Medicinal and edible extract degradable antibacterial preservative film as well as preparation method and application thereof

Abstract

The invention discloses a degradable antibacterial preservative film with medicinal and edible extracts as well as a preparation method and application of the degradable antibacterial preservative film, and belongs to the technical field of preservative films. The method comprises the following steps: (1) dissolving chitosan in an acetic acid aqueous solution, adding a wormwood extract into the obtained chitosan solution, and stirring at a certain temperature to form a mixed solution; (2) adding potato starch into water to prepare a potato starch solution; gelatinizing the potato starch solution, adding glycerol into the gelatinized solution at a certain temperature, and stirring to obtain potato starch gelatinized solution; (3) mixing the mixed solution and the potato starch gelatinization solution according to a certain proportion, pouring the mixture to a polytetrafluoroethylene substrate, and drying to form a film, so as to obtain the degradable antibacterial preservative film. The method has the advantages of being convenient in process, wide in raw material source and suitable for large-scale production. The prepared degradable antibacterial preservative film has excellent biodegradability, preservation performance and oxidation resistance, and has a wide application prospect in the field of food preservation.

Description

Technical Field

[0001] The present invention relates to the technical field of fresh-keeping films, in particular to a degradable antibacterial fresh-keeping film containing medicinal and edible extracts, and a preparation method and application thereof. Background Art

[0002] As society's living standards improve, fruit is increasingly appearing on people's tables. Preserving fruit is a hot topic. Traditional plastic films are commonly used for fruit preservation due to their low cost and stable performance. However, these films suffer from shortcomings such as low barrier properties, low efficiency, non-biodegradability, and environmental concerns. Coupled with the international trend to reduce the use of preservatives and adopt new approaches to preservation, people are increasingly turning their attention to sustainable, recyclable, and environmentally friendly materials to replace existing, highly polluting chemical compounds. A biodegradable, low-cost composite film based on starch or chitosan is emerging as a viable alternative to previously difficult-to-degrade plastic films. For example, new antimicrobial plastic wraps are being developed to extend the shelf life of food.

[0003] Chitosan possesses many unique properties, including biodegradability, cell affinity, and biological effects. Chitosan, in particular, contains free amino groups and is the only alkaline polysaccharide among natural polysaccharides. Chitosan possesses antioxidant and antibacterial properties, making it widely used in the food, pharmaceutical, and cosmetic industries, with promising development prospects. When the amylose chain in starch is heated in water to the gelatinization temperature, it rapidly ages and gradually forms a gel, which then forms a film.

[0004] Currently, finished films are made from chitosan, starch, gelatin, and other polysaccharides supplemented with plasticizers or crosslinkers. These films have already found application in the food packaging industry. These materials offer advantages such as widespread availability, environmental friendliness, and a lack of biotoxicity. However, these films still have some drawbacks, such as suboptimal antimicrobial properties and poor self-adhesion in chitosan films, and excessive hygroscopicity in starch films, resulting in poor water barrier properties. Therefore, future research and development is considering combining several polysaccharides to enhance the film's mechanical properties, as well as adding antimicrobial agents to the films to strengthen their antimicrobial properties.

[0005] Chinese invention patent publication number CN116874890A discloses an antibacterial cling film based on konjac glucomannan and its preparation method. The food packaging cling film produced by the invention has good mechanical properties, moisture and oxygen permeability, and a good antibacterial rate against common bacteria, but it still has the disadvantages of complicated steps and high cost. In addition, the antibacterial agents added are volatile substances such as cinnamon essential oil and ginger essential oil, which can easily evaporate over time and affect their antibacterial properties. Chinese invention patent publication number CN118127715A provides a new antiseptic and antibacterial cling film and its preparation method. The food cling film produced by the invention has good tensile strength at break, good air permeability to oxygen and carbon dioxide, and good inhibition rate against Escherichia coli, Staphylococcus aureus, and Penicillium suspensions, and has good preservation effect in subsequent preservation tests. However, this cling film still uses essential oil antibacterial agents, which can easily affect film stability.

