Temperature response type active film and method and application thereof

Abstract

The invention belongs to the technical field of food packaging materials, and particularly relates to a temperature response type active film and a method and application thereof. The method comprises the following steps: respectively adjusting the pH values of a whey protein isolate fibril solution and a glycyrrhizic acid solution to 4.0, and uniformly mixing to obtain a compound solution; dispersing essential oil into the compound solution, and then performing circulating homogenization treatment in microjet to obtain temperature response type emulsion; the preparation method comprises the following steps: mixing a sodium alginate solution with glycerol, stirring under a water bath condition, and carrying out ultrasonic treatment to obtain a basic film-forming solution; dispersing the temperature response type emulsion into the basic film forming liquid, performing ultrasonic treatment, then pouring into a container, and drying to obtain the temperature response type active film. The WPF-GA compound stable emulsion is added, so that the load and protection capability of the cinnamon essential oil can be remarkably improved, the hydrophobic essential oil can have good dispersity in a hydrophilic film, meanwhile, the film has better mechanical performance, and the essential oil can be regulated and released according to the temperature change.

Description

Technical Field

[0001] The present application belongs to the technical field of food packaging materials, and specifically relates to a temperature-responsive active film and a method and application thereof. Background Art

[0002] After the fruit is picked, its nutrients will gradually be lost due to the continuous physiological activities. Compared with before picking, the aging process is significantly accelerated, and it is easy to be contaminated by bacteria, resulting in rapid deterioration and rot. In addition, the fruit will lose water quickly due to transpiration, which significantly reduces the quality and freshness of the fruit. Therefore, it is crucial to use appropriate packaging and preservation technology to inhibit the corruption and deterioration of fruits.

[0003] Active packaging is a new type of food packaging. Because it contains active agents (antimicrobial agents or antioxidants), it can absorb or release ingredients into the packaged food or the surrounding environment, thereby maintaining the freshness and quality of the food and extending the shelf life of the food to a certain extent. Active film is a film with active ingredients added deliberately. Because of its ability to release or absorb active ingredients, it can be used for active packaging of food. Currently, the more commonly used active agents are essential oils from fruits, vegetables, beans, seeds, etc. These active agents with good antibacterial or antioxidant properties combined with biodegradable polymer matrices are promising tools for the development of films for food packaging. However, one of the challenges facing active films is to control the release of active agents from the film. If a high concentration of active agents is released, it will affect the quality of the food. Therefore, it is very necessary to study the construction of environmentally responsive controlled-release active films. Summary of the invention

[0004] The purpose of the present invention is to solve the deficiencies of the prior art and provide a temperature-responsive active film and a method and application thereof, specifically adopting the following technical solutions: In a first aspect, the present invention provides a method for preparing a temperature-responsive active film, comprising the following steps: S1: dissolving whey protein isolate in water and performing a hydration reaction. After the hydration reaction is completed, the pH is adjusted to 2.0, and then heated in a water bath and stirred for 5 h-7 h, and cooled to obtain a whey protein isolate fibril solution; S2: adjusting the pH of the whey protein isolate fibril solution and the glycyrrhizic acid solution to 4.0 respectively and then mixing them to obtain a complex solution; S3: dispersing the essential oil into the complex solution, and then circulating and homogenizing in a microjet to obtain a temperature-responsive emulsion; S4: mixing the sodium alginate solution with glycerol, stirring and ultrasonicating in a water bath to obtain a basic membrane-forming solution; S5: Disperse the temperature-responsive emulsion into the base film-forming liquid, sonicate, pour into a container, dry, peel off the film, and finally place the film in a constant temperature and humidity chamber for equilibration for 45 h-50 h to obtain the temperature-responsive active film.

[0005] In the above preparation process, the present invention first adjusts the pH to 2.0 to allow the whey protein isolate to unfold and form a fibrous rigid structure, and then adjusts the pH of the whey protein isolate fibril solution and the glycyrrhizic acid solution to 4.0 respectively, so that the whey protein isolate fibrils are partially degraded to expose internal groups, which is conducive to combining with glycyrrhizic acid, and then the two are mixed to form a complex.

[0006] As a further preferred embodiment, the water bath heating temperature in S1 is 90° C. and the heating time is 6 h.

