Nano-composite fiber membrane based on vegetable protein and application of nano-composite fiber membrane to freshness indication

Abstract

The invention belongs to the technical field of intelligent food packaging films, and particularly relates to a nanometer composite fiber film based on vegetable protein and application of the nanometer composite fiber film. The preparation method comprises the following steps: dissolving gallic acid, an anthocyanin composite extract and rapeseed protein in deionized water, and uniformly stirring to obtain a spinning core solution; the preparation method comprises the following steps: dissolving zein in acetic acid, and then adding into water to obtain zein soluble liquid; uniformly mixing and stirring the zein solution and the Arabic gum mixed solution to obtain a shell solution; the shell liquid and the core liquid are subjected to coaxial electrostatic spinning, tin foil paper serves as a receiving base material and is collected through a rotary drum, and finally the nano-composite fiber membrane is obtained. According to the method, the color development difference of anthocyanin under different pH conditions is widened, the color development sensitivity is improved, and the freshness of food can be judged more visually according to color changes. Meanwhile, the composite membrane prepared through electrostatic spinning has larger specific surface area and higher ductility, and the mechanical performance of the composite membrane is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of food intelligent packaging films, and specifically relates to a nano-composite fiber film based on plant protein and an application thereof. Background Art

[0002] At present, conventional detection methods for food freshness include electrochemical detection and fluorescence detection. Although these methods can detect the freshness of food, they also have many shortcomings. For example, electrochemical detection usually requires the help of chemical instruments, which is cumbersome to operate and the price of the instrument is relatively high. Fluorescence detection is mainly based on the change of the absolute intensity of fluorescence from a single light source, which is not very effective and is easily affected by external environments such as temperature and humidity. On the other hand, more than 90% of food packaging films are synthetic plastics derived from petroleum-based raw materials, which also have the problems of difficult degradation and environmental pollution. Therefore, in the context of focusing on food safety and environmental protection, studying an environmentally friendly film that can achieve freshness indication to replace traditional plastic films has become a development trend today and has great practical significance.

[0003] According to the current research situation, there are also many research reports on food packaging films. According to their functional characteristics, they can be divided into antibacterial, freshness indicator, anti-ultraviolet packaging and other types. However, the existing packaging films have the following problems: (a) When studying antibacterial films, preservatives are directly added to food. Although they can play a role in preservation and antibacterial, excessive use will affect the taste of the food itself; (b) When studying indicator films, natural anthocyanins are selected to achieve good indication effects, but there are problems such as poor stability, easy to be affected by the environment and oxidized by oxygen; (c) Moreover, in order to achieve antibacterial and freshness indicator functions, the existing food packaging films ignore the mechanical properties and stability of the packaging films. The film layer has defects such as poor mechanical properties and easy cracking and breaking; at the same time, in the final stage of film formation, mechanized hot air drying is often used. In this process, due to the low comprehensive performance of the film, it is also very easy to cause cracks in the prepared film. Summary of the invention

[0004] In view of the deficiencies of the prior art, the purpose of the present invention is to solve one of the problems; to provide a safe and environmentally friendly intelligent indicator film, which not only has good mechanical properties, but also can be used to indicate the freshness of meat products.

[0005] In order to achieve the above purpose, the present invention adopts the following scheme:

[0006] A method for preparing a nanocomposite fiber membrane based on plant protein comprises the following steps:

[0007] (1) dissolving gum arabic and polyvinyl alcohol in water, and stirring to obtain a gum arabic mixed solution;

[0008] (2) Crush the purple sweet potato and add it to ethanol A, heat it to 35-45° C., maintain the temperature and continue stirring for 30-40 minutes, then filter it, and adjust the pH of the filtered solution to 2-6 to obtain a purple sweet potato extract; and beat the fresh blueberries with a homogenizer, and obtain a blueberry slurry after filtering;

[0009] Add malic acid to ethanol B to obtain a mixed solution, then add purple sweet potato extract and blueberry slurry to the mixed solution, perform ultrasonic extraction at 32-37°C and 150-300W to obtain a purple sweet potato-blueberry extract, remove ethanol by rotary evaporation, and vacuum freeze-dry the obtained rotary evaporation solution to obtain anthocyanin composite extract;

