Preparation method of high-performance soybean protein emulsion film

Abstract

The invention relates to a preparation method of a high-performance soybean protein emulsion film, which comprises the step of carrying out fibrosis denaturation on soybean protein by adopting an acetic acid-water binary solution, so that the hydrophobic property, the film-forming ability and the environmental interference resistance of the soybean protein can be remarkably improved. And further starting from a protein self-assembly fibrosis principle and a protein film forming theory, a soybean protein-based biological membrane with certain mechanical strength and flexibility is constructed through self-assembly fibrosis denaturation of protein molecules in an aqueous solution, so that the problems of poor mechanical property and high solubility of the existing protein-based biological membrane are effectively solved.

Description

Technical Field

[0001] The invention belongs to the technical field of food packaging, and relates to a technology for preparing edible films, in particular to a method for preparing a high-performance soybean protein emulsion film. Background Art

[0002] Soy protein has a variety of biological functions, such as good biocompatibility, degradability and nutritional properties, and has great potential in replacing petroleum-based membrane materials. However, soy protein often exhibits poor mechanical and barrier properties when constructing membrane materials, and the construction and stability of its membrane materials have always been a difficult problem in this field.

[0003] Chinese Patent Publication No.: CN113308002A discloses a method for preparing a protein edible film, which uses protein as the main raw material, and adopts sodium chloride, potassium chloride, lysine, arginine, histidine, cysteine ​​and ascorbic acid to dissolve and prepare a Chaotropic ion solution, and further prepares the edible film. However, the tensile strength of the soybean protein edible film prepared by this method is only 2.2MPa, and the solubility of the film is 89.5%. The preparation process is complicated and the cost is high, and the improvement effect of the mechanical properties of the film is not obvious.

[0004] Chinese Patent Publication No.: CN111154128B discloses an antibacterial and antioxidant whey protein isolate edible film and a preparation method thereof. The invention uses whey protein isolate as the main film-forming matrix, and is supplemented with bamboo leaf antioxidants and sodium caseinate, and a plasticizer is added. The whey protein isolate edible film is prepared through the steps of mixing, thermal denaturation, vacuum degassing, flat plate casting, drying and peeling off the film. However, the elongation at break of the whey protein edible film prepared by the invention is only about 32%.

[0005] In summary, the existing preparation methods of protein-based edible films still have problems such as poor performance, unsafety and high cost. Finding a preparation method of protein-based edible films with simple process, low cost, good performance and low biological toxicity is an urgent problem to be solved in the current food packaging field. Summary of the invention

[0006] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a method for preparing a high-performance soybean protein emulsion film with high ductility, high barrier properties and high safety, which can effectively improve the hydrophilic and hydrophobic properties and film-forming ability of the protein, thereby increasing the mechanical properties of its edible film.

[0007] The present invention solves the technical problem by adopting the following technical solutions:

[0008] A method for preparing a high-performance soybean protein emulsion film comprises the following steps:

[0009] S1, adding 2-4wt% soy protein isolate powder into an acetic acid-water binary mixed solvent with a pH of 2.0-3.0, stirring and dissolving to obtain an acidified protein solution;

[0010] S2, encapsulating the protein solution obtained in step S1 in a sealed glass container, placing it in a constant temperature water bath and heating it at 65° C.-95° C. for 1-6 hours, and cooling the solution after heating to obtain a soy protein isolate fiberization solution;

[0011] S3, adding plant essential oil to the soy protein isolate fiberization solution obtained in step S2, with a mass ratio of 1:3-1:6, using a high-speed homogenizer to homogenize at a speed of 12000 rpm for 3 minutes, and placing it in an ultrasonic machine for degassing for 3 minutes to obtain a protein fiber emulsion;

[0012] S4, adding 2.0-6.0wt% polyvinyl alcohol and 10%-50% glycerol in a solid content in a mass ratio of 1-5:0.4-3.2 to the protein fiber emulsion prepared in step S3, stirring evenly to prepare a film-forming liquid,

[0013] S5. Pour the film-forming liquid prepared in step S4 into a glass tank covered with a polytetrafluoroethylene film, cover the surface of the glass tank with a layer of plastic wrap pierced with several holes to control the evaporation rate of the acid solvent, and dry at RH40% and 25°C for 24 hours to obtain a soybean protein edible film.

