Preparation method of sericin-soybean protein isolate-sodium alginate ternary composite membrane

Abstract

The invention belongs to the technical field of preparation of composite membranes in the field of food packaging materials, and particularly relates to a preparation method of a sericin-soybean protein isolate-sodium alginate ternary composite membrane. The high-performance ternary composite membrane is prepared by combining the soybean protein isolate and the sodium alginate as main membrane forming substrates, introducing the glycerol as a plasticizer and innovatively adding the sericin proteins in different proportions. According to the composite film, the advantages of various film forming substrates are ingeniously integrated, so that the mechanical property of the film material is remarkably improved, the film material has higher tensile strength and toughness, the antioxidant activity of the film material is greatly enhanced, and the composite film is endowed with more excellent protection function and longer service life. Wide application prospects are shown in the fields of food packaging, medical materials, biosensing and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of composite film preparation in the field of food packaging materials, and specifically relates to a method for preparing a sericin-soy protein isolate-sodium alginate ternary composite film. Background Art

[0002] Antheraea pernyi silk sericin (APSS) is one of the unique natural silk raw materials in my country. Its main components include outer layer sericin and inner layer fibroin. Antheraea pernyi silk sericin (APSS) has a variety of excellent biological activities and shows great application potential in the fields of nutritional foods, health care products and functional materials. However, the current development and utilization of APSS is still relatively low. During the processing, APSS is often directly discarded or discharged with wastewater, which not only leads to the waste of precious resources, but also causes a certain degree of pollution to the environment. Therefore, it is urgent to take effective measures to improve the recycling and utilization of APSS to promote sustainable development and reduce resource waste and environmental burden.

[0003] Edible films are made of natural polymers (such as polysaccharides, proteins and lipids) as film-forming matrices, with the addition of plasticizers and other ingredients, and are formed through intramolecular or intermolecular interactions to form films with certain barrier capabilities and mechanical properties. Compared with traditional films, edible films have the advantages of being non-toxic, easy to degrade and natural and environmentally friendly, and have become a research hotspot for new food packaging materials. These films are mainly applied to the surface of food by wrapping food or by dipping, spraying, brushing, etc., to effectively prevent food from spoiling, thereby extending the shelf life of food.

[0004] At present, many traditional packaging materials pollute the environment due to their non-degradability, and there is an urgent need to seek environmentally friendly alternatives. In this regard, edible films, as a pollution-free and degradable material, show great development potential. However, there are still some challenges with single edible films, such as insufficient mechanical strength, poor barrier properties, and lack of antioxidant and antibacterial functions, which are not conducive to food protection and shelf life extension. Therefore, the research on composite edible films has gradually received attention. By combining the advantages of different materials, the overall performance of the film is improved to meet the needs of food packaging. Continuous research in this field will provide stronger support for the widespread application and functionalization of edible films.

[0005] For a long time, sericin, as the main component of silkworm cocoons, has not been effectively utilized and is usually discharged with wastewater, which not only leads to resource waste but also pollutes the environment. Due to its unique chemical composition and structure, sericin exhibits good physical and chemical properties and biological activity, and has wide application potential in the fields of nutritional foods, health care products and functional materials. Therefore, it is feasible to use sericin as a film material, but the performance of single-component membranes is often not superior enough. In order to solve this problem, soy protein isolate and sodium alginate are widely used and become ideal film-forming materials. Combining sericin with these two materials can further improve the mechanical properties of the membrane and improve its biological activity, thereby expanding the application range of sericin. This method not only provides a theoretical basis for improving the utilization of sericin, but also lays a foundation for the development of new composite membrane materials and promotes the application of sustainable materials. Summary of the invention

[0006] The invention patent aims to prepare a high-performance ternary composite film by combining soy protein isolate and sodium alginate as the main film-forming matrix, introducing glycerol as a plasticizer, and innovatively adding sericin in different proportions. The design of the composite film of the invention cleverly integrates the advantages of multiple film-forming substrates, not only significantly improving the mechanical properties of a single film material, making it have higher tensile strength and toughness, but also greatly enhancing its antioxidant activity, giving the composite film a better protective function and a longer service life. It shows broad application prospects in many fields such as food packaging, pharmaceutical materials, and biosensors, providing new ideas and technical support for the development of composite material science.

