A storage-stable preservative developer and method of making the same

Abstract

The application discloses a kind of with storage-resistant preservative color developing agent and preparation method thereof, belong to intelligent packaging and functional technical field, the application provides a kind of with the storage-resistant preservative function of humidity response type color developing agent, the color developing agent is a kind of "core-shell" structure microsphere, its core is copper-based MOF limited encapsulation cyanine chelate, shell is the crosslinked polyacrylate-acrylamide hydrogel layer with environmental humidity sensitivity, shell is dense under dry state, can isolate oxygen, light, protect core;When environmental humidity exceeds threshold value, shell rapidly water-swelling, permeability sharply increases, triggers the rapid release of cyanine and copper ion in core, simultaneously realizes high sensitivity color development and high-efficiency antibiosis.

Description

Technical Field

[0001] This invention belongs to the field of intelligent packaging and functional technology, specifically a color-developing agent with long shelf life and preservation and its preparation method. Background Technology

[0002] Natural anthocyanins are widely available, safe, and non-toxic, and possess sensitive pH-sensitive color-changing properties, making them ideal candidate materials for developing intelligent indicators of food freshness. However, anthocyanins are extremely sensitive to light, heat, oxygen, and humidity in the environment, and are prone to irreversible degradation, causing their color-changing function to be rapidly lost during storage and use. Furthermore, anthocyanins themselves do not possess antibacterial properties; in packaging applications, they can only "indicate" spoilage but cannot "delay" it, resulting in a limited function.

[0003] In existing technologies, encapsulating anthocyanins with metal-organic frameworks (MOFs) can improve their stability to some extent. However, the powder materials prepared by this method still face two major bottlenecks in practical applications: first, anthocyanins located in the shallow layer of MOF channels will still slowly oxidize during long-term storage; second, their release behavior is passive diffusion, which cannot sense changes in environmental humidity and respond actively and quickly, resulting in a lag in color development sensitivity in real high-humidity and spoilage environments.

[0004] Therefore, there is an urgent need to develop an integrated functional material that can be stored stably for a long time and can actively and quickly release color-developing / preservative factors in response to changes in microenvironment humidity caused by microbial activity. Summary of the Invention

[0005] The purpose of this invention is to provide a moisture-responsive colorimetric agent with storage and preservation properties and its preparation method. This invention provides a moisture-responsive colorimetric agent with storage and preservation properties. The colorimetric agent is a core-shell structured microsphere. Its core is an anthocyanin chelate confined and encapsulated by a copper-based MOF, and its shell is a cross-linked polyacrylamide hydrogel layer that is sensitive to environmental humidity. The shell is dense in the dry state and can isolate oxygen and light to protect the core. When the environmental humidity exceeds the threshold, the shell rapidly absorbs water and swells, and its permeability increases dramatically, triggering the rapid release of anthocyanins and copper ions in the core, simultaneously achieving highly sensitive color development and efficient antibacterial properties.

[0006] The objective of this invention can be achieved through the following technical solutions: A method for preparing a storage-resistant, preservative-preservative, and color-developing agent includes the following steps: Step 1: Under light-protected and room-temperature conditions, dimethylimidazole and anthocyanins are dispersed in an aqueous solution to obtain solution A, which can be used for copper ion coordination.

[0007] Step 2: Slowly add copper nitrate solution dropwise to solution A under light-protected conditions. 2+It chelates with the hydroxyl and carbonyl groups on the anthocyanin molecule, while dimethylimidazole assists in coordination, forming anthocyanin copper chelate precipitate. After centrifugation, washing, and low-temperature vacuum drying to remove impurities and solvents, anthocyanin chelates with improved antioxidant stability are obtained.

[0008] Step 3: Using cyclohexane as the oil phase and Span-80 as the dispersant, a reverse-phase suspension system is constructed. First, acrylic acid is neutralized at low temperature to obtain partially neutralized acrylate monomers. Then, anthocyanin chelates, acrylamide monomers, ammonium persulfate initiator, and free radical copolymerization are added to form a three-dimensional cross-linked polymer gel network of polyacrylic acid-acrylamide. The anthocyanin chelates are encapsulated and fixed in the gel network to obtain a colorimetric agent with storage resistance and preservation properties.

