Degradable packaging film for fresh keeping of fruits and vegetables as well as preparation method and application of degradable packaging film

Abstract

The invention discloses a degradable packaging film for fresh keeping of fruits and vegetables as well as a preparation method and application of the degradable packaging film, and belongs to the technical field of food packaging materials. The preparation method of the degradable packaging film for fruit and vegetable preservation comprises the following steps: dissolving chitosan in an acetic acid solution, adding soybean protein isolate, adjusting the pH value of the solution to 2-4, and stirring at 80-90 DEG C to obtain a soybean protein fiber solution; adding plant essential oil into the soybean protein fiber solution, stirring at a high speed, adding into the konjac glucomannan solution, continuously stirring to obtain a film-forming solution, pouring the film-forming solution on a flat plate, and drying to obtain the degradable packaging film for fresh keeping of fruits and vegetables. The prepared degradable packaging film for fruit and vegetable fresh-keeping is degradable, capable of blocking gas, antibacterial and antioxidant, has high mechanical performance, can effectively keep the freshness of packaged fruits and vegetables, and can serve as a fruit and vegetable fresh-keeping packaging film to prolong the shelf life.

Description

Technical Field

[0001] The invention relates to a degradable packaging film for preserving fruits and vegetables and a preparation method and application thereof, belonging to the technical field of food packaging materials. Background Art

[0002] Fresh fruits and vegetables are prone to spoilage during storage and transportation, resulting in serious waste of food resources. The spoilage of fresh foods such as fruits and vegetables involves processes such as microbial contamination and respiration. Reducing microbial invasion and reducing respiration during the preservation process can extend the shelf life of most fruits. Low oxygen concentration and low water content have been proven to slow down plant physiological metabolism and inhibit the proliferation of microorganisms.

[0003] Konjac glucomannan is a natural, bio-rich polysaccharide with the biodegradability and biocompatibility of natural materials and good film-forming properties, making it an ideal food packaging material. However, the existing cling film prepared with konjac glucomannan as the base film has problems such as low mechanical strength and lack of antioxidant and antibacterial properties. The antibacterial and antioxidant properties of cling film can be enhanced by adding functional fillers, such as natural active substances (plant polyphenols, organic essential oils) or nanoparticles.

[0004] Plant essential oils are rich in phenols and terpenes, and are non-toxic, biodegradable natural antibacterial agents and antioxidants. Adding plant essential oils as functional fillers can enhance the antioxidant and antibacterial properties of cling film. The existing technology usually adds essential oils directly to the base film, but the direct addition of essential oils often causes phase separation in the system during the film formation process, and also destroys the continuity of the matrix network, thereby reducing the cohesion of the base film, resulting in a further decrease in the mechanical properties of the cling film. Summary of the invention

[0005] [Technical issues]

[0006] In the prior art, the cling film with konjac glucomannan as the base film has poor mechanical strength and lacks antioxidant and antibacterial properties. Although the use of plant essential oil as a functional filler can enhance the antioxidant and antibacterial properties of the konjac glucomannan base film to a certain extent, it usually leads to a further decrease in the mechanical properties of the film.

[0007] [Technical solution]

[0008] In view of the defects and shortcomings of the prior art, the present invention provides a degradable packaging film for preserving fruits and vegetables, and a preparation method and application thereof. Specifically, soybean protein fiber is used as a surfactant to improve the compatibility of konjac glucomannan and plant essential oils, while improving the mechanical strength and barrier properties of the packaging film.

[0009] The soy protein fiber formed by chitosan-induced soy protein isolate has a high aspect ratio and an ordered fiber structure, showing a high emulsification activity index and emulsion stability index, and also has high mechanical properties. Its stable essential oil emulsion can make up for the loss of cohesion caused by the direct addition of essential oil. The essential oil emulsion stabilized by soy protein fiber also enhances the mechanical properties, barrier properties and antioxidant and antibacterial properties of konjac glucomannan-based cling film, which can reduce the oxygen content in the storage environment of fruits and vegetables and inhibit the growth of pathogenic microorganisms, achieving the purpose of preservation.

