Preparation and application of aerogel colorimetric label based on walnut kernel oxidized ranialdehyde indicator

Abstract

The invention relates to the technical field of intelligent food detection, and particularly discloses a preparation method and application of an aerogel colorimetric label based on a walnut kernel oxidized ranialdehyde indicator. According to the label, carboxymethyl cellulose (CMC) and sodium alginate (SA) are used as gel matrixes, and aerogel with a high specific surface area and a porous structure is prepared through a mixed solution preparation process, an aldehyde colorimetric solution loading process, a pre-freezing process and a freeze-drying process. Wherein the aldehyde colorimetric solution is composed of Congo red and hydroxylamine sulfate, and the aldehyde colorimetric solution and aldehyde substances are subjected to specific color development through a connizaro reaction. The CMC / SA gel matrix forms a three-dimensional network structure, so that Congo red molecules can be effectively embedded and protected, the stability of the Congo red molecules in a complex food microenvironment is remarkably improved, and the problems that a free color developing agent is susceptible to interference and poor in stability are solved. The aerogel disclosed by the invention is sensitive in response to low-concentration aldehydes (112ppm) such as valeraldehyde, hexanal and the like generated by oxidation of the walnut kernels, remarkable in color difference and capable of monitoring the oxidation degree in real time.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of food intelligent detection, in particular to a kind of preparation and application of aerogel colorimetric label based on walnut kernel oxidation ha failed aldehyde class indication, through innovative aerogel structure design and specific color system combination, dynamic adsorption structure realizes the efficient capture of walnut kernel oxidation ha failed aldehyde class indication, and pigment molecules are protected by using gel matrix embedding, solve the problem of poor environmental stability of existing indicator, can be widely used in food warehousing logistics, retail terminal and quality monitoring in household scene. BACKGROUND

[0002] In the field of food, nuts are favored for their rich nutritional value, however, their high oil characteristics make them easily oxidized and spoiled during processing and storage. Unlike other nuts, walnut kernels, as a kind of nuts rich in unsaturated fatty acids, produce unique characteristic markers such as hexanal and pentanal during oxidation and spoilage. As oxidation of walnuts intensifies, the concentration of aldehydes will significantly increase. Therefore, as key products of walnut lipid oxidation, the content change of these aldehydes can accurately reflect the oxidation degree of walnuts, and is a key indicator for measuring the freshness and quality of walnuts.

[0003] In the current field of food monitoring, traditional detection methods such as gas chromatography-mass spectrometry (GC-MS) require professional equipment (single detection cost > $150) and 6-8 hours of pre-treatment, and destroy the integrity of the sample; chemical titration method has high error rate, cannot monitor food quality changes in real time, and is difficult to meet the needs of rapid and on-site detection. In recent years, biodegradable intelligent packaging (label) using edible ingredients and natural pigments has become one of the main development trends in food packaging, which can evaluate food freshness by detecting microorganisms, gases and other indicators, and has the characteristics of non-toxic, environmentally friendly, simple and convenient to prepare, and low cost. However, intelligent packaging materials are not biodegradable, which can cause environmental pollution and is contrary to the concept of green development. At present, intelligent films (labels) based on pH, nitrogen-containing compounds and microorganisms have been used to indicate the freshness of meat products. However, the aldehyde gas produced by walnut oxidation is relatively weak, and the existing indicator cards and films generally have the defects of small specific surface area and low response sensitivity, which cannot timely and accurately reflect the oxidation state of walnuts, and the detection effect is not good. In addition, the color developing agents (such as dyes and natural pigments) in the existing intelligent indicator materials are often directly exposed to the food packaging environment, which is easily affected by humidity, light, oxygen and other volatile components (such as alcohols, acids and esters) in food, resulting in unstable color development, color fading or false positive / negative response, reducing the reliability and service life of the indicator.

[0004] In comparison, aerogel, as a new material, offers advantages such as high specific surface area, porous structure, and strong adsorption, showing great potential in the field of gas sensing. The application of aerogel in food testing is expected to address the shortcomings of traditional detection methods and existing smart packaging materials. However, the application of aerogel in food aldehyde detection and its large-scale application still faces many challenges. These include the low diffusion efficiency of low-concentration aldehyde gases, resulting in delayed response; the susceptibility of exposed pigments to photothermal degradation, resulting in poor color stability; the complex and costly preparation process of some aerogels, and their poor compatibility with food ingredients. These challenges need to be overcome urgently. Summary of the Invention

[0005] To address the challenges of traditional food packaging testing materials for detecting aldehydes, including their small specific surface area, low sensitivity, and the fact that most are non-biodegradable and unstable, the primary objective of this invention is to provide a method for preparing an aerogel colorimetric label based on walnut kernel oxidative degradation as an indicator of aldehydes. This invention utilizes a triple set of technological innovations: matrix formulation, structural modulation, and color enhancement. The porous network structure formed by the CMC / SA gel matrix effectively entraps and immobilizes Congo red molecules, providing a physical barrier and reducing interference from environmental factors (such as humidity, temperature fluctuations, and non-target volatiles). This significantly improves the stability of the colorimetric system and its compatibility in complex food environments. This results in a colorimetric aerogel with core competitive advantages, including fast response, high sensitivity, real-time monitoring, long-lasting and stable color development, and biodegradability. This material is expected to bring new breakthroughs to the field of food packaging and testing, effectively addressing the shortcomings of current intelligent packaging materials while meeting the urgent market demand for accurate, efficient, and environmentally friendly food testing technologies.

[0006] The present invention innovatively selects carboxymethyl cellulose and sodium alginate as the gel matrix. By finely controlling the ratio of the two and optimizing the preparation process conditions, it successfully constructs an aerogel with a rich porous structure and a rapid gas diffusion channel, which triggers a significant reddish-brown color change reaction to valeraldehyde and hexanal at a low concentration of 112ppm. The detection sensitivity far exceeds that of traditional technologies and can accurately capture the trace aldehyde signals released by the early oxidation of walnut kernels, achieving advanced and accurate early warning of the degree of food oxidation, and providing a strong guarantee for food quality control. At the same time, the interpenetrating network structure formed by carboxymethyl cellulose and sodium alginate not only provides a high specific surface area and adsorption sites, but more importantly, effectively embeds Congo red molecules in its network pores. On the one hand, this encapsulation effect protects the Congo red molecules from the direct influence of high humidity, possible oil droplets or other non-target volatile substances in the packaging, maintaining their molecular structure and reactivity; on the other hand, it ensures that the color development reaction mainly occurs inside the aerogel and between the adsorbed aldehydes, reducing misjudgment caused by external interference, and significantly improving the reliability of the colorimetric label in the real food packaging environment and the durability of the color development signal (i.e., prolonging the color development).