[0014] Moreover, the protein in the protein powder is a globular protein, including but not limited to soy protein isolate, bovine serum albumin, whey protein, pea protein, and lysozyme.

[0015] Moreover, the concentration of the acetic acid solution is 30-50% by volume.

[0016] Moreover, the concentration of the acetic acid solution is 40% by volume.

[0017] Moreover, the plant essential oil is tea tree essential oil.

[0018] Furthermore, lauric acid or benzoic acid is included in the plant essential oil.

[0019] Moreover, the added amount is 1-10wt% of the plant essential oil.

[0020] The advantages and positive effects of the present invention are:

[0021] 1. The present invention introduces a dibasic weak acid, acetic acid, and uses acetic acid treatment to induce protein denaturation, thereby generating a large number of β-folded structures, thereby achieving an improvement in the hydrophobicity of the protein-based biomembrane.

[0022] 2. In order to improve the flexibility and elongation at break of the edible film, the present invention adds polyvinyl alcohol to form a double network structure, and innovatively applies the important stabilizing effects in the dispersed system - electrostatic hindrance and hydrogen bonding - to the construction and stabilization of protein fiber-based biofilms, thereby improving the flexibility and stability of the edible film.

[0023] 3. In order to improve the antibacterial and antioxidant activities of the emulsion edible film, the present invention adds plant essential oils to protect food from microbial contamination. The abundant phenolic compounds in plant essential oils can release active substances and migrate into food to protect them from free radicals, which can effectively extend the shelf life of packaged food.

[0024] 4. The preparation method of the present invention is simple, safe, low-cost, low-energy-consuming, and controllable in operation, and is suitable for large-scale industrial production and processing, and has broad application space in the food, daily chemical products and other industries.

[0025] 5. The present invention uses acetic acid-water binary solution to denature soybean protein, which can significantly improve the hydrophobicity, film-forming ability and environmental interference resistance of soybean protein. And further, based on the principle of protein self-assembly fibrillation and protein film-forming theory, a type of soybean protein-based biofilm with certain mechanical strength and flexibility is constructed by self-assembly fibrillation denaturation of protein molecules in aqueous solution, which effectively solves the problem of poor mechanical properties and high solubility of current protein-based biofilms. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 These are atomic force microscope images of soy protein isolate and soy protein isolate amyloid fibers. In the figure, A1 and A2 are soy protein isolate globulins, and B1 and B2 are soy protein isolate amyloid fibers.

[0027] Figure 2 They are optical microscope pictures and appearance pictures of soy protein isolate emulsion and soy protein isolate amyloid fiber emulsion, respectively. A1 and B1 in the picture are natural soy protein isolate emulsion, and A2 and B2 are soy protein isolate amyloid fiber emulsion.

[0028] Figure 3 These are scanning electron microscope images of Example 3 and Comparative Example 3 of the present invention, wherein Figures A1 and A2 are respectively a plan view and a cross-sectional view of an edible emulsion film prepared when the mass concentration of natural soy protein isolate (without acid-heat treatment) is 4wt% and the volume fraction of acetic acid is 40% (v / v); Figures B1 and B2 are respectively a plan view and a cross-sectional view of an edible emulsion film prepared when the mass concentration of soy protein isolate amyloid fibers is 4wt% and the volume fraction of acetic acid is 40% (v / v).

[0029] Figure 4 This is an appearance diagram of the protein emulsion edible film of Comparative Examples 1-3 of the present invention.

