Pectin-based nano antibacterial food preservative film and preparation method thereof

Abstract

The invention discloses a pectin-based nano bacteriostatic food preservative film and a preparation method thereof, and belongs to the field of food preservative films, the preservative film takes pectin as a film forming substrate, and is compounded with PA-Zn nanoparticles; the PA-Zn nano-particles are zinc-pyrogallic acid coordination polymer nano-particles which are generated by reacting zinc acetate dihydrate with pyrogallic acid under an alkaline hydrothermal condition. The preparation method comprises the following steps: hydro-thermally synthesizing PA-Zn nano-particles, blending the PA-Zn nano-particles with pectin, glycerol and calcium chloride to prepare a composite membrane solution, defoaming, casting, and drying to form the membrane. The composite preservative film has excellent antibacterial performance (especially for ESBL escherichia coli, MRSA and other drug-resistant bacteria), improved mechanical strength and barrier performance, good hydrophobicity and antioxidant activity, safety and biodegradability, and has wide application prospects in the field of fresh-keeping packaging of fruits, vegetables and other foods.

Description

Technical Field

[0001] This invention belongs to the field of food preservation film, specifically relating to a biodegradable pectin-based composite preservation film with antibacterial function and its preparation method. Background Technology

[0002] (I) Overview of Existing Technologies:

[0003] With increasing global concern about plastic pollution and food safety, the development of biodegradable food packaging materials with active preservation functions has become an important research direction. Natural polysaccharides (such as pectin, chitosan, and cellulose) are considered potential alternatives to traditional petroleum-based plastic films due to their excellent film-forming properties, biocompatibility, and biodegradability. Among them, pectin, as a widely available and inexpensive plant polysaccharide, shows promising application prospects in food packaging matrix materials. However, single-pectin-based films generally suffer from inherent defects such as insufficient mechanical strength and poor barrier properties (e.g., against water vapor and oxygen), limiting their practical application.

[0004] To improve the performance of pectin membranes and endow them with functional properties, existing technologies mainly achieve this by adding functional substances to the membrane matrix. A common approach is to add small-molecule antibacterial agents or essential oils, such as incorporating phenolic compounds like gallic acid and ferulic acid, or laurel leaf oil, into chitosan, carboxymethyl cellulose, or corn gluten composite membranes. These studies have confirmed that adding such substances can enhance the antioxidant and antibacterial activity of the membrane to some extent. However, these small-molecule active substances are prone to migration and are easily decomposed by light or heat, resulting in unstable antibacterial efficacy and poor durability; furthermore, high addition amounts may affect the mechanical integrity of the membrane or introduce odors.

[0005] Another approach is to utilize nanotechnology to introduce inorganic nanoparticles (such as iron(III) oxide and sulfur-containing nanoparticles) into polysaccharide matrices to enhance the mechanical properties and functionality of the film. Nanozymes, as a novel type of material combining the characteristics of nanomaterials and enzyme-like catalytic activity, have attracted attention in the field of antibacterial materials in recent years due to their ability to achieve highly efficient antibacterial activity by catalyzing the generation of highly reactive oxygen species (ROS). Existing research has demonstrated the potential of combining some nanozymes with substrates such as chitosan to enhance antibacterial effects.

[0006] (II) Analysis of the prior art related to this invention:

[0007] Through retrieval and analysis, the existing technologies most closely related to this invention mainly include:

[0008] Polysaccharide membranes modified with small-molecule phenolic acids: For example, some studies have introduced phenolic acids such as gallic acid into chitosan membranes through physical blending or chemical grafting. Although these methods improve the antioxidant properties of the membrane, gallic acid itself is prone to photodegradation, resulting in insufficient long-term stability of its antibacterial activity. Furthermore, the chemical grafting process is complex and may involve toxic cross-linking agents.

[0009] Edible films modified with essential oils or natural extracts: For example, adding bay leaf oil to carboxymethyl cellulose films or orange oil to pectin films to impart antibacterial properties. The main problem with this approach is that the volatility of essential oils leads to a rapid decline in antibacterial properties and can significantly alter the odor and optical properties of the film.

[0010] Polysaccharide membranes based on inorganic nanoparticle / nanozyme composites: Existing technologies have included research on combining iron oxide nanoparticles with chitosan-pectin composite membranes. However, the interfacial compatibility, dispersion uniformity, and long-term safety of these nanoparticles with the polysaccharide matrix in food contact materials still require further evaluation.