[0007] Another object of the present invention is to provide an aerogel colorimetric label based on walnut kernel oxidized aldehyde indicators prepared by the above preparation method.

[0008] Another object of the present invention is to provide the application of the above-mentioned aerogel colorimetric label based on walnut kernel oxidative rancidity indicator aldehydes in detecting walnut kernel oxidative rancidity.

[0009] The purpose of the present invention is achieved through the following technical solutions: The present invention realizes a method for preparing aerogel colorimetric labels based on walnut kernel oxidized aldehyde indicators through the following technical solutions: (1) Solution preparation: Dissolve carboxymethyl cellulose (CMC) and sodium alginate (SA) in deionized water, stir, and obtain CMC solution and SA solution.

[0010] (2) Preparation of polymer mixed solution: CMC solution and SA solution were mixed, the mixed volume ratio of the two solutions was adjusted, and the mixed solution was stirred at room temperature to form a polymer mixed solution; (3) Preparation of aldehyde colorimetric solution: Methanol, deionized water, and glycerol are mixed in appropriate proportions to form a mixed solution. A certain amount of Congo red and hydroxylamine sulfate are added to the mixed solution and stirred continuously to obtain an aldehyde colorimetric solution.

[0011] (4) Preparation of colorimetric aerogel solution: Add a small amount of aldehyde colorimetric solution to the carboxymethyl cellulose (CMC) / sodium alginate (SA) mixture prepared in step (2) and stir for a period of time to obtain a colorimetric aerogel solution.

[0012] (5) Colorimetric aerogel preparation: pour the colorimetric aerogel solution prepared in step (4) into a round polytetrafluoroethylene plate, pre-freeze, and then freeze-dry to obtain the colorimetric aerogel.

[0013] The colorimetric aerogel is prepared by the polymer complexing method and the freeze-drying method, the proportion of carboxymethyl cellulose and sodium alginate is reasonably adjusted, the aldehyde visual colorimetric aerogel for intelligent detection of freshness of nut food is successfully prepared, and the colorimetric aerogel has high sensitivity, low cost and green safety.

[0014] As a preferred scheme of the present application, the CMC and SA are dissolved in deionized water in a solid-liquid ratio of (1.0-5.0) / (60-140) (g / mL), and stirred at 50-70 DEG C for 1-4 h. As a preferred scheme of the present application, in step (1), the mass of deionized water is 60-140 mL, and further preferably 80-120 mL; As a preferred scheme of the present application, in step (1), the stirring is continuously carried out at 50-70 DEG C for 1-4 h, and further preferably at 55-65 DEG C for 2-3 h; As a preferred scheme of the present application, in step (2), the carboxymethyl cellulose solution and the sodium alginate solution are mixed in a ratio of 4:1-1:4 (v / v), and further preferably 3:1-1:3; As a preferred scheme of the present application, in step (2), the carboxymethyl cellulose / sodium alginate mixture is stirred at 15-35 DEG C for 30-60 min, and further preferably at 20-30 DEG C for 35-55 min; As a preferred scheme of the present application, in step (3), the volume ratio of methanol, deionized water and glycerol in step (3) is (8-12):(8-10):1, and preferably 10:9:1.

[0015] As a preferred scheme of the present application, in step (3), the addition amount of the Congo red is 1.0-3.0 mg / mL of the mixed solution, the addition amount of the hydroxylamine sulfate is 35-45 mg / mL of the mixed solution, the mass ratio of the Congo red to the hydroxylamine sulfate in the aldehyde colorimetric solution is 1:(15-25), and the stirring time is 25-35 min; As a preferred scheme of the present application, in step (4), 3-7% of the aldehyde colorimetric solution is added to the carboxymethyl cellulose / sodium alginate mixed solution, and stirred for 20-40 min, and further preferably 4-6% of the aldehyde colorimetric solution is added, and stirred for 15-25 min; As a preferred embodiment of the present invention, in step (5), the colorimetric aerogel solution is poured into a circular polytetrafluoroethylene plate and pre-frozen at -14-26°C for 20-30 h, more preferably at a pre-freezing temperature of -18-22°C and a freezing time of 22-28 h; As a preferred embodiment of the present invention, in step (5), freeze drying is performed at -40-60°C for 24-48 h, and more preferably, the freeze drying temperature is 45-55°C and the freezing time is 30-40 h.

[0016] An aerogel colorimetric label prepared by the method, wherein the aerogel has a wrinkled surface and a porous structure with dynamic adsorption function, a porosity of ≥88%, a density of 0.04-0.06 g / cm³, and is loaded with a Congo red-hydroxylamine sulfate composite color development system.

[0017] As a preferred embodiment of the present invention, the label and the walnut kernel are sealed together in the package. The label dynamically absorbs the aldehyde gas released by the walnut kernel and conducts it to the color development system through the pores. The concentration of the aldehyde substance is reflected by the color change of the aerogel, and the color difference ΔE is positively correlated with the degree of oxidation.

[0018] As a preferred embodiment of the present invention, the aldehyde substance includes at least one of valeraldehyde, hexanal, and butyraldehyde, and the detection sensitivity is 110-115 ppm for valeraldehyde, 110-115 ppm for hexanal, and 445-452 ppm for butyraldehyde. Preferably, the detection sensitivity is 112 ppm for valeraldehyde, 112 ppm for hexanal, and 448 ppm for butyraldehyde. The label is sealed together with the walnut kernels in a package and stored under accelerated oxidation conditions at 60° C. for 20 days, and the color difference ΔE is ≥ 46, the hardness increases by more than 1 times compared with the initial conditions, and the cohesion increases by more than 30%. The present invention features a simple, low-cost preparation process, biodegradable materials, and high sensitivity, along with environmental friendliness. The label intuitively reflects food freshness through color changes, eliminating the need for complex instrumentation. It is suitable for intelligent packaging inspection of nuts such as walnut kernels, resolving issues such as slow response, non-degradability, and insufficient color stability associated with existing technologies.

[0019] Compared with the existing technology, the present invention has the following beneficial effects: 1. Highly sensitive detection: The colorimetric aerogel prepared in this invention has a unique wrinkled surface and rich pore structure, significantly increasing its specific surface area and providing ample sites for the adsorption and reaction of aldehyde gases. Experiments have shown that it produces a distinct reddish-brown color change reaction to valeraldehyde and hexanal at a low concentration of 112 ppm, and a significant color change to butyraldehyde at 448 ppm. This sensitivity far exceeds that of traditional detection materials, enabling precise detection of trace aldehydes produced by early oxidation of walnut kernels, providing an early and accurate warning of their oxidation status.

