Tough soybean protein isolate-based film, preparation process therefor using pulsed electric field for precise control and use thereof

Abstract

Disclosed in the present invention are a tough soybean protein isolate-based film, a preparation process therefor using a pulsed electric field for precise control and a use thereof. The tough soybean protein isolate-based film is obtained by mixing a soybean protein isolate solution, a dialdehyde starch solution and a polyvinyl alcohol solution, adjusting the pH value of the mixture to 8.5-11, reacting at 60-100℃ under the action of a pulsed electric field for 10-50 min, pouring the product into a culture dish, and drying the product. Compared with other biomass film materials (cellulose, starch and chitosan films), the soybean protein isolate-based film prepared in the present invention has excellent mechanical properties, the tensile strength of the material can reach 18.3 MPa, and the elongation at break thereof can reach 240.5%; compared with conventional soybean protein isolate films added with glycerin plasticizers, the tensile strength and toughness of the soybean protein isolate-based film are improved by 631% and 654%, respectively; and the obtained soybean protein isolate-based film can block 97%-100% of ultraviolet transmission (≤ 400 nm).

Description

Preparation technology and application of strong soy protein isolate-based films and their precise control using pulsed electric fields Technical Field

[0001] The present invention relates to a protein-based film, in particular to a tough soy protein isolate-based film and a preparation process and application thereof using precise control of a pulsed electric field; and belongs to the field of biodegradable material development. Background Art

[0002] With the advancement of science and technology and the implementation of sustainable development strategies, biodegradable materials are attracting increasing attention. Among biopolymers, soy protein isolate is a renewable, environmentally friendly, highly processable biopolymer with a rich functional group structure; therefore, it is a promising alternative to synthetic polymers for the development of environmentally friendly composite films. However, the hydrophilicity and strong molecular interactions of natural soy protein isolate result in poor film-forming properties, mechanical properties, and toughness of the resulting films, significantly limiting the application of soy protein-based films. Therefore, the small molecule plasticizer glycerol has been added to reduce the strong intermolecular and intramolecular interactions between soy protein molecules and increase the mobility of protein chains. However, while glycerol-plasticized soy protein increases flexibility, it also reduces film strength. Furthermore, due to thermodynamic effects, the glycerol plasticizer readily migrates out of the protein matrix upon exposure to the external environment. Subsequently, various chemical crosslinkers, such as formaldehyde, glutaraldehyde, glyoxal, and epoxy resin compounds, have been used to improve the mechanical properties of soy protein isolate films. However, the resulting films exhibit significantly reduced ductility and exhibit certain toxicity. Therefore, developing soy protein film materials with both high strength and good ductility remains challenging.

[0003] As can be seen from the above background technology, current soy protein isolate-based films mainly suffer from poor mechanical properties, which limits their industrial and large-scale production applications. Other protein films also suffer from various deficiencies, including cost and performance issues. Chinese invention patent CN103627033B discloses a prolamin-starch-based degradable composite film and its preparation method. Its components and weight parts are: 100 parts starch, 10-15 parts prolamin, 6-10 parts glycerol, and 5-8 parts palygorskite clay. This technology utilizes the good compatibility between prolamin and starch. By adding a small amount of prolamin to the starch film, the strength of the plastic film can be increased while reducing the amount of glycerol used. The addition of palygorskite to the film is intended to improve the water retention of the composite material and reduce costs. Due to the poor ductility of starch-based materials, this invention improves the ductility of starch films by adding glycerol. However, the addition of glycerol reduces the strength of the material. Furthermore, due to the incompatibility between the polymer and the plasticizer, when the material is exposed to the external environment, changes in temperature and humidity can easily cause glycerol to migrate out of the material. The loss of glycerol can lead to reduced flexibility, embrittlement, and cracking of the material. Secondly, the starch-based film prepared by this technology requires the mixture to be gelatinized for 30 minutes and then dried at 60°C for 20 hours. After the film is removed, it needs to be vulcanized, sheeted, and injection molded again using hot and cold presses. This is time-consuming, labor-intensive, and energy-intensive, limiting its industrial and large-scale production applications.

