Double-layer multifunctional liner for intelligent packaging and preparation method of double-layer multifunctional liner

Abstract

The invention provides a double-layer multifunctional liner for intelligent packaging and a preparation method of the double-layer multifunctional liner, and belongs to the technical field of intelligent packaging, the environment-friendly liner with double-layer and multifunctional characteristics is prepared through multi-stage utilization of purple corn cob raw materials, the shelf life of high-protein food can be prolonged, the food freshness and the food storage time are visualized, and the production efficiency is improved. Therefore, the purpose of improving the commercial value of the high-protein food and the consumption experience of consumers is achieved; the upper-layer liner of the double-layer multifunctional liner is an antibacterial / freshness monitoring layer and shows freshness of high-protein food through color change, the lower-layer liner is a time-temperature indicating layer and shows storage time through color change, the upper-layer liner contains plant essential oil and is used for inhibiting growth and reproduction of microorganisms and achieving a fresh-keeping effect, and meanwhile, the upper-layer liner is a double-layer multifunctional liner. The anthocyanin and the Maillard reaction product provide a certain anti-oxidation effect so as to assist in improving the fresh-keeping effect.

Description

Technical Field

[0001] The present invention relates to the technical field of intelligent packaging, and in particular to a double-layer multifunctional liner for intelligent packaging and a preparation method thereof. Background Art

[0002] With the improvement of living standards, people pay more and more attention to the safety of high-protein foods. During storage, transportation and sales, high-protein foods are easily affected by environmental factors, leading to spoilage, thereby reducing their commercial value; traditional packaging methods for high-protein foods cannot effectively extend the shelf life of high-protein foods and maintain their freshness, and in sales scenarios, external factors such as lighting may cause consumers to misjudge their freshness; therefore, it is particularly important to develop multifunctional packaging liners for high-protein foods.

[0003] At present, some patents have disclosed multifunctional aerogel pads. In the invention patent "A 3D antibacterial water-absorbent aerogel for cold fresh meat tray packaging and its preparation method and application" (CN110846726A), cinnamaldehyde ethanol solution is added to a mixed solution of polyvinyl alcohol and citric acid, and a polyvinyl alcohol-based antibacterial water-absorbent pad is prepared by electrospinning technology. The polyvinyl alcohol nanofiber pad is then heated, homogenized, freeze-dried, and other processes to make it a hydrophobic polyvinyl alcohol-based antibacterial water-absorbent pad; however, the preparation method has a high preparation cost, is difficult to prepare, has high equipment requirements, and is difficult to promote and apply in the field of food packaging; in the invention patent "A degradable and antibacterial aerogel pad and its preparation method" (CN117866297A), the nanofiber is added to the mixed solution of polyvinyl alcohol and citric acid to prepare a polyvinyl alcohol-based antibacterial water-absorbent pad. A biodegradable antibacterial aerogel pad is prepared by freeze-drying a mixture of cellulose solution, chitosan solution and graphene oxide solution, which solves the problem of weak mechanical properties and antibacterial ability of aerogels prepared by existing methods. However, the graphene oxide in this preparation method may be harmful to the human body, and the realization of the antibacterial properties of graphene oxide and chitosan requires direct contact between food and aerogel containing graphene oxide and chitosan, and the antibacterial efficiency of the uncontacted part may be low; in the disclosed patents, the functionality of the pad is mainly focused on improving water absorption and preservation capabilities, and there is relatively little development of other functional aspects, which leads to certain limitations in its application scope; therefore, it is very necessary to develop a multifunctional pad with the functions of preservation, high-protein food freshness monitoring and storage time monitoring. Summary of the invention

