An antibacterial food packaging film containing propolis extract, a preparation method and application thereof

Abstract

This invention, entitled "Antibacterial Food Packaging Film Containing Propolis Extract, Preparation Method, and Application," belongs to the field of food packaging films. The technical problem to be solved is the poor mechanical properties, antibacterial properties, and antioxidant properties of the packaging film. The antibacterial food packaging film provided by this invention is made from the following raw materials: tamarind gum, pregelatinized starch, glycerin, and propolis extract. Xyloglucan in the tamarind gum is extracted by rapid high-temperature heating, and the propolis extract is integrated into the film-forming solution through simple blending. After drying, the film is obtained. The antibacterial food packaging film prepared by this invention solves the problem of poor mechanical properties in traditional tamarind gum-based packaging films and endows the packaging film with antibacterial and antioxidant functions, which can inhibit food spoilage and thus extend the shelf life of food.

Description

Technical Field

[0001] This invention belongs to the field of food packaging film, and specifically relates to an antibacterial food packaging film containing propolis extract, its preparation method, and its application. Background Technology

[0002] In the food industry, packaging is crucial for maintaining product quality, freshness, and safety. Plastic remains a primary material for food packaging, and while it does offer high resistance in the long run, it is also a cause of environmental hygiene problems because it is non-biodegradable. Food packaging is an important area of ​​food research because it plays a major role in protecting and sealing food. Traditionally, petroleum-derived polymers have met most packaging material requirements. Over the past few decades, consumers have become more aware of the environmental impact of plastics. Therefore, the demand for novel biodegradable packaging materials is critical in the food packaging industry, ensuring they possess sufficient strength, have a less environmental impact, and effectively extend the shelf life of food.

[0003] In recent years, with the rapid development of packaging technology, biodegradable packaging, as a member of green packaging materials, has significant environmental and economic value and is widely used, which will help control "white pollution." At the same time, consumers are increasingly concerned about the adverse effects of chemical preservatives. "Naturally sourced" antimicrobial and antioxidant agents include natural plant extracts, essential oils, alpha-tocopherol, ascorbic acid and citric acid, bee pollen, and propolis. These substances can be added alone or in combination to biodegradable films and coatings. Antioxidants and antimicrobial agents can be added to edible films / coatings to slow down the rate of oxidation, inhibit the growth and reproduction of microorganisms, improve food safety, and extend the shelf life of food.

[0004] Propolis is a colorful (green, red, yellow, and brown) resinous substance collected and processed by bees from the leaves, buds, stems, and bark crevices of many tree species (including poplar, alder, birch, and eucalyptus). It is then transported to the hive and mixed with beeswax to produce a highly adhesive substance. Also known as "purple gold," propolis-related products have become one of the mainstream products in the bee industry, with broad development prospects. Propolis is also widely used in the medical, food, daily chemical, and chemical industries. Propolis extract refers to the natural active substances extracted from propolis using solvents such as ethanol, glycerin, and water. Due to its rich bioactive components, propolis extract has great potential in extending the shelf life of food and improving the quality of various foods.

[0005] Relevant patent documents retrieved:

[0006] This document, published in China (CN120737443A) on October 3, 2025, discloses a ZIF-8 cellulose starch-based sustained-release membrane supported on propolis ethanol extract and its preparation method. The document specifies that the raw materials for the ZIF-8 cellulose starch-based sustained-release membrane supported on propolis ethanol extract include the following parts by weight: 30-70 parts starch, 30-70 parts cellulose nanofibers, 7.5-17.5 parts glycerol, and 4-8 parts filler, wherein the filler is ZIF-8 supported on propolis ethanol extract. This invention uses starch wastewater as the starch source and adds cellulose nanofibers supported on ZIF-8 by propolis ethanol extract. The resulting sustained-release membrane has high strength and good toughness, is biodegradable after use, reduces environmental pollution, ensures product safety, and also has antibacterial and antioxidant effects.

[0007] This document, published in China (CN116769198A) on September 19, 2023, discloses a method for preparing a bio-based active packaging film and the film itself. The method involves the following steps: S1, preparing a tamarind gum solution; S2, measuring a certain amount of tamarind gum gel and separating it into an α phase and a β phase in a ratio of (8-2):(2-8); S3, homogenizing the α phase tamarind gum gel with grapefruit essential oil using an ultra-high pressure cell disruptor to obtain an emulsion; S4, mixing the homogenized emulsion with the β phase tamarind gum gel to obtain a film-forming liquid; S5, measuring a certain amount of the film-forming liquid, pouring it into an acrylic plate, casting it evenly, allowing it to stand and dry, and then peeling off the film to obtain the bio-based active packaging film. This method yields a bio-based active packaging film with high film-forming performance and excellent active packaging mechanical properties, barrier properties, and antioxidant characteristics.

[0008] The prior art represented by the aforementioned documents has at least the following unresolved technical problems or defects: 1. Traditional packaging films, which use tamarind gum and starch as base materials, have problems such as low tensile strength, insufficient elongation at break, and fragility. Some solutions are even difficult to peel off smoothly, failing to meet the basic mechanical requirements of food packaging.

