Thin film loaded with tea polyphenol nanoparticles, preparation method and application

Abstract

The invention discloses a tea polyphenol nanoparticle loaded film, a preparation method and application. The film contains tea polyphenol nanoparticles, zein and a trace plasticizer. Compared with a zein film, the prepared film has the advantages that the mechanical property, the barrier property and the oxidation resistance are remarkably improved, the fresh-keeping property is remarkably superior to that of a common plastic fresh-keeping film, and various packaging requirements can be met; the film is simple in formula, does not use other additives, remarkably reduces the production and manufacturing cost, simplifies the preparation process, and has extremely high industrial application value.

Description

Technical Field

[0001] The invention relates to food fresh-keeping packaging, and in particular to a tea polyphenol-loaded nanoparticle film, a preparation method and application thereof. Background Art

[0002] Zein is a natural plant protein extracted from corn endosperm. With its unique molecular structure and high glutamine content, it exhibits excellent film-forming properties. As a new bio-based material in the field of food packaging, the preparation method of Zein film is simple, and its film layer has the characteristics of high transparency, strong oil resistance, and biodegradability, especially meeting the safety requirements of food contact materials. At present, Zein film has been used in the fields of fruit and vegetable preservation coating, food inner packaging, etc., which can effectively delay water loss and maintain the color of food. However, its practical application still faces significant limitations: on the one hand, the oxygen and water vapor barrier properties of Zein film are lower than those of traditional petroleum-based plastics, and it is difficult to meet the long-term storage requirements of high-barrier foods; on the other hand, the material itself lacks antibacterial and antioxidant activity, and has functional shortcomings in inhibiting microbial reproduction or delaying food oxidation and deterioration, which limits its promotion in the packaging of perishable products such as fresh food and high-fat food.

[0003] In order to improve the functional properties of Zein films, researchers generally adopt the strategy of composite modification of active factors. For example, Chinese patent CN104140568A "An edible film with continuous antioxidant function and its preparation method and application" discloses an edible film composed of tea polyphenols, chitosan hydrochloride, sulfobutyl-β-cyclodextrin and natural edible biomacromolecule film-forming matrix (such as zein). Although the film effectively improves the antioxidant activity compared with ordinary films, its production cost and complexity are also greatly improved. More importantly, the compatibility problem between multiple components in the composite system may cause nanoparticle agglomeration, which not only affects the uniformity of the film, but also reduces the effective utilization rate of the active ingredients, forcing the production process to introduce additional surfactants or ultrasonic dispersion equipment, further pushing up the preparation cost and technical threshold. Therefore, it is urgent to break through the contradiction between functional enhancement and cost control, simplify the production process, reduce dependence on exogenous additives, and promote the industrialization process of zein-based active packaging films. Summary of the invention

[0004] Purpose of the invention: The purpose of the present invention is to provide a tea polyphenol nanoparticle film with a simple formula and simplified production process; the second purpose is to provide a preparation method and application of the film.

[0005] Technical solution: The tea polyphenol nanoparticle film of the present invention contains 1-10 parts by weight of tea polyphenol nanoparticles, 2000-3000 parts by weight of zein, and 0.1-0.5 parts by weight of a plasticizer.

[0006] Wherein, the particle size of tea polyphenol nanoparticles is 10-100nm.

[0007] Preferably, the preparation method of the tea polyphenol nanoparticles is: adding tea polyphenols and oxidase to phosphate buffer, fully mixing and incubating to obtain tea polyphenol nanoparticles.

[0008] Preferably, the tea polyphenols are one or more of epigallocatechin gallate, epicatechin gallate, epigallocatechin, and epicatechin.

[0009] Preferably, the oxidase is laccase and / or peroxidase.

[0010] The method for preparing the tea polyphenols nanoparticle film of the present invention comprises the following steps:

[0011] (1) After tea polyphenol nanoparticles are added to an ethanol-water solution, zein and a plasticizer are added;

[0012] (2) heating and stirring the mixture obtained in step 1 for 0.5-1.5 h;

[0013] (3) After stirring, the film is dried by the casting method.

