A high-load-bearing bio-based double-layer active packaging film and preparation method thereof

Abstract

The present invention discloses a high-load bio-based double-layer active packaging film and a preparation method thereof, wherein the outer film is a cellulose film prepared from hydroxypropyl methylcellulose, and the inner film is an inner film prepared from glutenin, rutin and a silane coupling agent. The present invention adopts a double-layer film-forming process, giving full play to the synergistic advantages of hydroxypropyl methylcellulose and glutenin, thereby forming a bio-based film with good load-bearing capacity and gas selective permeability, and further loading rutin to improve the biocompatibility of glutenin and the antioxidant capacity of the film, thereby giving the above-mentioned bio-based film an active fresh-keeping effect, and finally successfully obtaining a high-load bio-based double-layer active packaging film. It has been proved by experiments that the bio-based double-layer packaging material provided by the present invention can well maintain the sensory quality of cherry tomatoes, maintain a high hardness and low weight loss rate, and significantly reduce the corruption rate of cherry tomatoes through spontaneous gas conditioning, which is conducive to extending its storage period.

Description

Technical Field

[0001] The invention belongs to the technical field of packaging materials and relates to a high-load-bearing bio-based double-layer active packaging film and a preparation method thereof. Background Art

[0002] Functional packaging is an important measure to effectively maintain the quality of fruits and vegetables after harvest, especially packaging materials developed with biodegradable materials have more advantages. On the one hand, it has good compatibility, air permeability and mechanical properties. On the other hand, its completely degradable characteristics will not only not pollute the environment, but can improve the soil. At the same time, in order to extend the shelf life of fruits and vegetables, antibacterial substances or other active substances are added to the packaging film or adsorbed on the surface of the film to ensure that the antibacterial properties are maintained in specific food matrices and modified atmosphere packaging systems.

[0003] At present, bio-based active packaging developed by multi-material blending technology has been promoted to a certain extent, which is of great significance to improving the environment and alleviating resource pressure, but the blending process has relatively stringent requirements on the biocompatibility characteristics of the substrate and production technology. At present, bio-based films are mainly prepared into macromolecular biological packaging materials with a certain network structure by methods such as cast film and molding, using natural materials such as chitosan, whey protein, zein, and biolipids as substrates, and further loaded with active ingredients to improve the packaging preservation properties. However, the blending of different substrates is prone to molecular rejection, resulting in uneven matrix blending and reducing the film-forming effect of a single substrate, while it is difficult to give full play to the advantages of a single substrate. At this time, the double-layer film-forming process can make full use of the characteristics of different substrates to improve the application value of packaging.

[0004] Hydroxypropyl methylcellulose, as a water-soluble cellulose derivative, has good mechanical properties and is the preferred material for improving packaging carrying capacity, but it is very easy to absorb moisture and swell, so it is necessary to improve the hydroxypropyl methylcellulose film. Gluten molecules are connected to each other through disulfide bonds, and have good film-forming, viscoelastic and hygroscopic properties, but poor mechanical properties. Summary of the invention

[0005] Based on this, the present invention provides a high-load bio-based double-layer active packaging film and a preparation method thereof. The present invention adopts a double-layer film-forming process, giving full play to the synergistic advantages of hydroxypropyl methylcellulose and glutenin, thereby forming a bio-based film with good load-bearing capacity and gas selective permeability, and further loading rutin to improve the biocompatibility of glutenin and the antioxidant capacity of the film, thereby giving the above-mentioned bio-based film an active fresh-keeping effect, and finally successfully obtaining a high-load bio-based double-layer active packaging film. Experiments have proved that the bio-based double-layer packaging material provided by the present invention can well maintain the sensory quality of cherry tomatoes, maintain a high hardness and low weight loss rate, and significantly reduce the corruption rate of cherry tomatoes through spontaneous gas conditioning, which is conducive to extending its storage period.

[0006] The technical solution of the present invention is: a high-load-bearing bio-based double-layer active packaging film, characterized in that the outer film is a cellulose film prepared from hydroxypropyl methylcellulose, and the inner film is an inner film prepared from glutenin, rutin and a silane coupling agent; wherein the mass ratio of hydroxypropyl methylcellulose, glutenin and rutin is 45:50-70:0.5-2.