[0011] (III) Problems and shortcomings of existing technologies:

[0012] Based on existing technologies, the main shortcomings in developing high-performance pectin-based antibacterial food preservation films are as follows:

[0013] The contradiction between function and stability: The activity of directly added natural antibacterial agents (such as gallic acid) or essential oils is easily affected by environmental factors (light, heat, migration), making it difficult to provide long-lasting and stable antibacterial protection during the shelf life of food.

[0014] Balancing performance and safety: While some synthetic antibacterial agents or nanomaterials are highly effective, they may raise concerns about biosafety or pose environmental risks, which contradicts the original intention of developing green and biodegradable packaging.

[0015] Challenges in synergistic improvement of multiple properties: Existing technical solutions often struggle to simultaneously and effectively address multiple issues in pure pectin films, such as weak mechanical and barrier properties, and unstable and unsustainable antibacterial properties. Many composite films may sacrifice other properties (such as mechanical strength, transparency) or ease of processing when enhancing one property (such as antibacterial properties).

[0016] There is a lack of research on the antibacterial efficacy against specific drug-resistant bacteria: existing studies have focused on the inhibition of common model bacteria (such as Escherichia coli and Staphylococcus aureus), while the inhibitory effects and mechanisms against increasingly serious foodborne drug-resistant pathogens (such as ESBL-producing Escherichia coli and methicillin-resistant Staphylococcus aureus) have been explored in a limited way.

[0017] Therefore, there is an urgent need to develop a new type of pectin-based composite film that can not only fundamentally improve the mechanical and barrier properties of the base film, but also achieve broad-spectrum and long-lasting inhibition of a variety of foodborne pathogens (including drug-resistant bacteria) by introducing a highly efficient, stable and safe antibacterial component, while maintaining excellent biodegradability, so as to meet the needs of the modern food industry for safe, green and intelligent packaging. Summary of the Invention

[0018] In view of the problems existing in the above-mentioned background technology, especially the shortcomings of existing pectin-based antibacterial films in terms of long-term stability, multi-performance synergistic improvement and safety, the present invention aims to provide a brand-new solution.

[0019] The purpose of this invention is to prepare a pectin-based nano-antibacterial food preservation film with excellent comprehensive performance by combining a novel PA-Zn nanoparticle, synthesized from zinc acetate dihydrate and pyrogallol via a hydrothermal method, with a pectin matrix. This composite film not only significantly enhances the mechanical strength and barrier properties (water vapor, oxygen) of the base pectin film, but more importantly, it utilizes the unique and stable enzyme-like catalytic antibacterial mechanism of PA-Zn nanoparticles to achieve highly efficient and long-lasting inhibition of common and drug-resistant foodborne pathogens, including ESBL-producing Escherichia coli and methicillin-resistant Staphylococcus aureus (MRSA).

[0020] A further objective of this invention is to provide a method for preparing the aforementioned food preservation film, which is simple, operates under mild conditions, and is easily scalable for mass production. Through a systematic study of the effects of the amount of PA-Zn nanoparticles added on the composite film structure, physical properties, antibacterial activity, antioxidant properties, and biodegradability, this invention provides important technical basis and innovative ideas for developing next-generation green, safe, and intelligent functional food packaging materials.

[0021] To achieve the above objectives, the present invention adopts the following technical solution:

[0022] A pectin-based nano-antibacterial food preservation film, wherein the film uses pectin as the film-forming matrix and is composited with PA-Zn nanoparticles; the PA-Zn nanoparticles are zinc-pyrogallic acid coordination polymer nanoparticles generated by reacting zinc acetate dihydrate and pyrogallic acid as precursors under alkaline hydrothermal conditions.

[0023] Furthermore, in the above-mentioned pectin-based nano-antibacterial food preservation film, the PA-Zn nanoparticles account for 1% to 7% of the mass percentage of the preservation film.

[0024] Furthermore, the above-mentioned pectin-based nano-antibacterial food preservation film also includes a plasticizer and a crosslinking agent; the plasticizer is glycerin, and the crosslinking agent is calcium chloride.

[0025] Furthermore, the above-mentioned pectin-based nano-antibacterial food preservation film, based on the weight percentage of the preservation film forming liquid, contains the following components: 1% pectin, 0.9% glycerol, 0.72% calcium chloride, with the remainder being water, and PA-Zn nanoparticles accounting for 1%-7% of the pectin mass percentage.

