PH response type double-layer membrane capable of improving stability of natural pigment as well as preparation method and application of pH response type double-layer membrane

Abstract

The invention relates to a preparation method of a pH response type double-layer membrane capable of improving the stability of a natural pigment. The preparation method comprises the following steps: S1, preparing zein-anthocyanin binary nanoparticles; s2, preparation of a zein-anthocyanin-sodium alginate ternary nano material, wherein the zein-anthocyanin-sodium alginate ternary nano material is prepared; and S3, preparing the pH response type double-layer membrane. According to the prepared pH response type double-layer film, on one hand, the deterioration speed of food can be delayed, and the good effect of prolonging the shelf life is achieved; the retention time of the plant source pigment in the packaging film is prolonged, so that the prepared packaging film has a long-acting service life, and the application limitation is reduced; on the other hand, the prepared packaging film has good pH responsiveness, the quality condition of food contained in the packaging film can be visually reflected, and convenience and sense of safety are provided for consumers.

Description

Technical Field

[0001] The invention belongs to the technical fields of nano-encapsulation, food packaging and material chemical engineering, and specifically relates to a pH-responsive double-layer film capable of improving the stability of natural pigments, and a preparation method and application thereof. Background Art

[0002] Anthocyanins from plant sources, such as pigments extracted from purple sweet potatoes, mulberries, blueberries, comfrey and other plants, have antioxidant and antibacterial properties, and have different colors in different pH environments. They can be used as natural indicators to replace traditional chemical pigments and are used in smart packaging films to facilitate the safe monitoring of the freshness of food.

[0003] However, due to its own instability, anthocyanins are easily decomposed by oxygen and light. Nanoencapsulation technology is often used to encapsulate active compounds. Intermolecular interactions are a way to improve the stability of active substances. Zein is considered a non-dietary plant protein. It contains three-quarters of hydrophobic amino acid residues, so it has amphiphilicity and is often used for drug delivery. The hydrophobic amino acid residues of zein can produce hydrophobic interactions with the benzene rings of anthocyanins, and then form small nanostructured particles using anti-solvent precipitation. However, zein nanoparticles tend to aggregate at their isoelectric points. This tendency is overcome by using polysaccharides as external coating structures to improve the dispersibility of nanoparticles and further improve the stability of anthocyanins. It also facilitates the dispersion of anthocyanin nanoencapsulation structures in film liquids to prepare uniform food packaging films. Sodium alginate is an anionic polysaccharide with good biocompatibility and low cost. It is widely used in the fields of food and medicine and is a good material for the coating layer in nanoencapsulation structures.

[0004] Polylactic acid is a biodegradable polymer with good application prospects in the current context of increasingly serious white pollution. Polylactic acid has good mechanical properties, excellent waterproof properties and good transparency, but the single-layer polylactic acid film has a single function and is not easy to mix with active substances such as anthocyanins, which limits its application in food. Chitosan is the only cationic polysaccharide in nature extracted from chitin, with good bioadhesion, compatibility, antibacterial properties and film-forming properties. The amino group of chitosan can produce electrostatic interactions with the carboxyl group of sodium alginate to produce a more cohesive structure, which can not only be well blended with nano-encapsulated anthocyanins, but also improve the overall performance of the film.

[0005] Therefore, the present invention develops and prepares a packaging film that can improve the stability of natural pigments. Summary of the invention

[0006] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a pH-responsive double-layer film that can improve the stability of natural pigments, as well as a preparation method and application thereof. The double-layer film has polylactic acid as an outer film and a mixture of chitosan and zein-anthocyanin-sodium alginate nanomaterials as an inner film. On the one hand, the speed of food spoilage can be slowed down, thereby playing a good role in extending the shelf life; the time for plant-derived pigments to be retained in the packaging film is increased, so that the prepared packaging film has a long service life and reduces application limitations; on the other hand, the prepared packaging film has good pH responsiveness, which can intuitively reflect the quality of the food inside, providing convenience and a sense of security for consumers.

