Preparation method and application of intelligent indication label based on microencapsulated anthocyanin

Abstract

The invention discloses a preparation method and application of an intelligent indication label based on microencapsulated anthocyanin, and belongs to the field of food monitoring. The preparation method comprises the following steps: (1) extracting pitaya peel anthocyanin; (2) preparing pitaya peel anthocyanin microcapsules; (3) providing a film-forming matrix solution; and (4) preparing a membrane solution. Compared with the traditional detection method which has the defects of time consumption, sample damage, need of expensive equipment and professional operators and the like, the invention aims at solving the industrial pain point of real-time, visual and nondestructive monitoring of the freshness of the aquatic products in the food supply chain, especially in the cold chain circulation process. The method has the characteristics of no toxicity, harmlessness, relatively low cost, simplicity and convenience in operation and the like.

Description

Technical Field

[0001] This invention belongs to the field of smart labels, specifically relating to a method for preparing and applying a smart indicator label based on microencapsulated anthocyanins. Background Technology

[0002] With increasing public concern about food safety and quality, food freshness monitoring technologies have been extensively studied. As a perishable food, the rapid and accurate monitoring of the freshness of aquatic products is particularly important. Currently, smart packaging technology, as a novel food packaging technology, can monitor changes in food quality in real time, providing consumers with intuitive information on food freshness, and has become a research hotspot in the food packaging field.

[0003] Anthocyanins, as natural pigments, possess excellent pH sensitivity, exhibiting different colors in response to changes in environmental pH. Therefore, they are widely used in the preparation of food freshness indicator labels. Dragon fruit peel anthocyanins stand out among many anthocyanins due to their abundant source, vibrant color, and good stability. However, anthocyanins have relatively poor stability and are easily affected by factors such as light, temperature, pH, oxygen, metal ions, and enzymes during dragon fruit peel processing, leading to loss of biological activity and fading. During film-forming solution preparation, drying, and subsequent storage, directly exposed anthocyanins are highly susceptible to degradation and oxidation, resulting in weakened or lost color development function and a short label lifespan. Furthermore, directly added water-soluble anthocyanins, similar to small-molecule amines, easily migrate or leak from hydrophilic polymer membrane networks, not only causing a decline in indicator function but also potentially contaminating the food. Furthermore, increasing the amount of anthocyanins required to improve sensitivity often disrupts the network structure of the membrane matrix, leading to decreased membrane mechanical properties (such as tensile strength and elongation at break) and increased susceptibility to breakage. Simultaneously, high concentrations of free anthocyanins are more prone to aggregation and degradation. Conversely, reducing the amount of anthocyanins to maintain membrane performance results in indistinct color changes and insufficient sensitivity. Direct mixing makes it difficult to ensure uniform distribution of anthocyanins within the membrane, potentially leading to aggregate formation and inconsistent local color responses, thus affecting the accuracy and reliability of the detection results.

[0004] Microencapsulation can effectively protect anthocyanins from the effects of high temperature, light, metal ions, pH, and oxygen. However, existing microencapsulation technologies still face challenges in anthocyanin preparation, such as inappropriate wall material selection and poor encapsulation performance, making it difficult to simultaneously achieve microcapsule stability, encapsulation efficiency, and bioavailability.

[0005] Furthermore, existing anthocyanin indicator labels often use a single wall material or matrix material, making it difficult to simultaneously meet requirements for good mechanical properties, breathability, and indicator sensitivity. For example, while chitosan alone provides good antibacterial properties, the membrane lacks flexibility and breathability; conversely, while protein-based materials offer good film-forming properties and flexibility, they exhibit poor antibacterial properties and stability.

