Soybean protein isolate coating for inhibiting falling of micro-plastics and preparation method of soybean protein isolate coating

Abstract

The invention discloses a soybean protein isolate coating capable of inhibiting microplastics from falling off and a preparation method of the soybean protein isolate coating, and belongs to the technical field of food packaging. The surface coating is formed on the basis of the soybean protein isolate self-assembled aggregate to inhibit falling of micro-plastic in food plastic packaging, the method is simple in preparation, the raw materials are wide in source and environmentally friendly, the coating can be formed on the surfaces of various plastic substrates, the method can also be suitable for various food systems, excellent biocompatibility is achieved, and the method is suitable for large-scale popularization and application. And the requirements of current food packaging can be met.

Description

Technical Field

[0001] The invention relates to a soybean protein isolate coating for inhibiting the shedding of microplastics and a preparation method thereof, and belongs to the technical field of food packaging. Background Art

[0002] Plastics have become a widely used packaging material in food due to their excellent properties. According to statistics, the current output of plastics in food is about 45 million tons. Microplastics are plastic particles with a diameter greater than 1 μm and less than 5 mm, with regular or irregular shapes, which fall off due to the influence of various external factors (mechanical force, heating, acid / alkali, ultraviolet light and microbial metabolism).

[0003] Microplastics enter the human body through ingestion, inhalation and direct contact, among which ingestion is the main route. Plastic packaging may generate microplastics during processing, storage, transportation and sales, and enter food and be ingested by humans. Currently, the main method to control the intake of microplastics is to reduce the use of plastic-packaged foods, and there are almost no other methods to inhibit the shedding of microplastics in food plastic packaging.

[0004] At the same time, in the food industry, the shedding of microplastics is affected by a variety of factors, including high temperature, high salt, high oil, and acid-base environmental conditions. High temperature may cause thermal decomposition of plastics, causing microplastics to enter food; high salt environment will accelerate plastic aging and increase the release of microplastics; high oil will dissolve additives in plastics and promote the shedding of microplastics; acid-base conditions will also destroy the chemical stability of plastics and cause material degradation. These factors together aggravate the shedding of microplastics and affect food safety, and need to be taken seriously in packaging selection and use.

[0005] At present, there are many processes for preparing coatings, most of which focus on the physical and chemical properties of the coatings, such as antibacterial properties and ductility. There are few coatings that are targeted at reducing the shedding of microplastics, and they perform poorly in harsh environments. For example: Patent CN116289330B discloses the use of soy protein isolate to prepare coatings; Patent CN117818157A discloses the use of soy protein isolate and high methoxy pectin to prepare coatings; Patent CN100341944C discloses the use of soy protein isolate and gelatin to prepare coatings; Patent CN118109125A discloses the use of glutenin and tricarboxyethylphosphine to prepare antibacterial coatings; The document "Preparation and Performance Study of Modified Soy Protein Isolate Film" discloses the use of polycaprolactone modified soy protein isolate to prepare coatings.

[0006] Therefore, developing a coating that can inhibit the shedding of microplastics under relatively harsh conditions has extremely high practical and economic value. Summary of the invention

[0007] To solve the above problems, the present invention forms a surface coating based on self-assembled aggregates of soy protein isolate to inhibit the shedding of microplastics in food plastic packaging. This method is simple to prepare, has a wide source of raw materials and is green. It can not only form a coating on the surface of various plastic substrates, but also is applicable to a variety of food systems and has excellent biocompatibility, which can meet the current needs of food packaging.

[0008] The first object of the present invention is a method for inhibiting the shedding of microplastic particles from a plastic substrate based on a soy protein isolate coating, the method comprising: (1) mixing a soy protein isolate solution and a disulfide bond reducing agent solution to obtain a self-assembly solution; immersing a plastic substrate in the self-assembly solution, incubating, washing, and drying; (2) After drying, the plastic substrate is immersed in a genipin solution, incubated, washed, and dried to obtain a plastic substrate with a soy protein isolate coating on the surface.