[0010] (3) Preparation of rapeseed protein: rapeseed is shelled, crushed and sieved to obtain powder, and the powder is added to petroleum ether for defatting. After defatting, the powder is filtered, dried, ground and sieved twice to obtain defatted rapeseed meal; the defatted rapeseed meal is added to water and stirred to obtain a rapeseed meal mixed solution, the pH is adjusted to 3-8, and then a protease is added for enzymolysis. After enzymolysis, the mixture is cooled to room temperature and the pH value is adjusted to neutral to obtain an enzymolysis solution; the obtained enzymolysis solution is subjected to ultrafiltration and freeze-dried to obtain rapeseed protein;

[0011] (4) dissolving gallic acid, the anthocyanin composite extract obtained in step (2), and the rapeseed protein obtained in step (3) in deionized water, mixing and stirring to obtain a spinning core solution;

[0012] (5) adding zein to acetic acid to dissolve it, and then adding it to water to obtain a zein solution; mixing the zein solution with the gum arabic mixture and stirring them uniformly to obtain a shell solution;

[0013] (6) The shell liquid and the core liquid are coaxially electrospun, and tin foil is used as a receiving substrate and collected by a drum to finally obtain a nanocomposite fiber membrane.

[0014] Preferably, the amount of gum arabic, polyvinyl alcohol and water in step (1) is 4-6 g: 1-2 g: 20-40 mL;

[0015] Preferably, in step (2), the dosage relationship of the purple sweet potato and ethanol A is 1 g: 3-5 ml; the dosage relationship of the purple sweet potato extract, blueberry slurry and mixed solution is 3-5: 1: 10-15, wherein the dosage relationship of malic acid and ethanol B is 1-5 g: 100 mL.

[0016] Preferably, the temperature of the rotary evaporation in step (2) is 50°C and the time is 30-50 min; the temperature of the vacuum freeze drying is -45°C and the time is 24-48 h.

[0017] Preferably, the mesh number of the sieve in step (3) is 80-100 mesh, the amount of powder and petroleum ether is 1g:5-10mL; the degreasing time is 8-10h, and the degreasing temperature is 40-45°C; the mesh number of the secondary sieve is 60-80 mesh;

[0018] Preferably, in step (3), the mass concentration of the rapeseed meal mixed liquid is 10-12%, the amount of protease added is 2-6% of the mass of the rapeseed meal mixed liquid, the pH during enzymolysis is 6-8, and the enzymolysis temperature is 40-50° C.; and the molecular weight cutoff of the ultrafiltration treatment is 10 to 50 kDa.

[0019] Preferably, the dosage of the anthocyanin composite extract, gallic acid, rapeseed protein and deionized water in step (4) is 1g: 2-3g: 3-5g: 20mL.

[0020] Preferably, in step (5), the dosage of zein, acetic acid and water is 1-2 g: 4-5 mL: 10 mL; and the volume ratio of the zein solution to the gum arabic mixture is 1:1.

[0021] Preferably, the condition parameters of the electrospinning technology described in step (6) are: the voltage applied by the high-voltage power supply is 15-20KV, the receiving distance is 10-15cm, the shell solution propulsion rate is 0.5-1mL / h, the core solution propulsion rate is 0.1-0.2mL / h, the spinning temperature is 30-40°C, the relative humidity is 30%-40%, and the roller speed is 40-50r / min.

[0022] Ethanol A and ethanol B are both ethanol, and the different letters only represent the difference in the name.

[0023] The prepared nanocomposite fiber membrane is used to detect the freshness of meat, and the specific steps are as follows:

[0024] Place fresh meat in a fresh-keeping box, then cut the nanocomposite fiber membrane according to the needs and seal the meat, and store it for a period of time after sealing; as the storage time of the meat increases, the TVB-N value of the meat will increase, and the corresponding pH will also change, which will cause the color of the nanocomposite fiber membrane to change. When the color of the nanocomposite fiber membrane changes from pink to blue-purple in time, it means that the meat changes from fresh to not fresh; thus, the freshness of the meat can be judged in time according to the color change, and visual detection can be achieved. The storage period is 10-20 minutes.

