Intelligent aerogel capable of being repeatedly used for indicating volatile biogenic amine and preparation method thereof

Abstract

The invention belongs to the field of intelligent aerogel, and discloses intelligent aerogel capable of being repeatedly used for indicating volatile biogenic amine and a preparation method of the intelligent aerogel. An anthocyanin natural extract is used as a specific color-sensitive responder of volatile biogenic amine, a naturally degradable cellulose material and a hydrophilic polymer are used as base materials of the intelligent aerogel, an edible plasticizer is used as a processing aid, and water is used as a solvent system of the material. And preparing the aerogel material for packaging the anthocyanin by adopting a directional freezing-vacuum freeze drying process. The intelligent aerogel prepared by the preparation method disclosed by the invention has the application advantages of being recyclable, high in indication (detection) sensitivity, low in detection limit, quick to use, high in use safety and capable of instantly identifying the existence and the concentration of the volatile biogenic amine by naked eyes.

Description

Technical Field

[0001] The invention belongs to the field of smart aerogels, and in particular relates to a smart aerogel which can be repeatedly used to indicate volatile biogenic amines, and also relates to a preparation method of the smart aerogel. Background Art

[0002] Volatile biogenic amines are a class of low molecular weight organic bases that are mostly produced in stale protein-rich foods. When present in high concentrations, they can cause adverse reactions such as dizziness, nausea, and retching. In severe cases, they can damage the respiratory mucosa and the nervous system, which poses a great threat to human health. Therefore, it is necessary to detect the content of volatile biogenic amines in real time and accurately. At present, there are two main types of methods for detecting / indicating the presence and concentration of volatile biogenic amines: (1) "High-precision" instruments and equipment such as gas chromatographs, ion chromatographs or electronic noses, which have the advantages of high sensitivity, high precision and ultra-low detection limits, such as CN 114594153 A, CN 114334017 A, etc., but they have the disadvantages of expensive equipment, complex and time-consuming detection, and inability to perform on-site / non-destructive / real-time detection. (2) Intelligent indication (detection) materials, such as CN 114624290 B, CN111472092 A, CN 118326621A, CN 117907302A, CN 112852001B, etc. Compared with the first method, intelligent indication (detection) materials are more in line with the market demand for instant non-destructive detection of volatile biogenic amines. Most of them use substrates to load substances that specifically respond to biogenic amines to achieve the purpose of indication / detection. They all have the advantages of quick use and instant identification, but they still have shortcomings in terms of material environmental protection, detection sensitivity and safety of use. The sensing film described in CN114624290 B has the disadvantages of poor environmental protection and low production efficiency due to the fact that the polypyrrole substrate used is not naturally degradable and the preparation process is complicated; the smart label described in CN 111472092 A uses chemically synthesized indicator dyes (such as phenolphthalein, methyl red, bromocresol green, perylene diimide, etc.) and volatile toxic solvents (such as hexafluoroisopropanol, acetone, trifluoroethanol, trifluoroacetic acid, acetone or chloroform, etc.), resulting in poor detection sensitivity of the smart label and food safety risks and production risks; the smart indicator label described in CN 118326621 A uses nano-TiO2 that is easy to agglomerate, which results in poor detection sensitivity of the smart label and food safety risks. The carbon quantum dots described in CN 117907302 A need to be roughly loaded on filter paper in advance by a "soaking-air-drying" method and used with an ultraviolet lamp when indicating the presence of biogenic amines, which results in a higher recognition difficulty, poor indication sensitivity and a higher detection limit. Summary of the invention

[0003] The object of the present invention is to provide a smart aerogel that can be repeatedly used to indicate volatile biogenic amines and a preparation method thereof. The smart aerogel has the application advantages of being recyclable, having high indication (detection) sensitivity, having a low detection limit, being quick to use, having high safety in use, and being able to instantly identify the presence and concentration of volatile biogenic amines with the naked eye, thereby solving the material defects of smart materials for indicating (detecting) volatile biogenic amines that are not recyclable or not naturally degradable, and also solving the application drawbacks of such smart materials, such as poor indication (detection) sensitivity, high detection limit, weak stability, and poor safety.

[0004] The present invention is achieved through the following technical solutions:

[0005] The present invention provides a method for preparing an intelligent aerogel that can be repeatedly used to indicate volatile biogenic amines. The method is characterized in that anthocyanin natural extract is used as a specific color-sensitive responder for volatile biogenic amines, naturally degradable cellulose materials and hydrophilic polymers are used as substrates of the intelligent aerogel, an edible plasticizer is used as a processing aid, water is used as a solvent system of the material, and a directional freezing-vacuum freeze-drying process is used to prepare an aerogel material encapsulating anthocyanins.