[0004] Summary of the Invention

[0005] In order to overcome the shortcomings of the existing technology and meet the huge market demand for degradable biomaterials, the purpose of the present invention is to provide a strong soy protein isolate-based film with obvious performance advantages in tensile strength and ductility, and an ultraviolet blocking rate of more than 99.9%, and a preparation process thereof using precise control of a pulsed electric field.

[0006] Another object of the present invention is to provide the use of the tough soy protein isolate-based film in the preparation of food active packaging or ultraviolet protection materials.

[0007] The purpose of the present invention is achieved through the following solutions:

[0008] A tough soy protein isolate-based film is prepared by mixing a soy protein isolate solution, a dialdehyde starch solution, and a polyvinyl alcohol solution, adjusting the pH to 8.5-11, reacting the mixture at 60-100°C under the action of a pulsed electric field for 10-50 minutes, pouring the product into a culture dish, and drying. The pulsed electric field has a frequency of 100-1000 Hz, a pulse width of 10-60 μs, and a field strength of 2-15 kV / cm.

[0009] To further achieve the purpose of the present invention, preferably, the mass content of the soy protein isolate solution is 1% to 10%.

[0010] Preferably, the mass content of the dialdehyde starch solution is 4% to 15%.

[0011] Preferably, the mass content of the polyvinyl alcohol solution is 5% to 20%.

[0012] Preferably, the mass ratio of the soy protein isolate to polyvinyl alcohol is 1:0.2-1.5, and the mass ratio of the soy protein isolate to dialdehyde starch is 2-9:1.

[0013] Preferably, the pH is adjusted to 8.5-11 by adding an alkaline solution, and the concentration of the alkaline solution is 0.05 mol / L-0.3 mol / L.

[0014] Preferably, the alkaline solution is sodium hydroxide solution or potassium hydroxide solution.

[0015] Preferably, the drying is carried out in an oven at a drying temperature of 30-60° C. and a drying time of 10-30 h.

[0016] The preparation process of the tough soy protein isolate-based film using precise control of a pulsed electric field comprises the following steps:

[0017] 1) Mixing the soy protein isolate solution, dialdehyde starch solution and polyvinyl alcohol solution;

[0018] 2) Adjust the pH to 8.5-11 and pump the mixture into a pulsed electric field at 60-100°C for 10-50 minutes;

[0019] 3) The product obtained in step 2) is poured into a culture dish and dried to obtain a soy protein isolate-based film.

[0020] Application of the tough soy protein isolate-based film in preparing food active packaging or ultraviolet protection materials.

[0021] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0022] 1) On the one hand, polyvinyl alcohol (PVA) acts as a soft component, ensuring the material's flexibility. Furthermore, the present invention utilizes pulsed electric field treatment to unfold the soy protein isolate structure, enhancing its flexibility and exposing more crosslinking sites. This promotes covalent crosslinking and non-covalent (hydrogen bonding) interactions between the protein and aldehyde groups. The amino groups of the soy protein isolate react with the aldehyde groups of dialdehyde starch through a Schiff base reaction, producing covalent crosslinks. This covalent crosslinking, combined with multiple non-covalent interactions, including hydrogen bonding and hydrophobic interactions, creates an interconnected crosslinked network within the soy protein isolate-based film, enhancing its strength and toughness. The resulting soy protein isolate-based film exhibits excellent tensile strength, high toughness, and high UV shielding properties. The soy protein isolate-based film achieves a tensile strength of 18.3 MPa and an elongation at break of 240.5%, representing a 654% increase in toughness compared to a soy protein isolate film containing only glycerol plasticizer. Soy protein isolate-based films can block 97%-100% of UV transmittance (≤400 nm) and have great application value in UV-resistant coating materials and tissue engineering.

[0023] 2) The soy protein isolate-based film of the present invention not only has excellent mechanical properties but also has good UV blocking properties. In addition, during the preparation process, the degree of soy protein isolate structure expansion is precisely controlled by adjusting the pulse energy, thereby achieving precise control over the range of mechanical properties of the film. At low field strength (<4kV / cm), the toughness of the material can be controlled to 19-27 MJ / m 3 Under medium to high field strength (4~15kV / cm), the toughness of the material can be controlled to 27~25 MJ / m 3 , to be used as active packaging materials for different foods.