[0006] In summary, providing a degradable antibacterial cling film that takes into account preservation, non-biotoxicity, stable physical and chemical properties during use, and biodegradability after use is of great significance for food preservation and environmental protection. Summary of the Invention

[0007] In view of the above-mentioned defects of the prior art, in a first aspect of the present invention, a method for preparing a degradable antibacterial cling film is provided, which has a convenient process, a wide range of raw material sources, and is suitable for large-scale production, comprising the following steps: (1) dissolving chitosan in an acetic acid aqueous solution, adding the mugwort extract to the obtained chitosan solution, and stirring at a certain temperature to form a mixed solution; (2) Adding potato starch to water to prepare a potato starch solution; gelatinizing the potato starch solution, adding glycerol to the obtained gelatinized solution at a certain temperature and stirring to obtain a potato starch gelatinized liquid; (3) The mixed liquid and potato starch gelatinized liquid are mixed in a certain proportion, poured onto a polytetrafluoroethylene substrate, and dried to form a film to obtain a biodegradable antibacterial cling film.

[0008] Preferably, in step (1), the concentration of the acetic acid aqueous solution is 1 vol.% to 2 vol.%.

[0009] Preferably, in step (1), the chitosan content of the chitosan solution is 1 wt.% to 2 wt.%; and the amount of wormwood extract added is 1 wt.% of the chitosan solution.

[0010] Preferably, in step (1), the stirring temperature is 45-60°C, the stirring time is 30-45 min, and the stirring speed is 400 rpm.

[0011] Preferably, in step (2), the concentration of the potato starch solution is 4-6 wt.%.

[0012] Preferably, in step (2), gelatinization is carried out under stirring conditions, the gelatinization temperature is 60-80°C, the gelatinization time is 30-45 min, and the stirring speed is 400 rpm.

[0013] Preferably, in step (2), 25 wt.% propylene glycol is added to the obtained gelatinized solution at 35-50°C and stirred for 30-45 min at a stirring speed of 400 rpm.

[0014] Preferably, in step (3), the volume ratio of the mixed solution to the potato starch gelatinized solution is 2:3 to 3:2.

[0015] Preferably, in step (3), the drying temperature is 65-75°C, and the drying time is 3-5 hours.

[0016] The film is formed by combining starch and chitosan and polytetrafluoroethylene. The film has certain antibacterial properties and has suitable adhesion on the contact surface with polytetrafluoroethylene, which is conducive to food packaging.

[0017] In a second aspect of the present invention, a degradable antibacterial fresh-keeping film with biodegradability, excellent fresh-keeping and antioxidant properties is provided, which is prepared by the preparation method provided by the first aspect of the present invention.

[0018] In a third aspect of the present invention, there is provided a use of the degradable antibacterial fresh-keeping film according to the second aspect of the present invention in food preservation.

[0019] Based on the above technical solutions, the design concept and principle of the present invention are as follows: The present invention uses biodegradable chitosan and potato starch as film-forming substrates, glycerin as a plasticizer, and mugwort extract as an antibacterial agent to address the pollution and safety issues associated with traditional plastic films and preservatives. The addition of mugwort extract enhances the film's antioxidant properties, helping to preserve food.

[0020] Among starches, amylopectin gels at a slower and lesser rate than amylose. The endogenous phosphate groups on the amylopectin chains contribute to the high transparency of the starch film after film formation. The present invention utilizes potato starch, which has a high amylose content of 24.1% to 35.55%, and exhibits excellent film-forming properties. The addition of wormwood extract reduces transparency, reducing light and UV exposure to food compared to pure chitosan starch films, preventing oxidation and color changes of beneficial ingredients in food. Wormwood extract is an effective ingredient extracted from wormwood using methods such as decoction, ultrasonic-assisted extraction, cold pressing, subcritical extraction, and supercritical extraction. Wormwood extract has a strong antibacterial effect against Staphylococcus aureus and Escherichia coli. The polyphenols it contains also provide a strong antioxidant effect. The present invention has simple ingredients, all derived from natural sources. Each added component is biodegradable and non-toxic to the human body. The preparation process is simple and easy to operate. Compared with the prior art, the present invention has the following advantages and beneficial effects: The invention provides a preparation method of a degradable antibacterial fresh-keeping film, which has the advantages of convenient process, wide source of raw materials and applicability to large-scale production.