[0009] In one embodiment, the concentration of soy protein isolate in the self-assembly solution of step (1) is 10-100 mg / mL; the concentration of the disulfide bond reducing agent solution is 5-100 mM; and the concentration of genipin in the genipin solution of step (2) is 0.1 mg / mL-20 mg / mL.

[0010] In one embodiment, the concentration of the soy protein isolate solution is 30-50 mg / mL; the concentration of the disulfide bond reducing agent solution is 40-60 mM; the concentration of genipin is 0.5 mg / mL-5 mg / mL; preferably, the concentration of genipin is 0.8 mg / mL-1.2 mg / mL.

[0011] In one embodiment, the plastic substrate includes one or more of polyethylene, polypropylene, polyvinyl chloride, polyester, polystyrene, and composite plastics; Preferably, the plastic substrate is food grade polypropylene (PP) or polyethylene terephthalate (PET); More preferably, the plastic substrate is food grade polypropylene (PP).

[0012] In one embodiment, the disulfide bond reducing agent includes any one or more of tris(2-carboxyethyl)phosphine, tris(2-carboxyethyl)phosphine hydrochloride, dithiothreitol, β-mercaptoethanol, sodium borohydride, thiourea dioxide, sodium sulfite, sodium bisulfite, stannous oxide, trismercaptoaluminum chloride, etc.; Preferably, the disulfide bond reducing agent is tris(2-carboxyethyl)phosphine and or dithiothreitol.

[0013] In one embodiment, the preparation method of the soy protein isolate solution is: mixing the soy protein isolate in a NaOH solution to obtain the soy protein isolate solution; the usage ratio of the soy protein isolate to the NaOH solution is 5-20 g: 20-100 mL; and the concentration of the NaOH solution is 0.008-0.012 M.

[0014] In one embodiment, the preparation method of tri(2-carboxyethyl)phosphine (TCEP) solution is: dissolving 50-150 mM tri(2-carboxyethyl)phosphine in PBS buffer, adjusting the pH to 7.5-8.0, and then diluting for use.

[0015] In one embodiment, in step (1), the incubation is performed at 15-50° C. for 5-24 h; and in step (2), the incubation is performed at 25-60° C. for 1-24 h.

[0016] In one embodiment, drying includes one or more of natural drying, forced air drying, vacuum drying, and heat drying.

[0017] A second object of the present invention is to provide a method for preparing a soy protein isolate coating, the method comprising the steps of: (1) mixing a soy protein isolate solution and a disulfide bond reducing agent solution to obtain a self-assembly solution; immersing a substrate in the self-assembly solution, incubating, washing, and drying; (2) After drying, the substrate is immersed in a genipin solution, incubated, washed, and dried; the surface of the substrate is coated with the soy protein isolate; The concentration of soy protein isolate in the self-assembly solution of step (1) is 10-100 mg / mL; the concentration of the disulfide bond reducing agent solution is 5-100 mM; in step (1), the incubation is 15-50° C. for 5-24 h; the concentration of genipin in the genipin solution of step (2) is 0.1 mg / mL-20 mg / mL; in step (2), the incubation is 25-60° C. for 1-24 h; The plastic substrate includes one or more of polyethylene, polypropylene, polyvinyl chloride, polyester, polystyrene, and composite plastics; The disulfide bond reducing agent includes any one or more of tris(2-carboxyethyl)phosphine, tris(2-carboxyethyl)phosphine hydrochloride, dithiothreitol, β-mercaptoethanol, sodium borohydride, thiourea dioxide, sodium sulfite, sodium bisulfite, stannous oxide, and trismercaptoaluminum chloride; Preferably, the disulfide bond reducing agent is tris(2-carboxyethyl)phosphine and or dithiothreitol.

[0018] Drying includes one or more of natural drying, forced air drying, vacuum drying, and heating drying.

[0019] The third object of the present invention is to provide a soy protein isolate coating prepared by the above method.

