Propolis ethanol extract loaded ZIF-8 cellulose starch-based sustained-release membrane and preparation method thereof

Abstract

The invention discloses a propolis ethanol extract loaded ZIF-8 cellulose starch-based sustained-release film and a preparation method thereof, and belongs to the technical field of food preservative films. The propolis ethanol extract loaded ZIF-8 cellulose starch-based sustained release membrane is prepared from the following raw materials in parts by weight: 30 to 70 parts of starch, 30 to 70 parts of cellulose nanofiber, 7.5 to 17.5 parts of glycerol and 4 to 8 parts of filler. The starch wastewater is used as a starch raw material source, and the cellulose nanofibers loaded with ZIF-8 by the propolis ethanol extract are added, so that the prepared slow-release film is high in strength and good in toughness, can be naturally degraded after being used, reduces environmental pollution, ensures the safety of the product, has antibacterial and antioxidant effects, provides benefits for fresh keeping of fruits, and has a wide application prospect. Meanwhile, a new thought is provided for resource utilization of the starch wastewater.

Description

Technical Field

[0001] The invention relates to the technical field of food fresh-keeping films, and in particular to a propolis ethanol extract-loaded ZIF-8 cellulose starch-based sustained-release film and a preparation method thereof. Background Art

[0002] Biodegradable materials, especially starch, are widely present in nature, have abundant reserves, are easy to obtain and are inexpensive. Since starch is a natural high molecular polymer, the interaction force between its macromolecules is very strong, which makes it difficult to melt-process the original starch, and its compatibility with other polymers in the blending process is also poor. Therefore, before the preparation of starch-based plastics, the starch must be chemically modified by chemical reactions to change its original structure, thereby changing the corresponding properties of the starch, turning the original starch into thermoplastic starch. The gelatinized film is very easy to form hydroxyl groups between the starch through intermolecular hydrogen bonds. Starch-based films have the characteristics of biodegradability, reproducibility, edibility, high transparency, biocompatibility and low odor, but starch-based packaging films are not widely used in the packaging industry, mainly because their mechanical properties, barrier properties and processing properties are relatively poor. In order to overcome these shortcomings, the present invention modifies the starch-based packaging film or mixes it with other materials to improve its scope of use. Summary of the Invention

[0003] To address the problems of the prior art, the present invention provides a naturally degradable propolis ethanol extract-loaded ZIF-8 cellulose starch-based sustained-release membrane. The membrane has high strength, good toughness, antibacterial and antioxidant properties, and can be naturally degraded after use, reducing environmental pollution. The membrane is prepared from 30 to 70 parts by weight of starch, 30 to 70 parts of cellulose nanofibers, 7.5 to 17.5 parts of glycerol, and 4 to 8 parts of a filler. The filler is ZIF-8 loaded with propolis ethanol extract, and the starch is derived from starch wastewater generated during the production of starchy crops or food processing.

[0004] Preferably, the diameter of the cellulose nanofibers of the present invention is 3-10 nm.

[0005] The method for preparing the propolis ethanol extract-loaded ZIF-8 cellulose starch-based sustained-release film of the present invention specifically comprises the following steps: S1. The starch wastewater is treated to remove impurities and obtain starch.

[0006] S2. Add water and glycerin to the starch, and stir and gelatinize under heating conditions to obtain a starch gelatinization slurry.

[0007] S3. The bamboo fibers are pretreated and modified, and then prepared into cellulose nanofibers through ultrasonic nanofibrillation.

[0008] S4. Dissolve Zn(NO3)2·6H2O and 2-methylimidazole in methanol to obtain a mixed solution; dissolve the propolis ethanol extract in ethanol to obtain a propolis ethanol extract ethanol solution; evenly mix the obtained mixed solution and the propolis ethanol extract ethanol solution, stir and react at room temperature to obtain an orange-yellow suspension, wash and dry, and add the dried propolis ethanol extract-ZIF-8 powder to ethanol to prepare a propolis ethanol extract-ZIF-8 ethanol dispersion.

[0009] S5. Evenly mix the starch gelatinized slurry and the cellulose nanofibers to obtain a membrane solution.

[0010] S6. Add the prepared propolis ethanol extract-ZIF-8 ethanol dispersion into the membrane liquid.

[0011] S7. Degas the membrane liquid under vacuum conditions to remove bubbles in the membrane liquid.

[0012] S8. The mixed material is fed into an extruder and extruded into a shape through a die. The prepared sustained-release film is placed at room temperature with a relative humidity of 55% to 75% for 24 to 48 hours to allow the sustained-release film to fully absorb moisture and plasticize, and then placed in a sample bag for storage.

[0013] Preferably, in step S1 of the present invention, the starch wastewater is subjected to impurity removal treatment by adopting an air flotation separation method at room temperature, centrifuging at a speed of 8000 rpm to remove upper impurities, washing the lower solid layer with deionized water, removing the brown layer of the slurry after each washing, and then drying in an oven at 40~50°C for 12~36h to obtain starch.

