Anti-ultraviolet, antibacterial, antioxidant and high-light-transmittance food packaging film as well as preparation method and application of anti-ultraviolet, antibacterial, antioxidant and high-light-transmittance food packaging film

Abstract

The invention discloses an anti-ultraviolet, antibacterial, antioxidant and high-light-transmittance food packaging film, and belongs to the field of food packaging materials, and the anti-ultraviolet, antibacterial, antioxidant and high-light-transmittance food packaging film comprises 40-60 parts of a chitosan solution; 40-60 parts of a gelatin solution; 0.01 to 0.2 part of nitrogen-doped carbon quantum dots; 0.001 to 0.02 part of an antibacterial agent; the invention further discloses a preparation method of the food packaging film. The preparation method comprises the following steps: S1, preparing a chitosan solution; s2, preparing a gelatin solution; s3, preparing nitrogen-doped carbon quantum dots; s4, the chitosan solution, the gelatin solution, the nitrogen-doped carbon quantum dots and the antibacterial agent are mixed and dried, and the multifunctional food packaging film is prepared. Generally speaking, the transparency of the food packaging film is greatly reduced while the ultraviolet barrier property of the food packaging film is improved. The nitrogen-doped carbon quantum dot disclosed by the invention has excellent absorption performance on ultraviolet light in a range of 200-400nm, almost has no absorption on visible light of 400nm or above, and has excellent oxidation resistance. The food packaging film prepared by the invention not only has excellent ultraviolet blocking capability and high visible light transmittance, but also has remarkable antibacterial and antioxidant characteristics, and shows an excellent fresh-keeping effect on strawberries and fresh-cut apples.

Description

Technical Field

[0001] This invention relates to a food packaging film with UV resistance, antibacterial properties, antioxidant properties, and high light transmittance, its preparation method, and its application, belonging to the field of food packaging materials. Background Technology

[0002] Food, rich in proteins, fats, vitamins, and other nutrients, is a core source of substances for maintaining human life and health. However, these nutrients are susceptible to microbial attack, oxidation, and light exposure, leading to food spoilage. This not only results in significant resource waste but also poses a potential threat to the stability of the food supply chain and public food safety. Statistics show that globally, food waste due to spoilage accounts for a high percentage, indirectly exacerbating food shortages in some regions.

[0003] To slow down food spoilage, packaging technology is widely used in food preservation. Traditional plastic packaging materials, with their lightweight, low cost, and excellent processing performance, once dominated the food packaging industry. However, practice has shown that these materials have significant drawbacks: First, most traditional plastics are difficult to degrade naturally, and their extensive use can easily lead to "white pollution," which contradicts current environmental policies and the concept of sustainable development. Second, their functions are limited, lacking key properties such as antibacterial, antioxidant, and UV blocking properties, making them unable to effectively inhibit food deterioration during storage and transportation. Third, some printing inks and additives used in traditional plastic packaging may migrate into food, posing a food safety hazard.

[0004] To address the limitations of traditional food packaging materials, researchers have developed biodegradable food packaging materials using natural biodegradable substances (such as chitosan and gelatin) as base materials. They have also improved the films' UV blocking ability, antioxidant properties, and antibacterial properties by adding active functional substances. For example, Li Yang et al.'s invention patent, "A Method for Preparing an Antibacterial Composite Film Loaded with Clove Essential Oil Pickering Emulsion" (application number: 202411127905.5), describes a method where clove essential oil is emulsified and added to a film to impart antibacterial and antioxidant properties. Another example is Tian Junfei et al.'s invention patent, "A Method for Preparing a Regenerated Composite Film Using Coffee Grounds" (application number: 202210853701.4), which describes a method where coffee grounds are dissolved with pulp fibers and directly prepared into a composite film. While the resulting composite film has strong UV blocking properties, its transparency is relatively low. Currently, existing multifunctional food packaging films still face several challenges, one of which is that while improving the UV blocking performance of food packaging films, their transparency often decreases significantly. The reduced transparency of food packaging materials can significantly impact consumers' sensory experience. Therefore, developing novel food packaging materials with antibacterial and antioxidant properties, strong UV blocking capabilities, and high visible light transmittance has become an urgent need in the food industry and materials science fields. Summary of the Invention

[0005] The purpose of this invention is to address the problems in the prior art by disclosing a food packaging film with UV resistance, antibacterial properties, antioxidant properties, and high light transmittance, comprising, by weight:

[0006] Chitosan solution: 40-60 parts;

[0007] Gelatin solution: 40-60 parts;

[0008] Nitrogen-doped carbon quantum dots: 0.01-0.2 parts;

[0009] Antibacterial agent: 0.001-0.02 parts.

