Chitosan / corn starch slow-release antibacterial and antioxidant multifunctional composite fresh-keeping film and preparation method thereof

Abstract

A chitosan / corn starch slow-release antibacterial and antioxidant multifunctional composite fresh-keeping film and its preparation method The present invention relates to a chitosan / corn starch slow-release antibacterial and antioxidant multifunctional composite fresh-keeping film and its preparation method, and belongs to the technical field of food preservation. First, chitosan and corn starch are used as main raw materials to prepare chitosan acetic acid aqueous solution and gelatinized corn starch solution respectively, and the two solutions are evenly mixed, and then a cross-linking agent is added to react at a certain temperature to obtain a chitosan / corn starch cross-linked liquid, and then the antibacterial and antioxidant agent is adsorbed in a porous corn starch slow-release carrier; then it is evenly dispersed in the chitosan / starch cross-linked liquid, and then a plasticizer is added to prepare a film-forming liquid; finally, vacuum degassing and drying film-forming methods are used in sequence to obtain a chitosan / corn starch multifunctional composite fresh-keeping film. The fresh-keeping film prepared by the present invention has the advantages of excellent slow-release performance, antibacterial and antioxidant properties and mechanical properties, simple preparation process, etc., avoids the use of chemical preservatives, conforms to the concept of green environmental protection, and has good application prospects.

Description

[0001] The invention relates to the technical field of meat food preservation, and in particular to a chitosan / corn starch slow-release antibacterial and antioxidant multifunctional composite fresh-keeping film and a preparation method thereof. Background Art

[0002] With the increasing demand for food preservation, traditional food preservation methods rely heavily on chemical preservatives and artificial additives. While these methods can extend food shelf life, they can pose potential risks to human health and the environment. Consequently, research on natural preservatives is gaining increasing attention. Plant essential oils, as natural antibacterial and antioxidant ingredients, show promising application prospects in food preservation. However, their high volatility and rapid release properties limit their widespread application.

[0003] In the prior art, invention patent CN115246945A provides a method for preparing a chitosan / starch / composite amino acid zinc edible film for preserving strawberries and other fruits and vegetables. The film is prepared by blending a chitosan solution with a corn starch solution and adding a composite amino acid zinc as a third component to produce an edible film with antibacterial and antioxidant activity. However, the antibacterial spectrum of the composite amino acid zinc is narrow, and the inhibitory effect on certain specific microorganisms is limited. Invention patent CN118240285A provides an oxidized corn starch / polyethyleneimine / carboxymethyl chitosan composite film material, which is oxidized by sodium periodate, and the aldehyde group of the oxidized corn starch is chemically cross-linked with the amino group of the polyethyleneimine, and then cross-linked with the amino group of carboxymethyl chitosan by genipin (genipin is the product of jasminoides hydrolyzed by B-glucosidase, an excellent natural biological cross-linking agent, which can be cross-linked with proteins, collagen, gelatin and chitosan to produce biomaterials) to prepare a composite film material with good tensile properties and biodegradability. However, the antibacterial, antioxidant, and sustained-release properties of the film have not been reported, so the preservation effect can be expected to be average. Invention patent CN106883465A provides a method for preparing a chitosan composite cling film. By combining chitosan with modified nanocarbon crystals, a cling film with excellent mechanical, antibacterial, and barrier properties is prepared, but the sustained-release properties are not good.

[0004] In order to solve the problems existing in aspects such as the antimicrobial property, antioxidant property and slow-release rate of the above-mentioned preservative film, the present invention proposes that plant essential oils are loaded on a carrier with slow-release properties to control the release rate of the antimicrobial antioxidant. Porous corn starch is adopted, because of its natural, degradable and non-toxic characteristics, it becomes an ideal slow-release carrier material. Chitosan is adopted as a biodegradable natural polymer material, has good biocompatibility and antimicrobial properties, and can be used for food packaging materials. Cross-linking corn starch with chitosan can not only improve the mechanical properties of the film, but also enhance its antimicrobial and antioxidant functions and slow-release properties, thereby achieving the purpose of multifunctional fresh-keeping. Summary of the Invention

[0005] The primary purpose of the present invention is to overcome the defect of insufficient antibacterial and antioxidant capacity of existing chitosan / corn starch films, while improving the mechanical properties and sustained-release properties of the films, and to provide a chitosan / corn starch sustained-release antibacterial and antioxidant multifunctional composite fresh-keeping film and a preparation method for food preservation.