[0020] The fourth object of the present invention is to provide the use of the above-mentioned soy protein isolate coating in the preparation of food packaging materials.

[0021] A fifth object of the present invention is to provide a food packaging material having a soy protein isolate coating on its surface.

[0022] In one embodiment, the food packaging material includes plastic wrap, plastic cups, plastic boxes, plastic bottles, coated iron cans, etc.

[0023] Beneficial effects of the present invention The present invention forms a surface coating based on self-assembled aggregates of soy protein isolate to inhibit the shedding of microplastics in food plastic packaging. The method is simple to prepare, has a wide source of raw materials and is green. It can not only form a coating on the surface of various plastic substrates, but also be applicable to a variety of food systems and has excellent biocompatibility, which can meet the current needs of food packaging.

[0024] Specifically: (1) The soy protein isolate coating of the present invention can effectively reduce the shedding of microplastics by more than 88.5%; (2) The soy protein isolate coating of the present invention has good biocompatibility at room temperature and high temperature, and the cell inhibition rate is extremely low (less than 5%); (3) The soy protein isolate coating of the present invention has good hydrophobicity and does not affect the properties of the substrate itself (water vapor permeability). BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The contact angle of a single layer of soy protein isolate coating on the PET plastic surface (A); the contact angles of PET, PS, PI, PE, PP, PC and PTFE plastic surfaces with and without soy protein isolate coating (B); the contact angles of coatings prepared with casein, collagen and zein on the plastic surface (C).

[0026] Figure 2 Scanning electron micrographs of the plane (A) and cross-section (B) of a single-layer soy protein isolate coating.

[0027] Figure 3 Typical PP microplastics (A, B) and PET microplastics (C, D) observed under bright field and fluorescence conditions in a fluorescence microscope.

[0028] Figure 4 The number of microplastics shed from PP plastic packaging (A) and the number of microplastics shed per unit area (B).

[0029] Figure 5 The number of microplastics shed from PET plastic packaging (A) and the number of microplastics shed per unit area (B).

[0030] Figure 6 The amount of microplastics shed by coatings obtained with different proteins and preparation methods on PP and PET plastic packaging.

[0031] Figure 7 The number of microplastics shed under alkaline high-oil conditions was inhibited by cross-linked coatings with different genipin concentrations.

[0032] Figure 8 The number of microplastics that are suppressed from falling off by coatings with different numbers of layers.

[0033] Fig. 9 is the cell inhibition rate of monolayer soy protein isolate on HEK293 cells.

[0034] Fig.10 This paper shows the effect of soy protein isolate coating on water vapor transmission rate of PET plastic. DETAILED DESCRIPTION

[0035] The preferred embodiments of the present invention are described below. It should be understood that the embodiments are for better explaining the present invention and are not used to limit the present invention.

[0036] raw material: Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0037] Food-grade polypropylene (PP) plastic bottles were purchased from Binzhou Samsung Packaging Technology Co., Ltd.; food-grade polyethylene terephthalate (PET) and polystyrene (PS) plastic bottles were purchased from Binzhou Longcheng Plastic Co., Ltd.; food-grade polyethylene (PE) plastic was purchased from Wuxi Baimao Plastic Co., Ltd.; food-grade polycarbonate (PC) plastic was purchased from Suzhou Subaijia New Materials Co., Ltd.; food-grade polyimide (PI) was purchased from Dongguan Qiangfeng New Materials Co., Ltd.; food-grade polytetrafluoroethylene (PTFE) was purchased from Langfang Ruixu Sealing Materials Co., Ltd.; Soy protein isolate, genipin, and glutathione were purchased from Shanghai MacLean Biochemical Technology Co., Ltd.; Casein, collagen, and zein were purchased from Sinopharm Biotechnology Co., Ltd.; Tris(2-carboxyethyl)phosphine and tris(2-carboxyethyl)phosphine hydrochloride were purchased from Shanghai Yuanye Biotechnology Co., Ltd.