[0030] Figure 5 This is an appearance diagram of the protein emulsion edible film of Examples 1-7 of the present invention. DETAILED DESCRIPTION

[0031] The present invention is further described in detail below through specific examples. The following examples are only illustrative and not restrictive, and the protection scope of the present invention cannot be limited thereto.

[0032] The principle of the present invention is that under the action of acid and heat, the protein will form amyloid fibers rich in β-folded structure and stable structure by means of non-covalent bond forces such as intermolecular hydrogen bonds, hydrophobic effects, π-π interactions, etc. This fiber structure has the characteristics of high stability and high hydrophobicity, and the fibrosis deformation is irreversible, thus showing excellent material properties. For example, the fibrous denatured protein produced by whey protein at pH = 2.0 and 90°C water bath for 5 hours can be used to prepare a transparent, flexible and bio-edible film. If a water-soluble polymer substance is added to the protein solution in advance, it can be further formed into a plastic film for fruit and vegetable packaging.

[0033] Acetic acid is a dibasic weak acid. At the same pH, it can slowly ionize more hydrogen ions, which helps to form hydrogen bonds between molecules and promotes the flexibility of the membrane. The present invention uses the principle of protein fiber assembly to deeply explore the regulation method of acetic acid-induced fibrosis transformation to improve the film-forming ability and stability of proteins, and master the preparation method of related high-performance protein emulsion edible films. Therefore, the establishment of this method can overcome the key limitations of water solubility and stability of protein membrane materials in industrial applications.

[0034] Example 1

[0035] Film formation of soybean 7S protein powder under the conditions of protein concentration of 2wt% and acetic acid volume fraction of 40%.

[0036] The method for extracting and separating soybean 7S protein components comprises the following steps:

[0037] (1) Low-temperature defatted soybean flour was dispersed in deionized water at a solid-liquid ratio of 1:15, and the dispersion was slowly adjusted to pH 7.5 with 2 mol / L NaOH solution and stirred for 2 h to ensure that the protein in the soybean flour was fully dissolved.

[0038] (2) Centrifuge at room temperature (9000 × g, 30 min) to remove insoluble matter, add NaCl to the supernatant to adjust the ion concentration to 0.25 mol / L, stir evenly and return to room temperature, readjust the solution pH to 5.4, centrifuge again at low temperature (9000 × g, 30 min) and collect the supernatant.

[0039] (3) The collected supernatant was diluted with 2 volumes of deionized water, the pH was adjusted to 4.8 again, centrifuged (6500 × g, 20 min) and the precipitate was collected.

[0040] (4) Finally, the collected protein precipitate was redispersed with deionized water, the pH of the dispersion was adjusted to 7.5, and the dispersion was stirred until it was completely dissolved. The redissolved protein solution was placed in a dialysis bag (molecular weight cutoff 8-14 kDa), dialyzed for 48 h, during which the water was changed every 12 h, and freeze-dried to obtain the 7S soybean protein component.

[0041] A method for preparing a high-performance soybean 7S protein edible film comprises the following steps:

[0042] S1. Accurately weigh 2 g of soybean 7S protein powder, disperse it in 100 g of 40% by volume acetic acid-water solution, seal the bottle mouth with tin foil, and stir continuously in an 85°C water bath for 5 h, then cool in ice water to obtain a soybean 7S protein isolate fiberization solution with a mass concentration of 2 wt%;

[0043] S2, adding 1.5ml of plant essential oil (tea tree essential oil) to the soybean 7S protein isolate fiber solution, using a high-speed homogenizer to homogenize at a speed of 12000rpm for 3min, placing it in an ultrasonic machine for degassing for 3min to obtain a protein fiber emulsion, measuring 2g of polyvinyl alcohol and 0.6g of glycerol, adding them to the above solution, stirring evenly, to obtain a film-forming solution;

[0044] S3. Pour 30 mL of the film-forming liquid into a glass tank (10 cm × 12 cm) covered with a polytetrafluoroethylene film. Cover the surface of the glass tank with a layer of plastic wrap with several holes to control the evaporation rate of the acid solvent. Dry at RH 40% and 25°C for 24 h to obtain the soybean 7S protein edible film.