[0006] The present invention first uses chitosan and corn starch as main raw materials, prepares chitosan acetic acid aqueous solution and gelatinized corn starch solution respectively, uniformly mixes the two solutions, then adds a cross-linking agent, and undergoes cross-linking reaction at a certain temperature to obtain a chitosan / corn starch cross-linked liquid, then adsorbs an antibacterial antioxidant into a porous corn starch slow-release carrier; then uniformly disperses the antibacterial antioxidant in the chitosan / starch cross-linked liquid, and then adds a plasticizer to obtain a film-forming liquid; finally, vacuum degassing and drying film-forming methods are sequentially used to obtain a chitosan / corn starch slow-release antibacterial and antioxidant multifunctional composite fresh-keeping film, thereby improving the mechanical properties, slow-release properties and antibacterial and antioxidant properties of the chitosan / corn starch, and significantly improving the fresh-keeping effect of the multifunctional composite film.

[0007] A chitosan / corn starch slow-release antibacterial and antioxidant multifunctional composite fresh-keeping film, characterized by comprising the following components (in parts by weight):

[0008] Corn starch: 10-20 parts;

[0009] Chitosan: 4-8 parts;

[0010] Porous corn starch: 2-3 parts;

[0011] Cross-linking agent: 10-12 parts;

[0012] Plasticizer: 6-8 parts;

[0013] Antibacterial antioxidant: 0.3-0.4 parts.

[0014] Preferably, the deacetylation degree of the chitosan is greater than 97%.

[0015] Preferably, the cross-linking agent is at least one of citric acid or malic acid.

[0016] Preferably, the antibacterial antioxidant is at least one of plant essential oils thymol or tea polyphenols.

[0017] Preferably, the plasticizer is glycerol, 1,3-butanediol or a combination thereof.

[0018] Preferably, the porous corn starch particles have a size of 1 to 10 μm and a specific surface area of ​​2 to 5 m 2 / g, pore volume is 0.8~1.5cm 3 / g.

[0019] Preferably, the method for preparing the multifunctional composite cling film comprises the following steps:

[0020] (1) Chitosan was dissolved in an acetic acid aqueous solution with a mass fraction of 1 wt%, and degassed by ultrasonic treatment for 10 to 20 min to obtain a clear and transparent chitosan acetic acid aqueous solution.

[0021] (2) Dispersing corn starch in water at a mass ratio of corn starch to water of 1:10-20, gelatinizing at 80-90° C. for 1-2 hours to obtain a gelatinized corn starch solution.

[0022] (3) The porous corn starch was dispersed in an ethanol-water system with a volume ratio of 1:3, and then the antibacterial antioxidant plant essential oil was added. The mixture was stirred at room temperature and adsorbed for 3 to 5 hours so that the active ingredients of the plant essential oil were fully loaded in the porous corn starch. The mixture was filtered and dried to obtain porous corn starch particles adsorbed with the plant essential oil.

[0023] (4) The chitosan-dissolved acetic acid aqueous solution obtained in step (1) and the gelatinized corn starch solution obtained in step (2) are uniformly mixed, and then a cross-linking agent is added. The mixture is stirred and heated to 50-60° C., and the cross-linking reaction is carried out for 30-60 minutes. The mixture is then cooled to room temperature to obtain a chitosan / corn starch cross-linked solution.

[0024] (5) adding the porous corn starch granules adsorbed with plant essential oil obtained in step (3) to the chitosan / corn starch cross-linked solution obtained in step (4), and then adding a plasticizer, controlling the stirring rate at 150 to 400 rpm and the stirring time at 10 to 15 minutes to obtain a film-forming solution.