[0025] Beneficial effects of the present invention:

[0026] (1) Anthocyanins are a large class of plant-derived, natural, water-soluble polyphenolic substances with a basic structure of 2-phenylbenzopyranyl cation, which are ubiquitous in fruits, vegetables, flowers, and grains. Anthocyanins have a variety of health-promoting properties, such as antioxidant, antibacterial, and anti-inflammatory. Among the various biological properties of anthocyanins, their antioxidant and antibacterial activities are particularly important for the development of active packaging. The use of anthocyanin-rich films can maintain food quality and extend shelf life. On the other hand, anthocyanins are very sensitive to changes in pH. Under different acid-base conditions, their own structure will change, thereby presenting different color changes, which enables anthocyanin-rich films to monitor the quality of packaged food. However, most of the anthocyanins currently used are single-source anthocyanins, which are easily affected by the environment during use, resulting in unstable or poor color development. The present invention has found through research that the combination of anthocyanins derived from purple sweet potatoes and blueberries not only improves the stability of color development, but also makes the color change more obvious and easy to distinguish.

[0027] (2) When preparing smart packaging films, gelatin, corn starch, etc. are generally selected as the main raw materials, but the tensile strength and elongation at break of corn starch films are not ideal, and the film material cannot have good mechanical properties; and when using conventional proteins as substrates to prepare anthocyanin indicator films, there are still many problems such as easy leaching of anthocyanins and poor stability of anthocyanins. In order to solve this problem, the present invention creatively co-spins rapeseed protein with zein, and the entanglement of rapeseed protein and zein molecular chains makes the obtained composite nanofiber film have a more compact structure, effectively improves the mechanical properties of zein nanofiber film, and improves tensile strength and elongation at break; at the same time, the present invention also adds gum arabic, which has unique thickening, film-forming and solubility, and can play a positive role in film formation and the mechanical properties of the film, significantly improving the mechanical properties of the composite nanofiber film. In addition, rapeseed protein is a complete protein, and its nutritional value is higher than that of animal protein. Compared with various oil protein and cereal protein, rapeseed protein has a higher digestibility and is safer and more environmentally friendly.

[0028] (3) The present invention also mixes rapeseed protein, anthocyanin and gallic acid before spinning and film making. The purpose is to further broaden the color difference of anthocyanin under different pH conditions and improve the color sensitivity through the intermolecular interaction between anthocyanin and gallic acid, so that the color change difference of the composite nanofiber membrane finally prepared under different pH conditions is greater, and the freshness of food can be judged more intuitively based on the color change.

[0029] (4) The present invention uses electrospinning technology to prepare nanofiber membranes. Compared with traditional membrane making methods, the composite membrane prepared by electrospinning has a larger specific surface area and higher ductility, and can be better applied to food preservation packaging. Moreover, the composite membrane prepared by the present invention is safe and non-toxic, meets food safety requirements, and the preparation method is simple, which has broad market application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 Schematic diagram of the electrospinning device used in the method of the present invention; wherein 1-1, shell layer solution; 1-2, shell layer syringe, 1-3: auxiliary mechanical pump, 2-1: core layer solution, 2-2: core layer syringe; 2-3: main machine.

[0031] Figure 2 This is a scanning electron microscope image of the nanocomposite fiber membrane prepared in the present invention. DETAILED DESCRIPTION

[0032] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0033] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0034] Embodiment 1:

[0035] (1) dissolving 6 g of gum arabic and 2 g of polyvinyl alcohol in 30 mL of water and stirring to obtain a gum arabic mixed solution;

[0036] (2) adding the crushed purple sweet potato into ethanol at a solid-liquid ratio of 1:5 (w / v), heating to 35° C., maintaining the temperature and stirring continuously for 30 min, filtering, and adjusting the pH of the filtered solution to 5 to obtain a purple sweet potato extract; and beating fresh blueberries with a homogenizer, and filtering to obtain a blueberry slurry;

[0037] Malic acid was added to ethanol in an amount of 3 g:100 mL to obtain a mixed solution, and then purple sweet potato extract and blueberry slurry were added to the mixed solution, and ultrasonic extraction was performed under the conditions of 35°C and 250W to obtain a purple sweet potato-blueberry extract, and the ethanol was removed by rotary evaporation at a temperature of 50°C and a time of 30 min. The obtained rotary evaporation liquid was vacuum freeze-dried at -45°C for 48 hours to obtain an anthocyanin composite extract;

