kind of preparation methods of plant polyphenol / cottonseed protein multifunctional film for food preservation, it is related to protein, fiber composition and preservative film preparation technical field, including following weight parts raw materials: 10~20 parts plant polyphenol, 30~50 parts cottonseed protein powder, 2~6 parts crosslinking agent, 5~10 parts konjac glucomannan, 2~4 parts carboxymethyl cellulose, 0.2~3 parts plasticizer, 5~8 parts nano silicon dioxide powder.The application uses plant polyphenol to modify cottonseed protein and prepare preservative film, plant polyphenol is modified on the structure of cottonseed protein by covalent grafting method, and plasticizer is added to form film at room temperature, obtain plant polyphenol / cottonseed protein preservative film.Using the abundant hydroxyl group of plant polyphenol to improve the antibacterial property, antioxidant and the performance of prolonging food shelf life of film, since the preservative film of the application uses plant polyphenol, cottonseed protein, konjac glucomannan, carboxymethyl cellulose and nano silicon dioxide powder as main raw materials, so that preservative film has degradable performance.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of protein, fiber composition and preservative film preparation in biological industry, and more particularly, the present application relates to a preparation method of a plant polyphenol / cottonseed protein multifunctional film for food preservation. BACKGROUND

[0002] In the modern food industry, as an important means to protect food quality and extend shelf life, the performance and safety of preservative films have been widely concerned. Traditional preservative film materials, such as polyethylene (PE), polypropylene (PP) and other synthetic plastics, have good mechanical properties and processability, but their non-degradability has caused long-term pressure on the environment, and these materials themselves do not have antibacterial or antioxidant functions, which is difficult to meet the growing demand for green and healthy consumption.

[0003] Therefore, developing an environmentally friendly and functional preservative film material has become a hot research topic. Plant protein-based preservative films, as a new type of biodegradable material, have shown great application potential in the field of food packaging due to their good biocompatibility, degradability and controllable functionality. Among them, cottonseed protein, as a widely available and low-cost agricultural byproduct, has a high content of amino acids and modifiable functional groups, providing a material basis for preparing high-performance preservative films.

[0004] However, single cottonseed protein film still has deficiencies in mechanical strength, water resistance and functionality, which limits its widespread application in practical application. In order to overcome these defects, researchers have begun to explore methods to improve its performance through chemical modification. Plant polyphenols, as a natural antioxidant widely existing in nature, not only have rich hydroxyl groups, which can endow the material with excellent antioxidant and antibacterial properties, but also can combine with protein molecules through covalent and non-covalent bonds to enhance the stability and functionality of the material. Currently, there is still a lack of related research on the preparation of preservative films using plant polyphenols combined with cottonseed protein. SUMMARY

[0005] An object of the present application is to solve at least the above problems and / or deficiencies, and to provide at least the advantages described later.

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

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

[0008] Preferably, wherein the plasticizer is one of glycerol, sorbitol, epoxy soybean oil, citric acid triester, acetyl citric acid tributyl ester.

[0009] Preferably, wherein the crosslinking agent is glutaraldehyde or genipin.

[0010] A preparation method of a plant polyphenol / cottonseed protein multifunctional film for food preservation, comprising the following steps:

[0011] Step one, heat the deionized water to 40~60℃, dissolve the plant polyphenol in the deionized water, stir to obtain a plant polyphenol solution; dissolve the cottonseed protein powder in the deionized water, stir to obtain a cottonseed protein powder solution;

[0012] Step two, stir the cottonseed protein powder solution at a certain speed, then drop in the crosslinking agent drop by drop, continue to stir and then stand still, to obtain a crosslinking system; stir the crosslinking system at a certain speed, drop in the plant polyphenol solution drop by drop into the crosslinking system, continue to stir, after the dropwise addition is completed, heat to 60~80℃ for 1~2h, stop stirring, and cool to obtain a plant polyphenol modified cottonseed protein;

[0013] Step three, put konjac glucomannan, carboxymethyl cellulose, and nano silicon dioxide into deionized water, ultrasonic dispersion to obtain a mixed suspension;

[0014] Step four, mix the mixed suspension with the plant polyphenol modified cottonseed protein, and add a plasticizer, ultrasonic oscillation at 40~120kHz for 1~3h, then stand still for aging for 12~24h to obtain a film forming solution; pour the film forming solution onto the surface of a glass plate, flow casting of the film forming solution on the surface of the glass plate to form a film, use a scraper to scrape and smooth the film, dry at a temperature of 30~55℃ for 12~24h to obtain a plant polyphenol / cottonseed protein multifunctional film.

