Method for preparing corn protein zein-sodium alginate composite film embedded with curcumin

Abstract

The application discloses a preparation method of curcumin-embedded zein nanoparticle / sodium alginate composite film and belongs to the technical field of edible composite film preparation. The method comprises the following steps: preparing a zein and curcumin mixture; ultrasonically treating the zein and curcumin mixture; preparing a curcumin-embedded zein nanoparticle suspension by means of an anti-solvent method; preparing a sodium alginate solution; preparing a curcumin-embedded zein nanoparticle / sodium alginate film-forming solution; and forming a film and drying the film to obtain the composite film. The curcumin-embedded zein nanoparticle is prepared by means of the anti-solvent method before the antibacterial agent curcumin is added to the film-forming solution, so as to solve the problems of incompatibility between the curcumin and the water-soluble film-forming matrix and explosive release of the curcumin in the film. Ultrasonic treatment can effectively regulate the physicochemical properties and structure of the curcumin-embedded zein nanoparticle and improve the performance of the composite film.

Description

Technical Field

[0001] This invention relates to the field of edible bioactive preservation film preparation technology, specifically to a zein nanoparticle / sodium alginate film packaging material prepared by using zein and sodium alginate as raw materials, adding the antibacterial agent curcumin, and employing ultrasonic treatment to obtain curcumin-encapsulated zein nanoparticle / sodium alginate film packaging material. Background Technology

[0002] The non-biodegradability of plastic packaging materials not only causes environmental problems but also may release potentially toxic substances that pose a serious risk to food safety. Developing environmentally friendly and sustainable food packaging films is of great significance to the food packaging industry. Therefore, packaging films based on low-cost, abundant, and renewable resources such as proteins, polysaccharides, and lipids have received widespread attention. Bioactive packaging films are a type of food preservation film further developed based on the above-mentioned food packaging films, possessing biological functional activity. They contain active substances such as antibacterial substances or antioxidants; after packaging food, these active substances are released from the film and interact with the food, improving its quality and safety. Currently, bioactive packaging films are considered one of the most innovative packaging types and have broad application prospects in the food packaging industry.

[0003] Curcumin, chemically known as 1,7-di(4-hydroxy-3-methoxyphenyl)-1,6-heptadien-3,5-dione, is a bioactive natural polyphenolic compound extracted from the root of the turmeric plant (Curcuma longa). Curcumin is not only used as a coloring and flavoring agent in food processing but also possesses remarkable biological functional activities. Numerous studies have shown that curcumin exhibits beneficial effects such as wound healing, antioxidant activity, anti-inflammatory properties, antimalarial activity, and antibacterial activity; furthermore, curcumin is non-toxic to humans and remains safe even at extremely high daily doses of 12g. Curcumin can be added to film-forming solutions as an effective antibacterial agent to prepare bioactive packaging films. However, curcumin's unique chemical structure results in poor water solubility, extreme sensitivity to environmental conditions, poor stability, and low bioavailability. Adding curcumin directly to the film-forming solution results in uneven distribution, poor compatibility with the film-forming matrix, and easy loss of biological activity. The resulting composite membrane exhibits unstable mechanical properties, poor membrane formation, weak antibacterial effect, explosive release of active substances, and short-lasting preservation. With the gradual maturation of nanotechnology, encapsulating curcumin with natural macromolecules to form nanoparticles before adding it to the film-forming solution can effectively protect its biological activity (Wang Qiming, Tang Yuwan, Yang Yaxuan, Tang Yu, Li Fuhua, Zhao Jichun, Ming Jian. Research progress on plant polyphenol-protein composite antibacterial membranes [J]. Food and Fermentation Industries, 2018). Compared to adding a simple protein solution, adding macromolecular proteins in nanoparticle form may endow the composite membrane with unique physicochemical properties and structural characteristics.

[0004] Zeadin is the main protein in corn, accounting for approximately 45-50% of the total protein. It contains a large number of hydrophobic nonpolar amino acids, exhibiting a structure that is hydrophilic at both ends and highly hydrophobic on the sides. This unique structure endows zeadin with self-assembly properties, amphiphilicity, controllable particle size, and a wide isoelectric point range. Under certain conditions, zeadin can self-assemble into nanoparticles, which are widely used for the controlled delivery of bioactive substances such as resveratrol, vitamin E, and grape seed extract. Encapsulating bioactive substances with zeadin can effectively protect these substances, and the resulting nanoparticles can achieve controlled release of the active ingredients. Recent studies have shown that encapsulating bioactive substances with natural proteins results in weak and uneven binding between the protein and bioactive substances due to the folded structure of natural proteins and the encapsulation of reactive groups within the molecule. Furthermore, the functional properties of the resulting protein nanoparticles encapsulating bioactive substances are not ideal and require further improvement. Ultrasonic technology, as an emerging non-thermal processing physical technology, has been widely applied in the food industry and related fields. Due to its unique mechanical, cavitation, and thermal effects, ultrasound has attracted much attention in areas such as assisted enzymatic hydrolysis, assisted extraction of bioactive components, and ultrasound-assisted freezing. Recently, ultrasound has been proven to be applicable to the encapsulation of bioactive substances in protein-based biomacromolecules. Previous research by our group found that ultrasound can promote the encapsulation of resveratrol by zein, improving its encapsulation and loading effects; and improving the physicochemical properties and structural characteristics of the resulting composite nanoparticles, such as particle size distribution, polydispersity index, and zeta potential (Liang Qiufang, Ren Xiaofeng, Zhang Xi, et al. Effect of ultrasound on the preparation of resveratrol-loaded zein particles[J]. Journal of Food Engineering, 2017, 221(MAR.):88-94; Ren Xiaofeng, Hou Ting, Liang Qiufang, et al. Effects of frequency ultrasound on the properties of zein-chitosan complexcoacervation for resveratrol encapsulation[J]. Food Chemistry, 2018, 279.). Based on previous research, this invention utilizes ultrasound to regulate the encapsulation of the bioactive substance curcumin in zein to prepare zein-curcumin nanoparticles.