[0009] 2. The sustained-release membrane prepared by CN120737443A has difficulty in achieving both mechanical and barrier properties, and lacks balance. It presents a contradiction that "high mechanical strength results in poor barrier properties, while excellent barrier properties result in insufficient toughness," and cannot simultaneously meet the dual requirements of food packaging for mechanical support and impermeability. 3. CN116769198A states that the process for preparing bio-based active packaging films is relatively complex, requires advanced equipment, is costly, and has poor antioxidant and antibacterial capabilities. The relevant evidence is as follows: electron micrographs show irregular aggregates on the surface of the films prepared in Examples 1-4, and optical microscopy shows that the particle size distribution of the film-forming liquid is relatively dispersed. Uneven dispersion of functional components leads to a decrease in antioxidant activity.

[0010] In solving the above problems or overcoming the above defects, the present invention encountered the following difficulties and obstacles: Firstly, there's the issue of dissolving and dispersing propolis. Propolis is almost insoluble in aqueous solutions. To ensure uniform dispersion of the propolis-ethanol solution in the film matrix solution, the concentration and volume of the propolis-ethanol solution must be adjusted. If the volume is too small, large clumps of propolis extract will aggregate. If the volume is too large, large molecular chains such as starch and xylan will precipitate out, forming flocculent matter and affecting the uniformity of the film. Secondly, the phenolic substances in propolis are easily deactivated at high temperatures, so the temperature must be controlled below 60℃ after adding propolis. Summary of the Invention

[0011] The purpose of this invention is to provide: An antibacterial food packaging film containing propolis extract, its preparation method and application, and related technologies, to solve technical problems such as poor mechanical properties, antibacterial properties, and antioxidant properties of packaging films, or combinations thereof.

[0012] Terminology Explanation: Unless otherwise defined, all technical terms in this document have the same meanings as commonly understood by one of ordinary skill in the art to which the subject matter of the claims pertains. Unless otherwise stated, all patents, patent inventions, and publications cited in this document are incorporated herein by reference in their entirety. If multiple definitions exist for terms in this document, the definitions in this chapter shall prevail.

[0013] It should be understood that the above brief description and the following detailed description are exemplary and for illustrative purposes only, and do not limit the subject matter of the invention in any way. In this invention, the singular is used in conjunction with the plural unless otherwise specifically stated. It should also be noted that, unless otherwise stated, the use of “or” or “or” means “and / or”. Furthermore, the use of the term “comprising” and other forms such as “including,” “containing,” and “contains” are not limiting.

[0014] The definitions of standard terms can be found in the references “Food Analysis, China Light Industry Press, Wang Yonghua and Qi Suijian, 4th Edition; Food Chemistry, China Agricultural University Press, Kan Jianquan, 4th Edition; Biomedical Polymer Materials (Volume 1), Science Press, Ding Jiandong; Biomedical Polymer Materials (Volume 2), Science Press, Ding Jiandong”.

[0015] Unless specifically defined herein, the use of all commercially available products herein employs standard techniques. For example, it may be carried out using the manufacturer's instructions for use with the kit, or in accordance with methods known in the art or the description of this invention. The techniques and methods described herein can generally be implemented according to conventional methods well known in the art, based on the descriptions in the various summary and more specific documents cited and discussed in this specification.

[0016] The terms “optional / arbitrary” or “optionally / arbitrarily” mean that the event or situation described below may or may not occur, including both the occurrence and non-occurrence of the event or situation.

[0017] The term "xyglucan" used in this article refers to a hemicellulose polysaccharide widely found in plant cell walls. Its main chain consists of D-glucose residues linked by β-1,4-glycosidic bonds, and its side chains are mainly linked by α-1,6-glycosidic bonds to D-xylose residues. Some xylose residues can also be further linked to glycosyl groups such as arabinose and galactose. It has thickening, gelling, and adhesive properties and is often used as a functional component in biomaterials to regulate the structure and properties of materials.

[0018] The term "biocompatibility" as used in this article refers to the characteristics of the material described in this invention when it comes into contact with or interacts with biological organisms (including cells, tissues, organs, and body fluids), exhibiting no significant toxicity, no severe inflammatory response, no immune rejection response, and no disruption of the body's normal physiological functions. Its core evaluation dimensions include cell compatibility, tissue compatibility, and blood compatibility, which are the core prerequisites for the clinical application of biomedical materials.

[0019] The term "degradability" as used in this article refers to the characteristic that the material described in this invention can be gradually decomposed into small molecules in the natural environment through chemical hydrolysis, enzymatic hydrolysis, microbial metabolism, etc., and ultimately be integrated into the environment without leaving any residue; its degradation rate and the safety of degradation products are key evaluation indicators for degradable materials.

[0020] The term "deionized water" as used in this article refers to water in which almost all ions (cations such as Ca2+) have been removed through ion exchange resins. 2+ Mg 2+ Anions such as SO4 2- Cl - Water with extremely low ion content is commonly used in laboratory analysis (such as HPLC, ICP-MS), electronic industry cleaning, and cosmetic formulation.

[0021] The term "mixing" as used in this article refers to the process of combining two or more different substances (which may be solid, liquid, gas, or a combination of different states) through physical or mechanical means to form a macroscopically homogeneous or relatively homogeneous dispersion system.

