Antibacterial starch, food preservation packaging film and preparation method and application thereof

Abstract

This invention discloses an antibacterial starch, a food preservation packaging film, its preparation method, and its application, belonging to the field of plastic packaging technology. Starch is modified with polyhexamethylene biguanide hydrochloride to obtain a hydrophobic antibacterial starch. Glycerol in the food preservation packaging film acts as a plasticizer. The PLA / PBAT / antibacterial starch food preservation packaging film prepared by co-extrusion casting enhances the moisture and oxygen barrier properties of the PLA / PBAT / starch food preservation packaging film, and the addition of polyhexamethylene biguanide hydrochloride imparts antibacterial properties to the film.

Description

Technical Field

[0001] This invention relates to an antibacterial starch, a food preservation packaging film, its preparation method and application, belonging to the field of plastic packaging technology. Background Technology

[0002] With social progress and the development of science and technology, plastic products have received widespread attention and research from scientists, leading to their increased use in people's daily lives. However, the frequent use of plastic products has caused a series of problems, such as energy depletion and white pollution, with white pollution caused by plastics becoming a global scourge. As living standards improve, people's demands for quality of life are also increasing, making them more focused on environmental protection. This will drive the reform and innovation of traditional plastics. Since the 1970s, biotechnology has emerged as a dark horse, achieving remarkable results in various fields. To solve the problem of plastic waste, in addition to recycling, developing renewable and biodegradable plastics has become the most fundamental approach.

[0003] Polylactic acid (PLA) possesses excellent physicochemical properties, extremely high transparency, good biodegradability and controllable degradation time, is non-toxic and odorless, resistant to acids and alkalis, antibacterial, UV resistant, easy to process and mold, and readily degrades into environmentally friendly compounds—qualities unmatched by traditional plastics. Polybutylene terephthalate (PBAT) is a thermoplastic biodegradable plastic. It possesses good ductility and elongation at break, as well as good heat resistance and impact resistance. After disposal, it degrades into water and carbon dioxide, demonstrating significant environmental benefits. PBAT exhibits high heat resistance, good film-forming properties, good toughness, and high hydrolysis resistance. Furthermore, it possesses excellent biodegradability.

[0004] Starch, as a usable biodegradable polymer, has advantages such as low cost, wide applicability, and excellent renewability.

[0005] Starch is a pure, natural, and pollution-free polymer material, widely used in fully biodegradable composite materials such as thermoplastic starch and starch / aliphatic polyester blends. However, natural starch has a polyhydroxyl structure, strong intermolecular forces, a microcrystalline structure, and is difficult to melt and plasticize. Furthermore, it is highly hydrophilic and has poor compatibility with most plastics, which limits its application in production and daily life. After modification, starch exhibits enhanced hydrophobicity, improving its interfacial compatibility with non-polar plastics, thus enabling the production of high-performance starch-plastic blend composites.

[0006] Current research on packaging films mainly focuses on improving mechanical properties. Our research group has previously reported on improving the mechanical properties of films by mixing starch, PLA, and PBAT (Zhao, M., Z. Zhang, H. Cai, L. Wang, C. Hu, D. Li, Y. Chen, Y. Kang and L. Li (2022). "Controlled moisture permeability of thermoplastic starch / polylactic acid / polybutylene adipate-co-terephthalate film for the autolysis of straw mushroom Volvariella volvacea." Food Chem 373(Pt A):131409.). However, antimicrobial properties are also crucial for food packaging. Our research group has also studied the incorporation of natural antibacterial materials into films (Zhao, M., Z. Zhang, H. Cai, L. Wang, C. Hu, D. Li, Y. Chen, Y. Kang and L. Li (2022). "Controlled moisture permeability of thermoplastic starch / polylactic acid / polybutylene adipate-co-terephthalate film for the autolysis of straw mushroom Volvariella volvacea." Food Chem 373(Pt A):131409.). Antibacterial packaging was prepared by adding essential oils. Although adding essential oils achieves antibacterial effects to some extent, essential oils are volatile and can migrate into food, affecting not only the flavor but also weakening the antibacterial properties over time. Therefore, developing an antibacterial starch, food preservation packaging film, its preparation method, and its applications are of great practical significance. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide an antibacterial starch, a food preservation packaging film, a preparation method thereof, and its application, which has a long-lasting antibacterial effect and aims to extend the food preservation time.