[0006] The specific steps are as follows:

[0007] (1) Preparation of pigment solution: adding anthocyanin natural extract to deionized water, with the mass ratio of anthocyanin to deionized water being 1:1-15, and stirring at a constant temperature of 25-30° C. until completely dissolved to obtain a pigment solution;

[0008] (2) Preparation of substrate solution: Add cellulose material to deionized water, stir at 200-500 r / s for 20-60 min at 20-30° C. using a heated magnetic stirrer; continue stirring and raise the heating temperature to 85-95° C., then add a hydrophilic polymer and an edible plasticizer and continue stirring for 2-3 h to obtain a substrate solution;

[0009] (3) Preparation of mixed base liquid: adding the pigment solution to the base material solution cooled to room temperature and stirring at a constant temperature of 25 to 30° C. until uniformly mixed to obtain a mixed base liquid;

[0010] (4) Preparation of smart aerogel: Use a high-speed shearing machine to disperse the mixed base liquid; then, pour the dispersion into a shaping mold, and then place the mold in a directional freezing device with a unidirectional temperature gradient distribution for directional freezing, and then take it out of the mold without damage.

[0011] Specifically, the anthocyanin natural extract is one or more of the anthocyanin natural extracts from grape skin, morning glory petals, mulberry fruit, blueberry fruit, and purple sweet potato rhizome; purity: ≥85%.

[0012] The cellulose material is selected from one or more of microfibrillated cellulose, cellulose nanofibers, and cellulose nanocrystals;

[0013] The hydrophilic polymer is selected from one or more of polyvinyl alcohol and polyvinyl alcohol ether;

[0014] The edible plasticizer is selected from one or more of glycerol, sorbitol, xylitol, maltitol, sucrose and glucose.

[0015] In a specific embodiment, in step (3), the cellulose material accounts for 3.0-15.0% of the mass of the mixed base liquid; the hydrophilic polymer accounts for 9.0-30.0% of the mass of the mixed base liquid; the plasticizer accounts for 5.0-10.0% of the mass of the mixed base liquid; and the anthocyanin natural extract accounts for 0.01-1.5% of the mass of the mixed base liquid.

[0016] In step (4), the mixed base liquid is dispersed at a speed of 3500 to 7500 r / s for 10 to 30 min using a high-speed shearing machine;

[0017] The shaping mold is a cylinder or a cuboid;

[0018] The directional freezing is to contact the bottom of the mold with a metal block (red copper block / brass block / pure copper block) in a directional freezing device, and the metal block plays a role of directional freezing. The directional freezing temperature is -70 to -196°C and the freezing time is 30 to 120 minutes. Subsequently, the mold is quickly transferred to a vacuum freeze dryer for freeze drying. When the vacuum freeze dryer is working, the internal environment temperature is -50 to -20°C, the water replenishment cold trap temperature is -70 to -45°C, the time is 48 to 72 hours, and the vacuum degree is 5 to 20Pa.

[0019] Optionally, the method further comprises cutting the smart aerogel as required to obtain a smart aerogel with a thickness of 40 μm to 10 mm, wherein the cutting direction is perpendicular to the process direction of directional freezing.

[0020] The invention provides an intelligent aerogel obtained by the preparation method and capable of being repeatedly used for indicating volatile biogenic amines.

[0021] The present invention also provides the use of the smart aerogel that can be repeatedly used to indicate volatile biogenic amines in judging the presence or concentration of volatile biogenic amines in a sealed space, specifically for instant judgment by naked eyes.

[0022] The present invention also provides a method for judging the presence or concentration of volatile biogenic amines in a sealed space, characterized in that a smart aerogel as described above that can be repeatedly used to indicate volatile biogenic amines (such as dimethylamine, trimethylamine, putrescine, cadaverine or methylamine, etc.) is placed in the sealed space, and the presence or concentration of the volatile biogenic amines can be instantly judged by the naked eye based on the color change of the smart aerogel.

[0023] Specifically, the smart aerogel gradually changes color from pink-purple to blue-green, corresponding to a detection limit of volatile biogenic amines of ≤1ppm and a concentration of 0 to 200ppm; more specifically, the color change from pink-purple to blue-green corresponds to a concentration of volatile biogenic amines of 0ppm→200ppm.

[0024] More specifically, the method includes:

[0025] Put the product to be tested and the smart aerogel into a sealed box / bag, or put the smart aerogel into the sealed package of the product to be tested, and judge the volatile biogenic amine content according to the color change of the smart aerogel after 1 minute;

[0026] Alternatively, the smart aerogel is pasted inside a commodity package and used without direct contact with the packaged commodity, and the presence or content of volatile biogenic amines inside the package can be determined based on its color change.