[0007] The method for preparing the above-mentioned high-load-bearing bio-based double-layer active packaging film specifically comprises the following steps:

[0008] 1) Preparation method of outer membrane (cellulose membrane) solution: Hydroxypropyl methylcellulose and glycerol are dissolved in an ethanol aqueous solution, stirred in a water bath at 80-90° C., and then allowed to stand to obtain an outer membrane solution;

[0009] 2) Preparation of inner membrane solution: Take glutenin and glycerol and dissolve them in Na 2 CO 3 The solution is stirred in a water bath at 80-90°C, a silane coupling agent is added at the initial stage of stirring, and the mixture is allowed to cool to room temperature; then rutin is dissolved in ethanol, added to the above glutenin membrane solution, and the mixture is continuously stirred in a water bath at 40-50°C, and then allowed to stand to room temperature to obtain an inner membrane solution loaded with rutin;

[0010] 3) When preparing a double-layer membrane, first pour the inner membrane solution prepared in step 2) into a container and dry it; then pour the outer membrane solution prepared in step 1) on top and dry it.

[0011] Furthermore, the above-mentioned glutenin is specifically derived from wheat.

[0012] Furthermore, the volume concentration of the ethanol solution in step 1) is 10-15%; the mass ratio of hydroxypropyl methylcellulose to glycerol is 45:10-20; and the concentration of hydroxypropyl methylcellulose in the outer membrane solution is 2.5-3.5%.

[0013] Further, in step 2) Na 2 CO 3 The concentration of the solution is 0.2-1.0g / L, and glutenin is 2 CO 3 The mass concentration in the solution is 2-4%. The silane coupling agent is preferably (3-chloropropyl)triethoxysilane. The mass ratio of glutenin to (3-chloropropyl)triethoxysilane is 1:0.05-0.2; the mass ratio of glutenin to glycerol is 2-4:1.

[0014] Furthermore, the drying in step 3) is: drying in a constant temperature and humidity chamber at a temperature of 45° C. and a relative humidity of 40%.

[0015] The principle of the present invention is: the present invention uses a double-layer process to make full use of the characteristics of different substrates, so that the outer layer of hydroxypropyl methylcellulose film can play a good packaging bearing property, and the inner layer can reduce the humidity inside the package through the moisture absorption advantage of glutenin itself, so as to prevent the excessive moisture content in the package from exacerbating the corruption of fruits and vegetables. In addition, glutenin has a certain barrier effect on CO 2 Function, CO released by fresh fruits and vegetables during post-harvest respiration 2 Can be trapped in the packaging environment, forming high CO 2 Low O 2 At the same time, with the selective permeability of the bio-based membrane itself, an appropriate amount of oxygen is supplied from the outside to reduce the CO in the packaging environment. 2 Too high a concentration causes anaerobic respiration of fruits and vegetables, which in turn leads to the occurrence of peculiar smell. Rutin, as a natural, non-toxic antioxidant small molecule, has the beneficial effect of removing active oxygen and delaying the oxidative aging of fruits and vegetables. By loading rutin on the inner layer of glutenin, the packaging can be given an active effect, thereby improving the preservation effect. At the same time, rutin can improve the biocompatibility of glutenin, thereby increasing the degree of fusion between the double-layer matrix, promoting interlayer fusion and reducing interlayer peeling. The present invention adopts a double-layer film-forming process, giving full play to the synergistic advantages of hydroxypropyl methylcellulose and glutenin, thereby forming a bio-based film with good carrying capacity and gas selective permeability, and further loading rutin to improve the antioxidant capacity of the film, thereby giving the above-mentioned bio-based film an active preservation effect, and finally obtaining a high-load bio-based double-layer active packaging film.

[0016] The present invention has the following beneficial effects:

[0017] 1. The bio-based packaging material of the present invention is a double-layer composite structure, which exerts synergistic effects through the single-substrate film-forming advantages of hydroxypropyl methylcellulose and glutenin, effectively avoiding the molecular rejection problem caused by multi-material blending. With the help of the high load-bearing performance of hydroxypropyl methylcellulose and the hygroscopic properties of glutenin, the packaging environment is effectively regulated, the mechanical properties and flexibility of the bio-based packaging material are greatly improved, and the air humidity in the packaging environment is effectively regulated.