[0022] The term "stirring" as used in this article refers to the operation of mixing multiple substances evenly by means of machinery or manual agitation. Specifically, it refers to the process of creating flow in a container with the help of external forces (such as rotating blades, stirring rods, airflow, etc.) to achieve uniform mixing of solids, liquids, or gases.

[0023] As used in this article, the term “selected from” means: one or more elements from the groups listed below, selected independently, and may include combinations of two or more elements.

[0024] In a first aspect, the present invention provides an antibacterial food packaging film containing propolis extract, comprising the following raw materials: propolis extract, tamarind gum, pregelatinized starch and glycerin, wherein the mass ratio of tamarind gum, pregelatinized starch and glycerin is 5-10:1-5:3-8.

[0025] Preferably, the mass ratio of tamarind gum, pregelatinized starch and glycerin is selected from any value or range between 5-10:1-5:3-8, specifically from: 5:5:3, 5:5:6, 7:3:6, 7:3:8, 10:1:5, 10:1:7, 9:1:4, 9:1:6, 10:5:8 or a range between the two.

[0026] More preferably, the mass ratio of tamarind gum, pregelatinized starch and glycerin is selected from any value or range between 5-9:1-5:3-8.

[0027] More preferably, the mass ratio of tamarind gum, pregelatinized starch and glycerin is 9:1:4.

[0028] Based on further solutions to the technical problems of the present invention, or simultaneous solutions to multiple technical problems, the preferred solution in the technical solution provided in the first aspect of the present invention includes: The first preferred solution is an antibacterial food packaging film containing propolis extract. This solution not only addresses the technical problem of "poor antibacterial and antioxidant properties of food packaging films," but also further solves the technical problem of "poor biocompatibility and biodegradability of food packaging films."

[0029] Secondly, the present invention provides a method for preparing the above-mentioned antibacterial food packaging film, comprising the following steps: S1. Dissolve tamarind gum, pregelatinized starch and glycerin in water, heat and stir, then cool to obtain a film-forming solution; S2. Dissolve propolis extract in ethanol to obtain propolis-ethanol solution, then add it to the film-forming solution prepared in step S1 and mix well to obtain composite film-forming solution. S3. After ultrasonication of the film-forming liquid from step S2, pour it into a mold, dry it, and then demold it to obtain the final product.

[0030] Preferably, the mass percentage of tamarind gum in the film-forming solution in step S1 is selected from any value or range between 0.8% and 2%, specifically from: 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, or a range between the two.

[0031] More preferably, the mass percentage of tamarind gum in the film-forming solution described in step S1 is selected from any value or range between 0.8% and 1.6%.

[0032] More preferably, the mass percentage of tamarind gum in the film-forming solution described in step S1 is any value or range between 1.5% and 1.6%.

[0033] Preferably, the water in step S1 is deionized water.

[0034] Preferably, the stirring temperature in step S1 is selected from any value or range between 80-100°C.

[0035] More preferably, the stirring temperature in step S1 is selected from any value or range between 90-100℃, specifically from 90℃, 95℃, 100℃ or a range between the two.

[0036] More preferably, the stirring temperature in step S1 is 90°C.

[0037] Preferably, the stirring time in step S1 is selected from any value or range between 10 and 20 min, specifically from: 10 min, 11 min, 12 min, 13 min, 14 min, 15 min, 16 min, 17 min, 18 min, 19 min, 20 min or a range between the two.

[0038] More preferably, the stirring time in step S1 is selected from any value or range between 15 and 20 minutes.

[0039] More preferably, the stirring time in step S1 is 15 minutes.

[0040] Preferably, the cooling temperature in step S1 is selected from any value or range between 40-50°C, specifically from: 40°C, 41°C, 42°C, 43°C, 44°C, 45°C, 46°C, 47°C, 48°C, 49°C, 50°C or a range between the two.

[0041] More preferably, the cooling temperature in step S1 is selected from any value or range between 45-50°C.

[0042] More preferably, the cooling temperature in step S1 is 50°C.

[0043] Preferably, the ethanol mentioned in step S2 is anhydrous ethanol.

[0044] Preferably, the concentration of propolis extract in the propolis-ethanol solution in step S2 is selected from any value or range between 0.01 and 0.03 g / mL, specifically from: 0.01 g / mL, 0.015 g / mL, 0.02 g / mL, 0.025 g / mL, 0.03 g / mL or a range between the two.

[0045] More preferably, the concentration of propolis extract in the propolis-ethanol solution described in step S2 is selected from any value or range between 0.02 and 0.03 g / mL.

[0046] More preferably, the concentration of propolis extract in the propolis-ethanol solution in step S2 is 0.03 g / mL.

[0047] Preferably, the volume ratio of the propolis-ethanol solution to the film-forming solution in step S2 is selected from any value or range between 1:5 and 15, specifically from: 1:5, 1:7, 1:9, 1:11, 1:13, 1:15 or a range between the two.

[0048] More preferably, the volume ratio of the propolis-ethanol solution to the film-forming solution in step S2 is selected from any value or range between 1:11 and 15.