[0004] The purpose of the present invention is to provide a double-layer multifunctional liner for intelligent packaging and a preparation method thereof, so as to overcome the problems existing in the prior art. The present invention can extend the shelf life of high-protein food, visualize the freshness of food and the storage time of food, thereby achieving the purpose of improving the commercial value of high-protein food and the consumption experience of consumers; the freshness of high-protein food is presented by the color change of the preservation indicator layer, and the storage time is presented by the color change of the time-temperature indicator layer. The preservation effect is mainly achieved by the plant essential oil in the preservation indicator layer through the inhibition of microbial growth and reproduction, and anthocyanins and Maillard reaction products provide a certain antioxidant effect to assist in improving the preservation effect.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is as follows: A method for preparing a double-layer multifunctional liner for smart packaging comprises the following steps: (1) vacuum drying the purple corn cob to constant weight and then crushing it into powder, screening the powder, mixing the screened powder with acidified ethanol and stirring, and then vacuum filtering to obtain purple corn cob residue and filtrate, concentrating the filtrate in the dark by rotary evaporation to obtain purple corn cob anthocyanin concentrate, and vacuum freeze-drying the purple corn cob anthocyanin concentrate to obtain purple corn cob anthocyanin; (2) mixing the purple corncob residue obtained in (1) with a sodium hydroxide aqueous solution, stirring for the first time and then centrifuging to obtain hemicellulose-free purple corncob residue and a filtrate containing hemicellulose, adding an acetic acid-ethanol mixed solution to the filtrate containing hemicellulose, stirring for a second time and then standing, then washing with an ethanol solution, centrifuging again, filtering and collecting the precipitate, and then drying to obtain a hemicellulose solid; (3) mixing the hemicellulose solid obtained in (2) with sulfuric acid, hydrolyzing the mixture to obtain a hydrolyzate, concentrating the hydrolyzate by rotary evaporation, neutralizing the pH with lime milk, and filtering the mixture to obtain a reducing sugar concentrate, and subjecting the reducing sugar concentrate and amino acids as substrates to a Maillard reaction to obtain a time-temperature indicating solution; (4) mixing the hemicellulose-free purple corn cob residue obtained in (2) with potassium permanganate, adding a sulfuric acid solution to obtain a mixed solution, reacting the mixture, adding a hydrogen peroxide solution to obtain a fiber gel product, vacuum filtering the fiber gel product, and repeatedly washing the fiber gel product until the pH is neutral, thereby obtaining a neutral fiber gel product; (5) preparing a polyvinyl alcohol solution and centrifuging it to obtain a polyvinyl alcohol solution from which impurities have been removed, and then adding the polyvinyl alcohol solution from which impurities have been removed to the neutral fiber gel product obtained in (4), shearing it, and mixing it evenly to obtain a CNC / PVA composite hydrogel; (6) preparing a plant essential oil alcohol solution, dissolving it in a β-cyclodextrin solution, stirring it, then subjecting it to ultrasonic treatment, sequentially refrigerating, filtering, washing, and vacuum drying to obtain a plant essential oil / β-cyclodextrin inclusion complex; (7) adding the purple corncob anthocyanin obtained in (1) to the CNC / PVA composite hydrogel obtained in (5), and then adding the plant essential oil / β-cyclodextrin inclusion complex obtained in (6) to perform treatment A to obtain an antibacterial / freshness monitoring hydrogel; adding the time-temperature indicating solution obtained in (3) to the CNC / PVA composite hydrogel obtained in (5), and performing treatment B to obtain a time-temperature indicating hydrogel; (8) adding a crosslinking agent to the surface of the time-temperature indicating hydrogel obtained in (7) and then allowing it to stand at room temperature for the first time to obtain a time-temperature indicating hydrogel crosslinked on one side with the crosslinking agent, then injecting the antibacterial / freshness monitoring hydrogel obtained in (7) onto the surface of the time-temperature indicating hydrogel crosslinked on one side with the crosslinking agent and then allowing it to stand at room temperature for a second time to obtain a multifunctional composite hydrogel, and then freezing the multifunctional composite hydrogel and drying it to obtain a multifunctional environmentally friendly liner; Furthermore, the temperature of vacuum drying in (1) is 40-60°C; the powder screening is specifically: screening powder with a particle size of 50-80 mesh; the mass ratio of the screened powder to acidified ethanol is 1:(10-20), wherein the acidified ethanol is prepared by mixing a citric acid solution with a concentration of 70 g / L and anhydrous ethanol in a volume ratio of 1:1; the stirring temperature is 40-50°C and the time is 1-3 h; the rotary evaporation concentration temperature is 40-50°C; the vacuum freeze drying time is 24-48 h; Furthermore, in (2), the mass ratio of purple corn cob residue to sodium hydroxide aqueous solution is 1:(30-40), wherein the mass concentration of sodium hydroxide aqueous solution is 2 g / L; the temperature of the first stirring is 80-100 °C, and the time is 3-5 h; the speed of the centrifugal treatment after the first stirring is 4000 r / min, and the time is 10 min; the volume of the acetic acid-ethanol mixed solution added is 4 times that of the filtrate containing hemicellulose; the acetic acid-ethanol mixed solution is prepared by mixing anhydrous acetic acid and anhydrous ethanol in a volume ratio of 1:(8-10); the standing time is 2-5 h; the volume fraction of the ethanol solution is 90%; the number of flushing is 3 times; the speed of the second centrifugal treatment is 5000-7000 rpm, and the time is 3-5 min; Furthermore, the mass ratio of hemicellulose solid to sulfuric acid in (3) is 1:(5-15), wherein the mass concentration of sulfuric acid is 0.5-1.5%; the hydrolysis temperature is 100-110°C, and the time is 3 h; the rotary evaporation concentration is specifically: the hydrolyzate is concentrated by rotary evaporation at 40-60°C to one third of the original volume; the neutralization pH is adjusted to 5-7; the Maillard reaction is specifically: the reducing sugar concentrate and a 0.2 M / L phosphate buffer are mixed at a volume ratio of 1:(1-3) to obtain a reducing sugar solution, and the reducing sugar solution is mixed with an amino acid at a volume ratio of 1:(0.5-1.5), wherein the amino acid is glycine, lysine or serine; Furthermore, the mass ratio of the hemicellulose-free purple corncob residue to potassium permanganate in (4) is 1:(1.2-1.4); the mass ratio of the hemicellulose-free purple corncob residue to sulfuric acid solution is 1:(35-45), wherein the mass concentration of the sulfuric acid solution is 1%-3%; the reaction is specifically as follows: the mixed solution is reacted at 50-60°C for 1-3 h; the mass ratio of the hemicellulose-free purple corncob residue to hydrogen peroxide solution is 1:(1-3), wherein the mass concentration of the hydrogen peroxide solution is 30%; and deionized water is used for washing; Furthermore, the preparation of the polyvinyl alcohol solution in (5) is specifically as follows: the polyvinyl alcohol powder is magnetically stirred at 90-100°C for 1-2 hours and then dissolved in deionized water to obtain a polyvinyl alcohol solution with a mass fraction of 0.5%-1%; the centrifugal speed is 4000 r / min and the time is 10 min; the mass ratio of the polyvinyl alcohol solution from which impurities are removed to the neutral fiber gel product is (10-50):1; Further, the prepared plant essential oil alcohol solution in (6) is dissolved in the β-cyclodextrin solution and stirred as follows: β-cyclodextrin and deionized water are mixed at a mass ratio of 1: (8-10), and the mixture is stirred at 60°C for 2 h to obtain a β-cyclodextrin solution; plant essential oil is dissolved in anhydrous ethanol at a mass ratio of 1: (10-20) to obtain a plant essential oil alcohol solution, wherein the plant essential oil is artemisia essential oil, ginger essential oil or cinnamon essential oil; then the plant essential oil alcohol solution is dissolved in the β-cyclodextrin solution at a mass ratio of 1: (5-10), and stirred at 50-70°C for 1-3 h; the ultrasonic treatment time is 0.5-1 h; the refrigeration temperature is 4°C and the time is 24 h; deionized water is used for washing; the vacuum drying temperature is 30°C and the vacuum drying time is 12 h; Furthermore, the mass ratio of purple corn cob anthocyanins, CNC / PVA composite hydrogel and plant essential oil / β-cyclodextrin inclusion complex in (7) is 1:(2000-4000):40; the treatment A is specifically: after stirring at 35-45 °C for 0.5-1.5 h, centrifuging at 4000 r / min for 10 min; the mass ratio of the time-temperature indicator solution to the CNC / PVA composite hydrogel is 1:(25-50); the treatment B is specifically: after stirring at 40-60 °C for 1-3 h, centrifuging at 4000 r / min for 10 min; Furthermore, the mass ratio of the time-temperature indicating hydrogel to the cross-linking agent in (8) is 100:(1-5), wherein the cross-linking agent is 1% by mass of succinaldehyde, glutaraldehyde or adipaldehyde; the first standing time at room temperature is 1-2 h; the mass ratio of the antibacterial / freshness monitoring hydrogel to the time-temperature indicating hydrogel cross-linked on one side with the cross-linking agent is 1:1; the second standing time at room temperature is 24 h; the freezing temperature is -60 °C and the time is 5-7 h; the drying is specifically: vacuum freeze drying for 36-48 h; the multifunctional environmentally friendly liner is a multifunctional composite aerogel.

[0006] A double-layer multifunctional liner for smart packaging, characterized in that it is obtained based on the above-mentioned preparation method of a double-layer multifunctional liner for smart packaging.

[0007] The above technical solution has the following advantages or beneficial effects: The present invention provides a double-layer multifunctional liner for intelligent packaging and a preparation method thereof. The environmentally friendly liner with double-layer and multifunctional characteristics is prepared by utilizing the abundant purple corn biological resources and multi-level utilization of purple corn cob raw materials. The environmentally friendly liner adopts a double-layer design to improve the freshness-keeping performance of high-protein foods and assist consumers in judging the freshness of foods. The upper liner contains anthocyanins and plant essential oil / β-cyclodextrin inclusion compounds, which have the dual functions of indicating the freshness of foods and reducing the activity of microorganisms, thereby achieving the freshness-keeping effect of foods and helping consumers to intuitively judge the freshness of foods. The lower liner contains a time-temperature indicator prepared with amino acids and reducing sugars, which can visually display the storage and transportation time of foods, so as to provide consumers with an understanding of the freshness of foods. The double-layer liner uses CNC / PVA mixed aerogel as the matrix, which has good mechanical properties, high specific surface area, thermal stability, water absorption and degradability; in the hydrogel stage, the use of a cross-linking agent achieves a close connection between the two layers of gel, effectively avoiding the stratification problem during use; purple corn cobs, as an agricultural waste, are widely available and inexpensive. Compared with traditional petroleum-based materials, purple corn cob aerogels have better renewability and are in line with the concept of sustainable development. They are also rich in anthocyanins, hemicellulose and cellulose, which provide a good foundation for the subsequent preparation of high value-added products; the present invention utilizes purple corn cob raw materials at multiple levels, such as extracting anthocyanins for the new high-protein food The invention can indicate the freshness, prepare reducing sugar by using purple corn cob hemicellulose, and prepare nanocellulose by using purple corn cob residue, etc., which can not only make full use of the effective ingredients in purple corn cobs and improve their added value, but also realize the recycling of resources and reduce environmental pollution. It is not only conducive to promoting the resource utilization of agricultural waste, but also helps to promote the development of the food packaging industry and improve the safety and quality of food. The present invention utilizes the hydrogen bonding effect between polyvinyl alcohol and purple corn cob nanocellulose to prepare a high-performance CNC / PVA hybrid aerogel matrix with high specific surface area, excellent mechanical properties, thermal stability, good water absorption and degradability, and the formation of a hydrogen bonding network between the hydroxyl group in the nanocellulose and the carboxyl group in the polyvinyl alcohol , which significantly improved the mechanical properties of aerogels and provided a solid foundation for the subsequent functional addition; the CNC / PVA hybrid aerogel matrix has a large specific surface area, which increases the contact area between anthocyanins, plant essential oil / β-cyclodextrin inclusion complexes and time-temperature indicator solutions fixed in the hybrid aerogel matrix and the environment, and can effectively improve the reaction sensitivity, so that the freshness of the food and the storage and transportation time experienced by the multifunctional composite aerogel during the storage and transportation of high-protein food can be more intuitively observed; when high-protein food exudes tissue fluid during storage and transportation, CNC / PVA aerogel can quickly absorb these liquids, thereby keeping the contact surface between the liner and the food dry, which helps prevent the growth of bacteria and mold, thereby extending the shelf life of the food;The invention constructs a time-temperature indicating solution, and utilizes reducing sugars abundant in purple corn cobs, such as xylose, glucose and mannose, as raw materials of indicators. These reducing sugars exist in purple corn cobs in a natural form, and a reducing sugar solution with a high concentration can be prepared by hydrolyzing hemicellulose rich in purple corn cobs; subsequently, through the Maillard reaction, these reducing sugars react with amino acids to generate Maillard reaction products, and the products change color with the change of time and temperature, thereby realizing visual monitoring of food storage time. The innovation of this time-temperature indicating solution is that, by utilizing the natural components in purple corn cobs, real-time monitoring of food storage time is realized, which is effective. It helps consumers judge the storage and transportation time of food; at the same time, this method has the advantages of environmental protection, low cost, and simple operation, and provides a new solution for the food packaging industry; β-cyclodextrin is a macrocyclic molecule that can effectively embed plant essential oils to form microcapsules. This embedding technology can significantly increase the stability of essential oils and achieve slow release of essential oils, prolong the action time of its active ingredients, and avoid the situation where plant essential oils completely evaporate when the microbial activity is not high and the food is fresh, and cannot continue to work when the microbial activity is high and the food is less fresh, ensuring that the overall release process of plant essential oils is slow and continuous. ;

