Preservative film and method for preparing the same

Abstract

The present application relates to fruit and vegetable preservation technology field, specifically relates to a kind of preservative film and its preparation method.The specific technical scheme includes the following steps: chitosan is dissolved in glacial acetic acid, and chitosan solution is prepared;Propylene aldehyde is added in chitosan solution, after reaction, resveratrol is added, and the solution obtained by continuing to react is washed with ethyl acetate;Excess acetone is added to the water phase of the solution after washing, and the precipitate is filtered;The chitosan hydrogel solid is obtained by freeze-drying the precipitate;Chitosan hydrogel solid is dissolved in glacial acetic acid, and then cysteine solid and glycerol are added, to obtain composite chitosan hydrogel solution;Composite chitosan hydrogel solution is applied on dried sodium alginate solution to obtain composite chitosan hydrogel-sodium alginate double-layer film.The present application uses propylene aldehyde as crosslinking agent, which not only improves the resveratrol loading capacity of chitosan film, but also improves the antioxidant and antibacterial capacity of the film.The addition of cysteine solves the problem of crosslinking agent residue.

Description

Technical Field

[0001] This invention relates to the field of fruit and vegetable preservation technology, specifically to a preservation film and its preparation method. Background Technology

[0002] The transportation and storage of fruits are often prolonged due to various reasons, leading to the spoilage of large quantities of perishable fruits, resulting in food waste and economic losses. Therefore, extending the shelf life of fruits, vegetables, and other foods is of great significance in reducing food waste.

[0003] Currently, there are many technologies for fruit preservation, such as coatings, plastic packaging films, low-temperature refrigeration, and gas preservation. However, most preservation technologies have their own drawbacks. For example, wax coatings are difficult to clean and remove, affecting not only the taste of the fruit but also posing potential health risks. Similarly, commercial packaging films often lack antibacterial and antioxidant properties, resulting in suboptimal preservation. Furthermore, most plastic packaging films are petroleum-based, non-biodegradable, and easily generate microplastic waste, posing a long-term health risk to the entire ecosystem. While low-temperature refrigeration and gas preservation technologies can extend the shelf life of fruit, their energy consumption is relatively high, leading to high economic costs. Different fruits require different technological support, thus limiting their application scenarios. Therefore, developing an environmentally friendly, simple, efficient, and multi-protective preservation film is urgently needed.

[0004] Natural biodegradable polysaccharides have been used as alternatives to plastics in the development of food packaging films. Chitosan is a linear cationic polysaccharide derived from the deacetylation of chitin. Due to its excellent biocompatibility, biodegradability, and inherent antibacterial properties, it has been used in food packaging. Currently, chitosan films under research mainly fall into two categories: blended films and cross-linked films. Blended films are formed by non-covalent bonding between chitosan and functional components. For example, some studies have combined bioactive extracts from Sichuan pepper leaves with chitosan to prepare preservation films. These films are highly safe and leave no chemical residues. However, they contain fewer functional components, resulting in poorer preservation. Cross-linked films connect chitosan and functional components using cross-linking agents. Studies have used citric acid as a cross-linking agent to prepare chitosan-red and white cabbage pigment films. Due to the cross-linking agent, these films can carry more functional components. However, cross-linking residues inevitably appear during the preparation process, affecting the safety of the film. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a food preservation film and its preparation method.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] This invention discloses a method for preparing a food preservation film, comprising the following steps:

[0008] (1) Chitosan was dissolved in glacial acetic acid to prepare a chitosan solution;

[0009] (2) Add acrolein to the chitosan solution, and after the reaction, add resveratrol. Continue the reaction and wash the resulting solution with ethyl acetate.

[0010] (3) Add excess acetone to the aqueous phase of the washed solution, filter to precipitate; freeze-dry the precipitate to obtain chitosan hydrogel solid;

[0011] (4) Dissolve the chitosan hydrogel solid in glacial acetic acid, then add cysteine ​​solid and glycerol to obtain a composite chitosan hydrogel solution.

[0012] (5) The composite chitosan hydrogel solution is coated onto the dried sodium alginate solution to obtain a composite chitosan hydrogel-sodium alginate bilayer film.