[0014] Preferably, the concentration of ethanol in step 1 is 70-90%.

[0015] Preferably, the plasticizer in step 1 is glycerol and / or polyethylene glycol.

[0016] Preferably, the heating temperature in step 2 is 55-75°C.

[0017] The invention discloses an application of the tea polyphenol nanoparticle-loaded film in food preservation.

[0018] Preferably, the application is an application for inhibiting the growth of bacteria or fungi.

[0019] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: 1. By adding tea polyphenol nanoparticles to the zein film liquid, the mechanical properties, barrier properties, antioxidant properties and preservation effects of the prepared film are significantly improved, and can meet a variety of packaging requirements; 2. The film formula is simple and does not use other additives, which significantly reduces the production cost, simplifies the preparation process, and has extremely high industrial application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The graphs of epigallocatechin gallate (EGCG) nanoparticle solutions obtained at different incubation times;

[0021] Figure 2 The UV-visible absorption spectra of EGCG nanoparticles obtained at different incubation times;

[0022] Figure 3 The graph shows the particle size analysis results of EGCG nanoparticles obtained at different incubation times;

[0023] Figure 4 Fourier transform infrared spectra of EGCG nanoparticles obtained at different incubation times;

[0024] Figure 5 This is the morphology of the film loaded with tea polyphenol nanoparticles;

[0025] Figure 6 The antibacterial performance test results and statistical chart of the film loaded with tea polyphenols nanoparticles;

[0026] Figure 7 The test results and statistical graphs of moisture permeability and mechanical properties of films loaded with tea polyphenol nanoparticles;

[0027] Figure 8 The test results and statistical graph of the antioxidant performance of the film loaded with tea polyphenols nanoparticles;

[0028] Fig. 9 This is a diagram showing the preservation effect of a film loaded with tea polyphenols nanoparticles. DETAILED DESCRIPTION

[0029] The technical solution of the present invention is further described below.

[0030] Example 1 Preparation and characterization of tea polyphenols nanoparticles

[0031] 1. Preparation of Epigallocatechin Gallate (EGCG) Nanoparticles by a Green One-Step Synthesis Method in Aqueous Phase

[0032] EGCG with a concentration of 5 mg / mL, 0.5% (w / v) laccase and 1.0% (w / v) peroxidase were incubated in 0.2 M PBS (pH 8.0) buffer for 6, 12, and 24 h to prepare EGCG nanoparticles with different polymerization degrees, which were named ENPs-6, ENPs-12, and ENPs-24, respectively; 5 mg / mL prototype EGCG solution was used as the control and named EGCG.

[0033] Depend on Figure 1 It can be seen that as the incubation time increases, the color of EGCG nanoparticles gradually changes from light to dark, indicating the formation of EGCG nanoparticles.

[0034] 2. Characterization of EGCG Nanoparticles

[0035] (1) diluting the aforementioned EGCG nanoparticles and prototype EGCG solution to 0.1 mg / mL, and then scanning the diluted samples by UV-visible absorption spectrum at 200-700 nm;

[0036] like Figure 2 As shown, all samples have a strong absorption peak at 275nm, while the tea polyphenol nanoparticle sample has a weaker absorption peak at 300-400nm, indicating that new products may be formed.

[0037] (2) Take 2 mL of tea polyphenol nanoparticle sample diluted to a concentration of 0.05 mg / mL, treat it with 300 W ultrasound for 3 minutes, filter it with a 0.45 μm pore size water filter membrane, and analyze the particle size of the sample using a particle size analyzer. Each sample is measured 3 times;

[0038] The particle size determination results are as follows Figure 3 As shown, with the increase of incubation time, the particle size of tea polyphenol nanoparticles gradually increased, and the particle sizes of ENPs-6, ENPs-12 and ENPs-24 were 29.73±8.49nm, 52.85±7.58nm and 86.13±9.77nm, respectively.