[0006] Therefore, developing a smart indicator technology that can monitor the freshness of aquatic products in real time, visually, non-destructively, and at low cost has significant market demand and application value. pH-sensitive smart indicator labels based on natural pigments (such as anthocyanins) are a research hotspot in this field, but the core challenge lies in improving the stability of anthocyanins during processing and use, and ensuring that the indicator labels have sensitive, reliable, and consistent response performance. Summary of the Invention

[0007] The purpose of this invention is to address the problems of poor stability of natural anthocyanins and the issues of improper selection of wall materials and poor encapsulation performance in the preparation of anthocyanins using microencapsulation technology. This invention provides a method for preparing and applying a smart indicator label based on microencapsulated anthocyanins. The product utilizes appropriate microencapsulation technology to improve the stability of anthocyanins, and through an optimized combination of wall and matrix materials, achieves long-term release of anthocyanins, improves the sensitivity of the indicator label, and enhances the encapsulation performance, mechanical properties, and stability of the microcapsules, thereby accurately monitoring changes in the freshness of aquatic products.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for preparing a smart indicator label based on microencapsulated anthocyanins, the method comprising: (1) Extraction of anthocyanins from dragon fruit peel: anthocyanins were extracted from dragon fruit peel using acidified ethanol; (2) Preparation of dragon fruit peel anthocyanin microcapsule powder: using gum arabic and maltodextrin as composite wall materials, dragon fruit peel anthocyanin extract was encapsulated by spray drying to obtain dragon fruit peel anthocyanin microcapsule powder. (3) Provide film-forming matrix solution: Mix chitosan solution and gelatin solution, add plasticizer, stir evenly to obtain film-forming matrix solution; (4) Preparation of film solution: Add the dragon fruit peel anthocyanin microcapsule powder obtained in step (2) to the film-forming matrix solution obtained in step (3), stir and mix and remove bubbles to obtain a uniform film-forming solution. Cast the obtained film-forming solution onto the substrate, and peel off the film after drying to obtain a smart indicator label.

[0009] Further, step (1) specifically involves: taking dragon fruit peel, using a 45-55% ethanol solution acidified with hydrochloric acid as the extraction solvent, mixing them at a material-to-liquid ratio of 1g:3-7mL, extracting with ultrasonic assistance, and then sequentially performing coarse filtration, purification, vacuum filtration, rotary evaporation concentration, and spray drying to obtain dragon fruit peel anthocyanin powder.

[0010] Furthermore, the conditions for ultrasound-assisted extraction are: ultrasound power of 200~400 W, ultrasound time of 30~50 min, and extraction in a water bath at 30~50℃ for 1~3 h.

[0011] Further, in step (2), the mass ratio of gum arabic to maltodextrin is from 1 to 3:1; the mass ratio of dragon fruit peel anthocyanin extract to the core wall of the composite wall material is from 1 to 5:1.

[0012] Further, in step (2), the solid content in the embedding process is 8%~12%, and a magnetic stirrer is used for mixing and stirring at a speed of 110~130 rpm for a stirring time of 40~60 min; the inlet air temperature of the spray drying is 160~180℃ and the outlet temperature is 90~110℃.

[0013] Further, in step (3), the chitosan is dissolved in an aqueous solution containing 1%~5% (v / v) glacial acetic acid to obtain a chitosan solution with a mass-volume concentration of 1%~3% (w / v); the gelatin solution has a mass-volume concentration of 1%-3% (w / v), and the volume ratio of the chitosan solution to the gelatin solution is from 1 to 3:1.

[0014] Further, in step (3), the plasticizer is glycerol, and its addition amount is 1~5% (v / v) of the total volume of the film-forming matrix solution.

[0015] Furthermore, in step (4), the mass ratio of the dragon fruit peel anthocyanin microcapsule powder to chitosan is 0.4~1.2:1.

[0016] Furthermore, in step (4), ultrasonic degassing is performed for 10-30 minutes to remove air bubbles.

[0017] An application of a smart indicator tag prepared by the above method in monitoring the freshness of aquatic products; the tag has good antioxidant properties and pH sensitivity.

[0018] The advantages of this invention over the prior art are as follows: 1. By extracting anthocyanins from dragon fruit peel and encapsulating them with a composite wall material of gum arabic and maltodextrin, and then preparing dragon fruit peel anthocyanin microcapsules using a spray drying process, the stability of anthocyanins was effectively improved. This combination effectively improved the thermal stability, environmental stability, and dispersibility of anthocyanins in the film-forming matrix, solving the key technical bottlenecks of easy degradation and unstable color change response of natural pigments.

[0019] 2. The prepared microencapsulated anthocyanins exhibit good sustained-release effects. By optimizing the core-to-wall ratio (1:2) and the wall material ratio (mass ratio of gum arabic to maltodextrin of 1:3), long-term release of anthocyanins was achieved, improving bioavailability.