[0008] Furthermore, in the vacuum drying step, a temperature range of 40-60 °C is selected, which can effectively remove moisture without causing thermal damage to the material, thereby ensuring the stability and performance of the material; the powder with a particle size of 50-80 mesh is screened to ensure the uniformity and consistency of the powder; the acidified ethanol is prepared by mixing a citric acid solution with a concentration of 70 g / L and anhydrous ethanol in a volume ratio of 1:1, which helps to improve the dispersibility of the powder in the solvent. At the same time, the citric acid solution can also provide a certain acidic environment, which is conducive to the subsequent reaction; stirring at 40-50 °C for 1-3 h ensures sufficient mixing between the reactants and avoids the influence of high temperature on the material properties, thereby ensuring the smooth progress of the reaction; rotary evaporation concentration at a temperature of 40-50 °C can effectively remove excess solvent while maintaining the stability and activity of the material; and the moisture in the material can be completely removed by vacuum freeze drying for 24-48 h. Furthermore, the mass ratio of purple corncob residue to sodium hydroxide aqueous solution was set to 1:(30-40), wherein the mass concentration of sodium hydroxide aqueous solution was 2 g / L, which not only ensured the full extraction of effective components in purple corncob residue, but also avoided the pollution of the environment and the damage to the material caused by excessive sodium hydroxide; the acetic acid-ethanol mixed solution was prepared by mixing anhydrous acetic acid and anhydrous ethanol in a volume ratio of 1:(8-10), which was beneficial to the precipitation and separation of hemicellulose; the standing time of 2-5 h ensured that the hemicellulose was fully precipitated in the solution, which was convenient for subsequent separation and purification; washing three times with 90% ethanol solution by volume could effectively remove impurities and residues in the filtrate and improve the purity of hemicellulose; centrifugation was performed again to quickly separate the precipitate from the solution to obtain a pure hemicellulose product.

[0009] Furthermore, the mass ratio of hemicellulose solids to sulfuric acid was set to 1:(5-15), and the mass concentration of sulfuric acid was controlled in the range of 0.5-1.5%, which ensured the efficient hydrolysis reaction and avoided the pollution of the environment and the damage to the materials caused by excessive use of sulfuric acid. The hydrolysis temperature was set at 100-110 °C for 3 hours, which helped to accelerate the hydrolysis process of hemicellulose and improve the yield and purity of the hydrolysate. The hydrolysate was concentrated to one-third of the original volume by rotary evaporation at 40-60 °C, which not only effectively removed the excess water in the hydrolysate, but also increased the concentration of the hydrolysate, providing favorable conditions for the subsequent Maillard reaction. The pH value of the hydrolysate was adjusted to 5-7 by neutralization reaction, which ensured that the subsequent Maillard reaction was carried out in a suitable acid-base environment, which was conducive to the smooth progress of the reaction and the stability of the product. Parameters such as the ratio of reducing sugars and amino acids, the concentration and pH value of the phosphate buffer were precisely controlled, ensuring the efficient Maillard reaction and the excellent performance of the product.

[0010] Furthermore, the mass ratio of the purple corncob residue from which hemicellulose is removed to potassium permanganate is set to 1:(1.2-1.4), which ensures that potassium permanganate can effectively oxidize the residual organic matter and impurities in the purple corncob residue, while avoiding excessive use of potassium permanganate, reducing environmental pollution and costs; the mass ratio of the purple corncob residue from which hemicellulose is removed to the sulfuric acid solution is 1:(35-45), wherein the mass concentration of the sulfuric acid solution is 1%-3%, which not only helps to further remove impurities in the purple corncob residue, but also promotes the oxidation of the purple corncob residue through the catalytic effect of sulfuric acid. The decomposition and modification of components such as lignin improve the porosity and adsorption performance of the material; the mass ratio of hemicellulose-removed purple corn cob residue to hydrogen peroxide solution is set to 1: (1-3), and the mass concentration of hydrogen peroxide solution is 30%, which not only helps to remove pigments and impurities in purple corn cob residue and improve the whiteness and purity of the material, but also can further activate the surface of the material through the oxidation of hydrogen peroxide, increase its reaction activity and adsorption capacity; using deionized water for washing can completely remove residues and impurities on the surface of the material and improve the cleanliness and purity of the material.

[0011] Furthermore, the polyvinyl alcohol powder was magnetically stirred at 90-100 °C for 1-2 h to ensure that the polyvinyl alcohol was completely dissolved in deionized water to obtain a polyvinyl alcohol solution with a mass fraction of 0.5%-1%, which not only ensured the uniformity and stability of the polyvinyl alcohol solution, but also provided a suitable material basis for the subsequent composite process by precisely controlling the concentration of polyvinyl alcohol; before preparing the polyvinyl alcohol solution, the raw materials were treated to remove impurities, which could avoid the negative impact of impurities on the performance of the composite material, help improve the purity and stability of the composite material, and ensure its excellent performance in practical applications; the mass ratio of the polyvinyl alcohol solution from which impurities were removed to the neutral fiber gel product was set to (10-50):1, which ensured that the polyvinyl alcohol solution could fully penetrate and coat the neutral fiber gel product to form a tight bond. At the same time, by adjusting the mass ratio, the structure and performance of the composite material could be optimized to meet different application requirements. Furthermore, β-cyclodextrin and deionized water were mixed at a mass ratio of 1: (8-10) and stirred continuously at 60 °C for 2 h to obtain a uniform and stable β-cyclodextrin solution, ensuring the full dissolution and dispersion of β-cyclodextrin, providing a good carrier for the subsequent embedding of plant essential oils; the plant essential oil was dissolved in anhydrous ethanol at a mass ratio of 1: (10-20) to obtain a plant essential oil alcohol solution, which not only achieved the dissolution and dispersion of the plant essential oil, but also facilitated the embedding and fixation of the plant essential oil in the subsequent steps through the volatility of anhydrous ethanol; the plant essential oil alcohol solution was dissolved in a β-cyclodextrin solution at a mass ratio of 1: (5-10) and stirred at 50-70 °C for 1-3 h. The cavity structure of β-cyclodextrin can accommodate and stabilize the plant essential oil molecules to form an inclusion complex, thereby improving the stability and durability of the plant essential oil; by 0.5-1 h of ultrasonic treatment can further promote the interaction between plant essential oil and β-cyclodextrin, accelerate the formation of inclusion complex, and help improve the uniformity and stability of the inclusion complex; refrigerating the inclusion complex solution at 4 ℃ for 24 h can promote the further solidification of the inclusion complex and enhance its stability and durability in the cushion material; washing the inclusion complex with deionized water can remove impurities such as unencapsulated plant essential oil and residual ethanol, thereby improving the purity and quality of the product.

