Safe and stable oxygen indicator and preparation method thereof

Abstract

The invention relates to the technical field of oxygen indicators, in particular to a safe and stable oxygen indicator which at least comprises the following preparation raw materials: iron and ferrite, ethylenediamine tetraacetic acid and salt thereof, ascorbic acid and salt thereof, an alkaline buffer solution and water. The mass ratio of the iron and ferrous salt to the ethylenediamine tetraacetic acid and salt thereof to the ascorbic acid and salt thereof is 1: (5-25): (15-50), the color can be obviously changed under the lower oxygen concentration, the monitoring precision is improved, the indicator can be repeatedly changed when the oxygen concentration changes, and the service life is prolonged.

Description

Technical Field

[0001] The present invention relates to the technical field of oxygen indicators, and particularly to a safe and stable oxygen indicator and a preparation method thereof. Background Art

[0002] With the widespread application of deoxidizers in the food field, the demand for oxygen indicators in related scenarios is increasing. On the one hand, the deoxidizing component rapidly reduces the oxygen concentration in the package, creating a low-oxygen environment for the oxygen-indicating component, enabling it to more accurately reflect the oxygen residue. On the other hand, the color change of the oxygen-indicating component can visually feedback the deoxidation effect. If the oxygen-indicating component does not change color as expected during the deoxidation process, it can indicate that the deoxidation function may be abnormal, helping to promptly detect problems during the preservation process. For example, when the deoxidizer is working properly and the oxygen concentration in the package decreases, the oxygen-indicating component should correspondingly change color, corroborating each other to ensure the reliability of the preservation effect. Therefore, through the color change of the oxygen indicator, the usage status of the deoxidizer, that is, the high or low level or the presence or absence of oxygen, can be displayed, and it can quickly identify whether the package is leaking air, ensuring the safety of food during transportation and storage.

[0003] The main component of the oxygen indicator commonly used in the food field is methylene blue, which is a substance that changes color with oxidation-reduction reactions. In the "oxidized state", methylene blue is blue; while in the "reduced state", it becomes colorless. In an oxygen-deficient environment, methylene blue will remain in the colorless "reduced state" under the action of reducing sugar; when it comes into contact with oxygen in the air, it will be oxidized and turn blue. Sometimes, in order to have a distinct color contrast, a non-reactive red pigment is added, so that this type of indicator will first show pink in an anaerobic environment and purple in an aerobic environment. However, this type of indicator needs to react under strong alkaline conditions, so it cannot be compatible with a carbon dioxide environment, and the effect of using this type of oxygen indicator in combination with a constant-pressure deoxidizer is poor. Another type is the resazurin oxygen indicator. Although it can be compatible with a carbon dioxide environment, due to its high cost, it is less used in the food field. In the "oxidized state" of this type of oxygen indicator, resazurin is dark blue or purple; while in the "reduced state", it becomes colorless or light blue. The reduction reaction of resazurin has two stages. First, it irreversibly forms fluorescein, and the color changes from blue and purple to pink, and then reversibly changes from fluorescein to colorless dihydroresorcinol. It is used for anaerobic environment testing in biological culture. When the color of the resazurin oxygen indicator changes from pink to white, it indicates that anaerobic conditions have been reached.

[0004] Existing oxygen indicators, whether it is methylene blue or resazurin, have certain toxicity and poor self-stability, and are easily affected by environmental factors (such as temperature and humidity, pH value, light, carbon dioxide, grease, etc.). Strict control of storage and use conditions is required, which greatly limits the use and promotion of oxygen indicator products. Some oxygen indicators (such as traditional methylene blue type) have a long reaction time (from several minutes to several hours), which cannot meet the requirements of rapid detection. Chinese Patent Application (Publication No. CN 109588479 A) discloses an organically modified polyoxovanadate derivative. After this substance interacts with oxygen within a suitable oxygen concentration range, it causes a color change of the derivative, thereby indicating the change in oxygen concentration; Chinese Patent Application (Publication No. CN 109856125 A) discloses a nanoscale polyoxotungstate cluster oxygen indicator, which is prepared from a polyoxotungstate cluster by electrochemical reduction. Its molecular size reaches the nanoscale, which can effectively prevent the color developer from migrating into food and causing unexpected dyeing of food and other phenomena. However, both of these two types of indicators have a gradual change process in their own colors with the change of oxygen concentration, with a small color contrast and low sensitivity. Summary of the Invention

[0005] To solve the above problems, the present invention provides a safe and stable oxygen indicator, which can undergo an obvious color change at a lower oxygen concentration, improve the monitoring accuracy, enable the indicator to change color repeatedly when the oxygen concentration changes, and extend the service life.

