CN114805876A - Preparation method of one-way water-blocking self-cleaning chitosan zein double-layer film - Google Patents
Preparation method of one-way water-blocking self-cleaning chitosan zein double-layer film Download PDFInfo
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Abstract
The invention discloses a preparation method of a one-way water-blocking self-cleaning chitosan zein double-layer film, which comprises the steps of firstly dissolving chitosan in acetic acid to prepare a chitosan solution, then adding nanoparticles co-embedding curcumin and nisin and plasticizer glycerol under a certain temperature condition, stirring, and ultrasonically degassing to obtain an active layer coating liquid; pouring the active layer coating liquid into a leveling die, and forming gel at a certain temperature; dissolving zein in ethanol to prepare zein solution, adding plasticizer glycerol, stirring, and ultrasonically degassing to obtain a moisture-proof and self-cleaning layer coating solution; and finally, uniformly paving the coating liquid of the damp-proof and self-cleaning layer on the surface of the gel, and drying at a certain temperature to form a double-layer film. According to the invention, zein is creatively used as a moisture-proof and self-cleaning layer, and nanoparticles with excellent antioxidant and antibacterial activities are added into the lower substrate of the double-layer film to be used as an active layer, so that the biological activity and the service life of the chitosan film are effectively improved.
Description
Technical Field
The invention belongs to the technical field of food green packaging, and particularly relates to a preparation method of a one-way water-blocking self-cleaning chitosan zein double-layer film.
Background
Petroleum-based synthetic polymers are widely used as packaging materials. However, the use of synthetic petroleum-based products poses health and environmental problems and suitable alternatives are being sought. Biodegradable natural polymers are being extensively studied. Among the different biodegradable polymers, chitosan stands out for its excellent film-forming properties and unique physicochemical properties (e.g. strong barrier capacity and mechanical properties). However, the pure chitosan film is difficult to resist moisture permeation of the external environment, stains are easily stained in the application process, favorable conditions are provided for the growth of microorganisms, and the functional characteristics of the chitosan film are low.
Therefore, it has been desired to design and produce chitosan films which absorb excess moisture from the food itself, and prevent moisture from the external environment from penetrating and removing stains from the surface of the package.
At present, how to provide a technology for improving the applicability, the air barrier performance and the heat sealing performance of a chitosan film is a technical problem to be solved urgently by technical personnel in the field.
Disclosure of Invention
This section is for the purpose of summarizing some aspects of embodiments of the invention and to briefly introduce some preferred embodiments. In this section, as well as in the abstract and the title of the invention of this application, simplifications or omissions may be made to avoid obscuring the purpose of the section, the abstract and the title, and such simplifications or omissions are not intended to limit the scope of the invention.
The present invention has been made keeping in mind the above and/or other problems occurring in the prior art.
Therefore, the invention aims to overcome the defects in the prior art and provide a preparation method of a self-cleaning type chitosan zein double-layer film with unidirectional water resistance.
In order to solve the technical problems, the invention provides the following technical scheme: a method for preparing a self-cleaning chitosan zein double-layer film with unidirectional water resistance comprises,
dissolving pectin, nisin and curcumin in pure water, acetic acid solution with pH of 4.0 and absolute ethyl alcohol respectively to obtain pectin solution, nisin solution and curcumin solution;
then adding the nisin solution into the pectin solution drop by drop, and stirring to obtain a composite solution;
then dropwise adding the curcumin solution into the composite solution to prepare a mixed solution system, stirring, and centrifugally freeze-drying to obtain nano-particles;
dissolving chitosan in acetic acid to prepare a chitosan solution, adding nanoparticles and a plasticizer into the chitosan solution, stirring, and performing ultrasonic degassing to obtain an active layer coating liquid;
pouring the prepared active layer coating liquid into a leveling die to form gel;
dissolving zein in ethanol, adding a plasticizer into the zein solution, stirring, and ultrasonically degassing to obtain a moisture-proof and self-cleaning layer coating solution;
and uniformly spreading the prepared coating liquid on the surface of the gel, cooling at room temperature to form double-layer hydrogel, and drying to form a double-layer film.
