Preparation method of modified montmorillonite antibacterial agent and application of modified montmorillonite antibacterial agent in modified atmosphere preservative film

Abstract

The invention belongs to the technical field of fruit and vegetable preservation, and provides a preparation method of a silver nanoparticle / titanium dioxide / polydopamine modified montmorillonite antibacterial agent and application of the antibacterial agent in a copolyester / poly (butylene adipate-succinate)-terephthalate degradable film. The preparation method comprises the following steps: firstly preparing montmorillonite modified by polydopamine, and then mixing the montmorillonite modified by polydopamine with AgNO3 / TiO2 composite sol to prepare the antibacterial agent AgNPs / TiO2 / PMMT. The preparation method comprises the following steps: preparing an antibacterial agent, blending the antibacterial agent with PBTF and PBAT to prepare the antibacterial degradable composite air-conditioning film, and the composite air-conditioning film has antibacterial performance, excellent mechanical performance and air-conditioning performance, and can be applied to fruit and vegetable preservation.

Description

Technical Field

[0001] The invention belongs to the technical field of fruit and vegetable preservation, and particularly relates to a preparation method of a modified montmorillonite antibacterial agent and application of the modified montmorillonite antibacterial agent in a modified atmosphere fresh-keeping film. Background Art

[0002] Fresh fruits and vegetables are rich in nutrition and have a large market demand. Consumers' requirements for the freshness of fruits and vegetables have become increasingly stringent as their health awareness increases. Reasonable fresh-keeping packaging is one of the important means to protect fruits and vegetables from environmental pollution during transportation and storage, ensure the safety and nutritional quality of fruits and vegetables, reduce the decay rate and extend the storage period. Traditional packaging methods such as PE film can no longer meet consumers' demand for high-quality fresh fruits and vegetables. The research and development and application of functional food packaging with antibacterial and antioxidant properties has become an important topic of preservation in the fruit and vegetable industry today.

[0003] During the transportation, storage and sales of fruits and vegetables, they are in a sealed packaging environment for a long time, which makes them very susceptible to contamination by microorganisms, resulting in economic losses and food safety risks. Therefore, antimicrobial packaging is extremely critical in food safety assurance. Nanoparticles are usually between 1-100 nm in size and have excellent antibacterial properties. They are a common antibacterial agent and generally work by dispersing them in polymer materials. However, direct blending with degradable materials has disadvantages such as difficulty in dispersion and easy migration.

[0004] Therefore, in view of the increasing demand for functional food packaging films and the severity of the white pollution problem, the degradable composite film developed in the early stage of the laboratory is endowed with antibacterial properties to replace traditional packaging materials, thereby reducing environmental pressure, which has important practical and social significance. Summary of the invention

[0005] Aiming at the problems of white pollution, poor antibacterial property and lack of spontaneous gas conditioning function in the existing fruit and vegetable cling film, the present invention provides a method for preparing silver nanoparticle / titanium dioxide / polydopamine modified montmorillonite. Titanium dioxide / polydopamine modified montmorillonite (TiO2 / PMMT) and silver nanoparticle / titanium dioxide / polydopamine modified montmorillonite (AgNPs / TiO2 / PMMT) are prepared by doping nanosilver (AgNPs) and titanium dioxide (TiO2) into polydopamine modified montmorillonite (PMMT).

[0006] The present invention proposes the application of antibacterial agent AgNPs / TiO2 / PMMT in modified atmosphere cling film, and composites the antibacterial agent AgNPs / TiO2 / PMMT with the previously developed copolyester-polybutylene adipate succinate-terephthalate degradable modified atmosphere film (PBTF / PBAT) modified atmosphere film to prepare a degradable modified atmosphere film with excellent antibacterial properties.

