A spontaneous gas-regulated membrane with hydrogel as gas-regulated switch and preparation method thereof

Abstract

The present invention proposes a spontaneous gas-regulating membrane with hydrogel as a gas-regulating switch and a preparation method thereof, belonging to the technical field of spontaneous gas-regulating membranes. The spontaneous gas-regulating membrane of the present invention comprises hydrogel particles, a film-forming matrix and a plasticizer, wherein the mass addition amount of the hydrogel particles in the film-forming matrix is ​​0.01% to 2.00%, and the hydrogel particles comprise shellac hydrogel particles with an average particle size of 15 to 160 μm. The present invention proposes for the first time to utilize the characteristics of hydrogel such as looseness and porosity, hygroscopicity and moisture retention, and to add hydrogel as a gas permeability regulating switch to other film-forming matrices, thereby regulating the CO of the membrane. 2 , O 2 The spontaneous atmosphere-controlled membrane prepared by the present invention has good preservation effect when used for preserving fresh-cut vegetables such as onions, leeks, cucumbers, spinach, etc.

Description

Technical Field

[0001] The invention belongs to the technical field of spontaneous gas-regulating membranes, and in particular relates to a spontaneous gas-regulating membrane with a hydrogel as a gas-regulating switch and a preparation method thereof. Background Art

[0002] The atmosphere around fresh agricultural products such as fruits and vegetables, especially the content of CO2, O2 and water vapor, plays a vital role in their storage period. Different types of fresh agricultural products with different respiratory metabolism require different CO2 and O2 contents for storage. High CO2 and low O2 content within the appropriate range can weaken the physiological metabolism of agricultural products such as fruits and vegetables and inhibit the growth of microorganisms. Spontaneous modified atmosphere packaging is a packaging technology that provides an ideal atmosphere to extend the shelf life of products and maintain food quality. It uses the gas permeability of the spontaneous modified atmosphere film and the respiratory metabolism of the agricultural products to change the gas composition and proportion of the products in the packaging. It has the advantages of low cost and no harmful effects on the packaged food. However, the successful application of spontaneous modified atmosphere packaging technology in the preservation of fresh agricultural products such as fruits and vegetables mainly depends on whether the gas permeability of the spontaneous modified atmosphere film, such as CO2, O2 and water vapor, matches the respiratory metabolism rate of the agricultural products to be preserved.

[0003] At present, the main technologies for regulating the permeability of gases such as CO2, O2 and water vapor in spontaneous atmosphere membranes include polymer membrane perforation, controllable polymer crystallization, nanoparticle-based hybrid system, polymer chain crosslinking, etc. Polymer membrane perforation is to use hot / cold needles, flames, low-charge discharge, lasers and other means to punch holes in polymer membranes, and the pore size is generally 40-200μm. However, the gas exchange capacity of the spontaneous atmosphere membrane prepared in this way is too high and there is no gas selectivity. In addition, microorganisms can also enter the package through the micropores. In the spontaneous atmosphere membrane prepared by controllable polymer crystallization and nanoparticle-based hybrid system, dense domains such as crystals and nanoparticles may block or elongate the gas permeation channel. Therefore, the atmosphere membrane often shows lower gas permeability, and the interface compatibility between nanoparticles and the spontaneous atmosphere membrane matrix is ​​poor, so the addition amount is limited, which limits the overall performance of the membrane in gas permeability control. In addition, nanoparticles are prone to agglomeration, which affects the packaging performance of the membrane. In addition, there is still controversy about the safety of nanomaterials, especially whether the nano components in packaging materials will migrate into food. In the polymer chain cross-linking technology, linear polymers with simple molecular structures can produce good chain stacking (or small cavities), and thus have lower permeability than polymers with a large number of side chain groups and loose structures. The cross-linking of polymer chains limits the mobility or viscosity of the chains, resulting in a decrease in the diffusion coefficient, and thus its gas permeability is reduced. However, most of the spontaneous gas-modified membranes synthesized and prepared by this method are difficult to degrade, and a large amount of toxic organic solvents are used in the synthesis process, which poses a safety hazard. Therefore, they are rarely used in food packaging such as fresh agricultural products. Therefore, the ideal spontaneous gas-modified membrane should contain a functional domain with a gas permeability control switch, so that it has a larger gas permeability adjustment range than a simple gas barrier membrane.

