Reversible color-changing oxygen indicator for food deoxidation and preservation and preparation method thereof

Abstract

The application relates to the technical field of food detection, and particularly discloses a reversible color-changing oxygen indicator for food deoxidization and preservation and a preparation method thereof, which comprises a reversible coloration main system, a composite buffer system, an irreversible failure warning component, a moisturizing film-forming aid and deionized water; the reversible coloration main system is composed of ferrous salt, EDTA tetrasodium, and L-sodium ascorbate; the composite buffer system is composed of sodium carbonate, sodium bicarbonate and sodium citrate; the irreversible failure warning component is a food-grade polyphenol pigment; and the moisturizing film-forming aid comprises glycerol, sodium carboxymethyl cellulose and malt dextrin. The polyphenol pigment is used as the irreversible failure warning component, the indicator can show a characteristic color different from normal air leakage after the activity of the indicator is exhausted, the color difference degree is high, and the staff can quickly distinguish the package air leakage or the aging failure of the indicator by naked eyes, so that the problem that the colors of two types of working conditions of the existing product are consistent and the product control is misjudged is solved.

Description

Technical Field

[0001] This application relates to the field of food testing technology, and more specifically, it relates to a reversible color-changing oxygen indicator for food deoxygenation and preservation, and its preparation method. Background Technology

[0002] Oxygen-absorbing preservation technology is widely used in the storage and transportation of foods such as baked goods, meat products, nuts, tea, and freeze-dried ingredients. It uses iron-based oxygen absorbers to reduce the oxygen concentration inside the packaging, inhibiting oil oxidation and mold growth, thus extending the shelf life of the food. To visually assess the packaging's airtightness and the oxygen absorber's working status, the industry commonly uses oxygen indicators, which rely on oxidation-reduction color changes to indicate the oxygen content inside the packaging.

[0003] Currently, the mainstream commercial oxygen indicator is the methylene blue system. This system has obvious drawbacks: methylene blue is an industrial dye and not a food-grade additive that is allowed to directly contact materials. It is prone to migration in high-oil and high-moisture food packaging, which may contaminate food and pose a safety hazard.

[0004] A search revealed Chinese patent publication number CN120121609B, which discloses a safe and stable oxygen indicator and its preparation method. This invention discloses a ferrous-EDTA-ascorbate reversible oxygen indicator, using food-grade raw materials to replace toxic organic dyes, thus solving dye migration and safety issues to some extent. However, when the buffer component is depleted or the reducing agent is exhausted after multiple redox cycles, the indicator's color change completely overlaps with the visual appearance of packaging leaks, making it difficult for staff to quickly identify the type of malfunction and easily leading to misjudgment and scrapping of batches of food. Summary of the Invention

[0005] To address the problem in related technologies where, when the buffer component is depleted or the reducing agent is exhausted after multiple redox cycles, the color of the indicator completely overlaps with the visual appearance of air leakage in the packaging, making it impossible for staff to quickly identify the type of malfunction and easily leading to the misjudgment and scrapping of batches of food, this application provides a reversible color-changing oxygen indicator for food deoxygenation and preservation, and its preparation method.

[0006] In a first aspect, this application provides a reversible color-changing oxygen indicator for food deoxygenation and preservation, which adopts the following technical solution: a reversible color-changing oxygen indicator for food deoxygenation and preservation, comprising a reversible color-developing main system, a composite buffer system, an irreversible failure warning component, a moisturizing film-forming aid, and deionized water.

[0007] The reversible colorimetric host system is composed of ferrous salt, tetrasodium EDTA, and sodium L-ascorbate, wherein the mass ratio of ferrous salt, tetrasodium EDTA, and sodium L-ascorbate is 1:(13-17):(26-34).

[0008] The composite buffer system is composed of sodium carbonate, sodium bicarbonate, and sodium citrate.

[0009] The irreversible failure warning component is a food-grade polyphenol pigment;

[0010] The moisturizing film-forming aids include glycerin, sodium carboxymethyl cellulose, and maltodextrin.

[0011] By adopting the above technical solution, this application constructs a reversible colorimetric main system using a compound of ferrous salt, tetrasodium EDTA, and sodium L-ascorbate. The ratio of the three components is limited to a reasonable range. Reversible colorimetry is achieved by relying on the oxidation-reduction of ferrous ions. Tetrasodium EDTA provides a stable chelating effect on ferrous ions, preventing their hydrolysis and precipitation. Sodium L-ascorbate continuously provides reducing power, ensuring that the indicator has multiple reversible color changes. A composite buffer system is formed by the compounding of sodium carbonate, sodium bicarbonate, and sodium citrate. Compared with a single carbonate buffer system, this significantly improves the buffer capacity, stabilizes the pH of the system, resists the continuous dissolution of carbon dioxide in food packaging such as pastries and meat products, alleviates the large pH fluctuations caused by carbon dioxide consuming the buffer components, and delays the failure of the colorimetric system. Food-grade polyphenol pigments are added as an irreversible failure warning component. This component is only added when the buffer salt is exhausted and the reducing agent is consumed in large quantities. The indicator exhibits color development under depletion conditions. During the conventional reversible color change stages in both aerobic and anaerobic environments, there is no color interference, allowing differentiation between indicator failure and packaging leakage. This results in a bright yellow indicator when the oxygen-free seal is intact, and a single reddish-brown indicator when the packaging leaks and oxygen is present. When prolonged exposure to high CO2 causes buffer depletion or repeated cycles of reducing agent consumption, the indicator displays a reddish-brown base with a dark purplish-brown composite warning color, allowing for direct visual differentiation between packaging leakage and permanent indicator failure. Combined with glycerin, sodium carboxymethyl cellulose, and maltodextrin, a moisturizing film-forming aid is formed. Glycerin maintains the trace amounts of moisture required for the system reaction, sodium carboxymethyl cellulose provides film-forming binding, reducing the migration of active components, and maltodextrin evenly disperses the functional components, improving the overall stability of the indicator. All components work synergistically, balancing adaptability to high CO2 environments, reversible color change stability, and the ability to intuitively identify failure states.