[0013] Preferably, in step (1), chitosan is dissolved in glacial acetic acid and stirred at room temperature for 1 to 4 hours; in step (2), the reaction time of chitosan solution with acrolein is 4 to 12 hours, and after adding resveratrol, the reaction time is 4 to 12 hours; in step (4), after adding solid cysteine ​​and glycerol, the reaction is stirred for 4 to 12 hours.

[0014] Preferably, in step (5), the sodium alginate solution is dried at 30-80°C for 1-3 hours, and after the composite chitosan hydrogel solution is applied, it is dried at 30-80°C for 2-6 hours.

[0015] Preferably, the amount of chitosan added is 0.8 to 1.0 wt%.

[0016] Preferably, in step (2), the amount of acrolein added is 5 to 20 mmol / L, and the amount of resveratrol added is 0.1 to 0.5 wt%.

[0017] Preferably, in step (4), the volume of glacial acetic acid is 80 to 130 times the amount of chitosan.

[0018] Preferably, in step (4), the amount of cysteine ​​added is 0.01-0.1 wt%, and the amount of glycerol added is 1-5 wt%.

[0019] Preferably, in steps (1) and (4), the concentration of the glacial acetic acid is 0.1 to 2 wt%.

[0020] Preferably, in step (5), the concentration of the sodium alginate solution is 1-3 wt%.

[0021] Preferably, the amount of chitosan added is 0.8 to 1.0 wt%.

[0022] Accordingly, the composite chitosan hydrogel-sodium alginate bilayer membrane prepared according to the above preparation method is obtained.

[0023] The present invention has the following beneficial effects:

[0024] This invention utilizes highly reactive acrolein as a crosslinking agent to prepare a chitosan / sodium alginate bilayer membrane loaded with resveratrol. This not only increases the resveratrol loading of the chitosan membrane but also enhances its antioxidant and antibacterial properties. Furthermore, cysteine ​​is added during the preparation process, which further improves the membrane's antioxidant capacity and addresses the issue of residual crosslinking agent, thereby improving the membrane's safety. Attached Figure Description

[0025] Figure 1 DPPH free radical scavenging rate of the chitosan preservation film prepared in each embodiment (corresponding to the amount of resveratrol added in each embodiment);

[0026] Figure 2 A comparison of resveratrol loading in chitosan films prepared with different crosslinking agents (the amount of resveratrol added in each crosslinking agent group was 0.2 wt%).

[0027] Figure 3 A comparison of the residual acrolein content in the film before and after the addition of cysteine;

[0028] Figure 4 The antibacterial effect of the chitosan preservation films prepared in each embodiment. Detailed Implementation

[0029] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] Unless otherwise specified, the technical means used in the implementation examples are conventional means well known to those skilled in the art.

[0031] This invention discloses a method for preparing a food preservation film, comprising the following steps:

[0032] (1) Dissolve chitosan (0.8-1.0 wt%) in 80-100 mL of 0.1-2 wt% glacial acetic acid and stir at room temperature for 1-4 h to obtain a chitosan solution;

[0033] (2) Add 5-20 mmol / L acrolein to the chitosan solution and stir at room temperature for 4-12 h. After the reaction, add 0.1-0.5 wt% resveratrol and continue stirring for 4-12 h. The resulting solution is washed 1-5 times with 5-1 times the volume of ethyl acetate.

[0034] (3) Add excess acetone to the aqueous phase of the washed solution, filter the precipitate, and freeze-dry the precipitate to obtain chitosan hydrogel solid;

[0035] (4) Dissolve the chitosan hydrogel solid in 0.1-2 wt% glacial acetic acid, then add 0.01-0.1 wt% cysteine ​​solid and 1-5 wt% glycerol, stir and react for 4-12 h to obtain a composite chitosan hydrogel solution; the volume of glacial acetic acid is based on the mass of the raw material chitosan, and the amount added is 80-130 times the amount of chitosan.

[0036] (5) Add 1-3 wt% sodium alginate solution to the container and dry at 30-80℃ for 1-3 h. Spread an equal volume of composite chitosan hydrogel solution on a dry round culture dish and dry at 30-80℃ for 2-6 h to obtain a composite chitosan hydrogel-sodium alginate bilayer membrane.

[0037] The present invention will be further described below with reference to specific embodiments.

[0038] Example 1

[0039] The preparation process of food preservation film is as follows:

[0040] (1) Dissolve chitosan (1.0g, 1.0wt%) in 100mL of 1.0wt% glacial acetic acid and stir at room temperature for 4h to obtain chitosan solution.