[0014] Preferably, in step S3 of the present invention, the pretreatment of the bamboo fiber includes alkali treatment and bleaching. The method for preparing the propolis ethanol extract loaded ZIF-8 cellulose starch-based sustained-release film according to claim 3 is characterized in that in step S3, the pretreatment of the bamboo fiber includes alkali treatment and bleaching, specifically: the alkali treatment of the bamboo fiber is to place the bamboo fiber in a 6% sodium hydroxide solution and heat it to 70~90℃ for 2~3h; the bleaching treatment is to place the alkali-treated bamboo fiber in a mixed solution consisting of an acetic acid aqueous solution and a sodium chlorite aqueous solution, the pH of the mixed solution is 3~5, and the mixed solution is heated in a water bath at 70~90℃ for 2~3h for bleaching, and then washed with deionized water to neutrality, and the washed and bleached bamboo fiber is dried in an oven at 40~50℃ for 24~48h to obtain the pretreated bamboo fiber.

[0015] Preferably, the mixed liquid of the present invention consists of 10% by volume of an acetic acid aqueous solution and 3.5% by mass of an sodium chlorite aqueous solution, wherein the volume ratio of the acetic acid aqueous solution to the sodium chlorite aqueous solution is 1:1; the bamboo fiber and the mixed liquid are mixed at a solid-liquid ratio of 1 g:20 mL.

[0016] Preferably, in step S3 of the present invention, the modification of the bamboo fiber refers to: adding a hydrated polycarboxylic acid deep eutectic solvent to the pretreated bamboo fiber at a mass volume ratio of 1:20 to the hydrated polycarboxylic acid deep eutectic solvent, heating the reaction at 110-130° C. for 2-3 hours, and centrifuging to obtain modified bamboo fiber; the hydrated polycarboxylic acid deep eutectic solvent is a uniform and transparent H-DES liquid mixed with citric acid, choline chloride and water in a mass ratio of 3:1:1.

[0017] Preferably, in step S3 of the present invention, the preparation of cellulose nanofibers by ultrasonic fibrillation includes: soaking the modified bamboo fiber in water, wherein the mass fraction of the modified bamboo fiber in the water is 1%, and then ultrasonicating for 30 to 45 minutes at a frequency of 20 kHz and an output power of 800 W to obtain cellulose nanofibers.

[0018] Preferably, in step S4 of the present invention, the concentration of Zn(NO3)2·6H2O in the mixed solution is 20~47g / L, the concentration of 2-methylimidazole in the mixed solution is 8~27g / L; and the concentration of the ethanol solution of propolis ethanol extract is 24~53g / L.

[0019] Preferably, in step S4 of the present invention, the reaction time at room temperature is 36 to 48 hours.

[0020] Preferably, in step S4 of the present invention, the drying condition is: drying in an oven at 50° C. for 20 to 40 hours.

[0021] Preferably, in step S4 of the present invention, the concentration of propolis ethanol extract-ZIF-8 in the propolis ethanol extract-ZIF-8 ethanol dispersion is 80-270 g / L.

[0022] The mechanism of this invention: The starch and glycerol slurry is prepared. The starch slurry fully penetrates the cellulose nanofibers, bonding and interweaving the cellulose nanofibers through hydrogen bonding. The synergistic effect of the starch slurry and cellulose nanofibers enhances the water resistance and mechanical properties of the sustained-release film. The nano-gaps within the starch-based film provide an ideal dispersion medium and interfacial interaction sites for the filler. The introduction of the propolis ethanol extract-ZIF-8 filler not only effectively regulates the film's microstructure but also, through nano-confinement effects and interfacial interactions, synergistically enhances the composite's barrier properties and mechanical strength.

[0023] The technical solution provided by the present invention can have the following beneficial effects: The invention uses starch wastewater as the source of starch, saves costs and realizes waste resource utilization, and the prepared slow-release film can be naturally degraded after use, reducing environmental pollution and ensuring product safety.

[0024] The present invention effectively overcomes the functional defects of starch film formation, and uses starch and glycerol to prepare a slurry, which is easier to process and shape; the cellulose nanofibers prepared by the present invention improve the strength and stability of the sustained-release film; the present invention uses the natural antibacterial properties of bamboo fiber and the synergistic effect of propolis ethanol extract to make the sustained-release film have excellent antibacterial and antioxidant properties.

[0025] The present invention provides an economical, environmentally friendly and high-performance solution for the utilization of starch wastewater and the development of degradable packaging materials, and provides strong support for the application of biomass starch and bamboo fiber in the field of food cling film technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a diagram of the sustained-release film prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0027] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments, but the protection scope of the present invention is not limited to the contents described above.

