CN117736477A

CN117736477A - Sandwich type multi-layer antibacterial composite film added with cinnamaldehyde and preparation method thereof

Info

Publication number: CN117736477A
Application number: CN202311740582.2A
Authority: CN
Inventors: 任雪娇; 郝子娜; 周铭懿
Original assignee: Jinzhou Medical University
Current assignee: Jinzhou Medical University
Priority date: 2023-12-18
Filing date: 2023-12-18
Publication date: 2024-03-22

Abstract

The invention provides a sandwich type multilayer antibacterial composite film added with cinnamaldehyde and a preparation method thereof, and belongs to the technical field of antibacterial film preparation. The preparation method comprises the steps of mixing chitosan, glycerol and tween-80, stirring to obtain chitosan film liquid, adding cinnamaldehyde to obtain chitosan+cinnamaldehyde film liquid, pouring the linseed film liquid into a linseed film, pouring the chitosan+cinnamaldehyde film liquid onto the linseed film, and finally continuously pouring the linseed film liquid onto the chitosan+cinnamaldehyde film. According to the invention, the cinnamaldehyde is clamped in the flaxseed adhesive film layer, and the release of the cinnamaldehyde is slowed down through the interaction of chitosan and the cinnamaldehyde, so that the acting time of the cinnamaldehyde in the packaging material is prolonged, the packaging material has longer-lasting antibacterial activity, and a foundation is provided for the application of the packaging material in meat product fresh-keeping.

Description

Sandwich type multi-layer antibacterial composite film added with cinnamaldehyde and preparation method thereof

Technical Field

The invention belongs to the technical field of antibacterial film preparation, and particularly relates to a sandwich type multilayer antibacterial composite film added with cinnamaldehyde and a preparation method thereof.

Background

As consumer demand for fresh, ready-to-eat or semi-finished food products increases, how to maintain food safety and quality further exacerbates the challenges of the various links of the supply chain. Spoilage of foods and contamination by pathogenic microorganisms remain a significant problem. For example, bacterial contamination can negatively impact the shelf life and overall quality of food products and increase the risk of food-borne diseases. However, consumer use of synthetic preservatives has been a long felt contradiction. Natural products containing plant components such as essential oils are used to prevent spoilage of foods and are becoming increasingly popular with consumers. Meat products are rich in proteins and lipids, which make them extremely susceptible to spoilage, and in order to solve this problem, researchers have developed food packaging materials containing antibacterial and antioxidant components. For example, tea polyphenols are added to multilayer films formed from polylactic acid, polyvinyl alcohol and polycaprolactone using lamination techniques to provide antioxidant and antimicrobial effects, improving shelf life and quality of meat products.

It has been found that Cinnamaldehyde (CIN) is a safe food additive with unique aroma. In addition, CIN has good antibacterial activity against a broad spectrum of pathogenic microorganisms, and can be used for preparing edible antibacterial film for inhibiting activity of food-borne pathogens by direct contact or release of steam in a closed container. However, CIN has a strong odor which may have adverse organoleptic effects if added directly to food products, and is unstable and volatile, and its direct addition to film-forming substrates causes rapid release of the active substances, resulting in a significant reduction in antibacterial activity.

Therefore, the invention provides a sandwich type multi-layer antibacterial composite film added with cinnamaldehyde and a preparation method thereof.

Disclosure of Invention

In order to solve the technical problems, the invention provides a sandwich type multilayer antibacterial composite film added with cinnamaldehyde and a preparation method thereof.

In order to achieve the above purpose, the present invention provides the following technical solutions:

the invention provides a sandwich type multi-layer antibacterial composite film added with cinnamaldehyde, wherein the cinnamaldehyde is positioned in the middle layer of the sandwich type multi-layer antibacterial composite film, and the sandwich type multi-layer antibacterial composite film sequentially comprises a flaxseed film layer, a chitosan and cinnamaldehyde film layer and a hemp seed film layer from top to bottom.

Wherein the symbol "+" represents the meaning of the sum.