[0025] (6) The film-forming liquid obtained in step (5) is cast into a film in a rectangular tempered glass tray, and then vacuumed in a room temperature vacuum oven for 2 to 3 hours to remove bubbles to obtain a vacuum degassing film.

[0026] (7) The tray containing the vacuum degassing film was placed in a forced air oven at 40-50°C to dry the film for 12-15 hours, and the film was gently torn off with tweezers to obtain a chitosan / corn starch slow-release antibacterial and antioxidant multifunctional composite film.

[0027] The advantages of the present invention are as follows:

[0028] (1) Natural and environmentally friendly: Corn starch and chitosan are used as the main raw materials, both of which are natural and biodegradable materials, non-toxic and harmless, in line with the concept of green environmental protection.

[0029] (2) Excellent sustained-release performance: By loading plant essential oils into porous corn starch, the release rate of essential oils can be effectively controlled, and the antibacterial and antioxidant effect time can be prolonged.

[0030] (3) Strong antibacterial and antioxidant properties: After chitosan is cross-linked with corn starch, it synergizes with plant essential oils to significantly enhance the antibacterial and antioxidant capabilities of the membrane.

[0031] (4) Enhanced mechanical properties: After chitosan is cross-linked with corn starch, the tensile strength increases.

[0032] (5) Simple preparation process: The preparation method is easy to operate, the raw materials are readily available, and it is suitable for large-scale production.

[0033] The present invention will be further described in detail below through specific examples. In the following examples, the test methods for various indicators of the chitosan / corn starch slow-release antibacterial and antioxidant multifunctional composite cling film are all commonly used methods for cling film performance testing in the industry, and are as follows:

[0034] (1) Mechanical properties: Refer to GB / T 1040 standard to test the tensile strength and elongation at break of the membrane.

[0035] (2) Antibacterial property: The antibacterial ability of the plastic wrap described in this patent application was tested using a coating method.

[0036] (3) Antioxidant activity: The antioxidant activity of the membrane was determined by DPPH free radical scavenging test.

[0037] (4) Sustained-release performance: 3 g of the membrane was immersed in 250 mL of 95% ethanol solution at room temperature. 1 mL of the solution was sampled at different time intervals to measure the amount of thymol or tea polyphenols in the solution using UV spectrophotometry. The time and release rate at which the membrane release of thymol or tea polyphenols reached equilibrium, i.e., when the amount of thymol or tea polyphenols in the solution remained unchanged, were determined. DETAILED DESCRIPTION

[0038] Example 1

[0039] (1) 8 parts of chitosan were dissolved in 200 mL of 1% acetic acid aqueous solution, and the bubbles were removed by ultrasonication for 10 min to obtain a clear and transparent chitosan acetic acid aqueous solution.

[0040] (2) Disperse 10 parts of corn starch in 190 mL of water, stir under reflux, and heat in a 90°C water bath for 2 h to obtain a gelatinized corn starch solution.

[0041] (3) 2 parts of porous corn starch were dispersed in 40 mL of a 1:3 ethanol-water mixed solution, and 0.3 parts of thymol were added. The mixture was stirred and adsorbed at room temperature for 3 h to allow the thymol active ingredient to be fully loaded in the porous corn starch. The mixture was filtered and dried to obtain porous corn starch particles adsorbing thymol.

[0042] (4) The chitosan acetic acid aqueous solution obtained in step (1) and the gelatinized corn starch solution obtained in step (2) were evenly mixed, 12 parts of anhydrous citric acid as a crosslinking agent were added, the mixture was stirred and heated to 60° C., cross-linked for 30 minutes, and then cooled to room temperature to obtain a chitosan / corn starch cross-linked solution.

[0043] (5) The porous corn starch adsorbed with thymol obtained in step (3) was added to the chitosan / corn starch cross-linked solution obtained in step (4), and then 6 parts of plasticizer glycerol were added. The stirring rate was controlled to 150 rpm and the stirring time was 10 min to obtain a film-forming solution.