[0007] The present invention is achieved through the following technical solutions: A method for preparing a modified montmorillonite antibacterial agent, characterized in that it comprises the following steps: I. Add montmorillonite powder to a buffer solution for ultrasonic dispersion, add dopamine hydrochloride for reaction, centrifuge to obtain a precipitate, wash and dry to obtain PMMT; II. Slowly drop tetrabutyl titanate and glacial acetic acid into anhydrous ethanol to obtain solution A; drop glacial acetic acid into the ethanol solution to adjust the pH, and add AgNO3 to obtain solution B; slowly drop solution B into solution A, stir the reaction to form a sol to obtain AgNO3 / TiO2 composite sol; III. Add PMMT to the AgNO3 / TiO2 composite sol, centrifuge and wash with ethanol solution, vacuum dry the precipitate, grind and sieve to obtain the antibacterial agent AgNPs / TiO2 / PMMT.

[0008] Preferably, the method for preparing the modified montmorillonite antibacterial agent comprises the following steps: I. After adding montmorillonite powder to a Tris-HCl buffer solution and ultrasonically dispersing for 20-40 min, dopamine hydrochloride was added, and the mixture was stirred at 300-500 rpm for 20-30 h for reaction, and then centrifuged at 3000-5000 rpm for 5-20 min. The precipitate was washed with distilled water until the upper layer became clear and transparent, and then dried at 50-120°C for 20-30 h to obtain PMMT. II. Slowly drop tetrabutyl titanate and glacial acetic acid into anhydrous ethanol to obtain solution A; add glacial acetic acid to the ethanol solution to adjust the pH, and then add AgNO3 until it is completely dissolved to obtain solution B; slowly drop solution B into solution A, stir magnetically for 20 to 60 minutes to fully react, form a sol after the reaction, and age it at room temperature for 10 to 15 hours to obtain AgNO3 / TiO2 composite sol; III. Add the PMMT obtained in step I to the AgNO3 / TiO2 composite sol obtained in step II, stir at 300-600 rpm for 20-30 h, then centrifuge at 3000-5000 rpm, wash with ethanol solution until the supernatant becomes clear, vacuum dry the precipitate for 20-30 h, grind and sieve, and collect the gray-brown powder, which is the antibacterial agent AgNPs / TiO2 / PMMT.

[0009] Preferably, the amount of dopamine hydrochloride added in step I is 5.0-20.0% of the montmorillonite powder. wt %; In the preparation of solution A in step II, the volume ratio of tetrabutyl titanate and glacial acetic acid is (2-10):1; Solution B in step II was prepared by dissolving 2 mL of deionized water in anhydrous ethanol, adding dropwise glacial acetic acid to adjust the pH to 3-4, and adding 0.6 g of AgNO3 until it was completely dissolved.

[0010] Preferably, in step III, the mass ratio of the PMMT to the AgNO3 / TiO2 composite sol is 1:(10-50).

[0011] Preferably, the amount of dopamine hydrochloride added in step I is 10±2 of the montmorillonite powder. wt %.

[0012] The modified montmorillonite antibacterial agent is prepared by the method of the invention.

[0013] The invention discloses an application of the modified montmorillonite antibacterial agent in atmosphere-controlled fresh-keeping film.

[0014] Preferably, the modified atmosphere cling film is a PBTF / PBAT cling film.

[0015] Preferably, copolyesters PBTF and PBAT are used as solutes, dichloromethane is used as solvent, antibacterial agent AgNPs / TiO2 / PMMT is added, a casting solution is prepared, the film is poured and dried to obtain a composite antibacterial atmosphere-controlled fresh-keeping film containing an antibacterial agent.

[0016] Preferably, the copolyester PBTF accounts for 1-5% of the total mass of the copolyester PBTF and PBAT; the added amount of the antibacterial agent AgNPs / TiO2 / PMMT is 1-5%.