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

[0016] Preferably, in step two, the stirring speed for obtaining the crosslinking system is 200~400rpm, the stirring time is 40~60min, and the standing time is 1~3h; the stirring speed for dropping in the plant polyphenol solution is 600~1200rpm.

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

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

[0019] The nano-silica with a particle size distribution of 10-200 nm is added into an ethanol solution, and polyethylene glycol-200 is added as a dispersant, and ultrasonic dispersion is carried out, the ultrasonic dispersion frequency is 20-40 kHz, and the ultrasonic dispersion time is 20-50 min; bis (dioctyloxy pyrophosphonate) ethylene titanate and 1,2-propanediol are added into the ethanol solution, and after ultrasonic dispersion at 60-120 kHz for 10-30 min, standing for 1-5 h, heating to 50-80 DEG C and keeping for 5-15 min, cooling to room temperature, and filtering and drying, the modified nano-silica is obtained.

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

[0021] The application has at least the following beneficial effects: the application discloses a preparation method of a plant polyphenol / cottonseed protein multifunctional film for food preservation, uses plant polyphenols to modify cottonseed protein to prepare a preservation film, modifies the plant polyphenols on the cottonseed protein structure through a covalent grafting method, adds a certain amount of plasticizer to form a film at room temperature, and obtains a plant polyphenol / cottonseed protein preservation film. The abundant hydroxyl groups of the plant polyphenols improve the antibacterial property, the antioxidant property and the performance of prolonging the shelf life of the film, and meanwhile, the preservation film uses plant polyphenols, cottonseed protein, konjac glucomannan, carboxymethyl cellulose and nano-silica powder as main raw materials, so that the preservation film has good degradability.

[0022] The plant polyphenol / cottonseed protein multifunctional film for food preservation prepared in the application adds nano-silica, improves the mechanical property of the preservation film, improves the elongation at break of the preservation film, and further improves the durability of the preservation film.

[0023] Meanwhile, the polyethylene glycol-200 is used to disperse the nano-silica, and the bis (dioctyloxyphosphato) ethylene titanate is used to coat the nano-silica, so that the modified nano-silica is prepared. In the preparation process, the polyethylene glycol-200 is used to disperse the nano-silica into a uniform dispersion system in the ethanol solution, so that the agglomeration of the nano-silica is reduced. Then, the bis (dioctyloxyphosphato) ethylene titanate is added, and the 1,2-propanediol is added as a dispersant at the same time, so that the nano-silica is dispersed in the modification process, and the uniformity of the coating of the bis (dioctyloxyphosphato) ethylene titanate on the nano-silica is improved. The modified nano-silica prepared by the above preparation method has high dispersibility, small agglomeration, and good compatibility with the cottonseed protein powder, konjac glucomannan and carboxymethyl cellulose. After the 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 by the plant polyphenol, and also has excellent fluidity and plasticity, so that the mechanical properties of the preservative film are further improved.

[0024] Other advantages, objects, and features of the present application will be better understood from the following description taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF DRAWINGS

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

[0026] The present application will be further described below in conjunction with the accompanying drawings, so that those skilled in the art can implement the present application according to the description and drawings.

[0027] It should be understood that the terms such as "have", "contain" and "include" used herein do not exclude the presence or addition of one or more other elements or combinations thereof.