[0026] This invention also discloses a method for preparing the above-mentioned food preservation film, comprising the following steps:

[0027] S1. Preparation of PA-Zn nanoparticles: Zinc acetate dihydrate and pyrogallic acid were dissolved together in water. The pH of the mixed solution was adjusted to 8.0-9.0 with alkali solution under stirring. Then, a hydrothermal reaction was carried out to generate zinc-pyrogallic acid coordination polymer nanoparticles. After the reaction was completed, the nanoparticles were centrifuged, washed and dried to obtain PA-Zn nanoparticle powder.

[0028] S2. Preparation of composite membrane solution: Dissolve pectin and glycerol in water, stir to dissolve, add calcium chloride solution, then add PA-Zn nanoparticle powder obtained in step S1, stir evenly to obtain composite membrane solution;

[0029] S3. Film formation: After degassing and defoaming, the composite film liquid is cast into a mold, dried, and then peeled off to obtain the pectin-based nano antibacterial food preservation film.

[0030] Furthermore, in the above preparation method, in step S1, the molar ratio of zinc acetate dihydrate to pyrogallol is 1:(1-1.2); the hydrothermal reaction temperature is 110-130℃, and the reaction time is 10-14 hours.

[0031] Furthermore, in the above preparation method, in step S2, the amount of PA-Zn nanoparticle powder added is such that its mass percentage in the final composite film liquid solid component is 1% to 7%.

[0032] Furthermore, in the above preparation method, in step S3, the degassing is performed by centrifugal degassing, the defoaming is performed by ultrasonic treatment, and the drying temperature is 55-65℃.

[0033] The present invention also discloses the application of the above-mentioned food preservation film in food packaging, for inhibiting foodborne pathogens and / or extending the shelf life of food; the foodborne pathogens include at least one of extended-spectrum β-lactamase-producing Escherichia coli and methicillin-resistant Staphylococcus aureus.

[0034] The present invention also discloses a food packaging article, comprising food and a food preservation film as described in any one of claims 1-4, which wraps the food.

[0035] Compared with the prior art, the beneficial effects of this invention are:

[0036] 1. Highly efficient and stable antibacterial properties: The PA-Zn nanoparticles prepared by this invention have stable peroxidase-like activity and can continuously catalyze the production of highly reactive oxygen species under light conditions. They exhibit strong inhibitory effects on a variety of foodborne pathogens, including ESBL-producing Escherichia coli and methicillin-resistant Staphylococcus aureus, and the antibacterial effect is not easily reduced by light or migration.

[0037] 2. Significantly improved overall performance: The addition of an appropriate amount of PA-Zn nanoparticles (e.g., 1%) can serve as a reinforcing phase to improve the mechanical properties (tensile strength and elongation at break are both improved) and barrier properties (reducing water vapor and oxygen permeability) of the pectin film.

[0038] 3. Imparting hydrophobicity and antioxidant properties: The introduction of PA-Zn nanoparticles significantly improves the hydrophobicity of the film surface (the water contact angle can reach up to about 102°), which helps to reduce the impact of moisture on food; at the same time, the composite film exhibits good antioxidant activity.

[0039] 4. Green, environmentally friendly, and highly safe: All raw materials (pectin, glycerol, calcium chloride, pyrogallol, zinc acetate dihydrate) are food-grade or recognized safe substances, and the preparation process requires no toxic solvents. The film can be rapidly biodegraded in soil, making it environmentally friendly.

[0040] 5. Simple and controllable preparation process: The preparation method is simple and the conditions are mild. The hydrothermal synthesis of PA-Zn particles and the subsequent casting film formation process are easy to operate and can be scaled up. Attached Figure Description

[0041] Figure 1 A schematic diagram illustrating the preparation of a pectin-based nano-antibacterial food preservation film;

[0042] Figure 2 For PA-Zn doped pectin composite membranes, (a) thickness; (b) water solubility and water content; (c) oxygen permeability; (d) water vapor permeability;

[0043] Figure 3 (a) Physical appearance of PA-Zn doped pectin composite membranes; (bf) Color characteristics of pectin composite membranes containing different concentrations of PA-Zn: (b) P; (c) P / ZP 1 (d) P / ZP 3 (e) P / ZP 5 (f) P / ZP 7 (g) Contact angle of pectin composite film;

[0044] Figure 4(a) Tensile strength (TS) and elongation at break (EB) of pectin composite film; (b) Mechanical property curves of different antibacterial films;

[0045] Figure 5 A schematic diagram of a cross-sectional electron microscope image of a PA-Zn doped pectin composite film;

[0046] Figure 6 A schematic diagram of the Fourier transform infrared spectrum of the PA-Zn doped pectin composite film;

[0047] Figure 7 A schematic diagram of a PA-Zn doped pectin composite film using TGA.

