A food intelligent packaging material with buffering performance and preparation method thereof

Abstract

Disclosed are a food intelligent packaging material with buffering properties and a preparation method thereof. The raw material components, measured by weight, comprise 4.5-12.0 parts of polyvinyl alcohol, 0.5-3.0 parts of chitosan, 0.5-1.5 parts of anthocyanin crude extract, and 10-40 parts of a nanosilver solution. The preparation method comprises the following steps: step 1, extracting a food freshness detection agent, namely anthocyanin crude extract; step 2, preparing a nanosilver aqueous solution using a green reduction method; and step 3, mixing the polyvinyl alcohol, chitosan, the anthocyanin crude extract prepared in step 1, and the nanosilver aqueous solution prepared in step 2 to prepare a high-strength and tough double-network hydrogel packaging material. The present invention can achieve the purpose of buffering and protecting food, while also having visual detection of food freshness and antibacterial functions, thereby ensuring food safety and extending the shelf life of food.

Description

Technical Field

[0001] The present invention relates to the technical field of material preparation, and in particular to a food intelligent packaging material with buffering performance and a preparation method thereof. Background Art

[0002] Food losses during transportation and storage are substantial, resulting in significant waste. The development of a new generation of active and intelligent packaging materials (AIPMs) using novel materials and structures to extend food shelf life, monitor food quality in real time, and provide efficient cushioning and protection is a cutting-edge research area receiving significant attention and support from many countries.

[0003] Cushioning packaging materials can reduce the external impact of food during storage, transportation and sales, and prevent food loss. With the rapid development of e-commerce and logistics industries, packaging waste has increased rapidly. Currently, the cushioning packaging used in my country is mainly foam plastics and corrugated cardboard. Foam plastics have the advantages of light weight and good cushioning performance, but they are difficult to degrade and have a low recycling rate, which brings serious environmental pollution problems. Corrugated cardboard is easily crushed and weakens when exposed to water. In addition, a large amount of wood is consumed during the manufacturing process, polluting the environment. Most importantly, traditional cushioning materials have a single function and cannot meet the increasingly diverse functional needs of food packaging (improving food safety and reducing food quality losses).

[0004] With growing awareness of food safety and environmental conservation, the demand for packaging materials with active protection, sensing, and tracking capabilities is increasing. Active packaging and intelligent packaging have emerged. Active packaging extends the shelf life of food by adding various active substances to the packaging. Intelligent packaging incorporates sensors and indicators (such as gas indicators, humidity sensors, and electrochemical biosensors) that can monitor and track product quality in real time. Currently, cushioning packaging and functional packaging (such as active packaging and intelligent packaging) in food packaging consist of different layers and materials, each layer performing its own function, increasing the overall size and cost of the food packaging system. Therefore, developing packaging materials that integrate active protection, intelligent monitoring, and cushioning protection, based on environmentally friendly and biodegradable raw materials, can significantly contribute to lightweighting, reduce packaging consumables, and alleviate both environmental and economic burdens.

[0005] In the field of cushioning packaging, several patent applications have disclosed methods for preparing biomass cushioning packaging materials. For example, the biomass cushioning packaging material produced in "A Biomass Cushioning Packaging Material" (Publication No. CN104804223A) exhibits excellent resilience and cushioning properties, resolving the issue of non-degradability of traditional cushioning packaging materials. However, this type of biodegradable cushioning packaging material lacks functionalities (such as freshness detection and antibacterial properties) and cannot meet the requirements of smart food packaging materials.

[0006] In the field of smart food packaging, some inventors have developed smart food packaging materials using hydrogels and functional substances. For example, "Anti-migration Hydrogel-Based Freshness Colorimetric Indicator Label and Preparation Method Thereof" (Publication No. CN113843937A) discloses a hydrogel-based freshness colorimetric label and its preparation method. Leveraging the properties of hydrogel and porous materials, an antibacterial smart label with a fast color response was developed. However, this type of smart food packaging only serves the purpose of functional packaging and lacks buffering and protective properties. Summary of the Invention

[0007] In order to overcome the defects of the above-mentioned prior art, the purpose of the present invention is to provide a food intelligent packaging material with buffering properties and a preparation method thereof. The present invention can achieve the purpose of buffering and protecting food, and at the same time has visual detection of food freshness and antibacterial functions, thereby achieving the purpose of ensuring food safety and extending the shelf life of food.