As an optimal scheme of the preparation method of the unidirectional water-blocking self-cleaning type chitosan zein double-layer film, the method comprises the following steps: in the mixed solution system, the concentrations of pectin, nisin and curcumin solution are 1-3 mg/mL, 3-6 mg/mL and 3-6 mg/mL respectively.
As an optimal scheme of the preparation method of the unidirectional water-blocking self-cleaning type chitosan zein double-layer film, the method comprises the following steps: the active layer coating liquid comprises 2-4% of chitosan by mass, 1-3% of nanoparticles by mass and 25-40% of a plasticizer by mass.
As an optimal scheme of the preparation method of the unidirectional water-blocking self-cleaning type chitosan zein double-layer film, the method comprises the following steps: the plasticizer comprises glycerin.
As an optimal scheme of the preparation method of the unidirectional water-blocking self-cleaning type chitosan zein double-layer film, the method comprises the following steps: the mass fraction of the nanoparticles is 2%.
As an optimal scheme of the preparation method of the unidirectional water-blocking self-cleaning type chitosan zein double-layer film, the method comprises the following steps: and pouring the prepared active layer coating liquid into a leveling die to form gel, wherein the gel forming temperature is 25-50 ℃.
As an optimal scheme of the preparation method of the unidirectional water-blocking self-cleaning type chitosan zein double-layer film, the method comprises the following steps: the ultrasonic degassing time is 10-20 minutes.
As an optimal scheme of the preparation method of the unidirectional water-blocking self-cleaning type chitosan zein double-layer film, the method comprises the following steps: and forming a double-layer film after drying, wherein the drying temperature is 40-50 ℃, and the drying time is 10-15 hours.
The invention further aims to overcome the defects in the prior art and provide the double-layer film prepared by the preparation method of the one-way water-blocking self-cleaning type chitosan zein double-layer film.
It is another object of the present invention to overcome the deficiencies of the prior art and to provide the use of said bilayer film as a food packaging film.
The invention has the beneficial effects that:
(1) according to the invention, through the design of the double-layer film, hydrophobic zein is creatively added to the outer layer to serve as a moisture-proof and self-cleaning layer, and nanoparticles with excellent antioxidant and antibacterial activities are added to the lower-layer matrix of the double-layer film to serve as an active and hydrated layer, so that the applicability of the film is remarkably improved; the mechanical property of the film is obviously improved by adding the nano particles, and meanwhile, the addition amount of the nano particles is preferably 2 percent, so that the mechanical property is optimal; films incorporating nanoparticles can significantly improve moisture barrier, higher opacity, because the nanoparticles can scatter transmitted light by occupying gaps in the polymer matrix, better protecting the food product.
(2) According to the invention, the zein with excellent moisture-proof and self-cleaning capabilities is added to the upper layer of the double-layer film, so that the moisture barrier capability of the double-layer film is obviously improved, the service life of the chitosan film can be prolonged, and the double-layer film is natural and pollution-free and can be widely applied to the fresh keeping of fruits, vegetables, meat and other foods.
(3) The method is simple to operate, easy to control, high in operability and suitable for industrial production.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings needed to be used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without inventive exercise. Wherein:
FIG. 1 is a graph of the mechanical properties of two-layer films of comparative and various examples of the present invention;
FIG. 2 is a diagram showing the moisture barrier of the two-layer film of the comparative example and each example of the present invention;
FIG. 3 is a graph showing the antioxidant activity of the two-layer film of the comparative example and each example of the present invention;
FIG. 4 is a diagram of the bacteriostatic activity of the double-layer film of the comparative example and each example;
FIG. 5 is a graph comparing the content of nisin and pectin versus nanoparticle encapsulation efficiency in comparative example 2 according to the present invention;
FIG. 6 is a graph comparing the content of nisin and pectin versus the nanoparticles PDI in comparative example 2 of the present invention;
FIG. 7 is a scanning electron micrograph of nanoparticles of comparative example 2 according to the present invention.
Detailed Description
In order to make the aforementioned objects, features and advantages of the present invention more comprehensible, specific embodiments thereof are described in detail below with reference to examples of the specification.
In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention, but the present invention may be practiced in other ways than those specifically described and will be readily apparent to those of ordinary skill in the art without departing from the spirit of the present invention, and therefore the present invention is not limited to the specific embodiments disclosed below.