[0012] Preferably, the indicator is bright yellow in the anaerobic and oxygen-free state, reddish-brown in the aerobic and leaky state, and reddish-brown with dark purplish-brown in the permanent failure state of buffer depletion and reducing agent failure, with a color difference value ΔE ≥ 7.5 between the leaky and failure states.

[0013] Preferably, the ferrous salt is ferrous sulfate monohydrate, and the polyphenolic pigment is ellagic acid.

[0014] Preferably, the proportions of each raw material by weight are as follows: 1 part ferrous sulfate monohydrate, 13-17 parts tetrasodium EDTA, 26-34 parts sodium L-ascorbate, 3.5-5.5 parts sodium carbonate, 7-9 parts sodium bicarbonate, 2-4 parts sodium citrate, 0.1-0.3 parts ellagic acid, 5-7 parts glycerol, 2-4 parts sodium carboxymethyl cellulose, 6-10 parts maltodextrin, and 10-30 parts deionized water.

[0015] Secondly, this application provides a method for preparing a reversible color-changing oxygen indicator for food deoxygenation and preservation, employing the following technical solution:

[0016] A method for preparing a reversible color-changing oxygen indicator for food deoxygenation and preservation includes the following steps:

[0017] S1. Preparation of premixed solution for composite buffer system: Take a portion of deionized water, add sodium carbonate, sodium bicarbonate and sodium citrate, stir at room temperature and low speed until completely dissolved to obtain composite buffer solution.

[0018] S2. Preparation of reducing agent water-locking matrix solution: Keep the same temperature as S1 and stir at low speed. Take all the remaining deionized water and add L-ascorbic acid sodium, glycerin and maltodextrin in sequence. After stirring to dissolve, slowly sprinkle in sodium carboxymethyl cellulose and stir until fully swollen and without lumps. Then add polyphenolic pigments and stir evenly to obtain matrix mixture.

[0019] S3, Coordination colorimetric system compounding: Keep the stirring at the same temperature as S1 and add EDTA tetrasodium and ferrous salt to the matrix mixture in sequence. Continue stirring until the solid is completely dissolved, so that the ferrous ions are completely chelated without precipitation, and obtain the coordination colorimetric solution.

[0020] S4. pH Adjustment and Homogenization: While maintaining the same temperature as in S1, stir at low speed and slowly add the composite buffer solution obtained in step S1 to the complexation colorimetric solution dropwise. Adjust the pH of the mixture to be stable at 9.5-10.5, filter to remove trace impurities, and obtain a clear reversible oxygen indicator stock solution.

[0021] Preferably, in step S1, 35-45% of the total deionized water is taken and stirred at low speed at 200-300 r / min in an environment of 15-25°C until sodium carbonate, sodium bicarbonate and sodium citrate are completely dissolved.

[0022] Preferably, in step S2, when adding sodium carboxymethyl cellulose, the sodium carboxymethyl cellulose is added at a uniform speed using a fine sieve at the center of the liquid surface vortex, with a total feeding time of 3 to 8 minutes; after feeding, the mixture is stirred for 25 to 35 minutes until the sodium carboxymethyl cellulose is fully swollen, the system is free of dry powder lumps, and the overall mixture is fine and uniform; then polyphenolic pigments are added and stirred for 3 to 8 minutes until completely dispersed and dissolved to obtain a matrix mixture.

[0023] Preferably, in step S3, EDTA tetrasodium is added first, and ferrous salt is added only after it is completely dissolved. This avoids the hydrolysis of ferrous salt under alkaline conditions to form ferric hydroxide precipitate, ensuring that the batch of stock solution is clear and free of turbidity.

[0024] Preferably, in step S4, the dropping rate is controlled such that no more than 1 / 4 of the total complex buffer volume is added every 8-12 minutes; the pH of the complex colorimetric solution is monitored in real time during the dropping process; after all the complex buffer has been added, the mixture is stirred for 15-25 minutes and filtered through a 180-220 mesh filter to remove trace amounts of insoluble impurities; the filtrate is the clear reversible oxygen indicator stock solution.

[0025] Preferably, in step S4, the reversible oxygen indicator stock solution is in liquid form, and the reversible oxygen indicator stock solution is modified to obtain oxygen indicator products in different forms. The oxygen indicator products include at least oxygen indicator powder, oxygen indicator line, or oxygen indicator paper.

[0026] In summary, this application has the following beneficial effects:

[0027] 1. This application uses polyphenolic pigments as an irreversible failure warning component. After the indicator loses its activity, it can show a characteristic color that is different from normal leakage. The color difference is highly distinguishable, and the staff can quickly identify packaging leakage or the aging and failure of the indicator itself with the naked eye, thus solving the problem of consistent color in two types of working conditions and misjudgment of quality control in existing products.

[0028] 2. This application constructs a ternary composite buffer system of sodium carbonate, sodium bicarbonate and sodium citrate. The three components work synergistically to broaden the stable pH range of the system, significantly improve the system's resistance to carbon dioxide erosion, effectively inhibit the precipitation caused by the hydrolysis of ferrous ions, and significantly extend the service life of the reversible color change cycle. It is suitable for long-term storage and transportation scenarios of high carbon dioxide release foods such as baked goods, fermented meat products and other foods.

