Use in metal-polyphenol coordination coloration systems and meat freshness monitoring.

Abstract

This invention discloses a metal-polyphenol coordination colorimetric system and its use in meat freshness monitoring, belonging to the field of intelligent monitoring technology. The method for preparing the metal-polyphenol coordination colorimetric system is as follows: S1, a metal salt solution and a polyphenol solution are mixed, the pH is adjusted to obtain a metal-polyphenol colorimetric solution; S2, the metal-polyphenol colorimetric solution is supported on a substrate, dried and cut to obtain a metal-polyphenolamine-responsive colorimetric element. [Effects] The metal-polyphenol colorimetric material of the present invention solves the problems of traditional chemical pigments, such as potential toxicity, primary discoloration, narrow discoloration range, and monochromatic color change, as well as the problems of natural pigments, such as low sensitivity, low stability, high cost, and complex preparation process. It can be recovered and reused from plant waste or industrial processing using a water-soluble extraction method, making it economically beneficial, greener, and more environmentally friendly. All prepared materials can be repeatedly recycled and reused.

Description

Technical Field

[0001] The present invention relates to the technical field of intelligent detection, and particularly relates to the use of a metal-polyphenol coordination coloring system in monitoring the freshness of meat.

Background Art

[0002] All food packaging has a description of the expiration date of the food. However, considering the complexity of the storage environment, the expiration date is often too cautious, and since the food can be eaten even beyond the expiration date, a large amount of waste phenomenon is caused. At the same time, fresh meat foods are constantly in a situation where the environmental temperature changes. For example, the repeated entry and exit of the refrigerator, etc., fresh meat foods are prone to deterioration and spoilage, and the above situation seriously threatens human health and social stability. Traditionally, the detection of the freshness of meat foods mainly depends on chemical titration, chromatography, electrochemical detection, etc. The complexity, specialty, time lag, and environmental impact of these methods no longer conform to the current development trend. Therefore, it is necessary to specifically develop new monitoring materials and technologies for the freshness of meat foods that are non-destructive, online, intelligent, and green.

[0003] Currently, research on intelligent monitoring of meat freshness mainly focuses on developing response materials such as pH, TVB-N, oxygen, carbon dioxide, and microorganisms based on volatile substances generated during the storage process of meat. The usage methods focus on methods such as intelligent colorimetric packaging, tags, and other electrical sensing. However, highly sensitive colorimetric monitoring materials usually use chemical pigments, and due to their potential toxicity, many consumers are concerned about the monitoring materials prepared with chemical pigments. In addition, chemical pigments with a chemical discoloration mechanism generally show disadvantages such as single-stage discoloration, a narrow discoloration range, and a single color change, and the color change is easily affected by external factors such as temperature and humidity. In recently popular research, natural dyes are used to prepare colorimetry to monitor the freshness of meat, but there are deficiencies such as low sensitivity, low stability, and high cost. Therefore, natural pigments need to be used in complex embedding, loading, etc. methods, which is disadvantageous for actual operation. [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] In response to the problems present in conventional technologies, the present invention provides the use of a metal-polyphenol coordination coloration system in meat freshness monitoring. The present invention can solve the problems of conventional chemical pigments, such as potential toxicity, single-stage color change, narrow color change range, and monochromatic color change, as well as the problems of natural pigments, such as low sensitivity, low stability, high cost, and complex preparation processes, resulting in a safe, non-toxic, inexpensive, and efficient monitoring method. [Means for solving the problem]

[0005] The technical solution of the present invention is as follows: This invention discloses a metal-polyphenol coordination color development system, and the method for preparing the metal-polyphenol coordination color development system is as follows: S1, the metal salt solution and the polyphenol solution are mixed, the pH is adjusted, and a metal-polyphenol colorimetric solution is obtained. S2, a metal-polyphenol colorimetric solution is supported on a substrate, dried, and cut to obtain a metal-polyphenolamine responsive colorimetric element.

[0006] In one embodiment of the present invention, in step S1, the concentration of the metal salt solution is 0.5 to 50 mM, the concentration of the polyphenol solution is 0.1 to 20 mM, and the ratio of metal salt to polyphenol substance in the metal-polyphenol colorimetric solution is 1:5 to 5:1.