[0021] The invention provides a degradable antibacterial fresh-keeping film, which has simple ingredients, is non-toxic to human body, and has excellent biodegradability, fresh-keeping and antioxidant properties.

[0022] The present invention provides an application of a degradable antibacterial fresh-keeping film, which has broad application prospects in the field of food preservation. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Schematic diagram of the process for preparing a degradable antibacterial cling film; Figure 2 Fourier transform infrared spectroscopy (FTIR) of chitosan, wormwood extract, Example 1, and Comparative Example 1; Figure 3 The scanning electron microscope (SEM) images of Comparative Example 1 (a) and Example 1 (b) are shown. Figure 4 This is the test result of the weight loss rate of red grapes; Figure 5 This is the test result of ascorbic acid in red grapes; Figure 6 This is the test result of the titratable acidity of red grapes; Figure 7 This is the test result of soluble solids of red grapes. DETAILED DESCRIPTION

[0024] The present invention is further illustrated by way of examples below, but the present invention is not limited to the scope of the examples. Experimental methods in the following examples where specific conditions are not specified were performed according to conventional methods and conditions, or selected according to the product specifications.

[0025] In the following embodiments: Chitosan, deacetylation degree ≥95%, Shanghai MacLean Biochemical Technology Co., Ltd.; Artemisia annua extract, food grade, Shaanxi New Horizon Biotechnology Co., Ltd. Potato starch, food grade, Milani Ltd., Netherlands; Polyethylene (PE) plastic wrap, food grade, Quanzhou Hexing Hardware & Plastic Products Co., Ltd.

[0026] Example 1 The preparation method of degradable antibacterial cling film is as follows: Figure 1 As shown, the steps are as follows: (1) Prepare an acetic acid aqueous solution, wherein the volume ratio of glacial acetic acid to deionized water is 1 mL / 100 mL; dissolve chitosan in the acetic acid aqueous solution, wherein the mass volume ratio of chitosan to the acetic acid aqueous solution is 1 g / 100 mL; add wormwood extract to the obtained chitosan solution, wherein the mass volume ratio of wormwood extract to chitosan solution is 1 g / 100 mL; and slowly stir the mixture in a water bath at 60°C for 45 min using an electric stirring device to form a mixed solution; (2) Potato starch was added to deionized water to prepare a potato starch solution, wherein the mass volume ratio of potato starch to deionized water was 4 g / 100 mL; the potato starch solution was heated in a water bath at 60-80 °C and slowly stirred with an electric stirring device for 45 min to gelatinize it; glycerol was added to the obtained gelatinized solution in an amount of 25 wt.% based on the mass of potato starch, and stirred in a water bath at 50 °C for 30 min to obtain a potato starch gelatinized solution; (3) Pipette 20 mL of the mixed solution and potato starch gelatinized solution into a small beaker according to a volume ratio of 1:1, stir evenly, and pour into a 9 cm culture dish with a polytetrafluoroethylene film on the bottom; place it in a forced air drying oven at 65 °C and dry it for 3 h to obtain a biodegradable antibacterial plastic wrap. Example 2 The preparation method of the degradable antibacterial cling film comprises the following steps: (1) Prepare an acetic acid aqueous solution, wherein the volume ratio of glacial acetic acid to deionized water is 1 mL / 100 mL; dissolve chitosan in the acetic acid aqueous solution, wherein the mass volume ratio of chitosan to the acetic acid aqueous solution is 1 g / 100 mL; add wormwood extract to the obtained chitosan solution, wherein the mass volume ratio of wormwood extract to chitosan solution is 1 g / 100 mL; and slowly stir the mixture in a water bath at 60°C for 45 min using an electric stirring device to form a mixed solution; (2) Potato starch was added to deionized water to prepare a potato starch solution, wherein the mass volume ratio of potato starch to deionized water was 4 g / 100 mL; the potato starch solution was heated in a water bath at 60-80 °C and slowly stirred with an electric stirring device for 45 min to gelatinize it; glycerol was added to the obtained gelatinized solution in an amount of 25 wt.% based on the mass of potato starch, and stirred in a water bath at 50 °C for 30 min to obtain a potato starch gelatinized solution; (3) Pipette 20 mL of the mixed solution and potato starch gelatinized solution into a small beaker according to a volume ratio of 2:3, stir evenly, and pour into a 9 cm culture dish with a polytetrafluoroethylene film on the bottom; place it in a forced air drying oven at 65 °C and dry it for 3 h to obtain a biodegradable antibacterial plastic wrap.