[0007] As a further preferred embodiment, the ratio of the whey isolate egg to water is 2g:100mL; the concentration of the glycyrrhizic acid solution is 2%; the concentration of the sodium alginate is 2%. Too high concentrations of these two are not conducive to forming a uniform and smooth film; the concentration of glycerol is 1%. Too high a concentration will affect the mechanical properties of the film.

[0008] As a further preferred embodiment, the volume ratio of the whey protein isolate fibril solution to the glycyrrhizic acid solution is 3-4:1.

[0009] As a further preferred embodiment, the essential oil is cinnamon essential oil.

[0010] As a further preferred embodiment, the volume concentration of the cinnamon essential oil after being dispersed in the complex solution is 2% to 3%.

[0011] As a further preferred embodiment, the water bath heating temperature in S4 is 50° C. and the heating time is 2 h.

[0012] As a further preferred embodiment, the volume ratio of the temperature-responsive emulsion to the basic membrane-forming liquid in S5 is 10%-50%:1.

[0013] In a second aspect, the present invention provides a temperature-responsive active film prepared by the above-mentioned preparation method.

[0014] In a third aspect, the embodiments of the present application provide the use of the above-mentioned temperature-responsive active film in the preparation of fruit fresh-keeping packaging materials.

[0015] The beneficial effects of the present invention are: The preparation method of the invention is simple, and the addition of an emulsion stabilized by a WPF-GA complex can significantly improve the loading and protection capabilities of cinnamon essential oil, so that the hydrophobic essential oil can have good dispersibility in a hydrophilic film, and the film also has better mechanical properties; compared with a common active film, the temperature-responsive active film prepared by the invention can controllably release active ingredients according to microenvironmental changes of temperature, and the raw materials are biocompatible and degradable, and the invention has good application prospects in the application of active packaging of fruits. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0017] Figure 1 The figure shows the apparent changes of the emulsions stored for 28 days at different dosage ratios of whey protein isolate fibril solution (WPF) and glycyrrhizic acid solution (GA).

[0018] Figure 2 Shown is the release curve of cinnamon essential oil in the temperature-responsive emulsion at different temperatures (4°C, 25°C, 45°C).

[0019] Figure 3 Shown are the surface and cross-sectional scanning electron microscope morphologies of temperature-responsive active films prepared with different addition amounts of temperature-responsive emulsions.

[0020] Figure 4 Shown is the release curve of the temperature-responsive active film at different temperatures (4°C, 25°C, and 45°C) with a temperature-responsive emulsion added at 20%.

[0021] Figure 5 Shown is the release curve of the temperature-responsive active film at different temperatures (4°C, 25°C, and 45°C) with a temperature-responsive emulsion addition amount of 30%.

[0022] Figure 6 Shown is the DPPH radical scavenging rate of the temperature-responsive active film prepared with different addition amounts of the temperature-responsive emulsion.

[0023] Figure 7 Shown are the changes in appearance of grapes treated with different coatings after storage at different temperatures. DETAILED DESCRIPTION

[0024] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0025] Example 1 A method for preparing a temperature-responsive active film, which specifically comprises the following steps: (1) Add 2 g of whey protein isolate (WPI) to 100 ml of distilled water and stir continuously until completely dissolved. Incubate at 4°C overnight to ensure complete hydration to obtain a 2% WPI solution. (2) The pH of the WPI solution was quickly adjusted to 2.0 using 5 M HCl, and then heated in a 90 °C water bath and stirred continuously for 6 h. The pH was maintained at about 2.0 during the entire heating process. After heating, the WPI solution was immediately placed in an ice water bath and cooled to room temperature to obtain a 2% whey protein isolate fibril (WPF) solution. (3) Accurately weigh 1 g of glycyrrhizic acid (GA) and place it in 50 ml of deionized water. Then place the sample in a 70°C water bath and stir to fully dissolve it to obtain a 2% GA solution. (4) The pH values ​​of the WPF solution and the GA solution were adjusted to 4.0 respectively, and then mixed in a ratio of WPF:GA=3:1, and stirred to make the mixture uniform, thereby obtaining a WPF-GA complex solution; (5) Dispersing cinnamon essential oil into the WPF-GA complex solution to a volume concentration of 3%, and circulating homogenization in the microfluidizer for 3 times to obtain a temperature-responsive emulsion; (6) Dissolve 2 g of sodium alginate (SA) in 100 mL of distilled water, add 1 g of glycerol to the beaker, heat in a 50 °C water bath and stir continuously for 2 h, let stand and cool, and remove bubbles by ultrasonication to obtain a basic membrane-forming solution; (7) adding a temperature-responsive emulsion accounting for 30% of the total volume of the basic film-forming solution to the basic film-forming solution, and mixing the emulsion with the basic film-forming solution at a speed of 11,000 rpm for 3 min using a high-speed disperser to ensure that the emulsion and the basic film-forming solution are fully mixed, and then performing ultrasound to remove bubbles to obtain a film-forming liquid; (8) Pour 20 g of the film-forming liquid into a 9 cm diameter Petri dish, place it in a 40°C constant temperature forced air drying oven and dry it for 12 h. After drying and cooling, remove the film. Finally, to ensure the stability of the film-forming performance, place the film in a constant temperature and humidity chamber at 25°C and 50% RH for 48 h to obtain an active film loaded with temperature-responsive emulsion (30% E-SA).