[0038] (3) Preparation of rapeseed protein: rapeseed is shelled, crushed, and sieved through an 80-mesh sieve to obtain a powder, and the powder is added to petroleum ether in a dosage ratio of 1 g:5 mL for degreasing. The degreasing temperature is 45° C. and the degreasing time is 8 h. After degreasing, the defatted rapeseed meal is filtered, dried, ground, and sieved twice (80 mesh) to obtain a defatted rapeseed meal; the defatted rapeseed meal is added to water and stirred to obtain a rapeseed meal mixture with a mass concentration of 10%, the pH is adjusted to 7, and then 5% of the mass of the rapeseed meal mixture is added with a protease for enzymolysis. The pH during enzymolysis is 7 and the enzymolysis temperature is 50° C. After enzymolysis, it is cooled to room temperature and the pH value is adjusted to neutral to obtain an enzymolysis solution; the obtained enzymolysis solution is subjected to 40 kDa ultrafiltration and freeze-dried to obtain rapeseed protein;

[0039] (4) anthocyanin compound extract, gallic acid and rapeseed protein are dissolved in deionized water, mixed and stirred evenly to form a spinning core solution; wherein the amount of anthocyanin compound extract, gallic acid, rapeseed protein and deionized water is in the order of 1 g: 3 g: 3 g: 20 mL;

[0040] (5) adding zein to acetic acid to dissolve it, and then adding it to water to obtain a zein solution; mixing the zein solution with a gum arabic mixture in a volume ratio of 1:1, and stirring them evenly to obtain a shell solution; wherein the amount of zein, acetic acid, and water is in the ratio of 2 g: 5 mL: 10 mL;

[0041] (6) The shell liquid and the core liquid are coaxially electrospun, and tin foil is used as the receiving substrate and collected by a drum to finally obtain a nanofiber membrane; wherein the condition parameters of the electrospinning technology are: the voltage applied by the high-voltage power supply is 15KV, the receiving distance is 12cm, the propulsion rate of the shell solution is 0.5mL / h, the propulsion rate of the core solution is 0.2mL / h, the spinning temperature is 35°C, the relative humidity is 40%, and the roller speed is 40r / min.

[0042] Embodiment 2:

[0043] (1) dissolving 4 g of gum arabic and 2 g of polyvinyl alcohol in 30 mL of water and stirring to obtain a gum arabic mixed solution;

[0044] (2) adding the crushed purple sweet potato into ethanol at a solid-liquid ratio of 1:3 (w / v), heating to 35° C., maintaining the temperature and stirring continuously for 30 min, filtering, and adjusting the pH of the filtered solution to 3 to obtain a purple sweet potato extract; and beating fresh blueberries with a homogenizer, and filtering to obtain a blueberry slurry;

[0045] Malic acid was added to ethanol in an amount of 1 g:20 mL to obtain a mixed solution, and then purple sweet potato extract and blueberry slurry were added to the mixed solution, and ultrasonic extraction was performed under the conditions of 35°C and 300W to obtain a purple sweet potato-blueberry extract, and the ethanol was removed by rotary evaporation at a temperature of 50°C and a time of 30 min. The obtained rotary evaporation liquid was vacuum freeze-dried at -45°C for 48 hours to obtain an anthocyanin composite extract;

[0046] (3) Preparation of rapeseed protein: rapeseed is shelled, crushed, and sieved through an 80-mesh sieve to obtain a powder, and the powder is added to petroleum ether in a dosage ratio of 1 g:8 mL for degreasing. The degreasing temperature is 40° C. and the degreasing time is 10 h. After degreasing, the defatted rapeseed meal is filtered, dried, ground, and sieved twice (80 mesh) to obtain a defatted rapeseed meal; the defatted rapeseed meal is added to water and stirred to obtain a rapeseed meal mixture with a mass concentration of 10%, the pH is adjusted to 8, and then 2% of the mass of the rapeseed meal mixture is added with a protease for enzymolysis. The pH during enzymolysis is 8 and the enzymolysis temperature is 50° C. After enzymolysis, it is cooled to room temperature and the pH value is adjusted to neutral to obtain an enzymolysis solution; the obtained enzymolysis solution is subjected to 40 kDa ultrafiltration and freeze-dried to obtain rapeseed protein;

