A soy protein isolate coating for inhibiting microplastic shedding and its preparation method

Abstract

The present invention discloses a soy protein isolate coating for inhibiting the shedding of microplastics and a preparation method thereof, belonging to the technical field of food packaging. The present invention is based on the self-assembled aggregates of soy protein isolate to form a surface coating for inhibiting the shedding of microplastics in food plastic packaging. This method is simple to prepare, has a wide range of raw material sources 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, meeting the current needs of food packaging.

Description

Technical Field

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

[0002] Plastic has become a widely used packaging material in food due to its excellent properties. It is estimated that the current plastic production in food is about 45 million tons. Microplastics are plastic particles with a diameter greater than 1 μm and less than 5 mm, having regular or irregular shapes, and are shed due to the influence of various external factors (mechanical force, heating, acid / alkali, ultraviolet light, and microbial metabolism) on plastics.

[0003] The main ways for microplastics to enter the human body include ingestion, inhalation, and direct contact, etc., among which ingestion is the most main route. Plastic packaging may generate microplastics during processing, storage, transportation, and sales, and enter food to be ingested by humans. Currently, the main method to control microplastic ingestion is to reduce the consumption of foods packaged in plastics, and there are almost no other methods to inhibit the shedding of microplastics in food plastic packaging.

[0004] Meanwhile, in the food field, the shedding of microplastics is affected by various factors, including environmental conditions such as high temperature, high salt, high oil, and acid / base. High temperature may trigger the thermal decomposition of plastics, resulting in microplastics entering food; a high-salt environment accelerates plastic aging and increases microplastic release; high oil dissolves additives in plastics and promotes microplastic shedding; acid / base conditions also destroy the chemical stability of plastics, leading to material degradation. These factors together exacerbate the shedding of microplastics and affect food safety, which need to be emphasized in packaging selection and use.

[0005] Currently, there are many coating preparation processes, mostly focusing on the physical and chemical properties of coatings, such as antibacterial properties, ductility, etc. There are few coatings targeting the reduction of microplastic shedding, and they perform poorly under relatively harsh conditions. For example: Patent CN116289330B discloses the preparation of a coating using soy protein isolate; Patent CN117818157A discloses the preparation of a coating using soy protein isolate and high-methoxyl pectin; Patent CN100341944C discloses the preparation of a coating using soy protein isolate and gelatin; Patent CN118109125A discloses the preparation of an antibacterial coating using gluten and tricarboxyethylphosphine; the literature "Study on the Preparation and Properties of Modified Soy Protein Isolate Films" discloses the preparation of a coating using polycaprolactone-modified soy protein isolate.

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

[0007] To solve the above problems, the present invention forms a surface coating based on the 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 range of raw material sources 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, meeting 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 plastic substrates based on a soy protein isolate coating, and the method includes:

[0009] (1) Mix a soy protein isolate solution and a disulfide bond reducing agent solution to obtain a self-assembly solution; immerse the plastic substrate in the self-assembly solution, incubate, wash, and dry.

[0010] After drying, immerse the plastic substrate in a genipin solution, incubate, wash, and dry to obtain a plastic substrate with a soy protein isolate coating on its surface.

[0011] In one embodiment, the concentration of soy protein isolate in the self-assembly solution in step (1) is 10 - 100 mg / mL; the concentration of the disulfide bond reducing agent solution is 5 - 100 mM; the concentration of genipin in the genipin solution in step (2) is 0.1 mg / mL - 20 mg / mL.

[0012] 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.

[0013] In one embodiment, the plastic substrate includes one or more of polyethylene, polypropylene, polyvinyl chloride, polyester, polystyrene, and composite plastics;

[0014] Preferably, the plastic substrate is food-grade polypropylene (PP) or polyethylene terephthalate (PET);

[0015] More preferably, the plastic substrate is food-grade polypropylene (PP).

[0016] 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, and trichloromercaptoaluminum;

[0017] Preferably, the disulfide bond reducing agent is tris(2-carboxyethyl)phosphine and / or dithiothreitol.

