Bio-based degradable food antioxidant packaging film and preparation process thereof

Abstract

The invention provides a bio-based degradable food antioxidant packaging film and a preparation process thereof, the packaging film comprises a hydrophilic bio-based film material matrix and temperature response type antioxidant composite microspheres uniformly dispersed in the hydrophilic bio-based film material matrix, and the film material matrix at least comprises carrageenan, a plasticizer and a network enhancing component. The temperature response type antioxidant composite microsphere is of a multi-layer core-shell structure and sequentially comprises a hydrophobic protein-antioxidant composite inner core, a hydrophilic polysaccharide transition coating layer and a temperature response type polymer outer layer from inside to outside. Through hydrophobic interaction, electrostatic interaction and a synergistic effect of reversible volume change of the temperature response type polymer in a food refrigeration and transportation temperature zone, stable dispersion, long-term retention and controllable release along with environment temperature change of a hydrophobic antioxidant in a hydrophilic membrane material are realized; the antioxidant function is introduced, meanwhile, the good mechanical property and barrier property are kept, and the antioxidant fresh-keeping packaging film is suitable for antioxidant fresh-keeping packaging in the food cold chain storage and transportation process.

Description

Technical Field

[0001] This invention relates to the technical field of food packaging materials, and in particular to a bio-based biodegradable food antioxidant packaging film and its preparation process. Background Technology

[0002] With increasing environmental awareness and the continued implementation of policies to control plastic pollution, bio-based biodegradable food packaging materials are gradually becoming an important development direction to replace traditional petroleum-based plastic packaging. While fulfilling basic packaging functions, bio-based food packaging films, when further incorporating antioxidant active ingredients, can effectively delay oxidative deterioration of food during storage and transportation, extending shelf life and demonstrating significant application value.

[0003] Carrageenan, a widely available natural hydrophilic polysaccharide, possesses excellent film-forming and biodegradable properties and has been widely used in the preparation of food packaging films. However, commonly used natural antioxidants such as curcumin are significantly hydrophobic and tend to aggregate and migrate within the hydrophilic carrageenan matrix, leading to unstable antioxidant effects and potentially damaging the mechanical and barrier properties of the film material.

[0004] In the prior art, the encapsulation of hydrophobic antioxidants by proteins or polysaccharides has been used to improve their dispersibility, but most methods only achieve physical encapsulation and are difficult to regulate the release behavior of antioxidants during food refrigeration and transportation. On the other hand, temperature-responsive polymers have been used for controlled release in the field of drug delivery, but their direct application in food packaging systems, especially in the synergistic design with natural polysaccharide film materials, still faces problems of insufficient structural matching and process adaptability.

[0005] Therefore, there is an urgent need for a food packaging material that can stably disperse hydrophobic antioxidants in hydrophilic bio-based membrane materials, achieve temperature-responsive release within the temperature range relevant to food refrigeration and transportation, and simultaneously take into account the mechanical and barrier properties of the membrane material.

[0006] In view of this, the inventors have specifically designed a bio-based biodegradable food antioxidant packaging film and its preparation process, which leads to this invention. Summary of the Invention

[0007] The present invention aims to address the problems in the prior art where hydrophobic antioxidants have poor dispersibility, insufficient stability, and release behavior that is difficult to match with food storage temperature conditions in hydrophilic bio-based membrane materials.

[0008] To solve the above problems, the technical solution of the present invention is as follows: A bio-based biodegradable food antioxidant packaging film includes a carrageenan-based hydrophilic film matrix and temperature-responsive antioxidant composite microspheres dispersed in the film matrix.

[0009] The temperature-responsive antioxidant composite microspheres have a three-layer core-shell structure, which, from the inside out, comprises: (1) Core layer: a nanoscale composite core formed by encapsulating curcumin in zein via antisolvent precipitation; (2) Intermediate coating layer: Pectin coating layer formed by electrostatic adsorption under pH 3.0–4.0 conditions; (3) Outer layer: a poly-N-isopropylacrylamide (PNIPAM) layer formed by in-situ polymerization on the surface of the pectin coating layer.

[0010] The PNIPAM layer has a low critical dissolution temperature of 28–32°C, and the temperature-responsive antioxidant composite microspheres have an average particle size of 150–250 nm and are dispersed in carrageenan-based film at a ratio of 5–8 parts by mass.