[0006] On the one hand, the present invention provides a safe and stable oxygen indicator, and its preparation raw materials at least include: iron and ferrous salts, ethylenediaminetetraacetic acid and its salts, ascorbic acid and its salts, alkaline buffer solution, water; the mass ratio of the iron and ferrous salts, ethylenediaminetetraacetic acid and its salts, ascorbic acid and its salts is 1:(5 - 25):(15 - 50).

[0007] In one embodiment, the concentration of the iron and ferrous salts is 0.02 - 0.1 mol / L.

[0008] In one embodiment, the concentration of the iron and ferrous salts is 0.05 mol / L.

[0009] In one embodiment, the mass ratio of the iron and ferrous salts, ethylenediaminetetraacetic acid and its salts, ascorbic acid and its salts is 1:(10 - 20):(20 - 40).

[0010] In one embodiment, the mass ratio of the iron and ferrous salts, ethylenediaminetetraacetic acid and its salts, ascorbic acid and its salts is 1:(15 - 18):(25 - 35).

[0011] In one embodiment, the mass ratio of the iron and ferrous salts, ethylenediaminetetraacetic acid and its salts, and ascorbic acid and its salts is 1:18:30.

[0012] In one embodiment, the iron and ferrous salts are selected from at least one of ferric chloride, ferrous chloride, ferric sulfate, ferrous sulfate, or sodium iron ethylenediaminetetraacetate.

[0013] In one embodiment, the ethylenediaminetetraacetic acid and its salts are selected from at least one of ethylenediaminetetraacetic acid, disodium ethylenediaminetetraacetate, or tetrasodium ethylenediaminetetraacetate.

[0014] In one embodiment, the ascorbic acid and its salts are selected from at least one of ascorbic acid, sodium ascorbate, isoascorbic acid, or sodium isoascorbate.

[0015] In one embodiment, the concentration of the alkaline buffer solution is 0.2 - 0.4 mol / L.

[0016] In one embodiment, the concentration of the alkaline buffer solution is 0.3 mol / L.

[0017] In one embodiment, the alkaline buffer solution is selected from one of the sodium dihydrogen phosphate - disodium hydrogen phosphate buffer solution, ammonia - ammonium chloride buffer solution, or sodium carbonate - sodium bicarbonate buffer solution.

[0018] In one embodiment, the alkaline buffer solution is the sodium carbonate - sodium bicarbonate buffer solution.

[0019] In one embodiment, the raw materials for preparing the safe and stable oxygen indicator include: ferrous salts, ethylenediaminetetraacetate salts, ascorbate salts, sodium carbonate - sodium bicarbonate buffer solution, and water.

[0020] In one embodiment, the ferrous salt is ferrous sulfate, the ethylenediaminetetraacetate salt is tetrasodium ethylenediaminetetraacetate, and the ascorbate salt is sodium ascorbate.

[0021] Currently, oxygen indicators developed based on methylene blue or resazurin have problems in both safety and stability. In the present invention, a complex is prepared by mixing (ferrous) iron salts with ethylenediaminetetraacetic acid (salts) and ascorbic acid (salts) in a specific ratio. The complex indicates bright yellow in the "anaerobic reduced state" and red - brown in the "aerobic oxidized state", with a large color contrast and high sensitivity. Further, by controlling the mass ratio of the iron and ferrous salts, ethylenediaminetetraacetic acid and its salts, and ascorbic acid and its salts to be 1:(10 - 20):(20 - 40), the present invention optimizes the cooperative working mode between the deoxidizing component and the oxygen - indicating component, avoiding inaccurate monitoring of the anaerobic environment caused by premature color change and delayed color change, being compatible with the carbon dioxide environment, and having a good effect when used in combination with a constant - pressure deoxidizer.