[0008] In order to achieve the above object, the technical solution of the present invention is:

[0009] A food intelligent packaging material with buffering properties comprises the following raw material components by weight: polyvinyl alcohol: 4.5-12.0 parts; chitosan: 0.5-3.0 parts; anthocyanin crude extract: 0.5-1.5 parts; and nanosilver solution: 10-40 parts.

[0010] A method for preparing a food intelligent packaging material with buffering performance, characterized by comprising the following steps:

[0011] Step 1: extracting a food freshness detection agent, namely anthocyanin crude extract;

[0012] Step 2: preparing nanosilver aqueous solution by green reduction method;

[0013] Step 3: Mix polyvinyl alcohol, chitosan, the crude anthocyanin extract prepared in step 1, and the nanosilver aqueous solution prepared in step 2 to prepare a high-strength and tough double-network hydrogel packaging material.

[0014] The step 1 specifically includes:

[0015] (1) washing anthocyanin-rich bio-based raw materials, drying at 30-45° C., and grinding into small particles; the anthocyanin-rich bio-based raw materials include purple cabbage, mulberry, or black wolfberry;

[0016] (2) grinding the anthocyanin extract raw material small particles and the extraction solution in a mass ratio of 1:5-1:30, and extracting at low temperature in the dark for 12-24 hours; the extraction solution is a 70-80% by volume ethanol solution containing a 0.5-1.5% by volume concentrated hydrochloric acid solution;

[0017] (3) Filter the solution after extraction for 12-24 hours and perform rotary distillation at 35-45°C for 2-3 hours;

[0018] (4) The concentrated solution obtained after rotary distillation is the crude anthocyanin extract, which should be stored in a refrigerated and dark environment.

[0019] The second step specifically includes:

[0020] (1) Dissolve 0.1-0.3 parts by weight of carboxypropyl methylcellulose (HPMC) in 90-270 parts by weight of ultrapure water in a water bath at 45-55°C and stir evenly;

[0021] (2) dissolving 0.1-0.3 parts by weight of silver nitrate in 10-30 parts by weight of ultrapure water;

[0022] (3) adding the silver nitrate aqueous solution dropwise to the carboxypropyl methylcellulose (HPMC) aqueous solution, adding 2-6 parts by weight of anhydrous glucose, and heating in a water bath at 75-80° C. for 5-7 hours;

[0023] (4) Dialyze the solution for 7-8 days, changing the water 2-3 times a day.

[0024] The step three specifically includes:

[0025] (1) Prepare a 5-15 wt.% polyvinyl alcohol / chitosan aqueous solution, i.e., a PVA / CS aqueous solution; stir in a water bath at 85-100°C until uniform;

[0026] (2) Adjust the pH of the PVA / CS aqueous solution to 5.0-6.0; add 0.5-1.5 parts by weight of anthocyanin crude extract and 10-40 parts by weight of nanosilver aqueous solution to 5.0-15.0 parts by weight of the PVA / CS aqueous solution, stir evenly, and ultrasonicate for 20-30 minutes;

[0027] (3) pouring the prepared solution into a mold and cross-linking the gel in a low temperature environment of -10-30°C;

[0028] (4) taking the cross-linked solidified gel out of the mold and drying it in a freeze dryer for 2-3 days to obtain a light and well-formed aerogel material;

[0029] (5) The prepared ultralight porous aerogel is placed in a 0.5-1M sodium citrate solution and soaked for one day to obtain a double-network tough hydrogel material with a micron porous structure.

[0030] The benefits of the present invention are:

[0031] 1. The double-network gel prepared by the present invention has a uniform micron-level porous structure, excellent toughness, and cushioning protection. It can provide a high humidity environment for food during transportation and storage for 2-7 days. This protects food from external damage during transportation and storage, reducing food damage and improving food quality and safety.