[0044] (6) The solution obtained in step (5) was poured into a rectangular tempered glass tray of 25.5×45 cm, and placed in a vacuum oven at room temperature for 3 h to remove bubbles and obtain a vacuum degassing film.

[0045] (7) The tray containing the vacuum degassing film was placed in a 40°C forced air oven to dry for 14 h, and the film was gently torn off with tweezers to obtain a chitosan / corn starch slow-release antibacterial and antioxidant multifunctional composite film.

[0046] Example 2

[0047] (1) Dissolve 4 parts of chitosan in 200 mL of 1% acetic acid aqueous solution and ultrasonicate for 10 min to remove bubbles to obtain a clear and transparent chitosan acetic acid aqueous solution.

[0048] (2) Disperse 20 parts of corn starch in 180 mL of water, stir under reflux, and heat in a 90°C water bath for 2 h to obtain a gelatinized corn starch solution.

[0049] (3) 3 parts of porous corn starch were dispersed in 40 mL of a 1:3 ethanol-water mixed solution, and 0.36 parts of antibacterial antioxidant tea polyphenols were added. The mixture was stirred and adsorbed at room temperature for 5 h to allow the active ingredients of tea polyphenols to be fully loaded in the porous corn starch. The mixture was filtered and dried to obtain porous corn starch particles adsorbed with tea polyphenols.

[0050] (4) The chitosan acetic acid aqueous solution obtained in step (1) and the gelatinized corn starch solution obtained in step (2) were mixed evenly, 12 parts of anhydrous citric acid as a crosslinking agent were added, the mixture was stirred and heated to 55° C., cross-linked for 45 minutes, and then cooled to room temperature to obtain a chitosan / corn starch cross-linked solution.

[0051] (5) The porous corn starch adsorbing tea polyphenols obtained in step (3) was added to the chitosan / corn starch cross-linked solution obtained in step (4), and then 8 parts of plasticizer glycerol were added. The stirring rate was controlled to 450 rpm and the stirring time was 15 minutes to obtain a film-forming solution.

[0052] (6) Pour the solution obtained in step (5) into a rectangular tempered glass tray of 25.5×45 cm, place it in a vacuum oven at room temperature and evacuate for 2.5 hours to remove bubbles, and obtain a vacuum degassing film

[0053] (7) The tray containing the vacuum degassing film was placed in a 40°C forced air oven to dry for 15 h, and the cling film was gently torn off with tweezers to obtain a chitosan / corn starch slow-release antibacterial and antioxidant multifunctional composite cling film.

[0054] Example 3

[0055] (1) Dissolve 6 parts of chitosan in 200 mL of 1% acetic acid aqueous solution, and remove bubbles by ultrasonication for 15 minutes to obtain a clear and transparent chitosan acetic acid aqueous solution.

[0056] (2) Disperse 15 parts of corn starch in 185 parts of water, stir under reflux, and heat in a 90°C water bath for 2 hours to obtain a gelatinized corn starch solution.

[0057] (3) 2.5 parts of porous corn starch were dispersed in 40 mL of an ethanol-water mixed solution with a volume ratio of 1:3, and 0.36 parts of the antibacterial antioxidant thymol were added. The mixture was stirred and adsorbed at room temperature for 4 h to allow the thymol active ingredient to be fully loaded in the porous corn starch. The mixture was filtered and dried to obtain porous corn starch particles adsorbed with thymol.

[0058] (4) The chitosan acetic acid aqueous solution obtained in step (1) and the gelatinized corn starch solution obtained in step (2) were mixed evenly, 10 parts of malic acid as a cross-linking agent were added, the mixture was stirred and heated to 50° C., cross-linked for 60 minutes, and then cooled to room temperature to obtain a chitosan / corn starch cross-linked solution.

[0059] (5) The porous corn starch adsorbing tea polyphenols obtained in step (3) was added to the chitosan / corn starch cross-linked solution obtained in step (4), and then 6 parts of plasticizer 1,3-butanediol were added. The stirring rate was controlled to 300 rpm and the stirring time was 10 min to obtain a film-forming solution.

