Double-layer preservative film as well as preparation method and application thereof

Abstract

The invention provides a double-layer preservative film as well as a preparation method and application thereof, belongs to the technical field of food preservation, and can solve the problems that a traditional fish gelatin liquid film is insufficient in mechanical property, not ideal in antibacterial effect and difficult to meet the preservation requirements of fresh fruits and vegetables. The double-layer preservative film comprises a physical protection film layer and an antibacterial volatilization film layer, and the physical protection film layer and the antibacterial volatilization film layer are bridged to form a double-layer solid film structure; wherein the antibacterial volatilization film layer is arranged on the inner side of the physical protection film layer, and the antibacterial volatilization film layer is used for being in direct contact with articles to be preserved. The preservative film has good mechanical property and antibacterial effect, and can prolong the preservation time to meet the preservation requirements of various foods. The method can be applied to the aspects of food preservation and storage.

Description

Technical Field

[0001] The present invention belongs to the technical field of food preservation, and particularly relates to a double-layer fresh-keeping film, a preparation method thereof, and an application thereof. Background Art

[0002] With the improvement of people's living standards and the enhancement of health awareness, consumers have put forward higher requirements for the quality and safety of fruits. However, for berry fruits such as strawberries, due to their high water content, soft tissues, and rich surface nutrients, they are extremely vulnerable to microbial infection and rapid spoilage. At the same time, during storage, transportation, and sales, strawberries are also easily affected by adverse factors such as mechanical damage and water loss, resulting in an accelerated deterioration rate and causing significant economic losses. Therefore, the research and development of new fresh-keeping packaging materials that can effectively inhibit bacteria and have environmental protection performance has become an important topic that urgently needs to be broken through in the field of food preservation.

[0003] Traditional food fresh-keeping films are mainly made of petroleum-based polymer materials such as polyethylene and polyvinyl chloride. Although they can block water evaporation and oxygen intrusion to a certain extent, they do not have good antibacterial functions and are insufficient in terms of degradability and environmental protection. In recent years, bio-polymer-based fresh-keeping films characterized by degradability and high biocompatibility have gradually attracted the attention of the academic and industrial circles. Among them, gelatin from natural sources has been widely used in fields such as food and medical dressings. As an important source of gelatin, fish skin gelatin has a moderate molecular weight, relatively low antigenicity, and high biological safety. Moreover, the use of fish skin gelatin can also realize the comprehensive high-value utilization of aquatic by-products, which conforms to the concept of green environmental protection.

[0004] Chinese invention patent CN116478545A discloses a fish gelatin liquid film with antibacterial activity. The fish gelatin liquid film is mainly prepared from fish gelatin and arabic gum as film-forming components and nisin as an antibacterial agent. However, this liquid film has problems such as insufficient mechanical properties and unsatisfactory antibacterial effects, and it is difficult to meet the fresh-keeping requirements of fresh fruits and vegetables, especially strawberries. Summary of the Invention

[0005] In view of the technical problems of the traditional fish gelatin liquid film, such as insufficient mechanical properties and unsatisfactory antibacterial effects, which are difficult to meet the fresh-keeping requirements of fresh fruits and vegetables, the present invention proposes a double-layer fresh-keeping film with good toughness and sealing performance. The fresh-keeping film is a double-layer solid fresh-keeping film, which is bridged by an outer physical protection film layer and an inner antibacterial volatile film layer. The physical protection film layer can not only improve the mechanical properties of the fresh-keeping film but also prevent the loss of antibacterial components embedded in the antibacterial volatile film layer, enabling the antibacterial components to fully play their antibacterial role, so as to further extend the fresh-keeping time and meet the fresh-keeping requirements of various fresh fruits and vegetables.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] A double-layer fresh-keeping film, comprising a physical protective film layer and an antibacterial volatile film layer, and a double-layer solid film structure is formed by bridging between the physical protective film layer and the antibacterial volatile film layer;

[0008] Wherein, the antibacterial volatile film layer is arranged inside the physical protective film layer, and the antibacterial volatile film layer is used for directly contacting the articles to be fresh-kept.

[0009] In an embodiment, the physical protective film layer is a protective film layer with a nano space grid structure, and the antibacterial volatile film layer is a polar hydrogel film layer embedded with antibacterial components.