[0032] 2. The raw materials of the present invention include chitosan, polyvinyl alcohol, mulberry, carboxypropyl methylcellulose, glucose, silver nitrate, etc., and the main raw materials are degradable materials or bio-based materials, which have good degradability. Bio-based materials are widely available, inexpensive, simple to prepare, and require fewer chemical synthesis reagents, resulting in a shorter cycle and no need for expensive equipment.

[0033] In summary, the present invention selects polyvinyl alcohol and chitosan as the three-dimensional network materials of porous hydrogel, the extracted mulberry crude extract is a pH sensitive agent for visually detecting changes in food quality, and the nanosilver aqueous solution prepared by the green reduction method is an antibacterial agent. Through the micron pore structure and high water content inside the hydrogel, active substances can be quickly transmitted. This gel has high strength and toughness and high porosity, and its density, pore size, and mechanical parameters can be adjusted according to the different proportions of each component in the formula. The gel can sensitively detect changes in the pH2-12 environment of food, has good antibacterial effects, and can extend the shelf life of food. The multifunctional hydrogel material prepared by the present invention is degradable, environmentally friendly, simple in preparation process, and low in cost. It solves the problem that traditional cushioning packaging does not have functionality and that the hydrogel material in smart food packaging does not have a cushioning protection function, thereby achieving the purpose of cushioning protection-functionality integration and lightweight in the packaging system. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 Schematic diagram of the porous gel according to the second embodiment of the present invention.

[0035] Figure 2 This is a diagram showing the pH detection capability of the product of Example 2 of the present invention.

[0036] Figure 3 This is a diagram showing the antibacterial effect of the product of Example 2 of the present invention on Staphylococcus aureus and Escherichia coli. Figure 3(a) is the inhibition zone test of the gel against Staphylococcus aureus; Figure 3 (b) is the inhibition zone experiment of the gel on Escherichia coli.

[0037] Figure 4 is the mechanical property result of the present invention, Figure 4 (a) is the compressive stress-strain curve of the gels with different solute concentrations under full swelling, that is, the compressive stress-strain curves of the products of Examples 1 to 5; (b) is the minimum buffering coefficient of the gels with different solute concentrations under full swelling, that is, the minimum buffering coefficient of the products of Examples 1 to 5; (c) is the compressive stress-strain curve of the gel of Example 2 and the homogeneous gel; (d) is the buffering coefficient-stress curve of the gel of Example 2 and the homogeneous gel.

[0038] Figure 5 This demonstrates the protective effect of the product of Example 2 of the present invention on fresh fruit. (a) A compression test of an apple protected by a gel pad; (b) A free-fall test of a cherry protected by a gel pad from a height of 1 meter. DETAILED DESCRIPTION

[0039] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0040] In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0041] Example 1

[0042] This embodiment provides a food intelligent packaging material with buffering properties. The raw material components thereof are, by weight, 4.5 parts of polyvinyl alcohol; 0.5 parts of chitosan; 1.0 parts of anthocyanin crude extract; and 10 parts of nanosilver solution.

[0043] This embodiment provides a method for preparing a food intelligent packaging material with buffering performance, characterized by comprising:

[0044] Step 1: extracting a food freshness detection agent, namely anthocyanin crude extract;

[0045] Step 2: preparing nanosilver aqueous solution by green reduction method;

[0046] Step 3: Mix polyvinyl alcohol, chitosan, the crude anthocyanin extract prepared in step 1, and the nanosilver aqueous solution prepared in step 2 to prepare a high-strength and tough double-network hydrogel packaging material.

[0047] The step one comprises:

[0048] (1) washing anthocyanin-rich bio-based raw materials, drying at 45° C., and grinding into small particles; the anthocyanin-rich bio-based raw materials include purple cabbage, mulberry, and black wolfberry;

[0049] (2) The ground anthocyanin raw material was mixed with an extraction solution at a mass ratio of 1:10 (w / w) and extracted at low temperature in the dark for 24 h; the extraction solution was an 80% (v / v) ethanol solution containing 1.0% (v / v) concentrated hydrochloric acid solution;

[0050] (3) The solution after 24 h of extraction was filtered and rotary distilled at 45 °C for 3 h;

[0051] (4) The concentrated solution obtained after rotary distillation is the crude anthocyanin extract, which should be stored in a refrigerated and dark environment.