[0026] Example 2 A method for preparing a temperature-responsive active film, wherein the specific process is similar to that of Example 1, except that in step (4), "WPF:GA=3:1" is changed to "WPF:GA=1:1" to obtain an active film loaded with a temperature-responsive emulsion.

[0027] Example 3 A method for preparing a temperature-responsive active film, wherein the specific process is similar to that of Example 1, except that in step (4), "WPF:GA=3:1" is changed to "WPF:GA=2:1" to obtain an active film loaded with a temperature-responsive emulsion.

[0028] Example 4 A method for preparing a temperature-responsive active film, wherein the specific process is similar to that of Example 1, except that in step (4), "WPF:GA=3:1" is changed to "WPF:GA=4:1" to obtain an active film loaded with a temperature-responsive emulsion.

[0029] Example 5 A method for preparing a temperature-responsive active film, wherein the specific process is similar to that of Example 1, except that in step (7), "adding a temperature-responsive emulsion accounting for 30% of the total volume of the basic film-forming liquid to the basic film-forming liquid" is changed to "adding a temperature-responsive emulsion accounting for 10% of the total volume of the basic film-forming liquid to the basic film-forming liquid" to obtain an active film loaded with a temperature-responsive emulsion (10% E-SA).

[0030] Example 6 A method for preparing a temperature-responsive active film, wherein the specific process is similar to that of Example 1, except that in step (7), "adding a temperature-responsive emulsion accounting for 30% of the total volume of the basic film-forming liquid to the basic film-forming liquid" is changed to "adding a temperature-responsive emulsion accounting for 20% of the total volume of the basic film-forming liquid to the basic film-forming liquid" to obtain an active film loaded with a temperature-responsive emulsion (20% E-SA).

[0031] Example 7 A method for preparing a temperature-responsive active film, wherein the specific process is similar to that of Example 1, except that in step (7), "adding a temperature-responsive emulsion accounting for 30% of the total volume of the basic film-forming liquid to the basic film-forming liquid" is changed to "adding a temperature-responsive emulsion accounting for 40% of the total volume of the basic film-forming liquid to the basic film-forming liquid" to obtain an active film loaded with a temperature-responsive emulsion (40% E-SA).

[0032] Example 8 A method for preparing a temperature-responsive active film, wherein the specific process is similar to that of Example 1, except that in step (7), "adding a temperature-responsive emulsion accounting for 30% of the total volume of the basic film-forming liquid to the basic film-forming liquid" is changed to "adding a temperature-responsive emulsion accounting for 50% of the total volume of the basic film-forming liquid to the basic film-forming liquid" to obtain an active film loaded with a temperature-responsive emulsion (50% E-SA).

[0033] The performance of the materials prepared above is investigated as follows: (1) The apparent changes of the temperature-responsive emulsions prepared in step (4) of Examples 1-4 at different WPF and GA ratios after storage for 28 days were investigated. The results are as follows: Figure 1 As shown in (WPF refers to a temperature-responsive emulsion prepared in the same manner without adding GA; GA refers to a temperature-responsive emulsion prepared in the same manner without adding WPF), and by Figure 1 It can be seen that the emulsions with WPF:GA=3:1 and 4:1 have better stability. The temperature response characteristics of the film are actually achieved through the temperature response characteristics of the added emulsion. The emulsion needs to be stable at low temperatures and demulsified at high temperatures to achieve the controlled release of essential oils. Therefore, 3:1 and 4:1, which are not easy to stratify at room temperature, were selected for subsequent experiments.