[0024] 3) Compared with other protein raw materials, the soy protein isolate of the present invention has obvious cost advantages. The present invention uses soy protein isolate to prepare a renewable, environmentally friendly and degradable soy protein isolate-based film, and the material processing process is simple and can be applied to industrial production. It has very obvious environmental advantages in replacing the non-degradable film of the existing technology. At the same time, the present invention also solves the mechanical property problem of the protein film, and has obvious market advantages.

[0025] 4) The present invention provides a simple and effective method for producing a degradable protein material with high strength and good ductility. Compared with other soy protein films, the film prepared by the present invention has improved mechanical properties and good UV blocking performance, showing potential application prospects in food active packaging, UV protective coatings and tissue engineering.

[0026] 5) Compared with other soy protein isolate-based films in the prior art, the tensile strength and ductility of the tough soy protein isolate-based film of the present invention are significantly improved, resulting in a soy protein film material with both high strength and good ductility. It is also a biodegradable material, alleviating the pressure on the environment caused by the non-degradable petroleum-based plastics. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is the photoelectron spectrum of soy protein isolate (SPI).

[0028] FIG2 is a photoelectron spectrum of the soy protein isolate-based film prepared in Comparative Example 3.

[0029] FIG3 is a stress-strain curve of the soy protein isolate-based films prepared in Examples and Comparative Examples.

[0030] FIG4 is a bar graph showing the toughness of the soy protein isolate-based films of the examples and comparative examples.

[0031] FIG5 shows the ultraviolet light blocking properties of the soy protein isolate-based films prepared in Examples and Comparative Examples.

[0032] DETAILED DESCRIPTION

[0033] The present invention will be further described below with reference to the examples and accompanying drawings, but the embodiments of the present invention are not limited thereto. Where specific conditions are not specified in the examples, the experiments were carried out under conventional conditions or conditions recommended by the manufacturer. Reagents or instruments used, where the manufacturer is not specified, are commercially available conventional products.

[0034] Example 1

[0035] (1) By adding distilled water to prepare 5% soy protein isolate solution and 4% dialdehyde starch solution, respectively, the pH was adjusted to 8.5 with 0.1 M sodium hydroxide solution, and heated at 40 °C for 10 min;

[0036] (2) Prepare a 10% polyvinyl alcohol solution by adding distilled water and heat at 80°C for 1 h to completely dissolve it.

[0037] (3) 70 g of the soy protein isolate solution, 20 g of the dialdehyde starch solution, and 30 g of the polyvinyl alcohol solution in steps (1) and (2) were mixed, and 0.1 M sodium hydroxide solution was added to adjust the pH to 9.5.

[0038] (4) The mixed solution in step (3) was maintained at 70°C and reacted under a pulsed electric field of 2 kV / cm for 20 min, with the pulse width and pulse frequency set to 40 μs and 1000 Hz, respectively;

[0039] (5) The reactants in step (4) were poured into a culture dish and dried in an oven at 45°C for 12 h to obtain a soy protein isolate-based film, which was named SPI / P / D-2.

[0040] The mechanical properties and UV-blocking properties of the soy protein isolate-based film (SPI / P / D-2) obtained in the above steps are shown in Figures 3, 4, and 5. The tensile strength of the SPI / P / D-2 film is 13.70±0.51MPa, the elongation at break is 217.71±5.3%, and the toughness is 23.6MJ / m 3 , UV blocking rate is 99.04%.

[0041] Example 2

[0042] (1) By adding distilled water to prepare 5% soy protein isolate solution and 4% dialdehyde starch solution, respectively, the pH was adjusted to 9.5 with 0.1 M sodium hydroxide solution, and heated at 40 °C for 10 min.

[0043] (2) Prepare a 10% polyvinyl alcohol solution by adding distilled water and heat at 80°C for 1 h to completely dissolve it.

[0044] (3) 70 g of the soy protein isolate solution, 20 g of the dialdehyde starch solution, and 30 g of the polyvinyl alcohol solution in steps (1) and (2) were mixed, and the pH was adjusted to 10 using a 0.2 M sodium hydroxide solution.