[0052] The second step includes:

[0053] (1) Dissolve 0.1 g of carboxypropyl methylcellulose (HPMC) in 90 mL of ultrapure water in a 50°C water bath and stir evenly.

[0054] (2) Dissolve 0.1 g of silver nitrate in 10 mL of ultrapure water;

[0055] (3) The prepared 0.01 g / mL silver nitrate aqueous solution was added dropwise to the carboxypropyl methylcellulose (HPMC) aqueous solution, 2 g of anhydrous glucose was added, and the mixture was heated in a water bath at 80°C for 6 h;

[0056] (4) The above solution was dialyzed for seven days, changing the water twice a day.

[0057] The step three includes:

[0058] (1) Prepare a 5 wt.% polyvinyl alcohol / chitosan solution (PVA / CS), wherein the polyvinyl alcohol is 4.5 wt.% and the chitosan is 0.5 wt.%, and stir in a water bath at 90°C until uniform;

[0059] (2) Adjust the pH of the PVA / CS aqueous solution to 5.0, add 1 part by weight of anthocyanin crude extract and 10 parts by weight of nanosilver aqueous solution to 5.0 parts by weight of the PVA / CS aqueous solution, stir evenly, and ultrasonicate for 25 minutes;

[0060] (3) Pour the prepared solution into a mold and crosslink the gel in a low temperature environment of -20°C;

[0061] (4) The cross-linked and solidified gel was removed from the mold and placed in a freeze dryer for 3 days to obtain a light and well-formed aerogel material;

[0062] (5) The prepared ultralight porous aerogel is placed in a 1M sodium citrate solution and soaked for one day to obtain a double-network tough hydrogel material with a micron porous structure.

[0063] Example 2

[0064] This embodiment provides a food intelligent packaging material with buffering properties. The raw material components thereof are, by weight, 6 parts of polyvinyl alcohol; 1.5 parts of chitosan; 1.0 parts of anthocyanin crude extract; and 10 parts of nanosilver solution.

[0065] This embodiment provides a method for preparing a food intelligent packaging material with buffering performance, characterized by comprising the following steps:

[0066] Step 1: extracting a food freshness detection agent, namely anthocyanin crude extract;

[0067] Step 2: preparing nanosilver aqueous solution by green reduction method;

[0068] Step 3: Mix polyvinyl alcohol, chitosan, the crude anthocyanin extract prepared in step 1, and the nanosilver aqueous solution prepared in step 2 to prepare a high-strength and tough double-network hydrogel packaging material.

[0069] The step one comprises:

[0070] (1) Washing anthocyanin-rich bio-based raw materials, drying at 45° C., and grinding into small particles; the anthocyanin-rich bio-based raw materials include purple cabbage, mulberry, and black wolfberry;

[0071] (2) The ground anthocyanin raw material was mixed with an extraction solution at a mass ratio of 1:10 (w / w) and extracted at low temperature in the dark for 24 h; the extraction solution was an 80% (v / v) ethanol solution containing 1.0% (v / v) concentrated hydrochloric acid solution;

[0072] (3) The solution after 24 h of extraction was filtered and rotary distilled at 45 °C for 3 h;

[0073] (4) The concentrated solution obtained after rotary distillation is the crude anthocyanin extract, which should be stored in a refrigerated and dark environment.

[0074] The second step includes:

[0075] (1) Dissolve 0.1 g of carboxypropyl methylcellulose (HPMC) in 90 mL of ultrapure water in a 50°C water bath and stir evenly.

[0076] (2) Dissolve 0.1 g of silver nitrate in 10 mL of ultrapure water;

[0077] (3) The prepared 0.01 g / mL silver nitrate aqueous solution was added dropwise to the carboxypropyl methylcellulose (HPMC) aqueous solution, 2 g of anhydrous glucose was added, and the mixture was heated in a water bath at 80°C for 6 h;

[0078] (4) The above solution was dialyzed for seven days, changing the water twice a day.