[0038] Test method: 1. Laboratory quality control methods During the entire experiment, atmospheric deposition, equipment and facilities used, and even the experimenter's clothing may cause sample contamination. Therefore, in order to reduce the resulting errors, the following measures are taken: (1) Before the experiment, the experimental equipment was cleaned with ultrapure water; (2) During the experiment, the experimenter wore cotton clothes and nitrile gloves, and all experiments used glass containers; (3) Close the doors and windows of the laboratory; (4) All processed containers and sample surfaces are sealed with tin foil; (5) Ultrapure water was used as a blank sample to clarify that the sample was almost free of contamination under laboratory conditions.

[0039] 2. Simulate the shedding of microplastics According to the methods provided in "GB 5009.156-2016 National Food Safety Standard General Rules for Pretreatment Methods for Migration Tests on Food Contact Materials and Articles", "GB 31604.1-2023 National Food Safety Standard General Rules for Migration Tests on Food Contact Materials and Articles" and "GB / T 32095.3-2015 Performance and Test Specifications for Non-stick Surfaces of Household Metal Cooking Utensils Part 3: Corrosion Resistance Test Specifications" and improved, the simulation systems are divided into neutral water, acidic water, alkaline water, acidic low oil, acidic high oil, alkaline high oil and high salt systems (see Table 1), and the release levels of microplastics under different simulation systems are compared.

[0040] The thickness of all plastic bottles is less than or equal to 0.5 mm, so the full immersion method was used. According to the requirements of national standards, when the ratio (S / V) of the contact area (S) between the food contact material and the product to the food mass or volume (V) is unknown, it is necessary to use 6 dm 2 The food contact material or product is tested in contact with 1 kg or 1 L of food. Therefore, the plastic bottle is cut into 0.6 dm 2 The plastic pieces were completely immersed in 100 mL of the prepared simulation system. The two were placed in a glass container, heated at 95 ° C and condensed under reflux for 2 h to release microplastics. The blank group was the number of microplastics after ultrapure water without plastic was heated and filtered.

[0041] Table 1 Food simulation system and solution composition

[0042] 3. Quantification of microplastics To simulate the shedding of microplastics, the solution in the glass container was vacuum filtered using glass fiber filter paper with a pore size of 0.45 μm, and the microplastics were filtered on the filter membrane. Subsequently, 20 μg / mL of Nile Red acetone aqueous solution was added to the filter membrane for staining, and they were stored in a glass culture dish and incubated in an oven at 60 °C for 15 min. Then, a fluorescence microscope was used to perform preliminary visual observation and microscopic counting of the microplastics on the filter paper under bright field conditions and fluorescence conditions (excitation wavelength range of 450-490 nm, emission wavelength range of 515-565 nm), so that the number of microplastics in the solution could be determined. The counted microplastics are particles that can be observed to emit obvious fluorescence under a fluorescence microscope.

[0043] 4. Cell proliferation inhibition rate detection The effect of the coating on the viability of HEK293 cells was evaluated by CCK-8 assay. The PET plastic sheets with a single layer of coating were immersed in 2 mL of saline for 24 h at 37°C and 95°C to obtain the extract. Then, the extract was filtered and DEME medium and fetal bovine serum (FBS) were added to prepare a medium containing 10% FBS. 100 μL of cells with a density of 30,000 cells / cm 2 The cell suspension was transferred to a 96-well plate and incubated in a 37°C, 5% CO2 incubator for 24 h. 2 / mL) of culture medium. After 24, 48, and 72 h of culture, 5 μL of CCK-8 was added to each well. After incubation for 2 h, the solution was mixed using a shaker; 5-Fu (5-fluorouracil) (5 μg / mL) was used as a positive control. Finally, the absorbance value at 450 nm was tested using a microplate reader.

[0044] 5. Determination of water vapor transmission rate The water vapor permeation rate was determined by the gravimetric method. A permeable cup (30 mm × 50 mm weighing bottle) filled with 10 mL of deionized water was sealed with a PET film coated with a single layer of soy protein isolate, and the initial weight was recorded and placed in a desiccator. The weight of the permeable cup was measured every 12 h for a total of 6 days.