[0007] The present invention solves the technical problem by the following technical solutions:

[0008] A method for preparing a pH-responsive double-layer membrane capable of improving the stability of natural pigments, wherein the double-layer membrane is a double-layer membrane with polylactic acid as an outer layer and a mixture of chitosan and zein-anthocyanin-sodium alginate nanomaterials as an inner layer;

[0009] The steps of the method are:

[0010] S1. Preparation of zein-anthocyanidin binary nanomaterials: dissolving zein in an ethanol solution, heating and stirring at a certain temperature until completely dissolved to form a zein solution for later use; dissolving different masses of anthocyanidins in an ethanol solution, heating and stirring at a certain temperature until completely dissolved to form anthocyanidin solutions of different concentrations for later use; uniformly mixing the zein solution and the anthocyanidin solution, dropping deionized water anti-solvent into the solution for precipitation, stirring and incubating, and removing ethanol by rotary evaporation to obtain zein-anthocyanidin binary nanoparticles;

[0011] S2, preparation of zein-anthocyanidin-sodium alginate ternary nanomaterial: taking the zein-anthocyanidin binary nanoparticles of S1, adding them into the sodium alginate solution and stirring them evenly to obtain the zein-anthocyanidin-sodium alginate ternary nanomaterial;

[0012] S3. Preparation of pH-responsive double-layer membrane: add zein-anthocyanin-sodium alginate ternary nanomaterials of S2 to the chitosan stock solution in sequence, heat and stir to mix evenly to obtain a mixed solution, use an ultrasonic reactor to remove bubbles in the mixed solution to obtain a film-forming solution, pour the film-forming solution into a square glass box, use an oven to dry to form an inner membrane; pour and cast a certain volume of polylactic acid solution on the surface of the dried inner membrane, let it stand and dry to form an outer membrane; remove the membrane to obtain pH-responsive double-layer membranes with different nanoparticle contents.

[0013] Moreover, the volume fraction of the ethanol solution in the S1 is 80%, the heating and stirring temperature is 20-60°C, and the stirring time is 1-5 hours; the mass ratio of the zein to anthocyanin is (1:0.1)-(1:1), the pH of the zein is 3.30, and the stirring incubation conditions are stirring at 25°C for 30 minutes.

[0014] Moreover, the mass ratio of the zein solution to the anthocyanin solution in S1 is 1:0.3.

[0015] Moreover, the mass ratio of the zein-anthocyanin binary nanoparticles to the sodium alginate solution is 4:1.

[0016] Moreover, the mass ratio of the zein-anthocyanin binary nanomaterial to the sodium alginate solution in S2 is (20:1) to (1:2).

[0017] Moreover, the concentration of the chitosan stock solution in S3 is 2% w / v, the concentration of the polylactic acid solution is 1% w / v, the mass ratio of the chitosan solution to the ternary nanomaterial of zein-anthocyanidin-sodium alginate is (1:0.01) to (1:0.03), the mixing and stirring time of the chitosan stock solution and the ternary nano dispersion of zein-anthocyanidin-sodium alginate is 1 hour, and the stirring and heating temperature is 25°C; the ultrasonic power of the ultrasonic reactor is 200W, and the ultrasonic time is 40 minutes; the drying temperature of the oven is 65°C, the drying time is 12 hours, and the static drying time is 6 hours.

[0018] A pH-responsive double-layer membrane capable of improving the stability of natural pigments, characterized in that it is prepared by adopting the preparation method.

[0019] A pH-responsive double-layer film that can improve the stability of natural pigments is used in food packaging. A certain mass of cheese is placed in a culture dish, and the pH-responsive double-layer film is cut to the same size and wrapped on the culture dish. The quality of the food inside is judged according to the color change of the pH-responsive double-layer film.

[0020] The advantages and beneficial effects of the present invention are:

[0021] 1. The present invention generates hydrophobic interactions between the hydrophobic amino acid residues of zein and the benzene rings of anthocyanins, and then forms nanoparticles by an anti-solvent precipitation method. Finally, sodium alginate is self-assembled on the surface of zein-anthocyanin nanoparticles by electrostatic interactions to form nanoparticles with a "core-shell" structure. The structure improves the light resistance and oxygen resistance of the encapsulated anthocyanins, as well as the thermal stability below 80°C.

[0022] 2. The present invention adds zein-anthocyanidin-sodium alginate nanomaterials to chitosan to prepare an inner film, and casts a layer of polylactic acid film on the surface of the inner film to form a double-layer intelligent composite packaging film. The prepared double-layer film has good mechanical properties and has a good protective effect on the food contained therein. The addition of nanoparticles, on the one hand, improves the antioxidant capacity of the film and improves the hydrophilic and hydrophobic properties of the inner film; on the other hand, it improves the stability of anthocyanidin in the film, which is beneficial to the long-term storage and application of the film, thereby improving the utilization value of the film.