[0039] (3) Use Fourier transform infrared spectrometer to perform infrared spectroscopy analysis on tea polyphenol nanoparticles with a concentration of 0.1 mg / mL and prototype EGCG solution samples.

[0040] Infrared spectrum Figure 4 As shown in Figure 2, the infrared spectrum of the prototype EGCG solution has the typical characteristics of phenolic compounds, while the infrared spectrum of the tea polyphenol nanoparticle sample is 1638 cm -1 The characteristic peaks decreased, which was mainly attributed to the CO stretching vibration of amide, indicating the formation of nano-EGCG nanopolymers.

[0041] Example 2 Antibacterial properties of EGCG nanoparticles

[0042] (1) Escherichia coli and Staphylococcus aureus were added to LB medium and cultured at 37°C for 12 h, and then diluted to a concentration of 1×10 8 CFU / mL;

[0043] (2) 200 μL of the diluted bacterial suspension was evenly spread on an LB agar plate, a hole with a diameter of 8 mm was made on the agar surface, and 90 μL of the ENPs-6, ENPs-12, ENPs-24 or EGCG solution obtained in Example 1 was added dropwise, and a blank control was set up at the same time, and cultured at 37°C for 16 h;

[0044] (3) Observe the colony formation.

[0045] The results are as follows Figure 6As shown, with the increase of the time of tea polyphenol nanoparticles, the antibacterial effect of tea polyphenol nanoparticles continued to increase, and was significantly better than the antibacterial effect of the same amount of prototype EGCG. The average diameter of the inhibition zone of ENPs-24 against Escherichia coli was 15.6 mm, and the average diameter of the inhibition zone against Staphylococcus aureus could reach 26.6 mm.

[0046] Example 3 Preparation and performance testing of tea polyphenol nanoparticle film

[0047] 1. Preparation of tea polyphenols nanoparticle film by tape casting

[0048] (1) 1 mL of ENPs-6, ENPs-12 and ENPs-24, or prototype EGCG prepared in Example 1 was directly added to 14 mL of 80% ethanol aqueous solution (v / v), and after thorough mixing, 2.5 g of zein, 0.05 g of glycerol and 0.17 g of polyethylene glycol were added to prepare a membrane solution;

[0049] (2) The membrane solution was stirred at 65°C and 1100 rpm for 30 min;

[0050] (3) The film is dried at room temperature using a casting method.

[0051] The obtained films were named Zein / ENPs-6, Zein / ENPs-12, Zein / ENPs-24 and Zein / EGCG, respectively. Figure 5 As shown, the prepared tea polyphenols nanoparticle-loaded film is transparent yellow, the surface of the film is smooth and flat without depressions, and has good ductility and can be bent.

[0052] 2. Mechanical properties of films loaded with tea polyphenols nanoparticles

[0053] (1) The film prepared above was cut into a rectangle with a length of 60 mm and a width of 15 mm. Each sample was measured 4 times using a texture analyzer, and the tensile properties and elongation at break were calculated based on the results.

[0054] (2) 3 mL of distilled water was placed in a moisture permeable cup with a depth of 39 mm and a diameter of 36 mm. The moisture permeable cup was sealed with the film prepared above and equilibrated at 25° C. and 70% relative humidity for 24 h. The quality difference of the moisture permeable cup before and after the experiment was measured.

[0055] The mechanical properties of the film are Figure 7As shown in the figure, with the addition of EGCG nanoparticles with a longer incubation time, the tensile properties and elongation at break of the film loaded with tea polyphenol nanoparticles were significantly improved; the tensile properties and elongation at break of the Zein / ENPs-24 film were increased by 2.96MPa and 2.84% respectively compared with the prototype EGCG control film. At the same time, its water vapor permeability decreased by 1.38×10 -7 g / m·s·Pa.

[0056] 3. Antioxidant properties of tea polyphenols nanoparticle films

[0057] 3.1 The total antioxidant capacity of tea polyphenols nanoparticle film was tested using the ABTS method.