[0009] Furthermore, the specific preparation steps for solution A are as follows: Dimethylimidazole, deionized water, and anthocyanins were added to a reaction vessel and stirred and dispersed for 20-30 minutes under conditions of darkness, 20-25℃, and 500-600 r / min. Then, 0.2-0.4 mol / L sodium hydroxide solution was added to adjust the pH value to 6-7 to obtain solution A.

[0010] Furthermore, the ratio of dimethylimidazole, deionized water, and anthocyanins is 20-22g: 800-900mL: 3-6g.

[0011] Furthermore, the specific preparation steps for anthocyanin chelates are as follows: Under light-protected conditions, a 0.16-0.19 mol / L copper nitrate solution was added dropwise to solution A at a rate of 50-60 drops / min. The mixture was stirred at 20-25℃ and 500-600 rpm for 20-30 min, centrifuged at 5000-6000 rpm for 3-5 min, filtered, and the precipitate was washed 2-4 times with deionized water and anhydrous ethanol. The precipitate was then vacuum dried at 40-50℃ for 1-2 h to obtain anthocyanin chelates.

[0012] Furthermore, the specific preparation steps for the storage-resistant, preservative-preservative, and color-developing agent are as follows: Span-80 and cyclohexane were added to a reaction vessel and stirred for 50-60 min under a nitrogen atmosphere, at 4-5℃ and 500-600 r / min. Then, acrylic acid neutralization solution, anthocyanin chelate, acrylamide, ammonium persulfate and N,N-methylenebisacrylamide were added. The mixture was heated to 80-90℃ and reacted for 6-8 h. After cooling to room temperature, the product was washed 2-4 times with anhydrous ethanol and dried under vacuum at 60-70℃ for 2-4 h to obtain a colorimetric agent with storage and preservation properties.

[0013] Furthermore, the ratio of Span-80, cyclohexane, acrylic acid neutralizing solution, anthocyanin chelate, acrylamide, ammonium persulfate, and N,N-methylenebisacrylamide is 8-10g: 130-140g: 30-40g: 12-14g: 12-14g: 0.4-0.6g: 0.9-0.12g.

[0014] Furthermore, the specific preparation steps for the acrylic acid neutralization solution are as follows: Sodium hydroxide is added dropwise to a mixture of acrylic acid and deionized water, and the mixture is stirred and neutralized at 4-5℃ and 500-600 r / min until the degree of neutralization is 70-80%, thus obtaining a neutralized acrylic acid solution.

[0015] Furthermore, the ratio of sodium hydroxide, acrylic acid, and deionized water is 30-40g: 110-120g: 90-100g.

[0016] The beneficial effects of this invention are: 1. This invention provides a moisture-responsive colorimetric agent with storage and corrosion resistance. The colorimetric agent is a core-shell structured microsphere. Its core is a copper-based MOF-encapsulated anthocyanin chelate, and its shell is a cross-linked polyacrylamide hydrogel layer that is sensitive to environmental humidity. The shell is dense in the dry state and can isolate oxygen and light to protect the core. When the environmental humidity exceeds the threshold, the shell rapidly absorbs water and swells, and its permeability increases dramatically, triggering the rapid release of anthocyanins and copper ions in the core, thus achieving highly sensitive color development and efficient antibacterial activity simultaneously.

[0017] 2. This invention, through the dual protection of MOF-confined chelation and a high-density shell, significantly blocks the damage from oxygen and light. This invention innovatively introduces polyacrylamide hydrogel as an environmentally sensitive shell. This shell remains in a glassy state in a dry condition with extremely low permeability; once the ambient humidity exceeds a threshold, the hydrophilic groups in the shell layer rapidly hydrate, the polymer chains relax and swell, and the permeability increases exponentially in a short time. This rapid "permeability switch" effect triggers the rapid release of anthocyanins and antibacterial copper ions from the core, thereby achieving "on-demand activation" of the color development and anti-corrosion functions. Detailed Embodiments The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0018] Example 1: A method for preparing a storage-resistant, preservative-preservative, and color-developing agent, comprising the following steps: S1: Add 20g of dimethylimidazole, 800mL of deionized water and 3g of anthocyanin to a reaction vessel, stir and disperse for 20min under the conditions of avoiding light, 20℃ and 500r / min, then add 0.2mol / L sodium hydroxide solution to adjust the pH value to 6 to obtain solution A.