[0023] 3. The pH-responsive double-layer film of the present invention is applied to food packaging and has a real-time monitoring effect on the food contained therein. In cheese applications, the prepared packaging film can be observed to have obvious color changes on the third day, and has good visual effects and application prospects in the food field. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 is a flow chart of the preparation method of the present invention;

[0025] Figure 2 is a scanning electron microscope image of the zein-anthocyanin nanoparticles of the present invention;

[0026] Figure 3 This is a transmission electron microscope image of the zein-anthocyanin-sodium alginate nanoparticles of the present invention;

[0027] Figure 4 This is an infrared spectrum analysis diagram of zein-anthocyanin-sodium alginate nanoparticles of the present invention;

[0028] Figure 5 This is a scanning electron microscope image of the pH-responsive double-layer membrane of the present invention;

[0029] Figure 6 This is a curve diagram of the absorbance value change of CS-0.02ACN / PLA of the present invention after irradiation for 20, 40, and 60 minutes;

[0030] Figure 7 This is a curve diagram of the absorbance value change of CS-0.02NPs / PLA after irradiation for 20, 40, and 60 minutes;

[0031] Figure 8 This is a diagram showing the color change of cheese at room temperature for 4 days after the pH-responsive double-layer film of the present invention is applied to cheese packaging;

[0032] Fig. 9 This is a graph showing the pH change of cheese packaged with the pH-responsive double-layer film of the present invention at room temperature for 4 days. DETAILED DESCRIPTION

[0033] The present invention is further described in detail below through specific examples. The following examples are only illustrative and not restrictive, and the protection scope of the present invention cannot be limited thereto.

[0034] like Figure 1 As shown, a method for preparing a pH-responsive double-layer film that can improve the stability of natural pigments is innovative in that: the packaging film is a double-layer film with polylactic acid as the outer layer and a mixture of chitosan and zein-anthocyanin-sodium alginate nanomaterials as the inner layer;

[0035] The steps of the method are:

[0036] 1. Preparation of zein-anthocyanidin nanomaterial structure: Accurately weigh 1g zein powder and add 100mL 80% v / v ethanol solution, stir at 40℃ for 2 hours to fully dissolve. Accurately weigh 0.3g blueberry anthocyanidin powder and add 100mL 80% v / v ethanol solution, stir at 25℃ for 4 hours to fully dissolve. Take 10mL 1% w / v zein stock solution and stir and mix with equal volumes of 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 1% w / v blueberry anthocyanidin stock solution at 20℃, then drop deionized water anti-solvent with pH=4 to precipitate. Stir and incubate at 25℃ for 30 minutes, remove ethanol by rotary evaporation, form zein-anthocyanidin binary nanoparticles, dilute to 100mL with deionized water, and put into refrigerator for standby use.

[0037] like Figure 2 The figure shows the scanning electron microscope image of the prepared zein-anthocyanin nanomaterial. It can be seen from the figure that the prepared nanomaterial is spherical and has a small amount of adhesion.

[0038] 2. Preparation of zein-anthocyanidin-sodium alginate nanomaterials with a "core-shell" structure: Accurately weigh 0.025 g of sodium alginate powder and add it to 400 mL of deionized water with a pH of 4 and stir at 60°C for 1 hour to fully dissolve it. Take 100 mL of zein-anthocyanidin nanoparticle material and add it dropwise to the stirred sodium alginate solution at a uniform speed at 25°C to form zein-anthocyanidin-sodium alginate nanomaterials, which are then placed in a refrigerator for later use.

[0039] like Figure 3 The transmission electron microscope image of the prepared zein-anthocyanin-sodium alginate nanomaterial is shown in Figure 1. It can be seen from the figure that the prepared nanomaterial is in a regular spherical shape and has a core-shell structure.

[0040] like Figure 4 This is the infrared spectrum analysis diagram of the prepared zein-anthocyanin-sodium alginate nanomaterial. It can be seen from the figure that there is an interaction force between the nanomaterials, which further illustrates the successful preparation of the nanomaterials.

