A method for preparing a high-toughness, long-lasting freshness-preserving composite coating material

Abstract

This invention discloses a method for preparing a high-toughness, long-lasting preservation composite coating material. Nanoparticles are obtained by combining soybean protein crosslinking with emulsified antibacterial components, and then mixed with chitosan and gluconolactone to form a film. The edible coating has high toughness and moisturizing effect, effectively isolating moisture and oxygen to achieve high-efficiency preservation. It is also stable, does not delaminate, and can exert its antioxidant and antibacterial properties for a long time. When applied to the preservation of agricultural products, it is safe, non-toxic, and edible, effectively alleviating decay and respiration, and extending shelf life.

Description

Technical Field

[0001] This invention relates to the field of food preservation technology, specifically to a method for preparing a high-toughness, long-lasting composite coating material for food preservation. Background Technology

[0002] Biodegradable materials have become a research hotspot in recent years. Although many biodegradable packaging products have appeared on the market, they are mainly in the form of shopping bags, garbage bags, and agricultural films, which have problems such as excessively high or low air permeability and low moisture permeability, which are not conducive to the post-harvest preservation of fresh agricultural products. In addition to film packaging, edible packaging (coatings) is also a hot trend. These are mainly based on plant-based polysaccharides and proteins, supplemented with functional modifications from active factors. They are completely biodegradable in the natural environment and can be recycled, essentially making them cleaner packaging. Existing research shows that edible coatings have great potential for the post-harvest preservation of fresh agricultural products. Chitosan is currently the most studied edible coating material for agricultural products. However, its acid solubility makes it prone to causing acid burn to fruits and vegetables, damaging their appearance and quality, and also producing off-flavors that affect the flavor of the agricultural products themselves. Water-soluble chitosan has poor antibacterial properties, and the films prepared from it have problems such as brittleness and hydrophilicity, which limit its application in the field of coating materials. Therefore, it is very necessary to construct a water-soluble chitosan coating with superior antibacterial activity and good toughness for the preservation of fresh agricultural products. Studies have shown that plant essential oils have many active antibacterial components, which can improve the antibacterial activity of chitosan coatings, but they impair the toughness of the coating. This is mainly because essential oils have strong hydrophobicity and poor dispersibility in aqueous solutions. They interact with chitosan molecules at the interface, causing the coating to become loose due to phase separation. Therefore, constructing a class of edible composite coating materials with good antibacterial and mechanical properties has good prospects. Summary of the Invention

[0003] To address the above problems, the present invention aims to provide a method for preparing a high-toughness, long-lasting, and fresh-keeping composite coating material.

[0004] The technical content of this invention is as follows:

[0005] This invention provides a method for preparing a high-toughness, long-lasting, fresh-keeping composite coating material, comprising the following steps:

[0006] (1) The soybean protein cross-linked product and antibacterial components were thoroughly mixed and reacted to obtain soybean protein cross-linked product-essential oil nanoparticles;

[0007] (2) Dissolve soluble chitosan in pure water, add the soybean protein crosslinking-antibacterial nanoparticles prepared in step (1), stir and mix, then add glucono-delta-lactone and continue to mix, then perform ultrasonic degassing to obtain an edible coating liquid.

[0008] The method for preparing the soybean protein crosslinker includes the following steps:

[0009] S1: Soy protein is initially modified to obtain a pre-modified soy protein concentrate;

[0010] S2: Mannitol and sodium ascorbate are thoroughly mixed with water at a mass ratio of 21-25:4-7 and then subjected to ultrasonic treatment. The pH is adjusted to 8-9. The pre-modified soybean protein concentrate is added to it and heated at 80-90℃ for 30-50 minutes. The pH is then adjusted to neutral to obtain the soybean protein crosslinking product.

[0011] The soy protein mentioned is a type of soy protein isolate or soy protein concentrate, with a concentration of 5%-10%.

[0012] The modification method of the primary modified soybean is to disperse soybean protein in water at a volume ratio of 5-7 times, mix thoroughly, and then add tris(2-carboxyethyl)phosphonic acid hydrochloride at a mass ratio of 30-36:4-7. After the reaction is complete, the mixture is obtained by dialysis and concentration under reduced pressure.

