An antibacterial film based on Pickering emulsion and its preparation method and application

Abstract

The invention discloses an antibacterial film based on Pickering emulsion, and a preparation method and application thereof, belonging to the technical field of food packaging film, wherein hexadecyltrimethylammonium bromide is dissolved in water to obtain a CTAB solution; graphene oxide is dissolved in water to obtain a GO solution; the CTAB solution and the GO solution are mixed in equal proportions to obtain an mGO solution; tannic acid is added to the mGO solution to obtain a TA / mGO solution; lemongrass essential oil and the above TA / mGO solution are homogenized and emulsified in a certain proportion to obtain a Pickering emulsion; the Pickering emulsion is homogenously mixed with a film-forming agent to obtain a film-forming liquid, the film-forming liquid is degassed and then cast into a mold, and dried to obtain an antibacterial film. The antibacterial film prepared by the preparation method of the invention not only gives the biodegradable cling film excellent mechanical properties, but also has long-lasting and stable antibacterial properties, and the essential oil incorporated into the film in the form of an emulsion can effectively enhance the antibacterial activity of the composite film, while also reducing its influence on the sensory properties of food.

Description

Technical Field

[0001] The invention belongs to the technical field of food packaging films, and in particular relates to an antibacterial fresh-keeping composite film based on Pickering emulsion, and a preparation method and application thereof. Background Art

[0002] The global hunger problem remains severe, however, about one-third of all food produced worldwide is wasted, a large part of which is perishable fruits and vegetables. Therefore, various preservation technologies have been developed, such as vacuum packaging, adding preservatives, irradiation treatment, etc., but these methods usually require high costs and time-consuming procedures. In addition, traditional plastic packaging is widely used due to its excellent ductility and good mechanical properties, but the excessive use of petroleum-based plastics has caused irreversible ecological damage. In order to ensure sustainable development, environmentally friendly solutions that can extend the shelf life of food must be developed.

[0003] Active packaging is based on the basic principle of releasing active compounds into food packaging to prevent the growth of undesirable microorganisms, which can protect the quality and safety of food, extend the shelf life of products, and reduce food spoilage and waste. Essential oils extracted from plants can produce strong antibacterial effects on foodborne bacteria and microorganisms and have been widely used in the development of active packaging materials.

[0004] However, essential oils are volatile and sensitive to light, temperature, and oxygen, which affects the biological activity of essential oils and weakens their antimicrobial and antioxidant capabilities. In addition, essential oils may negatively affect food flavor due to their strong odor, which may give consumers an unpleasant experience when used in active food packaging. Essential oils may also interact with food components such as starch and protein, thus affecting food quality. Summary of the invention

[0005] The object of the present invention is to provide an antibacterial film based on Pickering emulsion, and a preparation method and application thereof. The antibacterial film provided by the present invention is based on the Pickering emulsion green encapsulation technology, which can further improve the chemical stability of essential oil in the film and enhance the antibacterial ability of the film.

[0006] To achieve the above object, the present invention provides a method for preparing an antibacterial film based on Pickering emulsion, comprising the following steps:

[0007] S1. dissolving cetyltrimethylammonium bromide (CTAB) in water to obtain a CTAB solution; dissolving graphene oxide (GO) in water to obtain a GO solution;

[0008] S2, mixing the CTAB solution prepared in step S1 with the GO solution in equal proportions to obtain an mGO solution;

[0009] S3, adding tannic acid (TA) to the mGO solution prepared in step S2 to obtain a TA / mGO solution;

[0010] S4, homogenizing and emulsifying the lemongrass essential oil and the TA / mGO solution according to a certain ratio to obtain a Pickering emulsion;

[0011] S5. The Pickering emulsion and the film-forming agent are homogeneously mixed to obtain a film-forming liquid. The film-forming liquid is degassed and then cast into a mold, and then dried to obtain an antibacterial film.

[0012] Preferably, in step S1, the concentration of the CTAB solution is 0.1 mg / mL.

[0013] Preferably, in step S1, the concentration of the GO solution is 2 mg / mL.

[0014] Preferably, in step S3, the addition ratio of the tannic acid in the mGO solution is 0.002 g / mL.

[0015] Preferably, in step S4, the volume ratio of the lemongrass essential oil to the TA / mGO solution is 2:5.