[0005] Sodium alginate is a binary copolymer designed by linking β-D-mannuronic acid and α-L-guluronic acid with (1→4) bonds, and is a natural anionic linear polysaccharide. Sodium alginate has good film-forming ability, but films formed from sodium alginate alone have poor mechanical properties and a certain degree of hydrophilicity. Therefore, it needs to be appropriately modified to improve its film-forming properties (Chen Jingxin, Yang Mingliang, Ge Yonghong, et al. Research progress on edible films of sodium alginate and their application in food preservation [J]. Journal of Bohai University: Natural Science Edition, 2021.). Physical blending modification uses two or more components to change the original composition and structure to achieve the purpose of modification. It mainly involves adding proteins, polysaccharides, lipids, and other synthetic polymers to the sodium alginate film-forming solution to improve its film-forming properties. The mechanical properties and barrier properties of the composite film mainly depend on the properties and compatibility of each polymer. Zeatin nanoparticles exhibit positive charge in aqueous solution, while sodium alginate exhibits negative charge; the two interact strongly in water, readily forming polyelectrolyte complexes, ultimately resulting in a film. Furthermore, zeatin itself possesses excellent film-forming properties and superior vapor barrier capabilities, making it a potential biodegradable material for food packaging and a hot topic in engineering research (Chen Weiyan, Mu Yan, Zhu Aifang, Zhang Baohua. Preparation of zeatin film and evaluation of its preservation effect [J]. Modern Food Science and Technology, 2022, 38(11):141-147.). The addition of curcumin-encapsulated zeatin nanoparticles not only imparts antibacterial activity to the film but also helps improve the structure of the composite film, enhancing its water-blocking and mechanical properties.

[0006] Current research on antibacterial films based on zein and sodium alginate focuses on preparing solutions by blending zein, sodium alginate, and antibacterial agents, and then directly drying them using a casting method to prepare antibacterial films (Liu Xinxin, Liu Zhongdong. Preparation and properties of sodium alginate / zein antibacterial composite film [J]. Food Industry, 2020, 41(4):6.; Jin Fuxing, An antibacterial packaging film material and its preparation method. CN106479196A, 2017.03.08). There are few studies and patents on preparing active packaging films by encapsulating antibacterial agents in zein nanoparticles using nanotechnology and then adding them to polysaccharide-based film-forming solutions. Furthermore, there are no reports on the preparation of zein nanoparticle / sodium alginate composite films encapsulating curcumin using ultrasonic technology. Therefore, this invention utilizes curcumin, zein, and sodium alginate as materials. It employs ultrasound to control the encapsulation of curcumin in zein to form nanoparticles. These curcumin-encapsulated zein nanoparticles are then added to a sodium alginate film-forming solution to develop a novel bioactive food packaging film. This film effectively protects the antibacterial properties of curcumin and addresses issues such as the explosive release of the active ingredient curcumin. Furthermore, this invention incorporates ultrasound technology to address the problems of low bioactive substance loading and poor compatibility between the formed nanoparticles and the film, thereby improving the quality of the bioactive food packaging film. Summary of the Invention

[0007] A zein nanoparticle / sodium alginate composite membrane with curcumin encapsulated in curcumin was prepared by using zein and sodium alginate as the film matrix and adding the antibacterial agent curcumin. The effects of ultrasonic treatment conditions on the antibacterial and mechanical properties of the composite membrane were studied.

[0008] The preparation method of the zein nanoparticle / sodium alginate composite membrane encapsulating curcumin according to the present invention is carried out according to the following steps:

[0009] (1) Take a certain volume fraction of ethanol aqueous solution in a beaker, add zein powder and curcumin powder respectively under magnetic stirring at 1000 r / min and dissolve for 30 min to prepare zein and curcumin solution.

[0010] (2) After uniformly mixing equal volumes of the prepared zein and curcumin solutions to obtain a mixture, the mixture is then treated with ultrasound.

[0011] (3) After ultrasonic treatment, the mixture was magnetically stirred and a certain volume of deionized water was added immediately. After stirring for 10 minutes, the precipitate was centrifuged to prepare a suspension of zein nanoparticles containing curcumin.

[0012] (4) Weigh sodium alginate powder and put it into deionized water. Heat and stir it in a 40°C water bath until it is uniform and free of colloids. Then add 30% glycerol and stir evenly to prepare a sodium alginate film-forming solution with a concentration of 12.5 mg / mL.

[0013] (5) Add the zein nanoparticle suspension containing curcumin prepared in step (3) to the sodium alginate film-forming solution, and stir magnetically for 30 min to obtain a uniform zein nanoparticle / sodium alginate composite film-forming solution containing curcumin.

[0014] (6) Take the film-forming liquid prepared in (5) and cast it on a disposable plastic plate to form a film. Let it stand for 10 minutes and dry it in a constant temperature drying oven at 40℃ for 5 hours.

[0015] (7) Remove the formed composite membrane, cool it to room temperature, and place it in a desiccator for later use (the desiccator contains a saturated K2CO3 solution with a relative humidity of 43%).

[0016] In step (1), the volume fraction of ethanol is 70-90%, preferably 70%; the concentration of curcumin is 2 mg / mL; and the concentration of zein is 10-100 mg / mL, preferably 50 mg / mL.

[0017] The specific working conditions for the ultrasonic treatment in step (2) are as follows: ultrasonic time 5 min-40 min, preferably 20 min; ultrasonic power 20 W / L-100 W / L, preferably 80 W / L; ultrasonic frequency 20 kHz, 35 kHz, 20 / 35 kHz, 35 / 50 kHz, 20 / 35 / 50 kHz, preferably 35 / 50 kHz; ultrasonic interval ratio 5 s / 3 s.

[0018] In step (3), the volume ratio of the added deionized water to the mixed solution is 2:1-5:1, preferably 4:1.

[0019] In step (5), the ratio of the zein nanoparticle suspension containing curcumin and the sodium alginate film-forming solution is 2:1-1:3, with a preferred ratio of 1:1.

[0020] The beneficial effects of this invention are as follows:

[0021] (1) Before adding curcumin to the film-forming solution, the present invention uses zein to encapsulate curcumin to prepare composite nanoparticles, which can effectively solve the problems of incompatibility between curcumin and water-soluble film-forming matrix, explosive release of curcumin in the film, and the lack of long-lasting freshness preservation effect of the prepared active packaging film.

[0022] (2) Compared with adding zein directly to sodium alginate film-forming solution, the addition of zein in the form of nanoparticles significantly improves the mechanical properties and oxygen barrier properties of composite membrane.

[0023] (3) The nanoparticles used in this invention are prepared by ultrasonic treatment. Ultrasonic treatment is a non-thermal, green physical processing method that is widely used in the food industry. Ultrasonic treatment can effectively regulate the physicochemical properties and structure of zein nanoparticles encapsulating curcumin, which can affect the performance of the formed film. (4) This invention uses curcumin, zein and sodium alginate as raw materials to prepare a novel food bioactive packaging film, which improves the added value of zein and is conducive to the development of green and environmentally friendly antibacterial food packaging materials. Attached Figure Description

[0024] Figure 1 Flowchart for the preparation of zein nanoparticle / sodium alginate composite membrane encapsulating curcumin;

[0025] Figure 2 This is a diagram of a multi-mode ultrasonic device; where 1, 2, and 3 are ultrasonic transducers, 4 is a liquid container, 5 is a water bath, 6 is a temperature probe, 7 is a circulating pump, 8 is a computer program controller, and 9, 10, and 11 are ultrasonic controllers for different frequencies. 1, 2, and 3 are the ultrasonic generator, 4 is the liquid container, 5 is the constant temperature water bath, 6 is the temperature probe, 7 is the circulating pump, 8 is the computer program controller, and 9, 10, and 11 are ultrasonic controllers for different frequencies.