[0008] The technical problem to be solved by this invention is achieved by the following technical solution:

[0009] A method for preparing antibacterial starch includes the following steps: starch and maleic anhydride are mixed at a mass ratio of 10:0.5-1.5 and grafted to obtain esterified starch; the esterified starch is grafted with an antibacterial agent under the action of isophorone diisocyanate to obtain antibacterial starch, wherein the mass ratio of esterified starch to antibacterial agent is 1:0.15-0.25; and the mass ratio of isophorone diisocyanate to antibacterial agent is 2-3:1.

[0010] Preferably, the mass ratio of starch to maleic anhydride is 10:1, the mass ratio of esterified starch to antibacterial agent is 1:0.2, and the mass ratio of isophorone diisocyanate to antibacterial agent is 2.5:1.

[0011] Preferably, the reaction conditions are as follows: dried starch and maleic anhydride are mixed evenly according to the ratio, ball-milled and reacted at 75-85℃ for 1.5-2.5h, washed and dried to obtain esterified starch;

[0012] Esterified starch and dimethyl sulfoxide were mixed at a mass ratio of 1:9-12 and reacted at 75-85℃ for 1-1.5 h to obtain product 1;

[0013] Under the catalysis of dibutyltin dilaurate, isophorone diisocyanate and antibacterial agent were reacted at 55-65℃ for 1-1.5h in a certain ratio, and the product was obtained by washing and filtration.

[0014] According to the mass ratio of esterified starch to antibacterial agent 1: 0.15-0.25, product 1 and product 2 are mixed and reacted at 55-65℃ for 3-3.5h, washed and dried to obtain antibacterial starch.

[0015] Preferably, the antibacterial agent is polyhexamethylene biguanide hydrochloride or polyhexamethylene monoguanide hydrochloride.

[0016] In a preferred embodiment of the present invention, the method for preparing antibacterial starch comprises the following reaction conditions: starch is dried at 80°C, the dried starch is mixed with maleic anhydride at a mass ratio of 10:1, ball-milled for 10 min, reacted at 80°C for 2 h, washed with acetone, and dried at 45°C to obtain esterified starch.

[0017] Esterified starch and dimethyl sulfoxide were mixed at a mass ratio of 1:10 and reacted at 80°C for 1 h to obtain product 1;

[0018] Under the catalysis of dibutyltin dilaurate, isophorone diisocyanate and polyhexamethylene biguanide hydrochloride were reacted at 60°C for 1 h at a mass ratio of 5:2, and then filtered three times with xylene to obtain product 2.

[0019] According to the mass ratio of esterified starch to antibacterial agent 1:0.2, product 1 and product 2 were mixed and reacted at 60℃ for 3h, washed with ethanol, and dried at 45℃ to obtain antibacterial starch.

[0020] An antibacterial starch is prepared by the above-described preparation method.

[0021] The aforementioned antibacterial starch can be used in the preparation of food preservation packaging.

[0022] A biguanide-grafted antibacterial starch-based food preservation packaging film, comprising the following substrate:

[0023] Plasticized starch made from PLA, PBAT, and the aforementioned antibacterial starch; wherein the mass ratio of plasticized starch, PBAT, and PLA is 2–2.5:3.8–4.2:1.

[0024] Preferably, the mass ratio of plasticized starch, PBAT and PLA is 2.4:4:1.

[0025] The above-mentioned method for preparing food preservation packaging film includes the following steps:

[0026] (1) Antibacterial starch and glycerin are mixed evenly at a mass ratio of 10:2-4 and plasticized to obtain plasticized starch;

[0027] (2) Plasticized starch is dried with PBAT and PLA, and antioxidants and chain extenders are added in sequence. After mixing and granulation, antibacterial masterbatch is obtained, and then food preservation packaging film is obtained by casting.

[0028] Preferably, in step (1), the mass ratio of the antibacterial starch to glycerol is 10:3;

[0029] Preferably, in step (2), the antioxidant accounts for 1 to 1.5% of the total mass of plasticized starch, PBAT, PLA, antioxidant, and chain extender, preferably 1%; the chain extender accounts for 1 to 1.5% of the total mass of plasticized starch, PBAT, PLA, antioxidant, and chain extender, preferably 1%. The granulation conditions are: rotation speed of 260 to 280 rpm / min, temperature of 145 to 175°C, and the casting conditions are: temperature processing parameters of each zone of the single-screw casting machine of 145 to 175°C, and single screw rotation speed of 75 to 85 r / min.