[0045] As shown in Table 1, in this embodiment, when only glycerol and polyvinyl alcohol are added as plasticizers, the thickness of the soybean 7S protein edible film can reach 95.8 μm, the tensile strength can reach 8.5 MPa, the elongation at break can reach 80.57%, and the moisture permeability can reach 0.6851×10 -3 g mm / m 2 ·h·KPa, the film solubility is as low as 29.8%.

[0046] Example 2

[0047] Film formation of soybean 11S protein powder under the conditions of protein concentration of 2wt% and acetic acid volume fraction of 40%.

[0048] The method for extracting and separating soybean 11S protein components comprises the following steps:

[0049] (1) Low-temperature defatted soybean flour was dispersed in deionized water at a solid-liquid ratio of 1:15, and the dispersion was slowly adjusted to pH 7.5 with 2 mol / L NaOH solution and stirred for 2 h to ensure that the protein in the soybean flour was fully dissolved.

[0050] (2) Centrifuge at room temperature (9000 × g, 30 min) to remove insoluble matter, add 1.04 g / L NaHSO3 powder to the supernatant, and adjust the pH of the supernatant to 6.4 with 2 mol / L HCl solution. Then move the supernatant to a 4°C refrigerator for acid precipitation overnight. The next day, centrifuge at 4°C to obtain a precipitate.

[0051] (3) The protein precipitate was washed twice with deionized water and redispersed in deionized water, placed in a dialysis bag (molecular weight cutoff 8-14 kDa), dialyzed for 48 h, with the water changed every 12 h, and freeze-dried to obtain the 11S soybean protein component.

[0052] A method for preparing a high-performance soybean 11S protein edible film comprises the following steps:

[0053] S1. According to the method described in Example 1, 2 g of soybean 11S protein powder was accurately weighed and dispersed in 100 g of 40% by volume acetic acid-water solution, the bottle mouth was sealed with tin foil, and the mixture was continuously stirred in an 85°C water bath for 5 h, and then cooled in ice water to obtain a soybean 11S protein isolate fiberization solution with a mass concentration of 2 wt%;

[0054] S2, 1.5 ml of plant essential oil (rose essential oil) was added to the soybean 11S protein isolate fibrillation solution, and the solution was homogenized at a speed of 12000 rpm using a high-speed homogenizer for 3 min, and then placed in an ultrasonic machine for degassing for 3 min to obtain a protein fiber emulsion, 2 g of polyvinyl alcohol and 0.6 g of glycerol were added to the above solution, and stirred to obtain a film-forming solution;

[0055] S3. Pour 30 mL of the film-forming liquid into a glass tank (10 cm × 12 cm) covered with a polytetrafluoroethylene film. Cover the surface of the glass tank with a layer of plastic wrap pierced with several holes to control the evaporation rate of the acid solvent. Dry at RH 40% and 25°C for 24 hours to obtain an edible soybean 11S protein film.

[0056] As shown in Table 1, in this embodiment, when only glycerol and polyvinyl alcohol are added as plasticizers, the thickness of the soybean 11S protein edible film can reach 96.2 μm, the tensile strength can reach 10.2 MPa, the elongation at break can reach 72.83%, and the moisture permeability can reach 0.6251×10 -3 g mm / m 2 ·h·KPa, the film solubility is as low as 25.2%.

[0057] Example 3

[0058] Effect of the mixed ratio of 7S soybean protein and 11S soybean protein as soybean protein raw material on the properties of edible films

[0059] According to the method described in Example 1, a soy protein isolate edible film was prepared.