[0013] The preparation method of the soybean protein crosslinked compound-essential oil nanoparticles is as follows: the antibacterial component is emulsified and dispersed with the soybean protein crosslinked compound in water, the pH is adjusted to alkaline, and high-pressure homogenization is performed to obtain soybean protein crosslinked compound-antibacterial component nanoparticles.

[0014] The emulsification process involves adding the antibacterial component and sodium stearoyl lactylate to an equal volume of water at a mass ratio of 1-3:2-4 and mixing thoroughly at a temperature of 50-70°C.

[0015] The high-pressure homogenization temperature is 50-60℃, and the homogenization pressure is 1000-1400psi.

[0016] The antibacterial component is one or more of cinnamaldehyde, thymol, and eugenol;

[0017] The emulsified antibacterial components exhibit improved dispersibility and stronger antibacterial and antioxidant properties.

[0018] The soy protein crosslinking product is made by first modifying soy protein, and then modifying it under alkaline conditions by utilizing the electrophilic properties of the hydroxyl groups of mannitol and sodium ascorbate to react with the alkaline side amino groups and the carboxyl groups of the side chains. The hydrogen bonds formed weaken the intermolecular forces of soy protein, resulting in a soy protein crosslinking product with high elasticity and good extensibility. Sodium stearoyl lactylate further enhances its elasticity and extensibility by crosslinking with soy protein.

[0019] The composite coating material comprises the following components in parts by weight: 9-11 parts of soybean protein crosslinking agent, 23-26 parts of chitosan, 1-1.8 parts of antibacterial component, 0.5-1.1 parts of glucono-delta-lactone, and 900-1000 parts of water.

[0020] The composite coating material comprises the following components in parts by weight: 10 parts soybean protein crosslinker, 24 parts chitosan, 1.4 parts antibacterial component, 0.8 parts glucono-delta-lactone, and 950 parts water.

[0021] Gluconolactone can utilize its spontaneous hydrolysis properties to form gluconic acid, which has a hygroscopic and preservative effect. The formed gluconic acid has a slow acidification effect on soybean protein, but the hydroxyl and ether bonds of sugar alcohols in soybean protein cross-links can slow down this process.

[0022] Beneficial Effects: The method for preparing the composite coating material provided by this invention modifies soybean protein by linking it with mannitol and sodium ascorbate, resulting in a soybean protein cross-linked product with high extensibility. Nanoparticles are obtained by combining the soybean protein cross-linked product with emulsified antibacterial components. The self-assembly characteristics of soybean protein and the emulsifying stability of the cross-linked product encapsulate the antibacterial components, increasing their dispersion stability. When mixed with chitosan to form a film, the filling characteristics of the emulsified antibacterial components stably fill the chitosan. Together with the soybean protein cross-linked product, this improves the toughness of the edible coating, effectively isolating moisture and oxygen for efficient preservation. The coating is stable, does not delaminate, and maintains its antioxidant and antibacterial properties for a long time. When applied to the preservation of agricultural products, it is safe, non-toxic, and edible, effectively alleviating spoilage and respiration, and extending shelf life.

[0023] Instruction manual illustrations

[0024] Figure 1 Microstructure diagram of composite coating material;

[0025] Figure 2 This is a picture showing the appearance and quality of strawberries after storage. Detailed Implementation

[0026] The present invention will be further described in detail below through specific implementation examples. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of protection of the present invention. After reading the present invention, any modifications of the present invention in various equivalent forms by those skilled in the art fall within the scope of the appended claims.

[0027] Unless otherwise specified, all raw materials and reagents used in this invention are from the conventional market.

[0028] Example 1

[0029] A method for preparing a high-toughness, long-lasting freshness-preserving composite coating material

[0030] (1) 1.4 parts of antibacterial component were emulsified and dispersed in water with 10 parts of soybean protein crosslinking. The emulsification was carried out by adding thymol and sodium stearoyl lactylate in an equal volume of water at a mass ratio of 2:3 and mixing them thoroughly at a temperature of 50°C. The pH was adjusted to 8 and high pressure homogenization was performed to obtain soybean protein crosslinking-antibacterial component nanoparticles. The high pressure homogenization temperature was 55°C and the homogenization pressure was 12000psi.