[0028] Example 1 A propolis ethanol extract-loaded ZIF-8 cellulose starch-based sustained-release film, wherein the raw materials for preparation include, by weight, 50 parts of starch, 50 parts of cellulose nanofibers, 12.5 parts of glycerin, and 6 parts of filler, wherein the filler is ZIF-8 loaded with propolis ethanol extract. The preparation method of the sustained-release film specifically comprises the following steps: S1. At room temperature, the upper impurities were removed by centrifugation at a speed of 8000 rpm using flotation separation method, and the lower solid layer was washed with deionized water. The brown layer of the slurry was removed after each washing, and then dried in an oven at 40°C for 24 hours to obtain starch.

[0029] S2. Disperse 50 parts of starch and 12.5 parts of glycerol in distilled water, and continuously stir at 90° C. for 20 minutes to gelatinize to obtain a starch gelatinized slurry.

[0030] S3, placing the bamboo fiber in a 6% sodium hydroxide solution and heating it to 70°C for alkali treatment for 3 hours, then placing 5g of the alkali-treated bamboo fiber in a mixture of 50mL of a 10% volume percent acetic acid aqueous solution and 50mL of a 3.5% mass percent sodium chlorite aqueous solution with a pH of 3-5, heating it in a 70°C water bath for 3 hours for bleaching, then washing it with deionized water until it is neutral, and placing it in a 50°C oven to dry for 24 hours to obtain the pretreated bamboo fiber; according to the mass volume ratio of the pretreated bamboo fiber to the hydrated polycarboxylic acid deep eutectic solvent of 1:20, the hydrated polycarboxylic acid deep eutectic solvent was added. A solvent (a uniform, transparent H-DES liquid mixed with citric acid, choline chloride, and water in a mass ratio of 3:1:1) was added to the pretreated bamboo fibers, heated at 110°C for 2 hours, and centrifuged at 8000 rpm to obtain modified bamboo fibers. The modified bamboo fibers were filtered out and washed with deionized water. The washed bamboo fibers were then immersed in deionized water at a mass fraction of 1%; cellulose nanofibers were obtained by ultrasonic nanofibrillation at a frequency of 20 kHz and a power of 800 W for 30 minutes.

[0031] S4. Dissolve 0.6 g of Zn(NO3)2·6H2O and 0.3 g of 2-methylimidazole in 20 mL of methanol to obtain a mixed solution; dissolve 0.7 g of propolis ethanol extract in 20 mL of ethanol to obtain a propolis ethanol extract ethanol solution; then rapidly stir the obtained mixed solution and the propolis ethanol extract ethanol solution at room temperature and react for 48 hours to obtain an orange-yellow suspension. The suspension is washed three times with methanol and once with deionized water, and then dried in an oven at 50°C for 20 hours. 3.0 g of the dried propolis ethanol extract-ZIF-8 powder is added to 20 mL of ethanol to obtain a propolis ethanol extract-ZIF-8 ethanol dispersion. 3.0 g of the dried propolis ethanol extract-ZIF-8 powder is added to 15-25 mL of ethanol to obtain a propolis ethanol extract-ZIF-8 ethanol dispersion.

[0032] S5. Mix 50 parts of starch gelatinized slurry with 50 parts of cellulose nanofibers, and stir to obtain a sustained-release membrane solution.

[0033] S6. Add 6 portions of the prepared propolis ethanol extract-ZIF-8 ethanol dispersion into the sustained-release membrane solution.

[0034] S7. Degas the membrane liquid under 0.09 MPa vacuum conditions for 20 minutes to remove bubbles in the membrane liquid.

[0035] S8. The mixed material is fed into an extruder and extruded into a shape through a die. The prepared sustained-release film is placed at room temperature with a relative humidity of 55% for 36 hours to allow the sustained-release film to fully absorb moisture and plasticize, and then placed in a sample bag for storage.

[0036] Example 2 A propolis ethanol extract-loaded ZIF-8 cellulose starch-based sustained-release film, wherein the raw materials for preparation include, by weight, 30 parts of starch, 70 parts of cellulose nanofibers, 17.5 parts of glycerin, and 8 parts of filler, wherein the filler is ZIF-8 loaded with propolis ethanol extract. The preparation method of the sustained-release film specifically comprises the following steps: S1. At room temperature, the upper impurities were removed by centrifugation at a speed of 8000 rpm using flotation separation method, and the lower solid layer was washed with deionized water. The brown layer of the slurry was removed after each washing, and then dried in an oven at 45°C for 36 hours to obtain starch.

[0037] S2. Disperse 30 parts of starch and 17.5 parts of glycerol in distilled water, and continuously stir at 90° C. for 20 minutes to gelatinize to obtain a starch gelatinized slurry.

