Sichuan pepper essential oil Pickering emulsion starch-based active composite membrane and preparation method thereof

Abstract

The invention discloses a zanthoxylum bungeanum essential oil Pickering emulsion starch-based active composite membrane and a preparation method thereof. The preparation method specifically comprises the following steps: preparing nano cellulose; preparing a Chinese prickly ash essential oil Pickering emulsion by utilizing the nano cellulose; corn starch, deionized water and glycerin are mixed and stirred, and gelatinized starch liquid is obtained; adding the pepper essential oil Pickering emulsion into the gelatinized starch liquid, stirring, and standing in a vacuum state to remove bubbles, so as to obtain a film forming liquid; and pouring the film forming liquid into a polytetrafluoroethylene mold, and standing to obtain the active composite film. According to the composite membrane disclosed by the invention, due to the introduction of the Pickering emulsion, the transmission path of water molecules in the membrane is increased, and the content of a hydrophobic part in the membrane is increased, so that the barrier effect of the composite membrane is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of composite film preparation, and in particular relates to a method for preparing a Zanthoxylum essential oil Pickering emulsion starch-based active composite film, and also relates to a Zanthoxylum essential oil Pickering emulsion starch-based active composite film. Background Art

[0002] In the food industry, product packaging is widely used to ensure that products maintain quality, freshness and safety during production, transportation and sales. Currently, food packaging is mainly made of petroleum-based plastics. However, excessive use of petroleum-based plastics may lead to soil and water pollution, have adverse effects on the environment, and pose a threat to aquatic life. Discarded plastics gradually decompose into microplastics under the action of abiotic factors in the natural environment, further polluting the environment and posing risks to human health. In response to such problems, the research and development of bio-based plastics has gradually become the focus of attention, among which starch has attracted attention due to its degradability, renewability, abundant sources and cost-effectiveness. However, the hydrophilicity of starch significantly affects the key functional properties of its film, such as moisture resistance and mechanical properties. In addition, starch films lack antibacterial and antioxidant properties, which are essential for food packaging.

[0003] Cellulose nanocrystals (CNCs) can be extracted from agricultural residues, forestry wastes, algae and bacteria by mechanical, chemical or enzymatic selective hydrolysis of amorphous regions of cellulose. Their unique structural and physical properties make CNCs ideal for mechanical reinforcement, Pickering emulsion stabilization, thickening and drug delivery systems. Algae is a promising renewable cellulose source because it can grow on non-arable land and utilize carbon dioxide-rich waste gas and wastewater, while achieving nutrient recovery and reducing greenhouse gas emissions. This algal cellulose has the advantages of low lignin content, high crystallinity and large surface area compared to cellulose from other sources. Nannochloropsis oceanica The tensile strength of the extracted cellulose nanofibers is 3-4 GPa on average, which is comparable to that of ordinary fillers and even higher than that of wood cellulose nanofibers. However, only a few studies have used microalgae cellulose for the preparation of active films. Studies have shown that CNC extracted from Haematococcus pluvialis can be effectively used as a filler for polyvinyl alcohol (PVA) composite films. The study showed that adding 8wt% CNC to the PVA matrix can increase the Young's modulus by 215%, the tensile strength by 150%, and the toughness by 45%.

[0004] Zanthoxylum bungeanumEssential oil (ZBEO), due to its ingredients such as linalool, limonene and alkaloids, exhibits significant antibacterial and antioxidant activities. However, due to the poor compatibility of ZBEO with the starch matrix, a discontinuous phase is formed in the membrane, which significantly reduces the mechanical properties of the membrane. To solve this problem, Pickering emulsion technology was introduced to stabilize the oil-water interface through cellulose nanocrystals (CNCs) so that the essential oil is evenly dispersed in the starch matrix to improve the antibacterial and antioxidant properties of the membrane. Summary of the invention

[0005] The invention aims to provide a method for preparing a starch-based active composite film of a Pickering emulsion of pepper essential oil, thereby solving the problems of low mechanical properties and poor antibacterial properties of the existing starch-based active composite film.

[0006] Another object of the present invention is to provide a starch-based active composite film of Zanthoxylum essential oil Pickering emulsion.