[0022] The oxygen indicator provided by the present invention can be used in various fields that require indicating changes in oxygen concentration, with a wide range of applications. It is particularly suitable for the food field, and all raw materials are ingredients permitted for use in food additives, ensuring high safety. The complex prepared from ferrous salts, ethylenediaminetetraacetate salts, and ascorbate salts is only sensitive to oxygen, with little influence from light and heat, high stability, effectively avoiding phenomena such as moisture absorption and caking, and the migration of dye molecules to food resulting in unexpected staining of food.

[0023] On the other hand, the present invention provides a method for preparing a safe and stable oxygen indicator, which at least includes the following steps: dissolving ascorbic acid and its salts in water, adding an alkaline buffer solution until the pH = 9 - 11; adding iron and ferrous salts, and stirring to dissolve; adding ethylenediaminetetraacetic acid and its salts, and stirring to dissolve, thus obtaining a safe and stable oxygen indicator.

[0024] In one embodiment, the safe and stable oxygen indicator is in a liquid form, and different forms of oxygen indicator products are obtained by shaping the safe and stable oxygen indicator.

[0025] In one embodiment, the oxygen indicator products at least include oxygen indicator powder, oxygen indicator thread, or oxygen indicator paper.

[0026] In one embodiment, the method for preparing the oxygen indicator powder is: adding silica white to the safe and stable oxygen indicator and stirring to mix, thus obtaining the oxygen indicator powder. The addition amount of silica white is 30 - 50% of the weight of the safe and stable oxygen indicator.

[0027] In one embodiment, the addition amount of silica white is 45% of the weight of the safe and stable oxygen indicator.

[0028] In one embodiment, the method for preparing the oxygen indicator thread is: dipping a white cotton thread into the safe and stable oxygen indicator, after absorption to saturation, drying at 40 - 50 °C until the moisture content is 10 - 25 wt%, thus obtaining the oxygen indicator thread.

[0029] In one embodiment, the method for preparing the oxygen indicator thread is: dipping a white cotton thread into the safe and stable oxygen indicator, after absorption to saturation, drying at 40 - 50 °C until the moisture content is 18 wt%, thus obtaining the oxygen indicator thread.

[0030] In one embodiment, the method for preparing the oxygen indicator paper is: dipping absorbent paper into the safe and stable oxygen indicator, after absorption to saturation, drying at 40 - 50 °C until the moisture content is 10 - 25 wt%, thus obtaining the oxygen indicator paper.

[0031] In one embodiment, the method for preparing the oxygen indicator paper is: dipping a white cotton thread into the safe and stable oxygen indicator, after absorption to saturation, drying at 40 - 50 °C until the moisture content is 15 wt%, thus obtaining the oxygen indicator paper.

[0032] The safe and stable oxygen indicator provided by the present invention is applied in liquid form, or can be shaped into oxygen indicator products such as oxygen indicator powder, oxygen indicator line or oxygen indicator paper for application, meeting the application requirements of different fields and having extremely high market application and promotion value.

[0033] Beneficial effects

[0034] 1. The present invention provides a safe and stable oxygen indicator, which can have an obvious color change at a lower oxygen concentration, improve the monitoring accuracy, enable the indicator to change color repeatedly when the oxygen concentration changes, and extend the service life.

[0035] 2. The present invention forms a complex by mixing (ferrous) iron salts with ethylenediaminetetraacetic acid (salt) and ascorbic acid (salt). The complex indicates bright yellow in the "anaerobic reduced state" and indicates reddish-brown in the "aerobic oxidized state", with a large color contrast and high sensitivity.

[0036] 3. By controlling the mass ratio of iron and ferrous salts, ethylenediaminetetraacetic acid and its salts, and ascorbic acid and its salts to be 1:(10 - 20):(20 - 40), the present invention optimizes the cooperative working mode between the deoxidizing component and the oxygen-indicating component, avoids inaccurate monitoring of the anaerobic environment caused by premature color change and delayed color change, is compatible with the carbon dioxide environment, and has a good effect when used in combination with a constant-pressure deoxidizer.