[0026] Figure 3 The oxygen permeability of the composite membrane;

[0027] Figure 4 Scanning electron microscope (SEM) images and surface morphology images of different nanoparticles and the composite films they form;

[0028] Figure 5 The circular dichroism spectrum of the composite nanoparticles;

[0029] Figure 6 The infrared spectrum of the composite film;

[0030] Figure 7 The X-ray diffraction pattern of the composite film;

[0031] Figure 8 The TGA spectrum (A) and DTG spectrum (B) of the composite membrane are shown.

[0032] Examples in the figure are: SA, sodium alginate film; Cur@SA, free curcumin / sodium alginate composite film; ZNPs@SA, zein nanoparticles / sodium alginate composite film; ZcNPs@SA, zein nanoparticles encapsulating curcumin / sodium alginate composite film; U-ZcNPs@SA, ultrasound-assisted zein nanoparticles encapsulating curcumin / sodium alginate composite film. Detailed Implementation

[0033] Zeadin was purchased from Sigma-Aldrich; curcumin (98% purity) was purchased from Shanghai Adamas Reagent Co., Ltd.; sodium alginate, ethanol, and glycerol were purchased from Sinopharm Chemical Reagent Co., Ltd.

[0034] The mechanical properties of the composite membrane prepared in the embodiments of this invention are determined as follows: The tensile strength (TS) and elongation at break (EAB) of the composite membrane sample (20×60mm) are measured using a TA-XT2i physical property tester. The test probe is A / TG, the clamping distance is 30mm, and the test speed is 2mm / s. The calculation formulas for TS and EAB are as follows.

[0035] TS = F / (D×W) (1)

[0036] Where: TS—tensile strength, N / mm 2 F—Maximum tension at which the membrane breaks, N; D—Thickness of the membrane being measured, mm; W—Width of the membrane, mm.

[0037] EAB = (L-L0) / L0×100% (2)

[0038] Where: EAB—elongation at break, %; L—distance between the markings when the membrane breaks, mm; L0—original distance between the markings on the membrane, mm.

[0039] The method for determining the antibacterial effect of the composite membrane prepared in the embodiments of this invention is as follows: This patent determines the antibacterial activity of the composite membrane against *Escherichia coli* and *Staphylococcus aureus*. Solid agar culture medium is prepared and, after solidification, sterilized under ultraviolet light for 2 hours to ensure the sterility of the solid culture medium. A 10⁷ CFU / mL suspension of *Escherichia coli* and *Staphylococcus aureus* is prepared, and 0.1 mL is evenly spread onto the corresponding solid culture medium. Five wells are punched in the culture medium using a 5 mm diameter punch and numbered. 50 μL of the film-forming solution from the experimental group and the control group is injected into the punched wells. The mixture is incubated at 37°C for 10 hours. The antibacterial effect of the film-forming solution on bacteria is observed, and the diameter of the inhibition zone is measured using calipers. The measurements are performed in triplicate.

[0040] Abbreviations: SA, sodium alginate film; Cur@SA, free curcumin / sodium alginate composite film; ZNPs@SA, zein nanoparticles / sodium alginate composite film; ZcNPs@SA, zein nanoparticles encapsulated with curcumin / sodium alginate composite film; U-ZcNPs@SA, ultrasound-assisted zein nanoparticles encapsulated with curcumin / sodium alginate composite film.

[0041] Example 1: Optimization of zein concentration in the preparation of curcumin-encapsulated zein nanoparticle / sodium alginate composite membrane

[0042] Figure 1 A flowchart illustrating the preparation of a zein nanoparticle / sodium alginate composite membrane for encapsulating curcumin.

[0043] (1) Take a 70% ethanol aqueous solution in a beaker, add zein powder and curcumin powder under magnetic stirring at 1000 r / min and dissolve for 30 min to prepare zein solutions with concentrations of (10, 20, 40, 50, 100) mg / mL and curcumin solutions with a concentration of 2 mg / mL.

[0044] (2) Take 20 mL of the prepared zein and 20 mL of curcumin solution, mix them evenly to obtain a mixture, and then treat it with ultrasound. Figure 2 The diagram shows a multi-mode ultrasonic device; the ultrasonic processing conditions are: ultrasonic time 20 min; ultrasonic power 80 W / L; ultrasonic frequency 35 / 50 kHz; ultrasonic interval ratio 5 s / 3 s.

[0045] (3) After ultrasonic treatment, the mixture was magnetically stirred and deionized water was added immediately. The volume ratio of deionized water to the mixture was 4:1. After stirring for 10 minutes, the precipitate was centrifuged and the volume was adjusted to 400 mL to prepare a suspension of zein nanoparticles containing curcumin.

[0046] (4) Weigh sodium alginate powder and put it into deionized water. Heat and stir it in a 40°C water bath until it is uniform and free of colloids. Then add 30% glycerol and stir evenly to prepare a sodium alginate film-forming solution with a concentration of 12.5 mg / mL.

[0047] (5) Take the prepared zein nanoparticle suspension containing curcumin and add it to the sodium alginate film-forming solution. The volume ratio of the two is 1:1. After stirring magnetically for 30 minutes, a uniform zein nanoparticle / sodium alginate composite film-forming solution containing curcumin is obtained.

[0048] (6) Take 10 mL of the film-forming solution prepared in (5) and cast it onto a disposable plastic plate to form a film. Let it stand for 10 min and dry it in a constant temperature drying oven at 40℃ for 5 h. Take out the formed composite film, cool it to room temperature, and place it in a desiccator for later use (the desiccator contains a saturated K2CO3 solution with a relative humidity of 43%).

[0049] Table 1 shows the optimization of zein concentration in the zein nanoparticles encapsulating curcumin. It can be seen that the zein concentration significantly affects the mechanical properties of the final composite membrane, while its effect on the antibacterial effect is relatively weak. The composite membrane exhibits the best mechanical properties when the zein concentration is 50 mg / mL, with a TS of 48.32 N / mm. 2 The EBA concentration was 107.4%. The prepared composite membrane exhibited good antibacterial effects, with inhibition zones of 18.43 mm and 16.23 mm for E. coli and S. aureus, respectively, after treatment. Therefore, a concentration of 50 mg / mL of zein was selected for further optimization of the protein membrane preparation process.

[0050] Table 1. Effects of zein concentration on the mechanical properties and antibacterial effect of composite films.