[0010] In an embodiment, by mass percentage, the physical protective film layer comprises:

[0011] Carboxymethyl chitosan is 0.1% - 0.5%, divalent iron ions are 0.5% - 0.9%, glycerol is 0.1% - 0.5%, appropriate organic acid, and the balance is water.

[0012] In an embodiment, by mass percentage, the antibacterial volatile film layer comprises:

[0013] Essential oil is 5% - 10%, Tween 80 is 0.1% - 1%, pectin powder is 10% - 25%, fish gelatin powder is 10% - 20%, and the balance is water;

[0014] Wherein, the essential oil is extracted from the peel of citrus fruits, and the pectin powder is citrus pectin powder.

[0015] In an embodiment, the tearing strength of the double-layer fresh-keeping film is 6 - 7 Mpa, and the tensile elastic elongation distance is 50 - 100 mm.

[0016] In an embodiment, the thickness of the double-layer fresh-keeping film is 0.15 mm - 0.31 mm.

[0017] In an embodiment, the application of the double-layer fresh-keeping film in food storage and preservation, antibacterial and bacteriostatic, and fruit and vegetable anti-corrosion.

[0018] The present invention also provides a preparation method of a double-layer fresh-keeping film, comprising the following steps:

[0019] According to the mass ratio, add carboxymethyl chitosan, divalent iron ions, glycerol and appropriate organic acid to deionized water, homogenize to obtain a film-forming solution, and let it stand and dry in a mold to obtain the physical protective film layer;

[0020] According to the mass ratio, add essential oil, Tween 80, pectin powder and fish gelatin powder to deionized water, and obtain an essential oil gel nanoemulsion through homogenization treatment, which is the antibacterial volatile film layer in an emulsion state;

[0021] The essential oil gel nanoemulsion is evenly coated on the physical protective film layer and left to stand and dry to obtain the double-layer fresh-keeping film.

[0022] In one embodiment, the antibacterial volatile film layer in the double-layer fresh-keeping film is used to directly contact the items to be fresh-kept, and the physical protective film layer is used to contact the external environment;

[0023] Among them, the items to be fresh-kept include fresh food ingredients, processed foods or household items.

[0024] In one embodiment, the fresh food ingredients include vegetables, fruits, meats or fish.

[0025] Compared with the prior art, the advantages and positive effects of the present invention are as follows:

[0026] 1. The present invention proposes a double-layer fresh-keeping film, which is a double-layer solid film structure bridged between a physical protective film layer and an antibacterial volatile film layer, and has good toughness and sealing performance; in this double-layer fresh-keeping film, the physical protective film layer located on the outside is a protective film layer with a nano-space grid structure for contacting the external environment, and the antibacterial volatile film layer located on the inside is a polar hydrogel film layer embedded with antibacterial components for directly contacting the items to be wrapped (for example, fresh fruits and vegetables, etc.). The physical protective film layer can improve the mechanical properties of the fresh-keeping film on the one hand, and on the other hand, it can also prevent the antibacterial components embedded in the antibacterial volatile film layer from diffusing into the external environment, resulting in the loss of antibacterial components, so that the antibacterial components can fully play their antibacterial role, achieving the effect of further prolonging the fresh-keeping time to meet the fresh-keeping needs of various foods (including various fresh fruits and vegetables).

[0027] 2. The double-layer fresh-keeping film proposed by the present invention is a double-layer solid film structure bridged between a physical protective film layer and an antibacterial volatile film layer. All the materials used in this fresh-keeping film are biodegradable materials and will not cause environmental pollution. At the same time, the formula of this fresh-keeping film comes from extracts of natural agricultural products (for example, fish gelatin, pectin, chitosan, etc.) and does not contain any petroleum-based polymer materials such as polyethylene and polyvinyl chloride. The human body will not ingest microplastics because of this, and it will not cause any harm to the human body;

[0028] 3. The double-layer solid film structure proposed by the present invention has good toughness and sealing performance. Compared with traditional liquid fresh-keeping films, because of its more excellent toughness and sealing performance, it can not only prevent fruits and vegetables from being invaded by microorganisms, improve the fresh-keeping effect of fresh fruits and vegetables, and prolong the fresh-keeping time, but also avoid the influence of adverse factors such as mechanical damage and water loss of fruits and vegetables during storage, transportation and sales, so that the fruits and vegetables deteriorate rapidly and cause economic losses;