[0079] The step three includes:

[0080] (1) Prepare a 7.5 wt.% polyvinyl alcohol / chitosan solution (PVA / CS), wherein the polyvinyl alcohol is 6.0 wt.% and the chitosan is 1.5 wt.%, and stir in a water bath at 90°C until uniform;

[0081] (2) Adjust the pH of the PVA / CS aqueous solution to 5.0, add 1 part by weight of anthocyanin crude extract and 10 parts by weight of nanosilver aqueous solution to 7.5 parts by weight of the PVA / CS aqueous solution, stir evenly, and ultrasonicate for 30 minutes;

[0082] (3) Pour the prepared solution into a mold and crosslink the gel in a low temperature environment of -20°C;

[0083] (4) The cross-linked and solidified gel was removed from the mold and placed in a freeze dryer for 3 days to obtain a light and well-formed aerogel material;

[0084] (5) The prepared ultralight porous aerogel is placed in a 1M sodium citrate solution and soaked for one day to obtain a double-network tough hydrogel material with a micron porous structure.

[0085] Example 3

[0086] The present embodiment provides a food intelligent packaging material with buffering properties. The raw material components thereof are, by weight, 8.0 parts of polyvinyl alcohol; 2.0 parts of chitosan; 1.0 parts of anthocyanin crude extract; and 20 parts of nanosilver solution.

[0087] This embodiment provides a method for preparing a food intelligent packaging material with buffering performance, characterized by comprising the following steps:

[0088] Step 1: extracting a food freshness detection agent, namely anthocyanin crude extract;

[0089] Step 2: preparing nanosilver aqueous solution by green reduction method;

[0090] Step 3: Mix polyvinyl alcohol, chitosan, the crude anthocyanin extract prepared in step 1, and the nanosilver aqueous solution prepared in step 2 to prepare a high-strength and tough double-network hydrogel packaging material.

[0091] The step one comprises:

[0092] (1) Washing anthocyanin-rich bio-based raw materials, drying at 45° C., and grinding into small particles; the anthocyanin-rich bio-based raw materials include purple cabbage, mulberry, and black wolfberry;

[0093] (2) The ground anthocyanin raw material was mixed with an extraction solution at a mass ratio of 1:10 (w / w) and extracted at low temperature in the dark for 24 h; the extraction solution was an 80% (v / v) ethanol solution containing 1.0% (v / v) concentrated hydrochloric acid solution;

[0094] (3) The solution after 24 h of extraction was filtered and rotary distilled at 45 °C for 3 h;

[0095] (4) The concentrated solution obtained after rotary distillation is the crude anthocyanin extract, which should be stored in a refrigerated and dark environment.

[0096] The second step includes:

[0097] (1) Dissolve 0.1 g of carboxypropyl methylcellulose (HPMC) in 90 mL of ultrapure water in a 50°C water bath and stir evenly.

[0098] (2) Dissolve 0.1 g of silver nitrate in 10 mL of ultrapure water;

[0099] (3) The prepared 0.01 g / mL silver nitrate aqueous solution was added dropwise to the carboxypropyl methylcellulose (HPMC) aqueous solution, 2 g of anhydrous glucose was added, and the mixture was heated in a water bath at 80°C for 6 h;

[0100] (4) The above solution was dialyzed for seven days, changing the water twice a day.

[0101] The step three includes:

[0102] (1) Prepare a 10.0 wt.% polyvinyl alcohol / chitosan solution (PVA / CS), wherein the polyvinyl alcohol is 8.0 wt.% and the chitosan is 2.0 wt.%, and stir in a water bath at 90°C until uniform;

[0103] (2) Adjust the pH of the PVA / CS aqueous solution to 5.0, add 1 part by weight of anthocyanin crude extract and 20 parts by weight of nanosilver aqueous solution to 10.0 parts by weight of the PVA / CS aqueous solution, stir evenly, and ultrasonicate for 30 minutes;

[0104] (3) Pour the prepared solution into a mold and crosslink the gel in a low temperature environment of -20°C;

[0105] (4) The cross-linked and solidified gel was removed from the mold and placed in a freeze dryer for 3 days to obtain a light and well-formed aerogel material;

[0106] (5) The prepared ultralight porous aerogel is placed in a 1M sodium citrate solution and soaked for one day to obtain a double-network tough hydrogel material with a micron porous structure.