[0060] A method for preparing a high-performance soybean protein emulsion film comprises the following steps:

[0061] S1. Accurately weigh 1g of soybean 7S protein powder and 1g of soybean 11S protein powder (soy protein isolate powder), respectively, disperse them in 100g of 40% by volume acetic acid-water solution, seal the bottle mouth with tin foil, stir continuously in a 85°C water bath for 5h, and then cool in ice water to obtain a soybean protein isolate fiberization solution with a mass concentration of 2wt%;

[0062] S2, 1.5 ml of plant essential oil (tea tree essential oil) was added to the soy protein isolate fiber solution, and the solution was homogenized at a speed of 12000 rpm using a high-speed homogenizer for 3 min, and then placed in an ultrasonic machine for degassing for 3 min to obtain a protein fiber emulsion, 2 g of polyvinyl alcohol and 0.6 g of glycerol were added to the solution, and stirred to obtain a film-forming solution;

[0063] S3. Pour 30 mL of the film-forming liquid into a glass tank (10 cm × 12 cm) covered with a polytetrafluoroethylene film. Cover the surface of the glass tank with a layer of plastic wrap pierced with several holes to control the evaporation rate of the acid solvent. Dry at RH 40% and 25°C for 24 hours to obtain an edible protein film.

[0064] As shown in Table 1, this example investigates the effect of a mixed ratio of 7S soy protein and 11S soy protein as soy protein raw materials on edible films. The results show that the mixed ratio of the two proteins enhances the tensile strength and barrier properties of the edible films.

[0065] Among them, the microstructure of natural soy protein isolate and soy protein isolate amyloid fibers (atomic force microscope) is as follows Figure 1 As shown, it was observed that natural soy protein isolate with a size of 20-400 nm was in a spherical structure with a height of about 0.8-3.9 nm; after heat treatment at 85°C for 5 h, the soy protein isolate self-assembled into a large number of short rod-like fibers with a length of about 250 to 600 nm and a height of about 1.5 nm.

[0066] Optical microscope images and appearance images of soy protein isolate emulsion and soy protein isolate amyloid fiber emulsion are shown in Figure 2. Figure 2As shown in the figure, A1 is an optical microscope image of a natural soy protein isolate emulsion, B1 is an appearance image of a natural soy protein isolate emulsion, A2 is an optical microscope image of a soy protein isolate amyloid fiber emulsion, and B2 is an appearance image of a soy protein isolate amyloid fiber emulsion.

[0067] Example 4

[0068] Effect of protein concentration on properties of edible films

[0069] A method for preparing a high-performance soybean protein emulsion film comprises the following steps:

[0070] S1. Accurately weigh 2 g of soybean 7S protein powder and 2 g of soybean 11S protein powder (soy protein isolate powder), respectively, disperse them in 100 g of 40% by volume acetic acid-water solution, seal the bottle mouth with tin foil, stir continuously in a water bath at 85°C for 5 h, and then cool in ice water to obtain a soybean protein isolate fiberization solution with a mass concentration of 4 wt%;

[0071] S2, adding 1.5 ml of plant essential oil to the soy protein isolate fiber solution, using a high-speed homogenizer to homogenize at a speed of 12000 rpm for 3 min, placing it in an ultrasonic machine for degassing for 3 min to obtain a protein fiber emulsion, measuring 2 g of polyvinyl alcohol and 0.9 g of glycerol, adding them to the above solution, stirring evenly, to obtain a film-forming solution;

[0072] S3. Pour 30 mL of the film-forming liquid into a glass tank (10 cm × 12 cm) covered with a polytetrafluoroethylene film. Cover the surface of the glass tank with a layer of plastic wrap pierced with several holes to control the evaporation rate of the acid solvent. Dry at RH 40% and 25°C for 24 hours to obtain an edible protein film.

[0073] As shown in Table 1, this example investigates the effect of protein concentration on edible films. The results show that an increase in protein concentration has an enhancing effect on the tensile strength of the edible films.