[0041] (2) Add 1.5 mmol of acrolein to the chitosan solution and stir at room temperature for 12 h. Add 0.2 wt% resveratrol to the chitosan solution after the reaction and continue stirring for 12 h. Wash the resulting solution with ethyl acetate.

[0042] The specific washing steps are as follows:

[0043] a. Extract three times repeatedly with 100 mL of ethyl acetate;

[0044] b. Remove residual ethyl acetate from the chitosan solution by rotary evaporation.

[0045] (3) Add excess acetone to the washed chitosan solution, filter the precipitate, repeat several times until the acetone phase is nearly transparent, collect the precipitate, freeze dry, and obtain chitosan hydrogel solid.

[0046] (4) Dissolve the chitosan hydrogel solid in 100 mL of 1.0 wt% glacial acetic acid, then add 0.01 wt% cysteine ​​solid and 1 wt% glycerol, stir at room temperature for 12 h to obtain a composite chitosan hydrogel solution.

[0047] (5) Add 10 mL of 1 wt% sodium alginate solution to a round culture dish and dry at 50°C for 1.5 h. Spread 10 mL of composite chitosan hydrogel solution evenly over the dried round culture dish and continue drying at 50°C for 4 h to obtain a chitosan hydrogel-sodium alginate bilayer membrane.

[0048] The DPPH radical scavenging rate of the preservation film prepared in this example was 76.78%, as per reference. Figure 1 As shown. Compared to films without added cysteine, the residual amount of acrolein in the food preservation film was measured, and the results are as follows. Figure 3 As shown.

[0049] Example 2

[0050] The preparation process of food preservation film is as follows:

[0051] (1) Dissolve chitosan (1.0g, 1.0wt%) in 100mL of 1.0wt% glacial acetic acid and stir at room temperature for 4h to obtain chitosan solution.

[0052] (2) Add 1.5 mmol of acrolein to the chitosan solution and stir at room temperature for 12 h. Add 0.3 wt% resveratrol to the chitosan solution after the reaction and continue stirring for 12 h. Wash the resulting solution with ethyl acetate.

[0053] The specific washing steps are as follows:

[0054] a. Extract three times repeatedly with 100 mL of ethyl acetate;

[0055] b. Remove residual ethyl acetate from the chitosan solution by rotary evaporation.

[0056] (3) Add excess acetone to the washed chitosan solution, filter the precipitate, repeat several times until the acetone phase is nearly transparent, collect the precipitate, freeze dry, and obtain chitosan hydrogel solid.

[0057] (4) Dissolve the chitosan hydrogel solid in 100 mL of 1.0 wt% glacial acetic acid, then add 0.01 wt% cysteine ​​solid and 1 wt% glycerol, stir at room temperature for 12 h to obtain a composite chitosan hydrogel solution.

[0058] (5) Add 10 mL of 1 wt% sodium alginate solution to a round culture dish and dry at 50°C for 1.5 h. Spread 10 mL of composite chitosan hydrogel solution evenly over the dried round culture dish and continue drying at 50°C for 4 h to obtain a chitosan hydrogel-sodium alginate bilayer membrane.

[0059] The DPPH radical scavenging rate of the preservation film prepared in this example was 78.5%, as per reference. Figure 1 As shown.

[0060] Example 3

[0061] The preparation process of food preservation film is as follows:

[0062] (1) Dissolve chitosan (1.0g, 1.0wt%) in 100mL of 1.0wt% glacial acetic acid and stir at room temperature for 4h to obtain chitosan solution.

[0063] (2) Add 1.5 mmol of acrolein to the chitosan solution and stir at room temperature for 12 h. Add 0.4 wt% resveratrol to the chitosan solution after the reaction and continue stirring for 12 h. Wash the resulting solution with ethyl acetate.

[0064] The washing steps are as follows:

[0065] a. Extract three times repeatedly with 100 mL of ethyl acetate;

[0066] b. Remove residual ethyl acetate from the chitosan solution by rotary evaporation.

[0067] (3) Add excess acetone to the washed chitosan solution, filter the precipitate, repeat several times until the acetone phase is nearly transparent, collect the precipitate, freeze dry, and obtain chitosan hydrogel solid.