[0007] The technical solution adopted by the present invention is a method for preparing a starch-based active composite film of a Pickering emulsion of Zanthoxylum essential oil, which is specifically implemented according to the following steps: Step 1, preparing nanocellulose; Step 2, preparing a Pickering emulsion of Zanthoxylum bungeanum essential oil by using nanocellulose; Step 3, mixing corn starch, deionized water and glycerin, stirring to obtain gelatinized starch solution; Step 4, adding the Pickering emulsion of Zanthoxylum bungeanum essential oil to the gelatinized starch solution, stirring, placing the obtained film solution in a vacuum state to remove bubbles, and obtaining a film-forming solution; Step 5, pour the obtained film-forming liquid into a polytetrafluoroethylene mold, place it at room temperature to obtain an active composite membrane, and seal it for dry storage.

[0008] The present invention is also characterized in that: In step 1, specifically: The chlorella residue after oil extraction is dissolved in NaOH solution, placed in a constant temperature water bath at 50-65°C and heated with stirring for 12 hours, the solids are washed to a pH of 7, and stirred and bleached with sodium acetate buffer at a stirring temperature of 55-65°C for 3-4 hours until the suspension becomes milky white, centrifuged and washed, then placed in HCl solution for boiling, and allowed to stand at room temperature for 12 hours. The acidified mixture is washed to a pH of 7 and dried to obtain nanocellulose.

[0009] In step 2, specifically: Nanocellulose was ultrasonically dispersed in deionized water, and then Zanthoxylum bungeanum essential oil and Tween 20 were added and ultrasonically treated to form a Zanthoxylum bungeanum essential oil Pickering emulsion.

[0010] In step 3, the mass ratio of corn starch, deionized water and glycerol is 14-18:280-320:4.0-5.6; and the stirring time is 2-4 hours.

[0011] In step 4, the stirring time is 30 to 60 minutes.

[0012] Another technical solution adopted by the present invention is a Zanthoxylum essential oil Pickering emulsion starch-based active composite film prepared by a method for preparing a Zanthoxylum essential oil Pickering emulsion starch-based active composite film.

[0013] The beneficial effects of the present invention are: (1) In the composite membrane of the present invention, nanocellulose crystals are added to stably aggregate at the oil-water interface through electrostatic action and physical adsorption, thereby promoting the uniform dispersion of pepper essential oil droplets; at the same time, the homogeneity of the composite membrane is enhanced, and the tensile strength and light transmittance of the composite membrane are improved; (2) In the composite membrane of the present invention, the introduction of Pickering emulsion increases the transmission path of water molecules in the membrane, increases the content of the hydrophobic part in the membrane, and thus improves the barrier effect of the composite membrane; (3) The composite film of the present invention has certain antioxidant and antibacterial effects. According to the plate count method, the antibacterial effect on Escherichia coli and Staphylococcus aureus can exceed 90% after 16 hours of contact. When the addition amount of Pickering emulsion is 5%, the free radical quenching rate of DPPH by the film-forming liquid exceeds 60%. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 The electron microscope images of the composite membranes prepared in the examples and comparative examples; Figure 2 The mechanical properties diagram of the composite membranes prepared in the examples and comparative examples; Figure 3 The ultraviolet transmittance curves of the composite films prepared in the examples and comparative examples are shown; Figure 4 The UV transmittance images of the composite films prepared in the examples and comparative examples are shown; Figure 5 The contact angle diagrams of the composite films prepared in the examples and comparative examples; Figure 6 It is a swelling ratio diagram of the composite membranes prepared in the examples and comparative examples; Figure 7 The water vapor transmission rate graph of the composite films prepared in the examples and comparative examples; Figure 8 DPPH removal rate diagram of the composite membrane prepared in the embodiment and the comparative example; Fig. 9The antibacterial rate diagram of the composite membrane prepared in the embodiment and the comparative example; Fig.10 The fruit preservation diagram of the composite film prepared in the embodiment and the comparative example; Fig.11 The graph is a data chart of the fruit preservation experiment of the composite films prepared in the examples and comparative examples. DETAILED DESCRIPTION

[0015] The present invention is described in detail below in conjunction with specific implementation modes and accompanying drawings.