[0027] Example 3 The preparation method of the degradable antibacterial cling film comprises the following steps: (1) Prepare an acetic acid aqueous solution, wherein the volume ratio of glacial acetic acid to deionized water is 1 mL / 100 mL; dissolve chitosan in the acetic acid aqueous solution, wherein the mass volume ratio of chitosan to acetic acid aqueous solution is 2 g / 100 mL; add mugwort extract to the obtained chitosan solution, wherein the mass volume ratio of mugwort extract to chitosan solution is 1 g / 100 mL; and slowly stir the mixture with an electric stirring device under the condition of heating at 60°C in a water bath for 45 min to form a mixed solution; (2) Potato starch was added to deionized water to prepare a potato starch solution, wherein the mass volume ratio of potato starch to deionized water was 4 g / 100 mL; the potato starch solution was heated in a water bath at 60-80 °C and slowly stirred with an electric stirring device for 45 min to gelatinize it; glycerol was added to the obtained gelatinized solution in an amount of 25 wt.% based on the mass of potato starch, and stirred in a water bath at 50 °C for 30 min to obtain a potato starch gelatinized solution; (3) Pipette 20 mL of the mixed solution and potato starch gelatinized solution into a small beaker according to a volume ratio of 1:1, stir evenly, and pour into a 9 cm culture dish with a polytetrafluoroethylene film on the bottom; place it in a forced air drying oven at 65 °C and dry it for 3 h to obtain a biodegradable antibacterial plastic wrap.

[0028] Comparative Example 1 This comparative example is basically the same as Example 1, except that the wormwood extract is not added during the preparation process, and the remaining steps are the same to obtain a plastic wrap.

[0029] Comparative Example 2 This comparative example uses commercially available polyethylene cling film as a comparative sample.

[0030] Comparative Example 3 This comparative example is basically the same as Example 1, except that the drying temperature for film formation is set to 35° C. and the drying time is 3 hours. Under the process conditions of this comparative example, it was observed that the film-forming solution did not form a film.

[0031] Test Example 1 This test investigated the water solubility of biodegradable antibacterial cling film. The cling film from the examples and comparative examples was cut into 10 mm x 10 mm squares and dried in a 100°C oven to constant weight, with the weight at this point being recorded as M1. These dried squares were then placed in 50 mL of deionized water for 24 hours. The treated rectangular sheets were then dried in a 100°C oven to constant weight, with the weight at this point being recorded as M2. Water solubility (HS) was calculated using the following formula: .

[0032] The water solubility test results of various types of cling film are shown in Table 1.

[0033] Table 1: Water solubility test results of various types of cling film

[0034] From the results in Table 1, it can be seen that the water solubility of the plastic wrap is enhanced after the addition of mugwort extract. In some applications, such as when used as a packaging material, the better water solubility of the plastic wrap can ensure that the composite film is better degraded. The water solubility of the film may be brought by chitosan, starch and glycerol. Higher water solubility may also mean better moisturizing properties. When the plastic wrap is used to preserve fruits and vegetables, water will continue to evaporate and form water droplets on the film wall, causing microorganisms to multiply on the surface of the fruits and vegetables and cause corruption. Therefore, the plastic wrap needs to have a better effect of being quickly infiltrated by water rather than forming droplets. At the same time, higher water solubility may also mean higher safety. The packaging material can be washed away during the cleaning process to prevent residue.