[0010] In some preferred embodiments, the nitrogen-doped carbon quantum dots exhibit excellent absorption performance for ultraviolet light in the 200-400 nm range, almost no absorption for visible light above 400 nm, and also possess excellent antioxidant properties.

[0011] In some preferred embodiments, the antimicrobial agent includes: polyhexamethylene monoguanidine hydrochloride, polyhexamethylene biguanidine hydrochloride, and combinations thereof.

[0012] This application also discloses a method for preparing a food packaging film with UV resistance, antibacterial properties, antioxidant properties, and high light transmittance, the steps of which are as follows:

[0013] S1: Preparation of chitosan solution;

[0014] S2: Preparation of gelatin solution;

[0015] S3: Preparation of nitrogen-doped carbon quantum dots;

[0016] S4: A multifunctional food packaging film is prepared by mixing and drying chitosan solution, gelatin solution, nitrogen-doped carbon quantum dots and antibacterial agent.

[0017] In some preferred embodiments, the chitosan solution is prepared as follows: acetic acid is dissolved in deionized water, then chitosan and glycerol are added, and the mixture is stirred at room temperature for 12 hours to obtain a chitosan solution.

[0018] In some preferred embodiments, the raw materials for preparing the chitosan solution are as follows:

[0019] Chitosan: 1-4 parts;

[0020] Glycerin: 0.2-0.8 parts;

[0021] Acetic acid: 1-4 parts;

[0022] Deionized water: 90-99 parts.

[0023] In some preferred embodiments, the gelatin solution is prepared as follows: gelatin and glycerin are added to deionized water and stirred at 50°C for 1 hour to obtain a gelatin solution.

[0024] In some preferred embodiments, the raw materials for preparing the gelatin solution are as follows:

[0025] Gelatin: 1-4 parts;

[0026] Glycerin: 0.2-0.8 parts;

[0027] Deionized water: 90-99 parts.

[0028] In some preferred embodiments, the nitrogen-doped carbon quantum dots are prepared as follows: citric acid and 1,2-propanediamine are weighed and uniformly dispersed in deionized water, then transferred to a high-pressure reaction tube, and the reaction is carried out under controlled temperature with stirring. After cooling, the product is filtered through a 0.22 μm filter membrane, dialyzed in deionized water for 48 h, and then freeze-dried for later use.

[0029] This application also discloses the application of the aforementioned food packaging film with UV resistance, antibacterial properties, antioxidant properties, and high light transmittance in the preservation of fruits and vegetables.

[0030] This application uses chitosan and gelatin as base materials, and by adding synthesized nitrogen-doped carbon quantum dots and antibacterial agents, prepares a food packaging film with anti-ultraviolet, antibacterial, and antioxidant properties as well as high light transmittance. While chitosan and gelatin composite films possess excellent visible light transmittance and certain antibacterial properties, they suffer from weak ultraviolet blocking ability and poor antioxidant capacity. The nitrogen-doped carbon quantum dots prepared in this application exhibit excellent absorption performance for ultraviolet light in the 200-400nm range, and almost no absorption for visible light above 400nm. Therefore, adding them to the chitosan and gelatin composite film can endow the film with excellent blocking ability for ultraviolet light in the 200-400nm range, while maintaining excellent transmittance for visible light above 400nm. The food packaging film prepared in this application can achieve complete blocking of ultraviolet light in the 300-390nm range, while still maintaining a transmittance of over 10% for visible light at 450nm. Existing multifunctional food preservation films, while improving UV blocking capabilities in the 300-400nm range, often result in a significant decrease in visible light transmittance in the 400-600nm range. When existing multifunctional food preservation films completely block UV light in the 300-390nm range, their transmittance for visible light at 450nm is less than 10%, severely impacting the sensory experience of food consumption. Furthermore, the nitrogen-doped carbon quantum dots synthesized in this application possess excellent antioxidant properties, endowing the composite film with superior antioxidant performance; by adding antibacterial agents, the antibacterial properties of the composite film can be improved. The multifunctional film prepared in this application exhibits excellent preservation effects on both strawberries and fresh-cut apples. Attached Figure Description

[0031] Figure 1 UV transmittance diagram of the composite film

[0032] Figure 2 Image of the composite membrane

[0033] Figure 3 Image showing the preservation effect of composite film packaging on strawberries.