[0060] (6) The solution obtained in step (5) was poured into a rectangular tempered glass tray of 25.5×45 cm, and placed in a vacuum oven at room temperature for 3 h to remove bubbles and obtain a vacuum degassing film.

[0061] (7) The tray containing the vacuum degassing film was placed in a 50°C forced air oven to dry for 12 h, and the film was gently torn off with tweezers to obtain a chitosan / corn starch slow-release antibacterial and antioxidant multifunctional composite film.

[0062] Comparative Example 1

[0063] Comparative Example 1 does not add anhydrous citric acid crosslinking agent in Example 1, nor does it add porous corn starch particles adsorbing thymol. Other contents are the same as in Example 1, and the specific steps are as follows:

[0064] (1) Dissolve 7 parts of chitosan in 200 mL of 1% acetic acid aqueous solution, and remove bubbles by ultrasonication for 10 minutes to obtain a clear and transparent chitosan acetic acid aqueous solution.

[0065] (2) Disperse 10 parts of corn starch in 190 mL of water, stir under reflux, and heat in a 90°C water bath for 2 h to obtain a gelatinized corn starch solution.

[0066] (3) The chitosan acetic acid aqueous solution obtained in step (1) and the gelatinized corn starch solution obtained in step (2) were uniformly mixed, and then 6 parts of plasticizer glycerol were added, and the stirring rate was controlled to be 150 rpm and the stirring time was 10 min to obtain a chitosan / corn starch composite solution.

[0067] (4) The composite liquid obtained in step (3) was poured into a 25.5×45 cm tempered glass tray, placed in a vacuum oven and evacuated for 3 h to remove bubbles to obtain a vacuum degassing film.

[0068] (5) The tray containing the vacuum degassing film was placed in a 40°C forced air oven to dry for 15 hours, and the film was gently torn off with tweezers to obtain the comparative example 1 film.

[0069] Comparative Example 2

[0070] Comparative Example 2 is the same as Example 1 except that the porous corn starch granules adsorbed with thymol are not added. The specific steps are as follows:

[0071] (1) 8 parts of chitosan were dissolved in 200 mL of 1% acetic acid aqueous solution, and the bubbles were removed by ultrasonication for 10 min to obtain a clear and transparent chitosan acetic acid aqueous solution.

[0072] (2) Disperse 10 parts of corn starch in 190 mL of water, stir under reflux, and heat in a 90°C water bath for 2 h to obtain a gelatinized corn starch solution.

[0073] (3) The chitosan acetic acid aqueous solution obtained in step (1) and the gelatinized corn starch solution obtained in step (2) were evenly mixed, 12 parts of anhydrous citric acid as a crosslinking agent were added, the mixture was stirred and heated to 60° C., cross-linked for 30 minutes, and then cooled to room temperature to obtain a chitosan / corn starch cross-linked solution.

[0074] (4) 6 parts of plasticizer glycerol were then added to the chitosan / corn starch cross-linked solution obtained in step (3), and the stirring rate was controlled to 150 rpm and the stirring time was 10 min to obtain a film-forming solution.

[0075] (5) The film-forming solution obtained in step (4) was poured into a 25.5×45 cm tempered glass tray, placed in a vacuum oven and evacuated for 3 h to remove bubbles to obtain a vacuum degassing film.

[0076] (6) Place the tray containing the vacuum degassing film in a 40°C forced air oven to dry for 15 hours, and gently tear off the preservative film with tweezers to obtain the preservative film of Comparative Example 2.

[0077] Comparative Example 3

[0078] Comparative Example 3 is the same as Example 1 except that the porous corn starch granules adsorbed with thymol are not added in Example 1. Instead, thymol is directly added. The other contents are the same as Example 1. The specific steps are as follows:

[0079] (1) 8 parts of chitosan were dissolved in 200 mL of 1% acetic acid aqueous solution, and the bubbles were removed by ultrasonication for 10 min to obtain a clear and transparent chitosan acetic acid aqueous solution.

[0080] (2) Disperse 10 parts of corn starch in 190 mL of water, stir under reflux, and heat in a 90°C water bath for 2 h to obtain a gelatinized corn starch solution.