[0019] S2: Under light-protected conditions, 400 mL of 0.16 mol / L copper nitrate solution was added dropwise to solution A at a rate of 50 drops / min. The mixture was stirred at 20 °C and 500 r / min for 20 min, centrifuged at 5000 r / min for 3 min, filtered, and the precipitate was washed twice with deionized water and anhydrous ethanol. The precipitate was then dried under vacuum at 40 °C for 1 h to obtain anthocyanin chelates.

[0020] S3: Add 30g sodium hydroxide dropwise to a mixture of 110g acrylic acid and 90g deionized water, and stir at 4℃ and 500r / min until the degree of neutralization is 70% to obtain a neutralized acrylic acid solution. Add 8g Span-80 and 130g cyclohexane to a reaction vessel, and stir at 4℃ and 500r / min for 50min under a nitrogen atmosphere. Then add 30g of the neutralized acrylic acid solution, 12g of anthocyanin chelate, 12g of acrylamide, 0.4g of ammonium persulfate and 0.9g of N,N-methylenebisacrylamide, heat to 80℃, and continue the reaction for 6h. Cool to room temperature, wash the product twice with anhydrous ethanol, and dry under vacuum at 60℃ for 2h to obtain a colorimetric agent with storage and preservation properties.

[0021] Example 2: A method for preparing a storage-resistant, preservative-preservative, and color-developing agent, comprising the following steps: S1: Add 21g of dimethylimidazole, 850mL of deionized water and 4.5g of anthocyanin to a reaction vessel, stir and disperse for 25min under the conditions of avoiding light, 22.5℃ and 550r / min, and then add 0.3mol / L sodium hydroxide solution to adjust the pH value to 6.5 to obtain solution A.

[0022] S2: Under light-protected conditions, 450 mL of 0.175 mol / L copper nitrate solution was added dropwise to solution A at a rate of 55 drops / min. The mixture was stirred at 22.5 °C and 550 r / min for 25 min, centrifuged at 5500 r / min for 4 min, filtered, and the precipitate was washed three times with deionized water and anhydrous ethanol. The precipitate was then dried under vacuum at 45 °C for 1.5 h to obtain anthocyanin chelates.

[0023] S3: Add 35g sodium hydroxide dropwise to a mixture of 115g acrylic acid and 95g deionized water, and stir and neutralize at 4.5℃ and 550r / min until the degree of neutralization is 75% to obtain a neutralized acrylic acid solution. Add 9g Span-80 and 135g cyclohexane to a reaction vessel, and stir for 55min at 4.5℃ and 550r / min under a nitrogen atmosphere. Then add 35g of the neutralized acrylic acid solution, 13g of anthocyanin chelate, 13g of acrylamide, 0.5g of ammonium persulfate and 0.105g of N,N-methylenebisacrylamide, heat to 85℃, and continue to react for 7h. Cool to room temperature, wash the product three times with anhydrous ethanol, and dry under vacuum at 65℃ for 3h to obtain a colorimetric agent with storage and preservation properties.

[0024] Example 3: A method for preparing a storage-resistant, preservative-preservative, and color-developing agent, comprising the following steps: S1: Add 22g of dimethylimidazole, 900mL of deionized water and 6g of anthocyanin to a reaction vessel, stir and disperse for 30min under the conditions of avoiding light, 25℃ and 600r / min, and then add 0.4mol / L sodium hydroxide solution to adjust the pH value to 7 to obtain solution A.

[0025] S2: Under light-protected conditions, 500 mL of 0.19 mol / L copper nitrate solution was added dropwise to solution A at a rate of 60 drops / min. The mixture was stirred at 25 °C and 600 r / min for 30 min, centrifuged at 6000 r / min for 5 min, filtered, and the precipitate was washed four times with deionized water and anhydrous ethanol. The precipitate was then dried under vacuum at 50 °C for 2 h to obtain anthocyanin chelates.

[0026] S3: Add 40g sodium hydroxide dropwise to a mixture of 120g acrylic acid and 100g deionized water, and stir and neutralize at 5℃ and 600r / min until the degree of neutralization is 80% to obtain a neutralized acrylic acid solution; add 10g Span-80 and 140g cyclohexane to a reaction vessel, and stir for 60min at 5℃ and 600r / min under a nitrogen atmosphere. Then add 40g of the neutralized acrylic acid solution, 14g of anthocyanin chelate, 14g of acrylamide, 0.6g of ammonium persulfate and 0.12g of N,N-methylenebisacrylamide, heat to 90℃, and continue to react for 8h. Cool to room temperature, wash the product four times with anhydrous ethanol, and vacuum dry at 70℃ for 4h to obtain a colorimetric agent with storage and preservation properties.