[0007] In one embodiment of the present invention, in step S1, the metal salt is one of the following: hydrochloride of zinc, iron, ferrous oxide, aluminum, copper, cobalt, manganese, vanadium, molybdenum, or nickel; nitrate of zinc, iron, ferrous oxide, aluminum, copper, cobalt, manganese, vanadium, molybdenum, or nickel; or sulfate of zinc, iron, ferrous oxide, aluminum, copper, cobalt, manganese, vanadium, molybdenum, or nickel.

[0008] In one embodiment of the present invention, the polyphenol is one of the following: anthocyanin, gallic acid, catechin, caffeic acid, curcumin, protocatecaldehyde, epicatechin, epigallocatechin, epigallocatechin gallate (EGCG), tea polyphenols, and tannic acid.

[0009] In one embodiment of the present invention, an analytical balance is used to weigh a fixed amount of metal salt and polyphenol, which are then placed in separate beakers. A fixed amount of ultrapure water is added to dissolve them, and ultrasound is used to accelerate the dissolution. After washing the beakers three times, the contents are brought to a fixed volume in a 250 mL brown volumetric flask to prepare the metal salt solution and polyphenol solution, respectively, which are then stored and prepared for use.

[0010] In one embodiment of the present invention, a metal salt solution and a polyphenol solution are mixed and then reacted with aqueous ammonia. By obtaining and inferring from a series of characterizations the multi-stage competitive coordination color development mechanism of metal-polyphenol-amine, highly sensitive, sensitive, and low sensitive metal-polyphenol combinations are screened.

[0011] In one embodiment of the present invention, 0.2 mL of metal-polyphenol solution is taken, diluted 2 to 20 times with ultrapure water, and then 0.1 ppm to 2000 ppm of aqueous ammonia is added. A series of characterizations, including observation, ultraviolet-visible absorption spectroscopy, infrared spectroscopy, Raman spectroscopy, femtosecond transient absorption spectroscopy, and theoretical calculations, are performed to obtain and infer the multi-stage competitive coordination color development mechanism of metal-polyphenol-amine. Furthermore, based on the reaction intensity of metal-polyphenol and aqueous ammonia shown in the ultraviolet-visible absorption spectrum and theoretical calculation data, highly sensitive (0.1 to 10 ppm aqueous ammonia response) metal-polyphenol combinations are obtained, along with sensitive (11 to 200 ppm aqueous ammonia response) and low sensitive (201 to 2000 ppm aqueous ammonia response) metal-polyphenol combinations.

[0012] In one embodiment of the present invention, 2 mL of a metal-polyphenol solution is taken, diluted 2 to 10 times with ultrapure water, and then the pH is adjusted to a range of 3 to 5 with a 0.1 M sulfuric acid solution to obtain a metal-polyphenol colorimetric solution.

[0013] In one embodiment of the present invention, in step S1, the pH is 3 to 5.

[0014] In one embodiment of the present invention, in step S2, the substrate is one or more of the following: filter paper, PTFE film, PVDF film, pulp sheet, cellulose-based film, polyvinyl alcohol, chitosan, sodium alginate, and polysaccharide collagen.

[0015] In one embodiment of the present invention, in step S2, the loading method is one or more of spraying, immersion, suction filtration, printing, coating, 3D printing, and crosslinking.

[0016] In one embodiment of the present invention, in step S2, the drying conditions are to dry in an oven at 30-60°C for 2-20 minutes, then cut into tags, patterns, or assembled into an array.

[0017] The use of a metal-polyphenol coordination coloration system in meat freshness monitoring is as follows: (1) Establish a meat freshness index TVB-N and a storage time curve, (2) A metal-polyphenolamine-responsive colorimetric element is integrated inside the meat food packaging and combined with the curve from step (1) to establish the relationship between the color change of the metal-polyphenolamine-responsive colorimetric element and the freshness of the meat.