[0028] Example 1

[0029] The present embodiment provides a preparation method of a plant polyphenol / cottonseed protein multifunctional film for food preservation, which comprises the following steps:

[0030] Step one, 200 mL of deionized water is heated to 40 DEG C, 10 g of tea polyphenol is dissolved in the deionized water, and stirring is performed to obtain a tea polyphenol solution; 30 g of cottonseed protein powder is dissolved in 500 mL of deionized water, and stirring is performed to obtain a cottonseed protein powder solution; wherein, the scanning electron microscope image of the cottonseed protein powder (CPI) used in the present embodiment is as shown in Figure 1 ;

[0031] Step two, stirring the cottonseed protein powder solution at a speed of 400 rpm, then drop by drop into 2g glutaraldehyde, continue to stir for 40 min, then stand for 3h, get the cross-linking system; stirring the cross-linking system at a speed of 1200 rpm, drop by drop into the cross-linking system tea polyphenol solution, continue to stir, after the dropwise addition is completed, the temperature is raised to 80℃ and kept for 2h, stop stirring, and after cooling, tea polyphenol modified cottonseed protein is obtained;

[0032] Step three, 5g konjac glucomannan, 2g carboxymethyl cellulose and 6g nano silicon dioxide are put into 100mL deionized water, ultrasonic dispersion, ultrasonic frequency is 60kHz, ultrasonic time is 20min, get mixed suspension;

[0033] Step four, mix the mixed suspension with the polyphenol modified cottonseed protein, and add 1g glycerol, ultrasonic oscillation for 2h, then stand for 12h, get the film forming liquid; pour the film forming liquid on the surface of the glass plate, the film forming liquid is cast on the surface of the glass plate, use a scraper to scrape the film to be flat, dry at a temperature of 40℃ for 12h to get a plant polyphenol / cottonseed protein multifunctional film.

[0034] Example 2

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

[0036] Step one, heat 200mL deionized water to 50℃, dissolve 15g apple polyphenol in the deionized water, stir to get apple polyphenol solution; dissolve 40g cottonseed protein powder in 600mL deionized water, stir to get cottonseed protein powder solution;

[0037] Step two, stirring the cottonseed protein powder solution at a speed of 400 rpm, then drop by drop into 4g glutaraldehyde, continue to stir for 50 min, then stand for 3h, get the cross-linking system; stirring the cross-linking system at a speed of 1200 rpm, drop by drop into the cross-linking system apple polyphenol solution, continue to stir, after the dropwise addition is completed, the temperature is raised to 80℃ and kept for 2h, stop stirring, and after cooling, apple polyphenol modified cottonseed protein is obtained;

[0038] Step three, 5g konjac glucomannan, 2g carboxymethyl cellulose and 6g nano silicon dioxide are put into 100mL deionized water, ultrasonic dispersion, ultrasonic frequency is 60kHz, ultrasonic time is 20min, get mixed suspension;

[0039] Step four, mix the mixed suspension with the polyphenol modified cottonseed protein, add 1.2g sorbitol at the same time, and after 3h of 80kHz ultrasonic oscillation, stand and age for 12h to obtain a film forming solution; pour the film forming solution onto the surface of a glass plate, flow and form a film on the surface of the glass plate, use a scraper to scrape and smooth the film, and dry at a temperature of 45℃ for 12h to obtain a plant polyphenol / cottonseed protein multifunctional film.

[0040] Example 3

[0041] The present embodiment provides a preparation method of a plant polyphenol / cottonseed protein multifunctional film for food preservation, comprising the following steps:

[0042] Step one, heat 200mL of deionized water to 60℃, dissolve 20g of white resveratrol in the deionized water, and stir to obtain a white resveratrol solution; dissolve 50g of cottonseed protein powder in 1000mL of deionized water, and stir to obtain a cottonseed protein powder solution;

[0043] Step two, stir the cottonseed protein powder solution at a speed of 400rpm, then drop 6g of glutaraldehyde drop by drop, continue to stir for 60min, and stand for 3h to obtain a crosslinking system; stir the crosslinking system at a speed of 1200rpm, then drop the white resveratrol solution drop by drop into the crosslinking system, continue to stir, after the dropping is completed, heat to 80℃ and keep for 2h, stop stirring, and after cooling, obtain white resveratrol modified cottonseed protein;

[0044] Step three, put 10g of konjac glucomannan, 4g of carboxymethyl cellulose, and 8g of nano silicon dioxide into 100mL of deionized water, ultrasonic dispersion, ultrasonic frequency is 60kHz, ultrasonic time is 20min, to obtain a mixed suspension;

[0045] Step four, mix the mixed suspension with the polyphenol modified cottonseed protein, add 1.5g of epoxy soybean oil at the same time, 80kHz ultrasonic oscillation for 3h, and stand and age for 12h to obtain a film forming solution; pour the film forming solution onto the surface of a glass plate, flow and form a film on the surface of the glass plate, use a scraper to scrape and smooth the film, and dry at a temperature of 55℃ for 12h to obtain a plant polyphenol / cottonseed protein multifunctional film.