Furthermore, reference herein to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one implementation of the invention. The appearances of the phrase "in one embodiment" in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. The chitosan molecular weight of the invention is 500kDa, the deacetylation degree is 92 percent, and other raw materials are common commercial products.
The key properties of the bilayer membranes referred to in the various examples and comparative examples above were determined:
1. mechanical Properties
Elongation at break and tensile strength were measured using a TA texture analyzer, following ASTM standards (D882-02). Tensile Strength (TS) and Elongation (EB) were measured after cutting the film samples into rectangular samples 10mm wide and 70mm long.
2. Water vapour permeability
Weighing 3g of anhydrous CaCl 2 In the weighing bottle, the mouth of the weighing bottle is covered by a composite film, and then m is weighed and recorded 0 Placing the mixture into a constant temperature and humidity cabinet, keeping the relative humidity of 90 percent at 23 ℃, weighing and recording m after 24 hours 1 According to the front and back propertiesThe amount change calculates the water vapor permeability. The water vapor permeability is calculated according to the following formula:
WVP＝(Δm×d)/(A×t×P)
in which Δ m (kg) -the difference in mass of the weighing bottles, d (mm) -the thickness of the membrane; t(s) -time; a (m) 2 ) -an effective area of the membrane; p (KPa) -difference in water vapor pressure inside and outside the membrane.
3. Water content, water solubility, swelling degree and water contact angle
Weighing a 2X 2cm film (W) 0 ) Dried at 105 ℃ for 24 hours and then weighed (W) 1 ). The dried film was then immersed in 50mL of distilled water for 24 hours, the surface water was removed with absorbent paper, and the weight of the film (W) was measured 2 ) Drying in a 105 deg.C oven to constant weight (W) 3 ). The moisture content, water solubility and swell value of the film are determined by the following formulas:
the water contact angle of the films was measured using a contact angle analyzer (OCA15EC, dapphysicalincolumns GmbH, Filterstadt, Germany). The WCA was measured after 0 and 60 seconds by placing a drop of 2. mu.L of distilled water on the surface of the film using a micro-syringe.
4. Color and opacity
The color of the film was measured by a color difference meter (SC-80C, Beijing, China). The L (brightness), a (red-grey) and b (yellow-blue) parameters were determined from the reflectance measurements. Opacity was measured with a uv spectrophotometer. The dimensions of the film were 10mm by 40 mm. An empty quartz cell was used as a reference. Opacity is calculated as follows:
wherein A is 600 As absorbance, d (mm) is the film thickness.
5. Determination of antioxidant Activity of membranes
The double-layer membrane is cut into a square with the size of 2cm multiplied by 2cm, the square is placed into a sample bottle containing 10mL of distilled water, the sample bottle is placed on a magnetic stirrer at normal temperature and stirred for 30 minutes, and 1mL of a sample is added into 4mL of DPPH solution (150 mu mol/L), and the solution is uniformly stirred. The reaction mixture was left standing for 30 minutes in the dark to sufficiently remove the radicals, and the absorbance was measured at 517nm using a visible spectrophotometer (VIS-7220N, Rayleigh analysis instruments).
Will contain 2.4mM K 2 S 2 O 8 And ABTS of 7.0mMABTS + The free radical stock solution was incubated in the dark for 12-16 hours. ABTS was diluted with 5mM phosphate buffer (pH 7.4) + The radical stock solution was made to have an absorbance at 730nm of 0.70. + -. 0.02. The film samples were immersed in 5ml of phosphate buffer. 200. mu.l of the sample solution was mixed with 2mL of ABTS + The solutions were mixed as samples. A mixture of 2mL of phosphate buffered saline and 200. mu.l of the sample solution was used as a control, and a mixture of 200. mu.l of distilled water and 2mL of the ABTS working solution was used as a blank. The mixture was incubated in the dark for 20 minutes. The absorbance was measured at 730nm using a UV-visible spectrophotometer.
6. Determination of the antibacterial Activity of the membranes
The antibacterial activity of the double-layer membrane on staphylococcus aureus and escherichia coli is measured by adopting an agar plate test. After all films were sterilized under UV irradiation for 20 minutes, they were cut into 2 cm. times.2 cm and placed in a 6-well plate. Then 500. mu.L of sterilized LB medium was added to each well, followed by 100. mu.L of bacterial suspension (. about.10) 7 CFU·mL -1 ) The cells were incubated under white light irradiation and dark conditions at 37 ℃ for 24 hours with gentle shaking. The samples were removed after 3, 6, 9, 12 and 15 hours of incubation, diluted and placed on agar plates for viable cell count.