[0058] (1) Take 2 mL of ABTS with a concentration of 7.4 mM + The solution was mixed with 2 mL of 2.45 mM potassium persulfate solution in a 5 mL centrifuge tube; the mixed solution was placed in the dark at room temperature for 12 hours to obtain ABTS + The solution was then diluted 50 times with ethanol and the diluted ABTS was measured. + The absorbance of the solution at 734 nm;

[0059] (2) Cut the prepared film into 10 mm × 10 mm squares and place them in 2 mL of diluted ABTS. + The solution was allowed to stand for 6 minutes and the absorbance of the solution at 734 nm was measured after the reaction.

[0060] 3.2 The free radical scavenging activity of the films was determined using the DPPH method.

[0061] (1) Dissolve 3.9 mg DPPH in 50 mL anhydrous ethanol to prepare 2×10 -4 M DPPH solution, measure the absorbance of the diluted DPPH solution at 517 nm;

[0062] (2) Cut the prepared film into 10 mm × 10 mm squares and place them in test tubes respectively, and add 2 mL of anhydrous ethanol and 2 mL of DPPH solution into the test tubes in sequence;

[0063] (3) Incubate in dark for 30 minutes and measure the absorbance of the resulting solution at 517 nm.

[0064] The results are as follows Figure 8 As shown, with the addition of EGCG nanoparticles for a longer incubation time, the antioxidant activity of the tea polyphenol nanoparticle film was significantly improved and was significantly better than that of the prototype EGCG control film.

[0065] 4. Fresh-keeping performance of films loaded with tea polyphenols nanoparticles

[0066] Since it has been confirmed that all performance indicators of Zein / ENPs-24 are better than those of Zein / EGCG, Zein / ENPs-6 and Zein / ENPs-12, when tea polyphenols nanoparticle film is used for strawberry preservation, Zein / ENPs-24 is selected as the experimental group, and a blank control group, a polyethylene (PE) control group and a Zein / EGCG control group are set up for comparison to comprehensively evaluate the preservation performance of the tea polyphenols nanoparticle film.

[0067] Fresh strawberries were placed in polyethylene fresh-keeping boxes. The blank group did not receive any treatment. The PE control group used commercially available PE fresh-keeping film to cover the fresh-keeping boxes and sealed them with packaging tape. The Zein control group used zein film without EGCG added to cover the fresh-keeping boxes and sealed them with packaging tape, while the Zein / ENPs-24 experimental group used Zein / ENPs-24 film to cover the fresh-keeping boxes and sealed them with packaging tape.

[0068] The fruit was then stored at room temperature and regularly inspected and photographed to monitor the strawberries for signs of spoilage.

[0069] The results are as follows Fig. 9 As shown in the figure, on the first day of preservation, all the strawberries were bright red and in good condition. On the second day of preservation, the strawberries in the blank control group grew white mold and began to rot. The PE control group and the Zein control group began to mold and rot on the third day, and no signs of corruption were observed in the Zein / ENPs-24 group until the fifth day. It can be seen that the preservation performance of the Zein / ENPs-24 film is better than that of other groups, effectively extending the shelf life of strawberries.

[0070] Example 4 Preparation and performance testing of composite tea polyphenol nanoparticle film

[0071] 1. Preparation of epigallocatechin gallate (EGCG) nanoparticles by an aqueous green one-step synthesis method. A composite tea polyphenol with a concentration of 5 mg / mL EGCG:ECG:EGC:EC ratio of 62:24:8:6 and 0.5% (w / v) laccase were incubated in 0.2 M PBS (pH 8.0) buffer for 6, 12, and 24 h to prepare composite tea polyphenol nanoparticles with different polymerization degrees, which were named TPNP-6, TPNP-12, and TPNP-24, respectively; a 5 mg / mL prototype composite tea polyphenol solution was used as a control and named TP.