[0038] S3, placing the bamboo fiber in a 6% sodium hydroxide solution and heating it to 80°C for alkali treatment for 2h, then placing 7g of the alkali-treated bamboo fiber in a mixed solution of 70mL of a 10% volume percent acetic acid aqueous solution and 70mL of a 3.5% mass percent sodium chlorite aqueous solution with a pH of 3-5 and heating it in an 80°C water bath for 2h for bleaching, then washing it with deionized water until neutral, and placing it in a 45°C oven to dry for 36h to obtain the pretreated bamboo fiber; according to the mass volume ratio of the pretreated bamboo fiber and the hydrated polycarboxylic acid deep eutectic solvent of 1:20, the hydrated polycarboxylic acid deep eutectic solvent was added. A eutectic solvent (a uniform, transparent H-DES liquid mixed with citric acid, choline chloride, and water in a mass ratio of 3:1:1) was added to the pretreated bamboo fibers, heated at 120°C for 3 hours, and centrifuged at 8000 rpm to obtain modified bamboo fibers. The modified bamboo fibers were filtered out and washed with deionized water. The washed bamboo fibers were then immersed in water, where the mass fraction of the bamboo fibers in the water was 1%. Cellulose nanofibers were obtained by ultrasonic nanofibrillation at a frequency of 20 kHz and a power of 800 W for 35 minutes.

[0039] S4. Dissolve 0.5 g of Zn(NO3)2·6H2O and 0.2 g of 2-methylimidazole in 15 mL of methanol to obtain a mixed solution; dissolve 0.8 g of propolis ethanol extract in 15 mL of ethanol to obtain a propolis ethanol extract ethanol solution; then rapidly stir and mix the obtained mixed solution and the propolis ethanol extract ethanol solution at room temperature, react for 48 hours to prepare an orange-yellow suspension, wash three times with methanol and once with deionized water, dry in an oven at 50°C for 30 hours, add 4.0 g of the dried propolis ethanol extract-ZIF-8 powder to 35 mL of ethanol to prepare a propolis ethanol extract-ZIF-8 ethanol dispersion.

[0040] S5. Mix 30 parts of starch gelatinized slurry with 70 parts of cellulose nanofibers, and stir to obtain a sustained-release membrane solution.

[0041] S6. Add 6 portions of the prepared propolis ethanol extract-ZIF-8 ethanol dispersion into the sustained-release membrane solution.

[0042] S7. Degas the membrane liquid under 0.08 MPa vacuum conditions for 40 minutes to remove bubbles in the membrane liquid.

[0043] S8. The mixed material is fed into an extruder and extruded into a shape through a die. The prepared sustained-release film is placed at room temperature with a relative humidity of 65% for 48 hours to allow the sustained-release film to fully absorb moisture and plasticize, and then placed in a sample bag for storage.

[0044] Example 3 A propolis ethanol extract-loaded ZIF-8 cellulose starch-based sustained-release film, wherein the raw materials for preparation include, by weight, 70 parts of starch, 30 parts of cellulose nanofibers, 7.5 parts of glycerin, and 4 parts of filler, wherein the filler is ZIF-8 loaded with propolis ethanol extract. The preparation method of the sustained-release film specifically comprises the following steps: S1. At room temperature, the upper impurities were removed by centrifugation at a speed of 8000 rpm using flotation separation method, and the lower solid layer was washed with deionized water. The brown layer of the slurry was removed after each washing, and then dried in an oven at 50°C for 12 hours to obtain starch.

[0045] S2. Disperse 70 parts of starch and 7.5 parts of glycerol in distilled water, and continuously stir at 90° C. for 20 minutes to gelatinize to obtain a starch gelatinized slurry.

[0046] S3, placing the bamboo fiber in a 6% sodium hydroxide solution and heating it to 90°C for alkali treatment for 2 hours, then placing 3g of the alkali-treated bamboo fiber in a mixture of 30mL of a 10% volume percent acetic acid aqueous solution and 30mL of a 3.5% mass percent sodium chlorite aqueous solution with a pH of 3-5 and heating it in a 90°C water bath for 2 hours for bleaching, then washing it with deionized water until it is neutral, and placing it in a 40°C oven to dry for 48 hours to obtain the pretreated bamboo fiber; adding the hydrated polycarboxylic acid deep eutectic solvent at a mass volume ratio of 1:20 to the pretreated bamboo fiber; A deep eutectic solvent (a uniform, transparent H-DES liquid mixed with citric acid, choline chloride, and water in a mass ratio of 3:1:1) was added to the pretreated bamboo fibers, heated at 130°C for 3 hours, and centrifuged at 8000 rpm to obtain modified bamboo fibers. The modified bamboo fibers were filtered out and washed with deionized water. The washed bamboo fibers were then immersed in water with a mass fraction of 1% in the water. Cellulose nanofibers were obtained by ultrasonic nanofibrillation at a frequency of 20 kHz and a power of 800 W for 45 minutes.