[0004] Hydrogel is a three-dimensional polymer network formed by cross-linking polymer chains with hydrophilic groups. It can absorb a large amount of water and swell without dissolving in an aqueous environment. In recent years, hydrogels with the characteristics of moisture absorption and water retention and the ability to load antibacterial drugs have attracted the attention of scholars in the field of fresh food preservation. After the hydrogel solution is coated on the surface of fruits and vegetables, a layer of film can be formed on the surface of fruits and vegetables, but this film has extremely poor gas barrier and mechanical properties. Therefore, after coating, it needs to be placed in a fresh-keeping bag to achieve a certain preservation effect. On the other hand, some researchers have used hydrogels to wrap and load antibacterial substances for food preservation. Although it is initially involved in the application of hydrogels in food preservation, it only uses the hydrogel itself as a film-forming matrix or a carrier of antibacterial substances.

[0005] In order to make up for the lack of a controlled atmosphere membrane for self-regulating gas permeability of fresh agricultural products such as fruits and vegetables in the prior art, the present invention proposes a spontaneous controlled atmosphere membrane with hydrogel as a gas regulating switch and a preparation method thereof. Summary of the invention

[0006] In order to solve the problems existing in the gas permeability regulation technology of the existing spontaneous atmosphere-regulated membrane, such as too high gas permeability, no gas selectivity, narrow gas permeability regulation range, limited overall membrane performance, and potential safety hazards, the present invention proposes a spontaneous atmosphere-regulated membrane with hydrogel as a gas regulating switch and a preparation method thereof. The present invention proposes for the first time to utilize the loose porosity, hygroscopicity and moisture retention characteristics of hydrogel, and add hydrogel as a gas permeability regulation switch to other film-forming matrices, thereby regulating the CO2, O2 and water vapor permeability of the membrane, and obtaining a safe, non-toxic spontaneous atmosphere-regulated membrane that can be used for preserving fresh agricultural products such as fruits and vegetables.

[0007] To achieve the above object, the present invention provides the following technical solutions:

[0008] One of the technical solutions of the present invention:

[0009] A spontaneous gas-controlled membrane with hydrogel as a gas-controlled switch comprises hydrogel particles, a film-forming matrix and a plasticizer, wherein the mass addition amount of the hydrogel particles in the film-forming matrix is ​​0.01% to 2.00%. By utilizing the characteristics of the hydrogel such as looseness and porosity, moisture absorption and moisture retention, the hydrogel is added to other film-forming matrices as a gas permeability control switch, thereby adjusting the CO2, O2 and water vapor permeability of the membrane to match the respiratory metabolic rate of the agricultural products to be preserved. The specific control principle is: compared with a dense membrane, gases such as CO2, O2 and water vapor are easier to pass through the pores in the loose and porous hydrogel particles. Therefore, as the amount of hydrogel particles added increases, the permeability of CO2, O2 and water vapor of the gas-controlled membrane with the hydrogel particles added also increases significantly. Conversely, if the amount of hydrogel particles added decreases, the gas permeability of the gas-controlled membrane also decreases significantly. The mass addition amount of hydrogel particles in the film-forming matrix is ​​0.01% to 2.00%. When the addition amount is higher than 2.00%, the CO2, O2 and water vapor permeability of the controlled atmosphere film is too high, the moisture loss rate of the packaged vegetables is too fast, and the vegetables are prone to rapid water loss and wilt, which is not conducive to the preservation of fresh-cut vegetables. In addition, the mechanical strength of the controlled atmosphere film will also be affected, thereby affecting the overall performance of the film.

[0010] Preferably, the average particle size of the hydrogel particles is 15 to 160 μm. If the particle size is too small, the gel particles are easily encapsulated inside the membrane, which is not conducive to the passage of gas through the gel particles. If the particle size is too large, the gel particles may easily fall off, and the stability of the membrane is easily affected.