[0051]

[0052] Example 2: Optimization of the ratio of distilled water as an antisolvent for zein nanoparticles in the preparation of curcumin-encapsulated zein nanoparticle / sodium alginate composite membranes.

[0053] (1) Take a 70% ethanol aqueous solution in a beaker, add zein powder and curcumin powder under magnetic stirring at 1000 r / min and dissolve for 30 min to prepare a zein solution with a concentration of 50 mg / mL and a curcumin solution with a concentration of 2 mg / mL.

[0054] (2) Take 20 mL of the prepared zein and 20 mL of curcumin solution and mix them evenly to obtain a mixture. Then, treat it with ultrasound. The ultrasound treatment conditions are: ultrasound time 20 min; ultrasound power 80 W / L; ultrasound frequency 35 / 50 kHz; ultrasound interval ratio 5 s / 3 s.

[0055] (3) After ultrasonic treatment, the mixture was magnetically stirred and deionized water was added immediately. The volume ratio of deionized water to the mixture was 2:1-5:1. After stirring for 10 minutes, the precipitate was centrifuged and the volume was adjusted to 400 mL to prepare a suspension of zein nanoparticles containing curcumin.

[0056] (4) Weigh sodium alginate powder and put it into deionized water. Heat and stir it in a 40°C water bath until it is uniform and free of colloids. Then add 30% glycerol and stir evenly to prepare a sodium alginate film-forming solution with a concentration of 12.5 mg / mL.

[0057] (5) Take the prepared zein nanoparticle suspension containing curcumin and add it to the sodium alginate film-forming solution. The volume ratio of the two is 1:1. After stirring magnetically for 30 minutes, a uniform zein nanoparticle / sodium alginate composite film-forming solution containing curcumin is obtained.

[0058] (6) Take 10 mL of the film-forming solution prepared in (5) and cast it onto a disposable plastic plate to form a film. Let it stand for 10 min and dry it in a constant temperature drying oven at 40℃ for 5 h. Take out the formed composite film, cool it to room temperature, and place it in a desiccator for later use (the desiccator contains a saturated K2CO3 solution with a relative humidity of 43%).

[0059] Table 2 shows the optimization of the distilled water addition ratio during the preparation of zein nanoparticles containing curcumin. It can be seen that the addition ratio of distilled water significantly affects the mechanical properties of the final composite membrane, while its effect on the antibacterial effect is relatively weak. The composite membranes prepared with distilled water addition ratios of 4:1 and 5:1 exhibited the best mechanical properties, with no significant difference between the two ratios. The composite membrane with the worst antibacterial effect was obtained with a distilled water addition ratio of 2:1. There were no significant differences in the antibacterial effects among composite membranes with other distilled water addition ratios. When the distilled water addition ratio was 4:1, the TS of the composite membrane was 46.87 N / mm², and the EBA was 105.23%. The inhibition zones of the composite membrane against E. coli and S. aureus were 18.33 mm and 16.89 mm, respectively. Taking all factors into consideration, a 4:1 ratio of distilled water to antisolvent was selected for further optimization of the composite membrane preparation process.

[0060] Table 2. Effects of the proportion of distilled water added as an antisolvent during nanoparticle preparation on the mechanical properties and antibacterial effect of the composite membrane.

[0061]

[0062] Example 3: Optimization of ultrasonic time for preparing zein nanoparticles / sodium alginate composite membranes encapsulating curcumin.

[0063] (1) Take a 70% ethanol aqueous solution in a beaker, add zein powder and curcumin powder under magnetic stirring at 1000 r / min and dissolve for 30 min to prepare a zein solution with a concentration of 50 mg / mL and a curcumin solution with a concentration of 2 mg / mL.

[0064] (2) Take 20 mL of the prepared zein and 20 mL of curcumin solution and mix them evenly to obtain a mixture. Then, treat it with ultrasound. The ultrasound treatment conditions are: ultrasound time 5-40 min; ultrasound power 80 W / L; ultrasound frequency 35 / 50 kHz; ultrasound interval ratio 5 s / 3 s.

[0065] (3) After ultrasonic treatment, the mixture was magnetically stirred and deionized water was added immediately. The volume ratio of deionized water to the mixture was 4:1. After stirring for 10 minutes, the precipitate was centrifuged and the volume was adjusted to 400 mL to prepare a suspension of zein nanoparticles containing curcumin.

[0066] (4) Weigh sodium alginate powder and put it into deionized water. Heat and stir it in a 40°C water bath until it is uniform and free of colloids. Then add 30% glycerol and stir evenly to prepare a sodium alginate film-forming solution with a concentration of 12.5 mg / mL.

[0067] (5) Take the prepared zein nanoparticle suspension containing curcumin and add it to the sodium alginate film-forming solution. The volume ratio of the two is 1:1. After stirring magnetically for 30 minutes, a uniform zein nanoparticle / sodium alginate composite film-forming solution containing curcumin is obtained.

[0068] (6) Take 10 mL of the film-forming solution prepared in (5) and cast it onto a disposable plastic plate to form a film. Let it stand for 10 min and dry it in a constant temperature drying oven at 40℃ for 5 h. Take out the formed composite film, cool it to room temperature, and place it in a desiccator for later use (the desiccator contains a saturated K2CO3 solution with a relative humidity of 43%).

[0069] Table 3 shows the optimization of ultrasonic treatment time during the preparation of zein nanoparticles encapsulating curcumin. It can be seen that the ultrasonic treatment time significantly affects the mechanical properties and antibacterial effect of the final composite membrane. The composite membranes prepared with ultrasonic treatment times of 20 min and 30 min exhibited the best mechanical properties and antibacterial effect, with no significant difference between the two conditions. When the ultrasonic treatment time was 20 min, the TS of the composite membrane was 45.03 N / mm. 2 The EBA content was 107.40%; the inhibition zones of the composite membrane against E. coli and S. aureus were 18.55 mm and 17.09 mm, respectively. Based on the principle of energy conservation and comprehensive consideration, an ultrasonic treatment time of 20 min was selected for the next step of optimizing the composite membrane preparation process.

[0070] Table 3. Effects of ultrasonic treatment time on the mechanical properties and antibacterial effect of the composite membrane.

[0071]

[0072] Example 4: Optimization of ultrasonic power for zein nanoparticles in the preparation of curcumin-encapsulated composite membranes / sodium alginate.

[0073] (1) Take a 70% ethanol aqueous solution in a beaker, add zein powder and curcumin powder under magnetic stirring at 1000 r / min and dissolve for 30 min to prepare a zein solution with a concentration of 50 mg / mL and a curcumin solution with a concentration of 2 mg / mL.

[0074] (2) Take 20 mL of the prepared zein and 20 mL of curcumin solution and mix them evenly to obtain a mixture. Then, treat it with ultrasound. The ultrasound treatment conditions are: ultrasound time 20 min; ultrasound power 20 W / L-100 W / L; ultrasound frequency 35 / 50 kHz; ultrasound interval ratio 5 s / 3 s.