[0047] S4. Dissolve 0.7 g of Zn(NO3)2·6H2O and 0.4 g of 2-methylimidazole in 25 mL of methanol to obtain a mixed solution; dissolve 0.6 g of propolis ethanol extract in 35 mL of ethanol to obtain a propolis ethanol extract ethanol solution; then rapidly stir and mix the obtained mixed solution and the propolis ethanol extract ethanol solution at room temperature, react for 36 hours to prepare an orange-yellow suspension, wash three times with methanol, wash once with deionized water, and dry in an oven at 50°C for 40 hours. Add 2.0 g of the dried propolis ethanol extract-ZIF-8 powder to 15 mL of ethanol to prepare a propolis ethanol extract-ZIF-8 ethanol dispersion.

[0048] S5. Mix 70 parts of starch gelatinized slurry with 30 parts of cellulose nanofibers, and stir to obtain a sustained-release membrane solution.

[0049] S6. Add 4 portions of the prepared propolis ethanol extract-ZIF-8 ethanol dispersion into the sustained-release membrane solution.

[0050] S7. Degas the membrane liquid under 0.06 MPa vacuum conditions for 60 minutes to remove bubbles in the membrane liquid.

[0051] S8. The mixed material is fed into an extruder and extruded into a shape through a die. The prepared sustained-release film is placed at room temperature with a relative humidity of 75% for 24 hours to allow the sustained-release film to fully absorb moisture and plasticize, and then placed in a sample bag for storage.

[0052] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that no cellulose nanofibers are added. The specific preparation method is as follows: S1. At room temperature, the upper impurities were removed by centrifugation at a speed of 8000 rpm using flotation separation method, and the lower solid layer was washed with deionized water. The brown layer of the slurry was removed after each washing, and then dried in an oven at 40°C for 24 hours to obtain starch.

[0053] S2. Disperse 50 parts of starch and 12.5 parts of glycerol in distilled water, and continuously stir at 90° C. for 20 minutes to gelatinize to obtain a starch gelatinized slurry.

[0054] S3. Dissolve 0.6 g of Zn(NO3)2·6H2O and 0.3 g of 2-methylimidazole in 20 mL of methanol to obtain a mixed solution; dissolve 0.7 g of propolis ethanol extract in 20 mL of ethanol to obtain a propolis ethanol extract ethanol solution; then rapidly stir and mix the obtained mixed solution and the propolis ethanol extract ethanol solution at room temperature, react for 48 hours to prepare an orange-yellow suspension, wash three times with methanol, wash once with deionized water, and dry in an oven at 50°C for 20 hours. Add 3.0 g of the dried propolis ethanol extract-ZIF-8 powder to 20 mL of ethanol to prepare a propolis ethanol extract-ZIF-8 ethanol dispersion.

[0055] S4. Mix 50 parts of starch gelatinized slurry with 50 parts of cellulose nanofibers, and stir to obtain a sustained-release membrane solution.

[0056] S5. Add 6 portions of the prepared propolis ethanol extract-ZIF-8 ethanol dispersion into the sustained-release membrane solution.

[0057] S6. Degas the membrane liquid under 0.09 MPa vacuum conditions for 20 minutes to remove bubbles in the membrane liquid.

[0058] S7. The mixed material is fed into an extruder and extruded into a shape through a die. The prepared sustained-release film is placed at room temperature with a relative humidity of 55% for 36 hours to allow the sustained-release film to fully absorb moisture and plasticize, and then placed in a sample bag for storage.

[0059] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that no glycerol is added. The specific preparation method is as follows: S1. At room temperature, the upper impurities were removed by centrifugation at a speed of 8000 rpm using flotation separation method, and the lower solid layer was washed with deionized water. The brown layer of the slurry was removed after each washing, and then dried in an oven at 40°C for 24 hours to obtain starch.

[0060] S2. Disperse 50 parts of starch in distilled water, and continuously stir at 90° C. for 20 minutes to gelatinize to obtain a starch gelatinization slurry.

[0061] S3, placing the bamboo fiber in a 6% sodium hydroxide solution and heating it to 70°C for alkali treatment for 3 hours, then placing 5g of the alkali-treated bamboo fiber in a mixture of 50mL of a 10% volume percent acetic acid aqueous solution and 50mL of a 3.5% mass percent sodium chlorite aqueous solution with a pH of 3-5, heating it in a 70°C water bath for 3 hours for bleaching, then washing it with deionized water until neutral, and placing it in a 50°C oven to dry for 24 hours to obtain the pretreated bamboo fiber; according to the mass volume ratio of the pretreated bamboo fiber to the hydrated polycarboxylic acid deep eutectic solvent of 1:20, the hydrated polycarboxylic acid deep eutectic solvent was added. A eutectic solvent (a uniform, transparent H-DES liquid mixed with citric acid, choline chloride, and water in a mass ratio of 3:1:1) was added to the pretreated bamboo fibers, heated at 110°C for 2 hours, and centrifuged at 8000 rpm to obtain modified bamboo fibers. The modified bamboo fibers were filtered out, washed with deionized water, and immersed in water with a mass fraction of 1% for 1% of the bamboo fibers. Cellulose nanofibers were obtained by ultrasonic nanofibrillation at a frequency of 20 kHz and a power of 800 W for 30 minutes.