[0011] Preferably, the hydrogel particles include shellac hydrogel particles, but are not limited to shellac hydrogel particles, and may also be porous hydrogel particles prepared from other polymers. Taking shellac hydrogel particles as an example, the preparation method thereof includes the following steps:

[0012] The shellac is dissolved in a sodium carbonate solution, and then polyethylene glycol and gluconolactone are added, and the mixture is stirred at 15 to 35° C. for 2 to 10 minutes, and then allowed to stand for 0.5 to 24 hours to obtain a shellac hydrogel. The shellac hydrogel is then soaked in deionized water for 24 hours, freeze-dried, and then ground to obtain shellac hydrogel particles.

[0013] More preferably, the mass ratio of shellac to polyethylene glycol is 1:(0-0.5).

[0014] More preferably, the polyethylene glycol is polyethylene glycol 200-20000.

[0015] Preferably, the film-forming matrix includes chitosan and gelatin, but is not limited to chitosan and gelatin, and may also be other polymer film-forming matrices with film-forming properties.

[0016] Preferably, the plasticizer includes glycerol, but is not limited to glycerol, and may also be other plasticizers that can be dissolved in the film-forming matrix and can increase the toughness of the film.

[0017] Further preferably, the mass concentration of chitosan in the film-forming matrix is ​​0.5% to 10%, the mass concentration of gelatin is 0.05% to 5.00%, and the mass concentration of glycerol in the plasticizer is 0.05% to 2.00%. The film prepared with the above raw materials has strong toughness and excellent mechanical properties, and has good compatibility with shellac hydrogel particles.

[0018] The second technical solution of the present invention:

[0019] A method for preparing a spontaneous gas-regulated membrane using a hydrogel as a gas-regulated switch comprises the following steps:

[0020] Dissolving chitosan in an acetic acid solution, adding gelatin under stirring to obtain a film-forming matrix, and then adding a plasticizer to obtain a film-forming matrix mixture;

[0021] Hydrogel particles are added to the film-forming matrix mixture, and a solution casting method is used at room temperature to prepare a spontaneous gas-regulated membrane with the hydrogel as a gas-regulated switch.

[0022] Preferably, the thickness of the spontaneous gas-regulated membrane using hydrogel as the gas-regulated switch prepared by the solution casting method is 10 to 150 μm, which should theoretically be slightly smaller than the average particle size of the hydrogel particles.

[0023] The third technical solution of the present invention:

[0024] The application of the spontaneous atmosphere-controlled membrane using hydrogel as an atmosphere-controlled switch in the preservation of fresh-cut vegetables.

[0025] Compared with the prior art, the present invention has the following advantages and technical effects:

[0026] (1) The spontaneous atmosphere-modifying film of the atmosphere-modulating switch prepared by the present invention can control the CO2, O2 and water vapor permeability of the film by controlling the amount of hydrogel particles added to the film-forming matrix. At the same time, the addition of hydrogel particles will not significantly affect the mechanical strength of the atmosphere-modifying film, and will not affect the application of the atmosphere-modifying film in food packaging. For example, when the amount of hydrogel particles added increases from 0 to 0.5%, the water vapor permeability of the atmosphere-modifying film increases from 0.34 g·mm·kPa to 0.50 g·mm·kPa. -1 ·h -1 ·m -2 Increase to 0.65g·mm·kPa -1 ·h -1 ·m -2 The O2 transmission rate of the modified atmosphere membrane is from 7.62×10 -18 mol·m -1 ·s -1 ·Pa -1 Increased to 30.39×10 -18 mol·m -1 ·s -1 ·Pa -1 The CO2 permeability of the modified atmosphere membrane is from 8.67×10 -18 mol·m -1 ·s -1 ·Pa -1 Increased to 31.04×10 -18 mol·m -1 ·s -1 ·Pa -1 However, the mechanical strength of the membrane did not decrease too much. For example, when the addition amount of hydrogel particles increased from 0 to 0.5%, the tensile strength of the modified atmosphere membrane remained at around 8.8 MPa, and only the elongation at break decreased from 50% to 32%, but the puncture strength did not change significantly and was greater than 1200 N / mm.