[0018] In one embodiment of the present invention, in step (1), fresh meat is briefly processed, placed in a food box, stored in an incubator at 4-25°C, the TVB-N value of the meat is measured according to national standards, the meat is evaluated as fresh, near-fresh, or spoiled according to the TVB-N value, and a curve of change in meat freshness and storage time is established.

[0019] In one embodiment of the present invention, in step (1), the TVB-N value of the meat is measured every 2 to 12 hours using a Kjeldahl nitrogen analyzer (SKD-800, Shanghai Peiou Analytical Instruments Co., Ltd.) in accordance with the "GB 5009.228-2016 National Standard for Food Safety: Measurement of Volatile Basic Nitrogen in Food," and the meat is classified as fresh, near-fresh, or spoiled based on the TVB-N value in accordance with the "GB 2707-2016 National Standard for Food Safety: Fresh (Frozen) Livestock and Poultry Products."

[0020] In one embodiment of the present invention, in step (2), after attaching the metal-polyphenolamine-responsive colorimetric element to the wrap film, the food tray containing the meat is sealed, or the element is attached to the inside of the food box, or placed inside the food so that it does not come into contact with the food, and the top of the colorimetric element is transparent and clearly visible, and the container is stored in an incubator at 4°C to 25°C.

[0021] In one embodiment of the present invention, in step (2), parallel experiments are conducted with three groups to ensure that the experimental errors of the three groups are within an acceptable range.

[0022] This is a metal-polyphenol network colorimetric sensing array intelligent meat freshness monitoring platform. It simulates real-life test scenes by capturing images of the metal-polyphenol network colorimetric sensing array and varying the angle and lighting conditions. Each sensor captures approximately 20 images at each point in time. All experiments are performed on a 48 GB NVIDIA A40 GPU using PyTorch as a deep learning frame, with a batch size of 32. During the training and test periods, the image size for input is adjusted to 224 x 224 pixels.

[0023] The model uses a ResNet-50 backbone and a three-dimensional Softmax layer to predict the freshness state, sets the learning rate to 0.001, trains the model with 100 iteration cycles, and follows a 4:1 ratio for the training set and test set in deep learning. The number of usage photos for each type of meat exceeds 5000. By combining the change curves of the freshness and storage time of four types of meat, it monitors the freshness of meat online in the way of image identification or photographic scanning.

Advantages of the Invention

[0024] The advantageous technical effects of the present invention are as follows: The present invention utilizes that the metal-phenolic network (MPN) is a multivalent coordination bond induced by the pH value, complements the coordination mechanism of metal-phenols in different amine environments in the prior art, and proposes a multi-stage competitive coordination color development mechanism based on the metal-phenol-amine system. Different from the discoloration mechanisms of conventional chemical or natural pigments, factors such as the type, valence of the coordinated metal ions, and the number and position of hydroxyl groups on the polyphenols enable the metal-phenol to exhibit rich color changes, the sensitivity of the metal-phenol to amines becomes extremely high, and the multi-stage competitive coordination mechanism also enables the metal-phenol system to exhibit multi-stage color changes with the increase of amine concentration, and moreover, the response range is relatively wide. At the same time, the coordination bond formed by the metal-phenolic network can well avoid the oxidative discoloration of polyphenols, and its strong adhesion can also be actually used in a simple loading method, greatly improving the operability of monitoring the freshness of meat by colorimetry.

[0025] The present invention screens an appropriate metal-phenol combination according to factors such as the variety, quality, and storage environment of meat, and prepares colorimetric monitoring materials including colorimetric labels, colorimetric test papers, colorimetric gels, colorimetric films, and colorimetric sensing arrays in a simple method, and can monitor the freshness of meat by means of visual inspection, colorimetric cards, code scanning, electrical sensing, etc.

[0026] The present invention has relatively high safety, environmental effects and economic feasibility. Moreover, both polyphenols and metal salts can be recovered and utilized from plant waste or industrial processing using the method of water extraction, which has economic effects and is at the same time greener and more environmentally friendly. Moreover, all the prepared materials can be recycled repeatedly.