[0037] 4. The oxygen indicator provided by the present invention can be used in various fields that require indicating oxygen concentration changes, has a wide range of applications, and is particularly suitable for the food field. All raw materials are ingredients permitted for use in food additives, with high safety. The complex prepared from ferrous salts, ethylenediaminetetraacetate salts, and ascorbate salts is only sensitive to oxygen, has little influence of light and heat, and has high stability, effectively avoiding phenomena such as moisture absorption and caking, and migration of dye molecules to food resulting in unexpected dyeing of food.

[0038] 5. The safe and stable oxygen indicator provided by the present invention is applied in liquid form, or can be shaped into oxygen indicator products such as oxygen indicator powder, oxygen indicator line or oxygen indicator paper for application, meeting the application requirements of different fields and having extremely high market application and promotion value. Specific embodiments

[0039] Example 1

[0040] Example 1 of the present invention provides a safe and stable oxygen indicator on the one hand. The raw materials for its preparation include: ferrous salt, ethylenediaminetetraacetate, ascorbate, sodium carbonate-sodium bicarbonate buffer solution, and water; the ferrous salt is ferrous sulfate, the ethylenediaminetetraacetate is sodium ethylenediaminetetraacetate, and the ascorbate is sodium ascorbate; the concentration of the ferrous salt is 0.05 mol / L, and the mass ratio of the ferrous salt, ethylenediaminetetraacetate, and ascorbate is 1:18:30. The concentration of the sodium carbonate-sodium bicarbonate buffer solution is 0.3 mol / L.

[0041] Example 1 of the present invention provides a method for preparing a safe and stable oxygen indicator on the other hand, including the following steps: dissolving the ascorbate in water, adding the sodium carbonate-sodium bicarbonate buffer solution until the pH = 10; adding the ferrous salt and stirring until dissolved; adding the ethylenediaminetetraacetate and stirring until dissolved, thus obtaining the safe and stable oxygen indicator.

[0042] The safe and stable oxygen indicator is shaped to prepare oxygen indicator powder. The preparation method of the oxygen indicator powder is: adding silica white to the safe and stable oxygen indicator and stirring and mixing to obtain the oxygen indicator powder. The addition amount of silica white is 45% of the weight of the safe and stable oxygen indicator.

[0043] The safe and stable oxygen indicator is shaped to prepare oxygen indicator wire. The preparation method of the oxygen indicator wire is: dipping a white cotton thread into the safe and stable oxygen indicator, absorbing until saturated, and drying at 40°C until the water content is 18 wt%, thus obtaining the oxygen indicator wire.

[0044] The safe and stable oxygen indicator is shaped to prepare oxygen indicator paper. The preparation method of the oxygen indicator paper is: dipping absorbent paper into the safe and stable oxygen indicator, absorbing until saturated, and drying at 40°C until the water content is 15 wt%, thus obtaining the oxygen indicator paper.

[0045] Example 2

[0046] Example 2 of the present invention provides a safe and stable oxygen indicator and its preparation method. The specific implementation is the same as that of Example 1, except that the mass ratio of the ferrous salt, ethylenediaminetetraacetate, and ascorbate is 1:25:15.

[0047] Example 3

[0048] Example 3 of the present invention provides a safe and stable oxygen indicator and its preparation method. The specific implementation is the same as that of Example 1, except that the mass ratio of the ferrous salt, ethylenediaminetetraacetate, and ascorbate is 1:5:50.

[0049] Comparative Example 1

[0050] Comparative Example 1 of the present invention is methylene blue oxygen indicator powder (blue in the presence of oxygen → red in the absence of oxygen). Its preparation raw materials, by mass percentage, include 3% glucose, 0.3% methylene blue, 5% 30wt% sodium hydroxide solution, 0.2% rose red pigment, and the balance is made up with water. After stirring and dissolving each raw material according to the mass ratio, a liquid indicator is obtained. Silica white is added to the liquid indicator and mixed to prepare methylene blue oxygen indicator powder. The addition amount of silica white is 50% of the total mass of the liquid indicator.