[0016] The method for preparing the starch-based active composite film of the Pickering emulsion of Zanthoxylum bungeanum essential oil of the present invention is specifically implemented according to the following steps: Step 1, preparing nanocellulose (CNCs); Specifically, the chlorella residue after oil extraction is dissolved in a 0.5M NaOH solution, placed in a constant temperature water bath at 50-65°C and heated with stirring for 12 hours, the solids are washed to a pH of 7, and stirred and bleached with sodium acetate buffer at a stirring temperature of 55-65°C for 3-4 hours until the suspension becomes milky white, centrifuged and washed, and then placed in a 3-7% mass fraction HCl solution for boiling, and allowed to stand at room temperature for 12 hours, the acidified mixture is washed to a pH of 7, and dried to obtain nanocellulose; Sodium acetate buffer is specifically composed of sodium acetate, acetic acid and sodium hypochlorite; Step 2, preparing a Pickering emulsion of Zanthoxylum bungeanum essential oil; Specifically, nanocellulose was ultrasonically dispersed in deionized water, and then Zanthoxylum bungeanum essential oil and Tween 20 were added and ultrasonically treated for 15 min to form a stable Zanthoxylum bungeanum essential oil Pickering emulsion; The ultrasonic power was 300-500 W, and the ultrasonic dispersion time was 5 min; In the Pickering emulsion, the volume fraction of Zanthoxylum essential oil is 1.0-3.0%, and the volume fraction of Tween 20 is 0.5-2.0%; Step 3, starch gelatinization treatment; Specifically, corn starch, deionized water and glycerol are mixed and stirred at 80°C for 2-4 hours to obtain gelatinized starch solution; The mass ratio of corn starch, deionized water and glycerol is 14-18:280-320:4.0-5.6; Step 4, preparing the film-forming solution; Add the Pickering emulsion of pepper essential oil into the gelatinized starch solution, stir for 30-60 minutes, and place the obtained film solution in a vacuum state for 1 hour to remove bubbles to obtain a film-forming solution; Step 5, casting film; The obtained film-forming liquid is poured into a polytetrafluoroethylene mold and placed at room temperature for 24 hours to obtain an active composite membrane, which is then sealed and dried for storage.

[0017] Based on this, the present invention relates to a method for preparing a starch-based active composite film based on Pickering emulsion technology, aiming to improve the preservation effect of cherry tomatoes and solve the problems of insufficient antibacterial and antioxidant properties and poor mechanical properties of starch films in the prior art. The method uses cellulose nanocrystals (CNCs) as a stabilizer for the Pickering emulsion, uniformly disperses Zanthoxylum bungeanum essential oil (ZBEO) in the starch matrix, and significantly improves the antibacterial, antioxidant and mechanical properties of the composite film by improving the stability of the oil-water interface. The proposal of this method provides a new method and theoretical basis for the exploration of the field of bioactive composite film food packaging.

[0018] Example 1 The method for preparing the starch-based active composite film of the Pickering emulsion of Zanthoxylum essential oil stabilized by microalgae cellulose of the present invention comprises the following steps: (1) Extraction of CNCs: The Chlorella residue after oil extraction was collected and dissolved in 0.5 M NaOH solution, which was placed in a constant temperature water bath at 60 °C and heated with stirring for 12 h; the solids were washed to a neutral pH; sodium acetate buffer was used for bleaching, and stirred at 60 °C for 3.5 h until the suspension became milky white; the washed cellulose was collected by centrifugation, freeze-dried, placed in a 5% by mass HCl solution and boiled, and allowed to stand at room temperature for 12 h. The mixture was washed to a neutral pH and dried to obtain nanocellulose; (2) Preparation of Pickering emulsion: 0.02 g CNCs were dissolved in 8 mL deionized water and sonicated at 500 W for 5 min. 2.0% by volume of ZBEO and 1.0% by volume of Tween 20 were added and sonicated again at 500 W for 15 min to form a stable Pickering emulsion.

[0019] (3) Starch gelatinization treatment: 17 g corn starch was mixed with 320 mL deionized water and 5.0 g glycerol and stirred at 80 °C for 2.5 h. (4) Preparation of membrane-forming liquid: Add 0.50 mL of Zanthoxylum essential oil Pickering emulsion into 25 mL of gelatinized starch base, stir at 300 rpm for 60 min, and then place the membrane liquid under vacuum at room temperature for 1 h to remove bubbles; (5) Casting method: Pour 20 mL of the obtained membrane liquid into a polytetrafluoroethylene mold and place it at room temperature for 24 h to obtain a composite membrane. Seal and store it in a dry place.