[0027] (2) The present invention proposes for the first time to utilize the properties of hydrogels, such as being loose and porous, hygroscopic and moisturizing, and having strong compatibility with film-forming matrices, to add hydrogels as gas permeability control switches to other film-forming matrices, thereby regulating the CO2, O2 and water vapor permeabilities of the membrane, thereby obtaining a safe, non-toxic, spontaneously activated atmosphere membrane that can be used to preserve fresh agricultural products such as fruits and vegetables. The spontaneously activated atmosphere membrane prepared by the present invention is used to preserve fresh-cut vegetables such as onions, leeks, cucumbers, and spinach, and exhibits good preservation effects. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The drawings constituting a part of the present application are used to provide a further understanding of the present application. The illustrative embodiments and descriptions of the present application are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0029] Figure 1 This is a scanning electron microscope image of the shellac hydrogel particles prepared in Example 1 of the present invention at a magnification of 44,000 times;

[0030] Figure 2 This is a scanning electron microscope image of the spontaneous gas-regulated membrane with hydrogel as the gas-regulated switch prepared in Example 1 of the present invention at a magnification of 330 times;

[0031] Figure 3 The spontaneous atmosphere-controlled membrane prepared in Example 2 and the atmosphere-controlled membrane prepared in Comparative Example 1 (control group) were used to preserve fresh spinach, and the preservation conditions on the 1st day, the 3rd day, and the 5th day;

[0032] Figure 4 The spontaneous atmosphere-controlled membrane prepared in Example 1 and the atmosphere-controlled membrane prepared in Comparative Example 1 (control group) were used to preserve fresh leeks, and the preservation conditions on the 1st day, the 3rd day, and the 7th day;

[0033] Figure 5 The spontaneous atmosphere-controlled membrane prepared in Example 3 and the atmosphere-controlled membrane prepared in Comparative Example 1 (control group) were used to preserve fresh onions, and the preservation conditions on the 1st day and the 7th day. DETAILED DESCRIPTION

[0034] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0035] It should be understood that the terms described in the present invention are only for describing special embodiments and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. Each smaller range between the intermediate value in any stated value or stated range and any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0036] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0037] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to those skilled in the art. The present invention description and examples are exemplary only.

[0038] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0039] The solution casting method in the embodiment of the present invention is a conventional technical means in the art.

[0040] All raw materials used in the embodiments of the present invention are purchased from the market. Shellac, polyethylene glycol, gluconolactone, chitosan, sodium carbonate, acetic acid, glycerol, etc. are all raw materials permitted for use in the food additives use standard GB2760-2014. The prepared modified atmosphere membrane is safe and non-toxic.

[0041] The room temperature in the embodiment of the present invention refers to 25±2°C.

[0042] The technical solution of the present invention is further illustrated by the following embodiments.

[0043] Example 1

[0044] 9.70 g of shellac was dissolved in 62 mL of 0.1 mol / L sodium carbonate solution, and then 1.99 g of gluconolactone was added, and the mixture was stirred at 25°C for 5 min and allowed to stand for 6 h to obtain shellac hydrogel. The shellac hydrogel was then soaked in deionized water for 24 h, freeze-dried, and ground to an average particle size of 52 μm to obtain shellac hydrogel particles.

[0045] Dissolving chitosan in an acetic acid solution (the concentration of the acetic acid solution is 0.5%, w / v), adding gelatin under stirring to obtain a film-forming matrix, and adding glycerol as a plasticizer to obtain a film-forming matrix mixture containing 1% (w / w) chitosan, 0.75% (w / w) gelatin and 0.75% (w / w) glycerol;

[0046] Hydrogel particles were added to the film-forming matrix mixture, the mass addition amount of the hydrogel particles in the film-forming matrix was 0.3%, and a spontaneous gas-regulated membrane with a thickness of 20 μm and hydrogel as a gas-regulated switch was prepared by solution casting at room temperature.

[0047] The scanning electron microscope images of the shellac hydrogel particles prepared in Example 1 of the present invention at different magnifications are shown in FIG. Figure 1 (Magnification: 44000 times), the scanning electron microscope image of the spontaneous gas-controlled membrane with hydrogel as the gas-controlled switch prepared in Example 1 of the present invention at a magnification of 330 times is shown in Figure 2 ,Depend on Figure 1 It can be seen that the shellac hydrogel particles are loose and porous, with a large number of nanopores inside.