[0027] Comparative Example 1: Based on Example 3, anthocyanin powder without any treatment was used directly.

[0028] Comparative Example 2: Based on Example 3, the anthocyanin chelate prepared only according to step S1 was directly used as a colorimetric agent with good storage and preservation properties.

[0029] Comparative Example 3: Based on Example 3, the anthocyanin chelate in step S2 was omitted.

[0030] Performance and stability tests were conducted on Examples 1-3 and Comparative Examples 1-3. For each sample powder, it was spread evenly in a petri dish and placed under 45°C and 4500 Lux illumination for 30 days. The colorimetric values ​​(L, a, b) on day 0 and day 30 were measured using a colorimeter, and the color difference ΔE and color retention rate were calculated. The results showed that: Example 1 product had a ΔE of 2.8 and a color retention rate of 91.5%; Comparative Example 2 had a ΔE of 11.3 and a retention rate of 65.8%; Comparative Example 1 had a ΔE of 34.5 and a retention rate of 18.2%.

[0031] Antibacterial test: After pre-absorbing moisture at 75%RH for 1 hour, 0.1g of each sample powder was pressed into a thin sheet and attached to a substrate coated with 1×10 6 The bacterial suspension was incubated on agar plates at 37°C for 24 hours, and the diameter of the inhibition zone was measured. In Example 1, the inhibition zones against Escherichia coli and Staphylococcus aureus were 15.2 mm and 16.8 mm, respectively; in Comparative Example 2, the inhibition zones were 12.4 mm and 13.1 mm, respectively; and in Comparative Example 3, no inhibition zone was observed.

[0032] Humidity response colorimetric test: The powder from Example 1 was placed in a sealed container with adjustable humidity and kept at 33%RH and 75%RH for 30 minutes respectively. The change in its hue angle (h°) was measured. The results showed that h° = 332° (purple-blue) at 33%RH, and h° changed to 356° (pink-purple) at 75%RH. The difference was extremely obvious to the naked eye, and the response time was <5 minutes. The results are shown in Table 1. Table 1 As shown in Table 1, Comparative Example 1 exhibits extremely poor storage stability. The phenolic hydroxyl groups of free anthocyanins are directly exposed to light, heat, and oxygen environments, making them highly susceptible to oxidation and degradation. After accelerated testing, the color difference reached as high as 34.5, and the color retention rate was only 18.2%, which completely fails to meet the requirements for long-term storage. It lacks moisture-responsive switching characteristics and coating barrier regulation, and color drift occurs slowly even at low humidity. It lacks the selectivity of "humidity threshold-triggered color development," making it unable to achieve on-demand color development. It contains no copper ion antibacterial components, and only anthocyanins themselves have a very weak antibacterial effect, thus having no practical value for preservative applications. During use, the pigment degrades rapidly, and the color development intensity decays quickly, making it impossible to perform the color development function stably for a long time.

[0033] In Comparative Example 2, the storage stability was insufficient. Copper chelation could only partially improve the stability of anthocyanins, but the chelate was directly exposed to the outside world without a shell to isolate oxygen and light, and photothermal degradation was still significant, with ΔE reaching 11.3 and color retention rate of only 65.8%, which could not meet the requirements for long-term storage. Without the threshold regulation of the hydrogel shell, anthocyanins and copper ions were released uncontrolled, and they slowly leached out and were lost during the dry storage period, failing to achieve the on-demand response of "color development / antibacterial only when wet". Copper ions were not encapsulated and released irregularly and were easily lost. The antibacterial zone was significantly smaller than that of the example, and the duration of antibacterial effect was short. The chelate powder was not modified with a shell and was prone to agglomeration, resulting in poor uniformity of color development and antibacterial effects.

[0034] Comparative Example 3 lacks the core anthocyanin color-developing substance, and has no color response regardless of humidity changes. It does not possess the basic properties of a color developer, has no copper ion antibacterial component, and the hydrogel itself has no antibacterial effect and no preservative effect. It is merely a blank polymer microsphere and cannot achieve the dual core objectives of this invention: "storage resistance and preservation, and moisture-responsive color development".

[0035] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the invention.