[0029] 3. This application uses a compound system of glycerol, sodium carboxymethyl cellulose and maltodextrin as a ternary moisturizing film-forming aid. Sodium carboxymethyl cellulose forms a film to bind the active components and inhibit high humidity migration. Maltodextrin uniformly disperses the solid raw materials and adjusts the viscosity of the system. Glycerol continuously locks in water to ensure oxygen response speed. The three work together to make the color development uniform and stable. The stock solution is not prone to stratification and precipitation during long-term storage. It has good compatibility with coating and impregnation processing. Attached Figure Description

[0030] Figure 1 This is a flowchart of the preparation method of a reversible color-changing oxygen indicator for food deoxygenation and preservation provided in this application;

[0031] Figure 2 This is a 30-day pH fluctuation line graph of a reversible color-changing oxygen indicator for food deoxygenation and preservation provided in this application;

[0032] Figure 3 This is a diagram showing the reversible color-changing main system and manufacturing cost combination of a reversible color-changing oxygen indicator for food deoxygenation and preservation provided in this application;

[0033] Figure 4 This is a bar chart showing the stability test of a reversible color-changing oxygen indicator for food deoxygenation and preservation provided in this application. Detailed Implementation

[0034] The present application will be further described in detail below with reference to embodiments and comparative examples. Unless otherwise specified, the experimental methods used below are conventional methods. Unless otherwise specified, the materials, reagents, methods and instruments used are all conventional materials, reagents, methods and instruments in the art, which can be obtained by those skilled in the art through commercial channels or prepared according to literature methods.

[0035] Technical concept:

[0036] Iron-based oxygen absorbers are now widely used in the sealing and preservation packaging of various foods, such as baked goods, fermented meat products, nuts, and freeze-dried foods, to delay food oxidation and spoilage by reducing the oxygen concentration inside the packaging. To visually assess the working status of the oxygen absorber and whether there are leaks in the packaging, the industry uses oxygen indicators for visual oxygen monitoring. Currently, the mainstream oxygen indicator on the market is the methylene blue system. This system has significant drawbacks: methylene blue is not a compliant food additive that can directly contact food; it is prone to dye migration in high-oil, high-humidity food systems, posing a food safety risk. Furthermore, the methylene blue system relies on a strongly alkaline environment for reversible color change; fermented foods continuously release carbon dioxide, which quickly neutralizes the alkalinity of the system, causing the indicator to quickly become ineffective. Moreover, this indicator has a short reversible cycle life; after multiple leaks and resealing, the reducing agent is exhausted, resulting in permanent failure. The color appearance after failure is completely consistent with packaging leaks, making it impossible to distinguish the type of failure visually, leading to a high rate of misjudgment in quality control.

[0037] To overcome the shortcomings of the methylene blue system, existing technologies have proposed ferrous-EDTA-ascorbate reversible oxygen indicators, using all food-grade raw materials to avoid the safety hazards of dye migration. However, after multiple replication experiments, it was found that this type of existing system still has three major technical pain points: First, it only uses a single inorganic buffer combination of sodium carbonate and sodium bicarbonate, resulting in a low overall buffer capacity. When placed in a high carbon dioxide packaging environment for a long time, carbon dioxide continuously consumes the buffer salts, the pH of the system continues to decrease, the chelating ability of EDTA weakens, ferrous ions hydrolyze to form precipitates, the sodium ascorbate reducing agent is consumed more quickly, and the indicator ages and becomes unusable prematurely; Second, it only sets a single reversible oxygen indicator. The reverse color development unit can only distinguish between aerobic and anaerobic conditions in packaging. It does not have a dedicated failure warning component. When the buffer is depleted or the reducing agent is consumed below the threshold due to multiple redox cycles, there is no visual difference between the indicator color development and packaging leakage. Staff cannot quickly determine whether the packaging is damaged or the indicator itself has failed, which can easily lead to misjudgment and scrapping of a large number of food products. Third, it lacks a synergistic system of moisturizing film-forming aids compounded with glycerol, sodium carboxymethyl cellulose, and maltodextrin. The moisture content of the system cannot be stably controlled. In low humidity environments, rapid water loss interrupts the redox reaction, while in high humidity environments, active metal ions easily migrate, resulting in poor color uniformity and limited number of reversible cycles.

[0038] To address the aforementioned technical issues, an inorganic-organic composite buffer system is constructed using a combination of sodium carbonate, sodium bicarbonate, and sodium citrate. This significantly enhances the system's buffering capacity, stabilizes its pH range, and reduces the destructive effect of carbon dioxide on the colorimetric system. Based on the reversible primary colorimetric system of ferrous salt-tetrasodium EDTA-sodium L-ascorbate, a food-grade polyphenolic pigment is added as an independent irreversible failure warning component. This pigment only exhibits irreversible color development under failure conditions where the buffer salt is depleted and the reducing agent is consumed in large quantities. It does not interfere with conventional aerobic or anaerobic reversible color change processes, allowing for a direct distinction between packaging leaks and permanent indicator failure. Furthermore, glycerol, sodium carboxymethyl cellulose, and maltodextrin are combined as moisturizing film-forming aids. Glycerol continuously locks in moisture to ensure the redox reaction medium, sodium carboxymethyl cellulose forms a film that binds active components, reducing migration, and maltodextrin evenly disperses the various functional ingredients. These three components synergistically improve the indicator's adaptability to both dry and wet environments and its cycle life.

[0039] The raw materials and equipment used in the following embodiments of this application are described below:

[0040] Ferrous sulfate monohydrate, ferrous sulfate heptahydrate, ferrous chloride, tetrasodium EDTA, sodium L-ascorbate, sodium carbonate, sodium bicarbonate, sodium citrate, ellagic acid, grape seed anthocyanins, tannic acid, glycerol, sodium carboxymethyl cellulose, maltodextrin, silica, and water-based film-forming gums for food are all commercially available food-grade industrial raw materials that can be purchased directly from food additive suppliers.