[0047] (4) anthocyanin compound extract, gallic acid and rapeseed protein are dissolved in deionized water, mixed and stirred evenly to form a spinning core solution; wherein the amount of anthocyanin compound extract, gallic acid, rapeseed protein and deionized water is in the order of 1 g: 2 g: 5 g: 20 mL;

[0048] (5) adding zein to acetic acid to dissolve it, and then adding it to water to obtain a zein solution; mixing the zein solution with a gum arabic mixture in a volume ratio of 1:1, and stirring them evenly to obtain a shell solution; wherein the amount of zein, acetic acid, and water is in the ratio of 1 g: 2 mL: 5 mL;

[0049] (6) The shell liquid and the core liquid are coaxially electrospun, and tin foil is used as the receiving substrate and collected by a drum to finally obtain a nanofiber membrane; wherein the condition parameters of the electrospinning technology are: the voltage applied by the high-voltage power supply is 15KV, the receiving distance is 12cm, the propulsion rate of the shell solution is 0.5mL / h, the propulsion rate of the core solution is 0.2mL / h, the spinning temperature is 35°C, the relative humidity is 40%, and the roller speed is 40r / min.

[0050] Embodiment 3:

[0051] (1) dissolving 4 g of gum arabic and 1 g of polyvinyl alcohol in 30 mL of water and stirring to obtain a gum arabic mixed solution;

[0052] (2) adding the crushed purple sweet potato into ethanol at a solid-liquid ratio of 1:5 (w / v), heating to 35° C., maintaining the temperature and stirring continuously for 30 min, filtering, and adjusting the pH of the filtered solution to 5 to obtain a purple sweet potato extract; and beating fresh blueberries with a homogenizer, and filtering to obtain a blueberry slurry;

[0053] Malic acid was added to ethanol in an amount of 3 g:100 mL to obtain a mixed solution, and then purple sweet potato extract and blueberry slurry were added to the mixed solution, and ultrasonic extraction was performed under the conditions of 35°C and 150W to obtain a purple sweet potato-blueberry extract, and the ethanol was removed by rotary evaporation at a temperature of 50°C and a time of 30 min. The obtained rotary evaporation liquid was vacuum freeze-dried at -45°C for 48 hours to obtain an anthocyanin composite extract;

[0054] (3) Preparation of rapeseed protein: rapeseed is shelled, crushed, and sieved through an 80-mesh sieve to obtain a powder, and the powder is added to petroleum ether in a dosage ratio of 1 g:5 mL for defatting. The defatting temperature is 45°C and the defatting time is 10 h. After defatting, the mixture is filtered, dried, ground, and sieved twice (60 mesh) to obtain defatted rapeseed meal. The defatted rapeseed meal is then added to water and stirred to obtain a rapeseed meal mixture with a mass concentration of 12%. The pH is adjusted to 6, and then 5% of the mass of the rapeseed meal mixture is added with a protease for enzymolysis. The pH during enzymolysis is 6 and the enzymolysis temperature is 40°C. After enzymolysis, the mixture is cooled to room temperature and the pH is adjusted to neutral to obtain an enzymolysis solution. The obtained enzymolysis solution is subjected to 40 kDa ultrafiltration and freeze-dried to obtain rapeseed protein.

[0055] (4) anthocyanin compound extract, gallic acid and rapeseed protein are dissolved in deionized water, mixed and stirred evenly to serve as spinning core solution; wherein the amount of anthocyanin compound extract, gallic acid, rapeseed protein and deionized water is in the order of 1 g: 2 g: 3 g: 20 mL;

[0056] (5) adding zein to acetic acid to dissolve it, and then adding it to water to obtain a zein solution, mixing the zein solution with a gum arabic mixture in a volume ratio of 1:1, and stirring them evenly to obtain a shell solution; wherein the amount of zein, acetic acid, and water is in the ratio of 2 g: 5 mL: 10 mL;

[0057] (6) The shell liquid and the core liquid are coaxially electrospun, and tin foil is used as the receiving substrate and collected by a drum to finally obtain a nanofiber membrane; wherein the condition parameters of the electrospinning technology are: the voltage applied by the high-voltage power supply is 15KV, the receiving distance is 12cm, the propulsion rate of the shell solution is 0.5mL / h, the propulsion rate of the core solution is 0.2mL / h, the spinning temperature is 35°C, the relative humidity is 40%, and the roller speed is 40r / min.