[0010] In order to achieve the above purpose, the technical solutions provided are as follows:

[0011] The present invention provides a method for preparing a degradable packaging film for preserving fruits and vegetables, the preparation method comprising the following steps:

[0012] (1) dissolving chitosan in an acetic acid solution, adding soy protein isolate, adjusting the pH of the solution to 2-4, and stirring at 80-90° C. to obtain a soy protein fiber solution;

[0013] (2) dissolving konjac glucomannan in water, adding a plasticizer, and stirring to obtain a konjac glucomannan solution;

[0014] (3) adding plant essential oil to the soybean protein fiber solution obtained in step (1), stirring at high speed, and then adding it to the konjac glucomannan solution in step (2), and continuing to stir to obtain a film-forming solution;

[0015] (4) pouring the film-forming liquid obtained in step (3) onto a flat plate and drying it to obtain a degradable packaging film for preserving fruits and vegetables.

[0016] In one embodiment, the acetic acid solution in step (1) is an acetic acid aqueous solution with a volume fraction of 30-60%.

[0017] In one embodiment, the mass concentration of chitosan in the solution of step (1) is 2-5%, and the mass concentration of soy protein isolate is 5-10%.

[0018] In one embodiment, the mass fraction of konjac glucomannan in the konjac glucomannan solution in step (2) is 0.5-1.2%.

[0019] In one embodiment, the mass fraction of the plasticizer in the konjac glucomannan solution in step (2) is 0.1-0.5%.

[0020] In one embodiment, the mass ratio of the plasticizer to konjac glucomannan in step (2) is 0.1-0.3:1.

[0021] In one embodiment, the plasticizer in step (2) includes one or more of glycerol, epoxidized soybean oil, citric acid esters, and sorbitol.

[0022] In one embodiment, the stirring conditions in step (2) are: stirring at 40-60° C. and 300-500 rpm for 2-24 hours.

[0023] In one embodiment, the plant essential oil in step (3) includes one or more of tea tree essential oil, cinnamon essential oil, thyme essential oil, oregano essential oil and clove essential oil.

[0024] In one embodiment, the volume ratio of the soy protein fiber solution: plant essential oil: konjac glucomannan solution in step (3) is 2-10:1:100, wherein during the preparation of the soy protein fiber solution, the mass ratio of chitosan to soy protein isolate is 2-5:5-10, and the mass fraction of konjac glucomannan in the konjac glucomannan solution is 0.5-1.2%.

[0025] In one embodiment, the volume ratio of the soy protein fiber solution: plant essential oil: konjac glucomannan solution in step (3) is 2-10:1:100, wherein during the preparation of the soy protein fiber solution, the mass ratio of chitosan to soy protein isolate is 2:5, and the mass fraction of konjac glucomannan in the konjac glucomannan solution is 1%.

[0026] In one embodiment, the volume ratio of the soy protein fiber solution: plant essential oil: konjac glucomannan solution in step (3) is 2-5:1:100, wherein during the preparation of the soy protein fiber solution, the mass ratio of chitosan to soy protein isolate is 2:5, and the mass fraction of konjac glucomannan in the konjac glucomannan solution is 1%.

[0027] In one embodiment, the volume ratio of the soy protein fiber solution: plant essential oil: konjac glucomannan solution in step (3) is 4-5:1:100, preferably 4:1:100; wherein during the preparation of the soy protein fiber solution, the mass ratio of chitosan to soy protein isolate is 2:5, and the mass fraction of konjac glucomannan in the konjac glucomannan solution is 1%.

[0028] In one embodiment, the high-speed stirring conditions in step (3) are: 10,000 to 15,000 rpm, and the time is 3 to 5 min.

[0029] The present invention also provides a degradable packaging film for preserving fruits and vegetables prepared by the above method.

[0030] In one embodiment, the oxygen permeability of the degradable packaging film for preserving fruits and vegetables is (4.62-4.79) g / (m·s·Kpa), and the water vapor permeability is (0.269-0.326) g·mm / (m 2 ·day·Kpa), the tensile strength is 15.61Mpa~35.02Mpa, and the elongation at break is 46.6%~71.8%.

[0031] In one embodiment, the degradable packaging film for preserving fruits and vegetables has a DPPH free radical scavenging rate of about 27%, a hydroxyl free radical scavenging rate of about 21-25%, and an ABTS free radical scavenging rate of 42-75%.