[0035] Test Example 2 This test example investigated the tensile strength and elongation at break of biodegradable antibacterial cling film. The examples and comparative examples were tested using a tensile tester. The test specimens were 10 mm x 10 mm in size. The lengths before and after fracture, as well as the maximum tensile force, were recorded. The tensile strength and elongation at break were calculated using the following formula: ; Where: TS represents tensile strength, KPa; F is the maximum tensile force of the sample, N; S is the area of ​​the sample, mm 2 . ; Wherein: L represents the elongation at break, %; L1 represents the length after stretching, mm; L0 represents the length before stretching, mm. The test results of tensile strength and elongation at break are shown in Table 2.

[0036] Table 2: Test results of tensile strength and elongation at break of various types of cling film

[0037] It can be seen from Table 2 that after adding mugwort extract, the mechanical properties of the plastic wrap are enhanced, which may be related to the mugwort fiber in the mugwort extract, which is beneficial to enhancing the mechanical properties of the plastic wrap.

[0038] Test Example 3 This test investigates the water vapor permeability coefficient of a biodegradable, antimicrobial cling film. The water vapor permeability coefficients of the examples and comparative examples were tested using the method described in GB / T 1037-2021, "Plastic Film and Sheeting - Determination of Water Vapor Permeability - Cup Weight Gain and Loss Method." The results are shown in Figure 3.

[0039] Table 3: Water vapor transmission coefficient of various types of cling film

[0040] The test results in Table 3 show that the addition of mugwort extract reduces the water vapor permeability of the plastic wrap. For preserved foods, a high water vapor permeability can easily lead to moisture loss from the fruit. A low water vapor permeability can prevent moisture from evaporating from the fruit from the film and can lead to condensation on the surface, exacerbating spoilage. Test Example 4 This test investigates the transparency of biodegradable antibacterial cling film. Samples from the examples and comparative examples were cut into 10 mm x 30 mm sections and attached to cuvettes. Their absorbance was measured at 600 nm, with a blank cuvette used as a control. Transparency was calculated using the following formula: ; Where: OP stands for transparency; Abs 600 is the absorbance of the sample at a wavelength of 600 nm; d is the thickness of the sample, mm.

[0041] The transparency test results are shown in Table 4.

[0042] Table 4: Transparency test results of various types of cling film

[0043] From the results in Table 4, it can be seen that the transparency of the film decreases after the addition of mugwort extract, which may be helpful for preserving certain foods that are easily deteriorated by light.

[0044] Test Example 5 This test example investigated the antibacterial properties of a biodegradable antibacterial cling film. Using Escherichia coli and Bacillus subtilis as the experimental strains, the antibacterial properties of Example 1 and Comparative Example 1 were evaluated using the Oxford cup method. 100 μL of the bacterial suspension was dropped onto the surface of a solidified beef extract peptone culture medium and evenly spread with a coating rod. The Oxford cup was placed on the surface of the culture medium, and the film-forming solution was added to the Oxford cup. The film was then incubated at 37°C for 24 hours, and the diameter of the inhibition zone was measured. The antibacterial effects of each group were compared, and the test results are shown in Table 5.

[0045] Table 5: Antibacterial performance test results of various types of cling film

[0046] As can be seen from Table 5, the addition of wormwood extract improves the inhibitory performance against Escherichia coli and Bacillus subtilis. The plastic wrap of the present invention has good inhibitory performance against these two bacterial species.

[0047] Test Example 6 This test investigates the antioxidant properties of biodegradable antibacterial plastic wrap. The antioxidant properties of plastic wrap are determined by its ability to scavenge free radicals. Preparation of centrifuge: Weigh 0.5 g of membrane sample, place it in a 10 mL centrifuge tube, pour 10 mL of 50% (v / v) ethanol into it, and centrifuge at 3000 rpm for 30 min at room temperature to obtain the centrifuge. DPPH method: Prepare 0.2 mmol / L DPPH solution and the reaction solution according to Table 6. Place the reaction solution in a dark environment to react for 30 min. Then take out the reaction solution and measure the absorbance at 517 nm. The DPPH clearance rate is calculated as follows: .