[0018] 2. The bio-based double-layer packaging material of the present invention improves the biocompatibility of glutenin by loading rutin components in the inner layer, which not only solves the problem of pasting and connection between film layers, but also enhances the antioxidant properties of the packaging and exerts the synergistic advantages of rutin.

[0019] 3. The bio-based double-layer packaging material in the present invention not only has the characteristics of spontaneous gas conditioning and moisture barrier, but also introduces natural antioxidant material (rutin) into the inner layer matrix. The combined effect of the two gives the packaging material excellent preservation effect. As a food packaging material, it can promote high CO2 by combining the respiration of harvested fruits and vegetables. 2 Low O2 The creation of a spontaneous controlled atmosphere environment prolongs the shelf life of fruits and vegetables and reduces oxidative decay.

[0020] 4. The bio-based double-layer packaging material of the present invention introduces a silane coupling agent into the inner film, promotes the formation of the glutenin network structure through molecular bridging between the coupling agent and glutenin, enhances the cross-linking ability, and improves the film-forming properties.

[0021] 5. The bio-based double-layer packaging material provided by the present invention is mainly made of hydroxypropyl methylcellulose, glutenin and rutin, all of which have good biodegradable properties and can be decomposed and absorbed by environmental microorganisms after being discarded. It is an environmentally friendly material and can be used as a food packaging material.

[0022] 6. Experiments have shown that the bio-based double-layer packaging material provided by the present invention can well maintain the sensory quality of cherry tomatoes, maintain a high hardness and low weight loss rate, and significantly reduce the corruption rate of cherry tomatoes through spontaneous gas conditioning, which is conducive to extending its storage period. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The apparent morphologies of three types of cling film;

[0024] Figure 2 The SEM observation results of three packaging films;

[0025] Figure 3 Thermogravimetric analysis diagrams of three types of cling film;

[0026] Figure 4 The infrared spectra of three films are shown in Figure 2.

[0027] Figure 5 The results of total antioxidant capacity of the three membranes;

[0028] Figure 6 The effects of different plastic wraps on the surface characteristics of cherry tomatoes;

[0029] Figure 7 Effects of different plastic wraps on the hardness (A), spoilage rate (B), weight loss rate (C) and sensory evaluation (D) of cherry tomatoes. DETAILED DESCRIPTION

[0030] The present invention discloses a high-load bio-based double-layer active packaging film and a method for preparing the same. Those skilled in the art can refer to the content of the present invention and appropriately improve the process parameters to achieve the same. It should be particularly pointed out that all similar substitutions and modifications are obvious to those skilled in the art, and they are all considered to be included in the present invention. The methods and applications of the present invention have been described through preferred embodiments, and relevant personnel can obviously modify or appropriately change and combine the methods and applications described in the present invention without departing from the content, spirit and scope of the present invention to implement and apply the technology of the present invention.

[0031] The present invention will be further described below in conjunction with embodiments:

[0032] The materials and instruments used in the present invention are as follows:

[0033] 1.1 Materials

[0034] Rutin, hydroxypropyl methylcellulose, (3-chloropropyl) triethoxysilane: Shanghai Yien Chemical Technology Co., Ltd.; ethanol, glycerol: Yantai Yuandong Fine Chemical Co., Ltd.; glutenin: Tokyo Chemical Industry Co., Ltd.; sodium carbonate: Tianjin Hengxing Chemical Reagent Manufacturing Co., Ltd.

[0035] 1.2 Instruments

[0036] BSA223S electronic balance: Sartorius Instrument (Guangzhou) Co., Ltd.; SHJ-6 six-hole magnetic stirring water bath: Jincheng Jingze Experimental Instrument Factory; UV-1900i ultraviolet spectrophotometer: Shimadzu Corporation of Japan; DTG-60H thermogravimetric analyzer: Shimadzu Corporation of Japan; Thermo Nicolet 5700 Fourier transform infrared spectrometer: Thermo Fisher Scientific, USA; TA.XT Plus / 50 texture analyzer: Stable Micro Systems, UK; Quanta 250 scanning electron microscope: FEI Company, USA; DHG-9053A electric constant temperature blast drying oven: Shanghai Qixin Scientific Instrument Co., Ltd.