[0045] Example 1 A method for preparing a soy protein isolate coating for inhibiting the shedding of microplastics comprises the steps of: (1) Take 10 g of soy protein isolate in 50 mL of NaOH (0.01 M) solution and stir at 500 rpm for 1 h. Then add 50 mL of phosphate buffer (PBS, 10 mM, pH 7.4) and continue stirring for 1 h. Centrifuge at 4000 rpm for 10 min to obtain the supernatant. Dilute to obtain a 40 mg / mL soy protein isolate solution and store in a refrigerator at 4 ℃ for later use. (2) 100 mM tri(2-carboxyethyl)phosphine (TCEP) was dissolved in PBS buffer, and the pH was adjusted to 8.0 with NaOH solution to obtain TCEP solution; the soy protein isolate solution and the TCEP solution were mixed in a volume ratio of 1:1 to obtain a self-assembly solution, wherein the final concentration of the soy protein isolate was 20 mg / mL and the final concentration of TCEP was 50 mM; (3) An 8 cm × 8 cm plastic substrate (PET) was immersed in the self-assembly solution, incubated at 28 °C for 12 h, rinsed with ultrapure water and dried; then immersed in an acetone solution of 1 mg / mL genipin, incubated at 55 °C for 6 h, rinsed with ultrapure water and dried. The surface of the plastic substrate was coated with soy protein isolate (single layer).

[0046] The plastic substrates were changed to polystyrene (PS), polyimide (PI), polyethylene (PE), polypropylene (PP), polycarbonate (PC) and polytetrafluoroethylene (PTFE) respectively to prepare different plastic substrates with soy protein isolate coating.

[0047] Comparative Example 1 The plastic substrate (PP, PET) is not soaked, that is, the surface of the plastic substrate is not coated with soy protein isolate.

[0048] Comparative Example 2 On the basis of Example 1, the acetone solution of 1 mg / mL genipin was not used to immerse the plastic substrate, and the remaining steps were consistent with Example 1.

[0049] Comparative Example 3 On the basis of Example 1, the concentration of genipin in step (3) was changed to 0.01 mg / mL, and the remaining steps were consistent with Example 1.

[0050] Comparative Example 4 On the basis of Example 1, the concentration of genipin in step (3) was changed to 0.1 mg / mL, and the remaining steps were consistent with Example 1.

[0051] Comparative Example 5 On the basis of Example 1, soy protein isolate was replaced by casein, and step (1) was changed as follows: 50 mL of 0.01 M sodium hydroxide solution was added to 10 g of casein, heated to boil over low heat, and then the volume was adjusted to 100 mL with PBS buffer to obtain a casein solution, and a protein solution with a final concentration of 40 mg / mL was prepared. The remaining steps were consistent with Example 1.

[0052] Comparative Example 6 On the basis of Example 1, soy protein isolate was replaced by collagen, and step (1) was changed as follows: 50 mL of 0.3% v / v acetic acid solution was added to 10 g of collagen, and after it was completely dissolved, the volume was adjusted to 100 mL with PBS buffer to obtain a collagen solution, and a protein solution with a final concentration of 40 mg / mL was prepared. The remaining steps were consistent with Example 1.

[0053] Comparative Example 7 On the basis of Example 1, soy protein isolate was replaced by zein, and step (1) was changed as follows: 50 mL of ethanol was added to 10 g of zein, and after it was completely dissolved, the volume was fixed to 100 mL with PBS buffer to obtain a zein solution, and a protein solution with a final concentration of 40 mg / mL was prepared. The remaining steps were consistent with Example 1.

[0054] Comparative Example 8 On the basis of Example 1, step (3) was changed as follows: genipin (at a concentration of 1 mg / mL) was added to the self-assembly solution to prepare a mixed solution, an 8 cm×8 cm plastic substrate was immersed in the self-assembly solution, incubated at 28°C for 12 h, rinsed with ultrapure water, and dried, so that the surface of the plastic substrate was coated with soy protein isolate, and the remaining steps were consistent with Example 1.