[0048] Table 6: Configuration of DPPH reaction solution

[0049] ABTS method: Mix 7.4 mmol / L ABTS and 2.45 mmol / L K2S2O8, then place in the dark for at least 12 h. Dilute with anhydrous ethanol to an absorbance of 0.700 ± 0.001 at 734 nm. Prepare the reaction solution according to Table 7. Place the reaction solution in the dark for 7 min, then remove and measure the absorbance of the reaction solution at 734 nm. The ABTS clearance rate is calculated as follows: .

[0050] Table 7: Configuration of ABTS reaction solution

[0051] The free radical scavenging rates of various plastic wraps are shown in Table 8.

[0052] Table 8: Free radical scavenging rate of various cling films

[0053] Food packaging should have good antioxidant properties. There are flavonoids in the wormwood extract, and most of the flavonoids have varying numbers of phenolic hydroxyl groups, which can reduce free radicals to effectively remove free radicals, thereby achieving an antioxidant effect. As shown in Table 8, the scavenging rates of the film of Comparative Example 1 for DPPH radicals and ABTS+ radicals are 2.64% and 14.00%, respectively. After the wormwood extract is added to form the film, the antioxidant properties of the film are significantly improved. The scavenging rates of the film of Example 1 for DPPH radicals and ABTS+ radicals are 18.28% and 53.69%, respectively, and the scavenging rates for DPPH radicals and ABTS+ radicals are increased by 6.92 times and 3.84 times. The results show that the fresh-keeping film of the present invention has excellent antioxidant properties.

[0054] Test Example 7 Characterization was performed using Fourier transform infrared spectroscopy. Comparative Example 1 and Example 1 were tested using ATR mode, and chitosan and wormwood extracts were tested using the potassium bromide tablet method. The scanning range was 400-4000 cm-1, with a resolution of 4 cm-1. Figure 2The following are the infrared spectra of each substance and the plastic wrap. In the infrared spectrum of chitosan, the broad absorption peak at a wavenumber of 3460 cm-1 is a typical OH vibration absorption peak in the chitosan molecule. The absorption peak at a wavenumber of 1640 cm-1 is caused by the bending vibration of the stretching vibration of the amide C=O bond and is a characteristic peak of chitosan. The peak at a wavenumber of 1460 cm-1 is caused by the bending vibration of CH. In the infrared spectrum of Comparative Example 1, after potato starch was added to chitosan to form a film, the three characteristic peaks at 3460 cm-1, 1640 cm-1, and 1460 cm-1 all red-shifted to 3265 cm-1, 1558 cm-1, and 1410 cm-1, respectively. This indicates an interaction between chitosan and potato starch. The absorption peaks observed at 2928 cm-1 and 2886 cm-1 are also due to CH stretching vibration. In the infrared spectrum of the mugwort extract, a broad peak at 3400 cm⁻¹ indicates the presence of OH. Absorption peaks at 2920 cm⁻¹ and 1646 cm⁻¹ represent C=C and CH on unsaturated carbons, characteristic peaks of the flavonoids, the main components of mugwort extract. These characteristic peaks all decrease in wavenumber after the addition of mugwort extract, suggesting the possible formation of intermolecular hydrogen bonds. Flavonoids themselves have a certain color, which can reduce the transparency of the film and reduce the impact of light on preserved foods. Furthermore, the absorption peak at 997 cm⁻¹ of the comparative example 1 film originates from the hydrogen bond absorption peak formed between the OH on the glycerol molecule and the oxygen atom in the glycosidic bond on the starch molecule. After the addition of mugwort extract, the peak shifts to 1017 cm⁻¹, indicating that the mugwort extract replaces some of the glycerol molecules and forms hydrogen bonds with the starch molecules, resulting in a complex formation. For the comparative example 1 film, the addition of mugwort extract in Example 1 showed little change in the infrared spectrum, with no new characteristic peaks generated, indicating that the chemical structure of the degradable antibacterial plastic wrap remained unchanged.