[0037] 1.3 Data processing

[0038] All experimental results are the average of three times and are expressed as mean ± standard deviation. The significant differences between the mean values ​​of the variance coefficients were tested with Tukey HSD post hoc test, and one-way analysis of variance was performed using SPSS. The data between different samples are significantly different (p < 0.05) with lowercase letters.

[0039] Example 1: Preparation method of double-layer membrane with rutin

[0040] Preparation method of outer membrane (cellulose membrane) solution: Weigh 4.5g hydroxypropyl methylcellulose and 1.6g glycerol and dissolve them in 150mL ethanol solution (20mL ethanol, 130mL water). Stir continuously in a 85℃ water bath for 20min and let stand at 25℃.

[0041] Preparation method of inner membrane solution: weigh 6g glutenin and 2g glycerol and dissolve them in 0.5g / L Na 2 CO 3 Solution, dilute to 200mL. Stir continuously in 85℃ water bath for 30min, add 0.5mL (3-chloropropyl) triethoxysilane at the beginning of stirring, and let it cool to room temperature. Weigh 0.1g rutin and dissolve it in a small amount (5-10mL) of ethanol, add it to the above glutenin membrane solution, and stir continuously in 45℃ water bath for 15min. Let it stand to room temperature to obtain the inner membrane solution loaded with rutin.

[0042] When preparing a double-layer membrane, first pour 120 mL of the inner membrane solution into a 24×24 cm acrylic culture dish and place it in a constant temperature and humidity chamber (temperature 45°C, relative humidity 40%) to dry for 12 hours. Pour 100 mL of the outer membrane solution on top and place it in a constant temperature and humidity chamber at 45°C and relative humidity 40% until it is dried, then remove the membrane for later use.

[0043] Comparative Example 1: Cellulose film

[0044] Weigh 4.5g of hydroxypropyl methylcellulose and 1.6g of glycerol and dissolve them in 150mL of ethanol solution (20mL of ethanol and 130mL of water). Stir continuously in a 85℃ water bath for 20min and let stand at 25℃. Pour 100mL of cellulose membrane solution into a 24×24cm acrylic culture dish and place it in a constant temperature and humidity chamber (temperature 45℃, relative humidity 40%) for 12h to dry.

[0045] Comparative Example 2: (without rutin)

[0046] The preparation of the outer membrane solution is consistent with Example 1.

[0047] Preparation method of inner membrane solution: weigh 6g glutenin and 2g glycerol and dissolve them in 200mL 0.5g / L Na 2 CO 3 The solution was stirred continuously for 30 min in a water bath at 85°C. 0.5 mL of (3-chloropropyl)triethoxysilane was added at the initial stage of stirring and allowed to cool to room temperature.

[0048] When preparing a double-layer membrane, first pour 120 mL of the inner membrane solution into a 24×24 cm acrylic culture dish and place it in a constant temperature and humidity chamber (temperature 45°C, relative humidity 40%) for 12 hours. Pour 100 mL of the outer membrane solution into the top and place it in a constant temperature and humidity chamber at 45°C and relative humidity 40% until it is dried, then remove the membrane for later use.

[0049] 1. Film appearance observation, microscopic morphology scanning electron microscope observation, mechanical properties, water vapor permeability, carbon dioxide permeability determination

[0050] 1. Film appearance

[0051] like Figure 1 As shown. Through visual observation of the film image, it is found that the cellulose film will spontaneously form a curling memory at room temperature. This is because the cellulose film will shrink and curl during the water loss process. However, the use of double-layer packaging can effectively improve this phenomenon, making the packaging less likely to curl spontaneously and easier to change its packaging shape artificially. This characteristic can give double-layer packaging the universality of being widely applicable to various packaging scenarios.