[0107] Example 4

[0108] The present embodiment provides a food intelligent packaging material with buffering properties. The raw material components thereof are, by weight, 10.0 parts of polyvinyl alcohol; 2.5 parts of chitosan; 1.0 parts of anthocyanin crude extract; and 30 parts of nanosilver solution.

[0109] This embodiment provides a method for preparing a food intelligent packaging material with buffering performance, characterized by comprising the following steps:

[0110] Step 1: extracting a food freshness detection agent, namely anthocyanin crude extract;

[0111] Step 2: preparing nanosilver aqueous solution by green reduction method;

[0112] Step 3: Mix polyvinyl alcohol, chitosan, the crude anthocyanin extract prepared in step 1, and the nanosilver aqueous solution prepared in step 2 to prepare a high-strength and tough double-network hydrogel packaging material.

[0113] The step one comprises:

[0114] (1) Washing anthocyanin-rich bio-based raw materials, drying at 45° C., and grinding into small particles; the anthocyanin-rich bio-based raw materials include purple cabbage, mulberry, and black wolfberry;

[0115] (2) The ground anthocyanin raw material was mixed with an extraction solution at a mass ratio of 1:10 (w / w) and extracted at low temperature in the dark for 24 h; the extraction solution was an 80% (v / v) ethanol solution containing 1.0% (v / v) concentrated hydrochloric acid solution;

[0116] (3) The solution after 24 h of extraction was filtered and rotary distilled at 45 °C for 3 h;

[0117] (4) The concentrated solution obtained after rotary distillation is the crude anthocyanin extract, which should be stored in a refrigerated and dark environment.

[0118] The second step includes:

[0119] (1) Dissolve 0.1 g of carboxypropyl methylcellulose (HPMC) in 90 mL of ultrapure water in a 50°C water bath and stir evenly.

[0120] (2) Dissolve 0.1 g of silver nitrate in 10 mL of ultrapure water;

[0121] (3) The prepared 0.01 g / mL silver nitrate aqueous solution was added dropwise to the carboxypropyl methylcellulose (HPMC) aqueous solution, 2 g of anhydrous glucose was added, and the mixture was heated in a water bath at 80°C for 6 h;

[0122] (4) The above solution was dialyzed for seven days, changing the water twice a day.

[0123] The step three includes:

[0124] (1) Prepare a 12.5 wt.% polyvinyl alcohol / chitosan solution (PVA / CS), wherein the polyvinyl alcohol is 10.0 wt.% and the chitosan is 2.5 wt.%, and stir in a water bath at 90°C until uniform;

[0125] (2) Adjust the pH of the PVA / CS aqueous solution to 5.0, add 1 part by weight of anthocyanin crude extract and 30 parts by weight of nanosilver aqueous solution to 12.5 parts by weight of the PVA / CS aqueous solution, stir evenly, and ultrasonicate for 30 minutes;

[0126] (3) Pour the prepared solution into a mold and crosslink the gel in a low temperature environment of -20°C;

[0127] (4) The cross-linked and solidified gel was removed from the mold and placed in a freeze dryer for 3 days to obtain a light and well-formed aerogel material;

[0128] (5) The prepared ultralight porous aerogel is placed in a 1M sodium citrate solution and soaked for one day to obtain a double-network tough hydrogel material with a micron porous structure.

[0129] Example 5

[0130] The present embodiment provides a food intelligent packaging material with buffering properties. The raw material components thereof are, by weight, 12.0 parts of polyvinyl alcohol; 3.0 parts of chitosan; 1.5 parts of anthocyanin crude extract; and 40 parts of nanosilver solution.

[0131] This embodiment provides a method for preparing a food intelligent packaging material with buffering performance, characterized by comprising the following steps:

[0132] Step 1: extracting a food freshness detection agent, namely anthocyanin crude extract;

[0133] Step 2: preparing nanosilver aqueous solution by green reduction method;

[0134] Step 3: Mix polyvinyl alcohol, chitosan, the crude anthocyanin extract prepared in step 1, and the nanosilver aqueous solution prepared in step 2 to prepare a high-strength and tough double-network hydrogel packaging material.