[0030] Furthermore, in step (2), the antioxidant is antioxidant 245, the chain extender is chain extender ADR4380, and the content of both is 1% of the total mass of the mixture. The granulation conditions are: rotation speed of 270 rpm / min, temperature of 145℃, 155℃, 165℃, 175℃, 170℃, 165℃, and 160℃. The casting conditions are: temperature processing parameters of each zone of the single screw casting machine are 145℃, 155℃, 165℃, 175℃, 170℃, 165℃, and 160℃, and the single screw rotation speed is 80 r / min.

[0031] Beneficial effects

[0032] (1) The base materials PLA, PBAT and antibacterial starch used in this invention are all biodegradable materials, which makes the composite preservation film prepared from the above base materials in this invention have good biodegradability;

[0033] (2) In this invention, the hydrophobicity of the film is enhanced because the hydrophilic hydroxyl groups of starch are replaced by hydrophobic functional groups.

[0034] (3) The present invention has high moisture barrier, oxygen barrier and antibacterial properties. Moisture barrier can prevent the loss of moisture in food and the entry of moisture in the air; oxygen barrier can prevent the entry of oxygen, avoid the oxidation of food nutrients and the growth and reproduction of bacteria, thereby extending the shelf life of food; antibacterial property is achieved by electrostatic interaction between the guanidine cation and the anionic surface of the bacterial cell membrane, which leads to cell membrane damage, directly causing the loss of cell components, and ultimately cell death, thereby inhibiting food spoilage. Attached Figure Description

[0035] Figure 1 The Fourier transform infrared spectra of native starch (A), esterified starch (B), and antibacterial starch (C) in Example 1 are shown in comparison.

[0036] Figure 2 This is a comparison of scanning electron microscope images of native starch (A) and antibacterial starch (B) in Example 1;

[0037] Figure 3 This is a thermogravimetric comparison chart of native starch and antibacterial starch in Example 1;

[0038] Figure 4 The image shows a comparison of the antibacterial activity of native starch and antibacterial starch in Example 1. The left image shows a comparison of the antibacterial activity of native starch and antibacterial starch against Escherichia coli, and the right image shows a comparison of the antibacterial activity of native starch and antibacterial starch against Staphylococcus aureus.

[0039] Figure 5 This is a comparison diagram of the contact angles of ordinary film (A) and food preservation packaging film (B) in Example 2;

[0040] Figure 6 This is a scanning electron microscope comparison image of ordinary film and food preservation packaging film in Example 2;

[0041] Figure 7 The above are comparison images of the antibacterial activity of ordinary film and food preservation packaging film in Example 2. In Example 2, A is the antibacterial activity of ordinary film against Staphylococcus aureus, B is the antibacterial activity of food preservation packaging film against Staphylococcus aureus, C is the antibacterial activity of ordinary film against Escherichia coli, and A is the antibacterial activity of food preservation packaging film against Escherichia coli.

[0042] Figure 8 Images of fresh abalone during storage in Example 3;

[0043] Figure 9 The graph shows the malondialdehyde content of fresh abalone during refrigeration in Example 3.

[0044] Figure 10 This is a graph showing the relative moisture content of fresh abalone in three states during the refrigeration period in Example 3. Detailed Implementation

[0045] To facilitate a clear understanding of the technical means, creative features, objectives, and effects of this invention, the invention will be further described below in conjunction with specific embodiments.

[0046] Example 1: Preparation of Antibacterial Starch

[0047] (1) Preparation process of esterified starch: The starch was dried at 80℃, and then the starch and maleic anhydride were mixed evenly at a mass ratio of 10:1. After ball milling for 10 min, the mixture was reacted in an oven at 80℃ for 2 h. The starch was washed with acetone, and the obtained sample was dried in an oven to obtain esterified starch.

[0048] (2) Preparation process of antibacterial starch: Esterified starch and dimethyl sulfoxide were mixed at a mass ratio of 1:10 and reacted at 80℃ for 1 h to obtain product 1;

[0049] Under the catalysis of dibutyltin dilaurate, isophorone diisocyanate and polyhexamethylene biguanide hydrochloride were reacted at 60°C for 1 h at a mass ratio of 5:2. The resulting substance was filtered three times with xylene to obtain product 2. Then, product 1 and product 2 (esterified starch: polyhexamethylene biguanide hydrochloride mass ratio of 5:1) were reacted at 60°C for 3 h. The resulting product was washed with ethanol and dried in an oven at 45°C to obtain antibacterial starch.

[0050] Antimicrobial starch was characterized by FTIR, SEM, TG, and antimicrobial tests.

[0051] Through FTIR testing (such as...) Figure 1 As shown in the figure, the esterified starch content at 1721 cm⁻¹ was determined. -1 The characteristic peak of the ester group appears at 1555 cm⁻¹, and antibacterial starch shows a peak at 1555 cm⁻¹. -1 The presence of a characteristic peak of the guanidine group indicates successful grafting.