[0034] Figure 4 Image showing the preservation effect of composite film packaging on fresh-cut apples. Detailed Implementation

[0035] The present invention will be described in detail below through embodiments. It should be noted that the specific embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above description of the present invention should fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

[0036] I. Preparation of nitrogen-doped carbon quantum dots

[0037] 2.101 g of citric acid and 860 μL of 1,2-propanediamine were dispersed in 20 ml of deionized water by stirring, and then transferred to a 50 ml high-pressure reaction tube. The reaction was carried out at 220 °C for 12 h. After cooling, the product was filtered through a 0.22 μm filter membrane, dialyzed in deionized water for 48 h, and then freeze-dried for later use.

[0038] II. Preparation of Food Packaging Film

[0039] 1. Preparation of food packaging films with UV resistance, antibacterial properties, antioxidant properties, and high light transmittance (experimental group): A measured amount of acetic acid aqueous solution was prepared, followed by the addition of measured amounts of chitosan and glycerol. The mixture was stirred at room temperature for 12 hours to obtain a chitosan solution. Simultaneously, measured amounts of gelatin and glycerol were added to measured amounts of deionized water and stirred at 50°C for 1 hour to obtain a gelatin solution. The chitosan solution and gelatin solution were mixed, and measured amounts of antibacterial agent and nitrogen-doped carbon quantum dots (CDs) were added. The mixture was then stirred at room temperature for 1 hour and sonicated for 20 minutes to obtain a homogeneous film-forming solution. 30 ml of the film-forming solution was then poured into a 120 mm diameter plastic petri dish. The petri dish was dried in a 35°C oven and then equilibrated in a 20°C, 50%RH constant temperature and humidity chamber for 3 days to obtain a multifunctional food packaging film. The prepared film was tested for UV resistance, appearance, antioxidant properties, antibacterial properties, and preservation properties for strawberries and fresh-cut apples.

[0040] The specific formulations of the food packaging films with UV resistance, antibacterial properties, antioxidant properties, and high light transmittance are shown in Table 1.

[0041] Table 1

[0042]

[0043] 2. Preparation of food packaging film (control group): 50 ml of acetic acid aqueous solution (1 v / v%) was prepared, followed by the addition of 1.0 g chitosan and 0.3 g glycerol. The mixture was stirred at room temperature for 12 h to obtain a chitosan solution. Simultaneously, 1.0 g gelatin and 0.3 g glycerol were added to 50 ml of deionized water and stirred at 50 °C for 1 h to obtain a gelatin solution. The chitosan solution and gelatin solution were mixed, and a measured amount of polyhexamethylene biguanide hydrochloride or titanium dioxide was added. The mixture was then stirred at room temperature for 1 h and sonicated for 20 min to obtain a homogeneous film-forming solution. 30 ml of the film-forming solution was then poured into a 120 mm diameter plastic petri dish. The petri dish was dried in a 35 °C oven and then equilibrated in a 20 °C, 50% RH constant temperature and humidity chamber for 3 days to obtain the food packaging film. The prepared film was tested for UV resistance, appearance, antioxidant properties, antibacterial properties, and preservation performance on strawberries and fresh-cut apples.

[0044] The active functional substance formulations of the food packaging film control group are shown in Table 2.

[0045] Table 2

[0046]

[0047] III. Testing of the UV resistance, antioxidant, and antibacterial properties of food packaging films, as well as their preservation performance on strawberries and fresh-cut apples.

[0048] 1. UV resistance test

[0049] The film was cut into 3×6cm rectangular strips with scissors, and then the samples were placed in the sample holder of the UV spectrophotometer. The UV transmittance spectrum of the film in the 200-800nm ​​range was measured using the UV spectrophotometer to evaluate the film's UV blocking ability. The UV transmittance values ​​at 450 and 600nm were used to evaluate the visible light transmittance of the film.

[0050] 2. Appearance Test

[0051] Place the film on an A4 sheet of paper with the logo and use a camera to record the appearance of each sample.