[0048] Figure 8 A schematic diagram illustrating the antibacterial effect of PA-Zn doped pectin composite membrane;

[0049] Figure 9 Schematic diagram of the antioxidant activity of PA-Zn doped pectin composite film (left) dot scan of P / ZP fluorescence intensity; (right) range scan of P / ZP fluorescence intensity;

[0050] Figure 10 This is a schematic diagram of the degradation of the PA-Zn doped pectin composite film.

[0051] Figure 11 Schematic diagram of the effect of PA-Zn doped pectin composite membrane on cherry tomatoes for 7 days and 14 days. Detailed Implementation

[0052] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Of course, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0053] Tables 1 and 2 show the experimental reagents and instruments used in the embodiments of the present invention.

[0054] Table 1 Experimental Reagents

[0055] reagents purity Manufacturer pyrogallic acid Analytical Pure Sinopharm Chemical Reagent Co., Ltd. pectin Analytical Pure Shanghai Maclean Biochemical Co., Ltd. glycerin Analytical Pure Shanghai Maclean Biochemical Co., Ltd. Anhydrous calcium chloride Analytical Pure Shanghai Maclean Biochemical Co., Ltd. Zinc acetate dihydrate Analytical Pure Sinopharm Chemical Reagent Co., Ltd. Anhydrous ethanol Analytical Pure Sinopharm Chemical Reagent Co., Ltd. acetic acid Analytical Pure Sinopharm Chemical Reagent Co., Ltd. ELISA kit Analytical Pure Shanghai Beyotime Biotechnology Co., Ltd.

[0056] Table 2 Experimental Instruments

[0057] instrument model Manufacturer ELISA reader Infinite 200 PRO Diken Trading Co., Ltd. MilliQ Water Milli-Q Direct 8 / 16 syetem MERCK MILLIPORE Field emission scanning electron microscopy ESCALab220i-XL Edinburgh Instruments, UK Fourier transform infrared spectrometer JES-FA200 Nippon Electronics Co., Ltd. Water contact angle analyzer CA200 Kunshan Beidou Precision Instruments Co., Ltd. Electronic balance XB 220A Shanghai Prisus Group Color Analyzer Datacolor 850 Guangzhou Abixi Technology Co., Ltd. high-speed centrifuge TGL-15B Shanghai Anting Scientific Instrument Factory Universal testing machine Instron 5300 Shanghai Testing Equipment Trading Company Thermogravimetric analyzer TG209F3 Shanghai Netzsch Scientific Instruments Co., Ltd. ELISA reader Infinite 200 PRO Diken Trading Co., Ltd. Color Analyzer Datacolor 850 Guangzhou Abixi Technology Co., Ltd.

[0058] The experimental method of this invention is as follows:

[0059] 1. Film thickness:

[0060] The thickness of P / ZP was measured using a micrometer caliper (model DL9325, Deli Group Co., Ltd.).

[0061] 2. Moisture content and determination of moisture content in water-soluble films:

[0062] First, weigh the pectin-based composite film sample (W1), dry it at 60°C for 6 hours, and then weigh it again (W2), accurate to 0.0001 g. Repeat this process until the weight difference between two consecutive measurements is less than 0.0005 g. The moisture content is calculated as the percentage reduction in the initial film weight. Three replicate tests are performed for each film type, and the results are averaged. The moisture content (MC) is calculated using the following formula: MC (%) = (W1 - W2) / W1 × 100% Where: MC represents the percentage of moisture content (%), W1 is the initial weight of the film (g), and W2 is the final weight after drying.

[0063] To determine water solubility, the dried film obtained in the previous step was carefully removed after being immersed in water for 24 hours. Pre-weighed dried filter paper (W3) was used to absorb moisture from the film surface. The filter paper and film were then placed together in a vacuum oven and dried at 60°C for 6 hours to an accuracy of 0.0001 g, and weighed again (W4). This process was repeated until the weight difference between consecutive measurements was less than 0.0005 g. Water solubility (WS) was calculated as the percentage reduction in film weight after immersion in water, using the following formula: WS (%) = (W2 + W3 - W4) / (W2 + W3) where WS represents the percentage of water solubility (%), W3 represents the pre-weighed weight of the dried filter paper (g), and W4 represents the total weight of the dried filter paper and film.