[0020] 2. Innovative Detection Method: This method breaks through the limitations of traditional testing, which relies on specialized equipment, and utilizes the specific reaction between aerogel and aldehydes to achieve visual detection. Simply observing the color change of the aerogel allows for intuitive judgment of the degree of food oxidation, eliminating the need for complex instrumental analysis and offering convenient operation. This simple and accessible detection method not only lowers the threshold for testing but also broadens its application scenarios, making it suitable for non-professional environments such as homes and retail outlets, providing consumers with a convenient means of monitoring food quality.

[0021] 3. Low-cost preparation: The innovative use of widely available and affordable carboxymethyl cellulose and sodium alginate as matrix materials significantly reduces raw material costs. Furthermore, this invention eliminates the complex and expensive steps in traditional aerogel preparation, employing simple stirring, pre-freezing, and freeze-drying techniques. This significantly reduces equipment requirements and operational complexity, thereby significantly reducing production costs.

[0022] 4. Green, safe, and reliable: The main matrices of this invention are carboxymethyl cellulose and sodium alginate, both natural polymers with excellent biocompatibility. They are decomposed by microorganisms in natural environments, without causing environmental pollution. Compared with traditional indicator labels, this is more environmentally friendly and safer to use. The color display agents Congo red and hydroxylamine sulfate are non-toxic to humans and the environment within reasonable use, fully complying with food packaging safety standards, eliminating consumer concerns about food safety, and aligning with the development trend of green environmental protection.

[0023] 5. Environmental Stability and Food Compatibility: This invention utilizes a three-dimensional network structure formed by a carboxymethyl cellulose and sodium alginate gel matrix to effectively physically encapsulate and protect the core chromogen, Congo red. This protective effect significantly reduces the interference and degradation effects of Congo red from ambient humidity, temperature fluctuations, and other non-target food volatiles (such as alcohols and esters) coexisting in the package, thereby ensuring the specificity and stability of the colorimetric reaction. This enables the colorimetric label to maintain a sensitive, accurate, and long-lasting color response (i.e., prolonged color development) in actual food packaging environments such as walnut kernels, which are rich in oils and complex volatiles. This overcomes the bottleneck of traditional free chromogens or simple carrier materials, which are susceptible to environmental interference and have poor stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Actual images of the colorimetric aerogels of Examples 1-5; Figure 2 Colorimetric aerogel microstructure diagram of Examples 1-5; Figure 3 Colorimetric aerogel density and pore size distribution diagrams of Examples 1-5; Figure 4 Colorimetric aerogel hygroscopicity graphs of Examples 1-5; Figure 5 Thermogravimetric analysis of the colorimetric aerogels of Examples 1-6; Figure 6 Simulation of adsorption of aldehyde volatile substances in Example 1 and Examples 6-8: A. Example 1; B. Example 6; C. Example 7; D. Example 8; Figure 7 Comparative Example 1 shows the color rendering of the aldehyde volatility standard; Figure 8 Example 6 shows the color development effect and color difference diagram of aldehyde volatility standard products; Figure 9 Comparative Example 3 shows the aldehyde content at different storage times; Figure 10 Color development effect diagram of aerogel colorimetric labels of Example 7 and Comparative Example 4 at different storage times. DETAILED DESCRIPTION

[0025] In order to better understand the present invention, the contents of the present invention are further explained in conjunction with the embodiments and drawings below. However, in order to enable ordinary technicians in this field to fully understand the technical solutions and beneficial effects of the present invention, the present invention is further explained in conjunction with specific embodiments below. The embodiments are merely simple examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention shall be subject to the claims.

[0026] If the specific conditions are not specified in the examples, the experiments were carried out under conventional conditions or those recommended by the manufacturer. All reagents or instruments used, if the manufacturer is not specified, are commercially available conventional products.

[0027] Example 1 1) Solution Preparation: Weigh 2.0 g of sodium alginate and 2.0 g of carboxymethyl cellulose, dissolve each in 100 mL of deionized water, and stir continuously at 60°C for 2 h.

[0028] 2) Preparation of polymer mixed solution: Carboxymethyl cellulose solution and sodium alginate solution were mixed in a ratio of 1:2 (v / v), and the carboxymethyl cellulose-sodium alginate mixture was stirred at 25°C for 45 min.

[0029] 3) Preparation of aldehyde colorimetric solution: Mix methanol, deionized water, and glycerol in a ratio of 10:9:1, add 20 mg of Congo red and 400 mg of hydroxylamine sulfate, and stir continuously for 20 minutes to obtain the aldehyde colorimetric solution.

[0030] 4) Preparation of colorimetric aerogel solution: Add 5% aldehyde colorimetric solution to the carboxymethyl cellulose-sodium alginate mixture and stir for 30 min to obtain a colorimetric aerogel solution.

[0031] 5) Preparation of colorimetric aerogel: The colorimetric aerogel solution was poured into a circular polytetrafluoroethylene plate, pre-frozen at -20°C for 24 h, and freeze-dried at -50°C for 36 h to obtain the colorimetric aerogel.

[0032] Example 2 Based on Example 1, the difference is that in step 2) the ratio of carboxymethyl cellulose solution to sodium alginate is: 1) Solution Preparation: Weigh 2.0 g of sodium alginate and 2.0 g of carboxymethyl cellulose, dissolve each in 100 mL of deionized water, and stir continuously at 60°C for 2 h.

[0033] 2) Preparation of polymer mixed solution: Carboxymethyl cellulose solution and sodium alginate solution were mixed at a ratio of 3:1 (v / v), and the carboxymethyl cellulose-sodium alginate mixture was stirred at 25°C for 45 min.

[0034] 3) Preparation of aldehyde colorimetric solution: Mix methanol, deionized water, and glycerol in a ratio of 10:9:1, add 20 mg of Congo red and 400 mg of hydroxylamine sulfate, and stir continuously for 20 minutes to obtain the aldehyde colorimetric solution.

[0035] 4) Preparation of colorimetric aerogel solution: Add 5% aldehyde colorimetric solution to the carboxymethyl cellulose-sodium alginate mixture and stir for 30 min to obtain a colorimetric aerogel solution.