[0012] Furthermore, the mass ratio of purple corncob anthocyanins, CNC / PVA composite hydrogel and plant essential oil / β-cyclodextrin inclusion complex was set to 1:(2000~4000):40, which ensured the uniform distribution and effective effect of each component in the composite material; through treatment A, not only the full mixing and uniform dispersion of the components were achieved, but also the unmixed particles and impurities were removed by centrifugation, thereby improving the purity and stability of the composite material; by introducing a time-temperature indicator solution, the temperature and time changes of the composite material during the processing can be monitored and recorded in real time, thereby ensuring the stability and controllability of the processing process, and helping to improve the processing accuracy and product quality of the composite material; through treatment B, the interaction and combination of the components were promoted, and the overall performance and stability of the composite material were improved. At the same time, the unbound substances and impurities were removed again by centrifugation, ensuring the purity and quality of the composite material.

[0013] Furthermore, by selecting succinic dialdehyde, glutaraldehyde or adipaldehyde as cross-linking agents and mixing them with time-temperature indicating hydrogel in a mass ratio of 100:(1~5), the stabilization and strengthening of the hydrogel network structure was achieved, ensuring the effective effect of the cross-linking agent while avoiding the degradation of material performance caused by excessive cross-linking; the first standing at room temperature for 1~2 h was conducive to the full reaction and uniform distribution between the hydrogel and the cross-linking agent, providing a good foundation for the subsequent single-sided cross-linking; the mass ratio of the antibacterial / freshness monitoring hydrogel to the time-temperature indicating hydrogel for single-sided cross-linking of the cross-linking agent was 1:1, realizing the specific functional regionalization of the composite material; by freezing at -60 ℃ for 5-7 h and vacuum freeze-drying for 36~48 h, the structural stability and performance optimization of the composite material were achieved.

[0014] The present invention also provides a double-layer multifunctional liner for smart packaging. The multifunctional liner effectively inhibits the growth and reproduction of microorganisms in high-protein foods by integrating natural ingredients such as plant essential oils, anthocyanins, and Maillard reaction products, thereby significantly extending the shelf life of foods, helping to reduce food waste and improving food safety. The freshness indicator layer in the liner uses color changes to intuitively reflect the freshness of the food. As the freshness of the food decreases, the color of the freshness indicator layer will change, allowing consumers to understand the status of the food at a glance and make more informed purchasing and eating decisions. This visualization feature enhances consumers' trust in food quality and improves consumer experience. Through color changes, consumers can clearly understand the storage history of food from production to consumption, which helps to reduce health problems caused by accidentally eating expired food. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a schematic flow chart of a method for preparing a double-layer multifunctional liner for smart packaging according to the present invention; Figure 2 This is a schematic diagram of a multifunctional environmentally friendly liner obtained in Example 1 of a method for preparing a double-layer multifunctional liner for smart packaging of the present invention; Figure 3 This is a schematic diagram of Example 3 of a method for preparing a double-layer multifunctional liner for smart packaging of the present invention placed at 25° C. for 0 h; Figure 4 This is a schematic diagram of Example 3 of a method for preparing a double-layer multifunctional liner for smart packaging of the present invention placed at 25° C. for 96 hours. DETAILED DESCRIPTION

[0016] The present invention is further described in detail below in conjunction with specific embodiments, which are intended to explain the present invention rather than to limit it. In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention. It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0017] like Figure 1 As shown, the present invention provides a method for preparing a double-layer multifunctional liner for smart packaging, comprising the following steps: (1) The purple corn cob is vacuum dried at 40-60 °C to constant weight and then crushed into powder, and the powder with a particle size of 50-80 mesh is screened. The screened powder is mixed with acidified ethanol at a mass ratio of 1: (10-20) and stirred at 40-50 °C for 1-3 h, and then vacuum filtered to obtain purple corn cob residue and filtrate. The filtrate is concentrated by rotary evaporation at 40-50 °C in the dark to obtain purple corn cob anthocyanin concentrate. The purple corn cob anthocyanin concentrate is vacuum freeze-dried for 24-48 h to obtain purple corn cob anthocyanin; Preferably, the acidified ethanol is prepared by mixing a citric acid solution having a concentration of 70 g / L and anhydrous ethanol in a volume ratio of 1:1; (2) The purple corncob residue obtained in (1) is mixed with a sodium hydroxide aqueous solution at a mass ratio of 1:(30-40), stirred at 80-100°C for 3-5 h, and then centrifuged at 4000 r / min for 10 min to obtain hemicellulose-free purple corncob residue and a filtrate containing hemicellulose. A 4-fold acetic acid-ethanol mixed solution is added to the hemicellulose-containing filtrate, stirred evenly, and allowed to stand for 2-5 h, then rinsed three times with a 90% volume fraction ethanol solution, and centrifuged again at 5000-7000 rpm for 3-5 min, filtered and collected the precipitate, and then dried to obtain a hemicellulose solid; Preferably, the mass concentration of the sodium hydroxide aqueous solution is 2 g / L; Preferably, the acetic acid-ethanol mixed solution is prepared by mixing anhydrous acetic acid and anhydrous ethanol in a volume ratio of 1: (8-10); (3) The hemicellulose solid obtained in (2) is mixed with sulfuric acid in a mass ratio of 1:(5-15), and hydrolyzed at 100-110°C for 3 h to obtain a hydrolyzate, and the hydrolyzate is concentrated by rotary evaporation at 40-60°C to one third of the original volume, and then neutralized with lime milk to a pH of 5-7, and then filtered to obtain a reducing sugar concentrate, and the reducing sugar concentrate and amino acids are used as substrates for Maillard reaction to obtain a time-temperature indicating solution; Preferably, the mass concentration of sulfuric acid is 0.5-1.5%; Preferably, the Maillard reaction is specifically as follows: a reducing sugar concentrate and a phosphate buffer having a concentration of 0.2 M / L are mixed at a volume ratio of 1:(1-3) to obtain a reducing sugar solution, and the reducing sugar solution is mixed with an amino acid at a volume ratio of 1:(0.5-1.5), wherein the amino acid is glycine, lysine or serine; (4) The purple corn cob residue obtained in (2) without hemicellulose is mixed with potassium permanganate at a mass ratio of 1: (1.2-1.4), and a sulfuric acid solution with a mass concentration of 1%-3% is added at a mass ratio of the purple corn cob residue without hemicellulose and the sulfuric acid solution of 1: (35-45) to obtain a mixed solution, the mixed solution is reacted at 50-60 °C for 1-3 h, and then a hydrogen peroxide solution with a mass concentration of 30% is added to obtain a fiber gel product, the fiber gel product is vacuum filtered and repeatedly washed with deionized water until the pH is neutral, and a neutral fiber gel product is obtained; Preferably, the mass ratio of the hemicellulose-removed purple corncob residue to the hydrogen peroxide solution is 1:(1-3); (5) The polyvinyl alcohol powder was dissolved in deionized water under magnetic stirring at 90-100 °C for 1-2 h to obtain a polyvinyl alcohol solution with a mass fraction of 0.5%-1%, and then centrifuged at 4000 r / min for 10 min to obtain a polyvinyl alcohol solution with impurities removed. The polyvinyl alcohol solution with impurities removed was then added to the neutral fiber gel product obtained in (4), sheared, and mixed to obtain a CNC / PVA composite hydrogel. Preferably, the mass ratio of the polyvinyl alcohol solution from which impurities are removed to the neutral fiber gel product is (10-50):1; (6) β-cyclodextrin and deionized water are mixed at a mass ratio of 1: (8-10), and stirred continuously at 60 °C for 2 h to obtain a β-cyclodextrin solution; plant essential oil is dissolved in anhydrous ethanol at a mass ratio of 1: (10-20) to obtain a plant essential oil alcohol solution, wherein the plant essential oil is artemisia essential oil, ginger essential oil or cinnamon essential oil; then the plant essential oil alcohol solution is dissolved in the β-cyclodextrin solution at a mass ratio of 1: (5-10), stirred at 50-70 °C for 1-3 h, ultrasonically treated for 0.5-1 h, and then refrigerated at 4 °C for 24 h, filtered, washed with deionized water, and finally vacuum dried at 30 °C for 12 h to obtain a plant essential oil / β-cyclodextrin inclusion complex; (7) Add the purple corncob anthocyanin obtained in (1) to the CNC / PVA composite hydrogel obtained in (5), then add the plant essential oil / β-cyclodextrin inclusion complex obtained in (6), stir at 35-45 °C for 0.5-1.5 h, and centrifuge at 4000 r / min for 10 min to obtain an antibacterial / freshness monitoring hydrogel; add the time-temperature indicator solution obtained in (3) to the CNC / PVA composite hydrogel obtained in (5) at a mass ratio of 1:(25-50), stir at 40-60 °C for 1-3 h, and centrifuge at 4000 r / min for 10 min to obtain a time-temperature indicator hydrogel; Preferably, the mass ratio of purple corncob anthocyanins, CNC / PVA composite hydrogel and plant essential oil / β-cyclodextrin inclusion complex is 1: (2000-4000): 40; (8) After adding a crosslinking agent to the surface of the time-temperature indicating hydrogel obtained in (7), the hydrogel is allowed to stand at room temperature for 1 to 2 hours to obtain a time-temperature indicating hydrogel crosslinked on one side with the crosslinking agent. Then, the antibacterial / freshness monitoring hydrogel obtained in (7) is injected onto the surface of the time-temperature indicating hydrogel crosslinked on one side with the crosslinking agent, and the hydrogel is allowed to stand at room temperature for 24 hours to obtain a multifunctional composite hydrogel. The multifunctional composite hydrogel is then frozen at -60°C for 5 to 7 hours and then vacuum freeze-dried for 36 to 48 hours to obtain a multifunctional composite aerogel, i.e., a multifunctional environmentally friendly liner. Preferably, the mass ratio of the time-temperature indicating hydrogel to the cross-linking agent is 100:(1-5), wherein the cross-linking agent is 1% by mass of succinaldehyde, glutaraldehyde or adipaldehyde; Preferably, the mass ratio of the antibacterial / freshness monitoring hydrogel to the time-temperature indicating hydrogel that is single-sidedly cross-linked with a cross-linking agent is 1:1.