[0018] In one embodiment, the method for preparing the soy protein isolate solution is as follows: Dissolve soy protein isolate in an NaOH solution and mix well to obtain a soy protein isolate solution; the dosage ratio of soy protein isolate to the NaOH solution is 5 - 20 g: 20 - 100 mL; the concentration of the NaOH solution is 0.008 - 0.012 M.

[0019] In one embodiment, the method for preparing the tris(2 - carboxyethyl)phosphine (TCEP) solution is as follows: Dissolve 50 - 150 mM tris(2 - carboxyethyl)phosphine in PBS buffer, adjust the pH to 7.5 - 8.0, and dilute for subsequent use.

[0020] In one embodiment, in step (1), the incubation is carried out at 15 - 50 °C for 5 - 24 h; in step (2), the incubation is carried out at 25 - 60 °C for 1 - 24 h.

[0021] In one embodiment, the drying includes one or more of natural drying, forced - air drying, vacuum drying, and heat drying.

[0022] The second object of the present invention is to provide a method for preparing a soy protein isolate coating, and the method includes the steps:

[0023] (1) Mix the soy protein isolate solution and the disulfide - bond reducing agent solution to obtain a self - assembly solution; immerse the substrate in the self - assembly solution, incubate, wash, and dry;

[0024] (2) After drying, immerse the substrate in the genipin solution, incubate, wash, and dry; the surface of the substrate is the soy protein isolate coating;

[0025] In the self - assembly solution of step (1), the concentration of soy protein isolate is 10 - 100 mg / mL; the concentration of the disulfide - bond reducing agent solution is 5 - 100 mM; in step (1), the incubation is carried out at 15 - 50 °C for 5 - 24 h; in the genipin solution of step (2), the concentration of genipin is 0.1 mg / mL - 20 mg / mL; in step (2), the incubation is carried out at 25 - 60 °C for 1 - 24 h;

[0026] The plastic substrate includes one or more of polyethylene, polypropylene, polyvinyl chloride, polyester, polystyrene, and composite plastics;

[0027] 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 aluminum trichloride trisulfide;

[0028] Preferably, the disulfide - bond reducing agent is tris(2 - carboxyethyl)phosphine and / or dithiothreitol.

[0029] Drying includes one or more of natural drying, air-blowing drying, vacuum drying, and heat drying.

[0030] The third object of the present invention is to provide a soy protein isolate coating prepared by the above method.

[0031] The fourth object of the present invention is to provide the application of the above soy protein isolate coating in the preparation of food packaging materials.

[0032] The fifth object of the present invention is to provide a food packaging material, and the surface of the food packaging material is provided with a soy protein isolate coating.

[0033] In one embodiment, the food packaging material includes plastic wrap, plastic cups, plastic boxes, plastic bottles, film-coated iron metal cans, etc.

[0034] Advantages of the present invention

[0035] Based on the self-assembled aggregates of soy protein isolate to form a surface coating to inhibit the shedding of microplastics in food plastic packaging, the method is simple to prepare, has a wide range of raw material sources 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, meeting the current needs of food packaging.

[0036] Specifically:

[0037] (1) The soy protein isolate coating of the present invention can effectively reduce the shedding of microplastics by more than 88.5%.

[0038] (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%).

[0039] (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 transmission rate). Description of the drawings

[0040] Figure 1 Contact angle of the soy protein isolate monolayer coating on the PET plastic surface (A); contact angles of PET, PS, PI, PE, PP, PC, and PTFE plastic surfaces without and with the soy protein isolate coating (B); contact angles of coatings prepared from casein, collagen, and zein on the plastic surface (C).

[0041] Figure 2 Scanning electron microscope plan view (A) and cross-section (B) of the monolayer soy protein isolate coating.

[0042] Figure 3Typical PP microplastics (A, B) and PET microplastics (C, D) observed under bright field and fluorescence conditions in a fluorescence microscope.

[0043] Figure 4 The number of microplastics shed from PP plastic packaging (A) and the number of microplastics shed per unit area (B).

[0044] Figure 5 The number of microplastics shed from PET plastic packaging (A) and the number of microplastics shed per unit area (B).

[0045] Figure 6 The number of microplastics shed from PP and PET plastic packaging by coatings obtained with different proteins and preparation methods.