[0052] SEM testing of antibacterial starch (e.g.) Figure 2 As shown in the figure, it was found that after grafting polyhexamethylene biguanide hydrochloride, the structure of antibacterial starch was destroyed, its morphology changed, and it became irregular and rough.

[0053] Through the TG test of antibacterial starch (e.g.) Figure 3As shown in the figure, the antibacterial starch exhibits enhanced thermal stability after grafting with polyhexamethylene biguanide hydrochloride, and only begins to degrade after 350°C. It does not decompose in a high-temperature extrusion device.

[0054] The antibacterial properties of antimicrobial starch were tested using the Oxford cup method (e.g., ...). Figure 4 As shown in the figure, starch grafted with polyhexamethylene biguanide hydrochloride forms antibacterial starch with a distinct inhibition zone, indicating significant antibacterial activity against Escherichia coli and Staphylococcus aureus.

[0055] Example 2: Preparation of food preservation packaging film with antibacterial starch, PLA, and PBAT

[0056] (1) Antibacterial starch and glycerin are mixed evenly at a mass ratio of 10:3, and then placed in a self-sealing bag for plasticization to obtain plasticized starch.

[0057] (2) Plasticized starch, PBAT, and PLA were dried in an oven at a mass ratio of 2.4:4:1. Antioxidant 245 (1% of the total mass of the mixture) and chain extender ADR4380 (1% of the total mass of the mixture) were added and mixed evenly. The mixture was then granulated using a granulator to obtain antibacterial masterbatch. The twin-screw casting machine had a speed of 270 rpm / min and was divided into seven temperature zones with temperatures of 145, 155, 165, 175, 170, 165, and 160℃.

[0058] (3) The antibacterial masterbatch is fed and cast through a single-screw casting machine to produce a food preservation packaging film. The temperature processing parameters of each zone of the single-screw casting machine are 145, 155, 165, 175, 170, 165 and 160℃, and the single screw speed is set to 80 r / min.

[0059] Comparative Example 1: Preparation of food preservation packaging film with starch, PLA, and PBAT

[0060] This comparative example is basically the same as Example 2, except that this comparative example uses a common film made of starch / PLA / PBAT in a mass ratio of 2.4:4:1 as the substrate, and polyhexamethylene biguanide hydrochloride is not added to the common film.

[0061] Compared with Comparative Example 1, Example 2 was characterized by tests of moisture permeability, oxygen permeability, contact angle, SEM, and antibacterial properties of the film.

[0062] Table 1. Moisture permeability and oxygen permeability of the membrane

[0063]

[0064] As shown in Table 1, compared with the food preservation packaging film made of PLA / PBAT / antibacterial starch (Example 2), the water vapor transmission rate of the ordinary film made of PLA / PBAT / starch (Comparative Example 1) was 707.9 g / (m²). 2 ·d) decreased to 550.56 g / (m 2 ·d), oxygen permeability increased from 770.33 cm⁻¹ 3 / m 2 The pressure dropped from 0.1 MPa to 495.44 cm on day 1. 3 / m 2 The pressure was 0.1 MPa, indicating that the moisture barrier and oxygen barrier properties of the food preservation packaging film are stronger than those of ordinary films.

[0065] The contact angle diagram (CA) of the thin film shows that... Figure 5 As shown in the figure, the contact angle of the food preservation packaging film (Example 2) is larger than that of ordinary film, indicating enhanced hydrophobicity.

[0066] As can be seen from the scanning electron microscope images of the thin film (e.g.) Figure 6 As shown, the surface of ordinary film is relatively smooth, but it has many cracks; the surface of food preservation packaging film becomes rough, and many starch particles are embedded in the surface.

[0067] The antibacterial properties of the film can be seen from the graph (e.g.) Figure 7 As shown in the figure, the antibacterial properties of the food preservation packaging film were tested by the shake flask method. It can be seen that the film has inhibitory effects on both Escherichia coli and Staphylococcus aureus, and its antibacterial effect is stronger than that of ordinary film against Escherichia coli and Staphylococcus aureus. In addition, the antibacterial effect of the food preservation packaging film against Staphylococcus aureus is stronger than that against Escherichia coli.

[0068] Example 3: Abalone Preservation

[0069] (1) The food preservation packaging film prepared in Example 2 is sealed by a heat sealing machine to obtain a preservation bag.

[0070] (2) Experiment on the preservation of abalone.