[0041] 3. Preparation of pH-responsive double-layer membrane, i.e. chitosan-ternary nanomaterial / polylactic acid double-layer membrane: weigh 1g of chitosan and place it in 50mL of 1% v / v acetic acid solution, stir at 60℃ for 5 hours until completely dissolved, and cool to room temperature for use; weigh 1g of polylactic acid powder and place it in 80mL of dichloromethane, stir at 22℃ until completely dissolved. Take 50mL of 2% w / v chitosan solution and add 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, and 1g of anthocyanin equivalent of zein-anthocyanin-sodium alginate ternary nanoparticle dispersion in turn, stir at 25℃ for 2 hours to mix evenly, and use an ultrasonic reactor 200W ultrasound for 40 minutes to remove bubbles in the mixed solution. Pour the film-forming solution into a 150×150×15mm square glass box and dry it in an oven at 65℃ for 10 hours to form an inner layer membrane. The film was dried and cooled to room temperature, 60 mL of polylactic acid solution was poured and cast on the surface, and allowed to stand at room temperature for 6 hours to dry to form an outer film. The film was removed to obtain a double-layer film containing anthocyanin nanoparticles.

[0042] like Figure 5 This is a scanning electron microscope image of the smart composite packaging film with zein-anthocyanin-sodium alginate nanomaterials added. It can be seen that the ternary nanomaterials are well integrated with the film base, and the two layers of film are tightly attached without gaps, indicating the successful preparation of the two-layer film.

[0043] 4. Test of the photostability of anthocyanins by nanomaterials: Weigh 1g of chitosan and place it in 50mL of 1% v / v acetic acid solution, stir at 60℃ for 5 hours until completely dissolved, and cool to room temperature for use; weigh 1g of polylactic acid powder and place it in 80mL of dichloromethane, stir at 22℃ until completely dissolved. Take 50mL of 2% w / v chitosan solution and add 0.02g of anthocyanins and 0.103g of zein-anthocyanin-sodium alginate ternary nanomaterial (containing 0.02g of anthocyanins) respectively, stir at 25℃ for 2 hours to mix evenly, and use an ultrasonic reactor with 200W ultrasound for 40 minutes to remove bubbles in the mixed solution. Pour the film-forming solution into a 150×150×15mm square glass box respectively, and dry it in an oven at 65℃ for 10 hours to form an inner film. After the film is dried and cooled to room temperature, pour and cast 60mL of polylactic acid solution on its surface, and let it stand at room temperature to dry for 6 hours to form an outer film. After stripping, a double-layer film containing 0.02g of anthocyanin and a double-layer film containing 0.103g of ternary nanomaterials (containing 0.02g of anthocyanin) were obtained, which were named CS-0.02ACN / PLA and CS-0.02NPs / PLA, respectively. Using an ultraviolet lamp, CS-0.02ACN / PLA and CS-0.02NPs / PLA were exposed to ultraviolet light of 50W for 20, 40, and 60min, respectively. Using an ultraviolet-visible spectrophotometer, the absorbance value change was measured in the wavelength range of 200-800nm.

[0044] like Figure 6 , Figure 7 The absorbance changes of CS-0.02ACN / PLA and CS-0.02NPs / PLA after irradiation for 20, 40, and 60 minutes respectively reflect the color change of the film after ultraviolet irradiation. It can be seen from the figure that the change of CS-0.02NPs / PLA is significantly smaller than that of CS-0.02ACN / PLA, indicating that the nanomaterial has good ultraviolet protection properties for anthocyanins, and the prepared double-layer film can improve the stabilizer of natural pigments and has the advantage of long-term utilization.

[0045] A pH-responsive double-layer film is used in food packaging. 12 g of cheese is evenly spread on a culture dish. The chitosan-ternary nanomaterial / polylactic acid double-layer film is cut into circles of the same size with a diameter of 60 mm, and wrapped and sealed on the culture dish. The color change of the film, the change of the pH value of the cheese, and the change of the cheese quality are observed and recorded every 12 hours, and the quality of the food inside is judged according to the color change of the film.

[0046] like Figure 8 The color change of cheese packaged with pH-responsive double-layer film at room temperature for 4 days. The prepared double-layer film successfully showed obvious color change during the four-day cheese deterioration period, which has potential application value.

[0047] like Fig. 9 The pH change of cheese packaged with pH-responsive double-layer film at room temperature for 4 days. As shown in the figure, the pH of cheese changes and deteriorates within 4 days of storage, and the prepared double-layer film has good pH responsiveness.

[0048] As shown in the figure, Zein represents zein, ALG represents sodium alginate, ACN represents anthocyanin, CS represents chitosan, and PLA represents polylactic acid.