[0032] The present invention also provides application of the above-mentioned degradable packaging film for preserving fruits and vegetables in the field of food packaging.

[0033] Beneficial effects:

[0034] The degradable packaging film material for preserving fruits and vegetables provided by the present invention specifically introduces a plant essential oil emulsion stabilized by soybean protein fiber into the preparation of a food packaging film material to prepare a degradable, gas-barrier, antibacterial and antioxidant food packaging film, which effectively maintains the freshness of packaged fruits and vegetables and can be used as a fruit and vegetable preservative packaging film to extend the shelf life.

[0035] (1) Compared with the pure konjac glucomannan packaging base film, the water vapor permeability and oxygen permeability of the packaging film prepared by the present invention are significantly reduced, indicating that it has strong barrier properties; among them, the water vapor permeability and oxygen permeability can be significantly reduced by 43.3% and 88.2%, respectively;

[0036] (2) Compared with pure konjac glucomannan packaging base film, the mechanical properties of the packaging film prepared by the present invention are significantly enhanced, wherein the tensile strength and elongation at break can be increased by 210.5% and 82.7%, respectively;

[0037] (3) Compared with pure konjac glucomannan packaging film, the packaging film prepared by the present invention has enhanced antioxidant and antibacterial properties. The total antioxidant capacity of the packaging film prepared by the present invention can reach 9.92 times that of the pure konjac glucomannan base film, and can also completely inhibit the growth of Escherichia coli and Staphylococcus aureus. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 This is a transmission electron microscope image of the soybean protein fiber solution prepared by the present invention;

[0039] Figure 2 This is a transmission electron microscopy image of the soy protein isolate and chitosan complex of Comparative Example 2 of the present invention;

[0040] Figure 3This is a comparison chart of the antibacterial ability of different embodiments 1 to 4 of the present invention and comparative example 1;

[0041] Figure 4 This is a scanning electron microscope image of the surface of the packaging film prepared in Example 1 of the present invention;

[0042] Figure 5 This is a scanning electron microscope image of the surface of the packaging film prepared in Example 2 of the present invention;

[0043] Figure 6 This is a scanning electron microscope image of the surface of the packaging film prepared in Example 3 of the present invention;

[0044] Figure 7 This is a scanning electron microscope image of the surface of the packaging film prepared in Example 4 of the present invention. DETAILED DESCRIPTION

[0045] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work belong to the scope of protection of the present invention. The following specific implementation methods further describe the present invention.

[0046] The test method involved in the present invention is:

[0047] 1. Oxygen permeability

[0048] Add 1g activated carbon, 1.5g sodium chloride and 0.5g reduced iron powder to a weighing bottle, seal it with packaging film, weigh it and place it in a desiccator with constant temperature and humidity (temperature 25±5℃, relative humidity = 90%). Measure the weight of the bottle at 48 hours and calculate the oxygen transmission rate value according to the following formula:

[0049]

[0050] Where Δm (g) is the weight gain of the weighing bottle, t (h) is the test time, X (mm) is the thickness of the packaging film, S (m 2 ) is the area of ​​the weighing bottle mouth.

[0051] 2. Water vapor transmission rate

[0052] 3.0±0.1g of CaCl2 was accurately weighed and spread on the bottom of a flat weighing bottle, and the bottle mouth was sealed with a packaging film. Then the flat weighing bottle was placed in a desiccator (temperature 25±5°C, relative humidity = 75±5%), and the weight of each bottle was recorded after 24 hours. The water vapor transmission rate was calculated according to the following formula:

[0053]

[0054] In the formula, Δm (g) is the weight gain of the weighing bottle, Δt (h) is the test time, X (mm) is the thickness of the packaging film, A (m 2 ) is the weighing bottle mouth area, and Δp (kPa) is the water vapor pressure difference on both sides of the packaging film.

[0055] 3. Tensile strength and elongation at break

[0056] The test process is as follows: According to the standard method of the American Society for Testing and Materials (ASTM), the packaging film was cut into strips of 10mm×50mm to measure the tensile strength and elongation at break of the packaging film. The tensile strength and elongation at break were calculated according to the following formula:

[0057]

[0058] Where F(N) is the tensile force when the packaging film breaks, T(mm) is the thickness of the packaging film, W(mm) is the width of the packaging film, L(mm) is the final length of the packaging film, and L0(mm) is the initial length of the packaging film.