The preparation method of the nano-particles comprises the following steps:
dissolving pectin, nisin and curcumin in pure water, acetic acid solution with pH of 4.0 and absolute ethanol respectively to obtain pectin solution (1mg/mL), nisin solution (3mg/mL) and curcumin solution (3 mg/mL);
then adding the nisin solution into the pectin solution drop by drop, and stirring to obtain a composite solution;
and then dropwise adding the curcumin solution into the composite solution to prepare a mixed solution system, wherein the concentrations of the pectin, nisin and curcumin solution in the mixed solution system are respectively 1mg/mL, 6mg/mL and 4mg/mL, stirring, and centrifuging and freeze-drying to obtain the nanoparticles.
Example 1
(1) Dissolving chitosan in 1% (v/v) acetic acid solution to prepare solution with mass concentration of 2g/100mL, adding 1% of nanoparticles and 25% of glycerol based on the mass of the chitosan into the chitosan solution at 55 ℃, stirring for 1 hour, and ultrasonically degassing for 15 minutes to obtain chitosan-nanoparticle active layer coating solution;
(2) pouring the active layer coating liquid prepared in the first step into a leveling die, and forming gel at 40 ℃;
(3) dissolving zein in 90% (v/v) ethanol solution to prepare solution with mass concentration of 10g/100mL, adding glycerol accounting for 25% of the mass of the zein into the zein solution, stirring for 2 hours, and ultrasonically degassing for 20 minutes to obtain the zein moisture-proof and self-cleaning layer coating solution.
(4) Pouring the zein moisture-proof and self-cleaning layer coating solution prepared in the third step onto the chitosan-nanoparticle gel formed in the second step, and then drying in a drying oven at 40 ℃ for 12 hours to form a double-layer film.
Example 2
(1) Dissolving chitosan in 1% (v/v) acetic acid solution to prepare solution with mass concentration of 2g/100mL, adding 2% of nanoparticles and 25% of glycerol based on the mass of the chitosan into the chitosan solution at 55 ℃, stirring for 1 hour, and ultrasonically degassing for 15 minutes to obtain chitosan-nanoparticle active layer coating solution;
(2) pouring the active layer coating liquid prepared in the first step into a leveling die, and forming gel at 40 ℃;
(3) dissolving zein in 90% (v/v) ethanol solution to prepare solution with mass concentration of 10g/100mL, adding glycerol accounting for 25% of the mass of the zein into the zein solution, stirring for 2 hours, and ultrasonically degassing for 20 minutes to obtain the zein moisture-proof and self-cleaning layer coating solution.
(4) Pouring the zein moisture-proof and self-cleaning layer coating solution prepared in the third step onto the chitosan-nanoparticle gel formed in the second step, and then drying in a drying oven at 40 ℃ for 12 hours to form a double-layer film.
Example 3
(1) Dissolving chitosan in 1% (v/v) acetic acid solution to prepare solution with mass concentration of 2g/100mL, adding nanoparticles accounting for 3% of the mass of the chitosan and 25% of glycerol into the chitosan solution at 55 ℃, stirring for 1 hour, and then ultrasonically degassing for 15 minutes to obtain chitosan-nanoparticle active layer coating solution;
(2) pouring the active layer coating liquid prepared in the first step into a leveling die, and forming gel at 40 ℃;
(3) dissolving zein in 90% (v/v) ethanol solution to prepare solution with mass concentration of 10g/100mL, adding glycerol accounting for 25% of the mass of the zein into the zein solution, stirring for 2 hours, and ultrasonically degassing for 20 minutes to obtain the zein moisture-proof and self-cleaning layer coating solution.
(4) Pouring the zein moisture-proof and self-cleaning layer coating solution prepared in the third step onto the chitosan-nanoparticle gel formed in the second step, and then drying in a drying oven at 40 ℃ for 12 hours to form a double-layer film.