[0052] 2. Determination of film thickness and its microscopic morphology

[0053] The thickness of the film was measured using a spiral micrometer. Five points were randomly selected on the film to be tested and their thickness was measured. The average value was calculated as the film thickness. The result was accurate to 0.001 mm. Figure 2 As shown in the figure, the accumulation of solid base material addition leads to an increase in film thickness. The thicknesses of the cellulose film, the double-layer film without rutin, and the double-layer film with rutin are 0.0938 mm, 0.1318 mm, and 0.1384 mm, respectively. The film is cut into 4 mm 2The square piece of cellulose film was placed on an aluminum head platform with conductive gel, and after vacuum gold spraying, it was placed under an electron scanning microscope to take the plane and cross-sectional images of the film. The results showed that the inner and outer surfaces of the cellulose film showed a flat and smooth microscopic morphology. Further, through the cross-sectional image of the cellulose film, it can be found that pure cellulose can form a dense structure without generating excess cavities. After being mixed with the inner layer of glutenin packaging, its inner surface structure can be significantly changed and the roughness can be increased, thus having anti-slip properties. At the same time, the hygroscopic capacity of glutenin can further regulate the humidity of the environment in the package and reduce the direct contact between the outer cellulose film and water vapor, which is conducive to maintaining the load-bearing properties of the package. However, by observing the cross-sectional scanning electron microscope image, it can be seen that there is a fitting gap between the inner and outer layers. This is due to the molecular repulsion caused by the difference in biocompatibility between different substrates, which affects the effective adhesion between the two layers. However, after adding rutin to the inner layer matrix of glutenin, the microscopic morphology of the inner layer of the package was further changed and the roughness was increased, which further enhanced the connection degree of the adhesion interface between the two layers of film and effectively prevented the problem of interlayer peeling. At the same time, rutin can effectively improve the antioxidant properties of the packaging, thereby further improving the active efficacy of the packaging while improving the biocompatibility between the membrane matrix, allowing rutin to play a synergistic advantage in the preparation of active double-layer packaging.

[0054] 3. Mechanical properties test

[0055] The tensile strength of the packaging film was tested according to the method of GB / T 1040.3-2006. The results showed that the cellulose film had excellent mechanical properties, with a tensile strength of 30.035 MPa, showing excellent packaging properties. When rutin was not added to the inner layer of glutenin, the mechanical properties of the film were reduced. Further research found that after rutin was introduced into the inner layer matrix of glutenin, the tensile strength of the double-layer film was improved to a certain extent compared with the double-layer film without rutin. This shows that rutin can affect the spatial structure of glutenin and ultimately improve the mechanical properties of the packaging material, which is an additional advantage after the active efficacy of rutin (Table 1).

[0056] Table 1 Test results of barrier and mechanical properties of three films

[0057]

[0058] 4. Determination of water vapor permeability and carbon dioxide permeability

[0059] The water vapor permeability coefficient (WVP) of the composite film was tested according to the method of GB / T 30412-2013. The CO 2The results showed that the addition of rutin to the double-layer membrane significantly (p<0.05) increased the permeability of water vapor and CO 2 The barrier capacity is good, and it has advantages in maintaining the moisture content inside the package and the atmosphere, which is conducive to the formation of high CO 2 Low O 2 The internal atmosphere is controlled, ultimately extending the shelf life of fruits and vegetables (Table 1).

[0060] 2. Thermogravimetric analysis, infrared spectroscopy and antioxidant capacity determination of double-layer active packaging films containing rutin

[0061] 1. Thermogravimetric analysis

[0062] The film (10-15 mg) was subjected to thermogravimetric analysis using a DTG-60H thermogravimetric analyzer. The film sample was placed in a platinum pan and heated at 10 °C min -1 The film was heated from 40℃ to 660℃ at a rate of 1.5 ℃. The weight loss of the film at different temperatures was expressed by a function. The results showed that three obvious characteristic peaks were observed in the thermogravimetric curves during the heating process of all films ( Figure 3 ). The first characteristic peak appears between 70°C and 100°C, mainly reflecting the evaporation loss of water molecules in the polymer structure. Therefore, within this temperature range, the packaging material loses weight. The second characteristic peak is located in the range of 200-280°C, and the weight loss is mainly caused by the decomposition of the film matrix and the volatilization of the plasticizer. In particular, the cellulose monolayer film exhibits poor thermal stability at this stage and suffers the most severe heating loss. However, after the introduction of the glutenin inner layer into the cellulose monolayer film, its thermal stability can be significantly improved, indicating that the double-layer packaging has better application potential in high-temperature storage environments. The third characteristic peak is located in the range of 300-400°C, and the weight loss at this stage is mainly caused by the gradual decomposition of organic molecules in the blended film into inorganic residues to form ash. It is worth noting that the addition of rutin has little effect on the thermal stability of the packaging material, which shows that rutin does not change the film-forming properties of the double-layer packaging material itself.