[0007] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0008] A method for preparing a sericin-soy protein isolate-sodium alginate ternary composite film comprises the following steps:

[0009] 1) Accurately weigh soy protein isolate and sodium alginate as the main components of the membrane material; the two components are selected based on their respective excellent properties, such as the high protein content and good film-forming properties of soy protein isolate, and the thickening and stabilizing effects of sodium alginate;

[0010] 2) Adding plasticizer to the above raw materials, and adding distilled water as solvent, and stirring magnetically to ensure that all ingredients are fully dissolved and mixed evenly;

[0011] 3) adding sericin to the mixed solution obtained in step 2); the addition of sericin is intended to improve the mechanical properties, biocompatibility and other functional properties of the composite membrane, and by changing the amount of sericin added, composite membranes with different properties can be prepared to meet different application requirements;

[0012] 4) placing the mixture with sericin added in a constant temperature water bath and stirring, which helps to further promote the uniform mixing of the components and enables the sericin to better combine with the soy protein isolate and sodium alginate;

[0013] 5) pouring the mixed solution obtained in step 4) into a mold to form a film, and then placing the mold in a drying oven to dry to remove excess water and solvent, so that the film is solidified;

[0014] 6) After peeling off the film, place the composite film in a drying dish for equilibrium, which helps the composite film reach a stable humidity state, thereby improving its dimensional stability and other physical properties.

[0015] Furthermore, in the above preparation method, in step 1), the weighed amount of soy protein isolate is 4.00 g, and the weighed amount of sodium alginate is 1.00 g.

[0016] Furthermore, in the above-mentioned preparation method, in step 2), the plasticizer is 50% by mass of glycerol.

[0017] Furthermore, in the above preparation method, in step 2), the amount of distilled water added is 150 mL.

[0018] Furthermore, in the above preparation method, in step 2), the magnetic stirring is carried out on a magnetic stirrer for 30 minutes.

[0019] Furthermore, in the above preparation method, in step 3), the mass fraction of the sericin added to the soy protein isolate is 2%, 4%, 6%, or 8%.

[0020] Furthermore, in the above preparation method, in step 4), the temperature of the constant temperature water bath is 50° C., and the stirring time is 45 minutes.

[0021] Furthermore, in the above preparation method, in step 5), the drying condition is drying in a drying oven at 50° C. for 24 hours.

[0022] Furthermore, in the above preparation method, in step 6), the relative humidity of the drying dish is 75%.

[0023] Furthermore, in the above preparation method, in step 6), the equilibration time is 48 hours.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] 1. The composite film of the present invention has good compatibility: sericin, soy protein isolate and sodium alginate have good compatibility and can form a stable ternary composite film.

[0026] 2. The composite film of the present invention has excellent film-forming properties: the composite film has excellent mechanical properties, such as tensile force, elongation at break, etc., which meet the needs of practical applications.

[0027] 3. The composite film of the present invention has a wide range of applications: the composite film can be applied to food packaging, medical packaging and other fields, and has broad market prospects.

[0028] 4. The composite film of the present invention has a simple preparation method, a wide range of raw material sources, and the prepared composite film has excellent performance and wide application value. The preparation method provided by the present invention not only improves the utilization rate of sericin, but also develops a new composite film material with good performance, providing a theoretical basis and practical application value for the development of sustainable food packaging materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 The present invention provides a flow chart of the preparation process of the sericin-soy protein isolate-sodium alginate ternary composite membrane.

[0030] Figure 2 This is a comparison chart of the water solubility of sericin-soy protein isolate-sodium alginate ternary composite films with different sericin contents.

[0031] Figure 3 This is a comparison chart of water vapor permeability of sericin-soy protein isolate-sodium alginate ternary composite films with different sericin contents.

[0032] Figure 4 This is a comparison chart of the ABTS free radical scavenging rates of sericin-soy protein isolate-sodium alginate ternary composite membranes with different sericin contents.

[0033] Figure 5 This is a comparison chart of DPPH radical scavenging rates of sericin-soy protein isolate-sodium alginate ternary composite films with different sericin contents. DETAILED DESCRIPTION

[0034] In order to further understand the present invention, the preferred experimental scheme of the present invention is described below in conjunction with embodiments, but it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than limiting the requirements of the present invention.

[0035] Unless otherwise specified, the materials and reagents used in the following examples can be obtained from commercial sources.

[0036] Tussah cocoons: produced in Kuandian County, Dandong City, Liaoning Province.

