CN117694398A - Preparation method and application of silk fibroin-containing composite edible membrane liquid - Google Patents

Abstract

The invention discloses a preparation method and application of a composite edible film liquid containing silk fibroin, which relates to the field of food preservation. The raw materials include silk fibroin, chitosan and microemulsion. The microemulsion includes mixed surfactants and essential oils. , mixed surfactants include surfactants and co-surfactants. The preparation method is: prepare silk fibroin solution, chitosan solution and microemulsion respectively; mix the silk fibroin solution and chitosan solution, and then mix with the microemulsion. The composite edible film can be applied to food preservation. The composite edible film has good mechanical barrier properties, strong adhesion and strong antibacterial activity. It can effectively delay the oxidation and aging process of food and inhibit the growth of microorganisms in food.

Description

Preparation method and application of composite edible film liquid containing silk fibroin

Technical field

The invention relates to the field of food preservation, and in particular to a preparation method and application of a composite edible film liquid containing silk fibroin.

Background technique

Mechanical damage, physiological decay and microbial spoilage are the main factors leading to postharvest quality deterioration of fresh fruits and vegetables. Meat products are deeply loved by consumers due to their high nutritional value and delicious taste. However, they are easily contaminated by microorganisms during processing and storage, leading to spoilage and shortened shelf life. Therefore, the development and application of new preservation technologies for fruits, vegetables, meat products and other foods is imperative.

Edible film has the characteristics of safety and environmental protection. It is usually made of natural edible substances such as chitosan, pectin, soy protein or modified starch as raw materials, and is a film with a porous network structure formed through the interaction between different molecules. , can block gas exchange and microbial infection, and has a preservation effect. However, films formed from the above materials often have shortcomings such as poor mechanical barrier properties and poor antibacterial activity, which have an impact on the application effect.

Silk fibroin is extracted from silkworm cocoons or silk. It is a biopolymer that has passed the safety certification of GRAS (the safety indicator of food additives evaluated by the U.S. FDA). It can form transparent, colorless, odorless, strong, flexible, and durable through self-crosslinking. An edible film that is biodegradable and has good water and gas barrier properties.

Many studies have shown that chitosan and silk fibroin can complement each other. Silk fibroin-chitosan composite membranes can overcome the shortcomings of pure chitosan membranes such as high swelling, and compared with pure silk fibroin membranes, composite membranes have better Good film forming properties, mechanical properties and stability. At the same time, silk fibroin has the problem of high cost in edible film applications, while chitosan is rich in sources, cheap and easy to obtain, and is often used in food because of its biocompatibility, biodegradability and non-toxicity. Keep fresh. Silk fibroin-chitosan composite membrane reduces the application cost of silk fibroin to a certain extent and is more conducive to industrial application.

Silk fibroin membrane has good application advantages, but there are problems such as no antibacterial effect and easy utilization by microorganisms (S. Ghalei, H. Handa, Materials Today Chemistry, 2022, 23: 100673). Silk fibroin lacks inherent antibacterial activity and provides a good matrix for the growth of microorganisms. Studies have shown that the antibacterial activity of chitosan and silk fibroin composite films is weak and has no obvious antibacterial zone against Staphylococcus epidermidis and Escherichia coli (Guldemet Basal, DuyguAltiok, Oguz Bayraktar, Fibers And Polymers, 2010, 11(1 ):21-27)

Plant essential oils have strong antibacterial effects and are often used to preserve fruits, vegetables and meat products. However, there are problems such as low solubility and stability that need to be solved when applied in water-soluble systems. Plant essential oil microemulsions can improve the water solubility of essential oils and enable active ingredients to have a larger specific surface area and better dispersibility, making it easier to contact microbial cells, thus enhancing the antibacterial effect of essential oils. Microemulsion is a thermodynamically stable system with a transparent appearance and low viscosity. It has no significant impact on the light transmittance of edible films. At the same time, the essential oils and surfactants in the microemulsion formula can reduce the contact angle of the film liquid on the hydrophobic surface. Helps form a film on the surface of fruits and vegetables.