[0046] Example 4

[0047] The present embodiment provides a preparation method of a plant polyphenol / cottonseed protein multifunctional film for food preservation, which is different from example 1 in 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 of example 1; wherein the preparation method of the modified nano silicon dioxide is:

[0048] Select 50g particle size distribution in 10~200nm of nanometer silicon dioxide is added to 500mL 60wt% ethanol solution, while adding 2g polyethylene glycol-200 as dispersant, ultrasonic dispersion, ultrasonic dispersion frequency is 40kHz, ultrasonic dispersion time is 50min;To the ethanol solution, add 6g bis (dioctyloxy pyrophosphoric acid ester) ethylene titanium acid ester and 2g 1,2-propanediol, 120kHz ultrasonic dispersion 20min, after 5h, heating to 80℃, keep 10min, cooling to room temperature, filter, dry to obtain modified nanometer silicon dioxide.

[0049] Example 5

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

[0051] Select 80g particle size distribution in 10~200nm of nanometer silicon dioxide is added to ethanol solution, while adding 4g polyethylene glycol-200 as dispersant, ultrasonic dispersion, ultrasonic dispersion frequency is 40kHz, ultrasonic dispersion time is 30min;To the ethanol solution, add 8g bis (dioctyloxy pyrophosphoric acid ester) ethylene titanium acid ester and 3g 1,2-propanediol, 120kHz ultrasonic dispersion 30min, after 5h, heating to 80℃, keep 10min, cooling to room temperature, filter, dry to obtain modified nanometer silicon dioxide.

[0052] Comparative example 1

[0053] The embodiment provides a preparation method of a plant polyphenol / cottonseed protein multifunctional film for food preservation, which is different from example 1 in that modified nanometer silicon dioxide is used to replace nanometer silicon dioxide in step three, and the process parameters of the remaining steps are the same as those of example 1; wherein the preparation method of the modified nanometer silicon dioxide is:

[0054] Comparative example 2

[0055] The embodiment provides a preparation method of a plant polyphenol / cottonseed protein multifunctional film for food preservation. Compared with example 1, the method does not perform the step of modifying the cottonseed protein with tea polyphenols in step two, directly inputs the tea polyphenol solution obtained in step one, the cottonseed protein powder solution and the same amount of konjac glucomannan, carboxymethyl cellulose and nano silicon dioxide in example 1 into deionized water, performs ultrasonic dispersion to obtain a mixed suspension, then adds 1g of glycerol, performs 60kHz ultrasonic oscillation for 2h, and then stands and ages for 12h to obtain a film forming solution; the film forming solution is poured onto the surface of a glass plate, the film forming solution is cast on the surface of the glass plate to form a film, a scraper is used to scrape and coat the film to be flat, and the film is dried at 40 DEG C for 12h to obtain the plant polyphenol / cottonseed protein multifunctional film.

[0056] Comparative example 3

[0057] The comparative example provides a preparation method of a food preservation film, and the steps include:

[0058] Step one, 30g of cottonseed protein powder is dissolved in 500mL of deionized water to obtain a cottonseed protein powder solution;

[0059] Step three, 15g of konjac glucomannan, 2g of carboxymethyl cellulose and 6g of nano silicon dioxide are input into 100mL of deionized water, ultrasonic dispersion is performed, the ultrasonic frequency is 60kHz, and the ultrasonic time is 20min to obtain a mixed suspension;