[0020] Example 2 The method for preparing the starch-based active composite film of the Pickering emulsion of Zanthoxylum essential oil stabilized by microalgae cellulose of the present invention comprises the following steps: (1) Extraction of CNCs: Collect the algae residue after oil extraction, dissolve it in 0.5 M NaOH solution, and place it in a constant temperature water bath at 60°C and heat and stir for 12 h; wash the solids to neutral pH; use sodium acetate buffer for bleaching, stir at 60°C for 3.5 h, until the suspension becomes milky white; collect the washed cellulose by centrifugation, freeze-dry, and then use 5% HCl acid hydrolysis to separate CNCs, boil, and stand at room temperature for 12 h. Wash the mixture to neutral pH and dry to obtain nanocellulose; (2) Preparation of Pickering emulsion: 0.02 g CNCs were dissolved in 8 mL deionized water and sonicated at 500 W for 5 min. 2.0% by volume of ZBEO and 1.0% by volume of Tween 20 were added and sonicated again at 500 W for 15 min to form a stable Pickering emulsion.

[0021] (3) Starch gelatinization treatment: 16 g corn starch was mixed with 320 mL deionized water and 4.8 g glycerol and stirred at 80 °C for 2.5 h. (4) Preparation of membrane-forming solution: Add 0.75 mL of Zanthoxylum essential oil Pickering emulsion into 25 mL of gelatinized starch base and stir at 300 rpm for 60 min. Then, place the membrane solution at room temperature under positive vacuum for 1 h to remove bubbles.

[0022] (5) Casting method: Pour 20 mL of the obtained membrane liquid into a polytetrafluoroethylene mold and place it at room temperature for 24 h to obtain a composite membrane. Seal and store it in a dry place.

[0023] Example 3 The method for preparing the starch-based active composite film of the Pickering emulsion of Zanthoxylum essential oil stabilized by microalgae cellulose of the present invention comprises the following steps: (1) Extraction of CNCs: Collect the algae residue after oil extraction, dissolve it in 0.5 M NaOH solution, and place it in a constant temperature water bath at 60°C and heat and stir for 12 h; wash the solids to neutral pH; use sodium acetate buffer for bleaching, stir at 60°C for 3.5 h, until the suspension becomes milky white; collect the washed cellulose by centrifugation, freeze-dry, and then use 5% HCl acid hydrolysis to separate CNCs, boil, and stand at room temperature for 12 h. Wash the mixture to neutral pH and dry to obtain nanocellulose; (2) Preparation of Pickering emulsion: 0.02 g CNCs were dissolved in 8 mL deionized water and sonicated at 500 W for 5 min. 2.0% by volume of ZBEO and 1.0% by volume of Tween 20 were added and sonicated again at 500 W for 15 min to form a stable Pickering emulsion.

[0024] (3) Starch gelatinization treatment: Mix 15 g corn starch with 320 mL deionized water and 4.6 g glycerol and stir at 80 °C for 2.5 h.

[0025] (4) Preparation of membrane-forming liquid: Add 0.75 mL of Zanthoxylum essential oil Pickering emulsion into 25 mL of gelatinized starch base, stir at 300 rpm for 60 min, and then place the membrane liquid under vacuum at room temperature for 1 h to remove bubbles; (5) Casting method: Pour 20 mL of the obtained membrane liquid into a polytetrafluoroethylene mold and place it at room temperature for 24 h to obtain a composite membrane. Seal and store it in a dry place.

[0026] Example 4 The method for preparing the starch-based active composite film of the Pickering emulsion of Zanthoxylum essential oil stabilized by microalgae cellulose of the present invention comprises the following steps: (1) Extraction of CNCs: Collect the algae residue after oil extraction, redissolve it in 0.5 M NaOH solution, and place it in a constant temperature water bath at 60°C and heat and stir for 12 h; wash the solids to neutral pH; use sodium acetate buffer for bleaching, stir at 60°C for 3.5 h, until the suspension becomes milky white; collect the washed cellulose by centrifugation, freeze-dry, and then hydrolyze and separate CNCs with 5% HCl acid, boil, and stand at room temperature for 12 h. Wash the mixture to neutral pH and dry to obtain nanocellulose; (2) Preparation of Pickering emulsion: 0.02 g CNCs were dissolved in 8 mL deionized water and sonicated at 500 W for 5 min. 2.0% by volume of ZBEO and 1.0% by volume of Tween 20 were added and sonicated again at 500 W for 15 min to form a stable Pickering emulsion.