[0031] (2) Dissolve 24 parts of soluble chitosan in 1000 parts of pure water, add the soybean protein crosslinking-antibacterial nanoparticles prepared in step (1), stir and mix, then add 0.8 parts of glucono-delta-lactone and continue to mix, and then perform ultrasonic degassing to obtain an edible coating liquid.

[0032] The method for preparing the soybean protein crosslinker includes the following steps:

[0033] S1: The 8% soy protein isolate was initially modified to obtain a pre-modified soy protein concentrate: Soy protein was dispersed in water at a volume ratio of 6 times and thoroughly mixed. Tris(2-carboxyethyl)phosphonic hydrochloride (2-carboxyethyl)phosphonic hydrochloride at a mass ratio of 33:6 was added dropwise. After the reaction was complete, the concentrate was obtained by dialyzing and concentration under reduced pressure.

[0034] S2: Mannitol and sodium ascorbate were thoroughly mixed with water at a mass ratio of 23:6 and then subjected to ultrasonic treatment. The pH was adjusted to 9. The pre-modified soybean protein concentrate was added to the mixture and heated at 85°C for 40 minutes. The pH was then adjusted to neutral and concentrated under reduced pressure to obtain the soybean protein crosslinking product. The reduced pressure was 60 kPa.

[0035] Example 2

[0036] A method for preparing a high-toughness, long-lasting freshness-preserving composite coating material

[0037] (1) Emulsify 1 part of antibacterial component and disperse it with 9 parts of soybean protein crosslinking in water. Emulsify by adding eugenol and sodium stearoyl lactylate in an equal volume of water at a mass ratio of 1:2 and mixing them thoroughly at a temperature of 60°C. Adjust the pH to 9 and perform high pressure homogenization to obtain soybean protein crosslinking-antibacterial component nanoparticles. The high pressure homogenization temperature is 50°C and the homogenization pressure is 1000psi.

[0038] (2) Dissolve 23 parts of soluble chitosan in 900 parts of pure water, add the soybean protein crosslinking-antibacterial nanoparticles prepared in step (1), stir and mix, then add 0.5 parts of glucono-delta-lactone and continue to mix, and then perform ultrasonic degassing to obtain an edible coating liquid.

[0039] The method for preparing the soybean protein crosslinker includes the following steps:

[0040] S1: The 5% soy protein isolate was initially modified to obtain the initially modified soy protein concentrate: Soy protein was dispersed in water at a volume ratio of 5 times, mixed thoroughly, and then tris(2-carboxyethyl)phosphonic hydrochloride (2-carboxyethyl)phosphonic hydrochloride was added dropwise at a mass ratio of 30:4. After the reaction was complete, the concentrate was obtained by dialyzing and concentration under reduced pressure.

[0041] S2: Mannitol and sodium ascorbate were thoroughly mixed with water at a mass ratio of 21:4 and then subjected to ultrasonic treatment. The pH was adjusted to 8. The pre-modified soybean protein concentrate was added to the mixture and heated at 80℃ for 30 minutes. The pH was then adjusted to neutral and compressed under reduced pressure to obtain the soybean protein crosslinking product. The reduced pressure was 60 kPa.

[0042] Example 3

[0043] A method for preparing a high-toughness, long-lasting freshness-preserving composite coating material

[0044] (1) 1.8 parts of antibacterial component were emulsified and dispersed in water with 11 parts of soybean protein crosslinking. The emulsification was carried out by adding cinnamaldehyde and sodium stearoyl lactylate in an equal volume of water at a mass ratio of 3:4 and mixing them thoroughly at a temperature of 70°C. The pH was adjusted to 10 and high pressure homogenization was carried out to obtain soybean protein crosslinking-antibacterial component nanoparticles. The high pressure homogenization temperature was 60°C and the homogenization pressure was 1400psi.