Therefore, those skilled in the art are committed to developing a composite edible film with good mechanical barrier properties and strong antibacterial activity. The film is safe and environmentally friendly, has simple preparation and use methods, mild conditions, and is not highly dependent on equipment.

Contents of the invention

In view of the above-mentioned defects of the prior art, the technical problem to be solved by the present invention is how to develop a composite with good mechanical barrier properties, strong antibacterial activity, safety and environmental protection by combining silk fibroin with chitosan and plant essential oil microemulsion. The film is edible, has simple preparation and use methods, mild conditions, and is not highly dependent on equipment.

In order to achieve the above object, the present invention provides a method for preparing a composite edible film liquid containing silk fibroin, which includes the following steps:

Step 1. Prepare silk fibroin solution, chitosan solution and microemulsion respectively;

Step 2. Prepare the mixed film liquid, that is, fully mix the silk fibroin solution obtained in step 1 and the chitosan solution to obtain the silk fibroin-chitosan mixed film liquid; mix the silk fibroin-chitosan mixed film liquid with the step 1. The obtained microemulsion is mixed to obtain a silk fibroin-chitosan-microemulsion mixed film liquid.

Further, step 1 also includes:

Step 1.1. Prepare a silk fibroin solution. Degumm the mulberry silk with sodium carbonate solution, then wash it with distilled water to remove impurities and part of the residual sericin, and then dry it to obtain degummed silk fibroin; Dissolve the protein in the lithium bromide aqueous solution and heat to dissolve it; use dialysis, ultrafiltration or electrodialysis to remove the lithium bromide small molecules, centrifuge and take the supernatant to obtain the silk fibroin aqueous solution, and store it in the refrigerator;

Step 1.2, prepare chitosan solution, add chitosan into acetic acid solution, stir until chitosan is completely dissolved, and obtain chitosan solution;

Step 1.3, prepare microemulsion, mix surfactant and co-surfactant to obtain mixed surfactant; then mix mixed surfactant and essential oil to obtain mixed oil phase; then add dropwise to the mixed oil phase while stirring deionized water to obtain a microemulsion.

Further, the concentration of the sodium carbonate solution in step 1.1 is 0.01%-0.50%, the degumming temperature is 60°C-120°C, the degumming time is 20-120min, the concentration of the lithium bromide aqueous solution is 5-10M; the concentration of the acetic acid solution in step 1.2 The concentration of chitosan solution is 0.5%-1.0%, and the concentration of chitosan solution is 1.0%-3.0%. In step 1.3, the surfactant is Tween 80; the co-surfactant is absolute ethanol; the mass ratio of surfactant to co-surfactant is 1:1-4:1; the mass ratio of mixed surfactant to essential oil is 7 :3-9:1; deionized water accounts for 75%-95% of the microemulsion composition by weight;

Further, the distilled water washing step in step 1.1 is: rinse with pure water 3-7 times to remove impurities and some residual sericin; the drying step is: place it in a blast oven at 40°C-90°C to air-dry for about 12-24 hours ; The steps of heating and dissolving are: 40℃-90℃ water bath for 1-4h, and constant shaking is required during the dissolution process; the steps of dialysis are: dialyzing in distilled water for 48-72h with a dialysis bag (cut-off capacity: 3-20kDa), every 4- Change the water once every 8 hours; the centrifugation steps are: put the solution obtained after dialysis into a centrifuge tube, and centrifuge at 5000-10000 rpm for 10-30 minutes.

Further, step 1.2 also includes: diluting the silk fibroin solution, thoroughly mixing it with the chitosan solution, and heating and stirring to obtain a silk fibroin-chitosan mixed film liquid.