[0062] S4. Dissolve 0.6 g of Zn(NO3)2·6H2O and 0.3 g of 2-methylimidazole in 20 mL of methanol to obtain a mixed solution; dissolve 0.7 g of propolis ethanol extract in 20 mL of ethanol to obtain a propolis ethanol extract ethanol solution; then rapidly stir and mix the obtained mixed solution and the propolis ethanol extract ethanol solution at room temperature, react for 48 hours to prepare an orange-yellow suspension, wash three times with methanol and once with deionized water, dry in an oven at 50°C for 20 hours, add 3.0 g of the dried propolis ethanol extract-ZIF-8 powder to 20 mL of ethanol to prepare a propolis ethanol extract-ZIF-8 ethanol dispersion.

[0063] S5. Mix 50 parts of starch gelatinized slurry with 50 parts of cellulose nanofibers, and stir to obtain a sustained-release membrane solution.

[0064] S6. Add 6 portions of the prepared propolis ethanol extract-ZIF-8 ethanol dispersion into the sustained-release membrane solution.

[0065] S7. Degas the membrane liquid under 0.09 MPa vacuum conditions for 20 minutes to remove bubbles in the membrane liquid.

[0066] S8. The mixed material is fed into an extruder and extruded into a shape through a die. The prepared sustained-release film is placed at room temperature with a relative humidity of 55% for 36 hours to allow the sustained-release film to fully absorb moisture and plasticize, and then placed in a sample bag for storage.

[0067] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that the proportion of each raw material component is not within the scope of protection of the present invention. The raw materials for preparation include 20 parts of starch, 20 parts of cellulose nanofibers, 20 parts of glycerin, and 10 parts of filler by weight. The filler is ZIF-8 loaded with propolis ethanol extract. The preparation method of the sustained-release membrane specifically includes the following steps: S1. At room temperature, the upper impurities were removed by centrifugation at a speed of 8000 rpm using flotation separation method, and the lower solid layer was washed with deionized water. The brown layer of the slurry was removed after each washing, and then dried in an oven at 40°C for 24 hours to obtain starch.

[0068] S2. Disperse 20 parts of starch and 20 parts of glycerol in distilled water, and continuously stir at 90° C. for 20 minutes to gelatinize to obtain a starch gelatinization slurry.

[0069] S3, placing the bamboo fiber in a 6% sodium hydroxide solution and heating it to 70°C for alkali treatment for 3 hours, then placing 5g of the alkali-treated bamboo fiber in a mixture of 50mL of a 10% volume percent acetic acid aqueous solution and 50mL of a 3.5% mass percent sodium chlorite aqueous solution with a pH of 3-5 and heating it in a 70°C water bath for 3 hours for bleaching, then washing it with deionized water until it is neutral, and placing it in a 50°C oven to dry for 24 hours to obtain the pretreated bamboo fiber; according to the mass volume ratio of the pretreated bamboo fiber to the hydrated polycarboxylic acid deep eutectic solvent of 1:20, the hydrated polycarboxylic acid deep eutectic solvent was added. A molten solvent (a uniform, transparent H-DES liquid mixed with citric acid, choline chloride, and water in a mass ratio of 3:1:1) was added to the pretreated bamboo fibers, heated at 110°C for 2 hours, and centrifuged at 8000 rpm to obtain modified bamboo fibers. The modified bamboo fibers were filtered out, washed with deionized water, and immersed in water after washing, wherein the mass fraction of the bamboo fibers in the water was 1%. Cellulose nanofibers were obtained by ultrasonic nanofibrillation at a frequency of 20 kHz and a power of 800 W for 30 minutes.

[0070] S4. Dissolve 0.6 g of Zn(NO3)2·6H2O and 0.3 g of 2-methylimidazole in 20 mL of methanol to obtain a mixed solution; dissolve 0.7 g of propolis ethanol extract in 20 mL of ethanol to obtain a propolis ethanol extract ethanol solution; then rapidly stir and mix the obtained mixed solution and the propolis ethanol extract ethanol solution at room temperature, react for 48 hours to prepare an orange-yellow suspension, wash three times with methanol and once with deionized water, dry in an oven at 50°C for 20 hours, add 3.0 g of the dried propolis ethanol extract-ZIF-8 powder to 20 mL of ethanol to prepare a propolis ethanol extract-ZIF-8 ethanol dispersion.