Comparative example 1
Compared with the examples 1, 2 and 3, the difference is that no nano-particles are added, and the steps are as follows:
(1) dissolving chitosan in 1% (v/v) acetic acid solution to prepare solution with mass concentration of 2g/100mL, adding 25% glycerol based on the mass of chitosan into the chitosan solution at 55 ℃, stirring for 1 hour, and ultrasonically degassing for 15 minutes to obtain chitosan layer coating solution;
(2) pouring the active layer coating liquid prepared in the first step into a leveling die, and forming gel at 40 ℃;
(3) dissolving zein in 90% (v/v) ethanol solution to prepare solution with mass concentration of 10g/100mL, adding glycerol accounting for 25% of the mass of the zein into the zein solution, stirring for 2 hours, and ultrasonically degassing for 20 minutes to obtain the zein moisture-proof and self-cleaning layer coating solution.
(4) Pouring the zein moisture-proof and self-cleaning layer coating solution prepared in the third step onto the chitosan gel formed in the second step, and then drying in a drying oven at 40 ℃ for 12 hours to form a double-layer film.
The following tests on the performance of the two-layer film provided in comparative example 1 and examples 1 to 3 of the present invention are shown in fig. 1, where a is the tensile strength and elongation of the comparative example and examples, and B is the mechanical property comparison result of the conventional polymer film.
As can be seen from fig. 1, the tensile strength and elongation of the example bilayer film are higher than those of the comparative bilayer film, which shows that the mechanical properties of the film are significantly improved by the addition of the nanoparticles, wherein the tensile strength and elongation of example 2 are the highest. And the tensile strength value of the double-layer film added with the nano particles is equivalent to that of typical packaging plastics such as low-density polyethylene (LDPE,45.2-58.6MPa), but is slightly lower than Polystyrene (PS) (45-63MPa), and shows high potential as a packaging material.
Comparative example and example: (A) water content, (B) water solubility, (C) swelling degree, (D) water vapor transmission rate, (E) water contact angle on C side (chitosan side), and (F) water contact angle on Z side (zein side), as shown in fig. 2.
As can be seen from fig. 2, the film incorporating nanoparticles significantly improved the moisture barrier ability of the comparative example, and this phenomenon was caused because the nanoparticles and the chitosan matrix occupied hydroxyl groups of chitosan molecules through hydrogen bond interaction, and blocked the binding of water molecules. Measuring the water vapor transmission rate on both sides of the double-layer film also found that both sides of the double-layer film had different water vapor transmission rates, which is consistent with the double-layer film having the unidirectional water-blocking property mentioned in the present invention.
With the addition of nanoparticles, the chitosan side water contact angle value increased slightly, probably due to the interaction between chitosan and nanoparticles. And after the water drops are deposited for 60s, the water contact angle value of the chitosan layer is obviously reduced, but the water contact angle value of the zein layer is not changed greatly, which shows that the hydrophobic group of the zein hinders the water permeation, and the hydrophilic property of the chitosan accelerates the water permeation.
TABLE 1 comparative and examples two-layer film chroma and opacity
As can be seen from Table 1, all the bilayer films were smooth and uniform in surface. Upon addition of the nanoparticles, the Δ E of the bilayer membrane increased, mainly due to the decrease in L, the increase in a and b. It is noteworthy that the value of b represents a greater variation and, depending on the concentration effect of the nanoparticles, a lighter yellow color, due to the yellowish coloration of the nanoparticles.
All films had opacity values between 1.03 and 1.29, which is similar to the opacity value (1.67) of commercial films used for packaging. The increased mass ratio of nanoparticles resulted in higher opacity, since the nanoparticles can scatter transmitted light by occupying gaps in the polymer matrix, indicating that the presence of nanoparticles can better protect food.
The antioxidant activity of the bilayer films of the control and the examples is shown in FIG. 3. It can be seen that the DPPH radical activity of the control example was significantly improved after the nanoparticles were added, because curcumin had a strong antioxidant activity. This suggests that nano-encapsulated curcumin is an effective way to maintain its structural integrity and antioxidant activity. Similar to the DPPH test, the scavenging activity of ABTS radicals was significantly improved after the addition of nanoparticles, since nanoparticles have a good scavenging effect on OH radicals. The nano composite film has high antioxidant activity, and can be used for active packaging application to prevent food oxidation, maintain food quality and prolong the shelf life of food.