[0037] Example 1 Preparation method of sericin-soy protein isolate-sodium alginate ternary composite film

[0038] (I) Preparation method

[0039] 1) Accurately weigh 4.00 g of soy protein isolate and 1.00 g of sodium alginate as the main components of the membrane material;

[0040] 2) Add 50% glycerol as a plasticizer to the above raw materials, and add 150 mL of distilled water as a solvent, and then stir on a magnetic stirrer for 30 minutes;

[0041] 3) adding sericin in an amount of 2%, 4%, 6% and 8% of the soybean protein isolate in the film-forming solution to the mixed solution respectively;

[0042] 4) placing the mixture with sericin added in a constant temperature water bath at 50° C. and stirring for 45 minutes;

[0043] 5) pouring the mixed solution obtained in step 4) into a mold to form a film, and then placing the mold in a drying oven at 50° C. and drying for 24 hours;

[0044] 6) After peeling off the film, the composite film was placed in a drying dish at a relative humidity of 75% for 48 hours to obtain 2%, 4%, 6%, and 8% sericin-soy protein isolate-sodium alginate ternary composite films, named 2% APSS, 4% APSS, 6% APSS, and 8% APSS, respectively.

[0045] (II) Performance measurement

[0046] (1) Determination of mechanical strength: The composite film samples were cut into 1 cm × 4 cm rectangles with scissors and placed on a texture analyzer. The initial clamping distance of the texture analyzer was set to 30 mm and the test speed was 1 mm / s. The maximum force and length when the film sample broke were recorded and used to calculate the tensile strength (TS) and elongation at break (EAB) of the composite film according to formulas (1-1) and (1-2). The test was repeated 3 times for each sample.

[0047]

[0048] Where: F is the maximum tension (N); d is the thickness (mm); W is the width (cm).

[0049]

[0050] Where: L is the longest stretched length (mm), L0 is the original length (mm).

[0051] The results in Table 2 show that as the sericin content increases, the tensile strength first increases and then decreases; the elongation at break decreases continuously with the increase of sericin content. This is because the interaction between the protein molecules makes the structure of the membrane more rigid and the internal network structure becomes compact.

[0052] (2) Chroma measurement: Use a colorimeter to test the chroma of the film. After calibrating the colorimeter, place the composite film sample flat on a white calibration background plate (L * =89.24, a * =-0.28, b * =-2.67) above, the test hole diameter is 8mm, and each sample is measured at least 3 times. The total color difference ΔE is calculated according to formula (1-3):

[0053] ΔE=[(LL * ) 2 +(aa * ) 2 +(bb*) 2 ] 1 / 2 (1-3)

[0054] Where: ΔE is the total color difference; L is the brightness of the composite film; a is the red / green of the composite film; b is the yellow / blue of the composite film; L * To correct the brightness of the background; a * To correct the red / green of the background; b * To correct for the yellow / blue background.

[0055] Table 1 Chromaticity of composite films

[0056]

[0057] From the results in Table 1, it can be seen that the color difference between the ternary composite films increases with the increase of sericin content, which may be due to the fact that the color of sericin itself is light yellow.

[0058] (3) Determination of thickness: Use a vernier caliper (accuracy of 0.02 mm) to measure the thickness of the composite film sample at five points, including the four corners and the center. Repeat three times and take the average value.

[0059] The results in Table 2 show that as the content of sericin increases, the thickness of the composite film gradually increases.

[0060] (4) Determination of opacity: Cut the composite film into a strip of the same size as one side of the cuvette, with a length of h, and stick it on one side. Measure the absorbance A at 600 nm. 600 , determine the light transmittance of the film, and the calculation formula is as follows (1-4):

[0061]

[0062] From the results in Table 2, it can be seen that as the content of sericin increases, the opacity of the composite film gradually increases.

[0063] (5) Determination of moisture content: Place a composite film with a mass of m1 in a forced air drying oven and dry it at 105°C to a constant weight. Take out and weigh the mass m2. Take three parallel samples from each group of composite films. Calculate the moisture content according to formula (1-5):

[0064]

[0065] Where: m1 is the mass of the composite film before drying (g); m2 is the mass of the composite film after drying (g).

[0066] From the results in Table 2, it can be seen that as the sericin content increases, the moisture content decreases.

[0067] Table 2 Mechanical strength, thickness, opacity and moisture content of composite films

[0068]

[0069] (6) Determination of water solubility: Place the composite film in a 50 mL beaker, put it in a drying oven and dry it at 105°C to constant weight, and measure the mass m1. Add 30 mL of distilled water and let it stand at room temperature for 2 hours. Dry it at 105°C to constant weight, and measure the mass m2. The water solubility is calculated according to formula (1-6):

[0070]

[0071] Depend on Figure 2 The results showed that as the sericin content increased, the water solubility first decreased, then rebounded, and then decreased again.