[0045] (4) The mixed solution in step (3) was maintained at 70°C and reacted under a pulsed electric field of 4 kV / cm for 20 min, with the pulse width and pulse frequency set to 20 μs and 500 Hz, respectively;

[0046] (5) The reactants in step (4) were poured into a Petri dish and dried in an oven at 45°C for 12 h. A soy protein isolate-based film was obtained and named SPI / P / D-4.

[0047] The mechanical properties and UV-blocking properties of the soy protein isolate-based film (SPI / P / D-4) obtained in the above steps are shown in Figures 3, 4, and 5. The tensile strength of the SPI / P / D-4 film is 16.90±0.93MPa, the elongation at break is 220.92±10.3%, and the toughness is 27.4MJ / m 3 , UV blocking rate is 99.53%.

[0048] Example 3

[0049] (1) By adding distilled water to prepare 5% soy protein isolate solution and 4% dialdehyde starch solution, respectively, the pH was adjusted to 10 with 0.1 M sodium hydroxide solution, and heated at 40 °C for 10 min;

[0050] (2) Prepare a 10% polyvinyl alcohol solution by adding distilled water and heat at 80°C for 1 h to completely dissolve it.

[0051] (3) 70 g of the soy protein isolate solution, 20 g of the dialdehyde starch solution, and 30 g of the polyvinyl alcohol solution in steps (1) and (2) were mixed, and the pH was adjusted to 9.5 using a 0.3 M sodium hydroxide solution.

[0052] (4) The mixed solution in (3) was maintained at 70°C and reacted under a pulsed electric field of 6 kV / cm for 20 min, with the pulse width and pulse frequency set to 60 μs and 800 Hz, respectively;

[0053] (5) The reactants in (4) were poured into a Petri dish and dried in an oven at 45°C for 12 h. A soy protein isolate-based film was obtained and named SPI / P / D-6.

[0054] The mechanical properties and UV blocking properties of the soy protein isolate-based film (SPI / P / D-6) obtained in the above steps are shown in Figures 3, 4, and 5. The tensile strength of the SPI / P / D-6 film is 18.28±0.63MPa, the elongation at break is 240.53±3.9%, and the toughness is 36.2MJ / m 3 , UV blocking rate is 99.94%.

[0055] Example 4

[0056] (1) By adding distilled water to prepare 10% soy protein isolate solution and 15% dialdehyde starch solution, respectively, the pH was adjusted to 11 with 0.1 M sodium hydroxide solution, and heated at 40 °C for 10 min;

[0057] (2) Prepare a 20% polyvinyl alcohol solution by adding distilled water and heat at 80°C for 1 h to completely dissolve it.

[0058] (3) 60 g of the soy protein isolate solution, 5 g of the dialdehyde starch solution, and 15 g of the polyvinyl alcohol solution in steps (1) and (2) were mixed, and the pH was adjusted to 11 using a 0.05 M sodium hydroxide solution.

[0059] (4) The mixed solution in step (3) was maintained at 100°C and reacted under a pulsed electric field of 15 kV / cm for 40 min, with the pulse width and pulse frequency set to 10 μs and 100 Hz, respectively;

[0060] (5) The reactants in step (4) were poured into a culture dish and dried in an oven at 60°C for 8 h to obtain a soy protein isolate-based film.

[0061] The soy protein isolate film obtained by the above steps has a tensile strength of 15.2±0.33 MPa, an elongation at break of 183.36±2.7%, and a toughness of 25.4 MJ / m 3 , UV blocking rate is 99.32%.

[0062] Comparative Example 1

[0063] (1) Prepare a 5% soy protein isolate solution by adding distilled water, adjust the pH to 9.5 with 0.1 M sodium hydroxide solution, and heat at 40°C for 10 min.

[0064] (2) 1.5 g of glycerol was added to 100 g of the soy protein isolate solution in (1), and the pH was adjusted to 9.5 using a 0.1 M sodium hydroxide solution.

[0065] (3) Maintain the mixed solution in (2) at 70°C and react for 20 minutes;

[0066] (4) The reactants in (3) were poured into a Petri dish and dried in an oven at 45°C for 12 h. A soy protein isolate-based film was obtained and named SPI / G.