[0046] Figure 7 The number of microplastics whose shedding is inhibited by cross-linked coatings with different genipin concentrations under alkaline high-oil conditions.

[0047] Figure 8 The number of microplastics whose shedding is inhibited by coatings with different numbers of layers.

[0048] Figure 9 The cell inhibition rate of monolayer soy protein isolate on HEK293.

[0049] Figure 10 The effect of soy protein isolate coating on the water vapor transmission rate of PET plastic. Detailed implementation manners

[0050] The following are descriptions of the preferred embodiments of the present invention. It should be understood that the embodiments are for better explaining the present invention and are not used to limit the present invention.

[0051] Raw materials:

[0052] Unless otherwise specifically stated, all kinds of raw materials, reagents, instruments, and equipment used in the present invention can be obtained through market purchase or can be prepared by existing methods.

[0053] Food-grade polypropylene (PP) plastic bottles are purchased from Binzhou Sanxing Packaging Technology Co., Ltd.; food-grade polyethylene terephthalate (PET) and polystyrene (PS) plastic bottles are purchased from Binzhou Longcheng Plastics Industry Co., Ltd.; food-grade polyethylene (PE) plastics are purchased from Wuxi Baimao Plastic Co., Ltd.; food-grade polycarbonate (PC) plastics are purchased from Suzhou Subaijia New Materials Co., Ltd.; food-grade polyimide (PI) is purchased from Dongguan Qiangfeng New Materials Co., Ltd.; food-grade polytetrafluoroethylene (PTFE) is purchased from Langfang Ruixu Sealing Materials Co., Ltd.

[0054] Soy protein isolate, genipin, and glutathione are purchased from Shanghai Macklin Biochemical Co., Ltd.

[0055] Casein, collagen, and zein were purchased from Sinopharm Biotech Co., Ltd.

[0056] Tris(2-carboxyethyl)phosphine and tris(2-carboxyethyl)phosphine hydrochloride were purchased from Shanghai Yuanye Bio-Technology Co., Ltd.

[0057] Testing method:

[0058] 1. Laboratory quality control method

[0059] During the entire experimental process, atmospheric deposits, the equipment and facilities used, and even the clothing of the experimenters can cause sample contamination. Therefore, to reduce the resulting errors, the following measures are taken:

[0060] (1) Before the experiment, the experimental equipment was cleaned with ultrapure water.

[0061] (2) During the experiment, the experimenters wore cotton clothes and nitrile gloves, and all experiments were carried out using glass containers.

[0062] (3) The laboratory doors and windows were closed.

[0063] (4) All processed containers and sample surfaces were sealed with tin foil.

[0064] (5) Ultrapure water was used as a blank sample to clarify that the sample was hardly contaminated under laboratory conditions.

[0065] 2. Simulating microplastic shedding

[0066] Based on the methods provided in "GB 5009.156-2016 National Food Safety Standard General Rules for Pretreatment Methods of Migration Tests for Food Contact Materials and Articles", "GB 31604.1-2023 National Food Safety Standard Food Contact Materials and Articles General Rules for Migration Tests", and "GB / T 32095.3-2015 Non-stick Surface Performance and Test Specifications for Household Food Metal Cooking Utensils - Part 3: Corrosion Resistance Test Specifications", and with improvements, the simulation systems were divided into neutral water, acidic water, alkaline water, acidic low-oil, acidic high-oil, alkaline high-oil, and high-salt systems (see Table 1) to compare the release degrees of microplastics under different simulation systems.

[0067] The thickness of all plastic bottles was less than or equal to 0.5 mm, so the full immersion method was adopted. According to the requirements of the national standard, when the ratio (S / V) of the contact area (S) of food contact materials and products to the mass or volume (V) of food is unknown, it is necessary to use 6 dm 2 of food contact materials or products to contact 1 kg or 1 L of food for the experiment. Therefore, the plastic bottles were cut into 0.6 dm 2The plastic sheet was completely immersed in 100 mL of the prepared simulation system. The two were placed together in a glass container and heated at 95 °C with condensation reflux for 2 h to release microplastics. The blank group was the number of microplastics after heating and vacuum filtration of ultrapure water without plastic.