[0017] The present invention uses montmorillonite (MMT) modified by PDA to generate modified montmorillonite (PMMT). Silver nanoparticles (AgNPs) are combined with PMMT through chemical bonds, and TiO2 is embedded in the PMMT interlayer structure. The antibacterial agent can be effectively combined in the form of chemical bonds. The dopamine polymer (PDA) can form a uniform coating layer on the surface of various substances due to its extremely strong adhesion. In addition, PDA contains rich catechol and amino groups, which provide active sites for the introduction of functional substances, thereby preparing silver nanoparticles / titanium dioxide / polydopamine modified montmorillonite (AgNPs / TiO2 / PMMT), delaying the release process of antibacterial substances and maintaining a lasting antibacterial effect. Then, the prepared AgNPs / TiO2 / PMMT is blended with the PBTF / PBAT composite film to prepare the AgNPs / TiO2 / PMMT / PBTF / PBAT (abbreviated as ATPPP) antibacterial gas-conditioning membrane.

[0018] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention uses dopamine-modified montmorillonite with extremely strong adhesion to prepare a modified montmorillonite (PMMT), combines silver nanoparticles (AgNPs) with PMMT through chemical bonds, and embeds TiO2 into the PMMT interlayer structure. Compared with the preparation method of directly blending the antibacterial agent and the membrane material, this method avoids the disadvantages of easy agglomeration, difficult dispersion, and easy migration of the material.

[0019] (2) The antibacterial agent prepared by the present invention effectively delays the release process of the antibacterial substance due to its interlayer structure, giving the composite degradable film a long-lasting antibacterial effect. In addition, the operation is simple and efficient, the equipment requirements are not high, and large-scale industrial production can be realized.

[0020] (3) The present invention provides an application of a biodegradable film material. The biodegradable film material can be used in the preservation of fruits and vegetables, and has the functions of spontaneous gas regulation, inhibiting the respiration intensity of fruits and vegetables, and delaying corruption, thereby achieving the purpose of extending the storage time of fruits and vegetables. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a flow chart of the preparation process of the AgNPs / TiO2 / PMMT antibacterial agent in Example 1.

[0022] Figure 2 The degradation conditions of Example 1 and Comparative Examples 1-2 in 1 mol / L NaOH & pH = 12.0 alkali solution are shown.

[0023] Figure 3 The antibacterial test results of MMT (montmorillonite), PMMT and TiO2 / PMMT powders in Example 2 (E. coli is Escherichia coli, S. aureus is Staphylococcus aureus).

[0024] Figure 4 The antibacterial test results of the AgNPs / TiO2 / PMMT composite films with different contents in Example 1 (E. coli is Escherichia coli, S. aureus is Staphylococcus aureus).

[0025] Figure 5 The sensory evaluation results of the film-preserved strawberries of Example 1 and Comparative Examples 1-2 are shown.

[0026] Figure 6 This is an analysis of the changes in CO2 and O2 contents in the packaging during the film preservation of strawberries in Example 1 and Comparative Examples 1-2.

[0027] Figure 7 The total colony count results of Example 1 and Comparative Examples 1-2 during the film preservation of strawberries.

[0028] Figure 8The moisture content change analysis of strawberries during film preservation in Example 1 and Comparative Examples 1-2 is shown.

[0029] Fig. 9 The change analysis of mass loss during the film preservation of strawberries in Example 1 and Comparative Examples 1-2 is shown.

[0030] Fig.10 The hardness change analysis of strawberries during the film preservation process of Example 1 and Comparative Examples 1-2 is shown.

[0031] Fig.11 The solid content changes during the film preservation of strawberries in Example 1 and Comparative Examples 1-2 are analyzed.

[0032] Fig.12 The change of Vc content in strawberries during film preservation in Example 1 and Comparative Examples 1-2 is analyzed.

[0033] Fig.13 The change of total phenol content in strawberries during film preservation in Example 1 and Comparative Examples 1-2 is analyzed. DETAILED DESCRIPTION

[0034] The present invention is further described in detail below in conjunction with the embodiments and drawings.

[0035] Example 1 Preparation of antibacterial agent (AgNPs / TiO2 / PMMT), composite antibacterial and degradable modified atmosphere film and application in strawberry preservation Preparation of antibacterial agent AgNPs / TiO2 / PMMT: I. Weigh 5.0 g of montmorillonite powder, add it to Tris-HCl buffer solution, ultrasonicate for 30 min, add 0.5 g of dopamine hydrochloride, and stir magnetically at 400 r / min for 24 h. At the end of the reaction, the solution is gray-black. Use a centrifuge to separate, centrifuge at 4000 r / min for 10 min, and wash the precipitate with distilled water several times until the upper liquid becomes clear and transparent. Put the precipitate in a vacuum drying oven at 80°C and continue drying for 24 h. Get black powder, grind and sieve, which is dopamine modified montmorillonite (PMMT).