[0072] (7) Determination of water vapor transmission rate: Cover the mouth of the conical bottle with the composite film and seal the bottle mouth with vaseline. Spread 4g of anhydrous calcium chloride powder that has been crushed and dried to a constant weight in the conical bottle. After weighing, place the conical bottle in a constant temperature incubator and maintain constant humidity (50%) and temperature (25°C). Record the change in the weight of the conical bottle once every 24 hours for 7 consecutive days. The water vapor transmission rate (WVP) of the composite film is calculated according to formula (1-7):

[0073]

[0074] Where: WVP is water vapor transmission rate, gmm / (m 2 dkPa); Δ m / Δ t is the mass added by the conical flask per unit time (g / s); d is the film thickness (mm); A is the effective area of ​​the composite film (m 2 );Δ p is the water vapor pressure difference on both sides of the membrane (Pa).

[0075] Depend on Figure 3The results showed that as the sericin content increased, water vapor permeability first decreased, then increased, and then decreased again.

[0076] (8) Determination of ABTS cation radical scavenging ability: Mix ABTS stock solution (7.4mmol / L, 5mL) with potassium persulfate solution (2.6mmol / L, 88μL) and store at room temperature in the dark for 12h. Dilute ABTS stock solution at 1:50 before the experiment, prepare 2%, 4%, 6%, and 8% sericin composite film samples into 1mg / mL solution, take 0.4mL of each solution and add 3.9mL of diluent to mix, react in the dark for 30min, and measure the absorbance at 734nm. Vitamin C was used as the positive control group. ABTS cation radical scavenging rate was calculated according to formula (1-8):

[0077] Clearance rate (%) = [1-(A-A1) / A0] × 100 (1-8)

[0078] Wherein: A1 represents the absorbance value of the control group after the reaction; A represents the absorbance value of the sample group after the reaction; A0 represents the absorbance value of the blank group after the reaction.

[0079] Depend on Figure 4 The results showed that with the increase of sericin content, the ABTS cationic radical scavenging ability of the composite membrane was significantly improved.

[0080] (9) Determination of DPPH free radical scavenging ability: Prepare a 1 mg / mL solution of the composite film sample, take 2 mL of the composite film solution and add 2 mL of 0.5 mmol / LDPPH, react in the dark for 30 min, and measure the absorbance at 517 nm. The calculation formula is as follows (1-9):

[0081] Clearance rate (%) = [1-(AA i ) / A j ]×100 (1-9)

[0082] Where: A is the absorbance value measured at 517nm, A i is the absorbance value of the control group; A j is the absorbance value of the blank group (the sample was replaced with ethanol).

[0083] Depend on Figure 5 The results showed that with the increase of sericin content, the DPPH free radical scavenging ability of the composite film was significantly improved.

Claims

1. A method for preparing a ternary composite film of sericin-soy protein isolate-sodium alginate, characterized in that: The steps include: 1) Accurately weigh soy protein isolate and sodium alginate as the main components of the membrane material; 2) Adding plasticizer to the above raw materials, adding distilled water as solvent, and stirring with magnetic force; 3) adding sericin to the mixed solution obtained in step 2); 4) placing the mixture with sericin added in a constant temperature water bath and stirring; 5) pouring the mixed solution obtained in step 4) into a mold to form a film, and then placing the mold in a drying oven to dry; 6) After peeling off the film, place the composite film in a drying dish for balance.

2. The preparation method according to claim 1, characterized in that: In step 1), the weighed amount of soy protein isolate is 4.00 g, and the weighed amount of sodium alginate is 1.00 g.

3. The preparation method according to claim 1, characterized in that: In step 2), the plasticizer is 50% by mass of glycerol.

4. The preparation method according to claim 1, characterized in that: In step 2), the amount of distilled water added is 150 mL.

5. The preparation method according to claim 1, characterized in that: In step 2), the magnetic stirring is carried out on a magnetic stirrer for 30 minutes.

6. The preparation method according to claim 1, characterized in that: In step 3), the mass fraction of the sericin added to the soy protein isolate is 2%, 4%, 6% and 8%.

7. The preparation method according to claim 1, characterized in that: In step 4), the temperature of the thermostatic water bath is 50° C. and the stirring time is 45 minutes.

8. The preparation method according to claim 1, characterized in that: In step 5), the drying condition is drying in a drying oven at 50° C. for 24 hours.

9. The preparation method according to claim 1, characterized in that: In step 6), the relative humidity of the drying dish is 75%.

10. The preparation method according to claim 1, characterized in that: In step 6), the equilibration time is 48 hours.

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