[0049] More preferably, the volume ratio of the propolis-ethanol solution to the film-forming solution in step S2 is 1:11.

[0050] Preferably, the specific operation of the ultrasound in step S3 is as follows: the ultrasound power is used to remove air bubbles for 30 minutes.

[0051] Preferably, the mold described in step S3 is a disposable plastic petri dish with an inner diameter of 90 cm.

[0052] Preferably, the amount of molding in step S3 is 15 mL.

[0053] Preferably, the specific demolding operation in step S3 is as follows: after drying in a 45°C oven for 12 hours, remove the film, place it in an environment with a temperature of 25°C and a relative humidity of 70-75% for 24 hours to equilibrate, and then store it in a refrigerator at 4°C for later use.

[0054] Based on further solutions to the technical problems of the present invention, or simultaneous solutions to multiple technical problems, the preferred solution in the technical solution provided in the first aspect of the present invention includes: The first preferred solution is a method for preparing an antibacterial food packaging film containing propolis extract. This solution, in addition to addressing the technical problems of "poor antibacterial properties, poor antioxidant properties, poor biocompatibility and degradability of food packaging films," further solves the technical problem of "poor mechanical properties of food packaging films."

[0055] Thirdly, the present invention provides the application of the above-described antibacterial food packaging film or the antibacterial food packaging film prepared by the above-described preparation method in the preparation of food packaging.

[0056] Examples 1-3 of this invention at least support the protection scope of the ratio of propolis extract, tamarind gum, pregelatinized starch and glycerin as defined in claim 2.

[0057] Regarding the proportions of propolis extract, tamarind gum, pregelatinized starch, and glycerin involved in claim 2. The technical feature “the mass ratio of tamarind gum, pregelatinized starch and glycerin is 5-9:1-5:4-8” is summarized from the corresponding technical features in the foregoing explanation and / or Examples 1-3, such as the mass ratio of tamarind gum, pregelatinized starch and glycerin being 5:5:6, 9:1:4, 7:3:8, etc., which are derived from the common feature “the ratio of propolis extract, tamarind gum, pregelatinized starch and glycerin”. Therefore, those skilled in the art can reasonably infer that the technical feature “the mass ratio of tamarind gum, pregelatinized starch and glycerol is 5-9:1-5:4-8”, the subordinate concept and its essentially equivalent technical means, and the technical means that can replace “the mass ratio of tamarind gum, pregelatinized starch and glycerol is 5-9:1-5:4-8” based on existing technology and conventional technical means and common knowledge should all fall within the protection scope of claim 2. For example, if “the mass ratio of tamarind gum, pregelatinized starch and glycerol is 5-9:1-5:4-8” is replaced with a mass ratio of tamarind gum, pregelatinized starch and glycerol of 5.5:1.5:3, etc., while other technical features remain unchanged, it still falls within the protection scope of claim 2 of this invention.

[0058] Examples 1-3 of this invention at least support the protection scope of the mass percentage of tamarind gum as defined in claim 4.

[0059] Regarding claim 4: the mass percentage of tamarind gum The technical feature "tamarind gum mass percentage is 0.8-1.6%" is derived from the common feature "tamarind gum mass percentage" by summarizing the corresponding technical features of tamarind gum mass percentage of 0.8%, 1.2%, and 1.6% in the foregoing explanation and / or Examples 1-3. Therefore, those skilled in the art can reasonably infer that the technical feature "tamarind gum mass percentage is 0.8-1.6%", its subordinate concepts and their substantially equivalent technical means, and technical means that can replace "tamarind gum mass percentage is 0.8-1.6%" based on existing technology and conventional technical means and common knowledge, should all fall within the protection scope of claim 4. For example, replacing "tamarind gum mass percentage is 0.8-1.6%" with tamarind gum mass percentage of 0.9% while keeping other technical features unchanged still falls within the protection scope of claim 4 of this invention.

[0060] Examples 1-3 of this invention at least support the protection range of the concentration of propolis extract in the propolis-ethanol solution as defined in claim 6.

[0061] Regarding claim 6: the concentration of propolis extract in the propolis-ethanol solution The technical feature “the concentration of propolis extract in the propolis-ethanol solution is 0.01-0.03 g / mL” is summarized from the common feature “the concentration of propolis extract in the propolis-ethanol solution”, which is 0.01 g / mL, 0.02 g / mL, 0.03 g / mL, etc., as explained above and / or in Examples 1-3. Therefore, those skilled in the art can reasonably presume that the technical feature "the concentration of propolis extract in the propolis-ethanol solution is 0.01-0.03 g / mL", the subordinate concept and its essentially equivalent technical means, and the technical means that can replace "the concentration of propolis extract in the propolis-ethanol solution is 0.01-0.03 g / mL" based on the existing technical level and conventional technical means and common knowledge, should all fall within the protection scope of claim 6. For example, if other technical features remain unchanged, replacing "the concentration of propolis extract in the propolis-ethanol solution is 0.016 g / mL" with the concentration of propolis extract in the propolis-ethanol solution is 0.016 g / mL, it still falls within the protection scope of claim 6 of this invention.

[0062] Examples 1-3 of this invention at least support the protection scope of the volume ratio of propolis-ethanol solution to film-forming solution as defined in claim 8.