[0081] (3) 0.3 parts of thymol was dissolved in 40 mL of an ethanol-water mixed solution with a volume ratio of 1:3 to obtain an ethanol-water solution in which thymol was dissolved.

[0082] (4) The chitosan acetic acid aqueous solution obtained in step (1) and the gelatinized corn starch solution obtained in step (2) were evenly mixed, 12 parts of anhydrous citric acid as a crosslinking agent were added, the mixture was stirred and heated to 60° C., cross-linked for 30 minutes, and then cooled to room temperature to obtain a chitosan / corn starch cross-linked solution.

[0083] (5) The ethanol-water solution in which thymol is dissolved obtained in step (3) is added to the chitosan / corn starch cross-linked solution obtained in step (4), and then 6 parts of plasticizer glycerol are added. The stirring rate is controlled to 150 rpm and the stirring time is 10 min to obtain a film-forming solution.

[0084] (6) The solution obtained in step (5) was poured into a 25.5×45 cm tempered glass tray, placed in a vacuum oven and evacuated for 3 h to remove bubbles to obtain a vacuum degassing film.

[0085] (7) Place the tray containing the vacuum degassing film in a 40°C forced air oven to dry for 15 hours, and gently tear off the preservative film with tweezers to obtain the preservative film of Comparative Example 3.

[0086] Tensile properties and elongation at break tests

[0087] The chitosan / corn starch sustained-release antibacterial and antioxidant multifunctional composite fresh-keeping film provided by the present invention shows excellent performance in terms of tensile strength and elongation at break. The tensile strengths of Example 1, Example 2 and Example 3 reached 13.11 MPa, 11.21 MPa and 13.17 MPa respectively, and the elongation at break exceeded 218%, indicating that the cross-linked structure of chitosan and corn starch and the synergistic effect of plasticizers (glycerol, 1,3-butanediol) significantly improved the mechanical properties and flexibility of the film. The addition of porous corn and cross-linking agents (anhydrous citric acid, malic acid) further enhanced the tensile strength of the film, while the loading of plant essential oils (such as thymol) had little effect on the mechanical properties, but may slightly improve the strength by enhancing the intermolecular forces. Comparative Example 1 has a significantly lower tensile strength due to the lack of a cross-linking agent, reaching only 5.11 MPa, and has the worst mechanical properties, while Comparative Example 2 and Comparative Example 3 both have a cross-linking agent, and their mechanical properties are comparable to those of Example 1, Example 2 and Example 3, highlighting the key role of the cross-linking agent in film performance. In general, the present invention successfully develops a fresh-keeping film with high tensile strength and good flexibility by optimizing the formula and preparation process, which is suitable for the field of food preservation.

[0088] Table 1 Tensile properties and elongation at break of different examples

[0089] project Added / unadded agent Tensile strength (MPa) Elongation at break (%) Example 1 Cross-linking agent, sustained-release agent, antibacterial antioxidant 13.11 218.31 Example 2 Cross-linking agent, sustained-release agent, antibacterial antioxidant 11.21 223.12 Example 3 Cross-linking agent, sustained-release agent, antibacterial antioxidant 13.17 220.12 Comparative Example 1 No cross-linking agent, no sustained-release agent, no antibacterial antioxidant 5.11 180.12 Comparative Example 2 Cross-linking agent, no sustained-release agent, no antibacterial antioxidant 12.31 220.35 Comparative Example 3 Cross-linking agent, sustained-release agent, antibacterial antioxidant 13.34 222.34