[0052] 3. Antioxidant test

[0053] The composite membrane sample was dissolved in 60% ethanol solution at 35℃ for 24 hours. Then, 0.5 ml of the supernatant was mixed with 2.5 ml of ethanol and DPPH solution, respectively. The absorbance was measured using a UV spectrophotometer. The DPPH radical scavenging rate of the membrane was then calculated using the following formula:

[0054] DPPH free radical scavenging rate = [1-(A i -A j ) / A0]×100%

[0055] Where A i A represents the absorbance of the supernatant of the sample thin film solution and the DPPH ethanol solution. j A0 represents the absorbance of 0.5 ml of sample film solution supernatant and 2.5 ml of ethanol, while A0 represents the absorbance of 0.5 ml of ethanol and 2.5 ml of DPPH ethanol solution.

[0056] 4. Antibacterial performance test

[0057] Weigh 15 mg of the film and 1 ml of bacterial suspension, add them simultaneously to 100 ml of physiological saline, and shake them together in a shaker at 37°C and 150 rpm for 18 hours. Then, dilute the cultured liquid a certain factor and spread it on a plate. After incubation for 24 hours, count the colonies that have grown. Keeping other conditions unchanged, the sample without the film serves as a blank control group. Calculate the inhibition rate using the formula:

[0058] Antibacterial rate = (A0-A1) / A0 × 100%

[0059] Where A0 represents the number of colonies in the blank control group and A1 represents the number of colonies in the sample film group.

[0060] 5. Test on the preservation performance of strawberries

[0061] Place fresh strawberries in a clear plastic cup, seal the cup with a composite film, and store it at 20°C and 60% RH. Take out the strawberries daily and record their spoilage process with a camera.

[0062] 6. Test on the preservation performance of fresh-cut apples

[0063] Fresh apples were cut into regular cuboids of 2×3×1cm and placed in 9mm petri dishes, which were then sealed with a composite film. The dishes were then stored at 20℃ and 80% RH. The spoilage process of the fresh-cut apples was recorded using a camera over four days.

[0064] IV. Results

[0065] The test results of the UV resistance, antioxidant, antibacterial properties, and preservation performance of the food packaging films in the example group for strawberries and fresh-cut apples are shown in Table 3:

[0066] Table 3

[0067]

[0068]

[0069] The test results of the UV resistance, antioxidant, antibacterial properties, and preservation performance of the control group food packaging film for strawberries and fresh-cut apples are shown in Table 4:

[0070] Table 4

[0071]

[0072]

[0073] As shown in Table 3, the composite film in the examples exhibits several excellent properties: with the increase of nitrogen-doped carbon quantum content, the film's ability to block ultraviolet light in the 200-400 nm range and its antioxidant capacity are significantly enhanced, while maintaining high transmittance for visible light above 400 nm, and possessing excellent antibacterial and fruit preservation capabilities. Specifically:

[0074] 1) When the film achieves complete blocking of 200-400nm ultraviolet light, the transmittance of 450nm visible light is still higher than 10%, and the transmittance of 600nm visible light is higher than 60%, showing excellent ultraviolet blocking and visible light transmission performance.

[0075] 2) All examples showed a DPPH free radical scavenging rate of over 32%, and the proportion of the brownish-yellow area on the surface of fresh-cut apples was less than 10% on the 4th day, demonstrating strong antioxidant capacity.

[0076] 3) It has a 100% inhibition rate against Staphylococcus aureus and Escherichia coli, demonstrating significant antibacterial effects;

[0077] 4) It can extend the shelf life of strawberries to more than 5 days, with outstanding preservation effect.

[0078] As shown in Table 4, the performance of various films in the control group was significantly inadequate:

[0079] 1) Pure chitosan-gelatin film and chitosan-gelatin film with added polyhexamethylene biguanide hydrochloride, although for 400-600

[0080] It has high transmittance of visible light in the nm range, but poor blocking ability of ultraviolet light in the 220-400nm range (only 50%).

[0081] Both methods showed a DPPH free radical scavenging rate of less than 5%, and by day 4, over 60% of the surface area of ​​fresh-cut apples was burnt yellow, indicating extremely poor antioxidant capacity. They also only maintained the freshness of strawberries for 3 days, demonstrating poor preservation effects.

[0082] Pure chitosan-gelatin films can also promote the growth of E. coli and exhibit extremely poor antibacterial properties.