The invention also provides a preparation method of the sandwich type multi-layer antibacterial composite film added with cinnamaldehyde, which is characterized by comprising the following steps of:

dissolving Chitosan (CS) with glacial acetic acid, adding glycerol, stirring in water bath to obtain a mixture, cooling, adding tween-80, mixing, stirring to obtain chitosan membrane solution, adding Cinnamaldehyde (CIN) into the chitosan membrane solution, and continuously mixing and stirring to obtain chitosan+cinnamaldehyde membrane solution;

pouring a Flaxseed Gum (FG) film liquid into a flaxseed gum film, pouring the chitosan and cinnamaldehyde film liquid onto the flaxseed gum film, and drying to obtain a flaxseed gum double-layer film loaded with chitosan and cinnamaldehyde film;

pouring flaxseed adhesive film liquid on the double-layer chitosan and cinnamaldehyde film, and drying to obtain the sandwich type multilayer antibacterial composite film (FG/CS/CIN antibacterial composite film).

Further, the addition amount of the glycerol is 20% of the mass of the chitosan, and the addition amount of the tween-80 is 0.5% of the volume of the mixture.

Further, the addition amount of the cinnamaldehyde is 1.0% -1.5% of the volume of the chitosan membrane liquid, and the prepared antibacterial membrane is of a scale-shaped structure, which indicates that CIN promotes the close combination of surrounding CS and FG polysaccharide at the concentration.

When the adding amount of the cinnamaldehyde is too low, in the film forming process, the volatilization of the cinnamaldehyde and the hydrophobic interaction between the cinnamaldehyde and the polysaccharide group change the reticular structure of the film to form a lamellar structure with layering sense, and holes are filled in the lamellar structure, so that the mechanical property is reduced; when the addition amount of cinnamaldehyde is too high, white spots are generated due to agglomeration of cinnamaldehyde, a network structure between CS and FG is broken by high concentration of CIN, and a crystallization area starts to be reduced, so that the elongation at break of the antibacterial film is obviously reduced, and therefore, the optimal addition amount of CIN in CS film liquid is determined to be 1.0% -1.5%.

Further, the preparation method of the flaxseed adhesive film liquid comprises the following steps:

and dissolving the flaxseed gum with deionized water to obtain flaxseed gum solution, and then adding glycerol into the solution and stirring the mixture in a water bath to obtain the flaxseed gum film liquid.

Still further, the flaxseed gum solution has a concentration of 0.5g/100mL.

Further, the glycerol is added in an amount of 20% of the mass of the flaxseed gum.

The invention also provides application of the sandwich type multi-layer antibacterial composite film added with cinnamaldehyde in preparing food packaging materials.

Under the laboratory test level, the preparation method of the sandwich type multi-layer antibacterial composite film added with cinnamaldehyde provided by the invention more specifically comprises the following steps of:

preparation of Flaxseed Gum (FG) membrane liquid: accurately weighing 0.5g FG, dissolving in 100mL deionized water, continuously stirring at 60 ℃ by using a magnetic stirrer until the FG is dissolved, preparing to obtain FG solution, adding 20% (w/w, FG mass) of glycerin as a plasticizer, stirring in a water bath at 60 ℃ for 30min to promote uniform mixing of the glycerin and FG solution, taking out, standing at room temperature overnight, and removing bubbles to obtain FG membrane solution.

Preparation of FG film: 10mL of the FG film liquid prepared above was poured into a disposable sterile plastic plate with a diameter of 90mm, and the plate was placed horizontally in a forced air drying oven and dried at 40℃for 6 hours to obtain FG film, which had already been film-formed but still had tackiness.

Preparation of chitosan+cinnamaldehyde (CS+CIN) membrane liquid: accurately weighing 1.0g of CS, adding 100mL of 1wt% glacial acetic acid solution, fully stirring in a water bath at 60 ℃ until the solution is completely dissolved, adding 20% of glycerin (w/w, CS mass), stirring in the water bath at 60 ℃ for 30min to obtain a mixture, cooling, adding 0.5% of Tween-80 (v/v, mixture), mixing and stirring for 30min to obtain CS membrane solution, adding CIN of 1.0% -1.5% (v/v, CS membrane solution) into the CS membrane solution, continuously mixing and stirring for 30min to form CS+CIN membrane solution, and standing for 1h to enable the CS+CIN membrane solution to be fully emulsified and remove bubbles.

Preparation of flaxseed gum film loaded with chitosan+cinnamaldehyde film: and pouring 10mL of the prepared CS+CIN film liquid on the prepared FG film, uniformly casting the film liquid to completely cover the surface of the FG film, horizontally placing a plate in a blast drying box, and drying at 40 ℃ for 6 hours until the film still has viscosity to obtain the flaxseed gum double-layer film loaded with the chitosan+cinnamaldehyde film.