[0036] II. Slowly drop 7.5 mL of tetrabutyl titanate into anhydrous ethanol, add 1-3 ml of glacial acetic acid (HAC) as an inhibitor, and stir until completely dissolved to obtain solution A. Take 2 mL of deionized water and dissolve it in anhydrous ethanol, add HAC to adjust the pH to between 3.0 and 4, then add 0.6 g of AgNO3 until it is completely dissolved to obtain solution B. Slowly drop solution B into solution A, stir magnetically for 40 min to fully react, form a light yellow transparent and stable sol and age it at room temperature for 12 h, which is a titanium dioxide (AgNO3 / TiO2) composite sol doped with silver nitrate.

[0037] III. Weigh 1 g of PMMT and add it to 20 mL of AgNO3 / TiO2 composite sol, and stir the mixed solution at 400 r / min for 24 h. Subsequently, the mixed solution was centrifuged at 4000 r / min and washed with 25% anhydrous ethanol solution until the solution was clear. Finally, the sample was placed in a vacuum drying oven and dried for 24 h, then ground and sieved to collect the gray-brown powder, which was silver nitrate / titanium dioxide / polydopamine modified montmorillonite (AgNPs / TiO2 / PMMT).

[0038] Preparation of composite antibacterial and degradable modified atmosphere membrane: Taking the casting solution in which 3 wt.% PBTF and 97 wt.% PBAT were added in Comparative Example 1 as the base, 2.0 wt.% of the antibacterial agent (AgNPs / TiO2 / PMMT) was added, and the same process as in Comparative Example 1 was adopted to prepare a 2% ATPPP composite antibacterial and degradable modified atmosphere membrane.

[0039] Pretreatment of strawberries: Select strawberries with no mechanical damage, no pests and diseases, and uniform size and color, soak them in 100 mg / L sodium hypochlorite disinfectant for 2 min, rinse and drain. Then, place them in a constant temperature and humidity chamber at 4±1℃ and relative humidity of 85%~95% for precooling for 24 h. Weigh 100±5 g of strawberries and place them in a fresh-keeping box covered with 2%ATPPP composite antibacterial and degradable gas-controlled film, seal them with a hot melt gun, and store them in a constant temperature and humidity chamber at 8±1℃ and relative humidity of 85%~95%. The changes in O2 and CO2 concentrations in the package and the mass loss rate, moisture content, hardness, vitamin C (Vc) content, total phenol content and soluble solids content of strawberries are measured every 3 days, and the appearance of the strawberries is recorded by taking photos, so as to comprehensively evaluate the fresh-keeping quality of strawberries.

[0040] Example 2 Preparation of antibacterial agent (TiO2 / PMMT) In this example, the antibacterial agent TiO2 / PMMT was prepared by the same preparation method as in Example 2, except that in the preparation of solution B in step II, no AgNO3 was added, that is, 2 mL of deionized water was dissolved in anhydrous ethanol, and HAC was added dropwise to adjust the pH to between 3.0 and 4 to obtain solution B. Solution B was slowly added dropwise to solution A, and magnetic stirring was performed for 40 min to allow it to react fully, forming a light yellow, transparent and stable sol, which was aged at room temperature for 12 h, namely, TiO2 composite sol.

[0041] Comparative Example 1 Comparative Example 1: Prepare 3% PBTF / PBAT cling film and cover the PP box as a control to preserve strawberries.