[0029] 4. The present invention provides a double-layer fresh-keeping film, which can be used in multiple fields such as fresh food ingredients, processed foods, or household items. The fresh food ingredients include, but are not limited to, vegetables, fruits, meats, or fish, etc., and are particularly suitable for berry fruits with high water content, soft tissues, and rich surface nutrients, providing a new packaging material with both high-efficiency antibacterial and convenient use in the food field. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a schematic diagram showing the influence of different storage times and treatment methods on the quality of strawberries provided by the embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0031] Next, the technical solutions in the embodiments of the present invention will be described clearly and completely. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0032] The embodiment of the present invention provides a double-layer fresh-keeping film, including a physical protection film layer and an antibacterial volatile film layer. The physical protection film layer and the antibacterial volatile film layer are bridged to form a double-layer solid film structure;

[0033] Among them, the antibacterial volatile film layer is arranged inside the physical protection film layer, and the antibacterial volatile film layer is used to directly contact the items to be fresh-keeping.

[0034] The above embodiment provides a double-layer fresh-keeping film, which is formed by bridging between a physical protection film layer and an antibacterial volatile film layer to form a double-layer solid film structure. Among them, the physical protection film layer is a protection film layer with a nano-space grid structure, and the antibacterial volatile film layer is a polar hydrogel film layer embedded with antibacterial components. This double-layer solid film structure can not only improve the mechanical properties of the fresh-keeping film, but also avoid the loss of antibacterial components embedded in the antibacterial volatile film layer, enabling the antibacterial components to fully play their antibacterial role, achieving the purpose of further extending the fresh-keeping time to meet the fresh-keeping needs of various fresh fruits and vegetables.

[0035] Based on the above content, it can be seen that the double-layer fresh-keeping film provided by the present invention needs to simultaneously possess excellent mechanical properties and antibacterial properties in order to meet the fresh-keeping needs of various fresh fruits and vegetables, especially berry fruits such as strawberries.

[0036] First, regarding the mechanical properties, the physical protection layer in this double-layer solid film is composed of carboxymethyl chitosan and divalent iron ions (Fe 2+) It consists of an appropriate amount of organic acids (such as tannic acid, etc.) and glycerol. Among them, after the added divalent iron ions combine with phenolic hydroxyl compounds through hydrogen bonds, chemical bonds and van der Waals forces, it has the effect of enhancing the strength and toughness of the physical protection layer. At the same time, iron ions and organic acids can assemble to form dimers, obtaining a structure similar to a nano-space grid structure. This grid structure not only has strong toughness, endows the double-layer fresh-keeping film structure with ideal mechanical properties, effectively avoids mechanical damage to fresh fruits and vegetables caused by external forces, but also has excellent water-carrying capacity and strong adhesion. It further bridges with the antibacterial volatile film layer through chemical bonds, hydrogen bonds and van der Waals forces, thus obtaining a double-layer film structure with stable structure.

[0037] Secondly, regarding the antibacterial performance, the antibacterial volatile film layer in the double-layer solid film consists of fish gelatin, pectin, essential oil and water. Among them, pectin is a heteropolysaccharide polymerized from different kinds of monosaccharides, and fish gelatin is a water-soluble polypeptide protein obtained by partial hydrolysis of collagen. Both pectin and fish gelatin have good water compatibility, and a very polar hydrogel is formed by the combination of the above two components, generating very strong polar groups on the film layer surface. At the same time, the film layer selects essential oil extracted from the peel of citrus fruits as the antibacterial component, and the essential oil can achieve the effects of antifungal, antibacterial and mosquito repellent during the volatilization process. During the preparation process, cavitation effects will occur when the essential oil and the above hydrogel are in an ultra-high-speed stirring system, and then nano-scale water-in-oil / oil-in-water emulsions are formed. During storage, as the water volatilizes, the essential oil breaks out of the emulsion and slowly releases into the surrounding air, forming an effect of repelling disease-causing microorganisms, fully exerting the antibacterial and fresh-keeping performance. Through the synergistic effect among components such as fish gelatin, pectin and essential oil, the slow release effect of the antibacterial component - essential oil is achieved, inhibiting the growth of harmful microorganisms, so as to extend the action time of the antibacterial component and achieve the purpose of further improving the fresh-keeping effect.