[0048] Example 2

[0049] 11.20 g of lac was dissolved in 62 mL of 0.1 mol / L sodium carbonate solution, and then 2.40 g of polyethylene glycol (polyethylene glycol 4000) and 1.99 g of gluconolactone were added, stirred at 25°C for 5 min, and allowed to stand for 6 h to obtain lac hydrogel, and then the lac hydrogel was soaked in deionized water for 24 h, freeze-dried, and ground to an average particle size of 52 μm to obtain lac hydrogel particles;

[0050] Dissolving chitosan in an acetic acid solution (the concentration of the acetic acid solution is 0.5%, w / v), adding gelatin under stirring to obtain a film-forming matrix, and adding glycerol as a plasticizer to obtain a film-forming matrix mixture containing 1% (w / w) chitosan, 0.75% (w / w) gelatin and 0.75% (w / w) glycerol;

[0051] Hydrogel particles were added to the film-forming matrix mixture, the mass addition amount of the hydrogel particles in the film-forming matrix was 0.1%, and a spontaneous gas-regulated membrane with a thickness of 20 μm and hydrogel as a gas-regulated switch was prepared by solution casting at room temperature.

[0052] Example 3

[0053] 9.70 g of lac was dissolved in 70 mL of 0.1 mol / L sodium carbonate solution, and then 1.50 g of polyethylene glycol (polyethylene glycol 200-20000) and 1.99 g of gluconolactone were added, stirred at 25° C. for 5 min, and allowed to stand for 6 h to obtain lac hydrogel, and then the lac hydrogel was soaked in deionized water for 24 h, freeze-dried, and ground to an average particle size of 52 μm to obtain lac hydrogel particles;

[0054] Dissolving chitosan in an acetic acid solution (the concentration of the acetic acid solution is 0.5%, w / v), adding gelatin under stirring to obtain a film-forming matrix, and adding glycerol as a plasticizer to obtain a film-forming matrix mixture containing 1% (w / w) chitosan, 0.75% (w / w) gelatin and 0.75% (w / w) glycerol;

[0055] Hydrogel particles were added to the film-forming matrix mixture, the mass addition amount of the hydrogel particles in the film-forming matrix was 0.5%, and a spontaneous gas-regulated membrane with a thickness of 20 μm and hydrogel as a gas-regulated switch was prepared by solution casting at room temperature.

[0056] Example 4

[0057] 9.20 g of shellac was dissolved in 55 mL of 0.1 mol / L sodium carbonate solution, and then 4.60 g of polyethylene glycol 20000 and 1.99 g of gluconolactone were added, and the mixture was stirred at 35°C for 10 min and allowed to stand for 0.5 h to obtain shellac hydrogel. The shellac hydrogel was then soaked in deionized water for 24 h, freeze-dried, and ground to an average particle size of 160 μm to obtain shellac hydrogel particles.

[0058] Dissolving chitosan in an acetic acid solution (the concentration of the acetic acid solution is 0.5%, w / v), adding gelatin under stirring to obtain a film-forming matrix, and adding glycerol as a plasticizer to obtain a film-forming matrix mixture containing 10% (w / w) chitosan, 0.05% (w / w) gelatin and 2.00% (w / w) glycerol;

[0059] Hydrogel particles were added to the film-forming matrix mixture, the mass addition amount of the hydrogel particles in the film-forming matrix was 2.00%, and a spontaneous gas-regulated membrane with a thickness of 150 μm and hydrogel as a gas-regulated switch was prepared by solution casting at room temperature.

[0060] Example 5

[0061] 9.70 g of shellac was dissolved in 62 mL of 0.1 mol / L sodium carbonate solution, and then 0.97 g of polyethylene glycol 6000 and 1.99 g of gluconolactone were added, stirred at 15°C for 2 min, and allowed to stand for 24 h to obtain shellac hydrogel, and then the shellac hydrogel was soaked in deionized water for 24 h, freeze-dried, and ground to an average particle size of 30 μm to obtain shellac hydrogel particles;

[0062] Dissolving chitosan in an acetic acid solution (the concentration of the acetic acid solution is 0.5%, w / v), adding gelatin under stirring to obtain a film-forming matrix, and adding glycerol as a plasticizer to obtain a film-forming matrix mixture containing 0.5% (w / w) chitosan, 5.00% (w / w) gelatin and 0.05% (w / w) glycerol;

[0063] Hydrogel particles were added to the film-forming matrix mixture, the mass addition amount of the hydrogel particles in the film-forming matrix was 0.01%, and a spontaneous gas-regulated membrane with a thickness of 25 μm and hydrogel as a gas-regulated switch was prepared by solution casting at room temperature.