[0027] (3) Starch gelatinization treatment: 19 g corn starch was mixed with 320 mL deionized water and 5.2 g glycerol and stirred at 80 °C for 2.5 h.

[0028] (4) Preparation of membrane-forming solution: Add 1.25 mL of Zanthoxylum essential oil Pickering emulsion into 25 mL of gelatinized starch base and stir at 300 rpm for 60 min. Then, place the membrane solution under vacuum at room temperature for 1 h to remove bubbles.

[0029] (5) Casting method: Pour 20 mL of the obtained membrane liquid into a polytetrafluoroethylene mold and place it at room temperature for 24 h to obtain a composite membrane. Seal and store it in a dry place.

[0030] Comparative Example 1 The preparation method of the composite membrane of this comparative example comprises the following steps: (1) Extraction of CNCs: Collect the algae residue after oil extraction, dissolve it in 0.5 M NaOH solution, place it in a 60℃ constant temperature water bath and heat and stir for 12h; wash it to neutral pH, and bleach it with sodium acetate buffer solution at 65℃ for 3.5h, wash it repeatedly until the suspension turns milky white, collect the washed cellulose by centrifugation, and freeze-dry it. Separate CNCs by acid hydrolysis with 4% HCl, boil it, and let it stand at room temperature for 12h. Wash the mixture to neutral pH and dry it to obtain nanocellulose; (2) Starch gelatinization treatment: 14 g corn starch, 300 mL deionized water and 4.2 g glycerol were mixed and stirred at 80 °C for 2 h. (3) Preparation of membrane solution: 1% CNCs was added to 25 mL of gelatinized starch solution. After ultrasonic treatment at 500W for 5 min, the membrane solution was placed under vacuum at room temperature for 20 min to remove bubbles. (4) Casting method: Pour 20 mL of the obtained membrane solution into a 120 mm plastic culture dish and place it at room temperature for 24 h to obtain a composite membrane. Seal and store it in a dry place.

[0031] Comparative Example 2 The preparation method of the composite membrane of this comparative example comprises the following steps: (1) Extraction of CNCs: Collect the algae residue after oil extraction, dissolve it in 0.5M NaOH solution, place it in a 60℃ constant temperature water bath to heat and stir the mold; wash it to neutral pH, and bleach it with sodium acetate buffer solution at 50℃ for 3.5h, wash it repeatedly until the suspension turns milky white, collect the washed cellulose by centrifugation, and freeze-dry it. Then use 3% HCl acid hydrolysis to separate CNCs, boil it, and let it stand at room temperature for 12h. Wash the mixture to neutral pH and dry it to obtain nanocellulose; (2) Starch gelatinization treatment: 12 g corn starch was mixed with 280 mL deionized water and 4.0 g glycerol and stirred at 80 °C for 2 h. (3) Preparation of membrane-forming solution: 2% (v / v) Zanthoxylum bungeanum essential oil and 1% (v / v) Tween 20 were added to 25 mL of gelatinized starch base. After ultrasonic treatment at 500 W for 5 min, the solution was placed at room temperature under vacuum for 20 min to remove bubbles.

[0032] (4) Casting method: Pour 20 mL of the obtained membrane solution into a 120 mm plastic culture dish and place it at room temperature for 24 h to obtain a composite membrane. Seal and store it in a dry place.