[0059] 4. DPPH free radical scavenging ability test

[0060] Cut each membrane into pieces, take 10 mg of each packaging membrane and mix them with 1 mL of DPPH solution (0.1 mM). Take another portion of the same DPPH solution without adding any membrane as a blank control. After reacting in the dark for 30 minutes, measure the absorbance at a wavelength of 517 nm. Calculate the DPPH free radical scavenging rate according to the following formula:

[0061]

[0062] Where A0 and A1 are the absorbance of each test sample and blank, respectively.

[0063] 5. Hydroxyl free radical scavenging ability test

[0064] Cut each membrane into pieces, take 10 mg of each packaging membrane and mix them with 0.6 mL of salicylic acid ethanol solution (9 mM), 0.6 mL of FeSO4 aqueous solution (9 mM) and 0.6 mL of H2O2 solution (9.8 mM). Take another portion of the same mixed solution without adding any membrane as a blank control. After heating in a 37°C water bath for 30 minutes, measure the absorbance at a wavelength of 510 nm. Calculate the hydroxyl radical scavenging rate according to the following formula:

[0065]

[0066] In the formula, A c and A h are the absorbance of each test sample and blank, respectively.

[0067] 6. ABTS free radical scavenging ability test

[0068] Mix 7mM ABTS and 2.45mM K2O8S2 in a ratio of 1:1 to prepare a solution. After standing for 12 hours, dilute it with anhydrous ethanol to an absorbance of 0.70±0.02 at 734nm to obtain ABTS working solution. Cut each membrane into pieces, take 10mg of each packaging membrane and mix them with 10mL ABTS working solution (0.1mM). Take another portion of the same ABTS working solution without adding any membrane as a blank control. After reacting in the dark for 30 minutes, measure the absorbance at a wavelength of 734nm. Calculate the ABTS free radical scavenging rate according to the following formula:

[0069]

[0070] In the formula, A b and A s are the absorbance of each test sample and blank, respectively.

[0071] 7. Antibacterial performance test

[0072] The test process is as follows: Two typical bacteria, Gram-positive bacteria (Staphylococcus aureus) and Gram-negative bacteria (Escherichia coli), were selected to test the antibacterial activity. First, single colonies of Escherichia coli and Staphylococcus aureus were inoculated into sterilized LB medium, shaken in a thermostat (37°C, 200 rpm) for 12 hours, and then diluted with physiological saline to 1×10 7 CFU / mL. Take 400 mg of each packaging film and add it to 20 mL of E. coli solution and 20 mL of Staphylococcus aureus solution respectively, and continue to culture for 2 hours under magnetic stirring. After culturing in a 37℃ incubator for 24 hours, spread it on the plate and observe and record the growth of the colonies.

[0073] Example 1

[0074] A method for preparing a degradable packaging film for preserving fruits and vegetables comprises the following steps:

[0075] (1) Chitosan was dissolved in a 40% acetic acid solution, and soy protein isolate was added; wherein the mass concentration of chitosan was 2wt% and the mass concentration of soy protein isolate was 5wt%; the pH of the solution was adjusted to 2.0, and stirred at 85°C for 8h to obtain a soy protein fiber solution ( Figure 1 );

[0076] (2) dissolving konjac glucomannan in deionized water, stirring at 60° C. and 300 rpm for 6 h, adding glycerol and continuing stirring for 0.5 h to obtain a konjac glucomannan solution; wherein the mass fraction of konjac glucomannan is 1% and the mass fraction of glycerol is 0.3%;

[0077] (3) taking 2 mL of the soy protein fiber solution prepared in step (1), adding 1 mL of tea tree essential oil, stirring at high speed at 10000 rpm for 3 minutes, and then adding it to 100 mL of the konjac glucomannan solution in step (2), and stirring at high speed at 10000 rpm for 5 minutes to obtain a film-forming solution;

[0078] (4) The film-forming liquid obtained in step (3) is poured onto a flat plate and dried at 40° C. for 24 h to obtain a packaging film.