[0064] Comparative Example 1

[0065] Same as Example 1, except that no shellac hydrogel particles are added:

[0066] Dissolving chitosan in an acetic acid solution (the concentration of the acetic acid solution is 0.5%, w / v), adding gelatin under stirring to obtain a film-forming matrix, and adding glycerol as a plasticizer to obtain a film-forming matrix mixture containing 1% (w / w) chitosan, 0.75% (w / w) gelatin and 0.75% (w / w) glycerol;

[0067] The film-forming matrix mixture was prepared by solution casting at room temperature to obtain a modified atmosphere film with a thickness of 20 μm.

[0068] Comparative Example 2

[0069] The same as Example 1, except that the freeze-dried particles were ground to an average particle size of 200 μm to obtain shellac hydrogel particles, and the prepared film had a thickness of 20 μm.

[0070] Comparative Example 3

[0071] The same as Example 1, except that chitosan was dissolved in acetic acid solution, gelatin and glycerol were added under stirring to obtain a film-forming matrix containing 0.3% (w / w) chitosan, 0.03% (w / w) gelatin and 4.00% (w / w) glycerol.

[0072] Comparative Example 4

[0073] The same as Example 1, except that the shellac hydrogel was freeze-dried and ground to an average particle size of 5 μm, and the thickness of the film was 30 μm.

[0074] Performance Testing

[0075] Test object: the modified atmosphere films prepared in Examples 1 to 5 and Comparative Examples 1 to 4;

[0076] Test method:

[0077] Determination method of water vapor permeability of modified atmosphere film: refer to the national standard GB / T 1037-2021 Plastic film and sheet water vapor permeability performance determination cup weight gain and weight loss method.

[0078] Determination method of O2 permeability and CO2 permeability: refer to the national standard GB / T 1038-2000 Plastic film and sheet gas permeability test method - differential pressure method.

[0079] Determination method of tensile strength and elongation at break: The tensile strength and elongation at break were determined using a rotational rheometer (Discovery DHR-2, TA, USA). The gas-controlled film samples were placed at 20°C and 50% relative humidity for more than 48 hours before testing. The initial clamp distance was set to 30 mm, the sample width was 10 mm, and the stretching rate was 5 mm / min.

[0080] Puncture strength determination method: Puncture strength was determined using a texture analyzer (TMS-PRO, FTC, USA) with a crosshead speed of 250 mm / min and a cylindrical probe diameter of 12.7 mm, according to the standard method (ASTM d5748-95, 2012).

[0081] The measurement results of water vapor permeability, O2 permeability, CO2 permeability, tensile strength, elongation at break and puncture strength of the modified atmosphere films prepared in the examples and comparative examples are shown in Table 1.

[0082] Table 1 Performance test results

[0083]

[0084]

[0085] It can be seen from Table 1 that the spontaneous atmosphere-modulating membrane of the atmosphere-modulating switch prepared in the embodiment of the present invention can control the CO2, O2 and water vapor permeability of the membrane by controlling the amount of hydrogel particles added in the film-forming matrix. At the same time, the addition of hydrogel particles will not have a significant effect on the mechanical strength of the atmosphere-modulating membrane.

[0086] Freshness test

[0087] A hole with a diameter of about 8 cm is dug in the middle of the lid of a commercially available polypropylene fresh-keeping Lock&Lock box, and the hole is sealed with paraffin using the spontaneous atmosphere-controlled film prepared by the solution casting method of the present invention. Then, fresh vegetables are purchased from a vegetable wholesale market, washed and dried, cut into sections or slices, put into a fresh-keeping box, sealed with the lid sealed with the spontaneous atmosphere-controlled film, and left to stand at room temperature for fresh-keeping.

[0088] 1. Spinach preservation test

[0089] Fresh spinach was cut into 3 cm lengths and preserved using the self-regulated atmosphere membrane prepared in Example 2. The regulated atmosphere membrane prepared in Comparative Example 1 (control group) was used for preservation in the same manner. The preservation conditions on the first, third and fifth days were observed. The results are shown in Table 1. Figure 3 .