[0074] Example 5

[0075] Effect of polyvinyl alcohol addition ratio on the properties of edible films

[0076] According to the method described in Example 3, a soy protein isolate edible film was prepared.

[0077] A method for preparing a high-performance soybean protein emulsion film comprises the following steps:

[0078] S1. Accurately weigh 4 g of soy protein isolate powder, disperse it in 100 g of 40% by volume acetic acid-water solution, seal the bottle mouth with tin foil, and stir continuously in a water bath at 85°C for 5 h, then cool in ice water to obtain a soy protein isolate fiberization solution with a mass concentration of 4 wt%;

[0079] S2, add 1.5ml of plant essential oil (add 0.1-0.2ml of benzoic acid to 1.5ml of tea tree essential oil) to the soy protein isolate fibrillation solution, use a high-speed homogenizer to homogenize at a speed of 12000rpm for 3min, place it in an ultrasonic machine for degassing for 3min to obtain a protein fiber emulsion, measure 4g of polyvinyl alcohol and 1.2g of glycerol, add them to the above solution, stir evenly, and obtain a film-forming solution;

[0080] S3. Pour 30 mL of the film-forming liquid into a glass tank (10 cm × 12 cm) covered with a polytetrafluoroethylene film. Cover the surface of the glass tank with a layer of plastic wrap pierced with several holes to control the evaporation rate of the acid solvent. Dry at RH 40% and 25°C for 24 hours to obtain an edible protein film.

[0081] As shown in Table 1, this example investigates the effect of the proportion of polyvinyl alcohol added on the properties of the edible film. The results show that the higher the polyvinyl alcohol concentration, the higher the tensile strength and elongation at break of the edible film, and the lower the moisture permeability and solubility of the film.

[0082] Example 6

[0083] Effect of glycerol addition ratio on the properties of edible films

[0084] A method for preparing a high-performance soybean protein emulsion film comprises the following steps:

[0085] S1. Accurately weigh 4 g of soy protein isolate powder, disperse it in 100 g of 40% by volume acetic acid-water solution, seal the bottle mouth with tin foil, and stir continuously in a water bath at 85°C for 5 h, then cool in ice water to obtain a soy protein isolate fiberization solution with a mass concentration of 4 wt%;

[0086] S2, adding 1.5 ml of plant essential oil to the soy protein isolate fiber solution, using a high-speed homogenizer to homogenize at a speed of 12000 rpm for 3 min, placing it in an ultrasonic machine for degassing for 3 min to obtain a protein fiber emulsion, measuring 4 g of polyvinyl alcohol and 2.8 g of glycerol, adding them to the above solution, stirring evenly, to obtain a film-forming solution;

[0087] S3. Pour 30 mL of the film-forming liquid into a glass tank (10 cm × 12 cm) covered with a polytetrafluoroethylene film. Cover the surface of the glass tank with a layer of plastic wrap pierced with several holes to control the evaporation rate of the acid solvent. Dry at RH 40% and 25°C for 24 hours to obtain an edible protein film.

[0088] As shown in Table 1, this example investigates the effect of the addition ratio of glycerol on the properties of the edible film. The results show that the addition of glycerol has an effect on the edible film in that the tensile strength and elongation at break are reduced and the moisture permeability is increased.

[0089] Example 7

[0090] A method for preparing a high-performance soybean protein emulsion film comprises the following steps:

[0091] S1. Accurately weigh 4 g of soy protein isolate powder, disperse it in 100 g of 40% by volume acetic acid-water solution, seal the bottle mouth with tin foil, and stir continuously in a water bath at 85°C for 5 h, then cool in ice water to obtain a soy protein isolate fiberization solution with a mass concentration of 4 wt%;