[0060] Step four, the mixed suspension is mixed with the cottonseed protein powder solution, 1g of glycerol is added, 60kHz ultrasonic oscillation is performed for 2h, and then standing and aging is performed for 12h to obtain a film forming solution; the film forming solution is poured onto the surface of a glass plate, the film forming solution is cast on the surface of the glass plate to form a film, a scraper is used to scrape and coat the film to be flat, and the film is dried at 40 DEG C for 12h to obtain the 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 film for food preservation prepared in example 1 to example 5 and comparative example 1 to comparative example 2 are measured, and the following table is obtained:

[0062] Table 1: Mechanical property test table of film samples

[0063]

[0064] As can be seen from the above table, the plant polyphenol / cottonseed protein multifunctional film for food preservation prepared in Examples 1-5 all have excellent tensile strength, and the tensile strength and elongation at break of Examples 4 and 5 are further improved compared with Examples 1-3, and the tensile strength of the samples of Examples 4 and 5 reaches the standard of PE preservative film in GB / T 10457-2021. At the same time, the elongation at break of the samples prepared in Examples 1-5 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 application can meet the requirements of daily food preservation.

[0065] The antioxidant property of the plant polyphenol / cottonseed protein multifunctional film for food preservation was verified by detecting the clearance rate of the film sample on DPPH free radicals, ABTS + free radicals,

[0066] 0.05g of the plant polyphenol / cottonseed protein multifunctional film for food preservation prepared in Examples 1-5 and 0.05g of the preservative film prepared in Comparative Example 3 were weighed and respectively placed in 10mL of deionized water for oscillation and dissolution, and then centrifuged at 10000rpm for 5min to obtain the supernatant for standby;

[0067] The determination experiment method of DPPH free radical clearance rate is as follows:

[0068] 2mL of the supernatant was mixed with 2.5mL of DPPH methanol solution with a concentration of 0.1mmol, and the mixture was uniformly mixed under dark conditions for 30min, and the absorbance of the mixture was measured at 517nm. The calculation formula of DPPH free radical clearance rate is:

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

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

[0071] The determination experiment method of ABTS + free radical clearance rate is as follows:

[0072] 2mL of the supernatant was mixed with 2.5mL of ABTS +The absorbance of the ABTS+solution was measured at 734nm. The ABTS+radical scavenging rate was calculated according to the following formula:

[0073] RABTS + (%) = (A2-A1) / A0x100%

[0074] In the formula, A2 is the absorbance of the ABTS+solution at 734nm; A1 is the absorbance of the ABTS+solution mixed with the sample solution at 734nm; and A0 is the absorbance of the ABTS+solution mixed with the PBS solution at 734nm. + In the formula, A2 is the absorbance of the ABTS+solution at 734nm; A1 is the absorbance of the ABTS+solution mixed with the sample solution at 734nm; and A0 is the absorbance of the ABTS+solution mixed with the PBS solution at 734nm. + In the formula, A2 is the absorbance of the ABTS+solution at 734nm; A1 is the absorbance of the ABTS+solution mixed with the sample solution at 734nm; and A0 is the absorbance of the ABTS+solution mixed with the PBS solution at 734nm. + In the formula, A2 is the absorbance of the ABTS+solution at 734nm; A1 is the absorbance of the ABTS+solution mixed with the sample solution at 734nm; and A0 is the absorbance of the ABTS+solution mixed with the PBS solution at 734nm.

[0075] The following table was obtained through experiments:

[0076] Table 2: DPPH radical scavenging rate of the film samples

[0077]

[0078] As shown in the above table, the film samples prepared by using the plant polyphenol modified cottonseed protein in Examples 1-5 all have DPPH radical scavenging rate and ABTS + radical scavenging rate of more than 90%, which is much higher than that of Comparative Example 3, indicating that the plant polyphenol / cottonseed protein multifunctional film prepared in Examples 1 and 5 for food preservation has excellent antioxidant property.

[0079] The number of devices and the processing scale described herein are used to simplify the description of the present application. Applications, modifications and variations of the present application are obvious to those skilled in the art.

[0080] Although the embodiments of the present application have been disclosed as above, they are not limited to the applications and embodiments listed in the specification, and can be fully applied to various fields suitable for the present application, and additional modifications can be easily realized by those skilled in the art, and therefore the present application is not limited to specific details and the figures shown and described herein, without departing from the general concept defined by the claims and the equivalent scope.