[0064] 3. Determination of water vapor transmission rate:

[0065] The water vapor transmission rate (WVP) of P / ZP was evaluated using a WVP analyzer (C360, China Langguang Electromechanical Technology Co., Ltd., Jinan) according to the GB / T 1037-2021 standard test method. The membrane was mounted on the weighing cup of the WVP analyzer, pre-filled with 10 mL of distilled water, and placed under controlled conditions: a test wind speed of 0.5 m / s, a test area of ​​32.95 cm², and a test humidity maintained at 75%. The WVP of the composite membrane was measured every 4 hours.

[0066] 4. Oxygen permeability measurement:

[0067] A deoxidizer mixture consisting of 6.0 g of iron powder, activated carbon, and sodium chloride in a weight ratio of 1:2:3 was prepared. The mixture was placed in a weighing bottle, sealed with a sealing film, and immersed in a desiccator containing a saturated barium chloride solution for seven consecutive days. Samples were taken every 24 hours during this period. Oxygen permeability (OP) was calculated using the following formula: OP = Δm / tA, where OP represents the oxygen permeability (10... -4 g / m 2 / s), Δm represents the weight increment (g), t represents the time required to reach equilibrium (days), and A represents the permeation area of ​​the membrane (m²). 2 ).

[0068] 5. Film color and light transmittance:

[0069] The color characteristics of the composite film were evaluated using a colorimeter (Datacolor 850, Labmates Technology Co., Ltd., Hangzhou, China) in transmission mode, with a standard white board as a reference. The L*, a*, b* values, ΔE, and WI values ​​of the composite film were measured. ΔE and WI values ​​were calculated using the following formulas:

[0070] ;

[0071] ;

[0072] Where: L* represents film brightness; a* represents the red-green axis; b* represents the yellow-blue axis; L*, a*, and b* are the colorimetric parameters of a standard white board.

[0073] 6. Contact angle test:

[0074] The hydrophilicity of the bilayer membrane was observed using a contact angle meter (Theta Bio-Aolin (Shanghai) Trading Co., Ltd.). The membrane was attached to the moving platform of the water contact angle analyzer, and approximately 5 μL of water was dropped onto the membrane surface before rapid imaging. At least three measurements were taken for each concentration group. The contact angle coefficient (CA) of the membrane was measured using the five-point fitted ellipse method with an accuracy of 0.01° using ImageJ (Image Processing and Analysis in Java).

[0075] 7. Mechanical property testing:

[0076] The tensile strength (TS) and elongation at break (EB) of the composite film were tested using an Instron 5300 universal testing machine (Shanghai Tester Equipment Trading Co., Ltd., China). The experimental method was as described by Li et al.

[13] . After preparing a composite film sample with a size of 20 mm × 40 mm, it was firmly clamped on the testing machine fixture. The initial clamping distance was set to 20 mm, and a tensile speed of 50 mm / min was applied continuously until fracture. The tensile stress and elongation at break were then calculated using the following formula:

[0077] ;

[0078] ;

[0079] Where TS represents tensile stress (unit: MPa), F represents maximum force (unit: N), and S represents the cross-sectional area of ​​the film (unit: mm). 2 ), EB represents the elongation at break (percentage), L1 represents the length at break (unit: mm), and L0 represents the initial length (unit: mm).

[0080] 8. Cross-sectional morphology analysis:

[0081] To investigate the correlation between the distribution of PA-Zn in the thin film and its mechanical properties, water vapor barrier properties, and oxygen barrier properties, we used scanning electron microscopy (SEM) to examine the cross-sectional structure of the P / ZP composite film. Specifically, double-sided tape was used to fix the freeze-cracked film onto a support immersed in liquid nitrogen. All film samples underwent sputtering gold plating before testing and were analyzed at an accelerating voltage of 5 kV.

[0082] 9. Fourier Transform Infrared Spectroscopy (FT-IR):

[0083] The infrared spectrometer (Nicolet iS10, Thermo Fisher Scientific (China) Co., Ltd.) was used, with a scanning range of 4000 cm⁻¹. -1 -400 cm -1 The resolution is 4 cm. -1 PA-Zn and bilayer films were analyzed, with each spectrum acquired through 64 consecutive scans.

[0084] 10. Thermal performance analysis:

[0085] Thermogravimetric analysis (TG209F3, Netzsch Scientific Instruments Trading (Shanghai) Co., Ltd.) was used. 0.3g-0.5g of the membrane was placed in the sample dish of the thermogravimetric analyzer, with an empty dish as a reference. The temperature was set to rise from 25℃ to 600℃ at a rate of 10℃ / min, and the nitrogen flow rate was controlled at 50 mL / min.