[0135] The step one comprises:

[0136] (1) Washing anthocyanin-rich bio-based raw materials, drying at 45° C., and grinding into small particles; the anthocyanin-rich bio-based raw materials include purple cabbage, mulberry, and black wolfberry;

[0137] (2) The ground anthocyanin raw material was mixed with an extraction solution at a mass ratio of 1:10 (w / w) and extracted at low temperature in the dark for 24 h; the extraction solution was an 80% (v / v) ethanol solution containing 1.0% (v / v) concentrated hydrochloric acid solution;

[0138] (3) The solution after 24 h of extraction was filtered and rotary distilled at 45 °C for 3 h;

[0139] (4) The concentrated solution obtained after rotary distillation is the crude anthocyanin extract, which should be stored in a refrigerated and dark environment.

[0140] The second step includes:

[0141] (1) Dissolve 0.1 g of carboxypropyl methylcellulose (HPMC) in 90 mL of ultrapure water in a 50°C water bath and stir evenly.

[0142] (2) Dissolve 0.1 g of silver nitrate in 10 mL of ultrapure water;

[0143] (3) The prepared 0.01 g / mL silver nitrate aqueous solution was added dropwise to the carboxypropyl methylcellulose (HPMC) aqueous solution, 2 g of anhydrous glucose was added, and the mixture was heated in a water bath at 80°C for 6 h;

[0144] (4) The above solution was dialyzed for seven days, changing the water twice a day.

[0145] The step three includes:

[0146] (1) Prepare a 15.0 wt.% polyvinyl alcohol / chitosan solution (PVA / CS), wherein the polyvinyl alcohol is 12.0 wt.% and the chitosan is 3.0 wt.%, and stir in a water bath at 90°C until uniform;

[0147] (2) Adjust the pH of the PVA / CS aqueous solution to 5.0, add 1.5 parts by weight of anthocyanin crude extract and 40 parts by weight of nanosilver aqueous solution to 15 parts by weight of the PVA / CS aqueous solution, stir evenly, and ultrasonicate for 20 minutes;

[0148] (3) pouring the prepared composite solution into a mold and cross-linking the gel in a low temperature environment of -20°C;

[0149] (4) The cross-linked and solidified gel was removed from the mold and placed in a freeze dryer for 3 days to obtain a light and well-formed aerogel material;

[0150] (5) The prepared ultralight porous aerogel is placed in a 1M sodium citrate solution and soaked for one day to obtain a double-network tough hydrogel material with a micron porous structure.

[0151] The experimental data of the products obtained by the present invention are as follows:

[0152] Table 1 Mechanical properties of gel under full swelling

[0153]

[0154] Reference Figure 1 As can be seen, the gel prepared by the present invention has good formability, with a porous, double-layered network structure of 100-300 μm within the gel. The gel's molecular and micro-nanoscale structures contribute to its excellent mechanical and cushioning properties. Furthermore, the gel contains mulberry anthocyanins and nanosilver active substances, which impart visual freshness monitoring capabilities and antibacterial properties to the gel.

[0155] Reference Figure 2 It can be seen that the present invention can sensitively detect changes in the pH 2-12 environment of food.

[0156] Reference Figure 3 It can be seen that the present invention has obvious antibacterial effects on common foodborne bacteria Staphylococcus aureus and Escherichia coli.

[0157] Reference Figure 4 As can be seen, the product of the present invention has excellent mechanical properties, especially a minimum cushioning coefficient close to that of common porous cushioning packaging materials, demonstrating its cushioning and protective performance. Compared with homogeneous gel, the minimum cushioning coefficient of the porous gel obtained by the present invention is significantly lower.

[0158] Reference Figure 5 As can be seen, the gel padding of the present invention can provide protection for fresh apples and cherries, slowing or preventing tissue browning caused by external damage. This demonstrates the ability of the present invention to provide cushioning protection for fresh fruit and has the potential for application in food transport packaging.