[0045] (2) Dissolve 26 parts of soluble chitosan in 950 parts of pure water, add the soybean protein crosslinking-antibacterial nanoparticles prepared in step (1), stir and mix, then add 1.1 parts of glucono-delta-lactone and continue to mix, then perform ultrasonic degassing to obtain an edible coating liquid.

[0046] The method for preparing the soybean protein crosslinker includes the following steps:

[0047] S1: The 10% soy protein isolate was initially modified to obtain a pre-modified soy protein concentrate: Soy protein was dispersed in water at a volume ratio of 7 times, mixed thoroughly, and then tris(2-carboxyethyl)phosphonic hydrochloride (2-carboxyethyl)phosphonic hydrochloride was added dropwise at a mass ratio of 36:7. After the reaction was complete, the concentrate was obtained by dialyzing and concentration under reduced pressure.

[0048] S2: Mannitol and sodium ascorbate were thoroughly mixed with water at a mass ratio of 25:7 and then subjected to ultrasonic treatment. The pH was adjusted to 8. The pre-modified soybean protein concentrate was added to the mixture and heated at 90℃ for 50 minutes. The pH was then adjusted to neutral and compressed under reduced pressure to obtain the soybean protein crosslinking product. The reduced pressure was 60 kPa.

[0049] Comparative Example 1

[0050] The difference between Comparative Example 1 and Example 3 is that Comparative Example 1 uses equal amounts of soy protein, mannitol and sodium ascorbate instead of soy protein crosslinking, while the others remain unchanged.

[0051] Comparative Example 2

[0052] The difference between Comparative Example 2 and Example 3 is that in the preparation of the soybean protein crosslinking material added in Comparative Example 2, an equal amount of sodium ascorbate was used instead of mannitol, while everything else remained the same.

[0053] Comparative Example 3

[0054] The difference between Comparative Example 3 and Example 3 is that the antibacterial component added in Comparative Example 3 is not pre-emulsified, while everything else remains the same.

[0055] Comparative Example 4

[0056] The difference between Comparative Example 4 and Example 1 is that no gluconolactone was added to Comparative Example 4, while everything else remained the same.

[0057] I. The performance of the composite coating materials prepared in the examples and comparative examples was tested, and the test results are shown in Table 1.

[0058] Table 1

[0059]

[0060] Note: Antibacterial activity refers to the inhibitory activity of the coating solution against Staphylococcus aureus and Salmonella. - indicates no antibacterial activity, + indicates inhibitory activity, and ++ indicates strong inhibitory activity.

[0061] As shown in Table 1, the preservation composite coating material prepared by the present invention has good antibacterial effect, antioxidant properties, and high toughness. Its elongation at break can reach up to nearly 60%, which is high toughness.

[0062] II. Testing the Preservation Performance of Composite Coating Materials on Strawberries

[0063] (1) The microstructure of the composite coating material prepared in the example is as follows: Figure 1 As shown.

[0064] (2) Test on the appearance preservation effect of strawberries

[0065] The composite coating material prepared in Example 3 was used to soak freshly picked strawberries of similar ripeness. After drying, the strawberries were packaged in PET boxes and sealed, then stored at room temperature (28±2℃). A commercially available preservative coating was used as Control Example 1, and strawberries without preservative treatment were used as Control Example 2. The strawberries were stored for 3 days as follows: Figure 2 As shown, Example 3 of the present invention can effectively inhibit the rotting and spoilage of strawberries, extending the shelf life of strawberries at room temperature from 1 day to 3 days, which is more effective than ordinary preservation coatings on the market.

[0066] (3) Respiration test on strawberries

[0067] The composite coating materials prepared in the examples and comparative examples were used to preserve and seal strawberries according to the method in (1). One pound of strawberries was placed in a 2L sealed container in each group. A carbon dioxide concentration meter was placed in the container, and the gas changes were recorded within 6 minutes. The respiration intensity of the strawberries was calculated by the increase in carbon dioxide. The test results are shown in Table 2.

[0068] Table 2

[0069]

[0070] As shown in Table 2, the composite coating material prepared in the examples can effectively inhibit strawberry respiration, thereby reducing the self-loss caused by strawberry respiration.