[0090] Antibacterial performance test

[0091] The present invention significantly improves the antibacterial properties of fresh-keeping film by loading plant essential oils into porous corn starch and mixing them with the film-forming liquid after cross-linking with chitosan / corn starch. Table 2 shows the size of the antibacterial zone of the fresh-keeping film of different embodiments and different comparative examples. Example 1, Example 2, and Example 3 respectively use porous corn starch to load thymol, tea polyphenols, and thymol, and their fresh-keeping film inhibition zones reach 25.5mm, 20.7mm, and 23.4mm, respectively. The porous corn starch loaded with thymol has an antibacterial effect that is better than the porous corn starch loaded with tea polyphenols. Comparative Example 3 directly adds thymol, and its fresh-keeping film inhibition zone is 23.2mm, indicating that the addition of plant essential oils significantly improves its antibacterial properties, and its effect is significantly better than Comparative Example 1 and Comparative Example 2 to which no plant essential oils are added. Mainly due to the synergistic effect of thymol and chitosan, the antibacterial action time is extended, further enhancing the antibacterial ability of the film. In general, the present invention successfully develops a fresh-keeping film with excellent antibacterial properties, which is suitable for the field of food preservation.

[0092] Table 2 Antibacterial effect of plastic wrap at different time points

[0093] project Chemicals added / not added Inhibition zone size (mm) Example 1 Cross-linking agent, sustained-release agent, antibacterial antioxidant 25.5 Example 2 Cross-linking agent, sustained-release agent, antibacterial antioxidant 20.7 Example 3 Cross-linking agent, sustained-release agent, antibacterial antioxidant 23.4 Comparative Example 1 No cross-linking agent, no sustained-release agent, no antibacterial antioxidant 13.7 Comparative Example 2 Cross-linking agent, no sustained-release agent, no antibacterial antioxidant 14.1 Comparative Example 3 Cross-linking agent, sustained-release agent, antibacterial antioxidant 23.2

[0094] Antioxidant performance test

[0095] The present invention significantly improves the antioxidant properties of the fresh-keeping film by loading plant essential oils (such as thymol and tea polyphenols) into porous corn and cross-linking them with chitosan / corn starch, as shown in Table 3. The antioxidant activities of Example 1, Example 2, Example 3 and Comparative Example 3 shown in Table 3 all exceed 75%, and their antioxidant effects are significantly better than those of Comparative Example 1 and Comparative Example 2 without adding plant essential oils, and are comparable to the antioxidant effect of Comparative Example 3 with direct addition of plant essential oils. It can be seen that thymol or tea polyphenols plant essential oils can significantly enhance the antioxidant effect of the film. Overall, the present invention has successfully developed a fresh-keeping film with excellent antioxidant properties, which is suitable for the field of food preservation.

[0096] Table 3 Antioxidant properties of different examples

[0097] project Chemicals added / not added Antioxidant activity (%) Example 1 Cross-linking agent, sustained-release agent, antibacterial antioxidant 76.34 Example 2 Cross-linking agent, sustained-release agent, antibacterial antioxidant 75.48 Example 3 Cross-linking agent, sustained-release agent, antibacterial antioxidant 77.12 Comparative Example 1 No cross-linking agent, no sustained-release agent, no antibacterial antioxidant 10.13 Comparative Example 2 Cross-linking agent, no sustained-release agent, no antibacterial antioxidant 8.59 Comparative Example 3 Cross-linking agent, sustained-release agent, antibacterial antioxidant 74.81

[0098] Plant essential oil release performance test

[0099] Table 4 compares the release rates of the composite films of the examples and comparative examples in a 95% ethanol food simulant. The release times of thymol, tea polyphenols, and thymol in the composite films of Examples 1, 2, and 3 reached equilibrium at 3840, 3910, and 3720 min, respectively, with release rates of 75.45, 72.02, and 77.64%, respectively. In Comparative Example 3, thymol was not loaded with porous corn starch, but was directly loaded with thymol. The release rate of the composite film reached equilibrium at 3360 min, with a release rate of 80.34%. Compared with the multifunctional composite film loaded with porous corn starch, the time to equilibrium was shorter and the release rate was slightly higher, thus failing to achieve the purpose of sustained release. This shows that the porous corn starch plays a "protective" role for the plant essential oils, effectively extending the release time of the plant essential oils and achieving sustained release of the plant essential oils. Comparative Examples 1 and 2 did not use thymol, and therefore had no release equilibrium time or release rate. The porous corn acts as a slow-release carrier, effectively controlling the release rate of the plant essential oil. Overall, the present invention successfully develops a fresh-keeping film with excellent slow-release properties, which is suitable for the field of food preservation.