[0033] Comparative Example 3 The preparation method of the composite membrane of this comparative example comprises the following steps: (1) Extraction of CNCs: Collect the algae residue after oil extraction, dissolve it in 0.5 M NaOH solution, and place it in a constant temperature water bath at 60°C and heat and stir for 12 h; wash the solids to neutral pH; use sodium acetate buffer for bleaching, stir at 60°C for 3.5 h, until the suspension becomes milky white; collect the washed cellulose by centrifugation, freeze-dry, place it in a 5% HCl solution and boil it, let it stand at room temperature for 12 h, wash the mixture to neutral pH, and dry it to obtain nanocellulose; (2) Starch gelatinization treatment: 20 g corn starch was mixed with 310 mL deionized water and 5.6 g glycerol and stirred at 80 °C for 2.5 h. (3) Casting method: Pour 20 mL of gelatinized starch film solution into a 120 mm plastic culture dish and place it at room temperature for 24 h to obtain a composite film. Seal and store it in a dry place.

[0034] The properties of the composite membranes prepared in this embodiment and the comparative example were tested: 1. Scanning electron microscopy observation like Figure 1 As shown, it can be seen that all embodiments show a colorless and transparent appearance, and the addition of CNCs improves the visible light transmittance of the film. The microstructure of the film is mainly determined by the interaction between the components, which affects the mechanical properties, barrier properties and optical properties of the film. Comparing the surface micrographs of the composite film, the surfaces of all films are uniform, smooth, crack-free, and have similar morphologies. Comparing Comparative Examples 1 and 3, it can be seen that the surface and cross-section of Comparative Example 1 are flatter and smoother, with fewer wrinkles, indicating that CNCs have good compatibility with starch. However, the composite film (Comparative Example 2) formed by directly incorporating pepper essential oil shows that its surface flatness is low, and the cross-sectional structure is relatively loose, with a large number of pores and gaps. The poor biocompatibility between pepper essential oil and starch leads to the appearance of discontinuous structures, thereby forming a fragile membrane structure. The addition of CNCs enhances its dispersibility in the starch matrix.

[0035] In addition, from Figure 1 It can be seen from the scanning image that compared with Comparative Example 2, Example 2 has fewer micropores and a more uniform surface, indicating that the use of CNCs can make the pepper essential oil exist stably in the form of a Pickering emulsion, improve its biocompatibility with the starch base, and help to improve the continuity of the membrane.

[0036] 2. Mechanical properties test Elastic modulus (TS) and elongation at break (EAB) are indicators of the strength and flexibility of the film. In Comparative Example 3, the TS and EAB of the composite film were 19.14 MPa and 5.4%, respectively. With the addition of CNCs, the maximum TS of the composite film reached 35.66 MPa, which is 1.86 times that of the CS film (Comparative Example 1). This enhancement may be attributed to the anisotropic properties of CNCs derived from Chlorella, which exhibit superior physical adsorption ability at the liquid interface, thereby improving the continuity of the film. However, the EAB value of Comparative Example 1 is lower than that of the CS film. It may be due to the fact that the addition of CNCs enhances the interaction between the two phases in the polymer matrix, thereby restricting the movement of the polymer chains. However, with the increase of the Pickering emulsion content, the TS and EAB values ​​gradually decreased (Examples 1-4). In Example 3, TS dropped to 15.66 MPa, which is lower than the strength of Comparative Example 3. This is consistent with the commonly observed phenomenon that the addition of essential oils usually reduces mechanical properties. A large number of pores and gaps appeared in the cross-sectional structure of Comparative Example 2, indicating that its compatibility was poor, resulting in a decrease in mechanical strength. However, CNCs stabilized ZBEO through Pickering emulsion, and improved the dispersibility of ZBEO in the starch matrix by virtue of the interfacial hydrogen bond interaction, especially the interaction between the polyphenol components in ZBEO and the hydroxyl groups of nanocellulose. The results are shown in Figure 2 As shown; therefore, the TS of Example 1 and Example 2 is improved compared with the CS film, which is consistent with the microscopic observation results.