[0027] Compared with the prior art, the present invention has the following beneficial technical effects:

[0028] 1. The presence and concentration of volatile biogenic amines (0-200 ppm) can be instantly identified by naked eye: Figure 1 and Figure 3 .Depend on Figure 1 It can be seen that before the test, the smart aerogel was still pink-purple after being stored at room temperature and under normal lighting conditions for 10 days and had a specific color change response to volatile biogenic amines; during the test, the smart aerogel was placed in a 10ppm trimethylamine atmosphere for 1 minute and turned into a uniform dark blue-green color; after the test, the smart aerogel was placed in fresh air for 15 minutes and returned to the pink-purple state before the test and still had a specific color change response to volatile biogenic amines; repeating the above operation can still get the above conclusion. Figure 3 It can be seen that the smart aerogel maintains its original pink-purple color in a 0ppm dimethylamine / trimethylamine atmosphere, and gradually turns into blue-green in a 1, 3, 5, 10, 50, 100, and 200ppm dimethylamine / trimethylamine atmosphere, and the degree of blue-green color deepens with the increase of the concentration of volatile biogenic amines. This proves that the present invention successfully utilizes aerogels to embed anthocyanins that specifically change color in response to volatile biogenic amines, and judges the presence of volatile biogenic amines by the change of the overall color of the smart aerogel. The concentration of volatile biogenic amines can also be indirectly determined by identifying the degree of color change of the smart aerogel with the help of a colorimeter.

[0029] 2. High indication (detection) sensitivity, wide detection range (0-200ppm) and low target detection limit (≤1ppm): Please refer to Figure 2 and Figure 3 .Depend on Figure 2It can be seen that the smart aerogel has a honeycomb-shaped, vertically connected, nanometer-sized pore structure and no detached, powdery / granular pigment particles or lumps are observed. Figure 3 It can be seen that the smart aerogel maintains its original pink-purple color in a 0ppm dimethylamine and trimethylamine atmosphere, and gradually turns into blue-green in a 1, 3, 5, 10, 50, 100, 200ppm dimethylamine and trimethylamine atmosphere, and the degree of blue-green color it exhibits deepens with the increase of the concentration of volatile biogenic amines. This proves that the detection limit of the smart aerogel described in the present invention for volatile biogenic amines is ≤1ppm, and the detection range is 0-200ppm; at the same time, it also proves that the present invention utilizes the high porosity, high specific surface area, ultra-low density, low thermal conductivity and other characteristics of aerogel materials, which acts as a physical barrier while encapsulating anthocyanins to reduce the probability of active substances being exposed to oxygen, heat and strong light environments, and also avoids anthocyanins from being destroyed or dissolved from the substrate due to light, high temperature and contact with liquids, thereby improving the stability of anthocyanins. The aerogel prepared using the directional freezing-vacuum freeze-drying process has bottom-up, transparent nano / micro / mesopores, which use the capillary siphon effect of the pores to achieve rapid enrichment and transfer of volatile biogenic amines, thereby improving the response sensitivity and response stability of anthocyanins to volatile biogenic amines, thereby making the smart aerogel exhibit high indication (detection) sensitivity and low target detection limit.

[0030] 3. Recyclable (≥11 times of cycle detection that can be instantly identified by naked eyes): Please refer to Figure 1 and Figure 4 .Depend on Figure 1 It can be seen that before the test, the smart aerogel was still pink-purple after being stored at room temperature and under normal lighting conditions for 10 days and had a specific color change response to volatile biogenic amines; during the test, the smart aerogel was placed in a 10ppm trimethylamine atmosphere for 1 minute and turned into a uniform dark blue-green color; after the test, the smart aerogel was placed in fresh air for 15 minutes and returned to the pink-purple state before the test and still had a specific color change response to volatile biogenic amines; repeating the above operation can still get the above conclusion. Figure 4It can be seen that after the smart aerogel completes the color development test of 5ppm dimethylamine / trimethylamine, it can be restored to its original state and maintain the specific color change response to volatile biogenic amines after being placed in fresh air for 300s; in addition, the smart aerogel can still be restored to its original state and maintain the specific color change response to volatile biogenic amines after repeated detection of volatile biogenic amines (11 times), and the total color deviation difference (ΔΔE) of each color development indication of the smart aerogel during the entire cycle detection process is less than 5 (ΔΔE<5 means that there is no color difference between the two color samples in the naked eye). This proves that the present invention uses a substrate to embed anthocyanins, which will not cause anthocyanins to directly bind to biogenic amines to cause irreversible response color change, but will cause physical co-pigmentation reversible response color change between anthocyanins, substrates and biogenic amines, which gives the smart aerogel a recyclable indication / detection property.

[0031] 4. High safety and environmental protection: The smart aerogel described in the present invention uses anthocyanin natural extract as a specific color-sensitive responder of volatile biogenic amines, naturally degradable cellulose materials and hydrophilic polymers as substrates, edible plasticizers as processing aids, and water as the solvent system of the material. Directional freezing-vacuum freeze-drying is used to prepare anthocyanin-encapsulated aerogel material, which significantly improves the environmental protection and safety of the smart aerogel.