Claims

1. A method for preparing a plant polyphenol / cottonseed protein multifunctional film for food preservation, characterized by, The plant polyphenol / cottonseed protein multifunctional film comprises 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 crosslinking agent, 5-10 parts of konjac glucomannan, 2-4 parts of carboxymethyl cellulose, 0.2-3 parts of plasticizer, and 5-8 parts of modified nanosilica. The preparation method of the plant polyphenol / cottonseed protein multifunctional film comprises the following steps: In step one, deionized water is heated to 40-60 DEG C, plant polyphenol is dissolved in the deionized water, and stirring is performed to obtain a plant polyphenol solution; cottonseed protein powder is dissolved in the deionized water, and stirring is performed to obtain a cottonseed protein powder solution; In step two, the cottonseed protein powder solution is stirred, and glutaraldehyde or genipin is added dropwise, continuous stirring is performed, and then standing is performed to obtain a crosslinking system; the crosslinking system is stirred, the plant polyphenol solution is added dropwise into the crosslinking system, continuous stirring is performed, the temperature is increased to 60-80 DEG C for 1-2 h after the dropwise addition is completed, stirring is stopped, and cooling is performed to obtain plant polyphenol-modified cottonseed protein; In step three, konjac glucomannan, carboxymethyl cellulose, and modified nanosilica are added into deionized water, and ultrasonic dispersion is performed to obtain a mixed suspension; In step four, the mixed suspension and the plant polyphenol-modified cottonseed protein are mixed, the plasticizer is added, ultrasonic oscillation is performed at 40-120 kHz for 1-3 h, and then standing and aging are performed for 12-24 h to obtain a film-forming solution; the film-forming solution is poured onto the surface of a glass plate, the film-forming solution is cast into a film on the surface of the glass plate, a scraper is used to scrape and coat the film to be flat, and drying is performed at a temperature of 30-55 DEG C for 12-24 h to obtain the plant polyphenol / cottonseed protein multifunctional film. The preparation method of the modified nanosilica comprises the following steps: In the preparation method of the modified nanosilica, nanosilica with a particle size distribution of 10-200 nm is selected, added into an ethanol solution, and ultrasonic dispersion is performed at 20-40 kHz for 20-50 min; bis(dioctyloxyphosphato)ethyl titanate and 1,2-propanediol are added into the ethanol solution, ultrasonic dispersion is performed at 60-120 kHz for 10-30 min, standing is performed for 1-5 h, the temperature is increased to 50-80 DEG C for 5-15 min, and then cooling is performed to room temperature; filtration and drying are performed to obtain the modified nanosilica; the mass / volume ratio of the nanosilica, polyethylene glycol-200, bis(dioctyloxyphosphato)ethyl titanate, 1,2-propanediol, and the ethanol solution is 5-8 g:0.2-0.5 g:0.6-1 g:0.2-1:50-250 mL; and the concentration of the ethanol solution is 60-80 wt%.

2. The method for preparing a plant polyphenol / cottonseed protein multifunctional film for food preservation according to claim 1, characterized by, The plant polyphenol is one of tea polyphenol, apple polyphenol, grape polyphenol, white resveratrol, and bayberry tannin.

3. The method for preparing a plant polyphenol / cottonseed protein multifunctional film for food preservation according to claim 1, characterized by, The plasticizer is triester citric acid.

4. The method for preparing a plant polyphenol / cottonseed protein multifunctional film for food preservation according to claim 1, characterized by, The plasticizer is one of glycerol, sorbitol, epoxy soybean oil, and acetyl tri-butyl citrate.

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

6. The method for preparing a plant polyphenol / cottonseed protein multifunctional film for food preservation according to claim 1, characterized by, In the second step, the stirring speed of the crosslinking system is 200-400 rpm, the stirring time is 40-60 min, and the standing time is 1-3 h; the stirring speed of the plant polyphenol solution is 600-1200 rpm.

7. The method for preparing a plant polyphenol / cottonseed protein multifunctional film for food preservation according to claim 1, characterized by, In the third step, the mass-volume ratio of konjac glucomannan to deionized water is 5-10 g:40-100 mL.

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