[0051] Comparative Example 2

[0052] Comparative Example 2 of the present invention is resazurin oxygen indicator powder (pink in the presence of oxygen → colorless in the absence of oxygen). Its preparation raw materials, by mass percentage, include 5% glucose, 0.01% resazurin, 2.5% sodium chloride, and the balance is made up with citrate buffer solution (0.1M, pH6.0). After stirring and dissolving each raw material according to the mass ratio, a liquid indicator is obtained. Silica white is added to the liquid indicator and mixed to prepare resazurin oxygen indicator powder. The addition amount of silica white is 50% of the total mass of the liquid indicator.

[0053] Performance test

[0054] 1. The oxygen indicator powders prepared in Examples 1 - 3 are respectively packaged in polyethylene bags, pasted on 500cc iron-based deoxidizers, and then placed together in a KOP (coated biaxially oriented polypropylene) bag. An oxygen concentration tester and a thermometer and hygrometer are also placed in the bag. After filling with 500 mL of air, the bag is sealed and placed in an incubator at 25°C (measured 24.7°C, 62% RH). The change in the oxygen concentration in the bag and the change in the color of the oxygen indicator are detected. Two samples are tested in parallel for each example.

[0055] Test results of Example 1:

[0056] (1) Color change point: After 12 hours, the oxygen concentrations of the two parallel samples both showed 0.5% (v / v), and the colors of the oxygen indicators were both reddish-brown; after 24 hours, the oxygen concentrations of the two parallel samples both showed 0.0% (v / v), and the colors of the oxygen indicators both changed to bright yellow. The color change point fell within the oxygen concentration range of 0.0% - 0.5%, indicating normal.

[0057] (2) Thermal stability: The sample that changed color under anaerobic conditions was placed in a high-temperature environment of 45°C for 7 days. The color of the oxygen indicator did not change. It changed back to reddish-brown within 10 minutes (response time) after opening the bag. The thermal stability was good, denoted as "√" (the same below).

[0058] (3) Light stability: The sample that changed color under anaerobic conditions was placed in an environment irradiated by an ultraviolet lamp for 7 days. The color of the oxygen indicator did not change. It changed back to reddish-brown within 10 minutes (response time) after opening the bag. The light stability was good, denoted as "√" (the same below).

[0059] Test Results of Example 2:

[0060] (1) Color change point: After 12 hours, the oxygen concentrations of the two parallel samples both showed 0.5% (v / v). The color of the oxygen indicator had changed from reddish-brown to bright yellow, and the color change point was advanced, affecting the determination of the anaerobic condition.

[0061] (2) Thermal stability: The above-mentioned samples with anaerobic color change were placed in a high-temperature environment of 45°C for 7 days. The color of the oxygen indicator did not change. It changed back to reddish-brown within 10 minutes (response time) after opening the bag. The thermal stability was good, denoted as "√".

[0062] (3) Light stability: The above-mentioned samples with anaerobic color change were placed in an environment irradiated by ultraviolet light for 7 days. The color of the oxygen indicator did not change. It changed back to reddish-brown within 10 minutes (response time) after opening the bag. The light stability was good, denoted as "√".

[0063] Test Results of Example 3:

[0064] (1) Color change point: After 24 hours, the oxygen concentrations of the two parallel samples both showed 0.0%. The color of the oxygen indicator was still reddish-brown and changed from reddish-brown to bright yellow only after 48 hours. The color change point was delayed, affecting the determination of the anaerobic condition.

[0065] (2) Thermal stability: The above-mentioned samples with anaerobic color change were placed in a high-temperature environment of 45°C for 7 days. The color of the oxygen indicator did not change. It changed back to reddish-brown within 10 minutes (response time) after opening the bag. The thermal stability was good, denoted as "√".

[0066] (3) Light stability: The above-mentioned samples with anaerobic color change were placed in an environment irradiated by ultraviolet light for 7 days. The color of the oxygen indicator did not change. It changed back to reddish-brown within 10 minutes (response time) after opening the bag. The light stability was good, denoted as "√".

[0067] 2. The oxygen indicator lines prepared in Examples 1-3 were respectively pasted on 500 cc constant-pressure deoxidizers with transparent tape, then put together into a KOP bag, and then an oxygen concentration tester and a thermometer and hygrometer were put in. After filling with 500 mL of air, it was sealed, and the KOP bag was placed in a constant-temperature oven at 25°C (measured 25.1°C, 65% RH) to detect the change of oxygen concentration and the change of the color of the oxygen indicator in the bag. Each example was tested in parallel with two samples.