[0049] Although the embodiments and drawings of the present invention are disclosed for illustrative purposes, those skilled in the art will appreciate that various substitutions, changes and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the scope of the present invention is not limited to the contents disclosed in the embodiments and drawings.

Claims

1. A method for preparing a pH-responsive double-layer membrane capable of improving the stability of natural pigments, characterized in that: The double-layer membrane is a double-layer membrane with polylactic acid as the outer layer and a mixture of chitosan and zein-anthocyanin-sodium alginate nanomaterials as the inner layer; The steps of the method are: S1. Preparation of zein-anthocyanidin binary nanomaterials: dissolving zein in an ethanol solution, heating and stirring at a certain temperature until it is completely dissolved, to form a zein solution, which is set aside; dissolving different masses of anthocyanidins in an ethanol solution, heating and stirring at a certain temperature until it is completely dissolved, to form anthocyanidin solutions of different concentrations, which are set aside; The zein solution and the anthocyanin solution are mixed evenly, and a deionized water anti-solvent is added dropwise for precipitation. After stirring and incubation, the ethanol is removed by rotary evaporation to obtain zein-anthocyanin binary nanoparticles; S2, preparation of zein-anthocyanidin-sodium alginate ternary nanomaterial: taking the zein-anthocyanidin binary nanoparticles of S1, adding them into the sodium alginate solution and stirring them evenly to obtain the zein-anthocyanidin-sodium alginate ternary nanomaterial; S3. Preparation of pH-responsive double-layer membrane: add zein-anthocyanin-sodium alginate ternary nanomaterials of S2 to the chitosan stock solution in sequence, heat and stir to mix evenly to obtain a mixed solution, use an ultrasonic reactor to remove bubbles in the mixed solution to obtain a film-forming solution, pour the film-forming solution into a square glass box, use an oven to dry to form an inner membrane; pour and cast a certain volume of polylactic acid solution on the surface of the dried inner membrane, let it stand and dry to form an outer membrane; remove the membrane to obtain pH-responsive double-layer membranes with different nanoparticle contents.

2. The method for preparing a pH-responsive double-layer membrane capable of improving the stability of natural pigments according to claim 1, characterized in that: The volume fraction of the ethanol solution in the S1 is 80%, the heating and stirring temperature is 20-60° C., and the stirring time is 1-5 hours; the mass ratio of the zein to anthocyanin is (1:0.1)-(1:1), the pH of the zein is 3.30, and the stirring incubation condition is stirring at 25° C. for 30 minutes.

3. The method for preparing a pH-responsive double-layer membrane capable of improving the stability of natural pigments according to claim 1, characterized in that: The mass ratio of the zein solution to the anthocyanin solution in S1 is 1:0.

3.

4. The method for preparing a pH-responsive double-layer membrane capable of improving the stability of natural pigments according to claim 1, characterized in that: The mass ratio of the zein-anthocyanin binary nanoparticles to the sodium alginate solution is 4:

1.

5. The method for preparing a pH-responsive double-layer membrane capable of improving the stability of natural pigments according to claim 1, characterized in that: The mass ratio of the zein-anthocyanin binary nanomaterial to the sodium alginate solution in S2 is (20:1) to (1:2).

6. The method for preparing a pH-responsive double-layer membrane capable of improving the stability of natural pigments according to claim 1, characterized in that: The concentration of the chitosan stock solution in S3 is 2% w / v, the concentration of the polylactic acid solution is 1% w / v, the mass ratio of the chitosan solution to the ternary nanomaterial of zein-anthocyanidin-sodium alginate is (1:0.01) to (1:0.03), the mixing and stirring time of the chitosan stock solution and the ternary nano dispersion of zein-anthocyanidin-sodium alginate is 1 hour, and the stirring and heating temperature is 25°C; the ultrasonic power of the ultrasonic reactor is 200W, and the ultrasonic time is 40 minutes; the drying temperature of the oven is 65°C, the drying time is 12 hours, and the static drying time is 6 hours.

7. A pH-responsive double-layer membrane capable of improving the stability of natural pigments, characterized in that: The preparation method is as described in any one of claims 1 to 6.

8. An application of the pH-responsive double-layer film capable of improving the stability of natural pigments according to claim 7 in food packaging, wherein a certain mass of cheese is placed in a culture dish, the pH-responsive double-layer film is cut to the same size and wrapped on the culture dish, and the quality of the food inside is judged according to the color change of the pH-responsive double-layer film.

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