[0058] Comparative Example 1:

[0059] (1) dissolving 6 g of gum arabic and 2 g of polyvinyl alcohol in 30 mL of water and stirring to obtain a gum arabic mixed solution;

[0060] (2) adding the crushed purple sweet potato into ethanol at a solid-liquid ratio of 1:5 (w / v), heating to 35° C., maintaining the temperature and stirring continuously for 30 min, filtering, and adjusting the pH of the filtered solution to 5 to obtain a purple sweet potato extract; and beating fresh blueberries with a homogenizer, and filtering to obtain a blueberry slurry;

[0061] Malic acid was added to ethanol in an amount of 3 g:100 mL to obtain a mixed solution, and then purple sweet potato extract and blueberry slurry were added to the mixed solution, and ultrasonic extraction was performed under the conditions of 35°C and 250W to obtain a purple sweet potato-blueberry extract, and the ethanol was removed by rotary evaporation at a temperature of 50°C and a time of 30 min. The obtained rotary evaporation liquid was vacuum freeze-dried at -45°C for 48 hours to obtain an anthocyanin composite extract;

[0062] (3) adding zein to acetic acid to dissolve, thereby obtaining a zein-acetic acid solution; then adding the zein-acetic acid solution and a mixture of anthocyanidin compound extract, gallic acid and gum arabic to deionized water to obtain a mixed solution; wherein the amount of zein, acetic acid, anthocyanidin compound extract, gallic acid and gum arabic is in the order of 2 g: 5 mL: 1 g: 3 g: 5 mL;

[0063] (4) Pour the mixed solution of step (3) into the template and move it into an oven for drying. The oven temperature is set to 45° C. and the drying time is 24 hours. After drying to form a film, gently peel the film from the template to obtain a composite film.

[0064] Comparative Example 2:

[0065] (1) dissolving 6 g of gum arabic and 2 g of polyvinyl alcohol in 30 mL of water and stirring to obtain a gum arabic mixed solution;

[0066] (2) adding the crushed purple sweet potato into ethanol at a solid-liquid ratio of 1:5 (w / v), heating to 35° C., maintaining the temperature and stirring continuously for 30 min, filtering, and adjusting the pH of the filtered solution to 5 to obtain a purple sweet potato extract; and beating fresh blueberries with a homogenizer, and filtering to obtain a blueberry slurry;

[0067] Malic acid was added to ethanol in an amount of 3 g:100 mL to obtain a mixed solution, and then purple sweet potato extract and blueberry slurry were added to the mixed solution, and ultrasonic extraction was performed under the conditions of 35°C and 250W to obtain a purple sweet potato-blueberry extract, and the ethanol was removed by rotary evaporation at a temperature of 50°C and a time of 30 min. The obtained rotary evaporation liquid was vacuum freeze-dried at -45°C for 48 hours to obtain an anthocyanin composite extract;

[0068] (3) anthocyanin compound extract and gallic acid are dissolved in deionized water, mixed and stirred evenly to form a spinning core solution; wherein the amount of anthocyanin compound extract, gallic acid and deionized water is 1 g: 3 g: 20 mL;

[0069] (4) adding zein to acetic acid to dissolve it, and then adding it to water to obtain a zein solution, mixing the zein solution with a gum arabic mixture in a volume ratio of 1:1, and stirring them evenly to obtain a shell solution; wherein the amount of zein, acetic acid, and water is in the ratio of 2 g: 5 mL: 10 mL;

[0070] (5) The shell liquid and the core liquid are coaxially electrospun, and tin foil is used as the receiving substrate and collected by a drum to finally obtain a nanofiber membrane; wherein the condition parameters of the electrospinning technology are: the voltage applied by the high-voltage power supply is 15KV, the receiving distance is 12cm, the propulsion rate of the shell solution is 0.5mL / h, the propulsion rate of the core solution is 0.2mL / h, the spinning temperature is 35°C, the relative humidity is 40%, and the roller speed is 40r / min.