The bacteriostatic activity of the double-layer film of the control example and each example is shown in fig. 4.
Curcumin is effective in generating Reactive Oxygen Species (ROS) under white light, thus exhibiting enhanced antibacterial effects. The film is used as a packaging material and is easily influenced by light during use. Inspired by this, the antibacterial performance of the films under light and dark conditions was analyzed (fig. 4). Under the condition of illumination, all the nano composite films show effective killing effect on bacteria, and the inhibition effect is enhanced along with the prolonging of the illumination time. This is probably due to the fact that curcumin produces reactive oxygen species during light exposure, which may cause oxidative stress, destroying the integrity of bacterial membranes, and thus enhancing the antibacterial effect. In addition, the membrane containing the nanoparticles has stronger inhibition effect on gram-positive staphylococcus aureus than gram-negative escherichia coli, which is mainly because nisin has stronger inhibition effect on gram-positive bacteria, so that nisin mediates the interaction between curcumin and pectin and the nanoparticles have good antibacterial ability. Therefore, the nano-particle film developed by the research has the application potential of prolonging the shelf life of the packaged food.
Comparative example 2
The test method comprises the following steps: a proper amount of sample is taken to determine the particle size and the dispersity (PDI) of the nanoparticles by using a dynamic light scattering technology. The samples were equilibrated at 25 ℃ for 1 minute before measurement, the detection angle was 173 °, the refractive index of protein was set to 1.45, the refractive index of water was set to 1.33, and the measurement time was 180 seconds. All sample determinations were repeated three times.
Method for measuring Encapsulation Efficiency (EE): centrifuging the nanoparticle suspension to obtain free curcumin, and measuring at 426nm with ultraviolet spectrophotometer; free nisin was determined by a miniprotein kit.
The determination method of the Scanning Electron Microscope (SEM) comprises the following steps: the nanoparticle suspension was dropped onto a silicon wafer and after spraying the gold with a vacuum sputter coater (108Auto, TedPella inc., Redding, CA, USA), photographed at 10 kv accelerating voltage using a scanning electron microscope (S-4800, Hitachi, Tokyo, Japan).
On the basis of the preparation of the nano-particles, the influence of the pectin content on the nano-particles is researched.
And (3) analysis: as shown in fig. 5, the particle size of the nanoparticles gradually decreased with increasing pectin content, wherein nisin: 1, pectin: 6 (mass ratio), since when the added amount of pectin is small, not enough pectin is combined with nisin, resulting in complete exposure of the hydrophobic region of nisin, thus nisin is vulnerable to hydrophobic interaction with curcumin, the nanoparticle size is large, and when the proportion of pectin is increased, a large amount of pectin can be thoroughly combined with the hydrophilic region of nisin, thus the hydrophobic region of nisin is completely exposed, the hydrophobic interaction of nisin and curcumin becomes stronger, and the size of the synthesized nanoparticles is very small.
See fig. 6, when the ratio is increased to 1: at 6, too much pectin adheres to the nisin surface, increasing the nanocomposite particle size. PDI also exhibits the same trend, and in general PDI <0.3 is considered a stable system, nisin: 1, pectin: 6, the lowest PDI and the highest encapsulation efficiency are exhibited, so the optimal design of the nanoparticles to pectin can be obtained by optimization experiments: nisin ═ 1: 6. referring to fig. 7, it can be seen in the scanning electron micrograph that the nanoparticles exhibit a uniform spherical shape and have a smooth surface without cracks, and thus it is considered that the nanoparticles are successfully prepared.
In conclusion: compared with the chitosan/zein double-layer film prepared without the nano particles, the double-layer film prepared by the nano particles has better mechanical property, moisture resistance, oxidation resistance and bacterial inhibition, and stronger applicability.
The layer-by-layer self-assembly solution casting technology utilizes the principle that materials with opposite charges are sequentially adsorbed on a substrate, can control the thickness of the film, and is an ideal method for preparing the double-layer film. In addition, such a two-layer film substrate may be further formed into an active packaging material by combining an antimicrobial agent and an antioxidant.