[0063] Regarding the volume ratio of propolis-ethanol solution to film-forming solution involved in claim 8... The technical feature "the volume ratio of propolis-ethanol solution to film-forming solution is 1:5-15" is derived from the aforementioned explanation and / or the corresponding technical features in Examples 1-3, such as the volume ratio of propolis-ethanol solution to film-forming solution being 1:5, 1:11, 1:15, etc., summarized from the common feature "the volume ratio relationship between propolis-ethanol solution and film-forming solution". Therefore, those skilled in the art can reasonably infer that the technical feature "the volume ratio of propolis-ethanol solution to film-forming solution is 1:5-15", its subordinate concepts and their essentially equivalent technical means, and technical means that can replace "the volume ratio of propolis-ethanol solution to film-forming solution is 1:5-15" based on existing technology and conventional technical means and common knowledge, should all fall within the protection scope of claim 8. For example, replacing "the volume ratio of propolis-ethanol solution to film-forming solution is 1:5-15" with a volume ratio of propolis-ethanol solution to film-forming solution of 1:13, etc., while keeping other technical features unchanged, still falls within the protection scope of claim 8 of this invention.

[0064] The beneficial effects of this invention are as follows: The present invention has at least the following beneficial effects: 1. This invention uses tamarind gum and pregelatinized starch as film matrix materials, which can quickly prepare film-forming liquid and uniformly disperse propolis extract in it. The resulting propolis composite food packaging film has excellent mechanical properties, antioxidant properties, antibacterial properties and biosafety, and can be naturally degraded after use, reducing pollution.

[0065] 2. This invention overcomes the difficulty of extracting tamarind gum, retains tamarind kernel residue, and obtains food packaging films with excellent mechanical properties while reducing preparation costs, providing a more economical and efficient method for their industrial production and application. Attached Figure Description

[0066] Figure 1 Soil degradation performance of antibacterial food packaging films containing propolis extract prepared in Examples 1-3.

[0067] Figure 2 The preservation properties of antibacterial food packaging films containing propolis extract prepared in Examples 1-3 on grapes. Detailed Implementation

[0068] The following non-limiting embodiments are intended to enable those skilled in the art to gain a more comprehensive understanding of the present invention, but do not limit the invention in any way. The following content is merely an exemplary description of the scope of protection claimed by the present invention, and those skilled in the art can make various changes and modifications to the present invention based on the disclosed content, and such changes should also fall within the scope of protection claimed by the present invention.

[0069] The present invention will be further described below by way of specific embodiments. Unless otherwise specified, all instruments, devices, equipment, reagents, products, etc., used in the embodiments of the present invention are obtained through conventional commercial means.

[0070] Table 1. Reagent manufacturers and their models

[0071] Example 1: Preparation of an antibacterial food packaging film containing propolis extract The preparation method includes the following steps: S1. Dissolve 0.7g tamarind gum, 0.3g pregelatinized starch and 0.8g glycerol in 55mL of water. Heat at 90℃ for 15min, stir at room temperature and cool to 50℃ to obtain a film-forming solution. S2. Dissolve 0.05g of propolis extract in 5mL of anhydrous ethanol to obtain a propolis-ethanol solution, and then slowly add it dropwise to 25mL of film-forming solution and mix well (the volume ratio of propolis-ethanol solution to film-forming solution is 1:5) to obtain a composite film-forming solution. S3. After sonicating the composite film-forming solution prepared in step S2 for 30 minutes to remove air bubbles, pour it into a disposable plastic petri dish with an inner diameter of 9 cm. Dry it in an oven at 45℃ for 12 hours, then peel off the film. Place it in an environment with a temperature of 25℃ and a relative humidity of 70-75% for 24 hours to equilibrate. Store it in a refrigerator at 4℃ for later use.

[0072] Example 2: Preparation of an antibacterial food packaging film containing propolis extract The preparation method includes the following steps: S1. Dissolve 0.5g tamarind gum, 0.5g pregelatinized starch and 0.6g glycerol in 55mL of water. Heat at 90℃ for 15min, stir at room temperature and cool to 50℃ to obtain a film-forming solution. S2. Dissolve 0.1g of propolis extract in 5mL of anhydrous ethanol to obtain a propolis-ethanol solution. Take 3.6mL of the propolis-ethanol solution and slowly add it dropwise to 54mL of film-forming solution and mix well (the volume ratio of propolis-ethanol solution to film-forming solution is 1:15) to obtain a composite film-forming solution. S3. After sonicating the composite film-forming solution prepared in step S2 for 30 minutes to remove air bubbles, pour it into a disposable plastic petri dish with an inner diameter of 9 cm. Dry it in an oven at 45℃ for 12 hours, then peel off the film. Place it in an environment with a temperature of 25℃ and a relative humidity of 70-75% for 24 hours to equilibrate. Store it in a refrigerator at 4℃ for later use.