[0055] The results showed that this method could not prepare soy protein isolate coating.

[0056] Comparative Example 9 On the basis of Example 1, step (3) was changed as follows: immersing the 8 cm×8 cm plastic substrate in an acetone solution of 1 mg / mL genipin, incubating for 6 h, rinsing with ultrapure water, and drying; then immersing in a self-assembly solution, incubating at 28°C for 12 h, rinsing with ultrapure water, and drying; the surface of the plastic substrate was coated with soy protein isolate, and the remaining steps were consistent with Example 1.

[0057] Example 2 The plastic substrates obtained in Example 1 and Comparative Examples 1 to 9 were taken to test the coating properties.

[0058] (1) Hydrophobicity Example 1 The hydrophobicity test results of the plastic surface are as follows Figure 1As shown, the results show that the contact angle reaches 84.9°, that is, the soy protein isolate coating can change the hydrophilicity and hydrophobicity of the plastic packaging surface; when the plastic substrate is changed to polyethylene terephthalate (PET), polystyrene (PS), PI (polyimide), polyethylene (PE), polypropylene (PP), polycarbonate (PC) and polytetrafluoroethylene (PTFE), they all have good hydrophobicity. It can be seen that the soy protein isolate coating is suitable for most plastics.

[0059] (2) Cross section The cross section of the plastic substrate of Example 1 is as follows Figure 2 As shown, the results indicate that the surface of the soy protein isolate coating is composed of rough granular structures connected to each other to form a complete plane, while in the cross-sectional view it can be found that the coating is formed by dense accumulation of fine nanoparticles, thereby resisting the shedding of microplastics.

[0060] Fluorescent photos of microplastic particles Figure 3 As shown, it can be seen that the diameter of microplastic particles is 80~280 μm.

[0061] (3) Microplastic concentration The microplastic shedding results of Example 1 (PP) and Comparative Example 1 (PP) under different conditions are as follows: Figure 4 As shown; the microplastic shedding results of Example 1 (PET) and Comparative Example 1 (PET) under different conditions are shown Figure 5 As shown; the results show that the coated plastic substrate can significantly reduce the shedding of microplastics under different extreme conditions, and the concentration of microplastics in the solution is significantly lower than that in Comparative Example 1.

[0062] The microplastic shedding results of Comparative Examples 1, 5, 6, 7, and 9 are as follows: Figure 6 As shown, the results indicate that the coating prepared without using genipin or with a reduced concentration of genipin has a poor effect on the shedding of microplastics, which is lower than that of Example 1.

[0063] The microplastic shedding results of Example 1, Comparative Examples 2, 3, and 4 are as follows: Figure 7 As shown, the results indicate that when the protein type was changed, the prepared coating had no effect on reducing the shedding of microplastics.

[0064] (4) Cell proliferation inhibition rate The PET plastic substrate prepared in Example 1 was tested for cytotoxicity. Fig. 9 As shown, the inhibitory rates of the extracts of the soy protein isolate coating obtained at 37°C and 95°C on HEK293 cell proliferation were both lower than 10% within 24 to 72 h, indicating that the coating had no obvious cytotoxicity.

[0065] (5) Breathability The PET plastic substrate prepared in Example 1 was used to test the water vapor transmission rate. Fig.10 As shown, compared with no coating (33.58 g / m 2 ·24h) water vapor transmission rate is compared with the single layer (32.28 g / m 2 ·24h) The coating has little effect on the water vapor transmission rate of the substrate.

[0066] The above results show that the soy protein isolate coating prepared in Example 1 can effectively reduce the shedding of microplastics, has good hydrophobicity and biosafety, and does not affect the properties of the substrate itself.