[0068] Test Results of Example 1:

[0069] (1) Color change point: After 24 hours, the oxygen concentrations of the two parallel samples both showed 0.5% (v / v), and the colors of the oxygen indicators were both reddish-brown; after 48 hours, the oxygen concentrations of the two parallel samples both showed 0.0% (v / v), and the colors of the oxygen indicators both changed to bright yellow. The color change point fell within the oxygen concentration range of 0.0% - 0.5%, and the indication was normal, denoted as "√".

[0070] (2) Thermal stability: The sample that changed color under anaerobic conditions was placed in a high-temperature environment of 45°C for 7 days. The color of the oxygen indicator did not change. It changed back to red-brown within 10 minutes (response time) after opening the bag. The thermal stability was good and was marked as "√".

[0071] (3) Light stability: The sample that changed color under anaerobic conditions was placed in an environment irradiated by an ultraviolet lamp for 7 days. The color of the oxygen indicator did not change. It changed back to red-brown within 10 minutes (response time) after opening the bag. The light stability was good and was marked as "√".

[0072] Test results of Example 2:

[0073] (1) Color change point: After 24 hours, the oxygen concentrations of two parallel samples both showed 0.5% (v / v). The color of the oxygen indicator had changed from red-brown to bright yellow, and the color change point was advanced, affecting the determination of anaerobic conditions.

[0074] (2) Thermal stability: After 48 hours, the oxygen concentrations of two parallel samples both showed 0.0% (v / v). The sample that changed color under anaerobic conditions was placed in a high-temperature environment of 45°C for 7 days. The color of the oxygen indicator did not change. It changed back to red-brown within 10 minutes (response time) after opening the bag. The thermal stability was good and was marked as "√".

[0075] (3) Light stability: The sample that changed color under anaerobic conditions was placed in an environment irradiated by an ultraviolet lamp for 7 days. The color of the oxygen indicator did not change. It changed back to red-brown within 10 minutes (response time) after opening the bag. The light stability was good and was marked as "√".

[0076] Test results of Example 3:

[0077] (1) Color change point: After 48 hours, the oxygen concentrations of two parallel samples both showed 0.0% (v / v). The color of the oxygen indicator was still red-brown, and the color change point was delayed, affecting the determination of anaerobic conditions.

[0078] (2) Thermal stability: The sample that changed color under anaerobic conditions was placed in a high-temperature environment of 45°C for 7 days. The color of the oxygen indicator did not change. It changed back to red-brown within 10 minutes (response time) after opening the bag;

[0079] (3) Light stability: The sample that changed color under anaerobic conditions was placed in an environment irradiated by an ultraviolet lamp for 7 days. The color of the oxygen indicator did not change. It changed back to red-brown within 10 minutes (response time) after opening the bag.

[0080] 3. The oxygen indicator papers prepared in Examples 1 - 3 were respectively pasted onto 500 cc iron - based deoxidizers with transparent double - sided tape, and then placed together into a KOP bag. An oxygen concentration tester, a thermometer - hygrometer, and silica gel desiccant were also put into the bag. After filling with 500 mL of air, the bag was sealed and placed in an incubator at 25°C (measured at 24.9°C, 41% RH). The change in the oxygen concentration inside the bag and the change in the color of the oxygen indicator were detected. Two samples were tested in parallel for each example.

[0081] Test results of Examples 1 - 3:

[0082] Color change point of Example 1: After 12 h, the oxygen concentrations of the two parallel samples both showed 0.5% (v / v), and the color of the oxygen indicator was red - brown for both; after 24 h, the oxygen concentrations of the two parallel samples both showed 0.0% (v / v), and the color of the oxygen indicator changed to bright yellow for both.

[0083] Color change point of Example 2: After 12 h, the oxygen concentrations of the two parallel samples both showed 0.5% (v / v), and the color of the oxygen indicator had changed from red - brown to bright yellow, with the color change point advanced, which affected the determination of the anaerobic condition.