[0071] S5. Mix 20 parts of starch gelatinized slurry with 20 parts of cellulose nanofibers, and stir to obtain a sustained-release membrane solution.

[0072] S6. Add 10 portions of the prepared propolis ethanol extract-ZIF-8 ethanol dispersion into the sustained-release membrane solution.

[0073] S7. Degas the membrane liquid under 0.09 MPa vacuum conditions for 20 minutes to remove bubbles in the membrane liquid.

[0074] S8. The mixed material is fed into an extruder and extruded into a shape through a die. The prepared sustained-release film is placed at room temperature with a relative humidity of 55% for 36 hours to allow the sustained-release film to fully absorb moisture and plasticize, and then placed in a sample bag for storage.

[0075] Comparative Example 4 The difference between Comparative Example 4 and Example 1 is that ordinary bamboo fiber powder is used, and the specific preparation method is as follows: S1. At room temperature, the upper impurities were removed by centrifugation at a speed of 8000 rpm using flotation separation method, and the lower solid layer was washed with deionized water. The brown layer of the slurry was removed after each washing, and then dried in an oven at 40°C for 24 hours to obtain starch.

[0076] S2. Disperse 50 parts of starch and 12.5 parts of glycerol in distilled water, and continuously stir at 90° C. for 20 minutes to gelatinize to obtain a starch gelatinized slurry.

[0077] S3. Dissolve 0.6 g of Zn(NO3)2·6H2O and 0.3 g of 2-methylimidazole in 20 mL of methanol to obtain a mixed solution; dissolve 0.7 g of propolis ethanol extract in 20 mL of ethanol to obtain a propolis ethanol extract ethanol solution; then rapidly stir and mix the obtained mixed solution and the propolis ethanol extract ethanol solution at room temperature, react for 48 hours to prepare an orange-yellow suspension, wash three times with methanol, wash once with deionized water, and dry in an oven at 50°C for 20 hours. Add 3.0 g of the dried propolis ethanol extract-ZIF-8 powder to 20 mL of ethanol to prepare a propolis ethanol extract-ZIF-8 ethanol dispersion.

[0078] S4. Mix 50 parts of starch gelatinized slurry with 50 parts of ordinary bamboo fiber powder, and stir to obtain a sustained-release membrane solution.

[0079] S5. Add 6 portions of the prepared propolis ethanol extract-ZIF-8 ethanol dispersion into the sustained-release membrane solution.

[0080] S6. Degas the membrane liquid under 0.09 MPa vacuum conditions for 20 minutes to remove bubbles in the membrane liquid.

[0081] S7. The mixed material is fed into an extruder and extruded into a shape through a die. The prepared sustained-release film is placed at room temperature with a relative humidity of 55% for 36 hours to allow the sustained-release film to fully absorb moisture and plasticize, and then placed in a sample bag for storage.

[0082] The sustained-release films prepared in Examples 1 to 3 and Comparative Examples 1 to 4 were tested, and the results are shown in Table 1: Table 1 The present invention is based on lotus root starch wastewater and adds cellulose nanofibers to obtain a degradable starch-based food packaging film with light weight and good toughness, thereby improving the mechanical properties of the slow-release film. As shown in Table 1, the slow-release films prepared in Examples 1 to 3 of the present invention have good tensile strength and elongation at break, while the slow-release films prepared in Comparative Examples 1 to 4 have poor mechanical properties. The slow-release film prepared by the present invention can meet the requirements of film strength in food packaging. By modifying starch and adding additives, the slow-release film has good mechanical properties. At the same time, by adding bamboo fiber and other ingredients, the slow-release film has certain antibacterial and antioxidant effects, and can prolong the shelf life.

[0083] While various embodiments of the present invention have been described above, the foregoing description is intended to be illustrative, non-exhaustive, and not limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is selected to best explain the principles of the embodiments, their practical applications, or improvements to existing technologies, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A propolis ethanol extract loaded ZIF-8 cellulose starch-based sustained-release film, characterized in that: The raw materials for the preparation include, by weight, 30-70 parts of starch, 30-70 parts of cellulose nanofibers, 7.5-17.5 parts of glycerol, and 4-8 parts of filler, wherein the filler is ZIF-8 loaded with propolis ethanol extract.

2. The propolis ethanol extract loaded ZIF-8 cellulose starch-based sustained-release film according to claim 1, characterized in that: The diameter of the cellulose nanofibers is 3-10 nm.