[0018] like Figure 2As shown, the present invention also provides a double-layer multifunctional liner for smart packaging, which is obtained based on the above-mentioned method for preparing a double-layer multifunctional liner for smart packaging, including an antibacterial / freshness monitoring layer, which presents the freshness of high-protein food through color changes, and the bottom of the antibacterial / freshness monitoring layer is connected to an intermediate cross-linking layer, and the bottom of the intermediate cross-linking layer is connected to a time-temperature indicating layer, which presents the storage time through color changes.

[0019] Embodiment 1: like Figure 1 As shown, the present invention provides a method for preparing a double-layer multifunctional liner for smart packaging, comprising the following steps: (1) The purple corn cob was vacuum dried at 40°C to constant weight and then crushed into powder. The powder with a particle size of 50-60 mesh was screened. 10 g of the screened powder was mixed with 100 g of acidified ethanol and stirred at 40°C for 3 h, and then vacuum filtered to obtain purple corn cob residue and filtrate. The filtrate was concentrated by rotary evaporation at 40°C in the dark to obtain purple corn cob anthocyanin concentrate. The purple corn cob anthocyanin concentrate was vacuum freeze-dried for 24 h to obtain purple corn cob anthocyanin. Preferably, the acidified ethanol is prepared by mixing a citric acid solution having a concentration of 70 g / L and anhydrous ethanol in a volume ratio of 1:1; (2) Take 5 g of the purple corncob residue obtained in (1) and mix it with 150 g of a sodium hydroxide aqueous solution with a mass concentration of 2 g / L. After stirring at 80 °C for 5 h, centrifuge it at 4000 r / min for 10 min to obtain the purple corncob residue without hemicellulose and the filtrate containing hemicellulose. Add 400 mL of acetic acid-ethanol mixed solution to 100 mL of the filtrate containing hemicellulose, stir evenly and let it stand for 2 h, then rinse it with 90% ethanol solution three times, centrifuge it again at 5000 rpm for 5 min, filter and collect the precipitate, and then dry it in an oven to obtain hemicellulose solid. Preferably, the acetic acid-ethanol mixed solution is prepared by mixing anhydrous acetic acid and anhydrous ethanol in a volume ratio of 1: (8-10); (3) Take 2 g of the hemicellulose solid obtained in (2) and mix it with 10 g of sulfuric acid with a mass concentration of 0.5%, hydrolyze it at 100°C for 3 h to obtain a hydrolyzate, concentrate the hydrolyzate by rotary evaporation at 40°C to one third of the original volume, then neutralize it with lime milk to pH 5, and filter it to obtain a reducing sugar concentrate, take 4 mL of the reducing sugar concentrate and 4 mL of 0.2 M / L phosphate buffer to mix to obtain a reducing sugar solution, mix the reducing sugar solution with 4 mL of glycine to obtain a time-temperature indicating solution; (4) 3 g of the hemicellulose-free purple corn cob residue obtained in (2) was mixed with 3.6 g of potassium permanganate, and then 105 g of a 1% sulfuric acid solution was added to obtain a mixed solution. The mixed solution was reacted at 50 °C for 3 h, and then 3 g of a 30% hydrogen peroxide solution was added to obtain a fiber gel product. The fiber gel product was vacuum filtered and repeatedly washed with deionized water until the pH was neutral to obtain a neutral fiber gel product. (5) 0.5 g of polyvinyl alcohol powder was dissolved in 99.5 g of deionized water under magnetic stirring at 90 °C for 2 h to obtain a polyvinyl alcohol solution with a mass fraction of 0.5%, and then centrifuged at 4000 r / min for 10 min to obtain a polyvinyl alcohol solution with impurities removed. Then 100 g of the polyvinyl alcohol solution with impurities removed was added to 10 g of the neutral fiber gel product obtained in (4), sheared using a high-speed shearing machine, and mixed evenly to obtain a CNC / PVA composite hydrogel. (6) 10 g of β-cyclodextrin was mixed with 80 g of deionized water and stirred at 60 °C for 2 h to obtain a β-cyclodextrin solution; 1 g of mugwort essential oil was dissolved in 10 g of anhydrous ethanol to obtain a mugwort essential oil alcohol solution; then 10 g of the mugwort essential oil alcohol solution was dissolved in 50 g of β-cyclodextrin solution, stirred at 50 °C for 3 h, and then placed in an ultrasonic cleaner for 0.5 h, then refrigerated at 4 °C for 24 h, filtered, washed with deionized water, and finally vacuum dried at 30 °C for 12 h to obtain a mugwort essential oil / β-cyclodextrin inclusion complex; (7) Take 25 mg of the purple corn cob anthocyanin obtained in (1) and add it to 50 g of the CNC / PVA composite hydrogel obtained in (5), then add 1 g of the Artemisia argyi essential oil / β-cyclodextrin inclusion complex obtained in (6), stir at 35 °C for 1.5 h, and centrifuge at 4000 r / min for 10 min to obtain an antibacterial / freshness monitoring hydrogel; take 2 g of the time-temperature indicator solution obtained in (3) and add it to 50 g of the CNC / PVA composite hydrogel obtained in (5), stir at 40 °C for 3 h, and centrifuge at 4000 r / min for 10 min to obtain a time-temperature indicator hydrogel; (8) Take 50 g of the time-temperature indicating hydrogel obtained in (7), add 0.5 g of 1% by mass succinaldehyde on its surface, and let it stand at room temperature for 2 h to obtain a time-temperature indicating hydrogel that is single-sided cross-linked with the cross-linking agent. Then, take 50 g of the antibacterial / freshness monitoring hydrogel obtained in (7) and inject it on the surface of the time-temperature indicating hydrogel that is single-sided cross-linked with the cross-linking agent, and let it stand at room temperature for 24 h to obtain a multifunctional composite hydrogel. Then, the multifunctional composite hydrogel is frozen at -60 °C for 5 h and then vacuum freeze-dried for 36 h to obtain a multifunctional composite aerogel, i.e., a multifunctional environmentally friendly liner.