[0100] Table 4 Sustained release of plant essential oils (thymol and tea polyphenols)

[0101] project Plant essential oil status Time to reach release equilibrium, min Release rate (%) Example 1 Porous corn starch adsorbs thymol 3840 75.45 Example 2 Porous corn starch absorbs tea polyphenols 3910 72.02 Example 3 Porous corn starch adsorbs thymol 3720 77.64 Comparative Example 1 No essential oils none none Comparative Example 2 No essential oils none none Comparative Example 3 Add thymol directly 3360 80.34

[0102] In summary, the present invention successfully develops a multifunctional composite fresh-keeping film with excellent sustained-release properties, mechanical properties, antioxidant properties and antibacterial properties, which is suitable for the field of food preservation.

Claims

1. A chitosan / corn starch slow-release antibacterial and antioxidant multifunctional composite fresh-keeping film, characterized in that: The following components are included in parts by weight: Corn starch: 10-20 parts; Chitosan: 4-8 parts; Porous corn starch: 2-3 parts; Cross-linking agent: 10-12 parts; Plasticizer: 6-8 parts; Antibacterial antioxidant: 0.3-0.4 parts; Wherein, the cross-linking agent is at least one of citric acid or malic acid; the antibacterial antioxidant is at least one of thymol or tea polyphenols; the plasticizer is glycerol, 1,3-butanediol or a combination thereof; The method for preparing the chitosan / corn starch slow-release antibacterial and antioxidant multifunctional composite fresh-keeping film comprises the following steps: (1) Dissolving chitosan in a 1% by mass acetic acid aqueous solution and performing ultrasonic degassing for 10 to 20 minutes to obtain a clear and transparent chitosan acetic acid aqueous solution; (2) dispersing corn starch in water at a mass ratio of corn starch to water of 1:10-20, and gelatinizing at 80-90° C. for 1-2 hours to obtain a gelatinized corn starch solution; (3) The porous corn starch is dispersed in an ethanol-water system with a volume ratio of 1:3, and then an antimicrobial antioxidant is added. The mixture is stirred and adsorbed at room temperature for 3 to 5 hours so that the active ingredients of the antimicrobial antioxidant are fully loaded in the porous corn starch. The mixture is filtered and dried to obtain porous corn starch particles adsorbing the antimicrobial antioxidant. (4) uniformly mixing the chitosan-dissolved acetic acid aqueous solution obtained in step (1) and the gelatinized corn starch solution obtained in step (2), adding a crosslinking agent, stirring, heating to 50-60° C., crosslinking reaction for 30-60 minutes, and then cooling to room temperature to obtain a chitosan / corn starch crosslinked solution; (5) adding the porous corn starch granules adsorbed with antibacterial antioxidants obtained in step (3) to the chitosan / corn starch cross-linked solution obtained in step (4), adding a plasticizer, controlling the stirring rate at 150 to 400 rpm, and stirring for 10 to 15 minutes to obtain a film-forming solution; (6) The solution obtained in step (5) is cast into a film in a rectangular tempered glass tray, and then evacuated in a vacuum oven at room temperature for 2 to 3 hours to remove bubbles to obtain a vacuum degassing film; (7) The tray containing the vacuum degassing film was placed in a forced air oven at 40-50°C to dry the film for 12-15 hours, and the film was gently torn off with tweezers to obtain a chitosan / corn starch slow-release antibacterial and antioxidant multifunctional composite film.

2. The chitosan / corn starch slow-release antibacterial and antioxidant multifunctional composite fresh-keeping film according to claim 1, characterized in that: The deacetylation degree of the chitosan is greater than 97%.

3. The chitosan / corn starch slow-release antibacterial and antioxidant multifunctional composite fresh-keeping film according to claim 1, characterized in that: The porous corn starch particles have a size of 1 to 10 μm and a specific surface area of ​​2 to 5 m 2 / g, pore volume is 0.8~1.5cm 3 / g.