[0079] Example 2

[0080] A method for preparing a degradable packaging film for preserving fruits and vegetables comprises the following steps:

[0081] (1) dissolving chitosan in a 40% by volume acetic acid solution and adding soy protein isolate; wherein the mass concentration of chitosan is 2wt% and the mass concentration of soy protein isolate is 5wt%; adjusting the pH of the solution to 2.0, stirring at 85°C for 8h, and obtaining a soy protein fiber solution;

[0082] (2) dissolving konjac glucomannan in deionized water, stirring at 60° C. and 300 rpm for 6 h, adding glycerol and continuing stirring for 0.5 h to obtain a konjac glucomannan solution; wherein the mass fraction of konjac glucomannan is 1% and the mass fraction of glycerol is 0.3%;

[0083] (3) taking 3 mL of the soy protein fiber solution prepared in step (1), adding 1 mL of tea tree essential oil, stirring at high speed at 10000 rpm for 3 minutes, then adding to 100 mL of the konjac glucomannan solution in step (2), and stirring at high speed at 10000 rpm for 5 minutes to obtain a film-forming solution;

[0084] (4) The film-forming liquid obtained in step (3) is poured onto a flat plate and dried at 40° C. for 24 h to obtain a packaging film.

[0085] Example 3

[0086] A method for preparing a degradable packaging film for preserving fruits and vegetables comprises the following steps:

[0087] (1) dissolving chitosan in a 40% by volume acetic acid solution and adding soy protein isolate; wherein the mass concentration of chitosan is 2wt% and the mass concentration of soy protein isolate is 5wt%; adjusting the pH of the solution to 2.0, stirring at 85°C for 8h, and obtaining a soy protein fiber solution;

[0088] (2) dissolving konjac glucomannan in deionized water, stirring at 60° C. and 300 rpm for 6 h, adding glycerol and continuing stirring for 0.5 h to obtain a konjac glucomannan solution; wherein the mass fraction of konjac glucomannan is 1% and the mass fraction of glycerol is 0.3%;

[0089] (3) taking 4 mL of the soy protein fiber solution prepared in step (1), adding 1 mL of tea tree essential oil, stirring at high speed at 10000 rpm for 3 minutes, then adding to 100 mL of the konjac glucomannan solution in step (2), and stirring at high speed at 10000 rpm for 5 minutes to obtain a film-forming solution;

[0090] (4) The film-forming liquid obtained in step (3) is poured onto a flat plate and dried at 40° C. for 24 h to obtain a packaging film.

[0091] Example 4

[0092] A method for preparing a degradable packaging film for preserving fruits and vegetables comprises the following steps:

[0093] (1) dissolving chitosan in a 40% by volume acetic acid solution and adding soy protein isolate; wherein the mass concentration of chitosan is 2wt% and the mass concentration of soy protein isolate is 5wt%; adjusting the pH of the solution to 2.0, stirring at 85°C for 8h, and obtaining a soy protein fiber solution;

[0094] (2) dissolving konjac glucomannan in deionized water, stirring at 60° C. and 300 rpm for 6 h, adding glycerol and continuing stirring for 0.5 h to obtain a konjac glucomannan solution; wherein the mass fraction of konjac glucomannan is 1% and the mass fraction of glycerol is 0.3%;

[0095] (3) taking 5 mL of the soy protein fiber solution prepared in step (1), adding 1 mL of tea tree essential oil, stirring at high speed at 10000 rpm for 3 minutes, then adding to 100 mL of the konjac glucomannan solution in step (2), and stirring at high speed at 10000 rpm for 5 minutes to obtain a film-forming solution;

[0096] (4) The film-forming liquid obtained in step (3) is poured onto a flat plate and dried at 40° C. for 24 h to obtain a packaging film.

[0097] Comparative Example 1

[0098] A method for preparing a degradable packaging film for preserving fruits and vegetables, comprising the following steps:

[0099] Dissolve konjac glucomannan in deionized water, stir at 60°C and 300 rpm for 6 hours, add glycerol and continue stirring for 0.5 hour to form a film-forming solution, wherein the mass fraction of konjac glucomannan is 1%, and the mass fraction of glycerol is 0.3%; pour the obtained film-forming solution on a flat plate, and dry at 40°C for 24 hours to obtain a packaging film.