3. The method for preparing the propolis ethanol extract loaded ZIF-8 cellulose starch-based sustained-release film according to claim 1, characterized in that: The specific steps include: S1, removing impurities from starch wastewater to obtain starch; S2, adding water and glycerin to the starch, stirring and gelatinizing under heating conditions to obtain a starch gelatinization slurry; S3, pre-treating and modifying bamboo fibers, and preparing cellulose nanofibers by ultrasonic nanofibrillation; S4. Dissolve Zn(NO3)2·6H2O and 2-methylimidazole in methanol to obtain a mixed solution; dissolve the propolis ethanol extract in ethanol to obtain a propolis ethanol extract ethanol solution; uniformly mix the obtained mixed solution and the propolis ethanol extract ethanol solution, stir and react at room temperature to obtain an orange-yellow suspension, wash and dry, and add the dried propolis ethanol extract-ZIF-8 powder to ethanol to prepare a propolis ethanol extract-ZIF-8 ethanol dispersion; S5, uniformly mixing the starch gelatinized slurry and the cellulose nanofibers to obtain a membrane solution; S6. Add the prepared propolis ethanol extract-ZIF-8 ethanol dispersion into the membrane solution; S7, degassing the membrane liquid under vacuum conditions to remove bubbles in the membrane liquid; S8. The mixed material is fed into an extruder and extruded into a shape through a die. The prepared sustained-release film is placed at room temperature with a relative humidity of 55% to 75% for 24 to 48 hours to allow the sustained-release film to fully absorb moisture and plasticize, and then placed in a sample bag for storage.

4. The method for preparing the propolis ethanol extract-loaded ZIF-8 cellulose starch-based sustained-release film according to claim 3, characterized in that: In step S1, the starch wastewater is subjected to impurity removal treatment at room temperature by adopting an air flotation separation method, centrifuging to remove upper impurities, washing the lower solid layer with deionized water, removing the brown layer of the slurry after each washing, and then drying in an oven at 40-50°C for 12-36 hours to obtain starch.

5. The method for preparing the propolis ethanol extract-loaded ZIF-8 cellulose starch-based sustained-release film according to claim 3, characterized in that: In step S3, the pretreatment of the bamboo fiber includes alkali treatment and bleaching, specifically: the alkali treatment of the bamboo fiber is to place the bamboo fiber in a 6% sodium hydroxide solution and heat it to 70~90°C for 2~3h; the bleaching treatment is to place the alkali-treated bamboo fiber in a mixed solution consisting of an acetic acid aqueous solution and a sodium chlorite aqueous solution, and heat it in a water bath at 70~90°C for 2~3h for bleaching, and then wash it with deionized water until it is neutral, and dry the washed and bleached bamboo fiber in an oven at 40~50°C for 24~48h to obtain pretreated bamboo fiber.

6. The method for preparing the propolis ethanol extract-loaded ZIF-8 cellulose starch-based sustained-release film according to claim 3, characterized in that: In step S3, the modification of the bamboo fiber refers to: adding a hydrated polycarboxylic acid deep eutectic solvent to the pretreated bamboo fiber at a mass volume ratio of 1:20 to the hydrated polycarboxylic acid deep eutectic solvent, heating the reaction at 110-130° C. for 2-3 hours, and centrifuging to obtain modified bamboo fiber; the hydrated polycarboxylic acid deep eutectic solvent is a uniform and transparent H-DES liquid mixed with citric acid, choline chloride and water in a mass ratio of 3:1:

1.

7. The method for preparing the propolis ethanol extract-loaded ZIF-8 cellulose starch-based sustained-release film according to claim 3, characterized in that: In step S3, the ultrasonic fibrillation to prepare cellulose nanofibers includes: soaking the modified bamboo fibers in water, wherein the mass fraction of the modified bamboo fibers in the water is 1%, and then ultrasonically treating the fibers at a frequency of 20 kHz and an output power of 800 W for 30 to 45 minutes to obtain cellulose nanofibers.

8. The method for preparing the propolis ethanol extract-loaded ZIF-8 cellulose starch-based sustained-release film according to claim 3, characterized in that: In step S4, the concentration of Zn(NO3)2·6H2O in the mixed solution is 20~47g / L, the concentration of 2-methylimidazole in the mixed solution is 8~27g / L; the concentration of the propolis ethanol extract ethanol solution is 24~53g / L; the concentration of propolis ethanol extract-ZIF-8 in the propolis ethanol extract-ZIF-8 ethanol dispersion is 8~27g / L.

9. The method for preparing the propolis ethanol extract-loaded ZIF-8 cellulose starch-based sustained-release film according to claim 3, characterized in that: In step S4, the reaction time at room temperature is 36 to 48 hours; and the drying condition is: drying in an oven at 50° C. for 20 to 40 hours.

10. The method for preparing the propolis ethanol extract-loaded ZIF-8 cellulose starch-based sustained-release film according to claim 5, characterized in that: The mixed liquid consists of a 10% by volume acetic acid aqueous solution and a 3.5% by mass sodium chlorite aqueous solution, wherein the volume ratio of the acetic acid aqueous solution to the sodium chlorite aqueous solution is 1:1; the bamboo fiber and the mixed liquid are mixed at a solid-liquid ratio of 1g:20mL.

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