[0036] 5) Preparation of colorimetric aerogel: The colorimetric aerogel solution was poured into a circular polytetrafluoroethylene plate, pre-frozen at -20°C for 24 h, and freeze-dried at -50°C for 36 h to obtain the colorimetric aerogel.

[0037] Example 3 Based on Example 1, the difference is that in step 2) the ratio of carboxymethyl cellulose solution to sodium alginate is: 1) Solution Preparation: Weigh 2.0 g of sodium alginate and 2.0 g of carboxymethyl cellulose, dissolve each in 100 mL of deionized water, and stir continuously at 60°C for 2 h.

[0038] 2) Preparation of polymer mixed solution: Carboxymethyl cellulose solution and sodium alginate solution were mixed at a ratio of 2:1 (v / v), and the carboxymethyl cellulose-sodium alginate mixture was stirred at 25°C for 45 min.

[0039] 3) Preparation of aldehyde colorimetric solution: Mix methanol, deionized water, and glycerol in a ratio of 10:9:1, add 20 mg of Congo red and 400 mg of hydroxylamine sulfate, and stir continuously for 20 minutes to obtain the aldehyde colorimetric solution.

[0040] 4) Preparation of colorimetric aerogel solution: Add 5% aldehyde colorimetric solution to the carboxymethyl cellulose-sodium alginate mixture and stir for 30 min to obtain a colorimetric aerogel solution.

[0041] 5) Preparation of colorimetric aerogel: The colorimetric aerogel solution was poured into a circular polytetrafluoroethylene plate, pre-frozen at -20°C for 24 h, and freeze-dried at -50°C for 36 h to obtain the colorimetric aerogel.

[0042] Example 4 Based on Example 1, the difference is that in step 2) the ratio of carboxymethyl cellulose solution to sodium alginate is: 1) Solution Preparation: Weigh 2.0 g of sodium alginate and 2.0 g of carboxymethyl cellulose, dissolve each in 100 mL of deionized water, and stir continuously at 60°C for 2 h.

[0043] 2) Preparation of polymer mixed solution: Carboxymethyl cellulose solution and sodium alginate solution were mixed in a ratio of 1:1 (v / v), and the carboxymethyl cellulose-sodium alginate mixture was stirred at 25°C for 45 min.

[0044] 3) Preparation of aldehyde colorimetric solution: Mix methanol, deionized water, and glycerol in a ratio of 10:9:1, add 20 mg of Congo red and 400 mg of hydroxylamine sulfate, and stir continuously for 20 minutes to obtain the aldehyde colorimetric solution.

[0045] 4) Preparation of colorimetric aerogel solution: Add 5% aldehyde colorimetric solution to the carboxymethyl cellulose-sodium alginate mixture and stir for 30 min to obtain a colorimetric aerogel solution.

[0046] 5) Preparation of colorimetric aerogel: The colorimetric aerogel solution was poured into a circular polytetrafluoroethylene plate, pre-frozen at -20°C for 24 h, and freeze-dried at -50°C for 36 h to obtain the colorimetric aerogel.

[0047] Example 5 Based on Example 1, the difference is that in step 2) the ratio of carboxymethyl cellulose solution to sodium alginate is: 1) Solution Preparation: Weigh 2.0 g of sodium alginate and 2.0 g of carboxymethyl cellulose, dissolve each in 100 mL of deionized water, and stir continuously at 60°C for 2 h.

[0048] 2) Preparation of polymer mixed solution: Carboxymethyl cellulose solution and sodium alginate solution were mixed at a ratio of 1:3 (v / v), and the carboxymethyl cellulose-sodium alginate mixture was stirred at 25°C for 45 min.

[0049] 3) Preparation of aldehyde colorimetric solution: Mix methanol, deionized water, and glycerol in a ratio of 10:9:1, add 20 mg of Congo red and 400 mg of hydroxylamine sulfate, and stir continuously for 20 minutes to obtain the aldehyde colorimetric solution.

[0050] 4) Preparation of colorimetric aerogel solution: Add 5% aldehyde colorimetric solution to the carboxymethyl cellulose-sodium alginate mixture and stir for 30 min to obtain a colorimetric aerogel solution.

[0051] 5) Preparation of colorimetric aerogel: The colorimetric aerogel solution was poured into a circular polytetrafluoroethylene plate, pre-frozen at -20°C for 24 h, and freeze-dried at -50°C for 36 h to obtain the colorimetric aerogel.

[0052] Example 6 Based on Example 1, the difference is that in step 1), P-CMC is used instead of CMC, and G-SA is used instead of SA to prepare the aerogel label: 1) P-CMC synthesis: 5 g of CMC was dispersed in 100 mL of ethanol / water (4:1 v / v), 1.5 g of P2O5 was added, and the mixture was stirred at 70°C for 3 h. The mixture was neutralized with 5% NaOH to pH 7, dialyzed for 48 h, and then freeze-dried.

[0053] 2) G-SA synthesis: 3 g SA and 4.5 g glucose were dissolved in 150 mL water and reacted at 55°C for 4 h at pH 8.0. Dialyze and freeze-dry.

[0054] The other steps are the same as those in Example 1.

[0055] Example 7 Based on Example 1, the difference is that in step 1), P-CMC is used instead of CMC to prepare the aerogel label: 1) P-CMC synthesis: 5 g of CMC was dispersed in 100 mL of ethanol / water (4:1 v / v), 1.5 g of P2O5 was added, and the mixture was stirred at 70°C for 3 h. The mixture was neutralized with 5% NaOH to pH 7, dialyzed for 48 h, and then freeze-dried.

[0056] The other steps are the same as those in Example 1. Example 8 Based on Example 1, the difference is that in step 1), G-SA is used instead of SA to prepare the aerogel label: 1) G-SA synthesis: 3 g SA and 4.5 g glucose were dissolved in 150 mL water and reacted at 55°C for 4 h at pH 8.0. Dialyze and freeze-dry.

[0057] The other steps are the same as those in Example 1. Example 9 The gel colorimetric tag prepared in Example 6 was applied to detect the degree of oxidation during the storage of walnut kernels.

[0058] Specific detection method: Color development of colorimetric aerogel during walnut kernel oxidation: The colorimetric aerogel prepared in Example 6 was sealed together with 100.0 g of fresh walnut kernels in a PE packaging bag, and stored at 60°C. The colorimetric aerogel would respond to the color change as volatile aldehydes were produced during the oxidation of walnut kernels. The color change image of the colorimetric aerogel was recorded every 5 days.