[0067] The mechanical properties and UV blocking properties of the soy protein isolate-based film (SPI / G) obtained by the above steps are shown in Figures 3, 4, and 5. The tensile strength of the SPI / G film is 2.5±0.23MPa, the elongation at break is 231±6.2%, and the toughness is 4.8MJ / m 3 , UV blocking rate is 63.3%.

[0068] Comparative Example 2

[0069] (1) Prepare a 5% soy protein isolate solution by adding distilled water, adjust the pH to 9.5 with 0.1 M sodium hydroxide solution, and heat at 40°C for 10 min.

[0070] (2) Prepare a 10% polyvinyl alcohol solution by adding distilled water and heat at 80°C for 1 h to completely dissolve it.

[0071] (3) Mix 70 g of the soy protein isolate solutions in (1) and (2) and 30 g of the polyvinyl alcohol solution, and adjust the pH to 9.5 using 0.1 M sodium hydroxide solution.

[0072] (4) Maintain the mixed solution in (3) at 70°C and react for 20 minutes;

[0073] (5) The reactants in (4) were poured into a Petri dish and dried in an oven at 45°C for 12 h. A soy protein isolate-based film was obtained and named SPI / P.

[0074] The mechanical properties and UV-blocking properties of the soy protein isolate-based film (SPI / P) obtained in the above steps are shown in Figures 3, 4, and 5. The tensile strength of the SPI / P film is 7.06±0.36MPa, the elongation at break is 19.16±7.2%, and the toughness is 1.2MJ / m 3 , UV blocking rate is 79.02%.

[0075] Comparative Example 3

[0076] (1) By adding distilled water to prepare 5% soy protein isolate solution and 4% dialdehyde starch solution, respectively, the pH was adjusted to 9.5 with 0.1 M sodium hydroxide solution, and heated at 40 °C for 10 min.

[0077] (2) Prepare a 10% polyvinyl alcohol solution by adding distilled water and heat at 80°C for 1 h to completely dissolve it.

[0078] (3) Mix 70 g of the soy protein isolate solution, 20 g of the dialdehyde starch solution, and 30 g of the polyvinyl alcohol solution in (1) and (2), and adjust the pH to 9.5 using 0.1 M sodium hydroxide solution.

[0079] (4) Maintaining the mixed solution in (3) at 70°C;

[0080] (5) The reactants in (4) were poured into a Petri dish and dried in an oven at 45°C for 12 h. A soy protein isolate-based film was obtained and named SPI / P / D-0.

[0081] The mechanical properties and UV-blocking properties of the soy protein isolate-based film (SPI / P / D-0) obtained in the above steps are shown in Figures 3, 4, and 5. The tensile strength of the SPI / P / D-0 film is 12.79 ± 1.2 MPa, the elongation at break is 194.95 ± 4.1%, and the toughness is 19.1 MJ / m 3 , UV blocking rate is 97.23%.

[0082] The photoelectron spectrum of the soy protein isolate-based film (SPI / P / D-0) obtained in the above steps is shown in Figure 2. As shown in Figure 1, the N 1s spectrum of soy protein isolate (SPI) displays two primary peaks at 399.36 eV (CN) and 400.6 eV (NH). In contrast, a new C=N characteristic peak was observed in the N 1s spectrum of the SPI / P / D-0 film at 399.37 eV. This indicates that the amino groups in SPI react with the aldehyde groups in dialdehyde starch to form -HC=N- functional groups.

[0083] Comparative Example 4

[0084] (1) By adding distilled water, 8% soy protein isolate solution and 10% dialdehyde starch solution were prepared respectively, and the pH was adjusted to 10 with 0.1 M sodium hydroxide solution, and heated at 40 °C for 10 min;

[0085] (2) Prepare a 10% polyvinyl alcohol solution by adding distilled water and heat at 80°C for 1 h to completely dissolve it.

[0086] (3) 60 g of the soy protein isolate solution, 10 g of the dialdehyde starch solution, and 15 g of the polyvinyl alcohol solution in steps (1) and (2) were mixed, and the pH was adjusted to 11 using a 0.1 M sodium hydroxide solution.