[0020] 3. Chitosan (CS) and gelatin (SPI) are creatively used as film-forming matrices. The two form a dense composite network structure with excellent mechanical properties through intermolecular interactions (such as electrostatic attraction and hydrogen bonding). This not only provides a stable carrier for the indicator, but their good film-forming properties, barrier properties, and biocompatibility also ensure the practicality and safety of the film.

[0021] 4. A Systematic Solution for Synergistic Effects of Encapsulation and Film Formation: This solution is not a simple stacking of materials, but rather the construction of a synergistic system of "core (microcapsule) - outer shell (composite membrane)". Encapsulation technology protects the activity of the indicator, while film formation technology optimizes the immobilization and response environment of the indicator. The combination of the two achieves a highly sensitive, stable, and accurate visible color response of the indicator label to volatile amine compounds (such as ammonia and trimethylamine), thereby enabling precise visual indication of the freshness of aquatic products.

[0022] 5. The preparation method of this invention is simple to operate, the process is controllable, and it is easy to scale up for production, resulting in good economic benefits and practical value. Compared with the prior art, this invention optimizes the microcapsule preparation process and wall material selection, while simultaneously considering the stability, encapsulation rate, and bioavailability of the microcapsules, thus solving the problem that it is difficult to achieve these properties simultaneously in the prior art. Attached Figure Description

[0023] Figure 1 Flowchart for the preparation of smart indicator labels for microencapsulated anthocyanins.

[0024] Figure 2 Comparison of antioxidant capacity between freshness indicator labels prepared with added dragon fruit peel microcapsules and those prepared with added dragon fruit peel anthocyanins.

[0025] Figure 3 Comparison of the storage stability at 4°C for freshness indicator labels prepared with added dragon fruit peel microcapsules and those prepared with added dragon fruit peel anthocyanins.

[0026] Figure 4Comparison of the storage stability of freshness indicator labels prepared with added dragon fruit peel microcapsules and those prepared with added dragon fruit peel anthocyanins at -18°C.

[0027] Figure 5 Comparison of the storage stability at 25°C for freshness indicator labels prepared with added dragon fruit peel microcapsules and those prepared with added dragon fruit peel anthocyanins.

[0028] Figure 6 A comparison of the response of freshness indicator labels prepared with added dragon fruit peel microcapsules and added dragon fruit peel anthocyanins to ammonia. Detailed Implementation

[0029] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments, but it is not limited thereto. Any modifications or equivalent substitutions to the technical solution of the present invention that do not depart from the spirit and scope of the technical solution of the present invention should be covered within the protection scope of the present invention.

[0030] Example 1 (1) Preparation of anthocyanin extract from dragon fruit peel. Dragon fruit peel pulp was taken and mixed with a 50% ethanol solution acidified with hydrochloric acid at pH 4 as the extraction solvent at a material-to-liquid ratio of 1:5 (g / mL). Ultrasonic extraction was performed for 40 min under ultrasonic power of 300 W, followed by extraction in a 40℃ water bath for 2 h. After extraction, the extract was subjected to coarse filtration, purification, vacuum filtration, and rotary evaporation to obtain a concentrated solution. The solution was then spray-dried to obtain anthocyanin powder from dragon fruit peel.

[0031] (2) Microencapsulation treatment. Gum arabic and maltodextrin were used as composite wall materials, with a mass ratio of gum arabic to maltodextrin of 1:3. Dragon fruit peel anthocyanin extract was mixed with the composite wall material at a core-to-wall ratio of 1:2, and the solid content in the mixture was controlled to be 10%. The mixture was stirred at 120 rpm for 1 hour to form a uniform mixture. Then, spray drying was performed with an inlet air temperature of 160~180℃ and an outlet temperature of 90~110℃ to obtain dragon fruit peel anthocyanin microcapsule powder.