[0059] Color difference determination of colorimetric aerogel during walnut kernel oxidation: The color parameters L* (lightness), a* (red-green value) and b* (yellow-blue value) of the colorimetric aerogel prepared in Example 1 were measured every 3 days using a colorimeter, and the color difference (ΔE) was calculated according to the following equation:

[0060] where L0, a0 and b0 are the color parameters of the colorimetric aerogel before exposure to the environment to be tested, and a standard white plate is used as the color difference reference.

[0061] Texture properties of colorimetric aerogel during walnut kernel oxidation: A texture analyzer was used to measure the hardness of the aerogel. A cylindrical probe was selected as the test mold of the texture analyzer, the test speed was 0.5 mm / s, and the sample was compressed twice to 50% of its original height. The parameters evaluated included hardness, springiness and cohesiveness. All test samples maintained the same height-diameter ratio. The size (length and diameter) and mass of the aerogel were measured using an electronic vernier caliper and an analytical balance, respectively.

[0062] Comparative Example 1 1) Solution preparation: 2.0 g of sodium alginate and 2.0 g of carboxymethyl cellulose were weighed and dissolved in 100 mL of deionized water, respectively, and then continuously stirred at 60°C for 2 h.

[0063] 2) Preparation of polymer mixed solution: The carboxymethyl cellulose solution was mixed with the sodium alginate solution at a ratio of 1:2 (v / v), and the carboxymethyl-cellulose-sodium alginate mixture was stirred at 25°C for 45 min.

[0064] 3) Preparation of aldehyde colorimetric solution: methanol, deionized water and glycerol were mixed at a ratio of 10:9:1, 20 mg of Congo red and 400 mg of hydroxylamine sulfate were added, and continuously stirred for 20 min to obtain an aldehyde colorimetric solution.

[0065] Comparative Example 2 Determination of physicochemical indexes of walnut kernel during oxidation failure process: walnut kernels with the same quality and storage state as example 6 were selected and sealed in PE packaging bags. The determination of lipid peroxide value and acid value of walnut kernel was carried out according to Chinese national standards (GB5009.227-2016, GB 5009.229-2016, GB / T 24304-2009); the content of malondialdehyde (MDA) was determined, and the result was given in mg / kg as MDA equivalent. The calibration curve equation was y = 1.1866x + 0.0031, and the correlation coefficient was R 2 = 0.9989. The oxidation physicochemical properties (lipid peroxide value, acid value and malondialdehyde) of walnut kernel during storage were measured every 5 days.

[0066] Comparative example 3 Determination of traditional method of aldehyde volatile substances in walnut kernel: 2.0 g of walnut kernel was placed in a headspace bottle, equilibrated at 50°C water bath for 20 min, and inserted into a 50 / 30 μm DVB / CAR / PDMS extraction head for 30 min, and desorbed at 250°C for 5 min. Gas chromatography-mass spectrometry method was used to identify volatile substances by comparing the retention index (RI) of n-alkane standard C7~C 30 aldehydes such as hexanal and pentanal were determined by semi-quantitative analysis method, and the oxidation degree of walnut was judged.

[0067] Comparative example 4 The colorimetric aerogel prepared in example 1 was sealed in a PE packaging bag without walnut, and stored at 60°C. The colorimetric aerogel was photographed and recorded every 5 days to record the color change of the colorimetric aerogel.

[0068] In the above examples and comparative examples, the prepared colorimetric aerogel was analyzed for physical properties, including texture property analysis, microstructure, density, porosity and moisture absorption, color difference analysis and colorimetric label color development effect analysis. The specific methods are as follows: 1. Texture properties of colorimetric aerogel: a texture analyzer was used to measure the hardness of the aerogel. A cylindrical probe was selected as the test mold of the texture analyzer, the test speed was 0.5 mm / s, and the sample was compressed twice to 50% of its initial height. The evaluated parameters included hardness, springiness and cohesiveness. All test samples had the same height-diameter ratio. Electronic vernier caliper and analytical balance were used to measure the size (length and diameter) and mass of the aerogel, respectively.

[0069] 2. Colorimetric aerogel microstructure: The microstructure of the aerogels was analyzed at 50× and 150× magnifications using a scanning electron microscope with an accelerating voltage of 8 kV. The aerogel samples were cut (1 cm × 1 cm) and sputter-coated with a 10 nm thin layer of gold.

[0070] 3. Porosity and density determination of colorimetric aerogel: The porosity of aerogel is calculated using the following formula:

[0071] in is the apparent density of the aerogel, is the bulk density of the aerogel, which is calculated as =1 / 2 CMC +1 / 2 SA= 0.80 g / cm 3 (According to the reagent specifications, CMC=0.60 g / cm 3 ,in is the apparent density of the aerogel, is the bulk density of the aerogel, Aerogel density The calculation formula is:

[0072] where m is the mass of the sample measured using an analytical balance, and v is the volume calculated using an electronic vernier caliper.

[0073] 4. Determination of the hygroscopicity of colorimetric aerogels: First weigh the aerogel, then place it in a constant temperature and humidity chamber at 25°C and 100% relative humidity for 24 hours and weigh it again. Use the following formula to determine the result:

[0074] Where W a is the weight of the aerogel after moisture absorption, W b is the weight of the aerogel before moisture absorption.

[0075] 5. Thermal Stability of Colorimetric Aerogels: The thermal stability of the aerogels was analyzed using thermogravimetric analysis (TGA) and differential thermogravimetric analysis (DTG). Each sample (10 mg) was heated from room temperature to 600°C using a thermogravimetric analyzer at a flow rate of 20 mL / min and a heating rate of 10°C / min in the presence of nitrogen. The DTG curve, obtained by taking the first derivative of the temperature in the TGA curve, represents the relationship between the weight loss rate and temperature. A differential scanning calorimeter (DSC) was used with a heating rate of 10°C / min over a temperature range of 0–600°C. The sample weight was 10 mg.

[0076] 6. Colorimetric aerogel color difference determination: The colorimetric aerogel was exposed to volatile flavor standards (25°C) produced by oxidative rancidity of walnut kernels, such as hexanal and valeraldehyde, air (25°C and 60°C), and PE packaging bags (60°C). The color parameters L* (brightness), a* (red-green value), and b* (yellow-blue value) were measured using a colorimeter, and the color difference (ΔE) was calculated according to the following equation:

[0077] Where L0, a0, and b0 are the color parameters of the colorimetric aerogel before exposure to the test environment, and a standard white plate is used as a color difference reference.