Brief Description of the Drawings

[0027] [Figure 1] It is a freshness monitoring diagram of beef and pork by the iron chloride-tannic acid colorimetric tag prepared in Example 1 of the present invention. [Figure 2] It is a color response diagram of the metal-polyphenol colorimetric tag prepared in Example 2 of the present invention to ammonia, dimethylamine and trimethylamine. [Figure 3] It is a freshness monitoring diagram of fish meat by the metal-polyphenol prepared in Example 2 of the present invention. [Figure 4] It is a freshness monitoring diagram of sea bass meat by the polyvinyl alcohol-chitosan-collagen-iron chloride-anthocyanin colorimetric film prepared in Example 3 of the present invention. [Figure 5] It is the mold size of the metal-polyphenol network colorimetric sensing array in Example 4 of the present invention. [Figure 6] It is the color response of different metal-polyphenols to ammonia in Example 4 of the present invention. [Figure 7] It is the preparation process of the metal-polyphenol network colorimetric sensing array in Example 4 of the present invention. [Figure 8] It is a freshness monitoring diagram of meat by the metal-polyphenol network colorimetric array in Example 4 of the present invention. [Figure 9] It is the color change of preparing an iron chloride-tannic acid network colorimetric sensing array by adopting other substrates in Example 4 of the present invention, and the cost of the colorimetric sensing array adopting the substrate. [Figure 10]This is a stability test diagram after the reaction of iron chloride-tannic acid with ammonia in Example 4 of the present invention. [Figure 11] This describes the training process of a metal-polyphenol network colorimetric sensing array convolutional neural network and the flow of a metal-polyphenol network colorimetric sensing array meat freshness intelligent monitoring platform in Example 5 of the present invention. [Figure 12] This diagram shows a comparison of the lifecycle analysis of the metal-polyphenol network colorimetric sensing array meat freshness intelligent monitoring platform in Example 5 of the present invention and three TVB-N detection methods in national standards. [Figure 13] This is a schematic diagram of the color development mechanism and intelligent monitoring of the present invention. [Modes for carrying out the invention]

[0028] The present invention will be described in detail below with reference to the attached drawings and examples.

[0029] Example 1 Use of a metal-polyphenol coordination coloration system in meat freshness monitoring, comprising the following steps:

[0030] S1. Iron chloride and tannic acid solutions were prepared: Iron chloride hexahydrate and tannic acid powder were accurately weighed, dissolved in ultrapure water, and then combined into 1 mM and 0.5 mM solutions, respectively.

[0031] S2. A mixed solution of iron chloride and tannic acid was prepared: 2 mL of tannic acid solution was added to 4 mL of the above iron chloride solution and mixed thoroughly. Then, the pH of the mixed solution was adjusted to 3 using a 0.1 M sulfuric acid solution to obtain an iron chloride-tannic acid colorimetric solution.

[0032] S3. Iron chloride-tannic acid colorimetric tags were prepared: filter paper was punched into a 4 mm diameter disc, the disc was immersed in the iron chloride-tannic acid colorimetric solution, excess liquid was aspirated, and then it was dried to obtain the iron chloride-tannic acid colorimetric tags.

[0033] S4. Monitoring meat freshness using iron chloride-tannic acid colorimetric tags: 50g of fresh beef or pork was weighed and placed in a petri dish. The tag was taken and attached to the inside of the petri dish lid, and the dish was properly sealed. The dish was placed in a 10°C constant temperature incubator, and the change in the tag's color was observed every 12 hours. At the same time, the TVB-N of the meat was measured in a blank group, and the relationship between the TVB-N value and the color change was established. The freshness of the beef or pork was then determined using the iron chloride-tannic acid colorimetric tags.

[0034] As shown in Figure 1, the test results indicated that, under these storage conditions, the TVB-N measurement data showed that beef was fresh within 2 days, semi-fresh for 2-2.8 days, and spoiled and inedible thereafter. Under the same storage conditions, the TVB-N measurement data showed that pork was fresh within 2.5 days, semi-fresh for 2.5-3.5 days, and spoiled and inedible thereafter. The color change of the corresponding iron chloride-tannic acid colorimetric tags could be matched to the changes in the freshness of beef and pork. By extracting the chromaticity of the tags using ImageJ software and creating an iron chloride-tannic acid meat freshness colorimetric card, the freshness of beef and pork can be effectively determined.