[0084] Color change point of Example 3: After 24 h, the oxygen concentrations of the two parallel samples both showed 0.0% (v / v), and the color of the oxygen indicator was still red - brown, with the color change point lagged, which affected the determination of the anaerobic condition.

[0085] 4. The oxygen indicator papers prepared in Examples 1 - 3 were respectively pasted onto 500 cc iron - based deoxidizers with transparent double - sided tape, and then placed together into a KOP bag. An oxygen concentration tester, a thermometer - hygrometer, and a wet cotton ball were also put into the bag. After filling with 500 mL of air, the bag was sealed and placed in an incubator at 25°C (measured at 24.8°C, 87% RH). The change in the oxygen concentration inside the bag and the change in the color of the oxygen indicator were detected. Two samples were tested in parallel for each example.

[0086] Test results of Examples 1 - 3:

[0087] Color change point of Example 1: After 12 h, the oxygen concentrations of the two parallel samples both showed 0.5% (v / v), and the color of the oxygen indicator was red - brown for both; after 24 h, the oxygen concentrations of the two parallel samples both showed 0.0% (v / v), and the color of the oxygen indicator changed to bright yellow for both.

[0088] Color change point of Example 2: After 12 h, the oxygen concentrations of the two parallel samples both showed 0.5% (v / v), and the color of the oxygen indicator had changed from red - brown to bright yellow, with the color change point advanced, which affected the determination of the anaerobic condition.

[0089] Example 3 Color change point: After 24 hours, the oxygen concentrations of two parallel samples both showed 0.0% (v / v), and the color of the oxygen indicator remained reddish-brown. The color change point lagged, affecting the determination of anaerobic conditions.

[0090] 5. a: The methylene blue oxygen indicator powder provided in Comparative Example 1 was used in combination with a constant-pressure deoxidizer, and it always showed blue, unable to normally indicate the anaerobic color.

[0091] b: The methylene blue oxygen indicator powder provided in Comparative Example 1 was sealed with a polyethylene bag, pasted on a 500 cc iron-based deoxidizer, and then placed together in a KOP bag. An oxygen concentration tester and a thermometer-hygrometer were also placed in the bag. After filling with 500 mL of air and sealing, the KOP bag was placed in an incubator at 25°C (measured 24.7°C, 62% RH), and the changes in the oxygen concentration and the color of the oxygen indicator in the bag were detected.

[0092] (1) Color change point: After 12 hours, the oxygen concentration showed 0.5%, and the color of the oxygen indicator had changed from blue to red. The color change point advanced, affecting the determination of anaerobic conditions.

[0093] (2) Thermal stability: The above-mentioned anaerobic color-changing sample was placed in a high-temperature environment of 45°C for 7 days. The color of the oxygen indicator did not change. It changed back to blue only 30 minutes after opening the bag (response time), indicating poor thermal stability.

[0094] (3) Light stability: The above-mentioned anaerobic color-changing sample was placed in an environment irradiated by ultraviolet lamps for 7 days. After opening, it remained red and did not turn blue, marked as "×".

[0095] 6. The resazurin oxygen indicator powder provided in Comparative Example 2 was sealed with a polyethylene bag, pasted on a 500 cc iron-based deoxidizer, and then placed together in a KOP bag. An oxygen concentration tester and a thermometer-hygrometer were also placed in the bag. After filling with 500 mL of air and sealing, the KOP bag was placed in an incubator at 25°C (measured 24.7°C, 62% RH), and the changes in the oxygen concentration and the color of the oxygen indicator in the bag were detected.

[0096] (1) Color change point: After 48 hours, the oxygen concentration showed 0.0%, and the color of the oxygen indicator remained pink. The color change point lagged, affecting the determination of anaerobic conditions.

[0097] (2) Thermal stability: The above-mentioned anaerobic color-changing sample was placed in a high-temperature environment of 45°C for 7 days. After opening, it remained colorless and did not turn red, marked as "×".

[0098] (3) Light stability: The above-mentioned anaerobic color-changing sample was placed in an environment irradiated by ultraviolet lamps for 7 days. After opening, it remained colorless and did not turn red, marked as "×".