[0086] 11. Antibacterial activity assessment:

[0087] The antibacterial properties of the composite membrane were determined using the inhibition zone radius method. ESBL-resistant *Escherichia coli* and methicillin-resistant *Staphylococcus aureus* (MRSA) strains were selected. Single colonies were picked and inoculated into liquid LB medium and cultured to the logarithmic growth phase. The bacterial suspension concentration was adjusted to 1 × 10⁻⁶ using a bacterial turbidimeter. 8 After CFU / mL, a 100-fold dilution was performed. Then, 100 μL of the diluted solution was pipetted and evenly spread onto LB agar plates. All P / ZP films were sterilized under UV light for 30 minutes before testing. After sterilization, the films were attached to inoculation plates, and two control groups were set up for each film concentration: one group was incubated upright at 37°C, and the other group was irradiated with a xenon lamp for 30 minutes (simulating sunlight) and then incubated upside down. After 24 hours of incubation, the inhibition zone range of the pure pectin films containing / without PA-Zn against the two bacteria was observed and recorded.

[0088] 12. Antioxidant activity:

[0089] By leveraging the inherent properties of nanomaterials, the antioxidant properties of PA-Zn-added pectin membranes were evaluated using reactive oxygen species (ROS) degradation as a benchmark. This evaluation was conducted using a ROS detection kit (Beyotime Biotechnology Co., Ltd., Shanghai, China). After treatment, the antibacterial membrane was prepared into individual discs with a radius of 5 mm using a perforator. Before use, the biosafety cabinet was sterilized by UV irradiation for 30 minutes. The ESBL-containing *E. coli* strain was activated the day before the experiment. Subsequently, 1 mL of bacterial culture was transferred to a centrifuge tube, centrifuged at 3000 r / min for 5 minutes, and the bacterial pellet was collected. The bacteria were washed three times with sterile water under the same centrifugation conditions. After establishing the reaction system, it was irradiated under a full-power xenon lamp at 37°C for 1 hour. The bacterial pellet was then separated by centrifugation, washed once with sterile water, and incubated with 200 μL of DCFH probe dilution buffer for 20 minutes. During this period, the mixture was stirred every five minutes. Fluorescence emission was measured by scanning the emission wavelength (Em) from 495 nm to 560 nm (with a peak at 525 nm) and setting the excitation wavelength (Ex) to 448 nm.

[0090] 13. Degradation performance test:

[0091] Pectin film (P) and antibacterial film containing PA-Zn (P / ZP) 1 The edges of standard plastic film (PE) were cut into 50×50 mm squares and fixed to yellow paper for easy identification in the soil. After preparation in the previous stage, each sample was buried in a 5 cm thick soil layer. The degradation process was monitored by recording and photographing samples on days 7 and 14.

[0092] 14. Statistical Analysis:

[0093] All measurements were repeated in triplicate, and data are reported as mean ± standard deviation. Origin 2025 was used to create the figures. Statistical analysis of color difference, thermal stability, and texture characteristics was performed using IBM SPSS (version 22), with significance set at p < 0.05. One-way ANOVA with Duncan post-hoc test was used to determine significant differences, which were considered significant at p < 0.05.

[0094] Example:

[0095] Preparation, characterization and performance study of PA-Zn nanoparticle-doped pectin-based composite membrane (P / ZP).

[0096] 1. Preparation of PA-Zn nanoparticles (nanoparticles), such as... Figure 1 As shown.

[0097] (1) Weigh 0.878 g of zinc acetate dihydrate (C4H6O4Zn·2H2O) and 1.01 g of pyrogallol (C6H6O3), and dissolve them in 40 mL of deionized water.

[0098] (2) After stirring the mixed solution thoroughly until completely dissolved, adjust its pH to 8.0 using alkaline solution.

[0099] (3) Transfer the above solution to a reaction vessel and react at 120°C for 12 h.

[0100] (4) After the reaction is complete, the mixture is centrifuged at 8000 r / min for 10 min and the precipitate is collected.

[0101] (5) Wash the precipitate three times with deionized water and anhydrous ethanol alternately to remove impurities.

[0102] (6) The obtained product was dried in a room temperature oven for 12 h to obtain PA-Zn nanoparticle powder.

[0103] 2. Preparation of PA-Zn doped pectin-based composite film (P / ZP)

[0104] (1) Preparation of film forming solution: Dissolve pectin (1% w / w) and glycerin (0.9% w / w) in a certain amount of deionized water and stir until completely dissolved.