[0072] 2. Preparation of composite tea polyphenols nanoparticle film by tape casting

[0073] (1) 1 mL of TPNP-6, TPNP-12, TPNP-24, or prototype TP prepared above was added to 14 mL of 80% ethanol aqueous solution (v / v), mixed thoroughly, and then 2.5 g of zein, 0.05 g of glycerol, and 0.17 g of polyethylene glycol were added to prepare a membrane solution;

[0074] (2) The membrane solution was stirred at 65°C and 1100 rpm for 30 minutes;

[0075] (3) The film is dried at room temperature using a casting method.

[0076] The obtained films were named Zein / TPNP-6, Zein / TPNP-12, Zein / TPNP-24 and Zein / TP.

[0077] 3. Mechanical properties of films loaded with composite tea polyphenols nanoparticles

[0078] The mechanical properties of the composite tea polyphenol nanoparticle film prepared above were analyzed using the same steps as in Example 3.

[0079] The results are shown in Table 1. The tensile properties and elongation at break of the film loaded with composite tea polyphenol nanoparticles incubated for 24 hours can be significantly improved. At the same time, the water vapor permeability of the film loaded with tea polyphenol nanoparticles incubated for 24 hours is also significantly reduced compared with the TP control film.

[0080] Table 1 Mechanical properties of tea polyphenol nanoparticles with different polymerization degrees

[0081]

[0082] Note: * in the same column indicates significant difference from the control film (P<0.05).

[0083] 4. Antioxidant properties of films loaded with composite tea polyphenol nanoparticles

[0084] The antioxidant activity of the composite tea polyphenol nanoparticle film prepared above was analyzed in the same steps as in Example 3.

[0085] The results are shown in Table 2. With the addition of composite tea polyphenol nanoparticles with longer incubation time, the antioxidant activity of the film is significantly improved and is significantly better than that of the TP control film.

[0086] Table 2 Determination results of antioxidant properties of composite tea polyphenol nanoparticles with different polymerization degrees

[0087]

[0088] Note: * in the same column indicates significant difference from the control film (P<0.05).

Claims

1. A film loaded with tea polyphenol nanoparticles, characterized in that: The film contains 1-10 parts by mass of tea polyphenol nanoparticles, 2000-3000 parts by mass of zein, and 0.1-0.5 parts by mass of a plasticizer. Wherein, the particle size of tea polyphenol nanoparticles is 10-100nm.

2. The tea polyphenol nanoparticle film according to claim 1, characterized in that: The preparation method of the tea polyphenol nanoparticles comprises: adding tea polyphenols and oxidase to a phosphate buffer, fully mixing and then incubating to obtain the tea polyphenol nanoparticles.

3. The tea polyphenols nanoparticle film according to claim 2, characterized in that: The tea polyphenols are one or more of epigallocatechin gallate, epicatechin gallate, epigallocatechin and epicatechin.

4. The tea polyphenols nanoparticle film according to claim 2, characterized in that: The oxidase is laccase and / or peroxidase.

5. A method for preparing a film loaded with tea polyphenol nanoparticles according to claim 1, characterized in that the steps include: (1) After tea polyphenol nanoparticles are added to an ethanol-water solution, zein and a plasticizer are added; (2) heating and stirring the mixture obtained in step 1 for 0.5-1.5 h; (3) After stirring, the film is dried by the casting method.

6. The method for preparing a film loaded with tea polyphenol nanoparticles according to claim 5, characterized in that: The concentration of ethanol in step 1 is 70-90%.

7. The method for preparing a film loaded with tea polyphenol nanoparticles according to claim 5, characterized in that: The plasticizer in step 1 is glycerol and / or polyethylene glycol.

8. The method for preparing a film loaded with tea polyphenol nanoparticles according to claim 5, characterized in that: The heating temperature described in step 2 is 55-75°C.

9. Use of the tea polyphenol nanoparticle-loaded film according to claim 1 in food preservation.

10. The use according to claim 9, characterized in that: The application is to inhibit the growth of bacteria and / or fungi and prevent oxidation of food.

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