Further, the diluted concentration of the silk fibroin solution is 0.5%-3.0%, and the volume ratio of the silk fibroin solution and the chitosan solution is 5:1-1:5; the mixture is heated and stirred in a water bath of 50°C-70°C. Stir magnetically for 30-60 minutes.

Further, in step 2, the final concentration of the microemulsion in the mixed film liquid is 0.5%-5.0%.

Further, prepare a composite edible film for the determination of water vapor transmission rate and antibacterial activity; the steps are: slowly cast 10 mL of film liquid into a mold (90 mm × 15 mm), remove excess solution and bubbles, and place it on a level. Dry overnight to obtain a film with a thickness of 0.02-0.05mm. Peel the film from the mold and place it in a sealed box for testing.

Further, the drying temperature is 40°C-60°C.

The invention also provides an application of a composite edible film liquid containing silk fibroin in food preservation. The raw materials of the composite film liquid include silk fibroin, chitosan and microemulsion; the microemulsion includes mixed surfactants and essential oils. Mixed surfactants include surfactants and co-surfactants.

Further, the washed fruits, vegetables or meat products are soaked in the composite edible film liquid, and then taken out to dry.

Further, the soaking time is 0.5-20min.

In the preferred embodiment 1 of the present invention, the process of preparing chitosan film liquid is described in detail and applied to strawberry preservation;

In another preferred embodiment 2 of the present invention, the process of preparing silk fibroin film liquid is described in detail and applied to strawberry preservation;

In another preferred embodiment 3 of the present invention, the process of preparing silk fibroin-microemulsion mixed film liquid is described in detail and applied to strawberry preservation;

In another preferred embodiment 4 of the present invention, the preparation of silk fibroin-chitosan-microemulsion mixed film liquid and its application in strawberry preservation are described in detail;

In Comparative Example 1 of the present invention, the treatment process of the control group without film preservation is explained in detail;

In Examples 1-3 of the present invention, the freshness preservation experimental process of separately applying chitosan film liquid, silk fibroin film liquid and silk fibroin-3% microemulsion mixed film liquid respectively is explained in detail.

The beneficial technical effects of the present invention are as follows:

The silk fibroin-chitosan-microemulsion composite edible film liquid provided by the invention has good mechanical barrier properties, strong adhesion and strong antibacterial activity, and can effectively delay the oxidation and aging process of food and inhibit microorganisms in food. growth of. Applying it to food preservation can extend the storage period of food and maintain its original quality and commercial value to the maximum extent. It is also safe and environmentally friendly, has simple preparation and use methods, mild conditions, and is not highly dependent on equipment. Therefore, it has greater high economic, social and ecological value.

The concept, specific preparation process and technical effects of the present invention will be further described below in conjunction with the accompanying drawings to fully understand the purpose, features and effects of the present invention.

Description of the drawings

Figure 1 is a graph showing changes in light transmittance of the microemulsion of Example 4 of the present invention at different temperatures;

Figure 2 is a histogram of contact angles of the edible film liquids in Examples 1-4 of the present invention;

Figure 3 is a histogram of water vapor transmission rates of the edible films of Examples 1-4 of the present invention;

Figure 4 is a bar graph of the inhibitory rate of the edible film of Example 4 of the present invention on Escherichia coli and Staphylococcus aureus;

Figure 5 is a photo of the appearance of strawberries in Examples 1-4 and Comparative Example 1 of the present invention after being stored for 7 days under the same conditions (A-E are strawberries without coating in Comparative Example 1 and strawberries used alone in Examples 1-3, respectively). Strawberries preserved by chitosan film liquid, silk fibroin film liquid and silk fibroin-3% microemulsion mixed film liquid, strawberries preserved by silk fibroin-chitosan-3% microemulsion mixed film liquid in Example 4 ).

Detailed ways

The following describes multiple preferred embodiments of the present invention with reference to the accompanying drawings to make the technical content clearer and easier to understand. The present invention can be embodied in many different forms of embodiments, and the protection scope of the present invention is not limited to the embodiments mentioned herein.