[0034] (2) The release of cinnamon essential oil in the temperature-responsive emulsions prepared in step (4) of Example 1 and Example 4 at different temperatures (4°C, 25°C, 45°C) was investigated. The specific process is as follows: First, cinnamon essential oil was dissolved in ethanol solution, and then a series of cinnamon essential oil ethanol solutions with gradient concentrations were obtained by dilution. The maximum absorption wavelength of cinnamon essential oil was determined by full-band scanning with an ultraviolet spectrophotometer. Then, cinnamon essential oil ethanol solutions with concentrations of 0.5, 1, 2, 4, 6, 8, and 10 nL / mL were prepared, and anhydrous ethanol was used as a blank. The absorbance was measured at the maximum absorption wavelength, and a standard curve was drawn by fitting based on the concentration and absorbance. Finally, 1 ml of the emulsions of different groups were added to the dialysis bag (10 kDa) and immersed in 500 mL of PBS solution. The experiments were carried out at 4℃, 25℃, and 45℃, and 5 mL of dialysate was taken out from the beaker at 0, 0.5, 1, 2, 4, 6, 8, 12, and 24h, and an equal amount of buffer was added to the beaker to keep the total volume of buffer in the beaker at 500 mL. The absorbance of the dialysate was measured at 286 nm using an ultraviolet spectrophotometer, and its concentration was calculated using the standard curve, and the release rate of cinnamon essential oil was obtained by calculation.

[0035] The results are as follows Figure 2As shown in (WPF refers to a temperature-responsive emulsion prepared in the same manner without adding GA; GA refers to a temperature-responsive emulsion prepared in the same manner without adding WPF), Figure 2 It can be seen that the release rates of 3:1 and 4:1 at low temperatures are not as good as those of WPF and GA, while the release rates are significantly accelerated at high temperatures. Therefore, the temperature-responsive emulsion prepared by the present invention has certain temperature-responsive controlled release characteristics, and can achieve a sustained release effect at low temperatures, while achieving the characteristics of rapid release of active substances at high temperatures. By comparison, it is found that the response release effect of the WPF:GA=3:1 group emulsion is better than that of the WPF:GA=4:1 group.

[0036] (3) The surface and cross-sectional SEM morphologies of the temperature-responsive active films prepared in Examples 1 and 5-8 under conditions of different addition amounts of the temperature-responsive emulsion were investigated. The results are as follows: Figure 3 shown by Figure 3 It can be seen that with the increase of the amount of emulsion added, the surface of the film becomes rougher and rougher, and droplet-like traces appear on the surface.

[0037] (4) The release of the temperature-responsive active films prepared by adding 20% ​​and 30% of the temperature-responsive emulsion in Example 1 and Example 6 at different temperatures (4°C, 25°C, and 45°C) was investigated. The specific process is as follows: The prepared active films with two amounts of emulsion added and without emulsion added (Control group) were cut into 10 mm × 10 mm samples and placed in ethanol solutions at 4 °C, 25 °C, 45 °C, and RH 50% for release tests. At different time points, 5 mL of dialysate was taken out from the beaker, and an equal amount of buffer was added to the beaker to keep the total volume of buffer in the beaker unchanged. The absorbance of the dialysate was measured at 286 nm using an ultraviolet spectrophotometer, and its concentration was calculated using the standard curve. The results are as follows Figure 4-Figure 5 As shown in the results, under low temperature conditions (4°C), the release performance of the control group is better than that of the experimental group. Under normal temperature conditions (25°C), the release performance of the control group and the experimental group is equivalent. Under high temperature conditions (45°C), the release performance of the experimental group is better than that of the control group. Therefore, both groups of membranes can delay the release of essential oils encapsulated in the film matrix at low temperatures and accelerate the release of essential oils in the film matrix at high temperatures. The prepared emulsion composite membrane has obvious temperature-responsive controlled release characteristics.