[0041] The experimental mixing equipment includes a laboratory top-mounted electric stirrer and an industrial planetary mixing vessel; pH detection uses a portable digital pH meter; drying equipment is a constant temperature hot air oven; filtration uses a 200-mesh nylon filter; conventional chemical experimental equipment such as silica, fine sieves, and constant pressure dropping funnels can all be obtained through general chemical consumables channels, and those skilled in the art can purchase them through conventional commercial channels.

[0042] Example 1: This application provides a reversible color-changing oxygen indicator for food deoxygenation and preservation, comprising a reversible color-developing main system, a composite buffer system, an irreversible failure warning component, a moisturizing film-forming aid, and deionized water;

[0043] The reversible colorimetric main system consists of ferrous salt, tetrasodium EDTA, and sodium L-ascorbate, with a mass ratio of ferrous salt, tetrasodium EDTA, and sodium L-ascorbate of 1:15:30.

[0044] The composite buffer system is composed of sodium carbonate, sodium bicarbonate, and sodium citrate.

[0045] The irreversible failure warning component is a food-grade polyphenol pigment;

[0046] Moisturizing film-forming aids include glycerin, sodium carboxymethyl cellulose, and maltodextrin;

[0047] The indicator is bright yellow in the anaerobic and oxygen-free state, reddish-brown in the aerobic and leaky state, and reddish-brown with dark purplish-brown in the permanent failure state of buffer depletion and reducing agent failure. The color difference value ΔE between the leak and failure states is ≥7.5.

[0048] The ferrous salt is ferrous sulfate monohydrate, and the polyphenolic pigment is ellagic acid;

[0049] The proportions of each raw material by weight are as follows: 1 part ferrous sulfate monohydrate, 15 parts tetrasodium EDTA, 30 parts sodium L-ascorbate, 4.5 parts sodium carbonate, 8 parts sodium bicarbonate, 3 parts sodium citrate, 0.2 parts ellagic acid, 6 parts glycerol, 3 parts sodium carboxymethyl cellulose, 8 parts maltodextrin, and 20 parts deionized water.

[0050] A method for preparing a reversible color-changing oxygen indicator for food deoxygenation and preservation includes the following steps:

[0051] S1. Preparation of premixed solution for composite buffer system: Take a portion of deionized water, add sodium carbonate, sodium bicarbonate and sodium citrate, stir at room temperature and low speed until completely dissolved to obtain composite buffer solution.

[0052] Take 40% of the total deionized water and stir at 250 r / min in a 20°C environment until sodium carbonate, sodium bicarbonate and sodium citrate are completely dissolved.

[0053] S2. Preparation of reducing agent water-locking matrix solution: Keep the same temperature as S1 and stir at low speed. Take all the remaining deionized water and add L-ascorbic acid sodium, glycerin and maltodextrin in sequence. After stirring to dissolve, slowly sprinkle in sodium carboxymethyl cellulose and stir until fully swollen and without lumps. Then add polyphenolic pigments and stir evenly to obtain matrix mixture.

[0054] When adding sodium carboxymethyl cellulose, the sodium carboxymethyl cellulose is added at a uniform speed through a fine sieve at the center of the liquid vortex, with a total feeding time of 5 minutes. After feeding, the mixture is stirred for 30 minutes until the sodium carboxymethyl cellulose is fully swollen, the system is free of dry powder lumps, and the whole is fine and uniform. Then, polyphenolic pigments are added and stirred for 5 minutes until they are completely dispersed and dissolved to obtain the matrix mixture.

[0055] S3, Coordination colorimetric system compounding: Keep the stirring at the same temperature as S1 and add EDTA tetrasodium and ferrous salt to the matrix mixture in sequence. Continue stirring until the solid is completely dissolved, so that the ferrous ions are completely chelated without precipitation, and obtain the coordination colorimetric solution.

[0056] In this process, EDTA tetrasodium is added first and completely dissolved before ferrous salt is added to prevent ferrous hydrolysis in an alkaline environment from forming ferric hydroxide precipitate, thus ensuring that the batch of stock solution is clear and free of turbidity.

[0057] S4. pH-controlled homogenization: While maintaining the same temperature as in S1, stir at low speed and slowly add the composite buffer solution obtained in step S1 to the complex colorimetric solution by dropwise addition. Adjust the pH of the mixture to stabilize at 10, filter to remove trace impurities, and obtain a clear reversible oxygen indicator stock solution.

[0058] The dropping rate was controlled at 1 / 4 of the total complex buffer volume every 10 minutes. The pH of the complexing solution was monitored in real time during the dropping process. After all the complex buffer was added, the mixture was stirred for 20 minutes and filtered through a 200-mesh filter to remove trace amounts of insoluble impurities. The filtrate was the clear reversible oxygen indicator stock solution.

[0059] Example 2: The difference between this example and Example 1 is that this application provides a reversible color-changing oxygen indicator for food deoxygenation and preservation, wherein the mass ratio of ferrous salt, tetrasodium EDTA, and sodium L-ascorbate is 1:13:26.

[0060] The proportions of each raw material by weight are as follows: 1 part ferrous sulfate monohydrate, 13 parts tetrasodium EDTA, 26 parts sodium L-ascorbate, 3.5 parts sodium carbonate, 7 parts sodium bicarbonate, 2 parts sodium citrate, 0.1 parts ellagic acid, 5 parts glycerol, 2 parts sodium carboxymethyl cellulose, 6 parts maltodextrin, and 30 parts deionized water.

[0061] A method for preparing a reversible color-changing oxygen indicator for food deoxygenation and preservation includes the following steps:

[0062] S1. Preparation of premixed solution for composite buffer system: Take a portion of deionized water, add sodium carbonate, sodium bicarbonate and sodium citrate, stir at room temperature and low speed until completely dissolved to obtain composite buffer solution.

[0063] Take 35% of the total deionized water, stir at 200 r / min in a 15℃ environment at low speed, and continue stirring until sodium carbonate, sodium bicarbonate and sodium citrate are completely dissolved.