Preparation of a sandwich type multilayer antibacterial composite film: 10mL of prepared FG membrane solution is poured on the double-layer membrane (one side of chitosan and cinnamaldehyde membrane), and dried for 12 hours at 40 ℃ to obtain the sandwich type multi-layer antibacterial composite membrane (FG/CS/CIN antibacterial composite membrane).

Compared with the prior art, the invention has the following advantages and technical effects:

(1) After cinnamaldehyde is added into the multi-layer antibacterial composite film, interaction is generated among flaxseed gum, chitosan and cinnamaldehyde molecules to generate new chemical bonds, a new crystallization area is formed, the crystallinity of the antibacterial film is increased, movement among molecules is limited, and further the physical property and the barrier property of the antibacterial film are improved.

(2) According to the invention, the cinnamaldehyde is clamped in the flaxseed adhesive film layer, and the release of the cinnamaldehyde is slowed down through the interaction of chitosan and the cinnamaldehyde, so that the acting time of the cinnamaldehyde in the packaging material is prolonged, the packaging material has longer-lasting antibacterial activity, and a foundation is provided for the application of the antibacterial film in the fresh-keeping of meat products.

Drawings

The accompanying drawings, which are included to provide a further understanding of the application, illustrate and explain the application and are not to be construed as limiting the application. In the drawings:

FIG. 1 is an infrared spectrum test result of the film materials prepared in examples 1 to 4 and comparative examples 1 to 4;

FIG. 2 is SEM test results of films prepared in examples 1-4 and comparative example 1;

FIG. 3 is XRD test structures of films prepared in examples 1-4 and comparative examples 1-4;

FIG. 4 shows the results of stability testing of the films prepared in examples 1-4 and comparative example 1, wherein A is the thermogravimetric curve and B is the differential thermogravimetric curve;

FIG. 5 is a scanning electron microscope photograph of E.coli and Staphylococcus aureus treated with the antibacterial films of examples 2 and 4 and untreated E.coli and Staphylococcus aureus, wherein A is untreated E.coli, B is 0.5% CIN treated E.coli, C is 1.5% CIN treated E.coli, D is untreated Staphylococcus aureus, E is 0.5% CIN treated Staphylococcus aureus, F is 1.5% CIN treated Staphylococcus aureus;

FIG. 6 is a transmission electron micrograph of untreated E.coli;

FIG. 7 is a transmission electron micrograph of E.coli treated with 0.5% CIN;

FIG. 8 is a transmission electron micrograph of E.coli treated with 1.5% CIN;

FIG. 9 is a transmission electron micrograph of untreated Staphylococcus aureus;

FIG. 10 is a transmission electron micrograph of Staphylococcus aureus treated with 0.5% CIN;

FIG. 11 is a transmission electron micrograph of Staphylococcus aureus treated with 1.5% CIN.

Detailed Description

Various exemplary embodiments of the invention will now be described in detail, which should not be considered as limiting the invention, but rather as more detailed descriptions of certain aspects, features and embodiments of the invention.

It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. In addition, for numerical ranges in this disclosure, it is understood that each intermediate value between the upper and lower limits of the ranges is also specifically disclosed. Every smaller range between any stated value or stated range, and any other stated value or intermediate value within the stated range, is also encompassed within the invention. The upper and lower limits of these smaller ranges may independently be included or excluded in the range.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference for the purpose of disclosing and describing the methods and/or materials associated with the documents. In case of conflict with any incorporated document, the present specification will control.

It will be apparent to those skilled in the art that various modifications and variations can be made in the specific embodiments of the invention described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from consideration of the specification of the present invention. The specification and examples of the present invention are exemplary only.

As used herein, the terms "comprising," "including," "having," "containing," and the like are intended to be inclusive and mean an inclusion, but not limited to.

The raw materials used in the examples of the present invention are all commercially available.

In the examples of the present invention, room temperature refers to 25.+ -. 2 ℃.

The technical scheme of the invention is further described by the following examples.