The invention uses a layer-by-layer self-assembly casting method, uses a chitosan film containing nanoparticles co-embedded with curcumin and nisin as a hydration activity inner layer, uses a zein film as a moisture-proof and self-cleaning outer layer, and tries to prepare the preservative film with excellent physicochemical properties. The packaging and fresh-keeping agent is mainly used for packaging and fresh-keeping of foods with high moisture content, and effectively prolongs the shelf life of the foods. The method does not introduce exogenous reagents, and the preparation process has the characteristics of greenness, safety and convenience, and the technology of the invention can provide a reliable strategy for improving the applicability of the chitosan membrane.
It should be noted that the above-mentioned embodiments are only for illustrating the technical solutions of the present invention and not for limiting, and although the present invention has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that modifications or equivalent substitutions may be made on the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, which should be covered by the claims of the present invention.
Claims (10)
1. A preparation method of a one-way water-blocking self-cleaning chitosan zein double-layer film is characterized by comprising the following steps: comprises the steps of (a) preparing a mixture of a plurality of raw materials,
dissolving pectin, nisin and curcumin in pure water, acetic acid solution with pH of 4.0 and absolute ethyl alcohol respectively to obtain pectin solution, nisin solution and curcumin solution;
then adding the nisin solution into the pectin solution drop by drop, and stirring to obtain a composite solution;
then dropwise adding the curcumin solution into the composite solution to prepare a mixed solution system, stirring, and centrifugally freeze-drying to obtain nano-particles;
dissolving chitosan in acetic acid to prepare a chitosan solution, adding nanoparticles and a plasticizer into the chitosan solution, stirring, and performing ultrasonic degassing to obtain an active layer coating liquid;
pouring the prepared active layer coating liquid into a leveling die to form gel;
dissolving zein in ethanol, adding a plasticizer into the zein solution, stirring, and ultrasonically degassing to obtain a moisture-proof and self-cleaning layer coating solution;
and uniformly spreading the prepared coating liquid on the surface of the gel, cooling at room temperature to form double-layer hydrogel, and drying to form a double-layer film.
2. The method for preparing the self-cleaning chitosan zein double-layer film capable of unidirectionally blocking water as claimed in claim 1, wherein the self-cleaning chitosan zein double-layer film comprises the following steps: in the mixed solution system, the concentrations of pectin, nisin and curcumin solution are 1-3 mg/mL, 3-6 mg/mL and 3-6 mg/mL respectively.
3. The method for preparing the self-cleaning type chitosan zein double-layer film capable of unidirectionally blocking water as claimed in claim 1 or 2, wherein the self-cleaning type chitosan zein double-layer film comprises the following steps: the active layer coating liquid comprises 2-4% of chitosan by mass, 1-3% of nanoparticles by mass and 25-40% of a plasticizer by mass.
4. The method for preparing the self-cleaning type chitosan zein double-layer film capable of unidirectionally blocking water as claimed in claim 3, wherein the self-cleaning type chitosan zein double-layer film comprises the following steps: the plasticizer comprises glycerin.
5. The method for preparing the self-cleaning chitosan zein double-layer film capable of unidirectionally blocking water as claimed in claim 4, wherein the self-cleaning chitosan zein double-layer film comprises the following steps: the mass fraction of the nanoparticles is 2%.
6. The method for preparing the self-cleaning chitosan zein double-layer film capable of unidirectionally blocking water as claimed in claim 1, wherein the self-cleaning chitosan zein double-layer film comprises the following steps: and pouring the prepared active layer coating liquid into a leveling die to form gel, wherein the gel forming temperature is 25-50 ℃.
7. The method for preparing the self-cleaning chitosan zein double-layer film capable of unidirectionally blocking water as claimed in claim 1, wherein the self-cleaning chitosan zein double-layer film comprises the following steps: the ultrasonic degassing time is 10-20 minutes.
8. The method for preparing the self-cleaning chitosan zein double-layer film capable of unidirectionally blocking water as claimed in claim 1, wherein the self-cleaning chitosan zein double-layer film comprises the following steps: and forming a double-layer film after drying, wherein the drying temperature is 40-50 ℃, and the drying time is 10-15 hours.
9. A bi-layer film prepared by the method for preparing the self-cleaning type chitosan zein bi-layer film capable of unidirectionally blocking water according to any one of claims 1 to 8.
10. Use of the bilayer film of claim 9 as a food packaging film.
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