[0037] 3. Optical performance test Compared with Comparative Example 3, the light transmittance of Comparative Example 1 is higher, indicating that CNCs have good interfacial compatibility with CS and are uniformly dispersed in the membrane matrix. This also confirms the nanoscale dispersion of CNCs in the matrix, which is consistent with the observations of the SEM image. However, the addition of CNCs alone has limited effect on UV absorption in the entire spectral range, so it is necessary to add active substances to enhance the UV blocking ability of the composite film. Compared with the films of Comparative Examples 1 and 3, Examples 1-4 show obvious UV absorption peaks at 280 nm. With the addition of Pickering emulsion, the UV transmittances of Examples 1-4 at 280 nm were 40.16%, 11.64%, 7.08% and 0.65%, respectively. This phenomenon may be attributed to the light scattering caused by fat droplets dispersed in the membrane matrix, indicating that the Pickering emulsion significantly enhances the UV absorption ability of starch-based films. The results are shown in Figure 2. Figure 3 and Figure 4 As shown; 4. Barrier performance test like Figure 5-Figure 7 As shown, the water solubility and swelling rate of Comparative Example 3 are 48.99% and 159.35%, respectively; the corresponding values ​​of Example 1 are reduced to 18.52% and 130.19%, respectively. This reduction can be attributed to the increase in the content of monoterpene compounds in the composite film, which enhances its hydrophobicity, thereby reducing the concentration of hydrophilic substances, resulting in reduced solubility and swelling rate. A similar trend was observed in the contact angle measurement. Without the addition of Pickering emulsion, the contact angle of Comparative Example 3 was 73.33°, and when the emulsion content reached 3% (Example 3), the contact angle reached a maximum of 89.67°. However, when the emulsion concentration increased to 5% (Example 4), the contact angle dropped to 79.4°, which may be due to the reduced compatibility between the film components. Water absorption is an important factor in food quality, which affects the shelf life of food and maintains key texture, taste and flavor characteristics. The barrier performance of the film can be evaluated by the water vapor transmission rate (WVP). The smaller the WVP, the less material exchange between the environment and the food. Compared with Comparative Example 3, the WVP value of Comparative Example 1 was reduced to 5.062 × 10 -12 g cm -1 ·s -1 ·Pa -1 The rigid crystal structure and good dispersion of CNCs in CS hinder the path of molecules through the membrane matrix. When the concentration of Pickering emulsion increased from 1% (Example 1) to 3% (Example 3), the WVP value of the composite decreased from 4.62 to 4.45×10 -12 g cm -1 ·s -1 ·Pa -1This may be attributed to the improved dispersion of essential oils in the membrane matrix due to the uniformity and stability of the emulsion, which effectively reduced water loss. It is worth noting that the WVP of Example 4 increased compared to the other composite membranes, which was also due to the incompatibility and discontinuous structure in the membrane matrix caused by the interaction of excess ZBEO.

[0038] 5. Antioxidant and antibacterial performance test Antioxidant properties are crucial for evaluating the potential of composite films in food packaging applications. The antioxidant activity of the films was determined using the DPPH free radical scavenging method. The DPPH scavenging rate of Comparative Example 3 was 7.51% ( Figure 8 ). The scavenging activity increased with increasing Pickering emulsion concentration, reaching a maximum of 62.96% when 5% emulsion was added. This enhancement was attributed to the monoterpenoids in Zanthoxylum essential oil, which terminated the free radical chain reaction by donating hydrogen atoms through active methylene groups, thereby improving the antioxidant capacity of the membrane. Therefore, the antioxidant properties of CS membranes were improved by incorporating Pickering emulsions containing Zanthoxylum essential oil. However, factors such as membrane preparation methods, drying processes, storage conditions, and oil oxidation may weaken the efficacy of ZBEO. One advantage of Pickering emulsion technology is that it has been shown to slow down the loss of essential oils by encapsulating oil droplets in a layer of solid particles, thereby enhancing the overall antioxidant activity of the membrane.

[0039] like Fig. 9 As shown in the results of the inhibition zone experiment, with the increase of the concentration of Zanthoxylum bungeanum essential oil, the size of the inhibition zone first increased and then decreased, and Example 2 showed the most significant effect. This may be due to the reduced migration of the oil phase in the agar, and the high concentration of Zanthoxylum bungeanum essential oil increased the oil content in the film-forming liquid, limiting its diffusion in the agar, resulting in a smaller inhibition zone. The antibacterial mechanism of the monoterpenoid compounds in Zanthoxylum bungeanum essential oil mainly stems from its binding to the bacterial cell wall, leading to enzyme inactivation, and can also penetrate the cell wall or interfere with the intracellular DNA, rendering the pathogen inactive. In addition, the presence of terpenoid compounds destroys the function of the bacterial cell membrane and inhibits the growth and reproduction of bacteria. Against Staphylococcus aureus ( S. aureus ) may be related to the difference in cell wall structure. S. aureus It is a Gram-positive bacterium with a thicker peptidoglycan layer, but it lacks the outer membrane of Gram-negative bacteria, which makes it easier for the monoterpenoids in Zanthoxylum essential oil to penetrate the cell wall, leading to enzyme inactivation. In addition, the alcohols and ketones in Zanthoxylum essential oil have an effect on the cell wall by increasing the permeability of the membrane. S. aureus In contrast, Gram-negative bacteria such as Escherichia coli ( E. coli ) have an outer membrane, which may hinder the penetration of monoterpenoids, resulting in a relatively low antimicrobial effect.