[0032] (3) Dissolve chitosan in an aqueous solution containing 2% (v / v) glacial acetic acid to prepare a chitosan solution with a mass-volume concentration of 2% (w / v). Simultaneously, prepare a gelatin solution with a mass-volume concentration of 2% (w / v). Mix the chitosan solution and gelatin solution at a volume ratio of 1:1, and add glycerol as a plasticizer, with the amount of glycerol added being 2% (v / v) of the total volume of the film-forming matrix solution. Stir thoroughly to obtain a homogeneous film-forming matrix solution.

[0033] (4) The obtained dragon fruit peel anthocyanin microcapsule powder was added to the film-forming matrix solution at a concentration of 20% (w / w) of the solid mass in the solution. The mixture was thoroughly stirred to ensure uniform dispersion of the microcapsule powder in the matrix solution. To remove air bubbles generated during mixing, ultrasonic degassing was performed for 10 min to obtain a uniform, bubble-free film-forming solution. The resulting film-forming solution was cast onto a flat substrate, ensuring uniform casting thickness. The cast film was dried under suitable conditions. After drying, the formed film was carefully peeled off from the substrate to obtain the smart indicator label (CG@HP1) for monitoring the freshness of aquatic products.

[0034] Example 2 (1) Preparation of anthocyanin extract from dragon fruit peel. Dragon fruit peel pulp was taken and mixed with a 50% ethanol solution acidified with hydrochloric acid at pH 4 as the extraction solvent at a material-to-liquid ratio of 1:5 (g / mL). Ultrasonic extraction was performed for 40 min under ultrasonic power of 300 W, followed by extraction in a 40℃ water bath for 2 h. After extraction, the extract was subjected to coarse filtration, purification, vacuum filtration, and rotary evaporation to obtain a concentrated solution. The solution was then spray-dried to obtain anthocyanin powder from dragon fruit peel.

[0035] (2) Microencapsulation treatment. Gum arabic and maltodextrin were used as composite wall materials, with a mass ratio of gum arabic to maltodextrin of 1:3. Dragon fruit peel anthocyanin extract was mixed with the composite wall material at a core-to-wall ratio of 1:2, and the solid content in the mixture was controlled to be 10%. The mixture was stirred at 120 rpm for 1 hour to form a uniform mixture. Then, spray drying was performed with an inlet air temperature of 160~180℃ and an outlet temperature of 90~110℃ to obtain dragon fruit peel anthocyanin microcapsule powder.

[0036] (3) Dissolve chitosan in an aqueous solution containing 2% (v / v) glacial acetic acid to prepare a chitosan solution with a mass-volume concentration of 2% (w / v). Simultaneously, prepare a gelatin solution with a mass-volume concentration of 2% (w / v). Mix the chitosan solution and gelatin solution at a volume ratio of 1:1, and add glycerol as a plasticizer, with the amount of glycerol added being 2% (v / v) of the total volume of the film-forming matrix solution. Stir thoroughly to obtain a homogeneous film-forming matrix solution.

[0037] (4) The obtained dragon fruit peel anthocyanin microcapsule powder was added to the film-forming matrix solution at a concentration of 40% (w / w) of the solid mass in the solution. The mixture was thoroughly stirred to ensure uniform dispersion of the microcapsule powder. To remove air bubbles generated during mixing, ultrasonic degassing was performed for 10 minutes to obtain a uniform, bubble-free film-forming solution. The resulting film-forming solution was cast onto a flat substrate, ensuring uniform casting thickness. The cast film was dried under suitable conditions. After drying, the formed film was carefully peeled off from the substrate to obtain the smart indicator label (CG@HP2) for monitoring the freshness of aquatic products. Overall, the indicator label made with this formulation exhibits the best antioxidant effect and also demonstrates good storability.

[0038] Example 3 (1) Preparation of anthocyanin extract from dragon fruit peel. Dragon fruit peel pulp was taken and mixed with a 50% ethanol solution acidified with hydrochloric acid at pH 4 as the extraction solvent at a material-to-liquid ratio of 1:5 (g / mL). Ultrasonic extraction was performed for 40 min under ultrasonic power of 300 W, followed by extraction in a 40℃ water bath for 2 h. After extraction, the extract was subjected to coarse filtration, purification, vacuum filtration, and rotary evaporation to obtain a concentrated solution. The solution was then spray-dried to obtain anthocyanin powder from dragon fruit peel.