[0064] S2. Preparation of reducing agent water-locking matrix solution: Keep the same temperature as S1 and stir at low speed. Take all the remaining deionized water and add L-ascorbic acid sodium, glycerin and maltodextrin in sequence. After stirring to dissolve, slowly sprinkle in sodium carboxymethyl cellulose and stir until fully swollen and without lumps. Then add polyphenolic pigments and stir evenly to obtain matrix mixture.

[0065] When adding sodium carboxymethyl cellulose, the sodium carboxymethyl cellulose is added at a uniform speed through a fine sieve at the center of the liquid vortex, with a total feeding time of 3 minutes. After feeding, the mixture is stirred for 25 minutes until the sodium carboxymethyl cellulose is fully swollen, the system is free of dry powder lumps, and the whole is fine and uniform. Then, polyphenolic pigments are added and stirred for 3 minutes until they are completely dispersed and dissolved to obtain the matrix mixture.

[0066] S3, Coordination colorimetric system compounding: Keep the stirring at the same temperature as S1 and add EDTA tetrasodium and ferrous salt to the matrix mixture in sequence. Continue stirring until the solid is completely dissolved, so that the ferrous ions are completely chelated without precipitation, and obtain the coordination colorimetric solution.

[0067] In this process, EDTA tetrasodium is added first and completely dissolved before ferrous salt is added to prevent ferrous hydrolysis in an alkaline environment from forming ferric hydroxide precipitate, thus ensuring that the batch of stock solution is clear and free of turbidity.

[0068] S4. pH-controlled homogenization: While maintaining the same temperature as in S1, stir at low speed and slowly add the composite buffer solution obtained in step S1 to the complexation colorimetric solution by dropwise addition. Adjust the pH of the mixture to stabilize at 9.5, filter to remove trace impurities, and obtain a clear reversible oxygen indicator stock solution.

[0069] The dropping rate was controlled at 1 / 5 of the total complex buffer volume every 8 minutes. The pH of the complexing solution was monitored in real time during the dropping process. After all the complex buffer was added, the mixture was stirred for 15 minutes and filtered through a 180-mesh filter to remove trace amounts of insoluble impurities. The filtrate was the clear reversible oxygen indicator stock solution.

[0070] Example 3: The difference between this example and Example 1 is that this application provides a reversible color-changing oxygen indicator for food deoxygenation and preservation, wherein the mass ratio of ferrous salt, tetrasodium EDTA, and sodium L-ascorbate is 1:17:34.

[0071] The proportions of each raw material by weight are as follows: 1 part ferrous sulfate monohydrate, 17 parts tetrasodium EDTA, 34 parts sodium L-ascorbate, 5.5 parts sodium carbonate, 9 parts sodium bicarbonate, 4 parts sodium citrate, 0.3 parts ellagic acid, 7 parts glycerol, 4 parts sodium carboxymethyl cellulose, 10 parts maltodextrin, and 10 parts deionized water.

[0072] A method for preparing a reversible color-changing oxygen indicator for food deoxygenation and preservation includes the following steps:

[0073] S1. Preparation of premixed solution for composite buffer system: Take a portion of deionized water, add sodium carbonate, sodium bicarbonate and sodium citrate, stir at room temperature and low speed until completely dissolved to obtain composite buffer solution.

[0074] Take 45% of the total deionized water, stir at low speed at 300 r / min in a 25°C environment, and continue stirring until sodium carbonate, sodium bicarbonate and sodium citrate are completely dissolved.

[0075] S2. Preparation of reducing agent water-locking matrix solution: Keep the same temperature as S1 and stir at low speed. Take all the remaining deionized water and add L-ascorbic acid sodium, glycerin and maltodextrin in sequence. After stirring to dissolve, slowly sprinkle in sodium carboxymethyl cellulose and stir until fully swollen and without lumps. Then add polyphenolic pigments and stir evenly to obtain matrix mixture.

[0076] When adding sodium carboxymethyl cellulose, the sodium carboxymethyl cellulose is added at a uniform speed through a fine sieve at the center of the liquid vortex, with a total feeding time of 8 minutes. After feeding, the mixture is stirred for 35 minutes until the sodium carboxymethyl cellulose is fully swollen, the system is free of dry powder lumps, and the whole is fine and uniform. Then, polyphenolic pigments are added and stirred for 8 minutes until they are completely dispersed and dissolved to obtain the matrix mixture.

[0077] S3, Coordination colorimetric system compounding: Keep the stirring at the same temperature as S1 and add EDTA tetrasodium and ferrous salt to the matrix mixture in sequence. Continue stirring until the solid is completely dissolved, so that the ferrous ions are completely chelated without precipitation, and obtain the coordination colorimetric solution.

[0078] In this process, EDTA tetrasodium is added first and completely dissolved before ferrous salt is added to prevent ferrous hydrolysis in an alkaline environment from forming ferric hydroxide precipitate, thus ensuring that the batch of stock solution is clear and free of turbidity.

[0079] S4. pH-controlled homogenization: While maintaining the same temperature as in S1, stir at low speed and slowly add the composite buffer solution obtained in step S1 to the complexation colorimetric solution by dropwise addition. Adjust the pH of the mixture to stabilize at 10.5, filter to remove trace impurities, and obtain a clear reversible oxygen indicator stock solution.

[0080] The dropping rate was controlled at 1 / 3 of the total complex buffer volume every 12 minutes. The pH of the complex chromogenic solution was monitored in real time during the dropping process. After all the complex buffer was added, the mixture was stirred for 25 minutes and filtered through a 220-mesh filter to remove trace amounts of insoluble impurities. The filtrate was the clear reversible oxygen indicator stock solution.

[0081] Comparative Example 1: The only difference between this comparative example and Example 1 is that sodium citrate is not added; the other raw material components, proportions and preparation processes are the same as in Example 1.