[0020] like Figure 2 As shown, the multifunctional environmentally friendly liner obtained in Example 1 was placed at the bottom of a fresh food tray containing salmon and sealed. The tray was then placed under -10°C freezing conditions for 48 h. It was observed that the color of the upper liner, i.e., the antibacterial / freshness detection layer, remained bright yellow, proving that the salmon remained fresh, and the color of the lower liner, i.e., the time-temperature indicator layer, was still light yellow. After another three months, it was observed that the color of the antibacterial / freshness detection layer changed from bright yellow to grayish yellow, proving that the freshness of the salmon decreased, and the color of the time-temperature indicator layer became slightly darker.

[0021] Embodiment 2: like Figure 1 As shown, the present invention provides a method for preparing a double-layer multifunctional liner for smart packaging, comprising the following steps: (1) The purple corn cob was vacuum dried at 50 °C to constant weight and then crushed into powder. The powder with a particle size of 60-70 mesh was screened. 10 g of the screened powder was mixed with 150 g of acidified ethanol and stirred at 45 °C for 2 h, and then vacuum filtered to obtain purple corn cob residue and filtrate. The filtrate was concentrated by rotary evaporation at 45 °C in the dark to obtain purple corn cob anthocyanin concentrate. The purple corn cob anthocyanin concentrate was vacuum freeze-dried for 36 h to obtain purple corn cob anthocyanin. Preferably, the acidified ethanol is prepared by mixing a citric acid solution having a concentration of 70 g / L and anhydrous ethanol in a volume ratio of 1:1; (2) Take 5 g of the purple corncob residue obtained in (1) and mix it with 170 g of a sodium hydroxide aqueous solution with a mass concentration of 2 g / L. After stirring at 90 °C for 4 h, centrifuge it at 4000 r / min for 10 min to obtain the purple corncob residue without hemicellulose and the filtrate containing hemicellulose. Add 400 mL of acetic acid-ethanol mixed solution to 100 mL of the filtrate containing hemicellulose, stir evenly and let it stand for 3 h, then rinse it with a 90% ethanol solution for 3 times, centrifuge it again at 6000 rpm for 4 min, filter and collect the precipitate, and then dry it in an oven to obtain hemicellulose solid. Preferably, the acetic acid-ethanol mixed solution is prepared by mixing anhydrous acetic acid and anhydrous ethanol in a volume ratio of 1: (8-10); (3) Take 2 g of the hemicellulose solid obtained in (2) and mix it with 20 g of sulfuric acid with a mass concentration of 1%, and hydrolyze it at 105 °C for 3 h to obtain a hydrolyzate. Concentrate the hydrolyzate by rotary evaporation at 50 °C to one third of the original volume, and then neutralize it with lime milk to pH 6, and then filter it to obtain a reducing sugar concentrate. Take 4 mL of the reducing sugar concentrate and 8 mL of 0.2 M / L phosphate buffer to mix to obtain a reducing sugar solution. Mix the reducing sugar solution with 12 mL of lysine to obtain a time-temperature indicating solution. (4) 3 g of the hemicellulose-free purple corn cob residue obtained in (2) was mixed with 3.9 g of potassium permanganate, and then 120 g of a 2% sulfuric acid solution was added to obtain a mixed solution. The mixed solution was reacted at 55 °C for 2 h, and then 6 g of a 30% hydrogen peroxide solution was added to obtain a fiber gel product. The fiber gel product was vacuum filtered and repeatedly washed with deionized water until the pH was neutral to obtain a neutral fiber gel product. (5) 2.4 g of polyvinyl alcohol powder was dissolved in 297.6 g of deionized water under magnetic stirring at 95 °C for 1.5 h to obtain a polyvinyl alcohol solution with a mass fraction of 0.8%, and then centrifuged at 4000 r / min for 10 min to obtain a polyvinyl alcohol solution with impurities removed. Then 300 g of the polyvinyl alcohol solution with impurities removed was added to 10 g of the neutral fiber gel product obtained in (4), sheared using a high-speed shearing machine, and mixed evenly to obtain a CNC / PVA composite hydrogel. (6) Mix 10 g of β-cyclodextrin with 90 g of deionized water and stir continuously at 60 °C for 2 h to obtain a β-cyclodextrin solution; dissolve 1 g of ginger essential oil in 15 g of anhydrous ethanol to obtain a ginger essential oil alcohol solution; then dissolve 10 g of the ginger essential oil alcohol solution in 80 g of the β-cyclodextrin solution, stir at 60 °C for 2 h, and then place it in an ultrasonic cleaner for 0.8 h, then refrigerate at 4 °C for 24 h, filter, wash with deionized water, and finally vacuum dry at 30 °C for 12 h to obtain a ginger essential oil / β-cyclodextrin inclusion complex; (7) Take 25 mg of the purple corncob anthocyanin obtained in (1) and add it to 80 g of the CNC / PVA composite hydrogel obtained in (5), then add 1 g of the ginger essential oil / β-cyclodextrin inclusion complex obtained in (6), stir at 40 °C for 1 h, and centrifuge at 4000 r / min for 10 min to obtain an antibacterial / freshness monitoring hydrogel; take 2 g of the time-temperature indicator solution obtained in (3) and add it to 80 g of the CNC / PVA composite hydrogel obtained in (5), stir at 50 °C for 2 h, and centrifuge at 4000 r / min for 10 min to obtain a time-temperature indicator hydrogel; (8) Take 50 g of the time-temperature indicating hydrogel obtained in (7), add 1.5 g of 1% glutaraldehyde on its surface, and let it stand at room temperature for 1.5 h to obtain a time-temperature indicating hydrogel that is single-sided cross-linked with the cross-linking agent. Then, take 50 g of the antibacterial / freshness monitoring hydrogel obtained in (7) and inject it on the surface of the time-temperature indicating hydrogel that is single-sided cross-linked with the cross-linking agent, and let it stand at room temperature for 24 h to obtain a multifunctional composite hydrogel. Then, the multifunctional composite hydrogel is frozen at -60 °C for 6 h and then vacuum freeze-dried for 42 h to obtain a multifunctional composite aerogel, i.e., a multifunctional environmentally friendly liner.

[0022] The multifunctional environmentally friendly liner obtained in Example 2 was placed at the bottom of a fresh food tray containing fresh pork and sealed. The tray was then placed under refrigeration at 4°C for 24 h. It was observed that the color of the upper liner, i.e., the antibacterial / freshness detection layer, remained bright yellow, indicating that the pork was fresh, and the color of the lower liner, i.e., the time-temperature indicator layer, turned light yellow. After another 10 days, the color of the degradable plastic film was observed to change from bright yellow to gray-green, indicating that the pork had deteriorated, and the color of the time-temperature indicator layer turned to dark brown.