[0092] S2, adding 1.5ml of plant essential oil (adding 0.1-0.2ml of lauric acid to 1.5ml of tea tree essential oil) to the soy protein isolate fibrillation solution, using a high-speed homogenizer to homogenize at a speed of 12000rpm for 3min, placing it in an ultrasonic machine for degassing for 3min to obtain a protein fiber emulsion, measuring 4g of polyvinyl alcohol and 2g of glycerol, adding them to the above solution, stirring evenly, to obtain a film-forming solution;

[0093] S3. Pour 30 mL of the film-forming liquid into a glass tank (10 cm × 12 cm) covered with a polytetrafluoroethylene film. Cover the surface of the glass tank with a layer of plastic wrap pierced with several holes to control the evaporation rate of the acid solvent. Dry at RH 40% and 25°C for 24 hours to obtain an edible protein film.

[0094] like Figure 5 The figure shows the appearance of the protein emulsion edible film, which is uniform and transparent.

[0095] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

[0096] Comparative Example 1

[0097] The preparation method is similar to that of Example 1, except that the whole process does not involve acid-heat treatment.

[0098] A method for preparing a high-performance soybean protein emulsion film comprises the following steps:

[0099] S1. Accurately weigh 2 g of soybean 7S protein powder, disperse it in 100 g of deionized water solution, and stir at room temperature for 3 h to obtain a soybean protein isolate solution with a mass concentration of 2 wt%;

[0100] S2, adding 1.5 ml of plant essential oil to the soy protein isolate fiber solution, using a high-speed homogenizer to homogenize at a speed of 12000 rpm for 3 min, placing it in an ultrasonic machine for degassing for 3 min to obtain a protein fiber emulsion, measuring 2 g of polyvinyl alcohol and 0.6 g of glycerol, adding them to the above solution, stirring evenly, to obtain a film-forming solution;

[0101] S3. Pour 30 mL of the film-forming liquid into a glass tank (10 cm × 12 cm) covered with a polytetrafluoroethylene film. Cover the surface of the glass tank with a layer of plastic wrap pierced with several holes to control the evaporation rate of the acid solvent. Dry at RH 40% and 25°C for 24 hours to obtain an edible protein film.

[0102] Comparative Example 2

[0103] The preparation method is similar to that of Example 2, except that the entire process does not involve acid-heat treatment.

[0104] A method for preparing a high-performance soybean protein emulsion film comprises the following steps:

[0105] S1. Accurately weigh 2 g of soybean 11S protein powder, disperse it in 100 g of deionized water solution, and stir at room temperature for 3 h to obtain a soybean protein isolate solution with a mass concentration of 2 wt%;

[0106] S2, adding 1.5 ml of plant essential oil to the soy protein isolate fiber solution, using a high-speed homogenizer to homogenize at a speed of 12000 rpm for 3 min, placing it in an ultrasonic machine for degassing for 3 min to obtain a protein fiber emulsion, measuring 2 g of polyvinyl alcohol and 0.6 g of glycerol, adding them to the above solution, stirring evenly, to obtain a film-forming solution;

[0107] S3. Pour 30 mL of the film-forming liquid into a glass tank (10 cm × 12 cm) covered with a polytetrafluoroethylene film. Cover the surface of the glass tank with a layer of plastic wrap pierced with several holes to control the evaporation rate of the acid solvent. Dry at RH 40% and 25°C for 24 hours to obtain an edible protein film.

[0108] Comparative Example 3

[0109] The preparation method is similar to that of Example 3, except that the entire process does not involve acid-heat treatment to prepare a soy protein isolate film.