[0082] Comparative Example 2: The only difference between this comparative example and Example 1 is that ellagic acid is not added; the other raw material components, ratios and preparation processes are the same as in Example 1.

[0083] Comparative Example 3: The only difference between this comparative example and Example 1 is that sodium carboxymethyl cellulose was removed, glycerol was added to 9 parts, and maltodextrin was kept to 8 parts; the remaining raw material components, proportions and preparation processes were the same as in Example 1.

[0084] Comparative Example 4: The only difference between this comparative example and Example 1 is that maltodextrin was removed, glycerol was added to 14 parts, and sodium carboxymethyl cellulose was kept at 3 parts; the remaining raw material components, proportions and preparation processes were the same as in Example 1.

[0085] Comparative Example 5: This comparative example differs from Example 1 only in that it uses existing related technologies for formulation, wherein the mass ratio of ferrous sulfate, ethylenediaminetetraacetic acid tetrasodium salt, and ascorbate is 1:18:30, the concentration of ferrous salt is 0.05 mol / L, the concentration of sodium carbonate-sodium bicarbonate buffer solution is 0.3 mol / L, and the remainder is water; preparation method: dissolve ascorbate in water, add sodium carbonate-sodium bicarbonate buffer solution to pH=10; add ferrous salt and stir to dissolve; add ethylenediaminetetraacetic acid salt and stir to dissolve, thus obtaining a safe and stable oxygen indicator.

[0086] Experiment 1: Performance Comparison Experiment of a Reversible Color-Changing Oxygen Indicator for Food Deoxygenation and Preservation

[0087] 1. High CO2 buffer tolerance test

[0088] Test method: Each group of indicator strips was sealed in an independent packaging bag. A mixture of 3% carbon dioxide and air was introduced into the bag to simulate the packaging environment of fermented pastries and meat products. The bags were kept at a constant temperature of 25°C for 30 days. The pH of the indicator stock solution was measured using a portable pH meter on days 0, 5, 10, 20 and 30, and the maximum pH fluctuation difference of each group was recorded. At the same time, the presence of reddish-brown iron hydroxide precipitate and liquid stratification were observed visually.

[0089] 2. Reversible color-changing cycle life test

[0090] Detection method: Place each group of indicator strips in a sealed transparent container, and alternately introduce nitrogen and air to complete a single cycle: introduce nitrogen for 30 minutes, let stand for 10 minutes and record the color development as yellow under oxygen-free conditions; then introduce air for 30 minutes, let stand for 10 minutes and record the color development as reddish-brown under aerobic conditions; repeat the above operation until the sample can no longer recover its bright yellow color after introducing nitrogen, count the total number of valid cycles, and take the average value of parallel samples.

[0091] 3. Performance test for distinguishing between failure and leakage by color development

[0092] Detection method: 3% carbon dioxide by volume was continuously introduced to accelerate the aging and failure of each group of indicators. Color values ​​of the samples were collected under normal leakage and complete failure conditions. The color difference ΔE between the two conditions was measured using a colorimeter. It is stipulated that when ΔE>5, the two working conditions can be clearly distinguished by the naked eye, and when ΔE≤5, there is no obvious visual difference.

[0093] 4. Colorimetric development, anti-migration, and uniformity testing in high humidity environments

[0094] Testing Methods: Total migration and heavy metal migration were tested according to the GB4806 series standards. Each set of indicator strips was stored in a constant temperature, sealed environment at 85% relative humidity for 15 days. Color values ​​were measured at three points (left, center, and right) of the sample using a colorimeter, and the maximum color difference between the three points was calculated. Simultaneously, the sample surface was observed for color migration, mottling, or exudates. Judgment Criteria: A three-point color difference ≤ 1.5 indicates uniform color development; a difference > 1.5 indicates significant uneven migration. All raw materials were food additives or food contact auxiliaries permitted by GB2760. The total migration and heavy metal migration of the finished product met the requirements of the GB4806 series standards and were safe for direct contact with materials inside food packaging.

[0095] 5. Stability test of the stock solution at room temperature

[0096] Test method: Each group of indicator stock solution was filled with nitrogen gas, protected from light and sealed, and stored at room temperature of 25°C for 6 months. The stock solution was observed for layering and precipitation every month. In the 6th month, the oxygen response time was tested. The response time was the time from the introduction of air to the stable appearance of reddish-brown color.

[0097] 6. Viscosity test of the original solution

[0098] Test method: Under constant temperature of 25℃, take the clarified original liquid after preparation and filtration of each group, and test the dynamic viscosity using a rotational viscometer with the same rotor and the same rotation speed. The unit is mPa·s. Each group is measured in parallel 3 times and the average value is taken.

[0099] Viscosity grading standards: Low viscosity: <200 mPa·s, smooth impregnation and coating, not easy to clog; Medium viscosity: 200~400 mPa·s, suitable for general processing, the optimal processing range of this invention; High viscosity: >400 mPa·s, poor fluidity of the original solution, easy to have uneven coating thickness and slow impregnation penetration.

[0100] The experimental results are shown in Table 1.

[0101] Table 1:

[0102] Sample number Maximum pH fluctuation over 30 days Effective number of reversible cycles Leakage / Failure Color Difference ΔE Maximum color difference at three points during 15 days of high humidity Oxygen response time of the original solution after 6 months (s) Viscosity of the stock solution at 25℃ (mPa・s) 6-month storage of the original solution Example 1 0.3 35 11.2 0.8 20 292 The entire process is clear with no stratification or sedimentation. Example 2 0.65 32 7.5 1.4 32 168 Microparticles at the bottom Example 3 0.2 38 13.6 0.6 20 456 The entire process is clear with no stratification or sedimentation. Comparative Example 1 1.25 22 9.8 1.3 65 275 A reddish-brown precipitate appeared after 3 months of storage. Comparative Example 2 0.62 31 1.1 1.2 30 281 Slightly cloudy, with no obvious sediment. Comparative Example 3 0.6 26 8.1 3.2 48 364 After 4 months of storage, the layers separate and color migration occurs. Comparative Example 4 0.58 27 8.6 2.1 45 347 Slight stratification after 4 months of storage Comparative Example 5 1.32 21 0.9 3.8 68 263 After 3 months of storage, a large amount of sediment and inactivation occurred.