[0023] Embodiment 3: like Figure 1 As shown, the present invention provides a method for preparing a double-layer multifunctional liner for smart packaging, comprising the following steps: (1) The purple corn cob was vacuum dried at 60°C to constant weight and then crushed into powder. The powder with a particle size of 70-80 mesh was screened. 10 g of the screened powder was mixed with 200 g of acidified ethanol and stirred at 50°C for 1 h, and then vacuum filtered to obtain purple corn cob residue and filtrate. The filtrate was concentrated by rotary evaporation at 50°C in the dark to obtain purple corn cob anthocyanin concentrate. The purple corn cob anthocyanin concentrate was vacuum freeze-dried for 48 h to obtain purple corn cob anthocyanin. Preferably, the acidified ethanol is prepared by mixing a citric acid solution having a concentration of 70 g / L and anhydrous ethanol in a volume ratio of 1:1; (2) Take 5 g of the purple corncob residue obtained in (1) and mix it with 200 g of a sodium hydroxide aqueous solution with a mass concentration of 2 g / L. After stirring at 100 °C for 3 h, centrifuge it at 4000 r / min for 10 min to obtain the purple corncob residue without hemicellulose and the filtrate containing hemicellulose. Add 400 mL of acetic acid-ethanol mixed solution to 100 mL of the filtrate containing hemicellulose, stir evenly and let it stand for 5 h, then rinse it with a 90% ethanol solution for 3 times, centrifuge it again at 7000 rpm for 3 min, filter and collect the precipitate, and then dry it in an oven to obtain hemicellulose solid. Preferably, the acetic acid-ethanol mixed solution is prepared by mixing anhydrous acetic acid and anhydrous ethanol in a volume ratio of 1: (8-10); (3) Mix 2 g of the hemicellulose solid obtained in (2) with 30 g of 1.5% sulfuric acid, and hydrolyze at 110°C for 3 h to obtain a hydrolyzate. Concentrate the hydrolyzate by rotary evaporation at 60°C to one third of the original volume, and then neutralize it with lime milk to pH 7. Filter and obtain a reducing sugar concentrate. Mix 4 mL of the reducing sugar concentrate with 12 mL of 0.2 M / L phosphate buffer to obtain a reducing sugar solution. Mix the reducing sugar solution with 24 mL of serine to obtain a time-temperature indicating solution. (4) 3 g of the hemicellulose-free purple corn cob residue obtained in (2) was mixed with 4.2 g of potassium permanganate, and then 135 g of a 3% sulfuric acid solution was added to obtain a mixed solution. The mixed solution was reacted at 60 °C for 1 h, and then 9 g of a 30% hydrogen peroxide solution was added to obtain a fiber gel product. The fiber gel product was vacuum filtered and repeatedly washed with deionized water until the pH was neutral to obtain a neutral fiber gel product. (5) 5 g of polyvinyl alcohol powder was dissolved in 495 g of deionized water under magnetic stirring at 100 °C for 1 h to obtain a polyvinyl alcohol solution with a mass fraction of 1%, and then centrifuged at 4000 r / min for 10 min to obtain a polyvinyl alcohol solution with impurities removed. Then 500 g of the polyvinyl alcohol solution with impurities removed was added to 10 g of the neutral fiber gel product obtained in (4), sheared using a high-speed shearing machine, and mixed evenly to obtain a CNC / PVA composite hydrogel. (6) 10 g of β-cyclodextrin was mixed with 100 g of deionized water and stirred at 60 °C for 2 h to obtain a β-cyclodextrin solution; 1 g of cinnamon essential oil was dissolved in 20 g of anhydrous ethanol to obtain a cinnamon essential oil alcohol solution; then 10 g of the cinnamon essential oil alcohol solution was dissolved in 100 g of the β-cyclodextrin solution, stirred at 70 °C for 1 h, and then placed in an ultrasonic cleaner for 1 h, and then refrigerated at 4 °C for 24 h, filtered, washed with deionized water, and finally vacuum dried at 30 °C for 12 h to obtain a cinnamon essential oil / β-cyclodextrin inclusion complex; (7) Take 25 mg of the purple corn cob anthocyanin obtained in (1) and add it to 100 g of the CNC / PVA composite hydrogel obtained in (5), then add 1 g of the cinnamon essential oil / β-cyclodextrin inclusion complex obtained in (6), stir at 45 °C for 0.5 h, and centrifuge at 4000 r / min for 10 min to obtain an antibacterial / freshness monitoring hydrogel; take 2 g of the time-temperature indicator solution obtained in (3) and add it to 100 g of the CNC / PVA composite hydrogel obtained in (5), stir at 60 °C for 1 h, and centrifuge at 4000 r / min for 10 min to obtain a time-temperature indicator hydrogel; (8) Take 50 g of the time-temperature indicating hydrogel obtained in (7), add 2.5 g of 1% adipaldehyde on its surface, and let it stand at room temperature for 1 h to obtain a time-temperature indicating hydrogel that is single-sided cross-linked with the cross-linking agent. Then, take 50 g of the antibacterial / freshness monitoring hydrogel obtained in (7) and inject it on the surface of the time-temperature indicating hydrogel that is single-sided cross-linked with the cross-linking agent, and let it stand at room temperature for 24 h to obtain a multifunctional composite hydrogel. The multifunctional composite hydrogel is then frozen at -60 °C for 7 h and then vacuum freeze-dried for 48 h to obtain a multifunctional composite aerogel, i.e., a multifunctional environmentally friendly liner.

[0024] like Figure 3 As shown, the multifunctional environmentally friendly liner obtained in Example 3 was placed at the bottom of a fresh food tray containing raw shrimps, and after being sealed, it was placed at a room temperature of 25°C for 0 h. It was observed that the color of the upper liner, i.e., the antibacterial / freshness detection layer, was bright yellow, and the color of the lower liner, i.e., the time-temperature indication layer, was light yellow; then the tray was placed at a room temperature of 25°C for 48 h, and it was observed that the color of the antibacterial / freshness detection layer changed from bright yellow to gray-green, indicating that the raw shrimps were deteriorated, and the color of the time-temperature indication layer changed to dark brown; as shown Figure 4 As shown in the figure, after the raw shrimp were placed at 25 °C for 48 h, the color of the antibacterial / freshness detection layer was observed to change from gray-green to dark green, indicating that the raw shrimp had deteriorated more seriously. At this time, the time-temperature indicator layer had turned dark brown.

[0025] Table 1 shows the relationship between the color change of the upper liner, i.e., the antibacterial / freshness detection layer, and the food freshness. Table 2 shows the relationship between the color change of the lower liner, i.e., the time-temperature indicator layer, and time under different storage temperature conditions, as shown below: Table 1 Relationship between color change of upper liner and food freshness

[0026] Table 2 Relationship between color change and time of the lower liner under different storage temperature conditions

[0027] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a double-layer multifunctional liner for smart packaging, characterized in that: The following steps are involved: S1, vacuum drying the purple corn cob to constant weight and then crushing it into powder, screening the powder, mixing the screened powder with acidified ethanol and stirring, and then vacuum filtering to obtain purple corn cob residue and filtrate, concentrating the filtrate in the dark by rotary evaporation to obtain purple corn cob anthocyanin concentrate, vacuum freeze-drying the purple corn cob anthocyanin concentrate to obtain purple corn cob anthocyanin; S2, mixing the purple corncob residue obtained in S1 with a sodium hydroxide aqueous solution, stirring for the first time and then centrifuging to obtain hemicellulose-free purple corncob residue and a filtrate containing hemicellulose, adding an acetic acid-ethanol mixed solution to the filtrate containing hemicellulose, stirring for a second time and then standing, then washing with an ethanol solution, centrifuging again, filtering and collecting the precipitate, and then drying to obtain a hemicellulose solid; S3, mixing the hemicellulose solid obtained in S2 with sulfuric acid, hydrolyzing to obtain a hydrolyzate, concentrating the hydrolyzate by rotary evaporation, neutralizing the pH with lime milk, and filtering to obtain a reducing sugar concentrate, and subjecting the reducing sugar concentrate and amino acids as substrates to a Maillard reaction to obtain a time-temperature indicating solution; S4, mixing the hemicellulose-free purple corn cob residue obtained in S2 with potassium permanganate, adding a sulfuric acid solution to obtain a mixed solution, adding a hydrogen peroxide solution after reaction to obtain a fiber gel product, vacuum filtering the fiber gel product and repeatedly washing it until the pH is neutral, to obtain a neutral fiber gel product; S5, preparing a polyvinyl alcohol solution and then centrifuging it to obtain a polyvinyl alcohol solution from which impurities are removed, and then adding the polyvinyl alcohol solution from which impurities are removed to the neutral fiber gel product obtained in S4, shearing it, and mixing it evenly to obtain a CNC / PVA composite hydrogel; S6, preparing a plant essential oil alcohol solution, dissolving it in a β-cyclodextrin solution, stirring it, then subjecting it to ultrasonic treatment, sequentially refrigerating, filtering, washing, and vacuum drying to obtain a plant essential oil / β-cyclodextrin inclusion complex; S7, adding the purple corncob anthocyanin obtained in S1 to the CNC / PVA composite hydrogel obtained in S5, and then adding the plant essential oil / β-cyclodextrin inclusion complex obtained in S6, performing treatment A to obtain an antibacterial / freshness monitoring hydrogel; adding the time-temperature indicating solution obtained in S3 to the CNC / PVA composite hydrogel obtained in S5, performing treatment B to obtain a time-temperature indicating hydrogel; S8, after adding a cross-linking agent to the surface of the time-temperature indicating hydrogel obtained in S7, the hydrogel is allowed to stand at room temperature for the first time to obtain a time-temperature indicating hydrogel that is cross-linked on one side with the cross-linking agent, and then the antibacterial / freshness monitoring hydrogel obtained in S7 is injected onto the surface of the time-temperature indicating hydrogel that is cross-linked on one side with the cross-linking agent, and then the hydrogel is allowed to stand at room temperature for a second time to obtain a multifunctional composite hydrogel, and then the multifunctional composite hydrogel is frozen and dried to obtain a multifunctional environmentally friendly liner.