Example 1

Preparation of chitosan+cinnamaldehyde (CS+CIN) membrane liquid: accurately weighing 1.0g of CS, adding 100mL of 1wt% glacial acetic acid solution, fully stirring in a water bath at 60 ℃ until the solution is completely dissolved, adding 20% of glycerol (w/w, CS mass), stirring in the water bath at 60 ℃ for 30min to obtain a mixture, cooling, adding 0.5% of Tween-80 (v/v, mixture), mixing and stirring for 30min to obtain CS membrane solution, adding 2.0% (v/v, CS membrane solution) of CIN into the CS membrane solution, continuously mixing and stirring for 30min to form CS+CIN membrane solution, and standing for 1h to fully emulsify and remove bubbles.

Preparation of a sandwich type multilayer antibacterial composite film: 10mL of prepared FG membrane solution is poured on the double-layer chitosan and cinnamaldehyde membrane, and dried for 12 hours at 40 ℃ to obtain a sandwich type multi-layer antibacterial composite membrane (FG/CS/CIN antibacterial composite membrane) which is marked as 2.0% CIN.

Example 2

The difference from example 1 was that 1.5% (v/v, CS membrane solution) CIN was added to the CS membrane solution during the preparation of the chitosan+cinnamaldehyde (CS+CIN) membrane solution, and the result was designated as 1.5% CIN.

Example 3

The difference from example 1 was that, in the preparation of the chitosan+cinnamaldehyde (CS+CIN) membrane solution, CIN of 1.0% (v/v, CS membrane solution) was added to the CS membrane solution, which was designated as 1.0% CIN.

Example 4

The difference from example 1 was that 0.5% (v/v, CS membrane solution) CIN was added to the CS membrane solution during the preparation of the chitosan+cinnamaldehyde (CS+CIN) membrane solution, and the result was designated as 0.5% CIN.

Comparative example 1

CIN was not added:

Preparation of Chitosan (CS) membrane liquid: accurately weighing 1.0g of CS, adding 100mL of 1wt% glacial acetic acid solution, fully stirring in a water bath at 60 ℃ until the solution is completely dissolved, adding 20% of glycerol (w/w, CS mass), stirring in the water bath at 60 ℃ for 30min to obtain a mixture, cooling, adding 0.5% of Tween-80 (v/v, mixture), mixing and stirring for 30min to obtain CS membrane solution, and standing for 1h to fully emulsify and remove bubbles.

Preparing a linseed adhesive film loaded with chitosan: and pouring 10mL of the prepared CS film liquid on the prepared FG film, uniformly casting the film liquid to completely cover the surface of the FG film, horizontally placing a plate in a blast drying oven, and drying at 40 ℃ for 6 hours until the film still has viscosity to obtain the flaxseed gum double-layer film loaded with the chitosan film.

Preparation of a sandwich type multilayer antibacterial composite film: and pouring 10mL of prepared FG membrane solution on the double-layer chitosan membrane, and drying at 40 ℃ for 12 hours to obtain an FG/CS antibacterial composite membrane, which is marked as FG/CS.

Comparative example 2

Accurately weighing 1.0g of CS, adding 100mL of 1wt% glacial acetic acid solution, fully stirring in a water bath at 60 ℃ until the glacial acetic acid solution is completely dissolved, adding 20% of glycerol (w/w, CS mass), stirring in the water bath at 60 ℃ for 30min to obtain a mixture, cooling, adding 0.5% of Tween-80 (v/v, the mixture), mixing and stirring for 30min to obtain CS membrane solution, standing for 1h to fully emulsify and remove bubbles, pouring the CS membrane solution into a disposable sterile plastic plate with the diameter of 90mm, horizontally placing the plate in a blast drying box, and drying at 40 ℃ for 6h to obtain the CS membrane.

Comparative example 3

Comparative example 4

CIN essential oil (purchased from Shanghai Alasdine Biochemical technologies Co., ltd., purity: 95%).