[0038] It should also be added that for fresh fruits and vegetables, especially berry fruits with a relatively high water content, water loss is also one of the reasons for their spoilage. The antibacterial volatile film layer is a highly polar hydrogel composed of pectin and fish gelatin, which generates strong polar groups on the film surface. It can provide a storage environment with a relatively high water content for fresh fruits and vegetables. At the same time, the physical protective film layer arranged outside the antibacterial volatile film layer has a good sealing effect and a combined essential oil volatilization path, which can better lock in moisture, prevent water loss, further enhance the freshness preservation effect, and extend the essential oil freshness preservation time. Compared with the liquid fresh-keeping film in the prior art, the double-layer solid fresh-keeping film provided by the present invention has better mechanical properties, effectively avoiding mechanical damage to fresh fruits and vegetables during storage and transportation. At the same time, considering that the above traditional fresh-keeping film is liquid, it is equivalent to directly applying a liquid coating on the outer surface of the item to be fresh-kept (for example, fresh fruits and vegetables). In actual use, it may cause consumers to accidentally ingest the coating liquid remaining on the surface of agricultural products and cause harm to the body. In addition, since the coverage effect of the liquid coating material cannot be accurately evaluated, its sealing effect cannot be evaluated either, and there may be a problem of fresh fruits and vegetables spoiling due to poor sealing, resulting in economic losses.

[0039] In a specific embodiment, by mass percentage, the physical protective film layer includes:

[0040] Carboxymethyl chitosan is 0.1% - 0.5%, divalent iron ions are 0.5% - 0.9%, glycerol is 0.1% - 0.5%, an appropriate amount of organic acid, and the balance is water.

[0041] In the above embodiment, from the above components, it can be seen that the physical protective film layer does not contain any petroleum-based polymer materials such as polyethylene and polyvinyl chloride, and the human body will not ingest microplastics due to this. Regarding the dosage of the above components, the addition amount of carboxymethyl chitosan can be selected as 0.1%, 0.2%, 0.3%, 0.4%, 0.5% or any value within the above-defined range selected by those skilled in the art according to actual needs, and all fall within the protection scope of the present invention; the divalent iron ions can specifically be compounds containing divalent iron ions, such as ferrous sulfate, ferrous gluconate, ferrous acetate, ferrous chloride, etc. The specific types of compounds are not particularly limited here. The addition amount can be selected as 0.5%, 0.6%, 0.7%, 0.8%, 0.9% or any value within the above-defined range selected by those skilled in the art according to actual needs, and all fall within the protection scope of the present invention; the addition amount of glycerol can be selected as 0.1%, 0.2%, 0.3%, 0.4%, 0.5% or any value within the above-defined range selected by those skilled in the art according to actual needs, and all fall within the protection scope of the present invention; for the appropriate amount of organic acid, it can specifically be tannic acid, malic acid, ascorbic acid, oxalic acid, citric acid, etc., and the specific addition method is based on the range of pH 2 - 7.

[0042] In a specific embodiment, by mass percentage, the antibacterial volatile film layer comprises:

[0043] Essential oil is 5% - 10%, Tween 80 is 0.1% - 1%, pectin powder is 10% - 25%, fish gelatin powder is 10% - 20%, and the balance is water;

[0044] Among them, the essential oil is extracted from citrus fruit peels, and the pectin powder is citrus pectin powder.

[0045] In the above embodiment, from the above components, it can be seen that the components in the antibacterial volatile film layer also come from extracts of natural agricultural products (such as fish gelatin, pectin, etc.), are degradable, will not cause environmental pollution, and do not contain any petroleum-based polymer materials such as polyethylene and polyvinyl chloride, so the human body will not ingest microplastics. Regarding the dosage of the above components, the addition amount of the essential oil can be selected as 5%, 6%, 7%, 8%, 9%, 10% or any value within the above-defined range selected by those skilled in the art, which all fall within the protection scope of the present invention; the addition amount of Tween 80 can be selected as 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0% or any value within the above-defined range selected by those skilled in the art, which all fall within the protection scope of the present invention; the addition amount of pectin powder can be selected as 10%, 15%, 20%, 25% or any value within the above-defined range selected by those skilled in the art, which all fall within the protection scope of the present invention; the addition amount of fish gelatin powder can be selected as 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20% or any value within the above-defined range selected by those skilled in the art, which all fall within the protection scope of the present invention.