[0032] It is particularly noteworthy that the ammonia sensing aerogel described in CN 112852001 B and the smart aerogel described in the present invention have similar macroscopic material characteristics, but there are essential differences between the two: (1) The ammonia sensing aerogel described in patent CN 112852001 B is developed and designed for indicating inorganic amines - ammonia, while the smart aerogel described in the present invention is developed and designed for indicating and detecting volatile bio (organic) amines - dimethylamine, trimethylamine, etc.; (2) The color-sensitive responder used in the ammonia sensing aerogel described in CN 112852001 B is radish red pigment, while the color-sensitive responder used in the smart aerogel described in the present invention is anthocyanin. The two are different types of color-sensitive substances with color-changing responses, and the color change of anthocyanin is richer and more sensitive; (3) CN 112852001 The ammonia sensing aerogel described in B is a disordered pore structure, and the pores contained therein are mostly micrometer-sized, while the smart aerogel described in the present invention is a honeycomb-shaped, vertically connected pore structure, and the pores contained therein are mostly nanometer-sized; compared with the two, the nanoscale honeycomb-shaped, vertically connected pore structure has a faster and more efficient siphon effect (enrichment) on the gas, which makes the smart aerogel described in the present invention have a lower detection limit and more sensitive detection sensitivity. In addition, most of the existing smart indication (detection) products (patents) are disposable indication / detection products, which causes a huge waste of resources. In summary, there is an urgent need for a recyclable, high indication (detection) sensitivity, low target detection limit, high safety of use, and an indication material for volatile biogenic amines that can be judged instantly by the naked eye. To this end, the present invention proposes to use natural anthocyanin extracts as specific color-sensitive responders for volatile biogenic amines, and adopt a naturally degradable substrate through a directional freezing-vacuum freeze-drying process to prepare anthocyanin-encapsulated smart aerogel, which can be repeatedly used to indicate the presence and concentration of volatile biogenic amines. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without paying any creative work.

[0034] Figure 1 The corresponding states of the smart aerogel of the present invention before detection (standing for 10 days under normal lighting conditions at room temperature), during detection (standing for 1 minute in a 10 ppm trimethylamine atmosphere) and after detection (standing for 15 minutes in fresh air). Note: △△E>5 means that there is a color difference between the two color samples in naked eye vision.

[0035] Figure 2The scanning electron microscope images of the interior of the smart aerogel of the present invention are magnified 250 times and 1500 times.

[0036] Figure 3 The color performance of the smart aerogel of the present invention in the atmosphere of dimethylamine and trimethylamine with different concentrations. Note: △△E>5 means that there is a color difference between the two color samples in naked eye vision.

[0037] Figure 4 The color change curve of the smart aerogel of the present invention after standing in fresh air for 300 seconds after completing the color change detection and the color difference curve of repeated detection of volatile biogenic amines (11 times). Note: △△E>5 means that there is a color difference between the two color samples in naked eye vision. DETAILED DESCRIPTION

[0038] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions 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 are within the scope of protection of the present invention.

[0039] Embodiment 1:

[0040] The method for preparing the smart aerogel that can be repeatedly used to indicate volatile biogenic amines in this embodiment comprises the following steps:

[0041] S1: Add 1.5 g of natural extract of grape skin anthocyanins (purity: 90%) into 15 g of deionized water, and stir at a constant temperature of 28° C. until completely dissolved to obtain a pigment solution.

[0042] S2: Add 8 g of cellulose nanofibers into a beaker containing 40.5 g of deionized water, and stir at 350 r / s for 50 min at 28 °C using a heated magnetic stirrer; continue stirring and raise the temperature to 95 °C, then add 25 g of polyvinyl alcohol ether and 10 g of sorbitol into the beaker, and continue stirring for 3 h to obtain a substrate solution.

[0043] S3: Add the pigment solution to the base material solution, and stir at a constant temperature of 25°C until uniformly mixed to obtain a mixed base solution.

[0044] S4: Use a high-speed shearing machine to disperse the mixed base liquid at a speed of 6000r / s for 15min, pour the dispersion into a rectangular mold, and then put the mold into a directional freezing device for directional freezing. The directional freezing temperature is -120℃ and the directional freezing time is 80min. Subsequently, the mold is smoothly and quickly transferred to a vacuum freeze dryer for freeze drying. The internal environment temperature is -45℃, the water replenishment cold trap temperature is -60℃, the time is 36h, and the vacuum degree is 15Pa.

[0045] S5: After vacuum freeze-drying, the mold is taken out and non-destructively peeled off to obtain a rectangular smart aerogel, which is then cut into sheets with a thickness of 1 mm in a direction perpendicular to the process direction of directional freezing for use.

[0046] Embodiment 2:

[0047] The method for preparing the smart aerogel that can be repeatedly used to indicate volatile biogenic amines in this embodiment comprises the following steps:

[0048] S1: Add 0.1 g of morning glory petal-anthocyanin natural extract (purity: 90%) into 10 g of deionized water, and stir at a constant temperature of 30° C. until completely dissolved to obtain a pigment solution.