[0078] 7. Color development effect of aldehyde colorimetric solution: Add six aldehyde volatile standards (octanal, heptanal, butyraldehyde, 3-methylbutyraldehyde, hexanal, and valeraldehyde) at different concentrations to the prepared colorimetric solution and colorimetric aerogel, and observe the color changes of aldehyde substances at different concentrations in the colorimetric solution and colorimetric aerogel.

[0079] The following is an explanation of the measurement methods and results of Examples 1-6 to Comparative Examples 1-4. 1. Texture Analysis of Examples 1-5 The texture results of aerogel colorimetric labels with different CMC / SA ratios are shown in Table 1. Higher hardness makes the colorimetric aerogel more structurally stable in practical applications, preventing damage to the aerogel structure due to external pressure, which would affect detection performance. Examples 1 and 4 have high and similar hardness. Good elasticity enables the colorimetric aerogel to maintain structural and performance stability in complex environments. The results show that Example 3 has the best ratio, but Examples 1 and 4 also exhibit excellent elasticity. Similarly, colorimetric aerogels with strong cohesion have a tighter internal structure and greater intermolecular bonding, thereby ensuring the smooth progress of the detection process and the accuracy of the test results. Examples 1 and 5 have the best cohesion performance. Taking into account the three aspects of hardness, elasticity, and cohesion, Example 1 has the best texture characteristics. The colorimetric aerogels prepared in Examples 3-5 also have excellent texture characteristics.

[0080] Table 1 Colorimetric aerogel texture results of Examples 1-5

[0081] 2. Structural Analysis of Examples 1-5 Due to the uneven growth of ice crystals during freezing of higher CMC content aerogels, the pore size distribution is irregular, resulting in random agglomeration. Figure 1 Showing a physical picture of aerogel, Figure 2The scanning electron microscope images show the microstructure of the aerogels. The aerogel microstructure of Example 2 has relatively small and scattered pores; the structure of Example 3 shows a certain order, and the pore structure is relatively regular; the microstructure of Example 4 exhibits a relatively rich pore network, and the pore size is relatively uniform; in contrast, the aerogel of Example 1 has a more developed pore structure, forming larger and interconnected pore channels; the pores in the microstructure of Example 5 also exist, but the overall structure has a certain degree of compactness. This is because the SA has a higher concentration, and the hydrophilicity of SA is better, leading to ice cracking during freezing and processing. Therefore, the aerogel prepared in Example 1 is superior to other examples, and Examples 4 and 5 also have a developed pore structure.

[0082] 3. Porosity and density analysis of Examples 1-5 From Figure 3 It can be seen that Examples 1-5 all show a density below 0.075 g / cm 3 and a porosity of more than 88%, belonging to a lightweight structure. In terms of density, a lower density means that the internal structure of the aerogel is more loose, and the material quality is relatively lighter. The densities of Examples 1 and 5 are at a lower level, which is conducive to reducing costs in practical applications, and may also make the aerogel have better flexibility and operability. Similarly, Examples 1 and 5 also have a higher porosity in terms of pore size distribution (reflected by porosity), and the developed pore structure greatly increases the specific surface area of the aerogel. The increase in specific surface area is conducive to the adsorption and diffusion of aldehyde and other gas substances by the aerogel, which can improve the sensitivity and response speed of the aerogel in detecting aldehyde substances, thereby improving the detection effect. Therefore, the aerogels of Examples 1 and 5 have advantages in terms of cost, flexibility, adsorption and detection performance, etc. due to their lower density and higher porosity, and become the preferred preparation conditions for colorimetric aerogels.

[0083] 4. Analysis of the hygroscopicity of Examples 1-5 WVSC hygroscopicity is a key factor for the application of aerogels as food labels. Higher hygroscopicity means that the aerogel has a stronger adsorption capacity for water. In the application scenario of detecting aldehyde substances, environmental humidity may affect the detection, and an aerogel with higher hygroscopicity can better cope with humidity changes by adsorbing water to reduce the interference of environmental humidity on the detection process, thereby improving the accuracy and stability of the detection. The hygroscopicity results of Examples 1-5 are shown in Figure 4 , and Examples 1 and 5 have higher hygroscopicity, indicating that the aerogel has a strong adsorption capacity for water and is more advantageous in dealing with humidity environments.

[0084] 5. Analysis of the thermal stability of Examples 1-8 Thermogravimetric analysis further provides quantitative information on the thermal stability and decomposition stage of the aerogel. As shown inFigure 5 When heated under nitrogen, all aerogels exhibited multi-stage mass loss. The first stage, at approximately 30–150°C, primarily corresponds to the volatilization of adsorbed water and a small amount of glycerol. The mass loss during this stage accounted for approximately 5–10% of the total mass, with minimal variation among samples of different ratios. The second stage, beginning at approximately 200°C, saw a dramatic mass loss (the main peak of the DTG curve), corresponding to the thermal degradation of the organic polymer. Both SA and CMC are polysaccharides, and this stage saw the main chain scission and thermal decomposition. For the blended aerogels, the main degradation peak occurred in the 240–300°C range. The main degradation peak temperature increased slightly with increasing CMC content, indicating that the inclusion of CMC enhanced the material's heat resistance. Conversely, the carboxylic acid groups rich in SA are more susceptible to dehydration and cleavage at high temperatures, resulting in a slightly lower degradation onset temperature when the SA ratio was high. Overall, the residual rates of all samples were high before 200°C, indicating a stable structure that is less susceptible to premature decomposition. This is particularly critical for the heat resistance of colorimetric labels, as actual food storage may encounter higher ambient temperatures (such as summer transportation) or accelerated test temperatures (60°C). Improved thermal stability means that the label can maintain its structural and functional integrity under these conditions and will not fail due to self-decomposition.

[0085] According to TGA and DTG thermograms, increasing the CMC to SA ratio increased the thermal stability of the aerogels. Furthermore, at the optimal compounding ratio, aerogels with phosphorylated CMC and glycosylated SA exhibited greater thermal stability. Therefore, optimizing the CMC to SA ratio can improve the thermal stability of aerogels, thereby enhancing their performance and heat resistance in high-temperature environments.