[0083] 2) Although the chitosan-gelatin film with added titanium dioxide can achieve complete blocking of 220-400nm ultraviolet light, its visible light transmittance is poor: the transmittance of 450nm visible light is only 2.2%, and the transmittance of 600nm visible light is only 22.7%; its scavenging rate of DPPH free radicals is 0, and the surface of fresh-cut apples has turned completely brownish-yellow by the 4th day, with no antioxidant capacity; the antibacterial rate against Escherichia coli is only 85.4%, and the shelf life of strawberries is only 3 days, indicating poor preservation ability.

[0084] Appendix Figure 1-4 The images show the UV blocking ability and visible light transmittance of some examples and control groups, as well as images of the film appearance, strawberry preservation effect, and fresh-cut apple preservation.

[0085] In summary, combining Tables 3 and 4 and the appendix... Figure 1-4 The results show that the food packaging film prepared by this invention not only has excellent ultraviolet blocking ability and high visible light transmittance, but also has significant antibacterial and antioxidant properties, and exhibits excellent preservation effects on strawberries and fresh-cut apples.

Claims

1. A food packaging film with UV resistance, antibacterial properties, antioxidant properties, and high light transmittance, characterized in that: By weight, it includes: chitosan solution: 40-60 parts; Gelatin solution: 40-60 parts; Nitrogen-doped carbon quantum dots: 0.01-0.2 parts; Antibacterial agent: 0.001-0.02 parts.

2. The food packaging film with UV resistance, antibacterial properties, antioxidant properties, and high light transmittance according to claim 1, characterized in that, The nitrogen-doped carbon quantum dots exhibit excellent absorption performance in the ultraviolet light range of 200-400nm, but almost no absorption in visible light above 400nm, while also possessing excellent antioxidant properties.

3. The food packaging film with UV resistance, antibacterial properties, antioxidant properties, and high light transmittance according to claim 1, characterized in that, The antibacterial agents include: polyhexamethylene monoguanidine hydrochloride, polyhexamethylene biguanidine hydrochloride, and combinations thereof.

4. A method for preparing a food packaging film with UV resistance, antibacterial properties, antioxidant properties, and high light transmittance, characterized in that, Includes the following steps: S1: Preparation of chitosan solution; S2: Preparation of gelatin solution; S3: Preparation of nitrogen-doped carbon quantum dots; S4: A multifunctional food packaging film is prepared by mixing and drying chitosan solution, gelatin solution, nitrogen-doped carbon quantum dots and antibacterial agent.

5. The method for preparing the food packaging film with UV resistance, antibacterial properties, antioxidant properties, and high light transmittance according to claim 4, characterized in that, The chitosan solution is prepared as follows: acetic acid is dissolved in deionized water, then chitosan and glycerol are added, and the mixture is stirred at room temperature for 12 hours to obtain the chitosan solution.

6. The method for preparing the food packaging film with UV resistance, antibacterial properties, antioxidant properties, and high light transmittance according to claim 5, characterized in that, The raw materials for preparing chitosan solution are as follows: Chitosan: 1-4 parts; Glycerin: 0.2-0.8 parts; Acetic acid: 1-4 parts; Deionized water: 90-99 parts.

7. The method for preparing the food packaging film with UV resistance, antibacterial properties, antioxidant properties, and high light transmittance according to claim 5, characterized in that, The gelatin solution is prepared as follows: gelatin and glycerin are added to deionized water and stirred at 50°C for 1 hour to obtain the gelatin solution.

8. The method for preparing the food packaging film with UV resistance, antibacterial properties, antioxidant properties, and high light transmittance according to claim 7, characterized in that, The raw materials for preparing gelatin solution are as follows: Gelatin: 1-4 parts; Glycerin: 0.2-0.8 parts; Deionized water: 90-99 parts.

9. The method for preparing the food packaging film with UV resistance, antibacterial properties, antioxidant properties, and high light transmittance according to claim 8, characterized in that, The preparation method of nitrogen-doped carbon quantum dots is as follows: citric acid and 1,2-propanediamine are weighed and uniformly dispersed in deionized water, then transferred to a high-pressure reaction tube, and the temperature is controlled under stirring for reaction. After cooling, the product is filtered through a 0.22 μm filter membrane, dialyzed in deionized water for 48 h, and then freeze-dried for later use.

10. The application of the food packaging film with UV resistance, antibacterial properties, antioxidant properties, and high light transmittance as described in any one of claims 1-9 in the preservation of fruits and vegetables.

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