[0046] In a specific embodiment, the tearing strength of the double-layer fresh-keeping film is 6 - 7 Mpa, and the tensile elastic elongation distance is 50 - 100 mm.

[0047] In a specific embodiment, the thickness of the double-layer fresh-keeping film is 0.15 mm - 0.31 mm.

[0048] In a specific embodiment, the application of the double-layer fresh-keeping film in food storage and preservation, antibacterial and bacteriostatic, and fruit and vegetable preservation. In the actual application process, the application scope of the double-layer fresh-keeping film provided by the present invention includes but is not limited to the above aspects.

[0049] The embodiment of the present invention also provides a preparation method of the double-layer fresh-keeping film, comprising the following steps:

[0050] S1. According to the mass ratio, add carboxymethyl chitosan, divalent iron ions, glycerol and an appropriate amount of organic acid to deionized water, homogenize to obtain a film-forming solution, and leave it to stand and dry in a mold to obtain a physical protective film layer;

[0051] S2. According to the mass ratio, add essential oil, Tween 80, pectin powder and fish gelatin powder to deionized water, and obtain an essential oil gel nanoemulsion by homogenization treatment, which is an antibacterial volatile film layer in the form of an emulsion;

[0052] S3. Uniformly coat the essential oil gel nanoemulsion on the physical protective film layer, leave it to stand and dry to obtain the double-layer fresh-keeping film.

[0053] In a specific embodiment, the antibacterial volatile film layer in the double-layer fresh-keeping film is used to directly contact the items to be fresh-keeping, and the physical protective film layer is used to contact the external environment;

[0054] Among them, the items to be fresh-keeping include but are not limited to fresh food ingredients, processed foods or household items.

[0055] In a specific embodiment, the fresh food ingredients include but are not limited to vegetables, fruits, meats or fish, and are particularly suitable for the storage and preservation of berry fruits.

[0056] In order to introduce a double-layer fresh-keeping film, its preparation method and its application provided by the embodiments of the present invention more clearly and in detail, the following will be described in combination with specific embodiments.

[0057] Example 1

[0058] This example provides a preparation method of a double-layer fresh-keeping film, specifically as follows:

[0059] (1) Prepare fish gelatin: Remove the bones and internal organs of an appropriate amount of fresh Squalibarbus curriculus, add the skin and flesh to 100 parts by weight of deionized water, adjust the pH to the range of 2-5 with acid, then heat to 30-70 °C, keep for 60 min, centrifuge to obtain the supernatant, and then add 3 times the volume of 95% ethanol solution for precipitation for 24 h, filter to obtain the precipitate and dry it to obtain fish gelatin powder;

[0060] (2) Prepare the physical protective film layer: Dissolve 0.1-0.5% of carboxymethyl chitosan, 0.5% of iron ions (Fe 2+ ) and 0.1-0.5% of glycerol in 100 mL of deionized water, homogenize for 3 min to obtain a film-forming solution, place it in a mold in an environment of 60 °C for 12 h to obtain a dry physical protective film layer;

[0061] (3) Preparation of the antibacterial volatile film layer: Add essential oil (extracted from citrus fruit peels) with a mass ratio range of 5-10%, 0.1-1% of Tween 80, 10% of citrus pectin powder, and 10-20% of fish gelatin powder (obtained from the preparation in step 1) into 50 mL of deionized water, homogenize for 5 min, remove air bubbles by ultrasonic wave, then homogenize at a speed of 10000 r / min for 5 min to obtain essential oil gel nanoemulsion. Then place it in a 50 mL syringe and slowly inject it onto a physical protective film layer with a diameter of 20 mm, and try to make the essential oil gel nanoemulsion evenly distributed. Place it at room temperature and dry for 48 h to prepare a double-layer solid fresh-keeping film.