Claims

1. A method for preparing a storage-resistant, preservative-preserving, and color-developing agent, characterized in that, Includes the following steps: Step 1: Under light-protected and room-temperature conditions, dimethylimidazole and anthocyanins are dispersed in an aqueous solution to obtain solution A, which can be used for copper ion coordination. Step 2: Slowly add copper nitrate solution dropwise to solution A under light-protected conditions. 2+ It chelates with the hydroxyl and carbonyl groups on the anthocyanin molecule, and dimethylimidazole assists in coordination to form anthocyanin copper chelate precipitate. After centrifugation, washing and low-temperature vacuum drying to remove impurities and solvents, anthocyanin chelates with improved antioxidant stability are obtained. Step 3: Using cyclohexane as the oil phase and Span-80 as the dispersant, a reverse-phase suspension system is constructed. First, acrylic acid is neutralized at low temperature to obtain partially neutralized acrylate monomers. Then, anthocyanin chelates, acrylamide monomers, ammonium persulfate initiator, and free radical copolymerization are added to form a three-dimensional cross-linked polymer gel network of polyacrylic acid-acrylamide. The anthocyanin chelates are encapsulated and fixed in the gel network to obtain a colorimetric agent with storage resistance and preservation properties.

2. The method for preparing a storage-resistant, preservative-inhibiting, and color-developing agent according to claim 1, characterized in that, The specific preparation steps for solution A are as follows: Dimethylimidazole, deionized water, and anthocyanins were added to a reaction vessel and stirred and dispersed for 20-30 minutes under conditions of darkness, 20-25℃, and 500-600 r / min. Then, 0.2-0.4 mol / L sodium hydroxide solution was added to adjust the pH value to 6-7 to obtain solution A.

3. The method for preparing a storage-resistant, preservative-preserving, and color-developing agent according to claim 2, characterized in that, The ratio of dimethylimidazole, deionized water, and anthocyanin is 20-22g: 800-900mL: 3-6g.

4. The method for preparing a storage-resistant, preservative-inhibiting, and color-developing agent according to claim 1, characterized in that, The specific preparation steps for the anthocyanin chelate are as follows: Under light-protected conditions, a 0.16-0.19 mol / L copper nitrate solution was added dropwise to solution A at a rate of 50-60 drops / min. The mixture was stirred at 20-25℃ and 500-600 rpm for 20-30 min, centrifuged at 5000-6000 rpm for 3-5 min, filtered, and the precipitate was washed 2-4 times with deionized water and anhydrous ethanol. The precipitate was then vacuum dried at 40-50℃ for 1-2 h to obtain anthocyanin chelates.

5. The method for preparing a storage-resistant, preservative-preserving, and color-developing agent according to claim 1, characterized in that, The specific preparation steps of the storage-resistant, anti-corrosion, and color-developing agent are as follows: Span-80 and cyclohexane were added to a reaction vessel and stirred for 50-60 min under a nitrogen atmosphere, at 4-5℃ and 500-600 r / min. Then, acrylic acid neutralization solution, anthocyanin chelate, acrylamide, ammonium persulfate and N,N-methylenebisacrylamide were added. The mixture was heated to 80-90℃ and reacted for 6-8 h. After cooling to room temperature, the product was washed 2-4 times with anhydrous ethanol and dried under vacuum at 60-70℃ for 2-4 h to obtain a colorimetric agent with storage and preservation properties.

6. The method for preparing a storage-resistant, preservative-inhibiting, and color-developing agent according to claim 5, characterized in that, The ratio of Span-80, cyclohexane, acrylic acid neutralizing solution, anthocyanin chelate, acrylamide, ammonium persulfate and N,N-methylenebisacrylamide is 8-10g: 130-140g: 30-40g: 12-14g: 12-14g: 0.4-0.6g: 0.9-0.12g.

7. The method for preparing a storage-resistant, preservative-inhibiting, and color-developing agent according to claim 1, characterized in that, The specific preparation steps of the acrylic acid neutralization solution are as follows: Sodium hydroxide is added dropwise to a mixture of acrylic acid and deionized water, and the mixture is stirred and neutralized at 4-5℃ and 500-600 r / min until the degree of neutralization is 70-80%, thus obtaining a neutralized acrylic acid solution.

8. The method for preparing a storage-resistant, preservative-preserving, and color-developing agent according to claim 7, characterized in that, The ratio of sodium hydroxide, acrylic acid, and deionized water is 30-40g: 110-120g: 90-100g.

9. A color developer with storage resistance, corrosion resistance, and color development properties, characterized in that, It is prepared by the preparation method described in any one of claims 1-8.

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