[0042] Preparation of 3% PBTF / PBAT cling film: Weigh 0.1 mol of dimethyl furandicarboxylate and excess 1,4-butanediol, and add 0.2 mol% butyl titanate, 0.1 mol% trimethyl phosphate and 0.1 mol% antioxidant to a three-necked flask based on the content of dimethyl furandicarboxylate. Vacuum the container to reduce the pressure to 0.5 kPa and maintain it for 3 min, then immediately introduce nitrogen to replace all the O2 inside the reaction container. Heat to 180°C under magnetic stirring, and continue the reaction for about 2 h. When the methanol distillate in the receiving bottle below the condenser reaches the theoretical value (>90%), the transesterification reaction is terminated to generate the prepolymer BHBD. In a nitrogen environment, heat to 210°C, and add 0.15 mol% butyl titanate and polytetrahydrofuran diol (15%-55%wt) to the reaction system. Continue heating and stirring at 480 r / min for about 15 min. Subsequently, the system was placed in an ultra-vacuum state (80-100 Pa) and the temperature was set to 10 °C / h. Under high temperature and high vacuum conditions, the prepolymer gradually removed small molecular diols, and the molecular weight gradually increased, resulting in an increase in the viscosity of the system. When the climbing pole effect appeared, the polycondensation reaction was terminated to obtain PBTF copolyester. It was dissolved in chloroform and filtered to remove insoluble matter. Methanol was added to the mixed solution to produce white floccules. After centrifugation and repeated washing three times, the residual solvent was evaporated at room temperature. Then it was vacuum dried at 65 °C for 12 h to obtain the purified PBTF copolyester.

[0043] The copolyester PBTF and PBAT were used as solutes, with the addition amount of PBTF being 3 wt.%, and dichloromethane being the solvent, to prepare a casting solution with a total concentration of 15.0 wt.%. The film thickness was set to 75 μm using the differentiator of an adjustable scraper to complete the film coating. After the solvent evaporated, the film was placed in a vacuum drying oven and dried for 24 h to remove the residual solvent of the film sample, and finally a 3% PBTF / PBAT composite degradable gas-controlled film was obtained.

[0044] Pretreatment of strawberries: Select strawberries with no mechanical damage, no pests and diseases, and uniform size and color, soak them in 100 mg / L sodium hypochlorite disinfectant for 2 min, rinse and drain. Then, place them in a constant temperature and humidity chamber at 4±1℃ and relative humidity of 85%~95% for precooling for 24 h. Weigh 100±5 g of strawberries and place them in a fresh-keeping box covered with 3% PBTF / PBAT composite degradable atmosphere film, seal them with a hot melt gun, and store them in a constant temperature and humidity chamber at 8±1℃ and relative humidity of 85%~95%. The changes in O2 and CO2 concentrations in the package and the mass loss rate, moisture content, hardness, vitamin C (Vc) content, total phenol content and soluble solids content of strawberries are measured every 3 days, and the appearance of the strawberries is recorded by taking photos, so as to comprehensively evaluate the fresh-keeping quality of strawberries.

[0045] Comparative Example 2 PP boxes covered with PE film were used as a control to preserve strawberries.

[0046] Pretreatment of strawberries: Select strawberries with no mechanical damage, no pests and diseases, and uniform size and color, soak them in 100 mg / L sodium hypochlorite disinfectant for 2 min, rinse and drain. Then, place them in a constant temperature and humidity chamber at 4±1℃ and relative humidity of 85%~95% for precooling for 24 h. Weigh 100±5 g of strawberries and put them in a fresh-keeping box covered with PE film, seal them with a hot melt gun, and store them in a constant temperature and humidity chamber at 8±1℃ and relative humidity of 85%~95%. Every 3 days, measure the changes in O2 and CO2 concentrations in the package, as well as the strawberry mass loss rate, moisture content, hardness, vitamin C (Vc) content, total phenol content and soluble solids content. Take photos to record the appearance of the strawberries, so as to comprehensively evaluate the preservation quality of the strawberries.