Performance testing

1. Infrared spectroscopy testing

The film materials prepared in examples 1 to 4 and comparative examples 1 to 4 were subjected to infrared spectroscopic testing, and the results are shown in fig. 1. As can be seen from FIG. 1, in the process of forming the antibacterial film, 3050-3606cm ^-1 The shift of the broad absorption peak in the direction of the long wave indicates that new H bonds are generated in the reaction, and the strength of the H bonds increases with the increase of CIN content. 2925cm ^-1 And 2869cm ^-1 The absorption peak at the position gradually increases along with the CIN content, the intensity of the absorption peak is obviously enhanced, and the fact that R-CHO in CIN is combined with conjugated double bonds in CS and FG in the film forming process generates electrostatic interaction is indicated. At 1633cm ^-1 The peak at which the formation of the Schiff base during the reaction was confirmed by the generation of the C=N bond, while the formation of the CS and CIN films at 1548cm- ¹ The absorption peak intensity at the position gradually weakens, which indicates that N-H,1034cm is consumed by Maillard reaction and Schiff base generation during film forming ^-1 The intensity of the absorption peak is enhanced due to the interaction between FG, CS and CIN molecules, and the formation of new C-O-C cyclic ether bonds. The results show that after CIN is added, new chemical bonds are generated, movement among molecules is limited, and further the physical property and the barrier property of the antibacterial film are influenced, so that CIN has longer lasting activity.

2. SEM Performance test

SEM test of films prepared in examples 1-4 and comparative example 1, see FIG. 2, wherein A ₁ -E ₁ The surface structures of the films prepared in comparative example 1 and examples 1 to 4, respectively, A ₂ -E ₂ The cross-sectional structures of the films prepared in comparative example 1 and examples 1 to 4 were shown. As can be seen from fig. 2, the surfaces of all films were uniform, smooth, and free of cracks, indicating good fusion of the components. The FG/CS film has a dense network cross-section that appears as a hierarchical sheet-like structure with pores filled when the CIN content is 0.5% (v/v), probably due to cinnamaldehyde volatilization and hydrophobic interactions between cinnamaldehyde and polysaccharide groups during film formation. And when the CIN content is continuously increased to 1.0% -1.5%, the lamellar structure of the film with layering gradually disappears, and becomes a scaly structure, which shows that CIN promotes the close combination of surrounding CS and FG polysaccharides at the concentration. When the concentration is further increased to 2.0%, white spots are generated due to agglomeration of cinnamaldehyde, which shows that the high-concentration CIN breaks the network structure between CS and FG, so that the elongation at break of the antibacterial film is obviously reduced, and therefore, the optimal addition amount of CIN in CS film liquid is determined to be 1.0% -1.5%.

3. XRD testing

XRD measurements were performed on the films prepared in examples 1 to 4 and comparative examples 1 to 4, and as shown in FIG. 3, it can be seen from FIG. 3 that after CIN was added, significant diffraction peaks appear at diffraction angles 2θ=11.36° and around 19 °, indicating that after CIN was added, the crystallinity of the antibacterial films in examples 1 to 4 was increased as compared with that of the FG/CS film in comparative example 1. This is probably due to the interaction of CIN with CS and FG during film formation, which forms new crystalline regions and increases the crystallinity of the film. Whereas at a CIN content of 2.0%, the onset of the decrease in the crystalline region may be due to the destruction of intermolecular interactions by hydrophobic CIN.

4. Stability test

The films prepared in examples 1-4 and comparative example 1 were tested for stability and the results are shown in FIG. 4, where A is the thermogravimetric curve and B is the differential thermogravimetric curve. As can be seen from FIG. 4, the antibacterial film after CIN addition shows four weight loss peaks, and at 0-110 ℃, the temperature is slightly lowered compared with that of the FG/CS film of comparative example 1 due to water evaporation and decomposition of small molecules such as acetic acid, probably due to the fact that chemical bonds between hydrophilic substances and water molecules are broken after CIN addition, and the water molecules are more easily released. In the second stage 110-220 ℃, compared with FG/CS film of comparative example 1, the decomposition temperature of the antibacterial film added with different concentration CIN is slightly raised, and the analysis reason is probably due to the formation of Schiff alkali between CIN and CS in the film forming process, and meanwhile, the addition of Tween-80 plays a good role in emulsification and the degradation temperature is raised. The third stage is 220-340 deg.c, and this is mainly caused by degradation of molecular chain in FG/CS/CIN film, and the addition of CIN has no obvious effect on the maximum degradation temperature of the antibacterial film. The fourth stage 340-440℃which is not found in the FG/CS film of comparative example 1, is associated with decomposition of CIN. A smaller weight loss peak was also observed near 465℃which may be related to residual Tween-80. It can be seen that the difference in maximum degradation temperature of the antibacterial film of different concentration CIN is not significant compared with the FG/CS film of comparative example 1, and it is assumed that CIN has no significant effect on the thermal stability of the antibacterial film.