[0086] 6. Simulation of adsorption dynamics of aldehyde volatile substances in Example 1 and Examples 6-8 Figure 6Adsorption dynamics simulation of the aldehyde volatile substances by the aerogels prepared in Example 1 and Examples 6-8, respectively. Among them, the green ellipsoids are aldehyde substances, and the stick-like structures are aerogel matrices. The ordinary CMC / SA aerogel (Figure A) shows that the red dendritic aerogel structures are loosely distributed in the cubic space, and the green aldehyde substances are only sporadically attached to the edges of the structure, concentrated in the upper part, indicating that the aldehyde molecules cannot effectively penetrate into the interior of the aerogel, and the utilization rate of the adsorption site is low. The red molecular network structure in the modified P-CMC / SA aerogel (Figure B) and CMC / G-SA aerogel (Figure C) is relatively dense and orderly, and the green aldehyde substances diffuse in the cubic space, indicating that the aldehyde molecules can effectively penetrate into the interior of the aerogel, and the utilization rate of the adsorption site is significantly improved. The gel matrix in the double-modified P-CMC / G-SA aerogel (Figure D) is more dense and uniform, and the aldehyde substances are highly enriched in the core area of the network, forming obvious aggregation, confirming that the modified aerogel significantly improves the capture efficiency and enrichment capacity of aldehyde substances through electrostatic adsorption (P-CMC) and hydrophobic interaction (G-SA). At the same time, the energy analysis of the four kinds of aerogels is shown in Table 2, combined with van der Waals force and classical energy analysis, it is concluded that the P-CMC / G-SA aerogel has negative electrostatic energy, indicating that electrostatic attraction dominates, and the van der Waals force is also relatively strong, therefore the double-modified aerogel has the best adsorption capacity, indicating that phosphatization and glycosylation modification have a positive effect on improving the adsorption capacity of the material, especially by enhancing electrostatic attraction and appropriately adjusting van der Waals force. By comparing the two figures and combining with the energy analysis, it is revealed that the double modification of the matrix (P-CMC / G-SA) realizes the leap of the aldehyde substances from "edge dispersion adsorption" to "core efficient enrichment" by optimizing the orderliness of the aerogel structure and the surface properties.

[0087] Table 2

[0088] 7. Color development effect of Example 9 and Comparative Example 1 on aldehyde volatile standards The color development principle of the aldehyde colorimetric sensing solution used in the aerogel is that the aldehyde substance reacts with hydroxylamine sulfate through the Cannizzaro reaction and then reacts with Congo red to develop color. Different concentrations of six aldehyde volatile standards were added to the prepared Comparative Example 1, as shown in Figure 7 The color changes from red to purple to dark blue as the concentration of the standard increases. Among them, the reaction of pentanal and hexanal is the most sensitive, and it turns red-brown when the concentration reaches 112 ppm, and the response of octanal is weaker, and there is a slight color change effect when the concentration reaches 448 ppm.

[0089] Figure 8The color development effect of Example 9 on volatile aldehyde standards is shown. The aerogel prepared in Example 6 exhibited a color change from light red to brown to purple-black when exposed to volatile standards such as octanal, hexanal, and butyraldehyde. The color difference (ΔE) for each aldehyde generally increased with increasing concentration of the volatile aldehyde standards. The color development reaction with valeraldehyde was most pronounced, with a relatively low ΔE at 112 ppm and a maximum of approximately 25 at 1680 ppm. This indicates that the color development effect of the aerogel colorimetric label on aldehydes is concentration-dependent, with higher concentrations producing more pronounced color differences. This also suggests that the colorimetric aerogel prepared in Example 6 has the potential to determine aldehyde concentration based on color difference. Furthermore, the responsiveness of the six volatile aldehyde standards to the color development of the colorimetric solution in Comparative Example 1 is essentially consistent with that of the colorimetric solution.

[0090] 8. Texture changes during walnut kernel oxidative rancidity in Example 9 and changes in oxidation indexes in Comparative Example 2 As shown in Table 3, during the oxidation and rancidity of walnut kernels, the increase in color difference in Example 9 is consistent with the rising trend of PV, AV, and MDA contents measured in the comparative example, indicating that the oxidation physicochemical properties of walnut kernels correspond to the color difference values ​​of the aerogels, and a corresponding colorimetric relationship between the color difference values ​​and the oxidation values ​​can be established. In terms of texture, as the degree of oxidation rancidity deepens in Example 9, the hardness of the colorimetric aerogel continues to increase. This may be due to the polymerization and cross-linking reactions of substances inside the walnut kernels during the oxidation process. This is consistent with the increased oxidation reflected by the increase in PV, AV, and MDA contents. The material changes caused by oxidation cause the texture to become harder. The fluctuation of elasticity may be related to the dynamic changes in the internal structure of the walnut kernels during the oxidation process. The increase in cohesion may be due to changes in the interaction between substances inside the walnut kernels caused by oxidation, such as the formation of new chemical bonds or the enhancement of intermolecular forces, which is also consistent with the deepening oxidation trend reflected by the oxidation indicators. In summary, it is confirmed that the aerogel colorimetric label is sensitive to the oxidation products produced during the oxidation of walnut kernels, and its color and texture changes are closely related to the degree of oxidation reaction in the walnut kernels, which can be used as an effective means to quickly detect the oxidation state of walnut kernels.

[0091] Table 3 Determination of the texture properties of Example 9 and the oxidation physicochemical values ​​of Comparative Example 2

[0092] 9. Comparative Example 3: Analysis of volatile aldehydes in walnut kernels using traditional methods: Depend on Figure 8As shown in Comparative Example 3, the gas chromatography-mass spectrometry method for detecting volatile aldehydes in walnut kernels showed a complex trend of increasing (0-6 days), decreasing (6-9 days), and then increasing again (9-15 days) as storage time increased from 0 to 15 days. This trend is consistent with the trend in Example 6 where the color difference of the aerogel colorimetric label continued to increase throughout the storage period of the walnut kernels. This demonstrates that the colorimetric aerogel can respond to volatile aldehydes produced by walnut kernel oxidation, and its color change can, to a certain extent, reflect the changes in the aldehyde content and the degree of oxidation in the walnut kernels.

[0093] The detection method in Comparative Example 2 is difficult to implement in real time, is destructive to samples, and yields limited representative results. The detection method in Comparative Example 3 (GC-MS) requires sample pretreatment and instrumental analysis, which is time-consuming and requires specialized personnel to operate and maintain the instrument. Furthermore, the instrumentation is expensive, resulting in high testing costs. In contrast, the aerogel-based real-time detection method for walnut kernel oxidative rancidity in Example 7 allows for direct visual observation of changes, is simple to operate, reduces testing costs, and enables continuous monitoring. It also simultaneously monitors environmental factors and the oxidative state of the walnut kernel. Therefore, the detection method provided in Example 7 is rapid, accurate, and non-destructive, and holds great potential for intelligent monitoring of walnut kernel freshness.