[0071] The mechanical properties of the composite film prepared by the present invention are measured as follows:

[0072] The tensile strength and elongation at break of the film were tested using a physical property tester. All the composite films to be tested were cut into pieces with a length of 50 mm and a width of 20 mm. During the test, the composite films were fixed at both ends of the tension handles, with an initial handle distance of 40 mm and a tensile speed of 0.05 mm s -1 , each membrane sample was tested 3 times.

[0073] Table 1 Thickness and mechanical properties of composite films

[0074]

[0075] Note: The values ​​in the table are expressed as mean ± standard deviation; different lowercase letters indicate significant differences (P<0.05)

[0076] From the results in Table 1, it can be seen that the tensile strength and elongation at break of the composite film prepared by composite rapeseed protein and zein are significantly higher than those of the composite films in Comparative Examples 1 and 2. Moreover, from Comparative Examples 1-2, the mechanical properties of the composite film prepared by electrospinning technology are also better than those of the composite film prepared by conventional drying methods.

[0077] Figure 2 This is a scanning electron microscope image of the nanocomposite fiber membrane of Example 1, in which the entanglement of rapeseed protein and zein molecular chains makes the obtained composite nanofiber membrane have a denser structure and is free of large granular foreign matter.

[0078] The freshness indication experiment was carried out using the nanocomposite fiber membrane prepared in Example 1:

[0079] According to the national standard GB 2707-2016 Fresh (Frozen) Livestock and Poultry Products, the relationship between the volatile basic nitrogen content (TVB-N) and the freshness of food is established, that is, TVB-N ≤ 15 mg / 100 mg is fresh meat (fresh); 15 mg / 100 mg < TVB-N is stale meat products.

[0080] Taking pork as an example (purchased from a supermarket), the TVB-N and pH of fresh pork were first measured, and the initial TVB-N was 7.89 mg / 100 g (the pH value was measured to be 5.6); then the fresh meat was placed in a fresh-keeping box, and the nano-composite fiber membrane was cut according to needs and sealed to seal the meat. In the initial stage, the color of the nano-composite fiber membrane was pink; after sealing and storing at 4°C for 5 days, the TVB-N was measured again. After storage, the TVB-N was 31.27 mg / 100 g (the pH value was measured to be 6.4). At this time, the color of the nano-composite fiber membrane was blue-purple, indicating that the pork was no longer fresh.

[0081] The present invention adopts composite anthocyanins, and the color change is more stable, and the color change occurs very obviously and timely; the color of the membrane will change from pink to blue-purple as the pork is stored, so the freshness of the meat can be judged in time according to the color change, realizing visual detection.

[0082] Note: The above embodiments are only used to illustrate the present invention and are not intended to limit the technical solutions described in the present invention; therefore, although this specification has described the present invention in detail with reference to the above embodiments, a person skilled in the art should understand that the present invention can still be modified or replaced by equivalents; and all technical solutions and improvements thereof that do not depart from the spirit and scope of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A method for preparing a nanocomposite fiber membrane based on plant protein, characterized in that: The following steps are involved: (1) dissolving gum arabic and polyvinyl alcohol in water, and stirring to obtain a gum arabic mixed solution; (2) Crush the purple sweet potato and add it to ethanol A, heat it to 35-45° C., maintain the temperature and continue stirring for 30-40 minutes, then filter it, and adjust the pH of the filtered solution to 2-6 to obtain a purple sweet potato extract; and beat the fresh blueberries with a homogenizer, and obtain a blueberry slurry after filtering; Add malic acid to ethanol B to obtain a mixed solution, then add purple sweet potato extract and blueberry slurry to the mixed solution, perform ultrasonic extraction at 32-37°C and 150-300W to obtain a purple sweet potato-blueberry extract, remove ethanol by rotary evaporation, and vacuum freeze-dry the obtained rotary evaporation solution to obtain anthocyanin composite extract; (3) Preparation of rapeseed protein: rapeseed is shelled, crushed and sieved to obtain powder, and the powder is added to petroleum ether for defatting. After defatting, the powder is filtered, dried, ground and sieved twice to obtain defatted rapeseed meal; the defatted rapeseed meal is added to water and stirred to obtain a rapeseed meal mixed solution, the pH is adjusted to 3-8, and then a protease is added for enzymolysis. After enzymolysis, the mixture is cooled to room temperature and the pH value is adjusted to neutral to obtain an enzymolysis solution; the obtained enzymolysis solution is subjected to ultrafiltration and freeze-dried to obtain rapeseed protein; (4) dissolving gallic acid, the anthocyanin composite extract obtained in step (2), and the rapeseed protein obtained in step (3) in deionized water, mixing and stirring to obtain a spinning core solution; (5) adding zein to acetic acid to dissolve it, and then adding it to water to obtain a zein-soluble solution; The zein solution and the gum arabic solution are mixed and stirred evenly to form the shell solution; (6) The shell liquid and the core liquid are coaxially electrospun, and tin foil is used as a receiving substrate and collected by a drum to finally obtain a nanocomposite fiber membrane.