[0011] Preferably, the carrageenan-based membrane matrix further includes glycerol as a plasticizer and chitosan oligosaccharides as a network reinforcing component. Through hydrogen bonding and electrostatic interactions with the carrageenan molecular chains and pectin coating layer, the chitosan oligosaccharides form an interpenetrating network structure in the membrane, thereby maintaining the structural stability of the membrane while introducing functional microspheres.

[0012] At low temperatures (4–10°C), the outer layer of PNIPAM is in a swollen state, which hinders the diffusion of curcumin. When the ambient temperature rises to 30–35°C, the outer layer of PNIPAM shrinks in volume, forming diffusion channels, thereby promoting the release of curcumin.

[0013] Preparation method This invention also provides a method for preparing the above-mentioned bio-based biodegradable food antioxidant packaging film, comprising the following steps: (1) Core preparation: Zeatin was dissolved in an alcohol-water mixed solvent, and curcumin solution was added and mixed. Zeatin-curcumin nanocomposite core was prepared by antisolvent precipitation method; (2) Pectin coating: The nanocomposite core is dispersed in an aqueous phase, the pH of the system is adjusted to 3.0–4.0, and a pectin solution is added to form a pectin coating layer on the surface of the nanocomposite core by electrostatic adsorption. (3) Construction of PNIPAM outer layer: In the presence of the pectin coating layer, N-isopropylacrylamide monomer is introduced and in-situ polymerized under the action of free radical initiator to form PNIPAM outer layer, and a three-layer core-shell structure of temperature-responsive antioxidant composite microspheres is obtained. (4) Film formation: The temperature-responsive antioxidant composite microspheres are added to the carrageenan film material system, along with glycerol and chitosan oligosaccharide. After mixing, film formation and drying, a bio-based biodegradable food antioxidant packaging film is obtained.

[0014] Preferably, the free radical initiator is ammonium persulfate or potassium persulfate, the film is formed by solution casting, and the drying temperature is 38–42°C.

[0015] This invention also provides the following technical solutions: A process for preparing the aforementioned bio-based biodegradable food antioxidant packaging film includes the following steps: S1. Preparation of hydrophobic protein-antioxidant composite core: Dissolve hydrophobic protein material in alcohol-water mixed solvent, add hydrophobic antioxidant solution and mix, then prepare nano-scale hydrophobic protein-antioxidant composite particles by antisolvent precipitation method; S2. Constructing a hydrophilic polysaccharide transition coating layer: The nanoscale composite particles are dispersed in an aqueous phase, and a hydrophilic polysaccharide solution is added under acidic conditions to form a hydrophilic polysaccharide transition coating layer on the surface of the composite particles by electrostatic adsorption. S3. Introducing a temperature-responsive polymer outer layer: A temperature-responsive monomer is introduced onto the surface of the hydrophilic polysaccharide transition coating layer and polymerized under the action of an initiator to form a temperature-responsive polymer outer layer, thereby obtaining a multi-layer core-shell structured temperature-responsive antioxidant composite microsphere. S4. Film Forming: The temperature-responsive antioxidant composite microspheres are in situ incorporated into the carrageenan film system, plasticizers and network reinforcement components are added, and after mixing, film formation and drying, a bio-based biodegradable food antioxidant packaging film is obtained.

[0016] Furthermore, the initiator used in step S3 is a persulfate initiator.

[0017] Furthermore, the membrane material is formed using a solution casting method, and the drying temperature is 38–42℃.

[0018] The beneficial effects of this invention are as follows: This invention achieves stable dispersion of curcumin in hydrophilic carrageenan membrane materials through a three-layer core-shell structure of zein-pectin-PNIPAM; Meanwhile, this invention achieves matching of antioxidant release behavior with temperature changes through reversible volume changes of the PNIPAM outer layer within temperature zones relevant to food refrigeration and transportation; Furthermore, this invention also maintains good mechanical and barrier properties of the membrane material while introducing functional components through an interpenetrating network structure constructed from chitosan oligosaccharides. In particular, all raw materials used are bio-based or biodegradable, and the preparation process is mild and suitable for food packaging applications. Detailed Implementation

[0019] To make the technical problems, technical solutions, and beneficial effects of this invention clearer and more understandable, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are only for explaining the invention and are not intended to limit the invention. Example 1