[0099] 7. After encapsulating the resazurin oxygen indicator powder provided in Comparative Example 2 with a polyethylene bag, it was pasted onto a 500 cc constant-pressure deoxidizer, and the two were placed together in a KOP bag. Then, an oxygen concentration tester and a thermometer-hygrometer were put in. After filling with 500 mL of air, the bag was sealed and placed in an incubator at 25 °C (measured at 24.7 °C, 62% RH). The change in the oxygen concentration inside the bag and the change in the color of the oxygen indicator were detected.

[0100] (1) Color change point: After 48 h, the oxygen concentration showed 0.0%, and the color of the oxygen indicator was still pink. The color change point lagged, affecting the determination of the anaerobic condition.

[0101] (2) Thermal stability: The above-mentioned sample that changed color under anaerobic conditions was placed in a high-temperature environment of 45 °C for 7 days. After opening, the color of the oxygen indicator did not change and remained colorless without turning red, denoted as "×".

[0102] (3) Light stability: The above-mentioned sample that changed color under anaerobic conditions was placed in an environment irradiated by an ultraviolet lamp for 7 days. After opening, it remained colorless without turning red, denoted as "×".

[0103] The results of Performance Tests 1-7 are summarized in Table 1 below.

[0104] Table 1

[0105]

[0106] In Table 1, "-" indicates not measured; "--" indicates that relevant data could not be measured.

Claims

1. A safe and stable oxygen indicator, characterized in that: The preparation raw materials at least include: iron and ferrous salt, ethylenediaminetetraacetic acid and its salt, ascorbic acid and its salt, alkaline buffer solution and water; the mass ratio of the iron and ferrous salt, ethylenediaminetetraacetic acid and its salt, ascorbic acid and its salt is 1:(5-25):(15-50).

2. The safe and stable oxygen indicator according to claim 1, characterized in that: The mass ratio of the iron and ferrous salt, ethylenediaminetetraacetic acid and its salt, and ascorbic acid and its salt is 1:(10-20):(20-40).

3. The safe and stable oxygen indicator according to claim 1, characterized in that: The iron and ferrous salts are selected from at least one of ferric chloride, ferrous chloride, ferric sulfate, ferrous sulfate or sodium ferric ethylenediaminetetraacetate.

4. The safe and stable oxygen indicator according to claim 1, characterized in that: The ethylenediaminetetraacetic acid and its salt are selected from at least one of ethylenediaminetetraacetic acid, disodium ethylenediaminetetraacetate or tetrasodium ethylenediaminetetraacetate.

5. The safe and stable oxygen indicator according to claim 1, characterized in that: The ascorbic acid and its salt are selected from at least one of ascorbic acid, sodium ascorbate, isoascorbic acid or sodium isoascorbate.

6. The safe and stable oxygen indicator according to claim 1, characterized in that: The concentration of the alkaline buffer solution is 0.2-0.4 mol / L.

7. The safe and stable oxygen indicator according to claim 1, characterized in that: The alkaline buffer solution is selected from one of sodium dihydrogen phosphate-disodium hydrogen phosphate buffer solution, ammonia water-ammonium chloride buffer solution, and sodium carbonate-sodium bicarbonate buffer solution.

8. A method for preparing a safe and stable oxygen indicator according to any one of claims 1 to 7, characterized in that: The method comprises at least the following steps: dissolving ascorbic acid and its salt in water, adding alkaline buffer solution to pH=9-11; adding iron and ferrous salt, stirring and dissolving; adding ethylenediaminetetraacetic acid and its salt, stirring and dissolving, and obtaining a safe and stable oxygen indicator.

9. The method for preparing a safe and stable oxygen indicator according to claim 8, characterized in that: The safe and stable oxygen indicator is in liquid form. The safe and stable oxygen indicator is shaped to obtain oxygen indicator products in different forms. The oxygen indicator products at least include oxygen indicator powder, oxygen indicator thread or oxygen indicator paper.

10. The method for preparing a safe and stable oxygen indicator according to claim 9, characterized in that: The preparation method of the oxygen indicator powder is as follows: adding white carbon black to a safe and stable oxygen indicator, stirring and mixing, and then obtaining the oxygen indicator powder. The amount of the white carbon black added is 30-50% of the weight of the safe and stable oxygen indicator.

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