[0035] Example 2 Use of a metal-polyphenol coordination coloration system in meat freshness monitoring, comprising the following steps:

[0036] S1. Metal salt and polyphenol solutions were prepared: iron chloride hexahydrate, copper sulfate pentahydrate, tannic acid, EGCG, and anthocyanin powder were accurately weighed, dissolved in ultrapure water, and then combined with 1 mM metal salt solution and 0.5 mM polyphenol solution, respectively.

[0037] S2. A metal-polyphenol colorimetric solution was prepared: Add 2 mL of tannic acid solution to 4 mL of the iron chloride solution, or add 2 mL of EGCG solution to 4 mL of the iron chloride solution, or add 2 mL of tannic acid solution to 4 mL of copper sulfate solution, or add 2 mL of EGCG solution to 4 mL of copper sulfate solution, or add 2 mL of anthocyanin solution to 4 mL of copper sulfate solution, mix thoroughly, then adjust the pH of the mixed solution to 3 using 0.1 M sulfuric acid solution to obtain a metal-polyphenol colorimetric solution. These are labeled as follows: a: FeCl3 + tannic acid, b: FeCl3 + EGCG, c: CuSO4 + tannic acid, d: CuSO4 + EGCG, and e: CuSO4 + anthocyanin.

[0038] S3, metal-polyphenol colorimetric tags were prepared: filter paper was immersed in the five solutions described in S2 for 30 seconds, then removed and dried, and punched into a 4 mm diameter disc to obtain five metal-polyphenol colorimetric tags.

[0039] S4. Monitoring meat freshness using metal-polyphenol colorimetric tags: 50g of fresh fish meat was weighed and placed in a petri dish. The tag was removed and attached to the inside of the petri dish lid. The dish was properly sealed and placed in a refrigerator at 10°C. The color change of the tag was observed every 12 hours. At the same time, the TVB-N of the meat was measured in a blank group, and the relationship between the TVB-N value and the color change was established. The freshness of the fish meat was then determined using metal-polyphenol colorimetric tags.

[0040] Figure 2 shows the color response diagrams of the metal-polyphenol colorimetric tags prepared in this example to ammonia, dimethylamine, and trimethylamine. The results showed that all metal-polyphenol tags could change in response to changes in the amine concentration (a: change from white to brown, b: change from white to light brown, c: change from white to yellow, d: change from white to yellow, e: change from red to light blue, where the change was fastest for ammonia, followed by trimethylamine, and the change was slowest for dimethylamine).

[0041] Figure 3 is a fish meat freshness monitoring diagram using metal-polyphenols prepared in this embodiment. The results showed that, in this storage environment, the TVB-N measurement data indicated that the fish meat was fresh within 1.8 days, semi-fresh from 1.8 to 2.7 days, and spoiled and inedible thereafter. The colors of the five corresponding metal-polyphenol colorimetric tags changed according to the change in storage time. By extracting the chromaticity of the tags using ImageJ software and creating five metal-polyphenol meat freshness colorimetric cards, the freshness of the fish meat can be effectively determined.

[0042] Example 3 Use of a metal-polyphenol coordination coloration system in meat freshness monitoring, comprising the following steps:

[0043] S1. A colorimetric solution of iron chloride and anthocyanin was prepared: Iron chloride hexahydrate and anthocyanin powder were accurately weighed, dissolved in ultrapure water, and then mixed into 4 mM and 1 mM solutions, respectively. 5 mL each of the iron chloride solution and anthocyanin solution were taken and thoroughly mixed. The pH of the mixed solution was then adjusted to 3 using a 0.1 M sulfuric acid solution to obtain the iron chloride-anthocyanin colorimetric solution.