2. The method for preparing a nanocomposite fiber membrane based on plant protein according to claim 1, characterized in that: The dosage of the purple sweet potato and ethanol A in step (1) is 1 g: 3-5 ml; the dosage of the gum arabic, polyvinyl alcohol and water is 4-6 g: 1-2 g: 20-40 ml.

3. The method for preparing a nanocomposite fiber membrane based on plant protein according to claim 2, characterized in that: The dosage relationship of the purple sweet potato extract, blueberry slurry and mixed solution in step (2) is 3-5:1:10-15, wherein the dosage relationship of malic acid and ethanol B is 1-5g:100mL.

4. The method for preparing a nanocomposite fiber membrane based on plant protein according to claim 1, characterized in that: The temperature of the rotary evaporation in step (2) is 50° C. and the time is 30-50 min; the temperature of the vacuum freeze drying is -45° C. and the time is 24-48 h.

5. The method for preparing a nanocomposite fiber membrane based on plant protein according to claim 1, characterized in that: The mesh number of the sieve in step (3) is 80-100 mesh, and the dosage of the powder and petroleum ether is 1g:5-10mL; the degreasing time is 8-10h, and the degreasing temperature is 40-45°C; the mesh number of the secondary sieving is 60-80 mesh.

6. The method for preparing a nanocomposite fiber membrane based on plant protein according to claim 1, characterized in that: In step (3), the mass concentration of the rapeseed meal mixed liquid is 10-12%, the amount of protease added is 2-6% of the mass of the rapeseed meal mixed liquid, the pH during enzymolysis is 6-8, and the enzymolysis temperature is 40-50° C.; the molecular weight cut-off of the ultrafiltration treatment is 10-50 kDa.

7. The method for preparing a nanocomposite fiber membrane based on plant protein according to claim 1, characterized in that: The dosage of the anthocyanin composite extract, gallic acid, rapeseed protein and deionized water in step (4) is 1g: 2-3g: 3-5g: 20mL.

8. The method for preparing a nanocomposite fiber membrane based on plant protein according to claim 1, characterized in that: The dosage of zein, acetic acid and water in step (5) is 1-2 g: 4-5 mL: 10 mL; the volume ratio of zein solution to gum arabic mixture is 1:

1.

9. The method for preparing a nanocomposite fiber membrane based on plant protein according to claim 1, characterized in that: The condition parameters of the electrospinning technology described in step (6) are: the voltage applied by the high-voltage power supply is 15-20KV, the receiving distance is 10-15cm, the shell solution propulsion rate is 0.5-1mL / h, the core solution propulsion rate is 0.1-0.2mL / h, the spinning temperature is 30-40°C, the relative humidity is 30%-40%, and the roller speed is 40-50r / min.

10. Use of the plant protein-based nanocomposite fiber membrane prepared according to any one of claims 1 to 9 for detecting the freshness of meat, characterized in that: The specific steps are as follows: fresh meat is placed in a fresh-keeping box, and then the nano-composite fiber membrane is cut according to needs and sealed to seal the meat, and then stored for a period of time after sealing; as the storage time of the meat increases, the TVB-N value of the meat will increase, and the corresponding pH will also change, thereby causing the color of the nano-composite fiber membrane to change. When the color of the nano-composite fiber membrane changes from pink to blue-purple in time, it indicates that the meat has changed from fresh to not fresh; thus, the freshness of the meat can be judged in time according to the color change, and visual detection can be achieved; the storage period is 10-20 minutes.

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