[0075] (3) After ultrasonic treatment, the mixture was magnetically stirred and deionized water was added immediately. The volume ratio of deionized water to the mixture was 4:1. After stirring for 10 minutes, the precipitate was centrifuged and the volume was adjusted to 400 mL to prepare a suspension of zein nanoparticles containing curcumin.

[0076] (4) Weigh sodium alginate powder and put it into deionized water. Heat and stir it in a 40°C water bath until it is uniform and free of colloids. Then add 30% glycerol and stir evenly to prepare a sodium alginate film-forming solution with a concentration of 12.5 mg / mL.

[0077] (5) Take the prepared zein nanoparticle suspension containing curcumin and add it to the sodium alginate film-forming solution. The volume ratio of the two is 1:1. After stirring magnetically for 30 minutes, a uniform zein nanoparticle / sodium alginate composite film-forming solution containing curcumin is obtained.

[0078] (6) Take 10 mL of the film-forming solution prepared in (5) and cast it onto a disposable plastic plate to form a film. Let it stand for 10 min and dry it in a constant temperature drying oven at 40℃ for 5 h. Take out the formed composite film, cool it to room temperature, and place it in a desiccator for later use (the desiccator contains a saturated K2CO3 solution with a relative humidity of 43%).

[0079] Table 4 shows the optimization of ultrasonic power during the preparation of zein nanoparticles encapsulating curcumin. It can be seen that ultrasonic power significantly affects the mechanical properties and antibacterial effect of the final composite membrane. When the ultrasonic power is 80 W / L, the composite membrane exhibits the best mechanical properties and antibacterial effect, with a total stoichiometry (TS) of 46.13 N / mm. 2The EBA content was 108.23%; the inhibition zones of the composite membrane against E. coli and S. aureus were 19.23 mm and 18.11 mm, respectively. Taking all factors into consideration, an ultrasonic power of 80 W / L was selected for further optimization of the composite membrane preparation process.

[0080] Table 4. Effects of ultrasonic power on the mechanical properties and antibacterial effect of composite membranes

[0081]

[0082] Example 5: Optimization of ultrasonic frequency of nanoparticles in the preparation of zein nanoparticle / sodium alginate composite membrane encapsulating curcumin.

[0083] In the prepared state, zein powder and curcumin powder were added and dissolved for 30 minutes to prepare zein solutions with a concentration of 50 mg / mL and curcumin solutions with a concentration of 2 mg / mL.

[0084] (2) Take 20 mL of the prepared zein and 20 mL of curcumin solution and mix them evenly to obtain a mixture. Then, treat it with ultrasound. The ultrasound treatment conditions are: ultrasound time 20 min; ultrasound power 80 W / L; ultrasound frequency 20 kHz, 35 kHz, 20 / 35 kHz, 35 / 50 kHz, 20 / 35 / 50 kHz; ultrasound interval ratio 5 s / 3 s.

[0085] (3) After ultrasonic treatment, the mixture was magnetically stirred and deionized water was added immediately. The volume ratio of deionized water to the mixture was 4:1. After stirring for 10 minutes, the precipitate was centrifuged and the volume was adjusted to 400 mL to prepare a suspension of zein nanoparticles containing curcumin.

[0086] (4) Weigh sodium alginate powder and put it into deionized water. Heat and stir it in a 40°C water bath until it is uniform and free of colloids. Then add 30% glycerol and stir evenly to prepare a sodium alginate film-forming solution with a concentration of 12.5 mg / mL.

[0087] (5) Take the prepared zein nanoparticle suspension containing curcumin and add it to the sodium alginate film-forming solution. The volume ratio of the two is 1:1. After stirring magnetically for 30 minutes, a uniform zein nanoparticle / sodium alginate composite film-forming solution containing curcumin is obtained.

[0088] (6) Take 10 mL of the film-forming solution prepared in (5) and cast it onto a disposable plastic plate to form a film. Let it stand for 10 min and dry it in a constant temperature drying oven at 40℃ for 5 h. Take out the formed composite film, cool it to room temperature, and place it in a desiccator for later use (the desiccator contains a saturated K2CO3 solution with a relative humidity of 43%).

[0089] Table 5 shows the optimization of ultrasonic frequency during the preparation of zein nanoparticles encapsulating curcumin. It can be seen that the choice of ultrasonic frequency significantly affects the mechanical properties and antibacterial effect of the final composite membrane. The membrane exhibits the best mechanical properties at ultrasonic frequencies of 20 / 35 kHz and 20 / 35 / 50 kHz, with no significant difference in mechanical properties among the prepared membranes. The composite membranes show the best antibacterial effect at ultrasonic frequencies of 20 / 35 kHz, 20 / 50 kHz, and 20 / 35 / 50 kHz, with no significant difference in antibacterial effect among the membranes. When the ultrasonic treatment frequency is 20 / 35 kHz, the TS of the prepared composite membrane is 46.34 N / mm². 2 The EBA content was 108.32%; the inhibition zones of the composite membrane against E. coli and S. aureus were 18.13 mm and 16.98 mm, respectively. Taking all factors into consideration, an ultrasonic frequency of 20 / 35 kHz was selected for further optimization of the composite membrane preparation process.

[0090] Table 5. Effects of ultrasonic frequency on the mechanical properties and antibacterial effect of composite membranes.

[0091]

[0092] Example 6: Optimization of the volume of zein suspension and sodium alginate film-forming solution in the preparation of zein-encapsulated curcumin nanoparticle / sodium alginate composite membrane.

[0093] (1) Take a 70% ethanol aqueous solution in a beaker, add zein powder and curcumin powder under magnetic stirring at 1000 r / min and dissolve for 30 min to prepare a zein solution with a concentration of 50 mg / mL and a curcumin solution with a concentration of 2 mg / mL.

[0094] (2) Take 20 mL of the prepared zein and 20 mL of curcumin solution and mix them evenly to obtain a mixture. Then, treat it with ultrasound. The ultrasound treatment conditions are: ultrasound time 20 min; ultrasound power 80 W / L; ultrasound frequency 35 / 50 kHz; ultrasound interval ratio 5 s / 3 s.

[0095] (3) After ultrasonic treatment, the mixture was magnetically stirred and deionized water was added immediately. The volume ratio of deionized water to the mixture was 4:1. After stirring for 10 minutes, the precipitate was centrifuged and the volume was adjusted to 400 mL to prepare a suspension of zein nanoparticles containing curcumin.

[0096] (4) Weigh sodium alginate powder and put it into deionized water. Heat and stir it in a 40°C water bath until it is uniform and free of colloids. Then add 30% glycerol and stir evenly to prepare a sodium alginate film-forming solution with a concentration of 12.5 mg / mL.