[0044] S2. Polyvinyl alcohol-chitosan-collagen base material was prepared: 120 mL of a 3 wt% polyvinyl alcohol solution was mixed and placed in an oil bath pot at 95°C. After stirring thoroughly to dissolve, the temperature was lowered to 60°C, and 20 mL of the dissolved 1 wt% chitosan solution was added. Stirring was continued for 4 hours to obtain the polyvinyl alcohol-chitosan-collagen base material solution.

[0045] S3. A colorimetric film was prepared: The above solution was cooled to 40°C, and 10 mL of iron chloride-anthocyanin colorimetric mixed solution was added. Stirring was continued for 2 hours, and finally the mixture was poured into a petri dish. The film was prepared using the curtain coating method, and dried in a 40°C incubator for 48 hours to obtain a polyvinyl alcohol-chitosan-collagen-iron chloride-anthocyanin colorimetric film.

[0046] S5, Meat freshness monitoring using polyvinyl alcohol-chitosan-collagen-ferric chloride-anthocyanin colorimetric film: Weigh 200g of fresh sea bass meat and place it in a beaker, then take the above colorimetric film and measure 2 x 2 cm. 2 The film was cut into squares and attached to the inside of food boxes. The boxes were then placed in a 4°C refrigerator, and the color change of the film was observed every 24 hours. Simultaneously, the TVB-N of the fish meat was measured in a blank group. By establishing the relationship between the TVB-N value and the color change, the freshness of the sea bass meat was determined by the color of the polyvinyl alcohol-chitosan-collagen-iron chloride-anthocyanin colorimetric film.

[0047] Figure 4 shows a freshness monitoring diagram of sea bass meat using the polyvinyl alcohol-chitosan-collagen-iron chloride-anthocyanin colorimetric film prepared in this example. The results showed that although the color of the polyvinyl alcohol-chitosan-collagen-iron chloride-anthocyanin colorimetric film changed with storage time, the metal-polyphenol had a relatively high binding force to the substrate, and the film itself was coated, resulting in a relatively small contact area with gas and relatively small color changes. This demonstrated that the freshness of sea bass meat could be detected by identifying the color change of the colorimetric film within a certain range to a certain degree using ImageJ software.

[0048] Example 4 Use of a metal-polyphenol coordination coloration system in meat freshness monitoring, comprising the following steps:

[0049] S1, metal-polyphenol colorimetric solutions were prepared: a high-sensitivity group was selected: a metal ferrous chloride solution + a solution of tannic acid, gallic acid, caffeic acid, and catechin polyphenols; a sensitive group was selected: a metal ferrous chloride solution + a solution of tannic acid, gallic acid, caffeic acid, and catechin polyphenols; and a low-sensitivity group was selected: a metal copper sulfate solution + a solution of tannic acid, gallic acid, caffeic acid, and catechin polyphenols. Each solution was mixed with a 10 mM metal solution and a 2 mM polyphenol solution, and 2.5 mL of each metal and polyphenol solution was thoroughly mixed to obtain 12 groups of metal-polyphenol colorimetric solution combinations.

[0050] S2. Metal-polyphenol colorimetric sensing array was prepared: The above 5 ml of metal-polyphenol colorimetric solution was poured into a vacuum filter equipped with a PTFE membrane. After immersion for 30 seconds, it was filtered by suction, and then the membrane was dried in an oven at 40°C for 10 minutes. The above film was punctured using a 4 mm diameter punch and then sequentially arranged on a laser-etched plastic sheet to prepare a 3 × 4 metal-polyphenol network colorimetric sensing array.

[0051] S3. Monitoring of meat freshness by visual observation of a metal-polyphenol network colorimetric sensing array: 300g of fresh beef, chicken, fish, or shrimp was weighed and placed in a transparent food container. A metal-polyphenol network colorimetric sensing array was fixed inside the food container with UV glue, the container was tightly sealed, and stored in a refrigerator at 4°C. The color change of the colorimetric sensing array was observed every 12 hours, and at the same time, the TVB-N of the meat was measured in a blank group. By establishing the relationship between the TVB-N value and the color change, the freshness of the meat was determined by the color of the metal-polyphenol network colorimetric sensing array.