[0020] Preparation of temperature-sensitive composite microspheres Kernel preparation: A 2% (w / w) zein solution was prepared by dissolving 8000 Da (molecular weight) zein with 92% purity in 70% ethanol solution. Add curcumin to zein ethanol solution (concentration 1 mg / mL) at a ratio of 1:15 and stir at 500 rpm for 30 min to ensure complete combination. Slowly add the mixture dropwise to 3 times the volume of deionized water at a rate of 1 mL / min and stir continuously at 500 rpm for 15 min. Then centrifuge at 8000 rpm and 4℃ for 10 min, collect the precipitate, wash twice with deionized water to obtain zein-curcumin nanoparticles. Middle layer coating: The above nanoparticles were redispersed in deionized water to prepare a dispersion with a concentration of 1 mg / mL; the pH of the dispersion was adjusted to 3.5 with 0.1 mol / L citric acid solution; a 1% pectin solution (pectin molecular weight 35000 Da, degree of esterification 60%) was slowly added at a pectin to nanoparticle mass ratio of 1:5, stirred at 600 rpm for 20 min, and then centrifuged at 8000 rpm and 4℃ for 10 min to collect the precipitate; Outer layer grafting: The core-shell structure precipitate was dispersed in deionized water, and N-isopropylacrylamide monomer with a concentration of 0.5 mol / L was added. The mixture was ultrasonically dispersed at 300 W for 5 min. Ammonium persulfate initiator was added at 1% of the monomer mass. After deoxygenation by purging with nitrogen for 30 min, the mixture was reacted in a constant temperature water bath at 60℃ for 4 h. After the reaction was completed, the mixture was centrifuged at 8000 rpm and 4℃ for 10 min, washed 3 times with deionized water, and freeze-dried at -50℃ for 12 h to obtain temperature-sensitive composite microspheres with a particle size of about 200 nm. Example 2

[0021] Preparation of bio-based biodegradable food antioxidant packaging film Substrate solution preparation: Dissolve k-type carrageenan with a molecular weight of 150,000 Da in deionized water at 60°C to prepare a 3% carrageenan solution; add 20% glycerol by weight of carrageenan and stir at 500 rpm until completely dissolved; Preparation of composite membrane solution: Add 6% of the carrageenan mass of the temperature-sensitive composite microspheres prepared in Example 1, and ultrasonically disperse at 300W for 10 min. Then add 0.5% chitosan oligosaccharide solution (molecular weight 3000 Da, degree of deacetylation 93%). The amount of chitosan oligosaccharide added is 1% of the carrageenan mass. Continue stirring at 500 rpm for 30 min to obtain a uniform membrane solution. Molding and drying: The film liquid is poured into a polytetrafluoroethylene mold with a thickness of 0.2 mm, and dried in an oven at 40°C for 12 h. After demolding, a bio-based biodegradable food antioxidant packaging film with a thickness of 65 μm is obtained (denoted as E film).

[0022] Comparative Example 1 Preparation of carrageenan packaging film without curcumin encapsulation The difference between this comparative example and Example 2 is that: temperature-sensitive composite microspheres are not prepared, and curcumin is directly added to the carrageenan solution; the other preparation steps and parameters are completely consistent with those of Example 2.

[0023] Substrate solution preparation: Same as step 1 in Example 2; Preparation of composite membrane solution: According to the equivalent content of curcumin in Example 2 (i.e. the same mass of curcumin loaded on the composite microspheres in Example 2), curcumin ethanol solution was directly added, ultrasonically dispersed at 300W for 10 min, and then an equal amount of chitosan oligosaccharide solution was added and stirred at 500rpm for 30 min to obtain membrane solution. Shaping and drying: Same as step 3 in Example 2, to obtain the packaging film (denoted as C1 film).

[0024] Comparative Example 2 Preparation of composite microsphere-carrageenan packaging film without PNIPAM outer layer The difference between this comparative example and Example 2 is that the composite microspheres used are a double-layer core-shell structure without a PNIPAM outer layer, while the other preparation steps and parameters are completely consistent with Example 2.

[0025] Preparation of bilayer composite microspheres: Using the method in steps 1-2 of Example 1, bilayer core-shell microspheres of "zein-curcumin-pectin" were prepared without performing the PNIPAM outer layer grafting in step 3. Other parameters were the same as in Example 1. Packaging film preparation: Same as steps 1-3 in Example 2, except that the temperature-sensitive composite microspheres are replaced with the above-mentioned double-layer composite microspheres to obtain the packaging film (denoted as C2 film).