[0087] (4) The mixed solution in step (3) was maintained at 70°C and reacted under a pulsed electric field of 1 kV / cm for 40 min, with the pulse width and pulse frequency set to 8 μs and 50 Hz, respectively;

[0088] (5) The reactants in step (4) were poured into a culture dish and dried in an oven at 60°C for 8 h to obtain a soy protein isolate-based film.

[0089] After testing, the soy protein isolate-based film obtained in the above steps has a tensile strength of 12.8±0.23MPa, an elongation at break of 193.21±1.7%, and a toughness of 20MJ / m 3 , UV blocking rate is 97.5%.

[0090] Comparative Example 5

[0091] (1) By adding distilled water, 8% soy protein isolate solution and 12% dialdehyde starch solution were prepared respectively, and the pH was adjusted to 11 with 0.1 M sodium hydroxide solution, and heated at 40 °C for 10 min;

[0092] (2) In terms of mass percentage, a 20% polyvinyl alcohol solution was prepared by adding distilled water and heated at 80°C for 1 hour to completely dissolve it.

[0093] (3) 60 g of the soy protein isolate solution, 5 g of the dialdehyde starch solution, and 20 g of the polyvinyl alcohol solution in steps (1) and (2) were mixed, and the pH was adjusted to 9 using a 0.8 M sodium hydroxide solution.

[0094] (4) The mixed solution in step (3) was maintained at 90°C and reacted under a pulsed electric field of 18 kV / cm for 40 min, with the pulse width and pulse frequency set to 100 μs and 2000 Hz, respectively;

[0095] (5) The reactants in step (4) were poured into a culture dish and dried in an oven at 60°C for 8 h to obtain a soy protein isolate-based film.

[0096] After testing, the soy protein isolate-based film obtained in the above steps has a tensile strength of 10.9±0.43MPa, an elongation at break of 154.26±2.7%, and a toughness of 16.4MJ / m 3 , UV blocking rate is 95.93%.

[0097] The chemical structures of the raw soy protein isolate (SPI) and the soy protein isolate-based film (SPI / P / D-0) prepared in Comparative Example 3 were characterized using X-ray photoelectron spectroscopy (XPS). The test results are shown in Figures 1 and 2. The XPS method involves fixing the sample on a sample stage and measuring its chemical composition using monochromatized Al-Kα radiation (energy 1486.6 eV) as the excitation light source. The spectrum of each element was recorded in the order of C1s, O1s, and N1s at a pass energy of 25 eV and a resolution of 0.05 eV. The data were analyzed using XPS Peakfit 4.1 software.

[0098] The mechanical properties of the soy protein isolate-based films prepared in the above examples and comparative examples were measured, and the test results are shown in Figures 3 and 4. Mechanical properties testing method: The films were cut into 70 mm x 10 mm strips and subjected to tensile testing using a universal testing machine equipped with a 10 kg load cell. The tensile speed was set at 5 mm / s, and eight parallel tests were performed. The tensile strength, elongation at break, and toughness of the different samples were averaged.

[0099] The UV barrier properties of the soy protein isolate-based films prepared in the above examples and comparative examples were measured, and the test results are shown in Figure 5. Testing method: The samples were cut into 6 cm × 1 cm strips, placed in a cuvette, and tested using a UV spectrophotometer within a wavelength range of 200 nm to 800 nm. Figure 1 shows the photoelectron spectrum of soy protein isolate (SPI), and Figure 2 shows the photoelectron spectrum of the soy protein isolate-based film (SPI / P / D-0) prepared in Comparative Example 3. Figure 1 shows that the N1s spectrum of SPI exhibits two major peaks at 399.36 eV (CN) and 400.6 eV (NH). A new C=N characteristic peak was observed in the N1s spectrum of the SPI / P / D-0 film at 399.37 eV. This confirms that the amino groups in SPI react with the aldehyde groups in dialdehyde starch to form -HC=N- functional groups, indicating the formation of a covalently cross-linked network in the soy protein isolate film.