[0073] Example 3: Preparation of an antibacterial food packaging film containing propolis extract The preparation method includes the following steps: S1. Dissolve 0.9g tamarind gum, 0.1g pregelatinized starch and 0.4g glycerol in 55mL of water. Heat at 90℃ for 15min, stir at room temperature and cool to 50℃ to obtain a film-forming solution. S2. Dissolve 0.15g of propolis extract in 5mL of anhydrous ethanol to obtain a propolis-ethanol solution, and then slowly add it dropwise to 55mL of film-forming solution and mix well (the volume ratio of propolis-ethanol solution to film-forming solution is 1:11) to obtain a composite film-forming solution. S3. After sonicating the composite film-forming solution prepared in step S2 for 30 minutes to remove air bubbles, pour it into a disposable plastic petri dish with an inner diameter of 9 cm. Dry it in an oven at 45℃ for 12 hours, then peel off the film. Place it in an environment with a temperature of 25℃ and a relative humidity of 70-75% for 24 hours to equilibrate. Store it in a refrigerator at 4℃ for later use.

[0074] Comparative Example 1 The raw materials for preparation, by weight, include: 50 parts starch, 50 parts cellulose nanofibers, 12.5 parts glycerol, and 6 parts filler, wherein the filler is ZIF-8 supported on propolis ethanol extract; The preparation method of the sustained-release membrane specifically includes the following steps: S1. At room temperature, the upper layer of impurities is removed by air flotation separation at a speed of 8000 rpm. The lower layer of solid is washed with deionized water. After each washing, the brown layer of the slurry is removed. Then, the slurry is dried in an oven at 40°C for 24 hours to obtain starch.

[0075] S2. Disperse 50 parts starch and 12.5 parts glycerol in distilled water, and stir continuously at 90°C for 20 minutes to gelatinize, thus obtaining starch gelatinized slurry.

[0076] S3. Bamboo fiber was placed in a 6% sodium hydroxide solution and heated to 70°C for alkali treatment for 3 hours. Then, 5g of the alkali-treated bamboo fiber was placed in a mixture of 50mL of 10% acetic acid aqueous solution and 50mL of 3.5% sodium chlorite aqueous solution (pH 4) and heated in a 70°C water bath for 3 hours for bleaching. It was then washed with deionized water until neutral and dried in a 50°C oven for 24 hours to obtain pretreated bamboo fiber. The pretreated bamboo fiber and the hydrated polycarboxylic acid deep eutectic solvent were mixed at a mass-to-volume ratio of 1:20. A uniform, transparent H-DES liquid (a mixture of citric acid, choline chloride, and water in a mass ratio of 3:1:1) was added to the pretreated bamboo fiber. The mixture was heated at 110°C for 2 hours and then centrifuged at 8000 rpm to obtain modified bamboo fiber. The modified bamboo fiber was filtered out, washed with deionized water, and then soaked in deionized water with a mass fraction of 1%. Cellulose nanofibers were obtained by ultrasonic nanofiberization at a frequency of 20 kHz and a power of 800 W for 30 minutes.

[0077] S4. Dissolve 0.6g Zn(NO3)2·6H2O and 0.3g 2-methylimidazole in 20mL methanol to obtain a mixed solution; dissolve 0.7g propolis ethanol extract in 20mL ethanol to obtain a propolis ethanol extract ethanol solution; then rapidly stir and mix the obtained mixed solution and the propolis ethanol extract ethanol solution at room temperature for 48h to prepare an orange-yellow suspension. Wash three times with methanol and once with deionized water, and dry in an oven at 50℃ for 20h. Add 3.0g of the dried propolis ethanol extract ZIF-8 powder to 20mL ethanol to prepare a propolis ethanol extract-ZIF-8 ethanol dispersion.

[0078] S5. Mix 50 parts of starch gelatinized slurry with 50 parts of cellulose nanofibers and stir to obtain a slow-release membrane solution.

[0079] S6. Add 6 parts of the prepared propolis ethanol extract-ZIF-8 ethanol dispersion to the sustained-release membrane solution.

[0080] S7. Degas the membrane solution under a vacuum of 0.09 MPa for 20 minutes to remove air bubbles from the membrane solution.

[0081] S8. Feed the mixed materials into an extruder and extrude them into shape through a die. Place the prepared slow-release film at room temperature with a relative humidity of 55% for 36 hours to allow the slow-release film to fully absorb moisture and plasticize. Then pack it into a sample bag for storage.

[0082] Comparative Example 2 The difference from Example 1 is that no propolis extract is added, but all other dosages and steps are the same as in Example 1.

[0083] Comparative Example 3 The difference from Example 1 is that the amounts of tamarind gum, pregelatinized starch and glycerin added are changed to 0.4g, 0.6g and 0.9g respectively, that is, the mass ratio of tamarind gum, pregelatinized starch and glycerin is changed to 4:6:9. All other dosage steps are the same as in Example 1.

[0084] Comparative Example 4 The difference from Example 1 is that the amounts of tamarind gum, pregelatinized starch and glycerin added are changed to 1.2g, 0.05g and 0.2g respectively, that is, the mass ratio of tamarind gum, pregelatinized starch and glycerin is changed to 12:0.5:2, and the other dosage steps are the same as in Example 1.