Example 1 Preparation of chitosan film liquid and application to strawberry preservation

(1) Preparation of membrane liquid: Add 5g chitosan to 500mL 1% acetic acid solution and stir until the chitosan is completely dissolved to prepare a 1% chitosan membrane liquid. And the contact angle of the film liquid on the hydrophobic plate was measured.

(2) Slowly cast 10mL of 1% chitosan film solution into a mold (90mm×15mm), remove excess solution and air bubbles, place it on a level to dry overnight to obtain a film with a thickness of about 0.03mm, and remove the film from the mold Peel off and place in a sealed box to measure water vapor transmission rate and antibacterial activity.

(3) Soak the washed strawberries in 1% chitosan film solution for 10 minutes, take them out to dry and store them at 18±2°C. The weight loss rate, spoilage rate, and hardness of the treated strawberries were measured every 24 hours, and photos were taken to record the preservation effect.

Example 2 Preparing silk fibroin film liquid and applying it to strawberry preservation

(1) Preparation of membrane liquid: Degumm the mulberry silk with 0.2% sodium carbonate solution, then wash with distilled water to remove impurities and some residual sericin, and then dry at 50°C for 12 hours; the degummed silk fibroin is dissolved in 9.3M Dissolve the lithium bromide aqueous solution by heating at 60°C for 1 hour; use dialysis to remove the lithium bromide, centrifuge to take the supernatant, and dilute it to a silk fibroin concentration of 1% for later use. And the contact angle of the film liquid on the hydrophobic plate was measured.

(2) Slowly cast 10mL of 1% silk fibroin film solution into a mold (90mm×15mm), remove excess solution and air bubbles, place it on a level to dry overnight to obtain a film with a thickness of about 0.03mm, and remove the film from the mold Peel off and place in a sealed box to measure water vapor transmission rate and antibacterial activity.

(3) Soak the washed strawberries in 1% silk fibroin film solution for 10 minutes, and the post-processing is the same as in Example 1.

Example 3 Preparation of silk fibroin-microemulsion mixed film liquid and application to strawberry preservation

(1) Preparation of membrane liquid: The preparation of silk fibroin solution is consistent with that in Example 2. Mix Tween 80 and absolute ethanol at a mass ratio of 4:1 to form a mixed surfactant, then mix the mixed surfactant and cinnamon essential oil at a mass ratio of 9:1 to obtain a mixed oil phase, and then add the mixed oil phase while stirring. Deionized water is slowly added dropwise into the phase to obtain a cinnamon essential oil microemulsion. At the same time, characterization experiments of microemulsions were carried out. Finally, the 1% silk fibroin solution was mixed with a certain amount of microemulsion so that the final concentration of the microemulsion was 3%, and a 1% silk fibroin-3% microemulsion mixed film liquid was obtained for later use. And the contact angle of the film liquid on the hydrophobic plate was measured.

(2) Slowly cast 10mL of 1% silk fibroin-3% microemulsion mixed film solution into a mold (90mm×15mm), remove excess solution and air bubbles, and place it on a level to dry overnight to obtain a film with a thickness of about 0.03mm. , peel the film from the mold and place it in a sealed box to measure the water vapor transmission rate and antibacterial activity.

(3) Soak the washed strawberries in 1% silk fibroin-3% microemulsion mixed film liquid for 10 minutes, and the post-processing is the same as in Example 1.

Example 4 Preparation of silk fibroin-chitosan-microemulsion mixed film liquid and application to strawberry preservation

(1) Preparation of membrane liquid: This example provides a silk fibroin-chitosan-microemulsion membrane, which is basically the same as Example 3. The difference is that this example requires first mixing 1% silk fibroin solution and 1% silk fibroin solution. % chitosan solution was fully mixed according to the volume ratio of 1:1, and magnetically stirred in a 60°C water bath for 30 minutes to obtain a silk fibroin-chitosan mixed film liquid. Finally, the mixed film liquid was mixed with a certain amount of microemulsion. Mix until the final concentration of the microemulsion is 3% to obtain a 1% silk fibroin-1% chitosan-3% microemulsion mixed film liquid for later use. And the contact angle of the film liquid on the hydrophobic plate was measured.