[0094] 10. Analysis of color development effects of Example 9 and Comparative Example 4 The color development effects of the aerogel colorimetric labels of Example 9 and Comparative Example 4 at different storage times are as follows: Figure 9As shown. The aerogel exposed to air in Comparative Example 4 lightened in color after the same 60°C high-temperature accelerated storage. This is because Congo red is an azo dye. When the temperature rises, the violent molecular motion may cause the chemical bonds in the Congo red molecules to vibrate and twist to a certain extent, affecting the molecule's conjugated system and changing the molecule's light absorption and reflection properties, resulting in a lighter color. In contrast, the aerogel exposed to walnut kernels in Example 9 showed a gradual increase in color difference after storage. It is worth noting that although the high temperature environment may have an impact on free Congo red molecules (as shown by the slight color change of the aerogel in Comparative Example 4), the color change of the aerogel in Example 9 is significant, demonstrating its sustained response to the target aldehydes. This strongly demonstrates that the CMC / SA gel matrix effectively protects the embedded Congo red molecules, allowing them to maintain sufficient stability and reactivity under the harsh conditions of high-temperature accelerated oxidation, accurately responding to the aldehydes produced by walnut kernel oxidation. The color change of the aerogel colorimetric label placed in a walnut-free environment was small and stable. However, the color of the aerogel exposed to walnut kernels gradually changed from red to brown after storage, with a significant increase. This also confirms that the color change of the aerogel colorimetric label is mainly affected by substances such as aldehydes produced by walnut kernel oxidation, rather than simply environmental factors (such as other components in the air). This fully confirms that the aerogel colorimetric label has a specific response to the walnut kernel oxidation process. Thanks to the protective effect of the matrix, its color development system shows excellent stability and reliability in complex food environments (high temperature, high humidity, and coexisting volatiles), making it an effective tool for monitoring the oxidation status of walnut kernels.

[0095] In summary, the core innovation of the aerogel colorimetric label based on walnut kernel oxidized aldehyde indicators provided by this invention lies in the effective encapsulation and protection of the Congo red colorimetric molecule through the porous network structure of the CMC / SA gel matrix. This protective effect significantly improves the stability, anti-interference ability, and color durability (extending color development) of the colorimetric system in the complex microenvironment of food packaging (high temperature, high humidity, and coexisting volatile substances), thus resolving the key issues of existing smart indicator materials such as slow response, poor stability, and susceptibility to environmental interference.

[0096] The above embodiments are merely preferred technical solutions of the present invention and should not be construed as limiting the present invention. The embodiments and features in the embodiments of this application may be arbitrarily combined with each other unless they conflict. The scope of protection of the present invention shall be the technical solutions described in the claims, including equivalent alternatives to the technical features of the technical solutions described in the claims. Equivalent alternatives and improvements within this scope are also within the scope of protection of the present invention.

Claims

1. A method for preparing an aerogel colorimetric label based on walnut kernel oxidized aldehyde indicators, characterized in that: The method comprises the following steps: (1) dissolving carboxymethyl cellulose (CMC) and sodium alginate (SA) in deionized water respectively, stirring to obtain a CMC solution and a SA solution; (2) mixing the CMC solution with the SA solution, adjusting the mixing volume ratio of the two solutions, and stirring the mixed solution at room temperature to form a polymer mixed solution; (3) mixing methanol, deionized water, and glycerol to obtain a mixed solution, adding Congo red and hydroxylamine sulfate to the mixed solution, and stirring to obtain an aldehyde colorimetric solution; (4) adding the aldehyde colorimetric solution to the polymer mixture of step (2) and stirring to obtain a colorimetric aerogel solution; (5) pouring the colorimetric aerogel solution into a mold, pre-freezing it overnight at a low temperature, and then freeze-drying it at an ultra-low temperature to obtain the porous structure aerogel colorimetric label.

2. The preparation method according to claim 1, wherein: The CMC and SA described in step (1) are dissolved in deionized water at a solid-liquid ratio of (1.0-5.0) / (60-140) (g / mL), respectively, and stirred at 50-70°C for 1-4 h.

3. The preparation method according to claim 1, wherein: The mixing volume ratio of the CMC solution to the SA solution in step (2) is (1-3): (1-3), the stirring temperature is 20-30°C, and the stirring time is 35-55 min.

4. The preparation method according to claim 1, wherein: In step (3), the volume ratio of methanol, deionized water, and glycerol is (8-12):(8-10):1, preferably, 10:9:

1.

5. The preparation method according to claim 1, wherein: In step (3), the amount of Congo red added is 1.0-3.0 mg / mL of the mixed solution, and the amount of hydroxylamine sulfate added is 35-45 mg / mL of the mixed solution. The mass ratio of Congo red to hydroxylamine sulfate in the aldehyde colorimetric solution is 1:(15-25), and the stirring time is 25-35 min.

6. The preparation method according to claim 1, wherein: The amount of the aldehyde colorimetric solution added in step (4) is 4-6%, and the stirring time is 15-25 min.

7. The preparation method according to claim 1, wherein: The pre-freezing temperature in step (5) is -18~-22°C, and the pre-freezing time is 22-28 h; the freeze-drying temperature is -45~-55°C, and the drying time is 30-40 h.

8. An aerogel colorimetric label prepared according to the method of any one of claims 1 to 7, characterized in that: The aerogel has a wrinkled surface and a porous structure with dynamic adsorption function, a porosity of ≥88%, a density of 0.04-0.06 g / cm³, and is loaded with a Congo red-hydroxylamine sulfate composite color development system.

9. Use of the aerogel colorimetric label according to claim 8 in detecting the degree of oxidative rancidity of walnut kernels, characterized in that: The label and walnut kernels are sealed together in a package. The label dynamically absorbs aldehyde gas released by the walnut kernels and transmits it to the color development system through the pores. The color change of the aerogel reflects the concentration of the aldehyde substance, and the color difference ΔE is positively correlated with the degree of oxidation.

10. The use according to claim 9, characterized in that: The aldehyde substance includes at least one of valeraldehyde, hexanal, and butyraldehyde, and the detection sensitivity is 110-115 ppm for valeraldehyde, 110-115 ppm for hexanal, and 445-452 ppm for butyraldehyde. Preferably, the detection sensitivity is 112 ppm for valeraldehyde, 112 ppm for hexanal, and 448 ppm for butyraldehyde; The label is sealed together with the walnut kernels in a package and stored under accelerated oxidation conditions at 60° C. for 20 days, and the color difference ΔE is ≥ 46, the hardness increases by more than 1 times compared with the initial conditions, and the cohesion increases by more than 30%.

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