[0100] Comparative Example 2

[0101] A method for preparing a degradable packaging film for preserving fruits and vegetables, comprising the following steps:

[0102] (1) Chitosan was dissolved in a 40% by volume acetic acid solution, and soy protein isolate was added, wherein the mass concentration of chitosan was 2 wt % and the mass concentration of soy protein isolate was 5 wt %, and the mixture was stirred to obtain a soy protein isolate-chitosan complex ( Figure 2 );

[0103] (2) dissolving konjac glucomannan in deionized water, stirring at 60° C. and 300 rpm for 6 h, adding glycerol and continuing stirring for 0.5 h to obtain a konjac glucomannan solution; wherein the mass fraction of konjac glucomannan is 1% and the mass fraction of glycerol is 0.3%;

[0104] (3) taking 4 mL of the soy protein isolate-chitosan complex prepared in step (1), adding 1 mL of tea tree essential oil, stirring at high speed at 10000 rpm for 3 minutes, then adding to 100 mL of the konjac glucomannan solution in step (2), and stirring at high speed at 10000 rpm for 5 minutes to obtain a film-forming solution;

[0105] (4) The film-forming liquid obtained in step (3) is poured onto a flat plate and dried at 40° C. for 24 h to obtain a packaging film.

[0106] Comparative Example 3

[0107] A method for preparing a degradable packaging film for preserving fruits and vegetables, comprising the following steps:

[0108] (1) dissolving chitosan in a 40% by volume acetic acid solution and adding soy protein isolate; wherein the mass concentration of chitosan is 2wt% and the mass concentration of soy protein isolate is 5wt%; adjusting the pH of the solution to 2.0, stirring at 85°C for 8h, and obtaining a soy protein fiber solution;

[0109] (2) dissolving konjac glucomannan in deionized water, stirring at 60° C. and 300 rpm for 6 h, adding glycerol and continuing stirring for 0.5 h to obtain a konjac glucomannan solution; wherein the mass fraction of konjac glucomannan is 1% and the mass fraction of glycerol is 0.3%;

[0110] (3) taking 4 mL of the soy protein fiber solution prepared in step (1), 100 mL of the konjac glucomannan solution in step (2) and 1 mL of tea tree essential oil, and stirring at high speed at 10000 rpm for 5 minutes to obtain a film-forming solution;

[0111] (4) The film-forming liquid obtained in step (3) is poured onto a flat plate and dried at 40° C. for 24 h to obtain a packaging film.

[0112] Results Analysis

[0113] 1. The packaging films prepared in Examples 1 to 4 and Comparative Examples 1 to 2 were tested for barrier properties, including oxygen permeability and water vapor permeability. The results are shown in Tables 1 and 2:

[0114] Table 1 Oxygen transmission rate of biodegradable packaging films for fruit and vegetable preservation prepared under different conditions

[0115]

[0116] It can be seen from the results in Table 1 that the oxygen permeabilities of Examples 1 to 4 are all lower than that of Comparative Example 1, indicating that the food packaging films prepared in Examples 1 to 4 have stronger oxygen barrier properties.

[0117] Table 2 Water vapor transmission rate of biodegradable packaging films for fruit and vegetable preservation prepared under different conditions

[0118]

[0119] It can be seen from the results in Table 2 that the water vapor permeability of Examples 1 to 4 is significantly lower than that of Comparative Examples 1 and 2, indicating that the food packaging film prepared by the present invention has stronger water vapor barrier properties.

[0120] 2. The packaging films prepared in Examples 1-4 and Comparative Examples 1-3 were tested for mechanical properties, including tensile strength and elongation at break. The results are shown in Table 3:

[0121] Table 3 Mechanical properties of biodegradable packaging films for fruit and vegetable preservation prepared under different conditions

[0122]

[0123] From the results in Table 3, it can be seen that the tensile strength and elongation at break of Examples 1 to 4 are significantly higher than those of Comparative Examples 1 and 2, indicating that the food packaging films prepared in Examples 1 to 4 have stronger mechanical properties. Meanwhile, although Comparative Example 3 has a higher tensile strength, it has almost no stretchability and is very easy to break.