(2) Slowly cast 10mL of 1% silk fibroin-1% chitosan-3% microemulsion mixed film solution into a mold (90mm×15mm), remove excess solution and air bubbles, and place it on a level to dry overnight. For a film with a thickness of about 0.03mm, peel the film from the mold and place it in a sealed box to test the water vapor transmission rate and antibacterial activity.

(3) Soak the washed strawberries in a mixed film solution of 1% silk fibroin-1% chitosan-3% microemulsion for 10 minutes, and the post-processing is the same as in Example 1.

Comparative Example 1 Strawberries were stored directly without coating.

This comparative example provides a control treatment group for the strawberry preservation experiment. The strawberries are only washed and dried without coating, and are directly stored at 18±2°C. Post-processing is the same as in Example 1.

Specific experimental methods:

1. Microemulsion characterization experiment

The cinnamon essential oil microemulsion obtained in Example 3 was subjected to a microemulsion characterization experiment.

The steps for characterization of microemulsions are as follows:

Centrifugal stability: At a rotation speed of 2000-8000 r/min, observe the appearance changes of the microemulsion and measure the light transmittance of the sample after centrifugation to examine the centrifugal stability of the microemulsion system.

Thermal stability: Heating at different temperatures (40°C-90°C) for 30 minutes, and measuring the light transmittance of the microemulsion to examine the stability of the microemulsion at different temperatures.

The formula for calculating light transmittance is:

T(%)＝A ₀ /A ₁ ×100%

Among them, T is the light transmittance; A ₀ is the absorbance of the microemulsion before centrifugation/heating; A ₁ is the absorbance of the microemulsion after centrifugation/heating.

The results of the centrifugal stability experiment are shown in Table 1. It can be seen that the microemulsion did not appear turbid and stratified after centrifugation at different rotation speeds, and the light transmittance was above 100%.

Table 1 Microemulsion stability at different centrifugation rates

Thermal stability experimental results are shown in Figure 1. When the temperature is lower than 80°C, the microemulsion still maintains a clear and translucent state, and the light transmittance remains stable above 100%. At this time, the microemulsion has good thermal stability. When the heating temperature reaches 80°C, the microemulsion becomes turbid and stratified, and the light transmittance drops rapidly to about 20%. However, when the heated turbid sample is placed at room temperature and allowed to cool naturally, the solution quickly returns to a clear and transparent state. This is because, for polyoxyethylene nonionic surfactants, when the temperature is high, the hydrogen bonds between water and polyoxyethylene chains are broken, the solubility of the surfactant in water is rapidly reduced and precipitated, and the system changes from clarification to Turbidity or delamination, a phenomenon known as turbidity. The above results indicate that the microemulsion has good thermal stability and centrifugal stability.

2. Film-liquid contact angle experiment

The 1% chitosan film liquid, 1% silk fibroin film liquid, 1% silk fibroin-3% microemulsion mixed film liquid and 1% silk fibroin-1% chitosan obtained in Examples 1-4 respectively -3% microemulsion mixed film solution for contact angle experiments.

The contact angle experimental steps are as follows:

The contact angle of the membrane fluid was measured using the seat drop method to evaluate the surface hydrophobicity of the membrane fluid. 5 μL of film solution was carefully dropped onto a hydrophobic plate whose surface material was polypropylene, and the plate was placed on the surface of the substrate. Then a high-pixel digital camera was used to capture digital images, and the contact angle of the images was analyzed using Image J software. Each membrane liquid was measured in 3 parallel groups.