5. Sterilizing effect on colibacillus and staphylococcus aureus

Object of measurement: example 2, 1.5% CIN, 0.5% CIN prepared in example 4

The measuring method comprises the following steps:

sample pretreatment: inoculating activated Escherichia coli and Staphylococcus aureus into LB broth, shaking culturing at 37deg.C and 160rpm for 8 hr, centrifuging the bacterial suspension at 5000g for 10min, diluting with 0.01M PBS buffer to OD ₆₀₀ 0.4 mL of the diluted bacterial suspension was taken, 0.5g of the antibacterial film having 1.5% CIN and 0.5% CIN prepared in example 2 and example 4 was added thereto, and the mixture was subjected to shaking culture at 37℃for a suitable period of time at 160 rpm.

Shaking culture of the prepared bacterial suspension for 2h, centrifuging for 10min under 5000g, washing the bacterial cells with 0.01M PBS buffer solution for three times, collecting bacterial cells, dissolving the bacterial cells in 1mL of 2.5% glutaraldehyde solution, fixing for 2h, washing the bacterial cells with 0.01M PBS for three times, dehydrating the bacterial cells with ethanol of gradient concentration for 10min, spraying gold after drying the bacterial cells, and observing the bacterial cell morphology through SEM.

Pretreating a sample, fixing the sample in 2.5% glutaraldehyde at 4 ℃ for 24 hours, centrifugally collecting thalli, cleaning the thalli three times by using 0.01M PBS buffer solution, fixing the thalli for 2 hours by using 1% osmium acid, performing gradient elution by using ethanol with different concentrations, packaging the thalli by using resin after drying, slicing, dyeing, and observing by using a transmission electron microscope.

Scanning electron microscope measurement results:

scanning electron microscope pictures of the E.coli and Staphylococcus aureus treated with the antibacterial films of examples 2 and 4 and untreated E.coli and Staphylococcus aureus are shown in FIG. 5, wherein A is untreated E.coli, B is 0.5% CIN treated E.coli, C is 1.5% CIN treated E.coli, D is untreated Staphylococcus aureus, E is 0.5% CIN treated Staphylococcus aureus, and F is 1.5% CIN treated Staphylococcus aureus. As can be seen from FIG. 5, the untreated E.coli cell morphology exhibited a rod shape, the cell surface was smooth, and the cell structure was complete (A in FIG. 5). After the treatment with 0.5% CIN antibacterial film, the surface of the cells became rough, wrinkles appeared, and a significant depression appeared at one end of the cells (FIG. 5B). After treatment with 1.5% CIN antibacterial film, the cells were adhered and the surface was damaged, destroying the integrity of the cells (FIG. 5C). This is probably related to the cell wall structure of E.coli, and although the cell wall is thin, the structure is complicated, and thus the cell wall structure has a certain protective effect. The shrinkage deformation of the inner cavity of the escherichia coli cell can be obviously observed on the SEM image, and the cell loses the original shape. Untreated staphylococcus aureus cells had smooth surfaces and filled elasticity, independent of each other (D in fig. 5). After the antibacterial film treatment with 0.5% CIN, the cells lost smooth morphology, and the surface was broken by dissolution, and started to adhere (E in FIG. 5). After treatment with 1.5% CIN, the cells began to rupture, and leakage occurred, yielding a deformation, dent (F in FIG. 5). Although staphylococcus aureus has a compact peptidoglycan layer, which can play a role in protecting bacteria, the structure of the cell wall is single, once the protective layer is destroyed, antibacterial substances can easily permeate into cells, and the intracellular substances lose protection and can leak. In SEM, no large deformation as in E.coli was observed, but it can be seen from the figure that the cell wall had been broken, the cells were dented, and there was leakage of the endolysates.