[0071] The composite coating material prepared by this invention has excellent preservation properties, effectively scavenges free radicals, exhibits strong antibacterial activity, high extensibility, and high toughness. It effectively isolates air and water, thereby slowing down respiration and microbial decomposition. As shown in the examples and comparative examples, this invention modifies soybean protein by reacting mannitol and sodium ascorbate with soybean protein to form hydrogen bonds. The resulting soybean protein cross-linked material combines the physiological activities of the three, significantly improving antioxidant and antibacterial properties. The synthesis of hydrogen-bonded groups also enhances the extensibility of soybean protein, correspondingly increasing the toughness of the coating material. Furthermore, the emulsification of antibacterial components followed by nano-sizing with soybean protein cross-linked materials solves the problem of poor compatibility between hydrophobic antibacterial components and other materials, thus preserving the toughness of chitosan. The resulting coating material possesses the antioxidant and antibacterial properties of the antibacterial components, while glucono-delta-lactone has hygroscopic, moisturizing, and oxygen-absorbing properties, further improving the preservation and mechanical properties of the composite coating material.

Claims

1. A method for preparing a high-toughness long-lasting preservative composite coating film material, characterized by, Includes the following steps: (1) After emulsifying the antibacterial component, it was dispersed in water with soybean protein crosslinking material, the pH was adjusted to alkaline, and high pressure homogenization was performed to obtain soybean protein crosslinking material-antibacterial component nanoparticles. The antibacterial component is one or more of cinnamaldehyde, thymol, and eugenol; The emulsification process involves adding the antibacterial component and sodium stearoyl lactylate to an equal volume of water at a mass ratio of 1-3:2-4 and mixing thoroughly at a temperature of 50-70°C. The method for preparing the soybean protein crosslinker includes the following steps: S1: Soy protein is initially modified to obtain a pre-modified soy protein concentrate; S2: Mannitol and sodium ascorbate are thoroughly mixed with water at a mass ratio of 21-25:4-7 and then subjected to ultrasonic treatment. The pH is adjusted to 8-9. The pre-modified soybean protein concentrate is added to it and heated at 80-90℃ for 30-50 minutes. The pH is then adjusted to neutral and compressed under reduced pressure to obtain soybean protein crosslinks. The method for preparing the primary modified soybean protein is as follows: soybean protein is dispersed in water at a volume ratio of 5-7 times, thoroughly mixed, and then tris(2-carboxyethyl)phosphonic acid hydrochloride is added dropwise at a mass ratio of 30-36:4-7. After removing excess tris(2-carboxyethyl)phosphonic acid hydrochloride by dialysis, the mixture is concentrated under reduced pressure. (2) Dissolve soluble chitosan in pure water, add the soybean protein crosslinking-antibacterial nanoparticles prepared in step (1), stir and mix, then add glucono-delta-lactone and continue to mix, then perform ultrasonic degassing to obtain an edible coating liquid.

2. The method for preparing a high-toughness, long-lasting freshness-preserving composite coating material according to claim 1, characterized in that, The soy protein mentioned is a type of soy protein isolate or soy protein concentrate, with a concentration of 5%-10%.

3. The method for preparing a high-toughness, long-lasting freshness-preserving composite coating material according to claim 1, characterized in that, The high-pressure homogenizer has a temperature of 50-60℃ and a homogenization pressure of 1000-1400 psi.

4. The method for preparing a high-toughness, long-lasting freshness-preserving composite coating material according to claim 1, characterized in that, The composite coating material comprises the following raw materials in parts by weight: 9-11 parts of soybean protein crosslinking agent, 23-26 parts of chitosan, 1-1.8 parts of antibacterial component, 0.5-1.1 parts of glucono-delta-lactone, and 900-1000 parts of water.

5. The method for preparing a high-toughness, long-lasting freshness-preserving composite coating material according to claim 1, characterized in that, The composite coating material comprises the following raw materials in parts by weight: 10 parts soybean protein crosslinker, 24 parts chitosan, 1.4 parts antibacterial component, 0.8 parts glucono-delta-lactone, and 950 parts water.

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