[0068] (4) Dissolve the chitosan hydrogel solid in 100 mL of 1.0 wt% glacial acetic acid, then add 0.01 wt% cysteine ​​solid and 1 wt% glycerol, stir at room temperature for 12 h to obtain a composite chitosan hydrogel solution.

[0069] (5) Add 10 mL of 1 wt% sodium alginate solution to a round culture dish and dry at 50°C for 1.5 h. Spread 10 mL of composite chitosan hydrogel solution evenly over the dried round culture dish and continue drying at 50°C for 4 h to obtain a chitosan hydrogel-sodium alginate bilayer membrane.

[0070] The DPPH radical scavenging rate of the food preservation film prepared in this embodiment was 81.19%, as referenced. Figure 1 As shown.

[0071] According to the preparation method of Example 1, different crosslinking agents were selected to prepare food preservation films. The loading of resveratrol in each prepared food preservation film was as follows: Figure 2 As shown.

[0072] The antibacterial effect of the chitosan preservation films prepared in the above embodiments was tested:

[0073] Experimental procedure: Add 100 μL of bacterial suspension (~10 μL) to the membrane surface (3 cm × 3 cm). 5 The membrane was incubated at 37°C for 12 hours (CFU / mL), then the membrane surface was rinsed with 300 μL PBS solution. 20 μL of the washing solution was spread on a nutrient agar plate and incubated at 37°C for 12 hours. The surviving colonies were then observed.

[0074] Experimental Results: Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli were selected as model bacteria to evaluate the bactericidal performance of the membrane. For example... Figure 4 As shown, chitosan itself has antibacterial properties, therefore the chitosan membrane exhibits some antibacterial ability compared to the blank membrane. However, the effect is not very significant. The antibacterial ability of the membrane is significantly improved after the addition of resveratrol. With the addition of the cross-linking agent (acrylaldehyde), the resveratrol loading in the membrane also increases. Therefore, the antibacterial ability of the membrane is significantly improved. Furthermore, the antibacterial ability of the membrane is enhanced with increasing resveratrol content.

[0075] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for preparing a food preservation film, characterized in that: Includes the following steps: (1) Chitosan is dissolved in glacial acetic acid to prepare a chitosan solution; the amount of chitosan added is 0.8-1.0 wt%. (2) Acrolein is added to the chitosan solution, followed by resveratrol. The resulting solution is washed with ethyl acetate. The amount of acrolein added is 5–20 mmol / L, and the amount of resveratrol added is 0.1–0.5 wt%. (3) Add excess acetone to the aqueous phase of the washed solution, filter to precipitate; freeze-dry the precipitate to obtain chitosan hydrogel solid; (4) Dissolve the chitosan hydrogel solid in glacial acetic acid, then add cysteine ​​solid and glycerol to obtain a composite chitosan hydrogel solution; the amount of cysteine ​​added is 0.01-0.1 wt%, and the amount of glycerol added is 1-5 wt%. (5) The composite chitosan hydrogel solution is coated onto the dried sodium alginate solution to obtain a composite chitosan hydrogel-sodium alginate bilayer film.

2. The preparation method according to claim 1, characterized in that: In step (1), chitosan is dissolved in glacial acetic acid and stirred at room temperature for 1-4 hours; in step (2), the reaction time of chitosan solution with acrolein is 4-12 hours, and after adding resveratrol, the reaction time is 4-12 hours; in step (4), after adding solid cysteine ​​and glycerol, the reaction is stirred for 4-12 hours.

3. The preparation method according to claim 1, characterized in that: In step (5), the sodium alginate solution is dried at 30-80℃ for 1-3 hours. After the composite chitosan hydrogel solution is applied, it is dried at 30-80℃ for 2-6 hours.

4. The preparation method according to claim 1, characterized in that: In step (4), the volume of glacial acetic acid is 80 to 130 times that of chitosan.

5. The preparation method according to claim 1 or 4, characterized in that: In steps (1) and (4), the concentration of glacial acetic acid is 0.1 to 2 wt%.

6. The preparation method according to claim 1, characterized in that: In step (5), the concentration of the sodium alginate solution is 1-3 wt%.

7. The composite chitosan hydrogel-sodium alginate bilayer membrane prepared by the preparation method according to any one of claims 1 to 6.

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