[0097] (5) Take the prepared zein nanoparticle suspension containing curcumin and add it to the sodium alginate film-forming solution. The volume ratio of the two is 2:1-1:3. After stirring magnetically for 30 minutes, a uniform zein nanoparticle / sodium alginate composite film-forming solution containing curcumin is obtained.

[0098] (6) Take 10 mL of the film-forming solution prepared in (5) and cast it onto a disposable plastic plate to form a film. Let it stand for 10 min and dry it in a constant temperature drying oven at 40℃ for 5 h. Take out the formed composite film, cool it to room temperature, and place it in a desiccator for later use (the desiccator contains a saturated K2CO3 solution with a relative humidity of 43%).

[0099] Table 6 shows the optimized volume ratio of the curcumin-encapsulated zein nanoparticle suspension and the sodium alginate film-forming solution during the composite membrane preparation process. It can be seen that the choice of their volume ratio significantly affects the mechanical properties and antibacterial effect of the final composite membrane. When the volume ratio is 1:1, the TS of the prepared composite membrane is 47.21 N / mm². 2 The EBA content was 106.43%; the inhibition zones of the composite membrane against E. coli and S. aureus were 18.33 mm and 17.89 mm, respectively. Therefore, a volume ratio of zein nanoparticle suspension containing curcumin and sodium alginate film-forming solution of 1:1 was selected for the preparation of the composite membrane.

[0100] Table 6. Effects of the volume ratio of curcumin-encapsulated zein suspension and sodium alginate film-forming solution on the mechanical properties and antibacterial effects of the composite membrane.

[0101]

[0102] Physicochemical properties and structural characterization of zein nanoparticle / sodium alginate composite membranes encapsulating curcumin.

[0103] Based on the six embodiments, a zein nanoparticle suspension containing curcumin and a sodium alginate composite membrane were prepared using the optimized preparation conditions of the composite membrane, and the physicochemical properties and structure were characterized.

[0104] (1) Oxygen transmission rate

[0105] Test Method: The oxygen permeation rate (OP) was determined by slightly modifying the ASTM D3985 standard method. The membrane sample was conditioned at 25°C and 43% RH for 2 days. Then, the membrane sample was placed over a weighing bottle containing 20g of deoxidizer, and the edges of the membrane were sealed to the weighing bottle with Vaseline and secured with a rubber band. The weighing bottle was placed in a desiccator containing a saturated BaCl2 solution. The sample weight was measured after 48 hours. The OP value of the composite membrane was calculated using the following formula.

[0106]

[0107] where: Δm / Δt - the increment of oxygen transferred through the film surface per unit time, g / h; A - the water vapor permeation area, m 2 ;

[0108] Test results: Oxygen is prone to cause food oxidation, rancidity and promote the growth of some aerobic microorganisms. Measuring the oxygen permeability of the composite film is a very important indicator to evaluate its fresh-keeping effect. The smaller the oxygen permeability of the film, the better the performance of the fresh-keeping film. It can be seen from Figure 3 that the OP values of composite films with different raw material compositions are significantly different; the order of the films with increasing OP values is SA < Cur@SA < ZNPs@SA < ZcNPs@SA < U-ZcNPs@SA. Among them, the SA film has the largest OP value, indicating the worst oxygen barrier performance. The addition of zein nanoparticles, especially zein nanoparticles encapsulating curcumin, significantly reduces its OP value, indicating that the addition of composite nanoparticles improves the oxygen barrier performance of the film. This result also confirms that the proteoglycan composite film helps to improve the oxygen barrier performance of the film. The ZcNPs@SA film prepared by ultrasonic wave has the smallest OP value, indicating that ultrasonic preparation of nanoparticles helps to reduce the oxygen permeability of the film. The reason may be that ultrasonic treatment reduces the particle size of the nanoparticles, improving the uniformity of the prepared nanoparticles; thus making the nanoparticles more uniformly distributed in the film-forming solution, enhancing the intermolecular interaction between zein and sodium alginate, and thus improving its oxygen barrier performance. Generally speaking, the U-ZcNPs@SA film exhibits excellent oxygen barrier properties, can effectively delay the autoxidation effect of food, and also indirectly shows that the prepared U-ZcNPs@SA film has strong antioxidant effects.

[0109] (2) Scanning electron microscopy and apparent morphology diagrams of the composite film

[0110] Test method: Use a field emission scanning electron microscope (SEM) to observe the microstructure of the nanoparticles and the microstructure of the surface and cross-section of the composite film at an acceleration voltage of 15 kV. Immerse the composite film in liquid nitrogen and obtain the cross-section of the composite film after natural fracture.

[0111] Test results: Figure 4The images displayed are SEM images of different nanoparticles and the resulting composite films. The SEM images of the nanoparticles show that the zein powder is unevenly distributed, with most particles being ellipsoidal; the curcumin powder appears as irregular and uneven flakes, while ZNPs exhibit more regular spherical shapes, although their distribution is still uneven, though less so than that of the zein powder; the uniformity of ZcNPs loaded with curcumin is significantly improved, indicating that curcumin is successfully embedded in the zein nanoparticles, but their dispersion is poor, resulting in aggregation; compared to the partially aggregated ZcNPs, the uniformity of U-ZcNPs is further improved, and their particle size is significantly reduced; closer observation reveals certain connections between the nanoparticles, possibly due to intermolecular interactions arising from nano-ionic bonds.

[0112] The appearance of the composite membranes reveals that Cur@SA and ZNPs@SA have rough surfaces, especially Cur@SA, which contains numerous protruding particles. This is likely due to the incompatibility between curcumin and sodium alginate, leading to a large accumulation of hydrophobic curcumin on the surface of the composite membrane. The SA polysaccharide membrane has a smooth, flat, and dense surface with an orderly texture, indicating that the SA polysaccharide solution formed the membrane was uniform and formed a homogeneous structure after drying. Compared to ZNPs@SA, ZcNPs@SA has a relatively smooth surface with no large number of protruding small particles, only some protruding polymers. This suggests that the encapsulation of curcumin helps improve the appearance of the composite membrane. This may be because the curcumin in the zein composite nanoparticles interacts not only with zein but also with sodium alginate. Compared to ZcNPs@SA, the U-ZcNPs@SA composite membrane has a more uniform color. Careful observation revealed the absence of small particles on the membrane surface, reduced surface roughness, and more uniform texture. The cross-sectional height of the prepared composite membrane is also lower. These results indicate that ultrasonic treatment reduces the particle size of the composite nanoparticles and promotes the interaction between the composite nanoparticles and SA. This explains the improved mechanical properties and decreased oxygen permeability of the composite membrane after ultrasonic treatment.