[0062] Example 2

[0063] This example is for the performance test of the double-layer solid fresh-keeping film, mainly detecting the mechanical properties, elongation at break, air permeability and moisture permeability of the double-layer solid fresh-keeping film at room temperature. The test methods and results are as follows:

[0064] (1) Test methods:

[0065] Mechanical properties: Cut the double-layer solid fresh-keeping film into long strips (15 mm wide × 80 mm long), ensure that the edges are flat and without notches. Use a universal material testing machine, set the tensile rate to 50 mm / min, and the gauge length (initial gauge length) to 40 mm. Vertically clamp both ends of the specimen into the upper and lower fixtures to avoid skewing or slipping. Start the equipment and stretch the specimen at a constant rate until it breaks, and record the maximum tensile force value.

[0066] Tensile elastic elongation distance: Mark the initial gauge length of 40 mm in the middle of the specimen with a marker pen. Similar to the tensile strength test, stretch until the specimen completely breaks, and measure the gauge length after fracture.

[0067] Air permeability: Cut the double-layer solid fresh-keeping film into circular pieces with a diameter of 10 cm, place them in an environment of 23°C and 50% RH for 24 hours to balance. Place the specimen into the test chamber of the air permeability tester to ensure no leakage. Adjust the oxygen pressure difference to 1 atm, temperature to 25°C, and humidity to 0% RH (dry condition). Record the volume of oxygen passing through the specimen per unit time (cm 3 ), and continue for 24 h until the data is stable.

[0068] Moisture permeability: Cut the double-layer solid fresh-keeping film into circular pieces with a diameter of 7 cm, cover the mouth of the desiccant (such as anhydrous calcium chloride) cup, and seal the edge with wax. Place the sealed cup in a constant temperature and humidity chamber (25°C, 90% RH), and the humidity in the cup is 0% RH. Weigh it initially (W0), and weigh it every 1 hour until the weight gain rate is stable (usually 24 hours).

[0069] (2) Measurement results:

[0070] Table 1 Measurement results

[0071] Double-layer solid fresh-keeping film of the present invention Ordinary commercial fresh-keeping film Mechanical properties (MPa) 6.0-7.0 3.5-5.0 Tensile elastic elongation distance (mm) 50-100 80-120 <![CDATA[Air permeability (cm 3 / (m 2 ·day·atm))]]> 50-200 10-50 <![CDATA[Water vapor permeability (g / (m 2 ·day))]]> 100-500 5-20 Fresh-keeping film thickness (mm) 0.156-0.311 0.010～0.020

[0072] In addition, observe the integrity and adhesion stability of the double-layer solid fresh-keeping film during bending, pasting, and peeling processes. Fix the double-layer solid fresh-keeping film on a bending tester and repeatedly bend it at an angle of 180° (rate: 10 times / min), and observe cracks or delamination. Use a universal material testing machine to test the adhesion between the film and the glass substrate at a peeling angle of 90° (tensile rate: 50 mm / min). After peeling, observe the interface delamination through an optical microscope (100×) and count the proportion of the complete interface.

[0073] The test results are as follows: There are no visible cracks in the double-layer solid fresh-keeping film within 5 times of bending; after 10 times of bending, microcracks (length < 0.5 mm) appear in the edge area, and the delamination area accounts for ≤ 5%. The initial adhesion is 1.8 ± 0.3 N / cm (significantly higher than 1.0 ± 0.2 N / cm of ordinary PE film); at a humidity of 70% RH, the adhesion drops to 1.3 ± 0.2 N / cm (a decrease of 28%). By observing the interface delamination, it can be seen that 90% of the sample interfaces are intact without delamination, and only 10% show separation between the local active layer and the substrate layer (area ratio < 3%).

[0074] Example 3

[0075] This example is for testing the fresh-keeping effect of the double-layer solid fresh-keeping film on fresh fruits and vegetables, specifically as follows:

[0076] (1) Test materials and grouping:

[0077] A number of fresh strawberries are randomly grouped into a blank group, a control group, and an experimental group, where:

[0078] Blank group: Do not use any fresh-keeping film;

[0079] Control group: Ordinary commercial fresh-keeping film;

[0080] Experimental group: The double-layer solid fresh-keeping film prepared in Example 1 of the present invention.