Transmission electron microscope measurement results:

the transmission electron microscope pictures of the E.coli and Staphylococcus aureus treated with the antibacterial films of examples 2 and 4 and the untreated E.coli and Staphylococcus aureus are shown in FIG. 6-FIG. 11, wherein FIG. 6 is the untreated E.coli, FIG. 7 is the E.coli treated with 0.5% CIN, FIG. 8 is the E.coli treated with 1.5% CIN, FIG. 9 is the untreated Staphylococcus aureus, FIG. 10 is the Staphylococcus aureus treated with 0.5% CIN, and FIG. 11 is the Staphylococcus aureus treated with 1.5% CIN. As can be seen from FIGS. 6 to 11, the cell membrane structure of E.coli which is not treated (FIG. 6) is complete, and the content is filled with cells and uniformly distributed in the cells. After treatment with 0.5% CIN antimicrobial film (FIG. 7), the cell membrane structure was blurred in edge, the void was enlarged, and the cell content began to run off. After treatment with 1.5% CIN antimicrobial film (FIG. 8), the cell membrane was completely obscured, the structure was severely destroyed, and the contents were largely leaked. Untreated staphylococcus aureus (fig. 9), the cell morphology is round and full, the structure is complete and continuous, the layers are distinct, and the content can be uniformly filled in the cell. After treatment with 0.5% CIN antibacterial membrane (FIG. 10), the cytoplasmic wall becomes thin and the edges begin to blur, and the cell membrane has dissolved. After treatment with 1.5% CIN antibacterial film (FIG. 11), the cell wall was almost lost, the cell membrane was severely destroyed, and a large amount of endo-soluble substances in the cell leaked. It can be seen that the antibacterial film added with CIN significantly damages the integrity of the escherichia coli and staphylococcus aureus, thereby playing an antibacterial role.

In conclusion, the antibacterial composite film prepared by the invention is expected to be applied to food packaging materials or fresh-keeping materials.

The foregoing is merely a preferred embodiment of the present application, but the scope of the present application is not limited thereto, and any changes or substitutions easily conceivable by those skilled in the art within the technical scope of the present application should be covered in the scope of the present application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.

Claims

1. The sandwich type multi-layer antibacterial composite film with the addition of the cinnamaldehyde is characterized in that the cinnamaldehyde is positioned in the middle layer of the sandwich type multi-layer antibacterial composite film, and the sandwich type multi-layer antibacterial composite film sequentially comprises a flaxseed film layer, a chitosan and cinnamaldehyde film layer and a flaxseed film layer from top to bottom.

2. A method for preparing the cinnamaldehyde-added sandwich-type multi-layer antibacterial composite film according to claim 1, which is characterized by comprising the following steps:

dissolving chitosan, adding glycerol, stirring in a water bath to obtain a mixture, adding tween-80, mixing and stirring to obtain chitosan membrane solution, adding cinnamaldehyde into the chitosan membrane solution, and continuing mixing and stirring to obtain chitosan+cinnamaldehyde membrane solution;

pouring a flaxseed adhesive film liquid into a flaxseed adhesive film, pouring the chitosan and cinnamaldehyde film liquid onto the flaxseed adhesive film, and drying to obtain a flaxseed adhesive double-layer film loaded with chitosan and cinnamaldehyde film;

pouring flaxseed adhesive film liquid on the chitosan and cinnamaldehyde film of the double-layer film, and drying to obtain the sandwich type multilayer antibacterial composite film.

3. The method for preparing the sandwich-type multi-layer antibacterial composite membrane added with cinnamaldehyde according to claim 2, wherein the adding amount of the glycerol is 20% of the mass of chitosan, and the adding amount of the tween-80 is 0.5% of the volume of the mixture.

4. The method for preparing the sandwich-type multi-layer antibacterial composite membrane added with cinnamaldehyde according to claim 2, wherein the adding amount of the cinnamaldehyde is 1.0% -1.5% of the volume of the chitosan membrane liquid.

5. The method for preparing the sandwich-type multi-layer antibacterial composite film added with cinnamaldehyde according to claim 2, wherein the method for preparing the flaxseed adhesive film liquid comprises the following steps:

and (3) dissolving the flaxseed gum to obtain a flaxseed gum solution, and then adding glycerol into the solution to stir in a water bath to obtain the flaxseed gum film solution.

6. The method for preparing a sandwich-type multi-layer antibacterial composite film added with cinnamaldehyde according to claim 5, wherein the concentration of the flaxseed gum solution is 0.5g/100mL.

7. The method for preparing the sandwich-type multi-layer antibacterial composite film added with cinnamaldehyde according to claim 5, wherein the adding amount of the glycerol is 20% of the mass of the flaxseed gum.

8. The use of the cinnamaldehyde-added sandwich-type multi-layer antibacterial composite film according to claim 1 for preparing food packaging materials.