[0110] A method for preparing a high-performance soybean protein emulsion film comprises the following steps:

[0111] S1. Accurately weigh 4 g of soy protein isolate powder, disperse it in 100 g of deionized water solution, and stir at room temperature for 3 h to obtain a soy protein isolate solution with a mass concentration of 2 wt%;

[0112] S2, adding 1.5 ml of plant essential oil to the soy protein isolate fiber solution, using a high-speed homogenizer to homogenize at a speed of 12000 rpm for 3 min, placing it in an ultrasonic machine for degassing for 3 min to obtain a protein fiber emulsion, measuring 2 g of polyvinyl alcohol and 0.6 g of glycerol, adding them to the above solution, stirring evenly, to obtain a film-forming solution;

[0113] S3. Pour 30 mL of the film-forming liquid into a glass tank (10 cm × 12 cm) covered with a polytetrafluoroethylene film. Cover the surface of the glass tank with a layer of plastic wrap pierced with several holes to control the evaporation rate of the acid solvent. Dry at RH 40% and 25°C for 24 hours to obtain an edible protein film.

[0114] like Figure 3 As shown in the figure, A1 and A2 are respectively the plane view and cross-sectional view of the prepared emulsion edible film when the mass concentration of natural soy protein isolate (without acid-heat treatment) is 4wt% and the volume fraction of acetic acid is 40% (v / v); Figures B1-B2 are respectively the plane view and cross-sectional view of the prepared emulsion edible film when the mass concentration of soy protein isolate amyloid fiber is 4wt% and the volume fraction of acetic acid is 40% (v / v), as shown in Table 1. Table 1 Comparison of film properties of protein emulsion edible films prepared in Examples 1-7 of the present invention and Comparative Examples 1-3

[0115]

[0116] Although the embodiments of the present invention are disclosed for illustrative purposes, those skilled in the art will appreciate that various substitutions, changes and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the scope of the present invention is not limited to the contents disclosed in the embodiments.

Claims

1. A method for preparing a high-performance soybean protein emulsion film, characterized in that: The steps include: S1, adding 2-4wt% soy protein isolate powder into an acetic acid-water binary mixed solvent with a pH of 2.0-3.0, stirring and dissolving to obtain an acidified protein solution; S2, encapsulating the protein solution obtained in step S1 in a sealed glass container, placing it in a constant temperature water bath and heating it at 65° C.-95° C. for 1-6 hours, and cooling the solution after heating to obtain a soy protein isolate fiberization solution; S3, adding plant essential oil to the soy protein isolate fiberization solution obtained in step S2, wherein the amount of plant essential oil added is 0.5-2.5wt%, and homogenizing for 3 min at a speed of 12000 rpm using a high-speed homogenizer, and then placing it in an ultrasonic machine for degassing for 3 min to obtain a protein fiber emulsion; S4, adding 2.0-6.0wt% polyvinyl alcohol and 10%-50% glycerol in a solid content in a mass ratio of 1-5:0.1-3.5 to the protein fiber emulsion obtained in step S3, stirring evenly to prepare a film-forming liquid, S5. Pour the film-forming liquid prepared in step S4 into a glass tank covered with a polytetrafluoroethylene film, cover the surface of the glass tank with a layer of plastic wrap pierced with several holes to control the evaporation rate of the acid solvent, and dry at RH40% and 25°C for 24 hours to obtain a soybean protein edible film.

2. The method for preparing a high-performance soybean protein emulsion film according to claim 1, characterized in that: The protein in the protein powder is a globular protein, including but not limited to soy protein isolate, bovine serum albumin, whey protein, pea protein, and lysozyme.

3. The method for preparing a high-performance soybean protein emulsion film according to claim 1, characterized in that: The concentration of the acetic acid solution is 30-50% by volume.

4. The method for preparing a high-performance soybean protein emulsion film according to claim 1, characterized in that: The concentration of the acetic acid solution is 40% by volume.

5. The method for preparing a high-performance soybean protein emulsion film according to claim 1, characterized in that: The plant essential oil is tea tree essential oil.

6. The method for preparing a high-performance soybean protein emulsion film according to claim 1, characterized in that: The lauric acid or benzoic acid is included in the plant essential oil.

7. The method for preparing a high-performance soybean protein emulsion film according to claim 6, characterized in that: The added amount is 1-10wt% of the plant essential oil.

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