[0103] See attached document Figure 1 - Appendix Figure 4 Furthermore, based on the various embodiments and comparative examples, it can be seen that:

[0104] In summary, combining Examples 1-3 and Comparative Example 1 with Table 1, it can be seen that the ternary composite buffer system composed of sodium carbonate, sodium bicarbonate, and sodium citrate is the core synergistic component determining the indicator's CO2 tolerance and cycle life. With the increase in the amount of the three buffer salts added, the 30-day pH fluctuation in Examples 2, 1, and 3 decreased from 0.65 to 0.20, and the number of reversible cycles increased from 32 to 38, indicating a simultaneous improvement in buffer performance. In contrast, Comparative Example 1, which removed sodium citrate and retained only a binary inorganic buffer, exhibited a pH fluctuation as high as 1.25 and only 22 cycles, showing significant performance degradation. The mechanism of action involves the carbonate providing basic alkalinity to neutralize CO2, sodium citrate filling the buffer blind zone in the weakly alkaline range, and the three synergistically stabilizing the system pH, maintaining EDTA's chelation of ferrous ions, reducing precipitate formation, protecting the reducing activity of sodium ascorbate, and producing a synergistic effect that no single component can achieve. However, increasing the amount of buffer salt will increase the viscosity of the system. Example 3 has the best buffering performance but the viscosity is too high, which increases the processing difficulty and raw material cost. The midpoint ratio in Example 1 takes into account both the buffering effect and the processing fluidity, and has the best overall adaptability.

[0105] Based on Examples 1-3 and Comparative Example 2, and referring to Table 1, it can be seen that ellagic acid polyphenol warning pigments are the key components for visually distinguishing between gas leaks and indicator failures. Examples 1-3 all added ellagic acid, and the color differences ΔE between gas leaks and failures were 11.2, 7.5, and 13.6, respectively, all greater than 5. The two conditions were clearly distinguishable to the naked eye, and the higher the amount of ellagic acid added, the stronger the color difference distinction. Comparative Example 2, without added ellagic acid, had a color difference of only 1.1; after failure, the color was almost indistinguishable from the leak state, making it impossible to distinguish the fault type. The mechanism of action is as follows: During normal operation, this system maintains a weakly alkaline environment. Ellagic acid molecules are stable and do not undergo irreversible oxidative polymerization with ferrous ions or oxygen. Therefore, it does not participate in color development during normal anaerobic / aerobic reversible cycling and does not interfere with the ferrous-EDTA main color development system. When the system is subjected to continuous CO2 erosion, the buffer components are depleted, the pH drops significantly, and a large amount of L-ascorbic acid is consumed, disrupting the redox balance. Ellagic acid undergoes oxidative polymerization to generate dark quinone derivatives, producing irreversible characteristic color development. This color development only occurs during the complete inactivation stage of the indicator, distinguishing it from the reversible color development of ferrous ions during normal leakage, thus creating a clear visual color difference and effectively differentiating between the two operating conditions.

[0106] Combining Examples 1-3 and Comparative Example 3 with Table 1, it can be seen that sodium carboxymethyl cellulose is a key synergistic agent for improving the anti-migration and film-forming properties of indicators. In Examples 1-3, the ternary moisturizing film-forming system of glycerol, sodium carboxymethyl cellulose, and maltodextrin showed a maximum color difference of only 1.4 at three points after 15 days of high humidity, with uniform color development and no significant migration. In Comparative Example 3, which removed sodium carboxymethyl cellulose and retained only glycerol and maltodextrin, the color difference at three points increased to 3.2, with severe color variation and migration under high humidity. The oxygen response time also increased to 48 seconds after 6 months. The principle is that sodium carboxymethyl cellulose can form a high-molecular-weight film that binds ferrous ions, ellagic acid, and other active components, blocking the diffusion and migration of substances under high humidity, while simultaneously helping to lock in water and maintain the reaction medium.

[0107] Based on Examples 1-3 and Comparative Example 4, and referring to Table 1, it can be seen that maltodextrin is an important synergistic agent for balancing the dispersibility, viscosity, and color uniformity of the system. Comparative Example 4, which removed maltodextrin and retained only glycerol and sodium carboxymethyl cellulose, showed an increase in the three-point color difference to 2.1, and after 4 months of storage, slight stratification occurred, with a slower oxygen response rate. The principle is that maltodextrin can uniformly disperse solid components such as ferrous salts and ellagic acid, adjust the system viscosity, and alleviate the sedimentation of active substances.

[0108] As can be seen from Examples 1-3 and Comparative Example 5, and in conjunction with Table 1, the combined system of the ternary buffer, polyphenol warning pigment, and ternary moisturizing agent of this application has comprehensive synergistic advantages compared to the existing formulations in comparative documents that use only a single binary buffer, only glycerin for moisturizing, and no failure identification component. Comparative Example 5 showed significant deterioration in all indicators: pH fluctuation reached 1.32 after 30 days, reversible cycling was only 21 times, the color difference ΔE between leakage and failure was only 0.9, the three-point color difference under high humidity was 3.8, and it precipitated and became inactive after 3 months of storage. The existing system lacks the multiple functions of sodium citrate buffer enhancement, ellagic acid failure identification, and the dispersion and film formation of sodium carboxymethyl cellulose and maltodextrin. It cannot resist high carbon dioxide attack, cannot distinguish failure types, exhibits easy color migration, and has poor storage stability. Examples 1-3, with their complete compound systems, show significantly improved performance in all aspects.