[0063] 2. Infrared spectroscopy analysis

[0064] The interactions between the components of the films were analyzed using Fourier transform infrared spectroscopy (FTIR). The FTIR spectrum of each sample was recorded in the infrared spectrum at 400-4,000 cm -1 32 scans were performed over a wavelength range with a resolution of 4 cm -1 The results show that the infrared spectra of the composite films show a series of characteristic spectra ( Figure 4 ). The wavelength is 3359cm -1 The absorption peaks around 1652cm are related to the number and position of hydroxyl groups, and are caused by the stretching vibration of hydroxyl groups, which merge with the N-H stretching vibration in the same region. -1The absorption peak near is due to the presence of amide bonds and N—H stretching vibration. With the incorporation of the inner layer of glutenin, the absorption peak at this wavelength becomes sharper, which is caused by the amide groups in glutenin itself. When rutin is further added, the stretching vibration peak here is further enhanced, indicating that the loading of rutin will change the molecular interactions between the membrane matrix. The hydroxyamide band is more sensitive to changes in the secondary structure of proteins. With the incorporation of glutenin, non-covalent interactions occur between molecules, and the related 1652cm -1 The peak intensity at the position is enhanced, and the vibration of the protein amide band is enhanced. The wavelength is 800-1200cm -1 The peaks between 1015cm represent the highly coupled C—C—O, C—OH and C—O—C stretching modes of the polymer backbone. -1 The decrease in the intensity of the absorption peak is likely due to the interaction (hydrogen bonding, hydrophobic interaction) between rutin and the membrane substrate.

[0065] 3. Determination of antioxidant capacity

[0066] The antioxidant capacity of the membrane was determined by the ABTS method. Figure 5 As shown, the packaging film has certain antioxidant properties and can play a good storage effect in the preservation process. The cellulose film has almost no antioxidant capacity, and the double-layer film shows a certain antioxidant capacity. On the one hand, the structural characteristics of glutenin itself have a certain antioxidant capacity; on the other hand, by loading rutin, the ABTS clearance rate of the double-layer membrane is significantly improved (p<0.05), which shows that the effective release of rutin has an antioxidant effect, and its effective clearance rate is above 90%. At the same time, the chemical properties of rutin in the active film remain stable, and the double-layer film with rutin can effectively maintain its antioxidant activity. In summary, after adding rutin, the antioxidant capacity of the film is effectively improved.

[0067] 3. Determination of the relevant indicators of fresh-keeping quality of cherry tomatoes by bio-based rutin-loaded double-layer active film

[0068] The present invention investigates the effects of common commercial cling film (polyethylene material), double-layer film without rutin and double-layer film with rutin on the apparent properties of cherry tomatoes. Cherry tomato preservation experiments were carried out using commercial cling film, double-layer film without rutin and double-layer film with rutin. Cherry tomatoes were loaded into 1.5L acrylic circular containers, 0.5kg of cherry tomatoes were placed in each container, and the circular containers were sealed at the top with different films. Four groups of parallel treatments were set for each packaging film, and random sampling was performed every 3d, for a total of 12d.

[0069] 1. Sample appearance characteristics

[0070] The three treatments were observed on days 0, 3, 6, 9, and 12. Figure 6 As shown in the figure, the double-layer film without rutin and the commercial cling film began to rot on the third day of storage, and the commercial cling film was almost completely rotten on the sixth day. The double-layer film with rutin did not show the phenomenon of epidermal cracking until the ninth day, and did not rot until the twelfth day. The above results show that the rutin double-layer active film can effectively inhibit the infection of cherry tomato pathogens and extend the shelf life.