[0026] Comparative Example 3 Preparation of pure carrageenan packaging film The difference between this comparative example and Example 2 is that no temperature-sensitive composite microspheres and curcumin are added, while the other preparation steps and parameters are completely consistent with Example 2.

[0027] Substrate solution preparation: Dissolve k-type carrageenan with a molecular weight of 150,000 Da in deionized water at 60°C to prepare a 3% carrageenan solution; add 20% glycerol by weight of carrageenan and stir at 500 rpm until completely dissolved; Molding and drying: The above solution is poured into a polytetrafluoroethylene mold with a thickness of 0.2 mm, and dried in an oven at 40°C for 12 hours. After demolding, pure carrageenan packaging film (denoted as C3 film) is obtained. Example 3

[0028] Packaging film performance testing experiment The system performance of the E membrane prepared in Example 2, the C1 membrane prepared in Comparative Example 1, the C2 membrane prepared in Comparative Example 2, and the C3 membrane prepared in Comparative Example 3 was tested.

[0029] 1. Sample preparation The four types of membranes were all cut into standard samples of 2cm×2cm and placed in an environment of 25℃ and 60% relative humidity for 24 hours to equilibrate before various performance tests were conducted. Three parallel samples were set up for each test group, and the average value of the results was taken.

[0030] 2. Specific testing methods and results (1) Test of curcumin dispersion uniformity The cross-section and surface morphology of each group of films were observed using scanning electron microscopy (SEM), and the particle size distribution of curcumin particles was statistically analyzed (5 fields of view were randomly selected for each group, and 50 particles were counted in each field of view). The intensity of the characteristic absorption peak (wavelength 425 nm) of curcumin in different regions of the film was measured using a UV-Vis spectrophotometer, and the absorbance variation coefficient (CV) was calculated to evaluate the dispersion uniformity.

[0031] (2) Storage stability test of curcumin Each group of films was stored in an environment of 25℃ and 60% relative humidity for 30 days. Samples were taken on days 0, 10, 20 and 30. Curcumin was extracted from the films using ethanol extraction. The residual amount of curcumin was determined by high performance liquid chromatography (HPLC), and the residual rate was calculated (residual rate = curcumin content after storage / initial curcumin content × 100%).

[0032] (3) Temperature-sensitive sustained-release performance test An in vitro release simulation experiment was conducted: each group of films was cut into 2cm×2cm samples and immersed in 50mL of pH6.5 phosphate buffer solution (simulating food storage environment). The samples were placed in constant temperature shakers (100rpm) at 4℃ (refrigeration conditions) and 35℃ (high temperature fluctuation conditions). 5mL samples were taken at different time points (1h, 6h, 12h, 24h, 72h, 168h), and 5mL of fresh buffer solution was added simultaneously. The curcumin content in the released solution was determined by HPLC, and the cumulative release rate was calculated.

[0033] (4) Testing of basic properties of thin films Mechanical properties: The tensile strength (TS) and elongation at break (EAB) of the film were determined using a universal testing machine according to the GB / T1040.3-2006 standard. Five samples were prepared for each group, and the average value was taken. Water vapor barrier performance: The water vapor transmission rate (WVTR) of the film was measured using a water vapor transmission rate tester according to GB / T1037-2021 standard. The test conditions were 38℃ and 90% relative humidity. Each group was tested 3 times and the average value was taken.

[0034] (5) Verification of actual antioxidant preservation effect Using fresh pork as the packaging material, each group of films was made into packaging bags, and 20g of fresh pork (initial thiobarbituric acid value TBA≤0.1mgMDA / kg) was placed inside. The bags were stored at 4℃, and samples were taken on days 0, 3, 5 and 7 to determine the TBA value (reflecting the degree of lipid oxidation) and sensory scores (color, odor and texture, with a maximum score of 10).

[0035] 3. Summary Table of Experimental Data

[0036] Overall Conclusion Based on the above five core performance test results, it can be concluded that the bio-based biodegradable food antioxidant packaging film (E film) prepared by the present invention, through the design of a three-layer composite temperature-sensitive microsphere of zein, pectin and PNIPAM, successfully solves the problem of uneven dispersion and easy loss of activity of hydrophobic antioxidants in hydrophilic substrates in the prior art. At the same time, it realizes temperature-responsive intelligent release of curcumin, which can accurately match the antioxidant needs of the whole cycle of food refrigeration and transportation. Furthermore, through the interpenetrating network structure constructed from chitosan oligosaccharides, the E film achieves both excellent mechanical and barrier properties, meeting the practical requirements of food packaging. Moreover, all materials used are bio-based and biodegradable, aligning with the trend of green and environmentally friendly development. Compared to the C1 film without curcumin encapsulation, the C2 film without a PNIPAM outer layer, and the C3 film with pure carrageenan, the E film exhibits significant advantages in dispersion uniformity, storage stability, temperature-sensitive slow-release performance, basic physical properties, and actual preservation effect. This fully demonstrates the advanced nature, practicality, and innovation of the technical solution of this invention, and possesses promising prospects for industrial application.