[0049] S2: Add 12 g of microfibrillated cellulose into a beaker containing 39.4 g of deionized water, and stir at 350 r / s for 35 min at 30 °C using a heated magnetic stirrer; continue stirring and raise the temperature to 85 °C, then add 30 g of polyvinyl alcohol and 8.5 g of glucose into the beaker, and continue stirring for 2 h to obtain a substrate solution.

[0050] S3: Add the pigment solution to the base material solution, and stir at a constant temperature of 30°C until uniformly mixed to obtain a mixed base solution.

[0051] S4: Use a high-speed shearing machine to disperse the mixed base liquid at a speed of 7500r / s for 10 minutes, pour the dispersion into a cylindrical mold, and then put the mold into a directional freezing device for directional freezing. The directional freezing temperature is -90°C and the directional freezing time is 100 minutes. Subsequently, the mold is smoothly and quickly transferred to a vacuum freeze dryer for freeze drying. The internal environment temperature is -45°C, the water replenishment cold trap temperature is -60°C, the time is 72 hours, and the vacuum degree is 18Pa.

[0052] S5: After vacuum freeze drying, the mold is taken out and non-destructively peeled off to obtain a cylindrical smart aerogel, which can be directly used for the indication detection of volatile biogenic amines or cut into sheets with a thickness of 0.5 mm in a direction perpendicular to the process direction of directional freezing.

[0053] Embodiment 3:

[0054] The method for preparing the smart aerogel that can be repeatedly used to indicate volatile biogenic amines in this embodiment comprises the following steps:

[0055] S1: 0.25 g of mulberry-anthocyanidin natural extract (purity: 90%) was added to 6.75 g of deionized water, and stirred at a constant temperature of 28° C. until completely dissolved to obtain a pigment solution.

[0056] S2: Add 5 g of cellulose nanocrystals into a beaker containing 69 g of deionized water, and stir at 450 r / s for 50 min at 28 °C using a heated magnetic stirrer; continue stirring and raise the temperature to 90 °C, then add 12 g of polyvinyl alcohol and 7 g of sorbitol into the beaker, and continue stirring for 3 h to obtain a substrate solution.

[0057] S3: Add the pigment solution to the base material solution, and stir at a constant temperature of 28°C until uniformly mixed to obtain a mixed base solution.

[0058] S4: Use a high-speed shearing machine to disperse the mixed base liquid at a speed of 5500r / s for 15min, pour the dispersion into a rectangular mold, and then put the mold into a directional freezing device for directional freezing. The directional freezing temperature is -160℃ and the directional freezing time is 10min. Subsequently, the mold is smoothly and quickly transferred to a vacuum freeze dryer for freeze drying. The internal environment temperature is -50℃, the water replenishment cold trap temperature is -65℃, the time is 72h, and the vacuum degree is 16Pa.

[0059] S5: After vacuum freeze-drying, the mold is taken out and non-destructively peeled off to obtain a rectangular smart aerogel, which can be directly used for the indicator detection of volatile biogenic amines.

[0060] Embodiment 4:

[0061] The method for preparing the smart aerogel that can be repeatedly used to indicate volatile biogenic amines in this embodiment comprises the following steps:

[0062] S1: Add 0.1 g of purple sweet potato-anthocyanin natural extract (purity: 90%) to 3 g of deionized water, and stir at a constant temperature of 26° C. until completely dissolved to obtain a pigment solution.

[0063] S2: Add 8 g of cellulose nanofibers into a beaker containing 52.9 g of deionized water, and stir at 350 r / s for 20 min at 26 °C using a heated magnetic stirrer; continue stirring and raise the temperature to 85 °C, then add 26 g of polyvinyl alcohol and 10 g of glycerol into the beaker, and continue stirring for 2 h to obtain a substrate solution.

[0064] S3: Add the pigment solution to the base material solution, and stir at a constant temperature of 26°C until uniformly mixed to obtain a mixed base solution.

[0065] S4: Use a high-speed shearing machine to disperse the mixed base liquid at a speed of 5000r / s for 10min, pour the dispersion into a cylindrical mold, and then put the mold into a directional freezing device for directional freezing. The directional freezing temperature is -80℃ and the directional freezing time is 120min. Subsequently, the mold is smoothly and quickly transferred to a vacuum freeze dryer for freeze drying. The internal environment temperature is -55℃, the water replenishment cold trap temperature is -70℃, the time is 72h, and the vacuum degree is 6Pa.

[0066] S5: After vacuum freeze-drying, the mold is taken out and peeled off without loss to obtain a cylindrical smart aerogel, which is then cut into sheets with a thickness of 5 mm in a direction perpendicular to the process direction of directional freezing for use.