[0040] 6.Fruit preservation performance test To evaluate the preservation effect of the composite film, the appearance characteristics of cherry tomatoes under different treatments were recorded by digital photographs, e.g. Figure 10-11 As shown, in the control group (unpackaged), slight fruit shrinkage was observed on the 5th day. For tomatoes covered with Example 2, similar shrinkage only occurred on the 15th day, indicating that the onset of corruption was delayed. Since the loss of weight and hardness is an important indicator of the freshness of fruits and vegetables, after 25 days of storage, the weight and hardness losses of the unpackaged group reached 52.30% and 54.93%, respectively. In contrast, the tomatoes packaged in Example 2 only experienced a loss of 16.80% and 25.08%. At the same time, through the measurement of titratable acidity (TA) and soluble solids (TSS), it was found that the tomatoes covered with Example 2 had a slower decline in TA and TSS during storage, and the preservation effect was significantly better than that of the control group and the CS film group. Example 2 significantly maintained the quality of tomatoes by reducing water loss and delaying the changes in acidity and sugar content.

Claims

1. A method for preparing a starch-based active composite film of Zanthoxylum bungeanum essential oil Pickering emulsion, characterized in that: Follow the steps below to implement it: Step 1, preparing nanocellulose; Step 2, preparing a Pickering emulsion of Zanthoxylum bungeanum essential oil by using nanocellulose; Step 3, mixing corn starch, deionized water and glycerin, stirring to obtain gelatinized starch solution; Step 4, adding the Pickering emulsion of Zanthoxylum bungeanum essential oil to the gelatinized starch solution, stirring, placing the obtained film solution in a vacuum state to remove bubbles, and obtaining a film-forming solution; Step 5, pour the obtained film-forming liquid into a polytetrafluoroethylene mold, place it at room temperature to obtain an active composite membrane, and seal it for dry storage.

2. The method for preparing the starch-based active composite film of Zanthoxylum bungeanum essential oil Pickering emulsion according to claim 1, characterized in that: In the step 1, specifically: The chlorella residue after oil extraction is dissolved in NaOH solution, placed in a constant temperature water bath at 50-65°C and heated with stirring for 12 hours, the solids are washed to a pH of 7, and stirred and bleached with sodium acetate buffer at a stirring temperature of 55-65°C for 3-4 hours until the suspension becomes milky white, centrifuged and washed, then placed in HCl solution for boiling, and allowed to stand at room temperature for 12 hours. The acidified mixture is washed to a pH of 7 and dried to obtain nanocellulose.

3. The method for preparing the starch-based active composite film of Zanthoxylum bungeanum essential oil Pickering emulsion according to claim 1, characterized in that: In the step 2, specifically: Nanocellulose was ultrasonically dispersed in deionized water, and then Zanthoxylum bungeanum essential oil and Tween 20 were added and ultrasonically treated to form a Zanthoxylum bungeanum essential oil Pickering emulsion.

4. The method for preparing the starch-based active composite film of Zanthoxylum bungeanum essential oil Pickering emulsion according to claim 1, characterized in that: In step 3, the mass ratio of corn starch, deionized water and glycerol is 14-18:280-320:4.0-5.6; and the stirring time is 2-4 hours.

5. The method for preparing the starch-based active composite film of Zanthoxylum bungeanum essential oil Pickering emulsion according to claim 1, characterized in that: In step 4, the stirring time is 30 to 60 minutes.

6. The Zanthoxylum bungeanum essential oil Pickering emulsion starch-based active composite film prepared by the preparation method of the Zanthoxylum bungeanum essential oil Pickering emulsion starch-based active composite film as claimed in any one of claims 1 to 5.

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