[0039] (2) Microencapsulation treatment. Gum arabic and maltodextrin were used as composite wall materials, with a mass ratio of gum arabic to maltodextrin of 1:3. Dragon fruit peel anthocyanin extract was mixed with the composite wall material at a core-to-wall ratio of 1:2, and the solid content in the mixture was controlled to be 10%. The mixture was stirred at 120 rpm for 1 hour to form a uniform mixture. Then, spray drying was performed with an inlet air temperature of 160~180℃ and an outlet temperature of 90~110℃ to obtain dragon fruit peel anthocyanin microcapsule powder.

[0040] (3) Dissolve chitosan in an aqueous solution containing 2% (v / v) glacial acetic acid to prepare a chitosan solution with a mass-volume concentration of 2% (w / v). Simultaneously, prepare a gelatin solution with a mass-volume concentration of 2% (w / v). Mix the chitosan solution and gelatin solution at a volume ratio of 1:1, and add glycerol as a plasticizer, with the amount of glycerol added being 2% (v / v) of the total volume of the film-forming matrix solution. Stir thoroughly to obtain a homogeneous film-forming matrix solution.

[0041] (4) The obtained dragon fruit peel anthocyanin microcapsule powder was added to the film-forming matrix solution at a concentration of 60% (w / w) of the solid mass in the solution. The mixture was thoroughly stirred to ensure uniform dispersion of the microcapsule powder in the matrix solution. To remove air bubbles generated during mixing, ultrasonic degassing was performed for 10 minutes to obtain a uniform, bubble-free film-forming solution. The resulting film-forming solution was cast onto a flat substrate, ensuring uniform casting thickness. The cast film was dried under suitable conditions. After drying, the formed film was carefully peeled off from the substrate to obtain the smart indicator label (CG@HP3) for monitoring the freshness of aquatic products.

[0042] Comparative Example 1 First, anthocyanin extract from dragon fruit peel was prepared. Dragon fruit peel pulp was mixed with 50% ethanol solution (pH 4) as the extraction solvent at a material-to-liquid ratio of 1:5 (g / mL). Ultrasonic extraction was performed for 40 min at 300 W, followed by extraction in a 40℃ water bath for 2 h. After extraction, the extract was sequentially subjected to coarse filtration, purification, vacuum filtration, and rotary evaporation to obtain a concentrated solution. This concentrated solution was then spray-dried to obtain dragon fruit peel anthocyanin powder.

[0043] Chitosan was dissolved in an aqueous solution containing 2% (v / v) glacial acetic acid to prepare a chitosan solution with a volume concentration of 2% (w / v). Simultaneously, a gelatin solution with a volume concentration of 2% (w / v) was prepared. The chitosan solution and gelatin solution were mixed at a volume ratio of 1:1, and glycerol was added as a plasticizer at a volume of 2% (v / v) of the total volume of the film-forming matrix solution. The mixture was thoroughly stirred to obtain a homogeneous film-forming matrix solution.

[0044] The obtained dragon fruit peel anthocyanin powder was added to the film-forming matrix solution at a concentration of 20% (w / w) of the solid mass. The mixture was thoroughly stirred to ensure uniform dispersion. To remove air bubbles generated during mixing, ultrasonic degassing was performed for 10 minutes to obtain a uniform, bubble-free film-forming solution. The resulting film-forming solution was cast onto a flat substrate, maintaining a uniform casting thickness. The cast film was then dried under suitable conditions. After drying, the formed film was carefully peeled off the substrate, yielding the smart indicator label (CG-HP1) for monitoring the freshness of aquatic products.

[0045] Comparative Example 2 First, anthocyanin extract from dragon fruit peel was prepared. Dragon fruit peel pulp was mixed with 50% ethanol solution (pH 4) as the extraction solvent at a material-to-liquid ratio of 1:5 (g / mL). Ultrasonic extraction was performed for 40 min at 300 W, followed by extraction in a 40℃ water bath for 2 h. After extraction, the extract was sequentially subjected to coarse filtration, purification, vacuum filtration, and rotary evaporation to obtain a concentrated solution. This concentrated solution was then spray-dried to obtain dragon fruit peel anthocyanin powder.