[0068] Table 1 Food simulation system and solution components

[0069]

[0070] 3. Quantification of microplastics

[0071] To simulate microplastic shedding, the solution in the glass container was vacuum filtered using a glass fiber filter paper with a pore size of 0.45 μm, and the microplastics were filtered onto the filter membrane. Subsequently, a 20 μg / mL aqueous solution of Nile red in acetone was dropped onto the filter membrane for staining, and they were stored in a glass petri dish and incubated in an oven at 60 °C for 15 min. Then, the microplastics on the filter paper were preliminarily visually observed and counted under a fluorescence microscope under bright field conditions and fluorescence conditions (excitation wavelength range: 450 - 490 nm, emission wavelength range: 515 - 565 nm), so as to determine the number of microplastics in the solution. The counted microplastics were the particles that could clearly emit fluorescence under the fluorescence microscope.

[0072] 4. Detection of cell proliferation inhibition rate

[0073] The cytotoxicity experiment of the soy protein isolate coating was evaluated by the CCK-8 assay to assess the effect of the coating on the viability of HEK293 cells. The PET plastic sheet with a monolayer coating was immersed in 2 mL of physiological saline at 37 °C and 95 °C for 24 h to obtain the extract. Then, the extract was filtered and added to DEME medium and fetal bovine serum (FBS) to prepare a medium containing 10% FBS. 100 μL of a cell suspension with a cell density of 30,000 cells / cm 2 was transferred to a 96-well plate and inoculated in an incubator at 37 °C and 5% CO2 for 24 h. Media containing different concentrations of the extract (2.88, 1.44, 0.72 cm 2 / mL) were added. After culturing for 24, 48, and 72 h, 5 μL of CCK-8 was added to each well, and 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 measured using a microplate reader.

[0074] 5. Determination of water vapor transmission rate

[0075] The water vapor transmission rate was measured by the gravimetric method. A moisture permeation cup (a weighing bottle of 30 mm×50 mm) containing 10 mL of deionized water was sealed with a PET film coated with a single layer of soy protein isolate, and after recording the initial weight, it was placed in a desiccator. The weight of the moisture permeation cup was measured every 12 h for a total of 6 days.

[0076] Example 1

[0077] A method for preparing a soy protein isolate coating that inhibits the shedding of microplastics, comprising the steps of:

[0078] (1) Take 10 g of soy protein isolate and stir it in 50 mL of NaOH (0.01 M) solution at a rotation speed of 500 rpm for 1 h. Then add 50 mL of phosphate buffer solution (PBS, 10 mM, pH 7.4), continue to stir for 1 h, and centrifuge at 4000 rpm for 10 min to obtain the supernatant. Dilute and prepare a 40 mg / mL soy protein isolate solution, and store it in a refrigerator at 4 °C for later use;

[0079] (2) Dissolve 100 mM tris(2-carboxyethyl)phosphine (TCEP) in PBS buffer solution, and adjust the pH to 8.0 with NaOH solution to obtain a TCEP solution; mix the soy protein isolate solution and the TCEP solution according to a volume ratio of 1:1 to obtain a self-assembled solution, wherein the final concentration of soy protein isolate is 20 mg / mL and the final concentration of TCEP is 50 mM;

[0080] (3) Immerse an 8 cm×8 cm plastic substrate (PET) in the self-assembled solution, incubate it at 28 °C for 12 h, rinse it with ultrapure water and dry it; then immerse it in an acetone solution of 1 mg / mL genipin, incubate it at 55 °C for 6 h, rinse it with ultrapure water and dry it. The surface of the plastic substrate is the soy protein isolate coating (single layer).

[0081] The plastic substrate was changed to polystyrene (PS), polyimide (PI), polyethylene (PE), polypropylene (PP), polycarbonate (PC), and polytetrafluoroethylene (PTFE) respectively, and different plastic substrates with soy protein isolate coatings were prepared.

[0082] Comparative Example 1

[0083] The plastic substrates (PP, PET) were not subjected to the immersion treatment, that is, the surfaces of the plastic substrates did not have soy protein isolate coatings.