[0090] 2. Chives preservation test

[0091] Fresh leeks were cut into 3 cm lengths and preserved using the self-regulated atmosphere membrane prepared in Example 1. The regulated atmosphere membrane prepared in Comparative Example 1 (control group) was used for preservation in the same manner. The preservation conditions on the first, third and seventh days were observed. The results are shown in Table 1. Figure 4 .

[0092] 3. Onion preservation test

[0093] Fresh onions were cut into 1 cm thick slices and preserved using the spontaneous atmosphere-controlled membrane prepared in Example 3. The atmosphere-controlled membrane prepared in Comparative Example 1 (control group) was also used to preserve the onions in the same manner. The preservation conditions on the first and seventh days were observed. The results are shown in Table 1. Figure 5 .

[0094] Depend on Figure 3 , Figure 4 and Figure 5 It can be seen that the spontaneous atmosphere-controlled membrane prepared by the method of the present invention is used for preserving fresh-cut vegetables such as onions, leeks, spinach, etc., and shows good preservation effect, while Comparative Example 1 does not achieve excellent preservation effect. The reason is that the atmosphere-controlled membrane of Comparative Document 1 does not add hydrogel particles. In this case, the atmosphere-controlled membrane loses the ability to regulate the permeability of CO2, O2 and water vapor, and thus cannot match the respiratory metabolic rate of the agricultural products to be preserved, and loses the preservation effect.

[0095] The above are only preferred specific implementations of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A spontaneous gas-controlled membrane with hydrogel as a gas-controlled switch, characterized in that: It comprises hydrogel particles, a film-forming matrix and a plasticizer, wherein the mass addition amount of the hydrogel particles in the film-forming matrix is ​​0.01% to 2.00%; The average particle size of the hydrogel particles is 52 μm; The hydrogel particles include shellac hydrogel particles; The preparation method of the shellac hydrogel particles comprises the following steps: The shellac is dissolved in a sodium carbonate solution, and then polyethylene glycol and gluconolactone are added, and the mixture is stirred at 15 to 35° C. for 2 to 10 minutes, and then allowed to stand for 0.5 to 24 hours to obtain a shellac hydrogel, and then the shellac hydrogel is soaked in deionized water for 24 hours, freeze-dried, and then ground to obtain shellac hydrogel particles; the mass ratio of the shellac to the polyethylene glycol is 1:(0 to 0.5); the polyethylene glycol is polyethylene glycol 200-20000; The film-forming matrix includes chitosan and gelatin; The plasticizer is glycerol; The method for preparing the spontaneous gas-regulated membrane using the hydrogel as the gas-regulated switch comprises the following steps: Dissolving chitosan in an acetic acid solution, adding gelatin under stirring to obtain a film-forming matrix, and then adding a plasticizer to obtain a film-forming matrix mixture; Adding hydrogel particles to the film-forming matrix mixture, and preparing a spontaneous gas-regulated membrane with the hydrogel as a gas-regulated switch by a solution casting method at room temperature; The mass concentration of chitosan in the film-forming matrix mixture is 0.5% to 10%, and the mass concentration of gelatin in the film-forming matrix mixture is 0.05% to 5.00%; The mass concentration of glycerol in the film-forming matrix mixture is 0.05% to 2.00%.

2. A method for preparing a spontaneous gas-regulated membrane with hydrogel as a gas-regulated switch as claimed in claim 1, characterized in that: The following steps are involved: Dissolving chitosan in an acetic acid solution, adding gelatin under stirring to obtain a film-forming matrix, and then adding a plasticizer to obtain a film-forming matrix mixture; Hydrogel particles are added to the film-forming matrix mixture, and a solution casting method is used at room temperature to prepare a spontaneous gas-regulated membrane with the hydrogel as a gas-regulated switch.

3. The method for preparing a spontaneous gas-regulated membrane using hydrogel as a gas-regulated switch according to claim 2, characterized in that: The thickness of the spontaneous gas-regulated membrane with hydrogel as the gas-regulated switch prepared by the solution casting method is 10 to 150 μm.

4. Use of the spontaneous atmosphere-controlled membrane with hydrogel as the atmosphere-controlled switch as claimed in claim 1 in preserving fresh-cut vegetables.

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