[0071] 2. Determination of hardness

[0072] The hardness of cherry tomatoes was measured using a texture analyzer. A probe with a diameter of 4 mm was used and the hardness was measured at a rate of 1 mm s -1 The cherry tomatoes were punctured at a rate of 10 mm and the puncture depth was 10 mm. The results showed that with the extension of storage time, the hardness of cherry tomatoes in each treatment group showed a gradual downward trend. At the end of the 12th day of storage, the hardness of cherry tomatoes with the addition of rutin double-layer film decreased by 47.9%, which was lower than the 81.8% of commercial cling film. Therefore, compared with commercial cling film, the addition of rutin double-layer film can significantly inhibit the decline of cherry tomato hardness ( Figure 7 A).

[0073] 3. Determination of corruption rate

[0074] The counting method was used to measure the spoilage rate, and the calculation formula was as follows: spoilage rate (%) = number of spoilage / total number × 100%. The results showed that compared with commercial cling film, the double-layer film can effectively inhibit the increase in the spoilage rate of cherry tomatoes in the early stage of storage, with the most significant difference at 6 days; thereafter, the spoilage rate of cherry tomatoes packaged in double-layer film also increased rapidly, but the spoilage rate of double-layer film with rutin added was always lower than that of double-layer film without rutin added, and the spoilage rates were 50% and 78.04% at 12 days, respectively. Therefore, the double-layer film with rutin added can effectively delay the spoilage of cherry tomatoes ( Figure 7 B).

[0075] 4. Determination of weight loss rate

[0076] The weight loss rate was calculated by weighing the mass of cherry tomatoes before and after storage, and the percentage of the change in mass before storage. The results showed that the weight loss rate of each treatment group showed an upward trend during storage, and the rate of increase in the weight loss rate of cherry tomatoes packaged in commercial plastic wrap was significantly higher than that in double-layer film packaging. After 12 days of storage, the weight loss rate of fruits packaged in commercial plastic wrap increased by 3.9% and 4.2% respectively compared with the two double-layer film packaging. This is because the double-layer film has a good gas barrier effect, which delays the respiration of cherry tomatoes to a certain extent, and effectively reduces the transpiration rate of the fruit water, reducing its water loss rate ( Figure 7 C).

[0077] 5. Determination of overall sensory evaluation index

[0078] A panel of 10 trained judges evaluated the color, firmness, odor, aroma, and overall acceptability according to the method shown in Table 2. The results showed that the sensory quality of cherry tomatoes packaged in different plastic wraps decreased with the extension of storage time ( Figure 7 D). Among them, the preservation effect of commercial cling film was the worst, and the sensory score dropped from 98.2 points to 9.8 points. The second was the double-layer film without rutin. The double-layer film with rutin showed good preservation performance, and the sensory score after storage for 12 days was 49.8 points. The reasons for the good preservation effect are mainly the following two points. First, the double-layer film itself has the advantage of maintaining the atmosphere inside the package and delaying water loss. In addition, the addition of exogenous rutin improves the antioxidant capacity of the film environment and reduces the decay caused by microbial infection.

[0079] Table 2 Overall sensory evaluation standards

[0080]

[0081]

[0082] Example 2: Preparation method of double-layer membrane with rutin

[0083] Preparation method of outer membrane (cellulose membrane) solution: Weigh 4.5g hydroxypropyl methylcellulose and 1.5g glycerol and dissolve them in 150mL ethanol solution (20mL ethanol, 130mL water). Stir continuously in a 85℃ water bath for 20min and let stand at 25℃.

[0084] Preparation method of inner membrane solution: weigh 5.8g glutenin and 1.8g glycerol and dissolve them in 0.5g / L Na 2 CO 3 Solution, dilute to 200mL. Stir continuously in 85℃ water bath for 30min, add 0.45mL (3-chloropropyl) triethoxysilane at the beginning of stirring, and let it cool to room temperature. Weigh 0.1g rutin and dissolve it in a small amount (5-10mL) of ethanol, add it to the above glutenin membrane solution, and stir continuously in 45℃ water bath for 15min. Let it stand to room temperature to obtain the inner membrane solution loaded with rutin.

[0085] When preparing a double-layer membrane, first pour 120 mL of the inner membrane solution into a 24×24 cm acrylic culture dish and place it in a constant temperature and humidity chamber at 45°C and 40% relative humidity to dry for 12 hours. Pour 100 mL of the outer membrane solution on top and place it in a constant temperature and humidity chamber at 45°C and 40% relative humidity until it is dried, then remove the membrane for later use.