[0037] The present invention has been described above by way of example. Obviously, the specific implementation of the present invention is not limited to the above-described manner. Any non-substantial improvements made by adopting the inventive concept and technical solution of the present invention, or the direct application of the inventive concept and technical solution of the present invention to other occasions without modification, are all within the protection scope of the present invention.

Claims

1. A biobased degradable food antioxidant packaging film characterized in that, The temperature-responsive antioxidant composite microspheres are of a three-layer core-shell structure, which comprises from inside to outside: The inner core layer is a nanoscale composite inner core formed by embedding curcumin in zein through anti-solvent precipitation method; The intermediate coating layer is a pectin coating layer formed by electrostatic adsorption under the condition of pH 3.0-4.0; The outer layer is a poly-N-isopropyl acrylamide layer formed by in-situ polymerization on the surface of the pectin coating layer; The low critical solution temperature of the poly-N-isopropyl acrylamide layer is 28-32℃, the average particle size of the temperature-responsive antioxidant composite microspheres is 150-250nm, and the temperature-responsive antioxidant composite microspheres are dispersed in the carrageenan-based film material at a ratio of 5-8 parts by mass. The carrageenan-based hydrophilic film matrix comprises carrageenan, glycerol plasticizer and chitosan oligosaccharide network reinforcement component. The chitosan oligosaccharide forms an interpenetrating network structure in the film material through hydrogen bonding and electrostatic interaction between the chitosan oligosaccharide and the pectin coating layer.

2. The bio-based degradable food antioxidant packaging film according to claim 1, characterized in that, The poly-N-isopropyl acrylamide layer is in a swollen state under the condition of 4-10℃ to limit the diffusion of curcumin, and volume shrinkage occurs under the condition of 30-35℃ and diffusion channels are formed.

3. The bio-based degradable food antioxidant packaging film according to claim 2, characterized in that, The mass ratio of zein to curcumin is 10:1-20:

1.

4. The bio-based degradable food antioxidant packaging film according to claim 1, characterized in that, The molecular weight of the pectin is 20000-50000Da, and the esterification degree is 50-70%.

5. The bio-based degradable food antioxidant packaging film according to claim 1, characterized in that, The method comprises the following steps:

6. The bio-based degradable food antioxidant packaging film according to claim 1, characterized in that, S1, dissolving zein in an alcohol-water mixed solvent, adding curcumin, and then preparing a zein-curcumin nanocomposite inner core by anti-solvent precipitation method; 7. A process for the preparation of a bio-based degradable food antioxidant packaging film as claimed in any one of claims 1-6, characterized in that, S2, dispersing the nanocomposite inner core in an aqueous phase, adding a pectin solution under the condition of pH 3.0-4.0, and forming a pectin coating layer by electrostatic adsorption; S3, in the presence of the pectin coating layer, introducing N-isopropyl acrylamide monomer and performing in-situ polymerization under the action of a free radical initiator to form a PNIPAM outer layer, thereby obtaining temperature-responsive antioxidant composite microspheres with a three-layer core-shell structure; S4, adding the temperature-responsive antioxidant composite microspheres to a carrageenan film system, adding glycerol and chitosan oligosaccharide, and then mixing, film forming and drying to obtain a biobased degradable food antioxidant packaging film. The free radical initiator is ammonium persulfate or potassium persulfate. The film forming is performed by solution casting method, and the drying temperature is 38-42℃.

8. The process for the preparation of biobased degradable food antioxidant packaging film as claimed in claim 7, wherein, The in-situ polymerization of the PNIPAM outer layer is performed after the formation of the pectin coating layer, and the in-situ polymerization step is not performed when the pectin coating layer is not formed.

9. The process for the preparation of biobased degradable food antioxidant packaging film as claimed in claim 7, wherein, ​ 10. The process for the preparation of biobased degradable food antioxidant packaging film as claimed in claim 7, wherein, ​

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