[0105] (2) Add anhydrous calcium chloride (0.72% w / w) to the above solution as a crosslinking agent.

[0106] (3) Add PA-Zn nanoparticles of different mass fractions (0%, 1%, 3%, 5%, 7%) respectively, stir evenly for 5 minutes to obtain a series of P / ZP dispersions (denoted as P, P / ZP respectively). 1 , P / ZP 3 , P / ZP 5 P / ZP 7 ).

[0107] (4) Centrifuge the dispersion for 10 minutes to remove gas, and then sonicate it at 30°C, 40 kHz and 200 W for 10 minutes to remove bubbles and promote the dispersion of nanoparticles.

[0108] (5) Take 15 mL of the treated solution and pour it into a 90 × 15 mm petri dish. Dry it in a 60°C oven to form a film.

[0109] (6) Place the dried film in a constant temperature and humidity chamber with a relative humidity of 50% for equilibration and use.

[0110] 3. Characterization and performance test results of PA-Zn doped pectin composite membrane.

[0111] 3.1 Physical and mechanical properties.

[0112] thickness( Figure 2 As the PA-Zn concentration increased (from 0% to 7%), the film thickness gradually increased from about 0.05 mm to 0.08 mm, which may be related to the increase in solid content and the structural roughening caused by nanoparticles.

[0113] Hydrophobicity Figure 3 The water contact angle increased significantly with increasing PA-Zn content, from 24.58° (hydrophilic) for pure pectin film to P / ZP. 7 The 102.08° (hydrophobic) indicates that the hydrophobic properties of PA-Zn itself endow the film surface with hydrophobic properties.

[0114] Mechanical properties Figure 4 When 1% PA-Zn is added, the tensile strength (TS) and elongation at break (EB) of the film increase by approximately 15.85% and 35.17%, respectively, indicating that low concentration PA-Zn plays a filling and reinforcing role. However, when the concentration is ≥3%, both TS and EB decrease, which is attributed to the destruction of the internal structure of the film caused by nanoparticle aggregation.

[0115] Barrier performance:

[0116] Oxygen permeability (OP) Figure 2 c): The concentration of PA-Zn gradually decreases with increasing concentration, possibly due to the oxygen consumption reaction of pyrogallic acid in PA-Zn and the improvement of film density.

[0117] Water vapor transmission rate (WVP) Figure 2 d): WVP decreases first and then increases. At low concentrations (1%), WVP decreases due to the denser film structure; at high concentrations (≥3%), WVP increases due to defects formed by nanoparticle aggregation.

[0118] 3.2 Structural characterization.

[0119] Microscopic morphology (SEM) Figure 5 Pure pectin film has a uniform and smooth cross-section. Adding 1% PA-Zn results in a denser structure; concentrations ≥3% show roughness and cracks (P / ZP). 5 Even obvious cracks (ZP) 7 This confirms that nanoparticle aggregation at high concentrations disrupts the integrity of the thin film.

[0120] Chemical structure (FT-IR, Figure 6 All PA-Zn-doped pectin composite films at 3269 cm⁻¹ -1 (-OH stretching vibration), 1632.67 cm -1 (CH vibration), 10¹⁵ cm -1 The characteristic peaks at (CO vibration) and other locations are consistent with those of the pure pectin film, and no new peaks appeared. This indicates that the interaction between PA-Zn and the pectin matrix is ​​mainly physical filling, and no chemical bonds have been formed.

[0121] Thermal stability (TGA, Figure 7 All films exhibited two main weight loss phases at approximately 50°C (moisture evaporation) and 180°C (glycerol and pectin decomposition). The addition of PA-Zn slightly reduced the weight loss rate but did not significantly alter the thermal decomposition behavior of the films, and the residual amount increased slightly with increasing PA-Zn content.

[0122] 3.3 Functional performance.

[0123] Antibacterial activity ( Figure 8 PA / Zn exhibits inhibitory effects against methicillin-resistant Staphylococcus aureus (MRSA, Gram-positive) and extended-spectrum β-lactamase-producing Escherichia coli (ESBL-E. coli, Gram-negative), with the radius of the inhibition zone increasing with increasing PA-Zn concentration. Light exposure (simulated sunlight) significantly enhances its antibacterial effect, particularly against ESBL-E. coli.

[0124] Antioxidant activity ( Figure 9 ): Evaluation by reactive oxygen species (ROS) degradation experiment showed that the fluorescence intensity of PA-Zn doped pectin composite film with added PA-Zn was significantly lower than that of the control group, indicating that PA-Zn enhanced the antioxidant capacity of the film.