[0085] Comparative Example 5 The difference from Example 1 is that tamarind gum is replaced with xanthan gum, pregelatinized starch is replaced with corn starch, and propolis extract-ethanol solution is replaced with chitosan-water solution with a concentration of 0.01 g / mL. All other dosages and steps are the same as in Example 1.

[0086] Comparative Example 6 The difference from Example 1 lies in changing the concentration of propolis extract in the propolis-ethanol solution and the volume ratio of the propolis-ethanol solution to the film-forming solution, specifically: S2. Dissolve 0.25g of propolis extract in 5mL of anhydrous ethanol to obtain a propolis-ethanol solution. Then, slowly add 3.4375mL of the solution to 55mL of film-forming solution and mix well (the volume ratio of propolis-ethanol solution to film-forming solution is 1:16) to obtain a composite film-forming solution. The remaining dosage and steps are the same as in Example 1.

[0087] Comparative Example 7 The difference from Example 1 lies in changing the concentration of propolis extract in the propolis-ethanol solution and the volume ratio of the propolis-ethanol solution to the film-forming solution, specifically: S2. Dissolve 0.25g of propolis extract in 5mL of anhydrous ethanol to obtain a propolis-ethanol solution, and then slowly add it dropwise to 20mL of film-forming solution and mix well (the volume ratio of propolis-ethanol solution to film-forming solution is 1:4) to obtain a composite film-forming solution. The remaining dosage and steps are the same as in Example 1.

[0088] Example 1: Determination of the mechanical properties of food packaging film 1. Experimental Methods: Mechanical property testing The antibacterial food packaging films prepared in Examples 1-3 and Comparative Examples 1-7 were cut into strips 1 cm wide. Tensile strength and elongation at break were measured after fixing the samples using a tensile testing machine (CMT-1104, Sansitaijie). The experiment was repeated three times, and the average value was taken as the final result.

[0089] 2. Experimental Results Mechanical properties are one of the key performance characteristics of food packaging films. Good mechanical properties can protect the integrity of the food's surface and reduce mechanical damage during transportation and storage. Table 2 shows that the antibacterial food packaging films prepared in Examples 1-3, Comparative Examples 1-3, Comparative Examples 5, and Comparative Examples 7 all exhibit good uniformity. Active substances such as propolis are uniformly dispersed in the film matrix, and all films in each group have good mechanical properties. Among them, the antibacterial food packaging film prepared in Example 1 has the best tensile strength, significantly better than Comparative Example 1. Furthermore, the tensile strength at break of the antibacterial food packaging films prepared in Examples 1-3 is higher than that of Comparative Example 1. This indicates that the overall mechanical properties of the antibacterial food packaging films prepared in Examples 1-3 are more suitable for the application scenarios of food packaging films. Therefore, in subsequent testing, the antibacterial food packaging films prepared in Examples 1-3 and Comparative Examples 2-7 were tested.

[0090] Table 2. Test results of mechanical properties of food packaging film

[0091] Example 2: Determination of the mechanical properties of food packaging film 1. Experimental Methods: (1) Blood compatibility The antibacterial food packaging films prepared in Examples 1-3 and Comparative Examples 2-7 were cut into 0.5cm × 1.0cm pieces and incubated in 20mL PBS solution for 12h to obtain film extracts. Rat erythrocytes were washed with PBS solution and then used to prepare sample groups with the film extract and PBS solution. A positive control group was prepared with deionized water, and a negative control group was prepared with PBS solution. Each sample group was incubated at 37℃ for 3h and then centrifuged (3000rpm, 10min). The absorbance of the supernatant at 545nm was measured using a Spectramax 190 (Molecular Devices) and the hemolysis rate was calculated. The experiment was repeated three times.

[0092] (2) Cell compatibility 5 mg of the antibacterial food packaging films prepared in Examples 1-3 and Comparative Examples 2-7 were weighed and incubated in DMEM medium for 30 min to obtain an extract. L929 cells were cultured with the extract instead of the culture medium, and cell viability was assessed using a CCK-8 assay kit after 24 h. The experiment was repeated 3 times.

[0093] (3) Antibacterial properties Staphylococcus aureus (ATCC6538) and Escherichia coli (ATCC25922) were cultured to 10... 5 CFU / mL, add 0.2g of the antibacterial food packaging film prepared in Examples 1-3 and Comparative Examples 2-7 to 40mL of bacterial solution, incubate for 4h, then dilute the bacterial solution by 10. 5 After dilution, the cells were spread evenly on tryptic soy agar plates and incubated at 37°C for 15 hours. The number of colonies was recorded and the antibacterial rate was calculated. The experiment was repeated three times.

[0094] (4) Soil degradability The antibacterial food packaging films prepared in Examples 1-3 were cut into 2cm × 2cm pieces and buried 3cm deep in the soil. Water was sprayed on the soil surface daily. Every 6 days, the film was dug out, the surface soil was removed with a small brush, and photographs were taken for record-keeping. The experiment was repeated 3 times.

[0095] (5) Grape preservation level After cutting the grapes off their stems, they were washed with deionized water and air-dried. Grapes of similar size, with intact skin, and free from mold and pests were selected for subsequent experiments. The grapes were randomly grouped, wrapped in the antibacterial food packaging film prepared in Examples 1-3, and stored in separate polypropylene containers. The control group grapes were placed directly into the containers without any treatment. Grape morphology changes were recorded by photographing every two days at room temperature.