[0067] Embodiment 5:

[0068] See also Figure 1 The present invention is directed to the smart aerogel prepared in the above-mentioned Example 1 and repeatedly used to indicate volatile biogenic amines. The corresponding states before the detection (standing for 10 days under normal lighting conditions at room temperature), during the detection (standing for 1 minute under 10 ppm trimethylamine atmosphere) and after the detection (standing for 15 minutes under fresh air) are as follows: Figure 1 As shown. The detection method steps are as follows: before detection, the smart aerogel is stored in a transparent sealed box with a volume of 300mL for 10d; during detection, a sealed box with a volume of 3L and an air outlet is used as a trimethylamine gas volatilization device with a constant concentration, 2mL of trimethylamine solution and 40mL of distilled water are weighed and added to the sealed box, so that the mixed liquid of the two covers the bottom of the sealed box, and a heated magnetic stirrer is used to stir continuously at 700r / s for 30min at 25°C to make the trimethylamine vapor pressure in the headspace of the sealed box reach a stable saturated state, and then the smart aerogel (sheet) prepared in Example 1 is placed at the air outlet of the sealed box, the air outlet is opened to place the smart aerogel in a 10ppm trimethylamine atmosphere for 1min, and then the air outlet is closed; after detection, the smart aerogel is placed in fresh air for 15min. By Figure 1 It can be seen that before the test, the smart aerogel was still pink-purple after being stored under normal lighting conditions at room temperature for 10 days and had a specific color change response to volatile biogenic amines; during the test, the smart aerogel was uniformly dark blue-green after being allowed to stand in a 10ppm trimethylamine atmosphere for 1 minute; after the test, the smart aerogel was allowed to stand in fresh air for 15 minutes and then returned to its pink-purple state before the test and still had a specific color change response to volatile biogenic amines; the above conclusion can still be obtained by repeating the above operations.

[0069] This proves that the present invention uses aerogels to embed anthocyanins that specifically change color in response to volatile biogenic amines, and the presence of volatile biogenic amines can be judged by the change in the overall color of the smart aerogels. The concentration of volatile biogenic amines can also be indirectly determined by identifying the degree of color change of the smart aerogels with the help of a colorimeter. This shows that the smart aerogels provided by the present invention can instantly identify volatile biogenic amines with the naked eye and have good storage stability, detection sensitivity, detection stability and reusability.

[0070] Embodiment 6:

[0071] See also Figure 2 The present invention is directed to the smart aerogel prepared in the above-mentioned Example 3 and can be repeatedly used to indicate volatile biogenic amines. The scanning electron microscope images of the interior thereof at 250 times and 1500 times magnification are as follows: Figure 2 The observation method is as follows: soak the smart aerogel in liquid nitrogen for 5 minutes, then break it in the longitudinal direction to form a natural longitudinal section. The cross section is obtained using the same method. Use conductive double-sided tape to fix it on a conductive table and place it in a magnetron DC sputtering coating machine for gold spraying. The spraying metal type is platinum. The time is 5 minutes. Finally, use a scanning electron microscope at an acceleration voltage of 15kV to scan and observe its longitudinal cross-sectional characteristics. Figure 2 It can be seen that the smart aerogel has a honeycomb-shaped, nanometer-scale pore structure that runs through from top to bottom, and no detached, powdery / granular pigment particles or lumps are observed. This proves that the present invention utilizes the high porosity, high specific surface area, ultra-low density, low thermal conductivity and other characteristics of aerogel materials, and acts as a physical barrier while embedding anthocyanins to reduce the probability of exposure to oxygen, heat and strong light environments, and avoids anthocyanins from being destroyed or dissolved from the substrate due to light, high temperature and contact with liquid, thereby improving the stability of anthocyanins. The aerogel prepared using a directional freezing-vacuum freeze-drying process has bottom-up, transparent nano / micro / mesopores, and uses the capillary siphon effect of the pores to achieve rapid enrichment and transfer of volatile biogenic amines, thereby improving the response sensitivity and response stability of anthocyanins to volatile biogenic amines. This shows that the smart aerogel provided by the present invention has a low detection limit, good detection sensitivity, storage stability and detection stability for the indication (detection) of volatile biogenic amines.

[0072] Embodiment 7:

[0073] See also Figure 3 The present invention is directed to the detection of the intelligent aerogel prepared in the above-mentioned embodiment 2 and can be repeatedly used to indicate volatile biogenic amines. The color performance of the aerogel in the atmosphere of dimethylamine and trimethylamine with different concentrations is as follows: Figure 3As shown. The detection method steps are as follows: Use a sealed box with a volume of 3L and an air outlet as a trimethylamine gas volatilization device with a constant concentration, weigh 0 / 0.2 / 0.6 / 1.0 / 2.0 / 10.0 / 20.0 / 40.0mL of trimethylamine solution and 40mL of distilled water and add them into the sealed box so that the mixed liquid covers the bottom of the sealed box, use a heated magnetic stirrer to stir continuously at 700r / s for 30min at 25°C to make the trimethylamine vapor pressure in the air space of the sealed box reach a stable saturated state, then place the smart aerogel (sheet) prepared in Example 2 at the air outlet of the sealed box, open the air outlet to place the smart aerogel in a 0 / 1 / 3 / 5 / 10 / 50 / 100 / 200ppm trimethylamine atmosphere for 1min, and then close the air outlet. By Figure 3 It can be seen that the smart aerogel has different color performance in the atmosphere of dimethylamine and trimethylamine at 0, 1, 3, 5, 10, 50, 100, and 200 ppm. The smart aerogel maintains the original pink-purple color in the atmosphere of dimethylamine and trimethylamine at 0 ppm, and gradually turns into blue-green in the atmosphere of dimethylamine and trimethylamine at 1, 3, 5, 10, 50, 100, and 200 ppm, and the degree of blue-green color exhibited by the smart aerogel deepens with the increase of the concentration of volatile biogenic amines. This proves that the detection limit of the smart aerogel described in the present invention for volatile biogenic amines is ≤1ppm, and the detection range is 0 to 200ppm. This shows that the smart aerogel provided by the present invention has the characteristics of high detection sensitivity, low target detection limit, high efficiency and portability, identification and judgment by naked eye, wide detection range, and the ability to roughly judge the content of the target in the detection environment with the help of a colorimeter.

[0074] Embodiment 8:

[0075] See also Figure 4 The present invention is directed to the smart aerogel prepared in the above-mentioned Example 4 and capable of being repeatedly used to indicate volatile biogenic amines. The color change curve of the aerogel after standing in fresh air for 300 seconds after the color change detection is completed and the color difference curve of the repeated detection of volatile biogenic amines (11 times) are shown as follows: Figure 4As shown. The detection method steps are as follows: Use a sealed box with a volume of 3L and an air outlet as a trimethylamine gas volatilization device with a constant concentration, weigh 1mL of trimethylamine solution and 40mL of distilled water and add them into the sealed box so that the mixed liquid covers the bottom of the sealed box, use a heated magnetic stirrer to stir continuously at 700r / s for 30min at 25°C to make the trimethylamine vapor pressure in the headspace of the sealed box reach a stable saturated state, then place the smart aerogel (sheet) prepared in Example 4 at the air outlet of the sealed box, open the air outlet so that the smart aerogel is placed in a 5ppm trimethylamine atmosphere for 1min, and then close the air outlet. After the detection, place the smart aerogel in fresh air for 5min; then, place the smart aerogel back at the air outlet of the sealed box, open the air outlet so that the smart aerogel is placed in a 5ppm trimethylamine atmosphere for 1min, close the air outlet, and then place the smart aerogel in fresh air for 5min, and repeat this operation 10 times. By Figure 4 It can be seen that after the smart aerogel completes the color development test of 5ppm dimethylamine / trimethylamine, it can be restored to its original state and maintain the specific color change response to volatile biogenic amines after being placed in fresh air for 300s; in addition, the smart aerogel can still be restored to its original state and maintain the specific color change response to volatile biogenic amines after repeated detection of volatile biogenic amines (11 times), and the total color deviation difference (ΔΔE) of each color development indication of the smart aerogel during the entire cycle detection process is less than 5 (ΔΔE<5 means that there is no color difference between the two color samples in the naked eye). This proves that the present invention uses a substrate to embed anthocyanins, so that anthocyanins do not directly contact volatile biogenic amines to produce chemically combined irreversible response color change, but instead cause physical co-pigmentation reversible response color change between anthocyanins, substrates and volatile biogenic amines, which gives the smart aerogel good recyclability.

[0076] Comparative Example 1

[0077] On the basis of the above-mentioned embodiments, this comparative example provides the advantages and disadvantages of the smart aerogel that can be repeatedly used to indicate volatile biogenic amines described in the present invention and other ways / methods for detecting / indicating volatile biogenic amines in terms of usage / functional characteristics.

[0078]

[0079] Through the above comparison, it can be seen that the smart aerogel provided by this patent is slightly inferior to ion chromatographs or electronic noses in terms of sensitivity in indicating / detecting volatile biogenic amines, but is significantly better than existing related smart indicating (detecting) materials. On this basis, the unique advantage of the smart aerogel provided by this patent is that it can be repeatedly used to indicate volatile biogenic amines; at the same time, it also has the advantages of being easy and fast to use, low target detection limit, high safety in use, and the ability to instantly determine the presence and concentration of volatile biogenic amines with the naked eye, and green and environmentally friendly materials.

Claims

1. A method for preparing a smart aerogel that can be repeatedly used to indicate volatile biogenic amines, characterized in that: Anthocyanin natural extracts are used as specific color-sensitive responders for volatile biogenic amines, naturally degradable cellulose materials and hydrophilic polymers are used as the substrates of smart aerogels, edible plasticizers are used as processing aids, and water is used as the solvent system of the material. A directional freezing-vacuum freeze-drying process is used to prepare anthocyanin-encapsulated aerogel material.