[0081] Cover the strawberries with the blank group (without using any fresh-keeping film), the control group (ordinary commercial fresh-keeping film), and the double-layer solid fresh-keeping film of the experimental group respectively, so that their outer layers completely cover the fruits, and conduct comparative tests respectively. The fresh-keeping temperatures are room temperature (25°C) and refrigeration (4°C), and the storage time is 7 days.

[0082] Regularly observe the mildew spots, degree of rot, and fruit weight loss rate on the strawberry surface under different storage environments.

[0083] Measurement results:

[0084] Table 2 Measurement results

[0085]

[0086] Under room temperature and refrigeration conditions, the double-layer solid fresh-keeping film provided by the present invention shows good antibacterial and fresh-keeping effects. The strawberry rot rate is significantly lower than that of the control group and the blank group. Through the results of microbial culture, it is found that the total number of bacteria and fungi on the surface of strawberries using the fresh-keeping film of the present invention is significantly reduced; the fruit weight loss rate is also controlled to a certain extent, and the fresh-keeping film still maintains good adhesiveness in the later stage of storage and will not cause obvious indentations or damage to the fruits.

Claims

1. A double-layer fresh-keeping film, characterized in that, It includes a physical protective film layer and an antibacterial volatile film layer, and a double-layer solid film structure is formed by bridging between the physical protective film layer and the antibacterial volatile film layer; Among them, the antibacterial volatile film layer is arranged inside the physical protective film layer, and the antibacterial volatile film layer is used to directly contact the item to be preserved.

2. The double-layer plastic wrap according to claim 1, wherein The physical protective film layer is a protective film layer with a nano-space grid structure, and the antibacterial volatile film layer is a polar hydrogel film layer embedded with antibacterial components.

3. The double-layer plastic wrap according to claim 1, wherein By mass percentage, the physical protective film layer includes: Carboxymethyl chitosan is 0.1% - 0.5%, divalent iron ions are 0.5% - 0.9%, glycerol is 0.1% - 0.5%, an appropriate amount of organic acid, and the balance is water.

4. The double-layer plastic wrap according to claim 1, characterized in that, By mass percentage, the antibacterial volatile film layer includes: Essential oil is 5% - 10%, Tween 80 is 0.1% - 1%, pectin powder is 10% - 25%, fish gelatin powder is 10% - 20%, and the balance is water; Among them, the essential oil is extracted from the peel of citrus fruits, and the pectin powder is citrus pectin powder.

5. The double-layer plastic wrap according to claim 1, wherein, The tear strength of the double-layer fresh-keeping film is 6 - 7 Mpa, and the tensile elastic elongation distance is 50 - 100 mm.

6. The double-layer plastic food wrap according to claim 1, characterized in that, The thickness of the double-layer fresh-keeping film is 0.15 mm - 0.31 mm.

7. A double-layer plastic food wrap, characterized in that, The application of the double-layer fresh-keeping film in food storage and preservation, antibacterial and bacteriostatic, and the preservation of fruits and vegetables.

8. A preparation method of a double-layer fresh-keeping film, characterized in that, It includes the following steps: According to the mass ratio, add carboxymethyl chitosan, divalent iron ions, glycerol and an appropriate amount of organic acid to deionized water, homogenize to obtain a film-forming solution, and let it stand and dry in a mold to obtain the physical protective film layer; According to the mass ratio, add essential oil, Tween 80, pectin powder and fish gelatin powder to deionized water, and after homogenization treatment, obtain an essential oil gel nanoemulsion, which is the antibacterial volatile film layer in an emulsion state; Uniformly coat the essential oil gel nanoemulsion on the physical protective film layer, let it stand and dry to obtain the double-layer fresh-keeping film.

9. The preparation method of the double-layer plastic wrap according to claim 8, wherein, The antibacterial volatile film layer in the double-layer fresh-keeping film is used to directly contact the item to be preserved, and the physical protective film layer is used to contact the external environment; Among them, the items to be preserved include fresh food ingredients, processed foods or household items.

10. The preparation method of the double-layer plastic wrap according to claim 8, wherein, The fresh food ingredients include vegetables, fruits, meats or fishes.

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