[0100] Figures 3 and 4 show the stress-strain curves and toughness bar graphs of the soy protein isolate-based films prepared in Example and Comparative Example, respectively. Toughness indicates a material's ability to absorb energy during plastic deformation and rupture. The greater the toughness, the less likely it is to experience brittle fracture. Due to the weak interaction between SPI molecules and glycerol (G), the SPI / G film in Comparative Example 1 exhibited poor mechanical strength of 2.5 MPa, an elongation at break of 231%, and a toughness of 4.8 MJ / m. 3 Compared with the SPI / G film, the tensile strength of the SPI / P film of comparative example 2 was increased to 7.06 MPa, but its elongation at break and toughness were very poor; its elongation at break was 19.16 and its toughness was 1.2 MJ / m 3 After cross-linking with dialdehyde starch and soy protein isolate (Comparative Example 3), the toughness of SPI / P / D-0 film increased dramatically by 1492% to 19.1 MJ / m 3The tensile strength and elongation at break also increased significantly, reaching 12.79 MPa and 194.95%, respectively. This is likely due to a Schiff base reaction between the amino groups of soy protein isolate and the aldehyde groups of dialdehyde starch, resulting in covalent crosslinking. Furthermore, multiple non-covalent interactions (including hydrogen bonds and hydrophobic interactions) and covalent bonds between the hydroxyl groups of polyvinyl alcohol, the amino and hydroxyl groups of protein, and the hydroxyl groups of dialdehyde starch form an interconnected crosslinked network within the soy protein isolate-based film, enhancing the film's strength and toughness. Although the toughness, tensile strength and elongation at break of the film of Comparative Example 3 are significantly increased by cross-linking dialdehyde starch with soy protein isolate, the structure of the soy protein isolate cannot be fully expanded due to the lack of the cooperation of the pulsed electric field. The soy protein isolate-based film has a low toughness and few cross-linking sites, and the covalent cross-linking and non-covalent bond interaction between the protein and the aldehyde group is also weakened. Even the tensile strength of the SPI / P / D-0 film of Comparative Example 3 reaches 12.79±1.2MPa, the elongation at break is 194.95±4.1%, and the toughness is 19.1MJ / m 3 The ultraviolet blocking rate is 97.23%, but the tensile strength of the SPI / P / D-2 film of Example 1, which is relatively inferior to that of the examples, is 13.70±0.51MPa, the elongation at break is 217.71±5.3%, and the toughness is 23.6MJ / m 3 , compared with the ultraviolet blocking rate of 99.04%, there is still a comprehensive gap, and the ultraviolet blocking rate is difficult to meet the requirements of some applications. When the present invention further uses pulsed electric field to assist in the preparation of thin films on the basis of Comparative Example 3, Examples 1, 2, and 3 are soy protein isolate-based films prepared under electric field intensities of 2kV / cm, 4kV / cm, and 6kV / cm, respectively. The mechanical properties of the films increase with the increase of field strength. The toughness of the SPI / P / D-6 film of Example 3 is 36.2MJ / m 3 Compared with the film without pulsed electric field, it increased by 89.5%, and compared with the traditional film with glycerol (SPI / G), it increased by 654%. The tensile strength of SPI / P / D-6 film was 18.28MPa, which increased by 40.9% compared with the film without pulsed electric field and increased by 631% compared with the traditional film with glycerol (SPI / G), showing a very significant effect.

[0101] The present invention can also precisely control the mechanical properties of the material by adjusting the field strength (energy of the pulsed electric field). At low field strength (<4kV / cm), the toughness of the material can be controlled to 19~27 MJ / m 3 Under medium to high field strength (4~15kV / cm), the toughness of the material can be controlled to 27~25 MJ / m 3, to be applied to active packaging materials for different foods. Mainly, the treatment with the pulsed electric field unfolds the structure of the soy protein isolate, improves the toughness and flexibility of the protein, and exposes more sites for cross-linking with dialdehyde starch, promoting the covalent cross-linking and non-covalent bond (hydrogen bond) interaction between the amino group and the aldehyde group of the protein. Thus, a soy protein isolate-based film with excellent tensile strength and high toughness is produced. At the same time, the degree of unfolding of the soy protein isolate structure can be controlled by adjusting the magnitude of the pulsed electric field energy, thereby achieving precise control over the range of mechanical properties of the film. However, when the field strength of the PEF is too small (<2kV / cm) or too large (>15 kV / cm), such as in Comparative Examples 4 and 5, the tensile strength of the soy protein isolate film is less than 13MPa, and the toughness is ≤20MJ / m 3 However, due to the weakened mechanical properties, it is difficult to be used in food packaging bags. The SPI / P / D film prepared with the assistance of pulsed electric fields in this invention exhibits good mechanical properties, and the mechanical properties of the material can be precisely controlled by adjusting the magnitude of the pulsed electric field energy.