[0096] 2. Experimental Results Good antioxidant properties of food packaging films can reduce oxidative stress in food. Table 3 shows that the antioxidant properties of food packaging films are positively correlated with the amount of propolis. Bacterial contamination is one of the main causes of food spoilage. Excellent antibacterial properties can effectively extend the shelf life of food and improve food safety. As shown in Table 3, except for Comparative Examples 2 and 5 which do not contain propolis extract, the packaging films prepared in the other groups have excellent bactericidal properties against Gram-negative and Gram-positive bacteria. The food packaging films prepared in Examples 1-3 all have the function of extending the shelf life of grapes. Unpackaged grapes were contaminated with mold on day 6 and severely contaminated on day 10. However, the grape skins in Example 3 remained intact on day 10. Traditional plastic packaging films are prone to causing environmental pollution and "microplastic" problems. Tiny plastic fragments can cause a series of adverse reactions in the human body, including reproductive effects, intestinal damage, neurotoxicity, and immune health disorders. Therefore, the biosafety of food packaging films has received increasing attention in recent years. Table 3 shows that the hemolysis rate of the food packaging films prepared in Examples 1-3 and Comparative Examples 2-6 was less than 5%, and the cell survival rate was higher than 90%, indicating that they have good biosafety and pose no health risk even if ingested. Good degradability can reduce environmental pollution. Figure 1 It can be seen that the food packaging films prepared in Examples 1-3 can degrade rapidly in soil, with a degradation rate of approximately 80% by day 42. Rapid degradation reduces the environmental burden after the packaging films are discarded. Considering all the above properties, the food packaging film prepared in Example 3 exhibits the best overall performance, possessing excellent mechanical properties, antioxidant and antibacterial properties, and extending the shelf life of grapes. Furthermore, it places less burden on human health and the natural environment, and will not harm either.

[0097] Table 3. Results of antioxidant, cell compatibility, and blood compatibility tests on food packaging films.

[0098] Verification of technical effectiveness and / or analysis of solutions to technical problems: This invention uses tamarind gum, pregelatinized starch, and propolis extract as a base to prepare an antibacterial food packaging film. By adjusting the proportions of each component, a series of food packaging films are obtained. Tables 2 and 3 show that the food packaging films prepared in Examples 1-3 of this invention have good tensile strength and elongation at break, exhibiting excellent antibacterial properties and meeting the strength requirements for food packaging applications. The propolis extract imparts excellent antioxidant and antibacterial properties to the food packaging films. Although the food packaging films prepared in Comparative Examples 2-7 also contain propolis extract, their antibacterial properties, antioxidant properties, and uniformity are not as good as those of the packaging films prepared in Examples 1-3, which can achieve a balance of all these properties.

[0099] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, and is not intended to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions made by those skilled in the art to the technical solution of the present invention do not depart from the essence and scope of the technical solution of the present invention.

Claims

1. An antibacterial food packaging film containing a propolis extract, characterized by, It includes the following raw materials: propolis extract, tamarind gum, pregelatinized starch and glycerin, wherein the mass ratio of tamarind gum, pregelatinized starch and glycerin is 5-10:1-5:3-8.

2. The antibacterial food packaging film according to claim 1, characterized in that, The mass ratio of tamarind gum, pregelatinized starch and glycerol is 5-9:1-5:4-8; Preferably, the mass ratio of tamarind gum, pregelatinized starch and glycerol is 9:1:

4.

3. The method for preparing the antibacterial food packaging film according to any one of claims 1-2, characterized in that, Includes the following steps: S1. Dissolve tamarind gum, pregelatinized starch and glycerin in water, heat and stir, then cool to obtain a film-forming solution; S2. Dissolve propolis extract in ethanol to obtain propolis-ethanol solution, add it to the film-forming solution prepared in step S1 and mix well to obtain composite film-forming solution; S3. After ultrasonication of the composite film-forming liquid from step S2, pour it into a mold, dry it, and then demold it to obtain the final product.

4. The preparation method according to claim 3, characterized in that, The mass percentage of tamarind gum in the film-forming solution described in step S1 is 0.8-2%.

5. The preparation method according to claim 4, characterized in that, The mass percentage of tamarind gum in the film-forming solution described in step S1 is 0.8-1.6%.

6. The preparation method according to claim 3, characterized in that, The concentration of propolis extract in the propolis-ethanol solution described in step S2 is 0.01-0.03 g / mL.

7. The preparation method according to claim 6, characterized in that, The concentration of propolis extract in the propolis-ethanol solution described in step S2 is 0.03 g / mL.

8. The preparation method according to claim 3, characterized in that, The volume ratio of the propolis-ethanol solution to the film-forming solution in step S2 is 1:5-15.

9. The preparation method according to claim 8, characterized in that, The volume ratio of the propolis-ethanol solution to the film-forming solution in step S2 is 1:

11.

10. The application of the antibacterial food packaging film according to any one of claims 1-2 or the antibacterial food packaging film prepared by the preparation method according to any one of claims 3-9 in the preparation of food packaging.

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