[0113] (3) Circular dichroism spectroscopy (CD)

[0114] Experimental method: The composite sample was diluted 400 times and equilibrated at room temperature (23±2℃) for 1 hour. After subtracting the solvent background, a spectral scan was performed. The scanning wavelength range was 190-250 nm, the optical path length of the sample cell was 0.1 cm, and the experimental value was the average of three scans. The CD spectrum of the sample was measured according to the test parameters of the calibration sample, and the secondary structure of the measured sample was calculated by selecting an appropriate reference dataset.

[0115] Experimental results: CD diagrams of different nanoparticles are shown below. Figure 5As shown, the far-ultraviolet CD spectrum (190-240 nm) can reflect the secondary structure of the sample, including α-helices, β-sheets, β-turns, and random coil conformations. For the ZNPs complex sample, its CD spectrum has a positive peak near 197.5 nm and negative peaks at 211.5 nm and 227 nm, which are peaks of partial α-helical structures, while the average residual ellipticity at 219 nm can indicate the content of β-sheet structures; in the curve of the ZcNPs complex sample loaded with curcumin, the amplitude of this peak gradually increases, which to some extent reflects the formation of protein nanofiber structures. During the self-assembly of proteins into nanofibers, their repeating substructures consist of β chains perpendicular to the fiber axis, which extend to form infinitely long and unbranched antiparallel β-sheets. Therefore, the β-sheet structure in the ZcNPs complex increases. Conversely, the α-helix content and β-sheet content decrease, while the β-turn content increases in the U-ZcNPS complex. This also leads to the recombination and unfolding of the complex molecules and further changes in their secondary structure. The structural changes of zein induced by ultrasound indirectly indicate that ultrasound treatment alters the intermolecular interactions. The cavitation effect during ultrasound transmission may lead to the formation of more hydrogen bonds and stronger hydrophobic interactions between zein and curcumin.

[0116] (4) Attenuated total reflectance infrared spectrum

[0117] Experimental method: The FTIR spectra of the composite film were recorded using an attenuated total reflectance Fourier transform infrared spectrometer (ATR-FTIR), with a wavelength scanning range of 4000-600 cm⁻¹. -1 The number of scans was 16, and the resolution was 4cm. -1 .

[0118] Experimental results: FTIR displays of different composite films showed... Figure 6 The FTIR plot of ZNPs@SA shows that after adding zein nanoparticles to the sodium alginate film-forming solution, the peak values ​​of the O–H and N–H stretching vibrations of the protein increased from 3254 cm⁻¹. -1 Move to 3265cm -1 This indicates the formation of intermolecular hydrogen bonds between zein and sodium alginate. The composite membrane at 1548 cm⁻¹ correlated with amide I and amide II... -1 The presence of an absorption peak at 1000 cm⁻¹ indicates that the secondary structure of zein in the ZNPs@SA film has changed due to the interaction between the amino groups of the protein and the hydroxyl groups of sodium alginate. Cur@SA shows an absorption peak at 1000 cm⁻¹. -1 -1600cm -1Several characteristic absorption peaks were observed at 2935 cm⁻¹, while these peaks were not completely observed in ZcNPs@SA. This is because the hydrogen bonding or hydrophobic interaction between curcumin and zein and sodium alginate restricts the stretching and bending of the chemical bonds in curcumin, causing most of the characteristic peaks of curcumin in the complex to disappear. This indicates that directly adding curcumin to the sodium alginate film-forming solution cannot successfully encapsulate curcumin. However, encapsulating curcumin with zein before adding the resulting nanoparticles to the film-forming solution can effectively protect curcumin and facilitate the slow release of its antibacterial activity in the later stages. Compared with SA and ZNPs@SA films, ZcNPs@SA films showed better absorption at 2935 cm⁻¹. -1 -2886cm -1 The peak narrows at 1600 cm⁻¹. -1 1407cm -1 1296cm -1 1026cm -1 The absorption peak intensity decreased at 2935 cm⁻¹, a result likely attributed to the interactions between curcumin, zein, and sodium alginate (e.g., hydrogen bonds, π–π stacking, hydrophobic interactions, and van der Waals forces). Compared to ZcNPs@SA films, the ultrasonically treated U-ZcNPs@SA film showed a lower absorption peak intensity at 2935 cm⁻¹. -1 -2886cm -1 The peak intensity decreased significantly, with the vibration peak value decreasing from 3266 cm⁻¹. -1 Moved to 3269cm -1 The reason for these results is that ultrasonic treatment alters the secondary structure of zein, promoting the exposure of intramolecular bonds and changing the interaction between zein and curcumin. This alters the surface microstructure and exposed bonds of the formed nanoparticles, indirectly enhancing the intermolecular / intramolecular binding forces of the composite film and promoting non-covalent cross-linking, resulting in tighter molecular bonding. This helps to further explain why ultrasonic treatment improves the surface microstructure of the film.

[0119] (4) X-ray diffraction analysis

[0120] Experimental method: The crystal structure of the composite film sample was determined using an X-ray diffractometer (XRD, D8 ADVANCE). The XRD pattern of the sample was obtained under the conditions of a diffraction angle (2θ) of 5°-80° in the scanning area and a scanning speed of 5° / min.

[0121] Experimental results: Figure 7XRD patterns of different types of membranes were observed. XRD measurements can be used to detect the crystallization state of curcumin, and to observe the encapsulation effect of zein on it, as well as the effect of ultrasonic treatment on the structural characteristics of the prepared composite membrane. The SA membrane exhibits a broad peak near 21.22°, which is wider and flatter than other membranes, indicating that its molecular arrangement is more ordered and that sodium alginate is amorphous. The characteristic crystalline absorption peaks of Cur@SA are mainly distributed in the range of 2θ = 17.04° and 21.26-26.10°, showing a crystalline state with multiple sharp characteristic diffraction peaks. This proves that sodium alginate cannot completely encapsulate curcumin. If curcumin is directly added to the sodium alginate film-forming solution, the resulting composite membrane cannot effectively protect the biological functional activity of curcumin. This result is consistent with the results of FTIR spectroscopy.