[0159] This invention addresses the lack of functionality in traditional cushioning packaging and the lack of cushioning protection provided by hydrogel smart materials. By creating a packaging material that integrates cushioning protection with functionality, it achieves a multifunctional and lightweight packaging system. The raw materials used in this invention are widely available, inexpensive, safe, and environmentally friendly. Furthermore, it offers excellent cushioning and protection, enabling integrated packaging with cushioning protection, visual intelligent detection, and antimicrobial properties, minimizing food quality damage and reducing food safety threats.

[0160] This invention proposes a general strategy for preparing micron-scale uniformly porous hydrogel materials and applies it to functional hydrogel materials, imparting buffering and protective properties. Its active intelligent functions can also be expanded to oxygen-sensitive and antioxidant packaging by adding antioxidants, essential oils, and oxygen sensitizers. Applications can also be expanded to areas such as cultural relic preservation and biomedicine.

[0161] It will be easily understood by those skilled in the art that the above is only the best embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a food intelligent packaging material with buffering properties, characterized in that: The following steps are involved: Step 1: extracting a food freshness detection agent, namely anthocyanin crude extract; Step 2: preparing nanosilver aqueous solution by green reduction method; Step 3: Mixing polyvinyl alcohol, chitosan, the crude anthocyanin extract prepared in step 1, and the nanosilver aqueous solution prepared in step 2 to prepare a high-strength and tough double-network hydrogel packaging material; The step 1 specifically includes: (1) washing anthocyanin-rich bio-based raw materials, drying at 30-45° C., and grinding into small particles; the anthocyanin-rich bio-based raw materials include purple cabbage, mulberry, or black wolfberry; (2) grinding the anthocyanin extract raw material small particles and the extraction solution in a mass ratio of 1:5-1:30, and extracting at low temperature in the dark for 12-24 hours; the extraction solution is a 70-80% by volume ethanol solution containing a 0.5-1.5% by volume concentrated hydrochloric acid solution; (3) Filter the solution after extraction for 12-24 hours and perform rotary distillation at 35-45°C for 2-3 hours; (4) The concentrated solution obtained after rotary distillation is the crude anthocyanin extract, which should be stored in a refrigerated and dark environment; The second step specifically includes: (1) Dissolve 0.1-0.3 parts by weight of carboxypropyl methylcellulose (HPMC) in 90-270 parts by weight of ultrapure water in a water bath at 45-55°C and stir evenly; (2) dissolving 0.1-0.3 parts by weight of silver nitrate in 10-30 parts by weight of ultrapure water; (3) adding the silver nitrate aqueous solution dropwise to the carboxypropyl methylcellulose (HPMC) aqueous solution, adding 2-6 parts by weight of anhydrous glucose, and heating in a water bath at 75-80° C. for 5-7 hours; (4) dialyze the solution for 7-8 days, changing the water 2-3 times a day; The step three specifically includes: (1) Prepare a 5-15 wt.% polyvinyl alcohol / chitosan aqueous solution, i.e., a PVA / CS aqueous solution; stir in a water bath at 85-100°C until uniform; (2) Adjust the pH of the PVA / CS aqueous solution to 5.0-6.0; add 0.5-1.5 parts by weight of anthocyanin crude extract and 10-40 parts by weight of nanosilver aqueous solution to 5.0-15.0 parts by weight of the PVA / CS aqueous solution, stir evenly, and ultrasonicate for 20-30 minutes; (3) pouring the prepared solution into a mold and cross-linking the gel in a low temperature environment of -10-30°C; (4) taking the cross-linked solidified gel out of the mold and drying it in a freeze dryer for 2-3 days to obtain a light and well-formed aerogel material; (5) The prepared ultralight porous aerogel is placed in a 0.5-1M sodium citrate solution and soaked for one day to obtain a double-network tough hydrogel material with a micron porous structure.

2. The intelligent food packaging material with cushioning properties according to claim 1, characterized in that: The raw material components are calculated by weight as follows: polyvinyl alcohol: 6 parts; chitosan: 1.5 parts; anthocyanin crude extract: 1.0 parts; and nano silver solution: 10 parts.

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