2. The method for preparing a double-layer multifunctional liner for smart packaging according to claim 1, characterized in that: The temperature of vacuum drying in S1 is 40-60°C; the screening of powder is specifically as follows: screening powder with a particle size of 50-80 mesh; the mass ratio of the screened powder to acidified ethanol is 1:(10-20), wherein the acidified ethanol is prepared by mixing a citric acid solution with a concentration of 70 g / L and anhydrous ethanol in a volume ratio of 1:1; the stirring temperature is 40-50°C and the time is 1-3 h; the temperature of the rotary evaporation concentration is 40-50°C; and the time of the vacuum freeze drying is 24-48 h.

3. The method for preparing a double-layer multifunctional liner for smart packaging according to claim 1, characterized in that: The mass ratio of purple corn cob residue to sodium hydroxide aqueous solution in S2 is 1: (30-40), wherein the mass concentration of sodium hydroxide aqueous solution is 2 g / L; the temperature of the first stirring is 80-100 °C, and the time is 3-5 h; the speed of the centrifugal treatment after the first stirring is 4000 r / min, and the time is 10 min; the volume of the added acetic acid-ethanol mixed solution is 4 times that of the filtrate containing hemicellulose; the acetic acid-ethanol mixed solution is prepared by mixing anhydrous acetic acid and anhydrous ethanol in a volume ratio of 1: (8-10); the standing time is 2-5 h; the volume fraction of the ethanol solution is 90%; the number of flushing is 3 times; the speed of the second centrifugal treatment is 5000-7000 rpm, and the time is 3-5 min.

4. The method for preparing a double-layer multifunctional liner for smart packaging according to claim 1, characterized in that: The mass ratio of hemicellulose solid to sulfuric acid in the S3 is 1: (5-15), wherein the mass concentration of sulfuric acid is 0.5-1.5%; the hydrolysis temperature is 100-110°C, and the time is 3 h; the rotary evaporation concentration is specifically: the hydrolyzate is rotary evaporated to one third of the original volume at 40-60°C; the neutralization pH is adjusted to 5-7; the Maillard reaction is specifically: the reducing sugar concentrate and a phosphate buffer with a concentration of 0.2 M / L are mixed at a volume ratio of 1: (1-3) to obtain a reducing sugar solution, and the reducing sugar solution is mixed with amino acids at a volume ratio of 1: (0.5-1.5), wherein the amino acids are glycine, lysine or serine.

5. The method for preparing a double-layer multifunctional liner for smart packaging according to claim 1, characterized in that: The mass ratio of the hemicellulose-free purple corncob residue to potassium permanganate in S4 is 1:(1.2~1.4); the mass ratio of the hemicellulose-free purple corncob residue to sulfuric acid solution is 1:(35~45), wherein the mass concentration of the sulfuric acid solution is 1%~3%; the reaction is specifically as follows: the mixed solution is reacted at 50~60°C for 1~3 h; the mass ratio of the hemicellulose-free purple corncob residue to hydrogen peroxide solution is 1:(1~3), wherein the mass concentration of the hydrogen peroxide solution is 30%; and deionized water is used for washing.

6. The method for preparing a double-layer multifunctional liner for smart packaging according to claim 1, characterized in that: The preparation of the polyvinyl alcohol solution in S5 is specifically as follows: the polyvinyl alcohol powder is magnetically stirred at 90-100°C for 1-2 hours and then dissolved in deionized water to obtain a polyvinyl alcohol solution with a mass fraction of 0.5%-1%; the centrifugal speed is 4000r / min and the time is 10 min; the mass ratio of the polyvinyl alcohol solution from which impurities are removed to the neutral fiber gel product is (10-50):

1.

7. The method for preparing a double-layer multifunctional liner for smart packaging according to claim 1, characterized in that: The prepared plant essential oil alcohol solution in S6 is dissolved in the β-cyclodextrin solution and stirred specifically as follows: β-cyclodextrin and deionized water are mixed at a mass ratio of 1: (8~10), and stirred continuously at 60°C for 2 h to obtain a β-cyclodextrin solution; the plant essential oil is dissolved in anhydrous ethanol at a mass ratio of 1: (10~20) to obtain a plant essential oil alcohol solution, wherein the plant essential oil is artemisia essential oil, ginger essential oil or cinnamon essential oil; then the plant essential oil alcohol solution is dissolved in the β-cyclodextrin solution at a mass ratio of 1: (5~10), and stirred at 50~70°C for 1~3 h; the ultrasonic treatment time is 0.5~1 h; the refrigeration temperature is 4°C and the time is 24 h; deionized water is used for washing; the vacuum drying temperature is 30°C and the vacuum drying time is 12 h.

8. The method for preparing a double-layer multifunctional liner for smart packaging according to claim 1, characterized in that: The mass ratio of purple corncob anthocyanins, CNC / PVA composite hydrogel and plant essential oil / β-cyclodextrin inclusion complex in the S7 is 1: (2000~4000): 40; the treatment A is specifically: after stirring at 35~45 ℃ for 0.5~1.5 h, centrifuge at a speed of 4000 r / min for 10 min; the mass ratio of the time-temperature indicator solution to the CNC / PVA composite hydrogel is 1: (25~50); the treatment B is specifically: after stirring at 40~60 ℃ for 1~3 h, centrifuge at a speed of 4000 r / min for 10 min.

9. The method for preparing a double-layer multifunctional liner for smart packaging according to claim 1, characterized in that: The mass ratio of the time-temperature indicating hydrogel to the cross-linking agent in S8 is 100:(1~5), wherein the cross-linking agent is 1% by mass of succinic dialdehyde, glutaraldehyde or adipaldehyde; the first standing time at room temperature is 1~2 h; the mass ratio of the antibacterial / freshness monitoring hydrogel and the time-temperature indicating hydrogel cross-linked on one side with the cross-linking agent is 1:1; the second standing time at room temperature is 24 h; the freezing temperature is -60 ° C, and the time is 5-7 h; the drying is specifically: vacuum freeze drying for 36~48 h; the multifunctional environmentally friendly liner is a multifunctional composite aerogel.

10. A double-layer multifunctional liner for smart packaging, characterized in that: A double-layer multifunctional liner for smart packaging is obtained based on the method for preparing the double-layer multifunctional liner for smart packaging according to any one of claims 1 to 9.

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