[0071] Purchase live abalone, remove the shells and viscera, keeping the abalone meat. Rinse with sterile saline solution and pat dry with kitchen paper. Randomly divide the abalone meat into three groups: naked group (a), PLA / PBAT / starch group (b), and PLA / PBAT / antibacterial starch group (c). Refrigerate at 4±1℃.

[0072] It should be noted that the exposed group (a) refers to abalone meat that is not wrapped in a membrane and is left exposed.

[0073] PLA / PBAT / Starch group (b) refers to abalone meat wrapped in a preservation bag made of ordinary film, and PLA / PBAT / Antibacterial Starch group (c) refers to abalone meat wrapped in a preservation bag made of food preservation packaging film.

[0074] The preservation effect and shelf life of food preservation packaging film were characterized by measuring the malondialdehyde content and total bacterial count of fresh abalone during refrigeration.

[0075] By measuring the malondialdehyde content of fresh abalone during refrigeration (e.g.) Figure 9 As shown in the figure, the TBARS index shows that the TBARS value gradually increases with the passage of storage time, and the TBARS value of PLA / PBAT / antibacterial starch group (c) is the smallest, indicating that the food preservation packaging film has a significant preservation effect.

[0076] By measuring the total bacterial count of fresh abalone during refrigeration (e.g. Figure 10 As shown in the figure, the total number of colonies gradually increased over the storage time, and the PLA / PBAT / antimicrobial starch group (c) increased the slowest, indicating that food preservation packaging film can effectively extend the shelf life of abalone.

[0077] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments, and various changes and modifications can be made without departing from the spirit and scope of the invention, all of which fall within the scope of the claims. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing antibacterial starch, characterized in that, Includes the following steps: Starch and maleic anhydride are mixed at a mass ratio of 10:0.5-1.5 and grafted to obtain esterified starch; the esterified starch is then grafted with an antibacterial agent under the action of isophorone diisocyanate to obtain antibacterial starch. The mass ratio of esterified starch to antibacterial agent is 1:0.15-0.25; the mass ratio of isophorone diisocyanate to antibacterial agent is 2-3:1; wherein: the reaction conditions are: dried starch and maleic anhydride are mixed evenly according to the ratio, ball milled and reacted at 75-85℃ for 1.5-2.5h, washed and dried to obtain esterified starch; Esterified starch and dimethyl sulfoxide were mixed at a mass ratio of 1:9-12 and reacted at 75-85℃ for 1-1.5 h to obtain product 1; Under the catalysis of dibutyltin dilaurate, isophorone diisocyanate and antibacterial agent were reacted at 55-65℃ for 1-1.5h in a certain ratio, and the product was obtained by washing and filtration. According to the mass ratio of esterified starch to antibacterial agent 1: 0.15-0.25, product 1 and product 2 are mixed and reacted at 55-65℃ for 3-3.5h, washed and dried to obtain antibacterial starch; the antibacterial agent is polyhexamethylene biguanide hydrochloride or polyhexamethylene monoguanide hydrochloride.

2. An antibacterial starch, characterized in that, It is prepared by the preparation method described in claim 1.

3. The application of the antibacterial starch according to claim 2 in the preparation of food preservation packaging.

4. A biguanide-grafted antibacterial starch-based food preservation packaging film, characterized in that, By weight, it includes the following substrates: Plasticized starch made from PLA, PBAT, and the antibacterial starch of claim 2; wherein the mass ratio of plasticized starch, PBAT, and PLA is 2-2.5:3.8-4.2:

1.

5. The method for preparing the food preservation packaging film according to claim 4, characterized in that, Includes the following steps: (1) Antibacterial starch and glycerol are mixed evenly at a mass ratio of 10:2 to 4 and plasticized to obtain plasticized starch; (2) Plasticized starch is dried with PBAT and PLA, antioxidants and chain extenders are added in sequence, and after mixing and granulation, antibacterial masterbatch is obtained, and then food preservation packaging film is obtained by casting.

6. The method for preparing the food preservation packaging film according to claim 5, characterized in that... In step (2), the antioxidant accounts for 1 to 1.5% of the total mass of plasticized starch, PBAT, PLA, antioxidant, and chain extender. The chain extender accounts for 1 to 1.5% of the total mass of plasticized starch, PBAT, PLA, antioxidant, and chain extender. The granulation conditions are: rotation speed of 260 to 280 rpm and temperature of 145 to 175°C. The casting conditions are: temperature processing parameters of each zone of the single screw casting machine of 145 to 175°C and single screw rotation speed of 75 to 85 r / min.

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