[0084] Comparative Example 2

[0085] On the basis of Example 1, the plastic substrate was not immersed in the acetone solution of 1 mg / mL genipin, and the remaining steps were the same as those in Example 1.

[0086] Comparative Example 3

[0087] Based on Example 1, change the concentration of genipin in step (3) to 0.01 mg / mL, and the remaining steps are the same as those in Example 1.

[0088] Comparative Example 4

[0089] Based on Example 1, change the concentration of genipin in step (3) to 0.1 mg / mL, and the remaining steps are the same as those in Example 1.

[0090] Comparative Example 5

[0091] Based on Example 1, replace soy protein isolate with casein, and change step (1) to: add 50 mL of 0.01 M sodium hydroxide solution to 10 g of casein, heat it to boiling over low heat, and then make up the volume to 100 mL with PBS buffer to obtain a casein solution, and prepare a protein solution with a final concentration of 40 mg / mL. The remaining steps are the same as those in Example 1.

[0092] Comparative Example 6

[0093] Based on Example 1, replace soy protein isolate with collagen, and change step (1) to: add 50 mL of 0.3% v / v acetic acid solution to 10 g of collagen, wait until it is completely dissolved, and then make up the volume to 100 mL with PBS buffer to obtain a collagen solution, and prepare a protein solution with a final concentration of 40 mg / mL. The remaining steps are the same as those in Example 1.

[0094] Comparative Example 7

[0095] Based on Example 1, replace soy protein isolate with zein, and change step (1) to: add 50 mL of ethanol to 10 g of zein, wait until it is completely dissolved, and then make up the volume to 100 mL with PBS buffer to obtain a zein solution, and prepare a protein solution with a final concentration of 40 mg / mL. The remaining steps are the same as those in Example 1.

[0096] Comparative Example 8

[0097] Based on Example 1, change step (3) to: add genipin (concentration 1 mg / mL) to the self-assembly solution to prepare a mixed solution, immerse an 8 cm × 8 cm plastic substrate in the self-assembly solution, incubate at 28 °C for 12 h, rinse with ultrapure water and dry, and the surface of the plastic substrate is the soy protein isolate coating. The remaining steps are the same as those in Example 1.

[0098] The results show that the soy protein isolate coating cannot be prepared by this method.

[0099] Comparative Example 9

[0100] On the basis of Example 1, step (3) is changed to: Immerse an 8 cm × 8 cm plastic substrate in an acetone solution of genipin at 1 mg / mL, incubate for 6 h, rinse with ultrapure water and dry; then immerse it in the self-assembly solution, incubate at 28 °C for 12 h, rinse with ultrapure water and dry; the surface of the plastic substrate is the soy protein isolate coating, and the remaining steps are the same as those in Example 1.

[0101] Example 2

[0102] Take the plastic substrates obtained in Example 1 and Comparative Examples 1-9 to detect the coating performance.

[0103] (1) Hydrophobicity

[0104] The hydrophobicity detection results of the plastic surface in Example 1 are as Figure 1 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), all have good hydrophobicity. It can be seen that the soy protein isolate coating is suitable for most plastics.

[0105] (2) Cross-section

[0106] The cross-section of the plastic substrate in Example 1 is as Figure 2 shown. The results show that the surface of the soy protein isolate coating is formed by the rough granular structures connected to each other to form a complete plane, and it can be found from the cross-sectional view that the coating is formed by the dense packing of fine nanoparticles, so as to resist the shedding of microplastics.

[0107] The fluorescence photograph of the microplastic particles is as Figure 3 shown. It can be seen that the diameter of the microplastic particles is 80-280 μm.

[0108] (3) Microplastic concentration

[0109] The microplastic shedding results of Example 1 (PP) and Comparative Example 1 (PP) under different conditions are as Figure 4 shown; the microplastic shedding results of Example 1 (PET) and Comparative Example 1 (PET) under different conditions are as Figure 5 shown; the results show that the plastic substrates with coatings can significantly reduce the microplastic shedding under different extreme conditions, and the microplastic concentration in the solution is significantly lower than that in Comparative Example 1.