[0124] 3. Antioxidant performance test of the packaging films prepared in Examples 1-4 and Comparative Example 1

[0125] Three methods were selected to test the antioxidant properties of each packaging film, including DPPH free radical scavenging ability test, hydroxyl free radical scavenging ability test and ABTS free radical scavenging ability test; the results are shown in Tables 4 to 6:

[0126] Table 4 DPPH radical scavenging rate of biodegradable packaging films for fruit and vegetable preservation prepared under different conditions

[0127]

[0128] Table 5 Hydroxyl radical scavenging rate of biodegradable packaging films for fruit and vegetable preservation prepared under different conditions

[0129]

[0130] Table 6 ABTS free radical scavenging rate of biodegradable packaging films for fruit and vegetable preservation prepared under different conditions

[0131]

[0132] From the results in Tables 4 to 6, it can be seen that the DPPH radical scavenging ability, hydroxyl radical scavenging rate and ABTS radical scavenging ability of the packaging films prepared in Examples 1 to 4 are all higher than those in Comparative Example 1, indicating that the food packaging films prepared in Examples 1 to 4 have stronger antioxidant capacity.

[0133] 4. Antibacterial performance test of the packaging films prepared in Examples 1-4 and Comparative Example 1

[0134] The results are as follows Figure 3 As shown by Figure 3 The results show that the antibacterial ability of the packaging films prepared in Examples 1 to 4 against Escherichia coli and Staphylococcus aureus is significantly higher than that of Comparative Example 1, indicating that the food packaging films prepared in Examples 1 to 4 have stronger antibacterial ability.

[0135] The embodiments provided above are not intended to limit the scope of the present invention, and the steps described are not intended to limit the execution order thereof. Those skilled in the art may make obvious improvements to the present invention in combination with existing common knowledge, which also fall within the scope of protection defined by the claims of the present invention.

Claims

1. A method for preparing a degradable packaging film for preserving fruits and vegetables, characterized in that: The preparation method comprises the following steps: (1) dissolving chitosan in an acetic acid solution, adding soy protein isolate, adjusting the pH of the solution to 2-4, and stirring at 80-90° C. to obtain a soy protein fiber solution; (2) dissolving konjac glucomannan in water, adding a plasticizer, and stirring to obtain a konjac glucomannan solution; (3) adding plant essential oil to the soybean protein fiber solution obtained in step (1), stirring at high speed, and then adding it to the konjac glucomannan solution in step (2), and continuing to stir to obtain a film-forming solution; (4) pouring the film-forming liquid obtained in step (3) onto a flat plate and drying it to obtain a degradable packaging film for preserving fruits and vegetables.

2. The preparation method according to claim 1, characterized in that: In step (1), the chitosan mass concentration in the solution is 2-5%, and the soy protein isolate mass concentration is 5-10%.

3. The preparation method according to claim 1, characterized in that: The mass fraction of konjac glucomannan in the konjac glucomannan solution in step (2) is 0.5-1.2%.

4. The preparation method according to claim 1, characterized in that: The mass ratio of the plasticizer to konjac glucomannan in step (2) is 0.1-0.3:

1.

5. The preparation method according to claim 1, characterized in that: The plasticizer in step (2) includes one or more of glycerol, epoxy soybean oil, citric acid esters, and sorbitol.

6. The preparation method according to claim 1, characterized in that: The plant essential oil in step (3) includes one or more of tea tree essential oil, cinnamon essential oil, thyme essential oil, oregano essential oil and clove essential oil.

7. The preparation method according to claim 1, characterized in that: The volume ratio of the soy protein fiber solution: the plant essential oil: the konjac glucomannan solution in step (3) is 2-10:1:100, wherein during the preparation of the soy protein fiber solution, the mass ratio of chitosan to soy protein isolate is 2-5:5-10, and the mass fraction of konjac glucomannan in the konjac glucomannan solution is 0.5-1.2%.

8. The preparation method according to claim 1, characterized in that: The volume ratio of the soy protein fiber solution: the plant essential oil: the konjac glucomannan solution in step (3) is 2-5:1:100, wherein during the preparation of the soy protein fiber solution, the mass ratio of chitosan to soy protein isolate is 2:5, and the mass fraction of konjac glucomannan in the konjac glucomannan solution is 1%.

9. A degradable packaging film for preserving fruits and vegetables obtained by the preparation method according to any one of claims 1 to 8.

10. Use of the degradable packaging film for preserving fruits and vegetables as claimed in claim 9 in the field of food packaging.

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