[0016] Preferably, in step S5, the film-forming agent is a mixed solvent of 2% polyvinyl alcohol and 0.6% glycerol.

[0017] Preferably, in step S5, the mass fraction of the Pickering emulsion in the film-forming agent is 0%, 5%, 10%, 15% and 20% respectively.

[0018] Preferably, the drying time of the antibacterial film is 24 hours.

[0019] The present invention also provides an antibacterial film based on the Pickering emulsion prepared by the preparation method.

[0020] The invention provides the application of an antibacterial film based on Pickering emulsion in fruit packaging and preservation.

[0021] Therefore, the present invention adopts the above-mentioned antibacterial film based on Pickering emulsion and its preparation method and application, and its beneficial effects are:

[0022] The present invention utilizes Pickering emulsion encapsulation technology to add lemongrass essential oil to the film in the form of an emulsion. The particle stabilizer (TA / mGO) used not only has a certain antibacterial effect itself, but its special two-dimensional layered structure is more likely to form a three-dimensional network structure in a dispersed system, greatly improving the stability of the emulsion, achieving dual effects of emulsification and antibacterial, and solving the problems of oily antibacterial agents in the film being unable to disperse and having poor stability. In addition, the oxygen-containing functional groups in the particle structure can also form non-covalent bonds such as hydrogen bonds with PVA in the film-forming agent, which not only gives the biodegradable cling film excellent mechanical properties, but also has long-lasting and stable antibacterial properties. Since the emulsion increases the surface area and expands the contact area between the bioactive component and the food, the essential oil incorporated into the film in the form of an emulsion can effectively enhance the antibacterial activity of the composite film, while also reducing its influence on the sensory properties of the food.

[0023] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is an appearance image of the Pickering emulsion prepared in Example 1;

[0025] Figure 2 This is a microscope image of the Pickering emulsion prepared in Example 1;

[0026] Figure 3 This is an appearance image of the antibacterial film prepared in Example 1;

[0027] Figure 4 This is a graph showing the mechanical properties test results of the antibacterial film prepared in Example 1;

[0028] Figure 5 This is a graph showing the test results of the antioxidant properties of the antibacterial film prepared in Example 1;

[0029] Figure 6 This is a plate photo of the antibacterial film prepared in Example 1 after co-culture with Escherichia coli;

[0030] Figure 7 This is a flat plate photo of the antibacterial film prepared in Example 1 after co-culture with Staphylococcus aureus;

[0031] Figure 8 This is a diagram showing the preservation effect of the antibacterial film prepared in Example 1 on strawberries. DETAILED DESCRIPTION

[0032] The technical solution of the present invention is further described below through the accompanying drawings and embodiments.

[0033] Unless otherwise defined, technical or scientific terms used in the present invention shall have the common meanings understood by one having ordinary skills in the field to which the present invention belongs.

[0034] In addition, it should be understood that although this specification is described according to the implementation modes, not every implementation mode includes only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation modes that can be understood by those skilled in the art. These other implementation modes are also covered within the protection scope of the present invention.

[0035] The present invention provides a method for preparing an antibacterial film based on Pickering emulsion, comprising the following steps:

[0036] Dissolving hexadecyltrimethylammonium bromide in water to obtain a CTAB solution; dissolving graphene oxide in water to obtain a GO solution;

[0037] The CTAB solution and the GO solution were mixed in equal proportions to obtain an mGO solution;

[0038] adding tannic acid to the prepared mGO solution to obtain a TA / mGO solution;

[0039] In the present invention, the concentration of the CTAB solution is preferably 0.1 mg / mL, the concentration of the GO solution is preferably 2 mg / mL, and the amount of TA added is preferably 0.01 g (5 mL mGO solution).

[0040] Homogenize and emulsify lemongrass essential oil and the TA / mGO solution in a certain ratio to obtain a Pickering emulsion;

[0041] In the present invention, the preferred ratio of lemongrass essential oil to TA / mGO solution is 2:5, the speed during homogenization is preferably 12000 rpm, and the time is preferably 5 min.

[0042] The Pickering emulsion and the film-forming agent are homogeneously mixed to obtain a film-forming liquid, the film-forming liquid is degassed and then cast into a mold, and the antibacterial film is obtained after drying.