[0052] Figure 5 shows the mold size of the metal-polyphenol network colorimetric sensing array in this embodiment, and Figure 6 shows the color response of different metal-polyphenols to ammonia in this embodiment, from which a high-sensitivity group (whose color clearly changes within an ammonia aqueous concentration of 50 ppm, becoming darker or changing), a sensitive group (whose color changes within an ammonia aqueous concentration of 50 to 200 ppm, becoming darker or changing), and a low-sensitivity group (whose color changes above an ammonia aqueous concentration of 200 ppm, becoming darker or changing) are selected. A metal-polyphenol network colorimetric sensing array is then constructed using these, and Figure 7 shows the preparation process of the metal-polyphenol network colorimetric sensing array in this embodiment.

[0053] Figure 8 shows the meat freshness monitoring diagram using a metal-polyphenol network colorimetric array in this embodiment. Here, the top row of the array represents the high-sensitivity group, the middle row represents the sensitivity group, and the bottom row represents the low-sensitivity group. As a result, for each of the three freshness levels of meat—fresh, near-fresh, and spoiled—the array showed a clear change in tag color in at least one hole. For example, when beef went from near-fresh to spoiled, the color of the iron chloride-gallic acid tag clearly changed, indicating that the spoilage process in chicken meat was clearly reacted by iron chloride-tannic acid and iron chloride-caffeic acid. This demonstrated that the freshness of meat could be clearly distinguished visually.

[0054] Figure 9 shows the color change when preparing an iron chloride-tannic acid network colorimetric sensing array using other substrates in the embodiments of the present invention, and the cost of the colorimetric sensing array using these substrates. The results showed that using general filter paper and pulp sheets as array substrates significantly reduced costs, while the color change was appropriate and did not affect the monitoring effect.

[0055] Figure 10 shows the stability experiment diagram after the reaction of the iron chloride-tannic acid combination with ammonia in the example. The results showed that iron chloride-tannic acid did not detach after ammonia fumigation, regardless of whether it was immersed in water or ethanol or washed, demonstrating that it is not affected by the storage environment when used as a metal-polyphenol, is useful for long-term monitoring of food freshness, and has higher safety and accuracy.

[0056] Example 5 Metal-Polyphenol Network Colorimetric Sensing Array Meat Freshness Intelligent Monitoring Platform: Following the method described above, every 12 hours, boxes were removed from the refrigerator, and images of the metal-polyphenol network colorimetric sensing array were captured in a small recording studio. Real-world test scenes were simulated by varying the angle and lighting conditions, with each sensor capturing approximately 20 images at each point in time. All experiments were performed using a 48 GB NVIDIA A40 GPU as the deep learning frame with PyTorch, and a batch size of 32. During the training and test periods, the image size for input was adjusted to 224 x 224 pixels. The model predicted the freshness status using a ResNet-50 backbone and a three-dimensional Softmax layer. The learning rate was set to 0.001, and the model was trained for 100 iterations. The training and test sets in deep learning were in a 4:1 ratio, and the number of photos used for each type of meat exceeded 5000. By combining curves showing the changes in freshness and storage time for four types of meat, meat freshness was monitored online using image recognition or photographic scanning.

[0057] Figure 11 shows the training process of the metal-polyphenol network colorimetric sensing array convolutional neural network and the flow of the metal-polyphenol network colorimetric sensing array meat freshness intelligent monitoring platform in this embodiment. As a result, the accuracy was greatly improved by learning with the convolutional neural network, and the accuracy of the freshness judgment of four meats reached 99.83%, with the accuracy of chicken and shrimp reaching 100%.

[0058] Figure 12 shows a life cycle analysis comparison of the Metal-Polyphenol Network Colorimetric Sensing Array Intelligent Meat Freshness Monitoring Platform in this embodiment and three TVB-N detection methods in national standards (Semi-micro, Micro-diffusion, and Automated Instrumental Measurement). The results show that the Metal-Polyphenol Network Colorimetric Sensing Array Intelligent Meat Freshness Monitoring Platform is lower than the other measurement methods in all seven indicators: Abiotic Consumption (ADP), Acidification Potential (AP), Global Warming Potential (GWP), Eutrophication Potential (EP), Human Toxicity Potential (HTP), Photochemical Ozone Generation Potential (POCP), and Terrestrial Ecotoxicity Potential (TETP). This demonstrates that the Metal-Polyphenol Network Colorimetric Sensing Array Intelligent Meat Freshness Monitoring Platform has a better environmental impact.