[0047] Table 1 shows the O2, CO2 gas permeability and water vapor permeability of Example 1 and Comparative Examples 1-2 The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the embodiments. Any other changes, modifications, substitutions, combinations and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement modes and shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a modified montmorillonite antibacterial agent, characterized in that: The following steps are involved: I. Add montmorillonite powder to a buffer solution for ultrasonic dispersion, add dopamine hydrochloride for reaction, centrifuge to obtain a precipitate, wash and dry to obtain PMMT; II. Slowly add tetrabutyl titanate and glacial acetic acid to anhydrous ethanol to obtain solution A; Add glacial acetic acid to the ethanol solution to adjust the pH, and add AgNO3 to obtain a B solution; slowly add the B solution to the A solution, stir the solution to form a sol, and obtain an AgNO3 / TiO2 composite sol; III. Add PMMT to the AgNO3 / TiO2 composite sol, centrifuge and wash with ethanol solution, vacuum dry the precipitate, grind and sieve to obtain the antibacterial agent AgNPs / TiO2 / PMMT.

2. The method for preparing a modified montmorillonite antibacterial agent according to claim 1, characterized in that: The following steps are involved: I. After adding montmorillonite powder to a Tris-HCl buffer solution and ultrasonically dispersing for 20-40 min, dopamine hydrochloride was added, and the mixture was stirred at 300-500 rpm for 20-30 h for reaction, and then centrifuged at 3000-5000 rpm for 5-20 min. The precipitate was washed with distilled water until the upper layer became clear and transparent, and then dried at 50-120°C for 20-30 h to obtain PMMT. II. Slowly drop tetrabutyl titanate and glacial acetic acid into anhydrous ethanol to obtain solution A; add glacial acetic acid to the ethanol solution to adjust the pH, and then add AgNO3 until it is completely dissolved to obtain solution B; slowly drop solution B into solution A, stir magnetically for 20 to 60 minutes to fully react, form a sol after the reaction, and age it at room temperature for 10 to 15 hours to obtain AgNO3 / TiO2 composite sol; III. Add the PMMT obtained in step I to the AgNO3 / TiO2 composite sol obtained in step II, stir at 300-600 rpm for 20-30 hours, then centrifuge at 3000-5000 rpm, wash with ethanol solution until the supernatant becomes clear, vacuum dry the precipitate for 20-30 hours, grind and sieve, and collect the gray-brown powder, which is the antibacterial agent AgNPs / TiO2 / PMMT.

3. The method for preparing a modified montmorillonite antibacterial agent according to claim 2, characterized in that: The amount of dopamine hydrochloride added in step I is 5.0-20.0% of the montmorillonite powder. wt %; In the preparation of solution A in step II, the volume ratio of tetrabutyl titanate and glacial acetic acid is (2-10):1; Solution B in step II was prepared by dissolving 2 mL of deionized water in anhydrous ethanol, adding dropwise glacial acetic acid to adjust the pH to 3-4, and adding 0.6 g of AgNO3 until it was completely dissolved.

4. The method for preparing a modified montmorillonite antibacterial agent according to claim 3, characterized in that: In step III, the mass ratio of the PMMT to the AgNO3 / TiO2 composite sol is 1:(10-50).

5. The method for preparing a modified montmorillonite antibacterial agent according to claim 4, characterized in that: The amount of dopamine hydrochloride added in step I is 10±2 of the montmorillonite powder. wt %.

6. The modified montmorillonite antibacterial agent prepared by the method according to any one of claims 1 to 5.

7. Use of the modified montmorillonite antibacterial agent according to claim 6 in controlled atmosphere cling film.

8. The use according to claim 7, characterized in that: The modified atmosphere cling film is a PBTF / PBAT cling film.

9. The use according to claim 8, characterized in that: With copolyesters PBTF and PBAT as solutes and dichloromethane as solvent, antibacterial agent AgNPs / TiO2 / PMMT was added to prepare a casting solution, which was then poured and dried to obtain a composite antibacterial atmosphere-controlled fresh-keeping film containing an antibacterial agent.

10. The use according to claim 9, characterized in that: The copolyester PBTF accounts for 1-5% of the total mass of the copolyester PBTF and PBAT; the addition amount of the antibacterial agent AgNPs / TiO2 / PMMT is 1-5%.

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