The contact angle experimental results are shown in Figure 2. The contact angles of the 1% chitosan film liquid obtained in Example 1 and the 1% silk fibroin film liquid obtained in Example 2 are higher, and the contact angle with pure water (about 90° ) are close to each other, indicating that these film liquids are easy to drip like water on hydrophobic surfaces, so it is difficult to form a film on the fruit surface; while the 1% silk fibroin-3% microemulsion mixed film liquid obtained in Example 3 and The contact angle of the mixed film liquid of 1% silk fibroin-1% chitosan-3% microemulsion obtained in Example 4 is significantly reduced, that is, the film liquid exhibits strong hydrophobic characteristics. This may be because essential oils are mainly non-polar substances, which increase the hydrophobicity of the membrane liquid and also enhance the adhesion of the membrane liquid to the fruit surface.

3. Film water vapor transmission rate and antibacterial activity experiments

The 1% chitosan film, 1% silk fibroin film, 1% silk fibroin-3% microemulsion mixed film and 1% silk fibroin-1% chitosan-3% obtained in Examples 1-4 respectively The microemulsion mixed film was used to conduct water vapor transmission rate and antibacterial activity experiments. The steps are as follows:

Water Vapor Transmission: Measures the permeability of a film to water vapor according to ASTM E96-95a.

Antibacterial activity: Escherichia coli ATCC 25922 and Staphylococcus aureus ATCC 29213 were used as test strains. Weigh 0.20g of different membranes and put them into the corresponding 10mL liquid culture medium, and leave them at room temperature for 12 hours. Aseptically pipette 100 μL of 1×10 ⁵ CFU/mL test bacterial suspension into each group of liquid media, and incubate at 37°C for 24 h. After each sample was gradient diluted with sterile water, 100 μL of different gradient dilutions were applied to the corresponding solid culture medium, and incubated at 37°C for 12 h. Finally, after determining the number of viable bacteria according to GB/T 4789.2-2016, the inhibition rate against the test bacteria is calculated.

The experimental results of water vapor permeability are shown in Figure 3. It can be seen that the water vapor permeability of the 1% silk fibroin film obtained in Example 2 and the 1% silk fibroin-3% microemulsion mixed film obtained in Example 3 is There is not much difference in the pass rate, and it is slightly better than the 1% silk fibroin-1% chitosan-3% microemulsion mixed film obtained in Example 4; while the water vapor transmission rate of the films obtained in Examples 2, 3, and 4 All are significantly better than the 1% chitosan film obtained in Example 1. That is to say, the introduction of microemulsion has little effect on the mechanical barrier properties of silk fibroin films. The mechanical barrier properties of silk fibroin-chitosan-microemulsion composite films are slightly lower than those of silk fibroin films and silk fibroin-microemulsion films. , but still significantly better than chitosan film.

The experimental results of the antibacterial activity are shown in Figure 4. The number of original colonies in the system was approximately 3 log ₁₀ CFU/mL. The 1% silk fibroin solution obtained in Example 2 not only had no antibacterial activity, but also had a certain amount of proliferation of both bacteria. The membranes in Examples 1, 3, and 4 had varying degrees of inhibitory effects on the test bacteria. Among them, the number of residual colonies of Escherichia coli and Staphylococcus aureus in the pure chitosan film were 2.74±0.06 and 2.88±0.06log ₁₀ CFU/mL respectively, indicating that pure chitosan has a certain inhibitory effect on bacteria; while those containing microorganisms The number of residual colonies in the emulsion composite film ranged from 0.76±0.04log ₁₀ CFU/mL to 0.99±0.12log ₁₀ CFU/mL, indicating that the composite film not only had a bacteriostatic effect, but also had a good bactericidal effect. This may be related to the fact that the essential oil components in the microemulsion system have a large specific surface area, good dispersion, and are easy to contact with microbial cells. This result is consistent with the results of the spoilage rate of strawberries after coating and preservation in Table 2 in Examples 1, 3, and 4.