2. The preparation method according to claim 1, characterized in that The specific steps are as follows: (1) Preparation of pigment solution: add anthocyanin natural extract to deionized water, the mass ratio of anthocyanin to deionized water is 1:1-15, and stir at a constant temperature of 25-30°C until completely dissolved to obtain a pigment solution; (2) Preparation of substrate solution: Add cellulose material to deionized water and stir at 200-500 r / s for 20-60 min at 20-30°C using a heated magnetic stirrer; continue stirring and raise the heating temperature to 85-95°C, then add a hydrophilic polymer and an edible plasticizer and continue stirring for 2-3 h to obtain a substrate solution; (3) Preparation of mixed base liquid: Add the pigment solution to the substrate solution cooled to room temperature and stir at a constant temperature of 25-30°C until uniformly mixed to obtain a mixed base liquid; (4) Preparation of smart aerogel: Use a high-speed shear machine to disperse the mixed base liquid; then, pour the dispersion into a shaping mold, and then place the mold in a directional freezing device with a unidirectional temperature gradient distribution for directional freezing, and then take it out of the mold without damage.

3. The preparation method according to claim 2, characterized in that: The anthocyanin natural extract is one or more of anthocyanin natural extracts such as grape skin, morning glory petals, mulberry fruit, blueberry fruit, and purple sweet potato rhizome; Purity: ≥85%.

4. The preparation method according to claim 2, characterized in that: The cellulose material is selected from one or more of microfibrillated cellulose, cellulose nanofibers, and cellulose nanocrystals; The hydrophilic polymer is selected from one or more of polyvinyl alcohol and polyvinyl alcohol ether; The edible plasticizer is selected from one or more of glycerol, sorbitol, xylitol, maltitol, sucrose and glucose.

5. The preparation method according to claim 2, characterized in that: In step (3), the cellulose material accounts for 3.0-15.0% of the mass of the mixed base liquid; the hydrophilic polymer accounts for 9.0-30.0% of the mass of the mixed base liquid; the plasticizer accounts for 5.0-10.0% of the mass of the mixed base liquid; and the anthocyanin natural extract accounts for 0.01-1.5% of the mass of the mixed base liquid.

6. The preparation method according to claim 2, characterized in that: In step (4), the mixed base liquid is dispersed at a speed of 3500-7500 r / s for 10-30 min using a high-speed shearing machine; The shaping mold is a cylinder or a cuboid; The directional freezing is to contact the bottom of the mold with a metal block (red copper block / brass block / pure copper block) in a directional freezing device, and the metal block plays a role of directional freezing, the directional freezing temperature is -70~-196°C, and the freezing time is 30~120min; then, it is quickly transferred to a vacuum freeze dryer for freeze drying, and the vacuum freeze dryer is operated at an internal ambient temperature of -50~-20°C, a water replenishment cold trap temperature of -70~-45°C, a time of 48~72 h, and a vacuum degree of 5~20 Pa; Optionally, the method further comprises cutting the smart aerogel as needed to obtain a smart aerogel with a thickness of 40 μm to 10 mm, wherein the cutting direction is perpendicular to the process direction of directional freezing.

7. The smart aerogel obtained by the preparation method according to any one of claims 1 to 6 and can be repeatedly used to indicate volatile biogenic amines.

8. Use of the smart aerogel that can be repeatedly used to indicate volatile biogenic amines as claimed in claim 7 in judging the presence or concentration of volatile biogenic amines in a sealed space, specifically for instant judgment by naked eyes.

9. A method for determining the presence or concentration of volatile biogenic amines in a sealed space, characterized in that: Placing the smart aerogel that can be repeatedly used to indicate volatile biogenic amines as claimed in claim 7 in the sealed space, and instantly judging the presence or concentration of volatile biogenic amines by naked eyes according to the color change of the smart aerogel; Specifically, the volatile biogenic amine is dimethylamine, trimethylamine, putrescine, cadaverine or methylamine.

10. The method according to claim 9, characterized in that The color of the smart aerogel gradually changes from pink-purple to blue-green, corresponding to a detection limit of ≤ 1 ppm and a concentration of 0-200 ppm for volatile biogenic amines; more specifically, the color changes from pink-purple to blue-green, corresponding to a concentration of 0 ppm→200 ppm for volatile biogenic amines; More specifically, the method includes: Put the product to be tested and the smart aerogel into a sealed box / bag, or put the smart aerogel into the sealed package of the product to be tested, and judge the volatile biogenic amine content according to the color change of the smart aerogel after 1 minute; Alternatively, the smart aerogel is pasted inside a commodity package and used without direct contact with the packaged commodity, and the presence or content of volatile biogenic amines inside the package can be determined based on its color change.

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