[0067] Example 3 Based on Example 1, the plastic substrate with the soy protein isolate coating (single layer) is soaked once again in step (3) to prepare a plastic substrate with a soy protein isolate coating (double layer); The plastic substrate with the soy protein isolate coating (double layer) is soaked once again in step (3) to prepare a plastic substrate with the soy protein isolate coating (three layers).

[0068] The effects of different layers of soy protein isolate coatings in Example 1 and Example 3 on the shedding of microplastics and the water vapor transmission rate were tested. The results are as follows: Figure 8 , Fig.10 As shown, the results indicate that as the number of coating layers increases, the shedding of microplastics can be further reduced, and the double-layer coating has little effect on the water vapor permeability.

[0069] Comparative Example 10 On the basis of Example 1, TCEP was replaced by glutathione, and the remaining steps were consistent with Example 1.

[0070] The results showed that this method could not prepare soy protein isolate coating.

[0071] Example 4 On the basis of Example 1, TCEP was replaced by dithiothreitol, and the 1 mg / mL genipin acetone solution was not used to soak the plastic substrate. The remaining steps were consistent with Example 1.

[0072] Example 5 On the basis of Example 1, TCEP was replaced by dithiothreitol, and the remaining steps were consistent with Example 1.

[0073] The anti-falling effect of microplastics in Example 4 and Example 5 is as follows: Figure 7As shown, the results show that the soy protein isolate coating prepared using only dithiothreitol can reduce the shedding of microplastics, but the effect is poor; while the soy protein isolate coating prepared using dithiothreitol and genipin has a certain effect in preventing the shedding of microplastics, and its effect is slightly lower than that in Example 1. It can be seen that not all disulfide bond reducing agents can achieve good results in the process of preparing the coating.

[0074] Although the present invention has been disclosed as above in the form of a preferred embodiment, it is not intended to limit the present invention. Anyone familiar with this technology can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be based on the definition of the claims.

Claims

1. A method for inhibiting the shedding of microplastic particles from a plastic substrate based on a soy protein isolate coating, characterized in that: The method comprises the steps of: (1) A 30-50 mg / mL soy protein isolate solution and a 40-60 mM tri(2-carboxyethyl)phosphine solution were mixed at a volume ratio of 0.8-1.2:0.8-1.2 to obtain a self-assembly solution; a plastic substrate was immersed in the self-assembly solution, incubated, washed, and dried; (2) After drying, the plastic substrate is immersed in a 0.5 mg / mL to 5 mg / mL genipin solution, incubated, washed, and dried to obtain a plastic substrate with a soy protein isolate coating on the surface.

2. The method according to claim 1, characterized in that The plastic substrate includes one or more of polyethylene, polypropylene, polyvinyl chloride, polyester, polystyrene, and composite plastics.

3. The method according to claim 1, characterized in that In step (1), the incubation is at 15-50°C for 5-24 h.

4. The method according to claim 1, characterized in that In step (2), the incubation is at 25-60°C for 1-24 h.

5. The method according to claim 1, characterized in that The drying may be any one of natural drying, air-blast drying, vacuum drying, and heat drying.

6. A method for preparing a soy protein isolate coating, characterized in that: The method comprises the steps of: (1) A 30-50 mg / mL soy protein isolate solution and a 40-60 mM tri(2-carboxyethyl)phosphine solution were mixed at a volume ratio of 0.8-1.2:0.8-1.2 to obtain a self-assembly solution; a substrate was immersed in the self-assembly solution, incubated, washed, and dried; (2) After drying, the plastic substrate is immersed in a 0.5 mg / mL to 5 mg / mL genipin solution, incubated, washed, and dried, and the surface of the substrate is coated with soy protein isolate.

7. The method according to claim 6, characterized in that In step (1), the incubation is at 15-50°C for 5-24 h; in step (2), the incubation is at 25-60°C for 1-24 h.

8. The soy protein isolate coating prepared by the method according to any one of claims 6 to 7.

9. Use of the soy protein isolate coating according to claim 8 in preparing food packaging materials.

10. A food packaging material, characterized in that: The surface of the food packaging material is coated with a soybean protein isolate coating.

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