[0059] Figure 13 is a schematic diagram of the multi-stage competitive coordination color development mechanism process and intelligent monitoring of metal-polyphenols proposed in the present invention.

[0060] The embodiments provided above do not limit the scope covered by the present invention, nor do the steps described limit the order in which they are performed. Those skilled in the art will clearly improve upon the present invention based on common sense and will also fall within the scope of protection set forth in the claims of the present invention.

Claims

1. The metal-polyphenol coordination color system is described below as follows: S1. Mix the metal salt solution and the polyphenol solution, adjust the pH, and obtain a metal-polyphenol colorimetric solution. S2. A metal-polyphenol colorimetric solution is supported on a substrate, dried, and cut to obtain a metal-polyphenolamine responsive colorimetric element. A metal-polyphenol coordination color development system characterized by the following:

2. The metal-polyphenol coordination color development system according to claim 1, characterized in that, in step S1, the concentration of the metal salt solution is 0.5 to 50 mM, the concentration of the polyphenol solution is 0.1 to 20 mM, and the ratio of the metal salt to the polyphenol substance in the metal-polyphenol colorimetric solution is 1:5 to 5:

1.

3. The metal-polyphenol coordination color development system according to claim 1, characterized in that in step S1, the metal salt is one of the following: hydrochloride of zinc, iron, ferrous oxide, aluminum, copper, cobalt, manganese, vanadium, molybdenum, or nickel; nitrate of zinc, iron, ferrous oxide, aluminum, copper, cobalt, manganese, vanadium, molybdenum, or nickel; or sulfate of zinc, iron, ferrous oxide, aluminum, copper, cobalt, manganese, vanadium, molybdenum, or nickel.

4. The metal-polyphenol coordination color development system according to claim 1, characterized in that in step S1, the polyphenol is one of anthocyanins, gallic acid, catechin, caffeic acid, curcumin, protocatecaldehyde, epicatechin, epigallocatechin, epigallocatechin gallate, tea polyphenols, and tannic acid.

5. The metal-polyphenol coordination color development system according to claim 1, characterized in that in step S1, the pH is 3 to 5.

6. The metal-polyphenol coordination color development system according to claim 1, characterized in that in step S2, the substrate is one or more of the following: filter paper, PTFE film, PVDF film, pulp sheet, cellulose-based film, polyvinyl alcohol, chitosan, sodium alginate, and polysaccharide collagen.

7. The metal-polyphenol coordination color development system according to claim 1, characterized in that in step S2, the loading method is one or more of spraying, immersion, suction filtration, printing, coating, 3D printing, and crosslinking.

8. The use of the metal-polyphenol coordination coloration system described in claim 1 in meat freshness monitoring, the method of use being as follows: (1) Establish a meat freshness index TVB-N and a storage time curve, (2) A metal-polyphenolamine-responsive colorimetric element is integrated inside the meat food packaging, and combined with the curve from step (1), to establish the relationship between the color change of the metal-polyphenolamine-responsive colorimetric element and the freshness of the meat. The use of the metal-polyphenol coordination color development system described in feature 1 in meat freshness monitoring.

9. The use according to claim 8, characterized in that, in step (1), fresh meat is briefly processed, then placed in a food box, stored in an incubator at 4-25°C, the TVB-N value of the meat is measured according to national standards, the meat is evaluated as fresh, near-fresh, or spoiled according to the TVB-N value, and a curve of change in meat freshness and storage time is established.

10. The use according to claim 8, characterized in that, in step (2), after attaching the metal-polyphenolamine-responsive colorimetric element to the wrap film, the food tray containing the meat is sealed, or the element is attached to the inside of the food box, or placed in the food so that it does not come into contact with the food, and the top of the colorimetric element is transparent and clearly visible, and then stored in an incubator at 4°C to 25°C.

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