[0102] Figure 5 shows the UV shielding properties of soy protein isolate-based films prepared in Examples and Comparative Examples. The UV shielding rates of the SPI / G and SPI / P films were 63.3% and 79.02% (<400 nm), respectively. However, the UV shielding rate of the film cross-linked with dialdehyde starch and soy protein isolate (SPI / P / D-0) rapidly increased to 97.23% (<400 nm). This remarkable UV shielding performance is due to the strong absorption of UV light by the imine groups (C=N) generated by the Schiff base reaction. In Examples 1, 2, and 3, the UV shielding properties of the soy protein isolate-based films prepared using pulsed electric fields were all above 99% (<400 nm). This indirectly confirms that pulsed electric fields can promote the covalent cross-linking of protein amino groups with aldehyde groups, generating more imine groups. However, when the PEF field strength is too low (<2 kV / cm) or too high (>15), the UV shielding performance is weakened, falling below 99%, making it unsuitable for use in UV protective coatings. For example, it cannot be used in sun protection products such as parasols and outdoor tents.

[0103] The soy protein isolate-based film of the present invention has good mechanical properties and excellent ultraviolet barrier properties, and can therefore replace traditional plastic bags, plastic wrap, etc., and be used for packaging and preserving items, fruits and vegetables, etc., and can also be used in ultraviolet protection coating materials.

[0104] 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 considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A tough soy protein isolate-based film, It is characterized in that The method comprises mixing a soy protein isolate solution, a dialdehyde starch solution and a polyvinyl alcohol solution, adjusting the pH to 8.5-11, reacting the mixture at 60-100° C. and under the action of a pulse electric field for 10-50 minutes, pouring the product into a culture dish and drying the mixture; the frequency of the pulse electric field is 100-1000 Hz, the pulse width is 10-60 μs, and the field strength is 2-15 kV / cm.

2. The tough soy protein isolate-based film according to claim 1, It is characterized in that The mass content of the soy protein isolate solution is 1% to 10%.

3. The tough soy protein isolate-based film according to claim 1, It is characterized in that The mass content of the dialdehyde starch solution is 4% to 15%.

4. The tough soy protein isolate-based film according to claim 1, It is characterized in that The mass content of the polyvinyl alcohol solution is 5% to 20%.

5. The tough soy protein isolate-based film according to claim 1, It is characterized in that The mass ratio of the soybean protein isolate to polyvinyl alcohol is 1:0.2-1.5, and the mass ratio of the soybean protein isolate to dialdehyde starch is 2-9:

1.

6. The tough soy protein isolate-based film according to claim 1, It is characterized in that The pH value is adjusted to 8.5-11 by adding an alkaline solution, and the concentration of the alkaline solution is 0.05 mol / L-0.3 mol / L.

7. The tough soy protein isolate-based film according to claim 6, It is characterized in that The alkaline solution is a sodium hydroxide solution or a potassium hydroxide solution.

8. The tough soy protein isolate-based film according to claim 1, It is characterized in that The drying is carried out in an oven at a temperature of 30-60° C. and a drying time of 10-30 h.

9. A process for preparing the tough soy protein isolate-based film according to any one of claims 1 to 9 by precise control of a pulsed electric field, Features The following steps are involved: 1) Mixing the soy protein isolate solution, the dialdehyde starch solution and the polyvinyl alcohol solution; 2) Adjust the pH to 8.5-11, and pump the mixture into a pulsed electric field at 60-100°C for 10-50 minutes; 3) The product obtained in step 2) is poured into a culture dish and dried to obtain a soy protein isolate-based film.

10. Use of the tough soy protein isolate-based film according to any one of claims 1 to 9 in the preparation of food active packaging or ultraviolet protection materials.

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