[0055] Test Example 8 SEM was used to characterize and analyze the degradable antibacterial cling film. The degradable antibacterial cling film was cut into 10 mm × 10 mm square rectangular pieces, adhered to conductive adhesive, sprayed with gold, and then placed in SEM for detection. Figure 3 (a) Figure 3 (b) is a scanning electron microscope image of Comparative Example 1 and Example 1. Figure 3 (a) shows that the surface of the film of Comparative Example 1 is smooth but partially wrinkled. Potato starch and chitosan have good compatibility, which may be due to the hydrogen bonds between the hydroxyl groups in the potato starch molecules and the protonated amino groups in the chitosan molecules, thereby enhancing the compatibility of the two substances. Figure 3(b) is a scanning electron micrograph of Example 1. After adding mugwort extract, the film surface becomes rough. This is likely due to the poor solubility of mugwort extract, which fails to fully dissolve in the composite film, resulting in aggregation on the composite film surface. Mugwort extract contains mugwort fibers, which, when added to the composite film solution, impart a fibrous appearance to the composite film surface and enhance its tensile strength. Both films exhibit small fragments on their surfaces, likely caused by the drying process prior to SEM analysis.

[0056] Test Example 9 This test case tested the preservation of biodegradable antibacterial plastic wrap. Undamaged fresh red grapes of similar size and maturity were divided into three groups and then refrigerated at -4°C until use. Each group of red grapes was treated differently and divided into three experimental groups: Group 1 was wrapped with Example 1 and stored at room temperature; Group 2 was wrapped with Comparative Example 1 and stored at room temperature; and Group 3 was wrapped with Comparative Example 2 and stored at room temperature. The red grapes were tested for indices at 1, 3, 5, and 7 days.

[0057] Red grape weight loss rate: like Figure 4 As shown, the overall mass loss of red grapes is on an upward trend. Throughout the storage process, the mass loss of both Example 1 and Comparative Example 1 was significantly greater than that of the PE film. This may be due to the PE film's relatively dense structure and poor moisture permeability. The moisture released by the red grapes cannot quickly pass through the membrane surface and is instead accumulated on the surface of the fruit, which can accelerate spoilage. If the film's water vapor permeability is too high, the weight loss rate may be too high, leading to internal water loss in the fruit. If the film's water vapor permeability is too low, the weight loss rate may be lower, but moisture may accumulate on the surface of the fruit, accelerating spoilage.

[0058] Ascorbic acid in red grapes: like Figure 5 As shown, the overall trend of ascorbic acid content is downward throughout the storage period. Some individual data differ from the overall trend due to individual differences. On the third day of storage, the ascorbic acid content of the PE-wrapped red grapes increased, as did that of Comparative Example 1 and Example 1 on the fifth day. This is likely because red grapes still retain some living properties after harvest and still produce some ascorbic acid, but the rate of production cannot keep up with the rate of consumption during subsequent storage. On the seventh day of storage, all components showed a downward trend, but the downward trend in Example 1 was slower than that in the PE and Comparative Example 1 films. The Example 1 film can slow the loss of ascorbic acid.

[0059] Titratable acidity of red grapes: like Figure 6As shown, the titratable acid content of all three storage methods showed a downward trend during storage. From the third to the fifth day of storage, the PE component, due to its better sealing properties, could not release the CO2 produced during respiration, which had the effect of reducing respiration. After the fifth day, microorganisms multiplied within the PE film, accelerating its decay and causing a rapid decrease in its acid content. On the seventh day of storage, compared with the PE group, the films of Comparative Example 1 and Example 1 were able to slow the downward trend of titratable acid, thereby effectively reducing titratable acid loss. Furthermore, Example 1 was more effective in reducing titratable acid loss than the film of Comparative Example 1. Overall, the film of Example 1 was able to slow the loss of titratable acid in fruit.