[0122] In the XRD patterns, both ZNPs@SA and SA showed a broad peak around 21.16°, but their peak positions differed, with the addition of ZNPs increasing the peak intensity. This indicates that both films exist in an amorphous structure, and the difference in the XRD structure of ZNPs@SA is attributed to the intermolecular interaction between zein and sodium alginate, which alters the film's structure. Compared to ZNPs@SA, ZcNPs@SA exhibited similar peak positions and intensities, indicating that curcumin was successfully encapsulated in the composite film, effectively protecting its biological activity. SA, Cur@SA, ZNPs@SA, and ZcNPs@SA films showed a small sharp peak around 11.04°, which disappeared in the U-ZcNPs@SA composite film; furthermore, the diffraction peak of the U-ZcNPs@SA composite film changed from 20.76° to 21.04°, and after ultrasonic treatment, the peak of U-ZcNPs@SA became wider and flatter compared to ZNPs@SA and ZcNPs@SA. The above results demonstrate that ultrasonic treatment enhances the compatibility of macromolecules in the film, attributed to the more ordered molecular arrangement of the composite film and the enhanced intermolecular forces exhibited by FTIR. Furthermore, the cavitation effect of ultrasound alters the macromolecular structure, exposing more groups in the composite nanoparticles that can interact with sodium alginate, resulting in a more ordered arrangement of the final film structure. In addition, the physical impact of ultrasound induces a strong mechanical stirring-like effect, increasing the frequency of intermolecular collisions in the composite nanoparticles, reducing the particle size, and resulting in a more uniform distribution. These structural changes further explain why ultrasound enhances the mechanical and oxygen barrier properties of the U-ZcNPs@SA film.

[0123] (5) Thermal property analysis

[0124] Experimental method: Take an appropriate amount of sample and test the thermal stability of the composite membrane using an integrated thermal analyzer STA 449F3 Jupiter. The sample is heated from 30℃ to 500℃ at a rate of 10℃ / min under a N2 atmosphere, and the nitrogen flow rate in the sample chamber is 20mL / min.

[0125] Experimental results: The TGA and DTG of different composite membranes are shown in the figures below. Figure 8 A and Figure 8 B. Thermodynamics (TGA) was used to study the thermal stability and kinetic properties associated with the degradation process of biocomposite membranes, such as weight loss and maximum decomposition temperature, and the results are displayed as TGA / DTG thermal curves in the range of 30–600 °C. The TGA curves show that all film samples exhibit similar thermal stability trends, mainly consisting of three weight loss stages. The first stage of weight loss occurs between 30 and 124 °C, due to the evaporation of adsorbed water and some remaining solvent. The second stage of weight loss occurs between 124 and 276 °C, which is related to the degradation of glycerol, intramolecular interactions, and the weakening or loss of intermolecular forces. For the third stage of weight loss, the degradation rate of the film occurs approximately between 276 °C and 350 °C, attributed to the decomposition of the film sample matrix. For the second and third stages, the thermal decomposition temperatures of different film samples, from highest to lowest, are U-ZcNPs@SA > Cur@SA > ZNPs@SA > ZcNPs@SA > SA, indicating that the addition of nanoparticles improves the thermal stability of the film compared to the pure film, especially U-ZcNPs@SA, whose thermal stability is significantly higher than other composite films. The slightly lower thermal stability of the ZcNPs@SA film compared to the standard ZcNPs@SA film may be due to the reaction between zein and curcumin during encapsulation, which disrupts the original molecular arrangement and reduces thermal stability. A decomposition peak was observed in both the ZcNPs@SA and U-ZcNPs@SA curves, but this peak was not observed in the ZNPs@SA, Cur@SA, and SA curves, indicating that the thermal stability of the ternary composite differs from that of the binary composite. The results clearly show that ultrasonic treatment increases the thermal decomposition temperature of the film, indicating that the thermal stability of the U-ZcNPs@SA film is significantly higher than that of the ZcNPs@SA film. Ultrasonic treatment homogenizes the nanoparticles, allowing smaller nanoparticles to be uniformly distributed in the film-forming solution, inducing an ordered molecular arrangement, thereby improving the thermal stability of the composite film.

Claims

1. A process for the preparation of curcumin-embedded zein nanoparticles / sodium alginate composite films, characterized by Follow these steps: (1) Take a certain volume fraction of ethanol aqueous solution in a beaker, add zein powder and curcumin powder respectively under magnetic stirring at 1000 r / min and dissolve for 30 min to prepare zein and curcumin solution. (2) After uniformly mixing equal volumes of the prepared zein and curcumin solution to obtain a mixture, the mixture is then treated with ultrasound. (3) After ultrasonic treatment, the mixture was magnetically stirred and a certain volume of deionized water was added immediately. After stirring for 10 min, the precipitate was centrifuged to prepare a suspension of zein nanoparticles containing curcumin. (4) Weigh sodium alginate powder and put it into deionized water. Heat and stir it in a 40°C water bath until it is uniform and free of colloids. Then add 30% glycerol and stir evenly to prepare a sodium alginate film-forming solution with a concentration of 12.5 mg / mL. (5) Add the zein nanoparticle suspension containing curcumin prepared in step (3) to the sodium alginate film-forming solution, and stir magnetically for 30 min to obtain a uniform zein nanoparticle / sodium alginate composite film-forming solution containing curcumin. (6) Take the film-forming liquid prepared in (5) and cast it on a disposable plastic plate to form a film. Let it stand for 10 min and dry it in a constant temperature drying oven at 40℃ for 5 h. (7) Remove the formed composite membrane, cool it to room temperature, and place it in a desiccator for later use. The desiccator contains a saturated K2CO3 solution with a relative humidity of 43%. In step (1), the volume fraction of ethanol is 70-90%, the concentration of curcumin is 2 mg / mL, and the concentration of zein is 10-100 mg / mL. The specific working conditions for the ultrasonic treatment in step (2) are as follows: ultrasonic time 5 min-40 min; ultrasonic power 20 W / L-100 W / L; ultrasonic frequency 20 kHz, 35 kHz, 20 / 35 kHz, 20 / 50 kHz, 20 / 35 / 50 kHz; ultrasonic interval ratio 5 s / 3 s. The volume ratio of deionized water to the mixture in step (3) is 2:1-5:1; The ratio of the zein nanoparticle suspension containing curcumin and the sodium alginate film-forming solution described in step (5) is 2:1-1:

3.

2. The method for preparing the zein nanoparticle / sodium alginate composite membrane encapsulating curcumin according to claim 1, characterized in that... In step (1), the volume fraction of ethanol is 70%, the concentration of curcumin is 2 mg / mL, and the concentration of zein is 50 mg / mL.

3. The method for preparing the zein nanoparticle / sodium alginate composite membrane encapsulating curcumin according to claim 1, characterized in that... The specific working conditions for the ultrasonic treatment in step (2) are: ultrasonic time of 20 min, ultrasonic power of 80 W / L, and ultrasonic frequency of 20 / 50 kHz.

4. The method for preparing the zein nanoparticle / sodium alginate composite membrane encapsulating curcumin according to claim 1, characterized in that... The volume ratio of deionized water to the mixture in step (3) is 4:

1.

5. The method for preparing the zein nanoparticle / sodium alginate composite membrane encapsulating curcumin according to claim 1, characterized in that... The ratio of the zein nanoparticle suspension containing curcumin and the sodium alginate film-forming solution described in step (5) is 1:1.

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