The above results show that the edible film liquid prepared by the present invention takes advantage of the complementarity of chitosan and silk fibroin and the antibacterial properties of microemulsion, has good adhesion on the food surface, and also has good adhesion after forming the film. Mechanical barrier properties and antibacterial activity.

4. Strawberry preservation experiment

The strawberries treated with 1% silk fibroin-1% chitosan-3% microemulsion mixed film liquid to preserve freshness in step (3) of Example 4 and the strawberries not subjected to film treatment in Comparative Example 1 and the implementation In Example 1-3, the appearance, weight loss rate, and appearance of the strawberries that were preserved by coating alone with chitosan film solution, silk fibroin film solution, and silk fibroin-3% microemulsion mixed film solution were stored under the same conditions for 7 days. Spoilage and hardness results.

The steps are:

Weight loss rate: The difference between the initial mass of the strawberry and the mass of the same group in each measurement is defined as the mass loss of the strawberry, and the weight loss rate is calculated as the percentage of the initial mass loss. The weight loss rate calculation formula is as follows:

Weight loss rate (%) = (m ₀ -m _n )/m _n ×100%

Among them, m ₀ is the initial mass of strawberry, and m _n is the mass of strawberry on the nth day. The experiment was repeated three times.

Rot rate: According to the size of the rotten area of strawberries, it is divided into 4 levels and the rot index is calculated. Level 0 means strawberries without rot; level 1 means the rotten area is less than 25%; level 2 means the rotten area reaches 25%-50%; level 3 means the rotten area is more than 50%. Three parallel groups were set up in each embodiment, with 10 strawberries in each group. The rot rate calculation formula is as follows:

Corruption rate (%) = (ΣY ₁ × a)/(Y ₂ × b) × 100%

Among them, Y ₁ is the rot level, Y ₂ is the highest rot level, a is the number of rotten fruits, and b is the total number of fruits.

Hardness: Randomly select 3 strawberries from each group, and use Edberg GY-4 Fruit Hardness Tester to test the hardness of the strawberries.

The specific measurement results are shown in Table 2.

Table 2 Preservation results of strawberries in different embodiments after 7 days of storage

Weight loss rate (%) Corruption rate (%) Hardness(N) Comparative example 1 7.01±0.44 53.33±3.33 0.69±0.07 Example 1 6.59±0.80 41.11±1.92 1.95±0.02 Example 2 2.51±0.46 54.44±5.09 1.69±0.07 Example 3 2.20±0.56 4.44±5.09 4.52±0.04 Example 4 2.11±0.48 2.22±1.92 4.49±0.05

The appearance of strawberries in different embodiments is shown in Figure 5. A-E are respectively the strawberries without coating treatment in Comparative Example 1, the chitosan film liquid, silk fibroin film liquid and silk fibroin alone in Examples 1-3. The appearance of the strawberries preserved by the protein-3% microemulsion mixed film liquid and the strawberries preserved by the 1% silk fibroin-1% chitosan-3% microemulsion mixed film liquid in Example 4 after being stored for 7 days under the same conditions. photo. Strawberries are perishable fruits. In Examples 1-2, chitosan film liquid and silk fibroin film liquid alone have no obvious preservation effect on strawberries, and the 7-day spoilage rate is not significantly different from the control group; Example 3 uses silk fibroin alone. The protein-3% microemulsion mixed film liquid and the strawberry treated with the 1% silk fibroin-1% chitosan-3% microemulsion mixed film liquid in Example 4 have good preservation effects, and the spoilage rate of strawberries after 7 days of preservation is lower than 5%. And because chitosan is rich in sources, cheap and easy to obtain, it can reduce the cost of the composite edible film to a certain extent, so the method of Example 4 also has higher economic value.