[0086] Example 3: Preparation method of double-layer membrane with rutin

[0087] Preparation method of outer membrane (cellulose membrane) solution: Weigh 4.5g hydroxypropyl methylcellulose and 1.7g glycerol and dissolve them in 150mL ethanol solution (20mL ethanol, 130mL water). Stir continuously in a 85℃ water bath for 20min and let stand at 25℃.

[0088] Preparation method of inner membrane solution: weigh 6.2g glutenin and 2g glycerol and dissolve them in 0.5g / L Na 2 CO 3 Solution, dilute to 200mL. Stir continuously in 85℃ water bath for 30min, add 0.55mL (3-chloropropyl) triethoxysilane at the beginning of stirring, and let it cool to room temperature. Weigh 0.15g rutin and dissolve it in a small amount (5-10mL) of ethanol, add it to the above glutenin membrane solution, and stir continuously in 45℃ water bath for 15min. Let it stand to room temperature to obtain the inner membrane solution loaded with rutin.

[0089] When preparing a double-layer membrane, first pour 120 mL of the inner membrane solution into a 24×24 cm acrylic culture dish and place it in a constant temperature and humidity chamber at 45°C and 40% relative humidity to dry for 12 hours. Pour 100 mL of the outer membrane solution on top and place it in a constant temperature and humidity chamber at 45°C and 40% relative humidity until it is dried, then remove the membrane for later use.

Claims

1. A high-load-bearing bio-based double-layer active packaging film, characterized in that: The outer membrane is a cellulose membrane prepared from hydroxypropyl methylcellulose, and the inner membrane is an inner membrane prepared from glutenin, rutin and silane coupling agent; wherein the mass ratio of hydroxypropyl methylcellulose, glutenin and rutin is 45:50-70:0.5-2.

2. The method for preparing the high-load-bearing bio-based double-layer active packaging film according to claim 1, characterized in that: The specific steps include: 1) Preparation method of outer membrane solution: dissolve hydroxypropyl methylcellulose and glycerol in ethanol aqueous solution, stir in a water bath at 80-90° C., and then stand to obtain an outer membrane solution; 2) Preparation method of inner membrane solution: glutenin and glycerol are dissolved in Na2CO3 solution, stirred in a water bath at 80-90°C, silane coupling agent is added at the initial stage of stirring, and the mixture is allowed to cool to room temperature; then rutin is dissolved in ethanol, added to the glutenin membrane solution, stirred continuously in a water bath at 40-50°C, and then allowed to stand to room temperature to obtain an inner membrane solution loaded with rutin; 3) When preparing a double-layer membrane, first pour the inner membrane solution prepared in step 2) into a container and dry it; then pour the outer membrane solution prepared in step 1) on top and dry it.

3. The preparation method according to claim 2, characterized in that: The volume concentration of the ethanol aqueous solution in step 1) is 10-15%.

4. The preparation method according to claim 2, characterized in that: In the step 1), the mass ratio of hydroxypropyl methylcellulose to glycerol is 45:10-20.

5. The preparation method according to claim 2, characterized in that: In the step 1), the concentration of hydroxypropyl methylcellulose in the outer membrane solution is 2.5-3.5%.

6. The preparation method according to claim 2, characterized in that: The concentration of the Na2CO3 solution in step 2) is 0.2-1.0 g / L.

7. The preparation method according to claim 2, characterized in that: In the step 2), the mass concentration of glutenin in the Na2CO3 solution is 2-4%.

8. The preparation method according to claim 2, characterized in that: The silane coupling agent in step 2) is (3-chloropropyl)triethoxysilane, and the mass ratio of glutenin to (3-chloropropyl)triethoxysilane is 1:0.05-0.

2.

9. The preparation method according to claim 2, characterized in that: In the step 2), the mass ratio of glutenin to glycerol is 2-4:

1.

10. The preparation method according to any one of claims 2 to 9, characterized in that: The drying in step 3) is as follows: drying in a constant temperature and humidity chamber at a temperature of 45° C. and a relative humidity of 40%.

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