[0046] Chitosan was dissolved in an aqueous solution containing 2% (v / v) glacial acetic acid to prepare a chitosan solution with a volume concentration of 2% (w / v). Simultaneously, a gelatin solution with a volume concentration of 2% (w / v) was prepared. The chitosan solution and gelatin solution were mixed at a volume ratio of 1:1, and glycerol was added as a plasticizer at a volume of 2% (v / v) of the total volume of the film-forming matrix solution. The mixture was thoroughly stirred to obtain a homogeneous film-forming matrix solution.

[0047] The obtained dragon fruit peel anthocyanin powder was added to the film-forming matrix solution at a concentration of 40% (w / w) of the solids content. The mixture was thoroughly stirred to ensure uniform dispersion. To remove air bubbles generated during mixing, ultrasonic degassing was performed for 10 minutes to obtain a uniform, bubble-free film-forming solution. The resulting film-forming solution was cast onto a flat substrate, maintaining a uniform casting thickness. The cast film was then dried under suitable conditions. After drying, the formed film was carefully peeled off the substrate, yielding the smart indicator label (CG-HP2) for monitoring the freshness of aquatic products.

[0048] Comparative Example 3 First, anthocyanin extract from dragon fruit peel was prepared. Dragon fruit peel pulp was mixed with 50% ethanol solution (pH 4) as the extraction solvent at a material-to-liquid ratio of 1:5 (g / mL). Ultrasonic extraction was performed for 40 min at 300 W, followed by extraction in a 40℃ water bath for 2 h. After extraction, the extract was sequentially subjected to coarse filtration, purification, vacuum filtration, and rotary evaporation to obtain a concentrated solution. This concentrated solution was then spray-dried to obtain dragon fruit peel anthocyanin powder.

[0049] Chitosan was dissolved in an aqueous solution containing 2% (v / v) glacial acetic acid to prepare a chitosan solution with a volume concentration of 2% (w / v). Simultaneously, a gelatin solution with a volume concentration of 2% (w / v) was prepared. The chitosan solution and gelatin solution were mixed at a volume ratio of 1:1, and glycerol was added as a plasticizer at a volume of 2% (v / v) of the total volume of the film-forming matrix solution. The mixture was thoroughly stirred to obtain a homogeneous film-forming matrix solution.

[0050] The obtained dragon fruit peel anthocyanin powder was added to the film-forming matrix solution at a concentration of 60% (w / w) of the solid mass. The mixture was thoroughly stirred to ensure uniform dispersion. To remove air bubbles generated during mixing, ultrasonic degassing was performed for 10 minutes to obtain a uniform, bubble-free film-forming solution. The resulting film-forming solution was cast onto a flat substrate, maintaining a uniform casting thickness. The cast film was then dried under suitable conditions. After drying, the formed film was carefully peeled off the substrate, yielding the smart indicator label (CG-HP3) for monitoring the freshness of aquatic products.

[0051] The manufacturing process of smart indicator labels based on microencapsulated anthocyanins is as follows: Figure 1 As shown. To determine antioxidant capacity, an ABTS stock solution (7.4 mM ABTS + 2.6 mM potassium persulfate) needs to be prepared and stored overnight. The absorbance at 734 nm is adjusted to 0.70 ± 0.01 by diluting with distilled water. 1 mL of the membrane soaking solution is mixed thoroughly with 4 mL of diluted ABTS solution. After incubation in the dark for 10 min, the absorbance at 734 nm is measured. The results show that... Figure 2 It is evident that the smart indicator label based on microencapsulated anthocyanins exhibits better antioxidant effects than the smart indicator label with unencapsulated anthocyanins, especially Example 2, which demonstrates the best antioxidant effect. This is because free anthocyanins are rapidly oxidized and deactivated due to direct exposure, while encapsulated anthocyanins are protected by the wall material, thus better preserving their antioxidant activity. This indicates that the indicator label of the present invention has a longer functional lifespan. Figures 3-5 As can be seen from the color difference values ​​of the membrane stored at 4℃, -18℃, and 25℃ for 28 days, microencapsulation technology significantly improves the long-term storage stability of anthocyanins within the membrane. This is crucial for the labeling of goods during storage and transportation, ensuring consistent performance throughout its shelf life. Figure 6 As can be seen, 15 mL of 8 mmol / L ammonia solution was added to a 90 mm petri dish, and a 20 mm × 20 mm membrane was suspended 1 cm above the liquid surface. Image information of the membrane was collected every 5 minutes using a colorimeter, for a total of 6 times. The obtained color difference values ​​were plotted. The experimental results show that the indicator label has good pH response capability and can be used for monitoring the freshness of aquatic products. Using microencapsulated dragon fruit peel anthocyanins as an indicator not only improves the stability of anthocyanins but also enhances the durability and sensitivity of the indicator label. The chitosan and gelatin composite film-forming matrix provides good mechanical strength and permeability, making it suitable for use as a food packaging material. This smart indicator label can be directly applied to aquatic product packaging, providing consumers with intuitive information on food freshness, effectively reducing food waste and improving food safety.