[0038] (5) The DPPH radical scavenging rate of the temperature-responsive active films prepared under the conditions of different addition amounts of the temperature-responsive emulsion in Examples 1 and 5-8 was investigated. The specific process is as follows: Accurately weigh 9.8 mg DPPH into a 250 mL volumetric flask and dilute to 100 μmol / L DPPH ethanol solution with anhydrous ethanol. Take 50 mg of the film sample and dissolve it in 2 mL of methanol and stir for 3 h. Mix the sample solution with 4 mL of DPPH ethanol solution in a brown centrifuge tube, let it stand in a dark environment at room temperature for 30 min, and measure its absorbance, which is recorded as A1. Take an equal amount of anhydrous ethanol solution and DPPH ethanol solution in a brown centrifuge tube as a control group, let it stand for 30 minutes under the same conditions, and measure its absorbance, which is recorded as A0. And calculate according to the following formula: The results are as follows Figure 6 As shown, it can be seen from the results that when the emulsion addition amount is 10%-50%, the DPPH removal rate of the composite membrane is significantly improved compared with the SA membrane (temperature-responsive active film prepared without adding WPF and the other preparation processes are the same as those in Example 1), indicating that the addition of active ingredients can significantly improve the antioxidant properties of the composite membrane.

[0039] Example 9 The temperature-responsive active films prepared in Examples 1 and 6 were used to preserve grapes, and the preservation effects at different temperatures and times were investigated. The results are as follows: Figure 7 As shown by Figure 7 It can be seen that the temperature-responsive active film prepared by the present invention still has a good preservation effect on grapes at high temperatures.

[0040] The embodiments of the present application are described above in conjunction with the accompanying drawings. Specific examples are used herein to illustrate the principles and implementation methods of the present application. The description of the above embodiments is only used to help understand the core idea of ​​the present application, but the present application is not limited to the above-mentioned specific implementation methods. The above-mentioned specific implementation methods are merely illustrative and not restrictive. Under the inspiration of the present application, ordinary technicians in this field can also make many forms without departing from the scope of protection of the purpose of the present application and the claims, all of which are within the protection of the present application.

Claims

1. A method for preparing a temperature-responsive active film, characterized in that: The following steps are involved: S1: dissolving whey protein isolate in water and performing a hydration reaction. After the hydration reaction is completed, the pH is adjusted to 2.0, and then heated in a water bath and stirred for 5 h-7 h, and cooled to obtain a whey protein isolate fibril solution; S2: adjusting the pH of the whey protein isolate fibril solution and the glycyrrhizic acid solution to 4.0 respectively and then mixing them to obtain a complex solution; S3: dispersing the essential oil into the complex solution, and then circulating and homogenizing in a microjet to obtain a temperature-responsive emulsion; S4: mixing the sodium alginate solution with glycerol, stirring and ultrasonicating in a water bath to obtain a basic membrane-forming solution; S5: Disperse the temperature-responsive emulsion into the base film-forming liquid, sonicate, pour into a container, dry, peel off the film, and finally place the film in a constant temperature and humidity chamber for equilibration for 45 h-50 h to obtain the temperature-responsive active film.

2. The preparation method according to claim 1, characterized in that: The water bath heating temperature in S1 is 90°C and the heating time is 6 h.

3. The preparation method according to claim 1, characterized in that: The usage ratio of the whey separated egg to water is 2g:100mL; the concentration of the glycyrrhizic acid solution is 2%; the concentration of the sodium alginate is 2%; and the concentration of the glycerol is 1%.

4. The preparation method according to claim 3, characterized in that: The volume ratio of the whey protein isolate fibril solution to the glycyrrhizic acid solution is 3-4:

1.

5. The preparation method according to claim 1, characterized in that: The essential oil is cinnamon essential oil.

6. The preparation method according to claim 5, characterized in that: The volume concentration of the cinnamon essential oil after being dispersed in the complex solution is 2% to 3%.

7. The preparation method according to claim 1, characterized in that: The water bath heating temperature in S4 is 50°C and the heating time is 2h.

8. The preparation method according to claim 1, characterized in that: The volume ratio of the temperature-responsive emulsion to the basic film-forming liquid described in S5 is 10%~50%:

1.

9. A temperature-responsive active film, characterized in that: The invention is prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the temperature-responsive active film according to claim 9 in preparing fruit fresh-keeping packaging materials.

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