[0043] In the present invention, the film former is preferably 2% polyvinyl alcohol (PVA) and 0.6% glycerol, the concentration of the emulsion in the film former is preferably 5% to 20%, and the film drying time is preferably 24 hours.

[0044] The following non-limiting embodiments may enable a person skilled in the art to more fully understand the present invention, but are not intended to limit the present invention in any way.

[0045] Example 1

[0046] 5 mL of 0.1 mg / mL CTAB solution was added dropwise to 5 mL of 2 mg / mL GO aqueous suspension, and ultrasonicated for 10 min at room temperature to reach adsorption equilibrium. The resulting complex was named mGO. 0.01 g of TA was weighed and added to 5 mL of mGO solution to obtain a TA / mGO solution. 5 mL of TA / mGO solution was mixed with 2 mL of lemongrass essential oil and rapidly emulsified at 12000 rpm for 5 min in a homogenizer to form a Pickering emulsion.

[0047] PVA (2%, w / v) was dissolved in distilled water, and glycerol (0.6%, w / v) was added, and the mixture was heated in a water bath at 95°C and magnetically stirred for 3h to obtain a basic film former. Pickering emulsion was then added to the film former at a ratio of 0%, 5%, 10%, 15%, and 20%, and mixed at 10000rpm for 2min. The mixture (20mL) was poured onto a Petri dish (9cm in diameter) and dried in a vacuum oven at 40°C for 24h to obtain films, which were named PVA (0%), TGPF-5 (5%), TGPF-10 (10%), TGPF-15 (15%), and TGPF-20 (20%).

[0048] Example 2

[0049] 5 mL of 0.1 mg / mL CTAB solution was added dropwise to 5 mL of 2 mg / mL GO aqueous suspension, and ultrasonicated for 10 min at room temperature to reach adsorption equilibrium. The resulting complex was named mGO. 0.01 g of TA was weighed and added to 5 mL of mGO solution to obtain a TA / mGO solution. 5 mL of TA / mGO solution was mixed with 2 mL of lemongrass essential oil and rapidly emulsified at 12000 rpm for 5 min in a homogenizer to form a Pickering emulsion.

[0050] PVA (2%, w / v) was dissolved in distilled water, glycerol (0.6%, w / v) was added, and the mixture was heated in a water bath at 95°C and magnetically stirred for 3 h to obtain a basic film former. Then, Pickering emulsion was added to the film former at a ratio of 8% and mixed at 10000 rpm for 2 min. The mixture (20 mL) was poured onto a petri dish (9 cm in diameter) and dried in a vacuum oven at 40°C for 24 h to obtain a film.

[0051] Example 3

[0052] 5 mL of 0.1 mg / mL CTAB solution was added dropwise to 5 mL of 2 mg / mL GO aqueous suspension, and ultrasonicated for 10 min at room temperature to reach adsorption equilibrium. The resulting complex was named mGO. 0.01 g of TA was weighed and added to 5 mL of mGO solution to obtain a TA / mGO solution. 5 mL of TA / mGO solution was mixed with 2 mL of lemongrass essential oil and rapidly emulsified at 12000 rpm for 5 min in a homogenizer to form a Pickering emulsion.

[0053] PVA (2%, w / v) was dissolved in distilled water, and glycerol (0.6%, w / v) was added, and the mixture was heated in a water bath at 95°C and magnetically stirred for 3 h to obtain a basic film former. Then, Pickering emulsion was added to the film former at a ratio of 13% and mixed at 10000 rpm for 2 min. The mixture (20 mL) was poured onto a petri dish (9 cm in diameter) and dried in a vacuum oven at 40°C for 24 h to obtain a film.

[0054] Example 4

[0055] 5 mL of 0.1 mg / mL CTAB solution was added dropwise to 5 mL of 2 mg / mL GO aqueous suspension, and ultrasonicated for 10 min at room temperature to reach adsorption equilibrium. The resulting complex was named mGO. 0.01 g of TA was weighed and added to 5 mL of mGO solution to obtain a TA / mGO solution. 5 mL of TA / mGO solution was mixed with 2 mL of lemongrass essential oil and rapidly emulsified at 12000 rpm for 5 min in a homogenizer to form a Pickering emulsion.