[0110] The microplastic shedding results of Comparative Examples 1, 5, 6, 7, and 9 are as Figure 6As shown, the results indicate that the coatings prepared without using genipin or by reducing the concentration of genipin have a poor effect on microplastic shedding, both lower than that of Example 1.

[0111] The results of microplastic shedding in Example 1, Comparative Examples 2, 3, and 4 are as Figure 7 shown. The results show that when the protein type is changed, the prepared coating has no effect on reducing microplastic shedding.

[0112] (4)Cell proliferation inhibition rate

[0113] Take the PET plastic substrate prepared in Example 1 and detect its cytotoxicity. The results are as Figure 9 shown. The leaching solutions obtained from the soy protein isolate coating at 37 °C and 95 °C have a cell proliferation inhibition rate of less than 10% on HEK293 cells within 24 - 72 h, indicating that the coating has no obvious cytotoxicity.

[0114] (5)Gas permeability

[0115] Take the PET plastic substrate prepared in Example 1 and detect the water vapor transmission rate. The results are as Figure 10 shown. Compared with the water vapor transmission rate of the substrate without coating (33.58 g / m 2 ·24 h), the single-layer coating (32.28 g / m 2 ·24 h) has a very small impact on the water vapor transmission rate of the substrate.

[0116] In summary, the results show that the soy protein isolate coating prepared in Example 1 has good hydrophobicity and biosafety on the basis of effectively reducing microplastic shedding, and does not affect the properties of the substrate itself.

[0117] Example 3

[0118] On the basis of Example 1, soak the plastic substrate with a soy protein isolate coating (single layer) once again following the process in step (3) to prepare a plastic substrate with a soy protein isolate coating (double layer);

[0119] Soak the plastic substrate with a soy protein isolate coating (double layer) once again following the process in step (3) to prepare a plastic substrate with a soy protein isolate coating (triple layer).

[0120] Detect the effects of soy protein isolate coatings with different numbers of layers in Example 1 and Example 3 on microplastic shedding and the water vapor transmission rate. The results are as Figure 8 、 Figure 10 shown. The results indicate that as the number of coating layers increases, microplastic shedding can be further reduced, and the double-layer coating has a smaller impact on the water vapor transmission rate.

[0121] Comparative Example 10

[0122] On the basis of Example 1, replace TCEP with glutathione, and the remaining steps are the same as those in Example 1.

[0123] The results show that the soy protein isolate coating cannot be prepared by this method.

[0124] Example 4

[0125] On the basis of Example 1, replace TCEP with dithiothreitol, and do not soak the plastic substrate with a 1 mg / mL genipin acetone solution. The remaining steps are the same as those in Example 1.

[0126] Example 5

[0127] On the basis of Example 1, replace TCEP with dithiothreitol, and the remaining steps are the same as those in Example 1.

[0128] The anti-shedding effects of microplastics in Example 4 and Example 5 are as Figure 7 shown. The results show that the soy protein isolate coating prepared only with dithiothreitol can reduce the shedding of microplastics, but the effect is poor; while the soy protein isolate coating prepared with dithiothreitol and genipin has a certain anti-shedding effect on microplastics, and its effect is slightly lower than that of Example 1. It can be seen that not all disulfide bond reducing agents can achieve good effects during the preparation of the coating.

[0129] Although the present invention has been disclosed above with preferred embodiments, 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 protection scope of the present invention should be defined by 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, immersing the plastic substrate in a 0.8 mg / mL to 1.2 mg / mL genipin solution, incubating, washing, and drying to obtain a plastic substrate with a soy protein isolate coating on the surface; The plastic substrate is food-grade polypropylene or polyethylene terephthalate.

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

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

4. 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.

5. 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 0.8 mg / mL to 1.2 mg / mL genipin solution, incubated, washed, and dried, and the surface of the substrate is coated with the soy protein isolate; The plastic substrate is food-grade polypropylene or polyethylene terephthalate.

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

7. The soy protein isolate coating prepared by the method according to any one of claims 5 to 6.

8. Use of the soy protein isolate coating according to claim 7 in preparing food packaging materials.

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