[0109] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A reversible color-changing oxygen indicator for food deoxygenation and preservation, characterized in that, It includes a reversible color development system, a composite buffer system, an irreversible failure warning component, a moisturizing film-forming aid, and deionized water; The reversible colorimetric host system is composed of ferrous salt, tetrasodium EDTA, and sodium L-ascorbate, wherein the mass ratio of ferrous salt, tetrasodium EDTA, and sodium L-ascorbate is 1:(13-17):(26-34). The composite buffer system is composed of sodium carbonate, sodium bicarbonate, and sodium citrate. The irreversible failure warning component is a food-grade polyphenol pigment; The moisturizing film-forming aids include glycerin, sodium carboxymethyl cellulose, and maltodextrin.

2. The reversible color-changing oxygen indicator for food deoxygenation and preservation according to claim 1, characterized in that, The indicator is bright yellow in the anaerobic and oxygen-free state, reddish-brown in the aerobic and leaky state, and reddish-brown with dark purplish-brown in the permanent failure state of buffer depletion and reducing agent failure. The color difference value ΔE between the leak and failure states is ≥7.

5.

3. The reversible color-changing oxygen indicator for food deoxygenation and preservation according to claim 1, characterized in that, The ferrous salt is ferrous sulfate monohydrate, and the polyphenolic pigment is ellagic acid.

4. The reversible color-changing oxygen indicator for food deoxygenation and preservation according to claim 3, characterized in that, The proportions of each raw material by weight are as follows: 1 part ferrous sulfate monohydrate, 13-17 parts tetrasodium EDTA, 26-34 parts sodium L-ascorbate, 3.5-5.5 parts sodium carbonate, 7-9 parts sodium bicarbonate, 2-4 parts sodium citrate, 0.1-0.3 parts ellagic acid, 5-7 parts glycerol, 2-4 parts sodium carboxymethyl cellulose, 6-10 parts maltodextrin, and 10-30 parts deionized water.

5. A method for preparing a reversible color-changing oxygen indicator for food deoxygenation and preservation, characterized in that, The reversible color-changing oxygen indicator for food deoxygenation and preservation as described in any one of claims 1-4 comprises the following steps: S1. Preparation of premixed solution for composite buffer system: Take a portion of deionized water, add sodium carbonate, sodium bicarbonate and sodium citrate, stir at room temperature and low speed until completely dissolved to obtain composite buffer solution. S2. Preparation of reducing agent water-locking matrix solution: Keep the same temperature as S1 and stir at low speed. Take all the remaining deionized water and add L-ascorbic acid sodium, glycerin and maltodextrin in sequence. After stirring to dissolve, slowly sprinkle in sodium carboxymethyl cellulose and stir until fully swollen and without lumps. Then add polyphenolic pigments and stir evenly to obtain matrix mixture. S3, Coordination colorimetric system compounding: Keep the stirring at the same temperature as S1 and add EDTA tetrasodium and ferrous salt to the matrix mixture in sequence. Continue stirring until the solid is completely dissolved, so that the ferrous ions are completely chelated without precipitation, and obtain the coordination colorimetric solution. S4. pH Adjustment and Homogenization: While maintaining the same temperature as in S1, stir at low speed and slowly add the composite buffer solution obtained in step S1 to the complexation colorimetric solution dropwise. Adjust the pH of the mixture to be stable at 9.5-10.5, filter to remove trace impurities, and obtain a clear reversible oxygen indicator stock solution.

6. The method for preparing a reversible color-changing oxygen indicator for food deoxygenation and preservation according to claim 5, characterized in that, In step S1, take 35-45% of the total deionized water and stir at low speed at 200-300 r / min in an environment of 15-25℃ until sodium carbonate, sodium bicarbonate and sodium citrate are completely dissolved.

7. The method for preparing a reversible color-changing oxygen indicator for food deoxygenation and preservation according to claim 5, characterized in that, In step S2, when adding sodium carboxymethyl cellulose, the sodium carboxymethyl cellulose is added at a uniform speed through a fine sieve at the center of the liquid vortex, with a total feeding time of 3 to 8 minutes. After feeding, the mixture is stirred for 25 to 35 minutes until the sodium carboxymethyl cellulose is fully swollen, the system is free of dry powder lumps, and the whole system is fine and uniform. Then, polyphenolic pigments are added and stirred for 3 to 8 minutes until they are completely dispersed and dissolved to obtain the matrix mixture.

8. The method for preparing a reversible color-changing oxygen indicator for food deoxygenation and preservation according to claim 5, characterized in that, In step S3, first add tetrasodium EDTA, and after it is completely dissolved, add ferrous salt to avoid the hydrolysis of ferrous salt in an alkaline environment to form ferric hydroxide precipitate, thus ensuring that the batch of stock solution is clear and free of turbidity.

9. The method for preparing a reversible color-changing oxygen indicator for food deoxygenation and preservation according to claim 5, characterized in that, In step S4, the dropping rate is controlled so that no more than 1 / 4 of the total complex buffer volume is added every 8-12 minutes. The pH of the complex colorimetric solution is monitored in real time during the dropping process. After all the complex buffer has been added, the mixture is stirred for 15-25 minutes and filtered through a 180-220 mesh screen to remove trace amounts of insoluble impurities. The filtrate is the clear reversible oxygen indicator stock solution.

10. The method for preparing a reversible color-changing oxygen indicator for food deoxygenation and preservation according to claim 5, characterized in that, In step S4, the reversible oxygen indicator stock solution is in liquid form. The reversible oxygen indicator stock solution is then modified to obtain oxygen indicator products in different forms. The oxygen indicator products include at least oxygen indicator powder, oxygen indicator line, or oxygen indicator paper.

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