[0056] PVA (2%, w / v) was dissolved in distilled water, and glycerol (0.6%, w / v) was added, and the mixture was heated in a water bath at 95°C and magnetically stirred for 3 h to obtain a basic film former. Then, Pickering emulsion was added to the film former at a ratio of 18% and mixed at 10000 rpm for 2 min. The mixture (20 mL) was poured onto a petri dish (9 cm in diameter) and dried in a vacuum oven at 40°C for 24 h to obtain a film.

[0057] Example 5

[0058] 5 mL of 0.1 mg / mL CTAB solution was added dropwise to 5 mL of 2 mg / mL GO aqueous suspension, and ultrasonicated for 10 min at room temperature to reach adsorption equilibrium. The resulting complex was named mGO. 0.01 g of TA was weighed and added to 5 mL of mGO solution to obtain a TA / mGO solution. 5 mL of TA / mGO solution was mixed with 2 mL of lemongrass essential oil and rapidly emulsified at 12000 rpm for 5 min in a homogenizer to form a Pickering emulsion.

[0059] PVA (2%, w / v) was dissolved in distilled water, and glycerol (0.6%, w / v) was added and heated in a water bath at 95°C and the mixture was magnetically stirred for 3 h to obtain a basic film former. Then, Pickering emulsion was added to the film former at a ratio of 3% and mixed at 10000 rpm for 2 min. The mixture (20 mL) was poured onto a petri dish (9 cm in diameter) and dried in a vacuum oven at 40°C for 24 h to obtain a film.

[0060] Figure 1 The appearance image of the Pickering emulsion prepared in Example 1 is shown in FIG. Figure 1 It can be seen that the GO-stabilized emulsion has stratification, which indicates that the emulsification ability of GO is poor. After CTAB modification, the height of the emulsion layer stabilized by mGO becomes larger, indicating that its emulsification ability has improved. This is because CTAB is positively charged and GO is negatively charged. The two can be combined through electrostatic attraction, thereby reducing the hydrophilicity of GO and increasing its interfacial activity. After adding TA, the emulsion stratification phenomenon disappears and the emulsion stability is good. This is because TA and mGO can form a complex through hydrophobic interaction, electrostatic attraction and other interactions, which can better wrap on the surface of oil droplets to form a stable emulsion.

[0061] Figure 2 This is a microscope image of the Pickering emulsion prepared in Example 1. Figure 2 It can be seen that with the modification of GO and the addition of TA, the emulsion droplets become smaller, and the smaller the droplet size, the more stable the emulsion, and the better the continuity of the membrane.

[0062] Figure 3 This is an image of the antibacterial film prepared in Example 1. As can be seen from the figure, as the emulsion content increases, the film color becomes darker, which is the effect of the color of the emulsion itself. All film samples have good transparency, and the pattern under the film can be clearly seen even in the case of a high emulsion content (TGPF-20).

[0063] Mechanical properties test of the antibacterial film prepared in Example 1

[0064] The mechanical properties of the antibacterial film were measured using a microelectronic universal tensile test machine. The samples were cut into 80×20 mm 2 The stretching rate was 50 mm / min and each film type was repeated 3 times. Figure 4 The tensile strength (TS) and elongation at break (EB) of the antibacterial film can be observed. The tensile strength of the PVA film is 8.62 MPa and the strain at break is 123%. The tensile strength and strain at break of the film increase with the increase of the emulsion content, which is because the hydrogen bonding reaction formed between the PVA molecules and the TA / mGO molecules enhances the cohesion of the polymer network. However, the excess of lemongrass essential oil molecules may weaken the hydrogen bonds between the polymer chains, resulting in a looser network and a lower elongation at break.

[0065] Antioxidant performance test of the antibacterial film prepared in Example 1

[0066] Take 3 mg of ABTS diammonium salt and add 0.735 mL of distilled water to obtain ABTS diammonium salt stock solution. Take 1 mg of K2S2O8 and add 1.43 mL of distilled water to obtain K2S2O8 stock solution. Mix 0.2 mL of ABTS diammonium salt stock solution and 0.2 mL of K2S2O8 stock solution, place at room temperature in a dark environment for 12 hours, and dilute the mixture 10-20 times with pH 7.4 phosphate buffer until the absorbance is 0.7. This solution is ABTS﹒ + Free radical working solution. Place 0.05 g sample in 5 mL ABTS﹒ + The reaction was carried out in the dark for 60 min in the free radical working solution. Then, the absorbance was measured using a UV spectrophotometer. 734nm The value decreases, indicating that ABTS﹒ + Free radicals are scavenged.