Claims

1. A method for preparing a smart indicator label based on microencapsulated anthocyanins, characterized in that: The method is as follows: (1) Extraction of anthocyanins from dragon fruit peel: anthocyanins were extracted from dragon fruit peel using acidified ethanol; (2) Preparation of dragon fruit peel anthocyanin microcapsule powder: using gum arabic and maltodextrin as composite wall materials, dragon fruit peel anthocyanin extract was encapsulated by spray drying to obtain dragon fruit peel anthocyanin microcapsule powder. (3) Provide film-forming matrix solution: Mix chitosan solution and gelatin solution, add plasticizer, stir evenly to obtain film-forming matrix solution; (4) Preparation of film solution: Add the dragon fruit peel anthocyanin microcapsule powder obtained in step (2) to the film-forming matrix solution obtained in step (3), stir and mix and remove bubbles to obtain a uniform film-forming solution. Cast the obtained film-forming solution onto the substrate, and peel off the film after drying to obtain a smart indicator label.

2. The preparation method according to claim 1, characterized in that: The specific steps (1) are as follows: take dragon fruit peel, use 45-55% ethanol solution acidified with hydrochloric acid as the extraction solvent, mix them at a material-liquid ratio of 1g:3-7mL, extract with ultrasonic assistance, and then perform coarse filtration, purification, vacuum filtration, rotary evaporation concentration and spray drying in sequence to obtain dragon fruit peel anthocyanin powder.

3. The preparation method according to claim 2, characterized in that: The conditions for ultrasound-assisted extraction are: ultrasound power 200~400 W, ultrasound time 30~50 min, and extraction in a water bath at 30~50℃ for 1~3 h.

4. The preparation method according to claim 1, characterized in that: In step (2), the mass ratio of gum arabic to maltodextrin is from 1 to 3:1; the mass ratio of dragon fruit peel anthocyanin extract to the core wall of the composite wall material is from 1 to 5:

1.

5. The preparation method according to claim 1, characterized in that: In step (2), the solid content during the embedding process is 8%~12%, and a magnetic stirrer is used for mixing and stirring at a speed of 110~130 rpm for 40~60 min; the inlet air temperature of the spray drying is 160~180℃ and the outlet temperature is 90~110℃.

6. The preparation method according to claim 1, characterized in that: In step (3), the chitosan is dissolved in an aqueous solution containing 1% to 5% (v / v) glacial acetic acid to obtain a chitosan solution with a mass-volume concentration of 1% to 3% (w / v); the gelatin solution has a mass-volume concentration of 1% to 3% (w / v), and the volume ratio of the chitosan solution to the gelatin solution is from 1 to 3:

1.

7. The preparation method according to claim 1, characterized in that: In step (3), the plasticizer is glycerol, and its addition amount is 1~5% (v / v) of the total volume of the film-forming matrix solution.

8. The preparation method according to claim 1, characterized in that: In step (4), the mass ratio of the dragon fruit peel anthocyanin microcapsule powder to chitosan is 0.4~1.2:

1.

9. The preparation method according to claim 1, characterized in that: In step (4), ultrasonic degassing is performed for 10-30 minutes to remove air bubbles.

10. The application of a smart indicator tag prepared by the preparation method according to any one of claims 1 to 9 in monitoring the freshness of aquatic products, wherein the tag has good antioxidant properties and pH sensitivity.

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