[0125] Degradation performance ( Figure 10Soil burial experiments showed that the PA-Zn doped pectin composite film showed obvious signs of degradation within 7 days and almost complete degradation after 14 days, while the traditional plastic film showed no change, proving that it has good environmental degradability.

[0126] Preservation applications ( Figure 11 Using cherry tomatoes as a model, PA-Zn-doped pectin composite film coating can significantly delay the wrinkling, softening, and browning of the fruit skin. The preservation effect increases with increasing PA-Zn concentration, especially P / ZP. 5 With P / ZP 7 A group is preferred.

[0127] 4. Conclusion.

[0128] This example successfully prepared a PA-Zn nanoparticle-doped pectin-based composite film (P / ZP). Studies show that low concentrations (1%) of PA-Zn can improve the mechanical strength and barrier properties of the film, while high concentrations (≥3%) of PA-Zn endow the film with excellent antibacterial, antioxidant, hydrophobic, and preservation functions. However, this can lead to nanoparticle aggregation, impairing the film's mechanical integrity and uniformity. The PA-Zn-doped pectin composite film combines biodegradability with active packaging functionality, demonstrating good potential in replacing traditional plastic preservation films and extending food shelf life.

[0129] Of course, the above description is not intended to limit the present invention, and the present invention is not limited to the examples given above. Any changes, modifications, additions or substitutions made by those skilled in the art within the scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. A pectin-based nano-antibacterial food preservation film, characterized in that, The plastic wrap uses pectin as the film-forming matrix and is composited with PA-Zn nanoparticles; the PA-Zn nanoparticles are zinc-pyrogallic acid coordination polymer nanoparticles generated by the reaction of zinc acetate dihydrate and pyrogallic acid as precursors under alkaline hydrothermal conditions.

2. The pectin-based nano-antibacterial food preservation film according to claim 1, characterized in that, The PA-Zn nanoparticles in the plastic wrap account for 1% to 7% of the total mass.

3. The pectin-based nano-antibacterial food preservation film according to claim 1 or 2, characterized in that, The plastic wrap also includes a plasticizer and a crosslinking agent; the plasticizer is glycerin, and the crosslinking agent is calcium chloride.

4. The pectin-based nano-antibacterial food preservation film according to claim 3, characterized in that, Based on the weight percentage of the plastic wrap forming liquid, the contents of each component are: pectin 1%, glycerin 0.9%, calcium chloride 0.72%, the balance being water, and PA-Zn nanoparticles accounting for 1%-7% of the pectin mass.

5. The method for preparing the food preservation film according to any one of claims 1-4, characterized in that, Includes the following steps: S1. Preparation of PA-Zn nanoparticles: Zinc acetate dihydrate and pyrogallic acid were dissolved together in water. The pH of the mixed solution was adjusted to 8.0-9.0 with alkali solution under stirring. Then, a hydrothermal reaction was carried out to generate zinc-pyrogallic acid coordination polymer nanoparticles. After the reaction was completed, the nanoparticles were centrifuged, washed and dried to obtain PA-Zn nanoparticle powder. S2. Preparation of composite membrane solution: Dissolve pectin and glycerol in water, stir to dissolve, add calcium chloride solution, then add PA-Zn nanoparticle powder obtained in step S1, stir evenly to obtain composite membrane solution; S3. Film formation: After degassing and defoaming, the composite film liquid is cast into a mold, dried, and then peeled off to obtain the pectin-based nano antibacterial food preservation film.

6. The preparation method according to claim 5, characterized in that, In step S1, the molar ratio of zinc acetate dihydrate to pyrogallol is 1:(1-1.2); the hydrothermal reaction temperature is 110-130℃, and the reaction time is 10-14 hours.

7. The preparation method according to claim 5, characterized in that, In step S2, the amount of PA-Zn nanoparticle powder added is such that its mass percentage in the final composite film liquid solid component is 1% to 7%.

8. The preparation method according to claim 5, characterized in that, In step S3, the degassing is performed by centrifugal degassing, the defoaming is performed by ultrasonic treatment, and the drying temperature is 55-65℃.

9. The application of the food preservation film as described in any one of claims 1-4 in food packaging, characterized in that, Used to inhibit foodborne pathogens and / or extend the shelf life of food; the foodborne pathogens include at least one of extended-spectrum β-lactamase-producing Escherichia coli and methicillin-resistant Staphylococcus aureus.

10. A food packaging product, characterized in that, Includes food and food preservation film as described in any one of claims 1-4, which wraps the food.

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