[0067] from Figure 5 It can be seen that the antioxidant activity of pure PVA film is low, while the addition of lemongrass essential oil Pickering emulsion enhances the antioxidant activity of the antibacterial film. As the amount of Pickering emulsion added increases, the antioxidant activity of the antibacterial film is improved, and the antibacterial film has a high antioxidant capacity, indicating that lemongrass essential oil Pickering emulsion can improve the antioxidant activity of the antibacterial film. The improvement of the antioxidant capacity of the antibacterial film is mainly attributed to the high antioxidant properties of lemongrass essential oil, and the phenols and terpenes in the essential oil play an important role in the antioxidant activity.

[0068] Antibacterial test of the antibacterial film prepared in Example 1

[0069] Dilute the activated bacterial solution to 10 8CFU / mL, after irradiating the film sample with UV light for 30 min, 0.3 g of the sample was immersed in 20 mL of Escherichia coli and Staphylococcus aureus suspension. Then, the mixture was incubated at 37 °C with shaking at 180 rpm / min for 9 h. The cultured bacterial solution was diluted to 10 5 Then, 100 μL of bacterial suspension was taken and spread on nutrient agar plates to preliminarily evaluate the antibacterial activity. Figure 6 and Figure 7 It can be seen that with the increase of the emulsion content in the film, the colony counts of Escherichia coli and Staphylococcus aureus in the culture medium gradually decrease, which shows that the antibacterial film prepared in Example 1 has excellent antibacterial properties.

[0070] The preservation effect of the antibacterial film prepared in Example 1 on strawberries

[0071] Before packaging, soak the strawberries in 250ppm sodium hypochlorite for 5 minutes to eliminate external contamination. Then wash the strawberries with distilled water, drain and cover with the prepared film.

[0072] from Figure 8 It can be seen that the strawberries packaged with PVA film and commercial plastic wrap were almost completely rotten on the 7th day, while the visual rot area of ​​the strawberries packaged with the antibacterial film with essential oil emulsion added was much smaller than that of the strawberries packaged with commercial plastic wrap during storage, which shows that the prepared antibacterial emulsion film has a good preservation effect.

[0073] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for preparing an antibacterial film based on Pickering emulsion, characterized in that: The following steps are involved: S1. dissolving hexadecyltrimethylammonium bromide in water to obtain a CTAB solution; dissolving graphene oxide in water to obtain a GO solution; S2, mixing the CTAB solution prepared in step S1 with the GO solution in an equal volume ratio to obtain an mGO solution; S3, adding tannic acid to the mGO solution prepared in step S2 to obtain a TA / mGO solution; S4, homogenizing and emulsifying the lemongrass essential oil and the TA / mGO solution according to a certain ratio to obtain a Pickering emulsion; S5, homogeneously mixing the Pickering emulsion and the film-forming agent to obtain a film-forming liquid, degassing the film-forming liquid and casting it in a mold, and drying it to obtain an antibacterial film; In step S1, the concentration of the CTAB solution is 0.1 mg / mL; in step S1, the concentration of the GO solution is 2 mg / mL; In step S3, the addition ratio of the tannic acid in the mGO solution is 0.002 g / mL; In step S4, the volume ratio of the lemongrass essential oil to the TA / mGO solution is 2:5, the homogenization speed is 10000-12000 rpm, and the time is 3-5 min; In step S5, the film-forming agent is a mixed aqueous solution of 2% (w / v) polyvinyl alcohol and 0.6% (w / v) glycerol.

2. The method for preparing an antibacterial film based on Pickering emulsion according to claim 1, characterized in that: In step S5, the mass fraction of the Pickering emulsion in the film-forming agent is 5% to 20%.

3. The method for preparing an antibacterial film based on Pickering emulsion according to claim 1, characterized in that: The drying time of the antibacterial film is 24 h.

4. An antibacterial film based on Pickering emulsion, characterized in that: The Pickering emulsion-based antibacterial film is prepared by the method for preparing the Pickering emulsion-based antibacterial film according to any one of claims 1 to 3.

5. The antibacterial film based on Pickering emulsion according to claim 4, characterized in that: Antibacterial films based on Pickering emulsions are used in fruit packaging and preservation.

Images