Based on the above experimental results, the silk fibroin-chitosan-microemulsion composite edible film liquid involved in the present invention has the characteristics of good mechanical barrier properties, strong adhesion and strong antibacterial activity, and can more effectively delay food oxidation, aging and The microbial spoilage process further extends the shelf life of the product.

The preferred embodiments of the present invention are described in detail above. It should be understood that those skilled in the art can make many modifications and changes according to the concept of the present invention without creative efforts. Therefore, any technical solutions that can be obtained by those skilled in the art through logical analysis, reasoning or limited experiments based on the concept of the present invention and on the basis of the prior art should be within the scope of protection determined by the claims.

Claims (10)

1. A method for preparing a silk fibroin-containing composite edible membrane liquid, which is characterized by comprising the following steps:

step 1, respectively preparing a silk fibroin solution, a chitosan solution and a microemulsion;

step 2, preparing a mixed membrane solution, namely fully mixing the silk fibroin solution obtained in the step 1 with the chitosan solution to obtain a silk fibroin-chitosan mixed membrane solution; and (2) mixing the silk fibroin-chitosan mixed membrane liquid with the microemulsion obtained in the step (1) to obtain the silk fibroin-chitosan-microemulsion mixed membrane liquid.

2. The method of claim 1, wherein step 1 further comprises:

step 1.1, preparing the silk fibroin solution, degumming mulberry silk by using a sodium carbonate solution, washing by using distilled water to remove impurities and partial residual sericin, and drying to obtain degummed silk fibroin; dissolving the degummed silk fibroin in a lithium bromide aqueous solution, and heating to dissolve; removing lithium bromide by dialysis, ultrafiltration or electrodialysis, centrifuging to obtain supernatant to obtain aqueous solution of silk fibroin, and storing in refrigerator;

step 1.2, preparing the chitosan solution, adding the chitosan into an acetic acid solution, and stirring until the chitosan is completely dissolved to obtain the chitosan solution;

step 1.3, preparing the microemulsion, and mixing a surfactant and a cosurfactant to obtain a mixed surfactant; mixing the mixed surfactant with essential oil to obtain a mixed oil phase; and then dropwise adding deionized water into the mixed oil phase while stirring to obtain the microemulsion.

3. The method according to claim 2, wherein the concentration of the sodium carbonate solution in the step 1.1 is 0.01% -0.50%, the degumming temperature is 60 ℃ -120 ℃, the degumming time is 20-120min, and the concentration of the lithium bromide aqueous solution is 5-10M; the surfactant in the step 1.2 is Tween 80; the cosurfactant is absolute ethyl alcohol; the mass ratio of the surfactant to the cosurfactant is 1:1-4:1; the mass ratio of the mixed surfactant to the essential oil is 7:3-9:1; the deionized water accounts for 75-95% of the microemulsion composition by weight percent; the concentration of the acetic acid solution in the step 1.3 is 0.5% -1.0%, and the concentration of the chitosan solution is 1.0% -3.0%.

4. The method of claim 1, wherein step 2 further comprises: diluting the silk fibroin solution, fully mixing the silk fibroin solution with the chitosan solution, and heating and stirring the mixture to obtain the silk fibroin-chitosan mixed membrane solution.

5. The method according to claim 4, wherein the concentration of the diluted silk fibroin solution is 0.5% -3.0%, and the volume ratio of the silk fibroin solution to the chitosan solution is 5:1-1:5; the heating and stirring are carried out for 30-60min under the water bath of 50-70 ℃.

6. A silk fibroin-containing composite edible film prepared by the method of any one of claims 1-5.

7. The composite edible film of claim 6, wherein the thickness of the composite edible film is from 0.02 mm to 0.05mm.

8. Use of a composite edible film according to claim 6 or 7 for preserving food.

9. The method of claim 8, wherein the cleaned fruit and vegetable is immersed in the composite edible film liquid, taken out and dried.

10. The method of claim 9, wherein the soaking time is 0.5-20 minutes.