[0060] Soluble solids of red grapes: like Figure 7 As shown, on the first day of storage, the soluble solids content of the red grapes wrapped in Example 1 was relatively stable, while that of the red grapes wrapped in Comparative Example 1 and PE decreased. On the third day of storage, the soluble solids content of Example 1 remained relatively stable, but the soluble solids content of the PE and Comparative Example 1 decreased rapidly. On the fifth day of storage, the soluble solids content of all red grapes showed a downward trend, and on the seventh day of storage, it showed an upward trend. Overall, the overall soluble solids content showed a downward and then upward trend, and the film of Example 1 was able to reduce fluctuations in the soluble solids content. This trend may be due to the increase in soluble solids content caused by the reduction of ascorbic acid and individual differences.

[0061] In summary, the film produced by the present invention, based on the combination of chitosan and potato starch supplemented with a plasticizer, exhibits excellent tensile and moisture retention properties, effectively preventing spoilage of packaged food. Mugwort extract, with its excellent antibacterial and antioxidant properties, can be used as an antimicrobial agent to enhance the antimicrobial effect of plastic wrap, prevent microbial growth in food, reduce oxidative damage, and thus extend the shelf life of food.

[0062] The raw materials used in the present invention have a synergistic effect on each other and can improve various properties of the film. In addition, the chitosan, potato starch and mugwort extract used in the present invention are all extracted from nature and have the advantages of low cost, safety, reliability and good degradation performance.

[0063] The above describes in detail the preferred embodiments of the present invention. It should be understood that those skilled in the art can make numerous modifications and variations based on the concepts of the present invention without inventive effort. Therefore, any technical solutions that can be derived by those skilled in the art through logical analysis, reasoning, or limited experimentation based on the concepts of the present invention and the prior art should be within the scope of protection defined by the claims.

Claims

1. A method for preparing a degradable antibacterial cling film, characterized in that: The steps include: (1) dissolving chitosan in an acetic acid aqueous solution, adding the mugwort extract to the obtained chitosan solution, and stirring at a certain temperature to form a mixed solution; (2) Add potato starch to water to prepare a potato starch solution; The potato starch solution is gelatinized, and glycerol is added to the obtained gelatinized solution at a certain temperature and stirred to obtain a potato starch gelatinized liquid; (3) The mixed liquid and potato starch gelatinized liquid are mixed in a certain proportion, poured onto a polytetrafluoroethylene substrate, and dried to form a film to obtain a biodegradable antibacterial cling film.

2. The method for preparing the degradable antibacterial fresh-keeping film according to claim 1, wherein: In the step (1), the concentration of the acetic acid aqueous solution is 1 vol.% to 2 vol.%; the chitosan content of the chitosan solution is 1 wt.% to 2 wt.%; and the amount of the wormwood extract added is 1 wt.% of the chitosan solution.

3. The method for preparing the degradable antibacterial fresh-keeping film according to claim 1, wherein: In the step (1), the stirring temperature is 45-60°C, the stirring time is 30-45 min, and the stirring speed is 400 rpm.

4. The method for preparing the degradable antibacterial fresh-keeping film according to claim 1, wherein: In the step (2), the concentration of the potato starch solution is 4-6 wt.%.

5. The method for preparing the degradable antibacterial fresh-keeping film according to claim 1, wherein: In the step (2), gelatinization is carried out under stirring conditions, the gelatinization temperature is 60-80°C, the gelatinization time is 30-45 min, and the stirring speed is 400 rpm.

6. The method for preparing the degradable antibacterial fresh-keeping film according to claim 1, wherein: In the step (2), 25 wt.% propylene glycol is added to the obtained gelatinized solution at 35-50°C and stirred for 30-45 minutes at a stirring speed of 400 rpm.

7. The method for preparing the degradable antibacterial fresh-keeping film according to claim 1, wherein: In the step (3), the volume ratio of the mixed solution to the potato starch gelatinized solution is 2:3 to 3:

2.

8. The method for preparing the degradable antibacterial fresh-keeping film according to claim 1, wherein: In the step (3), the drying temperature is 65-75°C and the drying time is 3-5 hours.

9. A degradable antibacterial cling film, characterized by: The method is as described in any one of claims 1 to 8.

10. Use of the degradable antibacterial fresh-keeping film according to claim 9 in food preservation.

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