Preparation method and application of intelligent freshness indicating film

Abstract

The invention provides a preparation method and application of an intelligent freshness indicating film, and the preparation method comprises the following steps: dissolving sodium alginate in distilled water to prepare a film-forming solution; dissolving anthocyanin in the film forming solution to prepare a sodium alginate / anthocyanin film forming solution; dissolving rhizoma anemarrhenae polysaccharide in distilled water, and mixing in the film-forming solution obtained in the previous step to prepare a sodium alginate / anthocyanin / rhizoma anemarrhenae polysaccharide film-forming solution; and carrying out ultrasonic treatment on the sodium alginate / anthocyanin / rhizoma anemarrhenae polysaccharide film forming solution, removing bubbles, pouring on the film blank, drying, and uncovering the film to obtain the intelligent indication film. By adding the rhizoma anemarrhenae polysaccharide, the water, color and heat stability of the intelligent indication film are remarkably improved, and the service life is prolonged. The adopted sodium alginate, black rice anthocyanin and rhizoma anemarrhenae polysaccharide are all environment-friendly degradable materials, and the requirements of green packaging and sustainable development are met.

Description

Technical Field

[0001] The present invention relates to the field of food intelligent indicator packaging, in particular to a preparation method and application of a freshness intelligent indicator film. Background Art

[0002] With improving living standards, people's demands for food quality are becoming increasingly stringent, particularly for fresh meat. As one of the most consumed meats in my country, the freshness of pork is directly related to consumer health and safety. Given the current immature cold chain system, meat is susceptible to environmental and microbial influences during storage, transportation, processing, and sales. Meat is inherently nutrient-rich, which allows microorganisms to proliferate rapidly. The combined effects of enzymatic hydrolysis and microbial decomposition can alter the sensory and physicochemical properties of meat, reducing its freshness. Failure to detect pork spoilage in a timely manner can pose a serious threat to public health. Therefore, tracking and testing meat freshness is crucial.

[0003] Freshness indicators monitor or react with metabolites (such as volatile basic nitrogen, organic acids, carbon dioxide, or sulfur derivatives) produced by microbial growth in fresh foods, subsequently revealing a visible color change that reveals the quality of the food within the package. A variety of methods exist for assessing meat freshness, encompassing sensory evaluation, physicochemical analysis, and microbiological evaluation. Sensory evaluation is one of the most intuitive and commonly used methods. Meat freshness can be initially assessed by observing its sensory properties, such as color, odor, and tactile feel. Physicochemical analysis primarily measures physical properties (such as pH, viscosity, and conductivity) and chemical properties (such as ammonia, hydrogen sulfide, and volatile basic nitrogen (TVB-N)). While physicochemical analysis can accurately determine meat freshness, it is cumbersome, requires lengthy pretreatment, and damages the sample, making it difficult to rapidly and nondestructively measure meat freshness. In recent years, intelligent food indicator films have garnered widespread attention due to their rapid, nondestructive, and portable nature. These films can be laminated, printed, or affixed to conventional packaging, providing information on the freshness of the meat within the package through color changes, enabling real-time monitoring of its safety. Therefore, the development of smart food freshness indicator films can improve consumers' health protection and promote the sustainable development of the food industry and continuous technological advancement.

[0004] At present, in the research and development of smart indicator films, artificial synthetic dyes such as methyl red, bromocresol purple, and bromothymol blue are prevalent. However, the use of these synthetic dyes is often associated with toxicity and pollution problems. Natural dyes are widely used in the field of smart food packaging materials due to their inherent safety, biological activity and abundant sources. Among various natural dyes, anthocyanins, as an edible pigment, can produce a variety of color changes with changes in pH value and are ideal pH-responsive indicators in smart food packaging. At the same time, by utilizing the indicative properties of anthocyanins (color changes caused by structural transformations at different pH values), the acidic and alkaline substances generated by the corruption of fresh meat can be displayed by color, thereby realizing visual freshness monitoring.

[0005] Among existing smart packaging technologies, most literature focuses on the development of various anthocyanin / polysaccharide smart indicator films, such as wolfberry anthocyanin / starch smart indicator film, purple sweet potato anthocyanin / starch smart indicator film, and red cabbage anthocyanin / chitosan smart indicator film. However, these technologies may have the following drawbacks:

[0006] (1) The stability of anthocyanins involved in smart indicator films is poor. Anthocyanins are key indicators in smart indicator films, and their color changes can reflect the freshness of food. However, anthocyanins are easily affected by external factors such as light, temperature, humidity, storage time, and metal ions, which can cause their structure to be destroyed and their ionic form to change, thereby reducing their stability and reliability. Under high temperature conditions, anthocyanins will accelerate decomposition and reduce their stability. Under low temperature conditions, although some transformations are reversible, the overall stability is still poor. This instability limits the use of anthocyanin smart indicator films in complex environments.

[0007] (2) The hydrophilic nature of anthocyanins also brings new problems. In high humidity environments, anthocyanins in the film are easily dissolved, resulting in inaccurate color changes or failure of the smart indicator film. This not only affects the sensitivity and accuracy of the smart indicator film, but may also cause consumers to misjudge the freshness of food.

[0008] (3) In addition, existing studies have found that the performance of smart indicator films may deteriorate after repeated use, and the reversibility of natural anthocyanins may be insufficient, which limits the reuse of smart indicator films. Summary of the Invention

[0009] The purpose of the present invention is to provide a preparation method and application of a freshness intelligent indicator film to solve the problems of unstable pigment and short service life of the existing intelligent indicator film.

[0010] One object of the present invention is achieved by the following technical solution: a method for preparing a freshness intelligent indicator film, comprising the following steps:

[0011] Step S1: dissolving sodium alginate in distilled water and mixing thoroughly to obtain a sodium alginate film-forming solution;

[0012] Step S2: dissolving anthocyanidin in the sodium alginate film-forming solution prepared in step S1, and mixing thoroughly to obtain a sodium alginate / anthocyanidin film-forming solution;

[0013] Step S3: dissolving the Anemarrhena polysaccharide in distilled water to obtain a Anemarrhena polysaccharide suspension after sufficient dissolution, and thoroughly mixing the Anemarrhena polysaccharide suspension with the sodium alginate / anthocyanidin film-forming solution prepared in step S2 to obtain a sodium alginate / anthocyanidin / Anemarrhena polysaccharide film-forming solution;

[0014] Step S4: The obtained sodium alginate / anthocyanidin / anemarrhena polysaccharide film-forming solution is placed in an ultrasonic cleaner to remove bubbles; the sodium alginate / anthocyanidin / anemarrhena polysaccharide film-forming solution is poured onto the film embryo, dried, and peeled off to obtain the freshness intelligent indicator film.

[0015] Preferably, in step S1, the mass concentration of sodium alginate in the sodium alginate film-forming solution is 1.5-2.5 g / 100 mL.

[0016] Preferably, in step S2, the mass concentration of anthocyanins in the sodium alginate / anthocyanin film-forming solution is 0.026-0.046 g / 100 mL.

[0017] Preferably, in step S3, the mass concentration of Anemarrhena asphodeloides polysaccharide in the sodium alginate / anthocyanidin / Anemarrhena asphodeloides polysaccharide film-forming solution is 0.01125-0.01875 g / 100 mL;

[0018] Preferably, in step S4, the ultrasonic cleaning time is 25-35 minutes, the volume of the film-forming solution is 30-40 mL, and the drying conditions are a temperature of 25-35° C., a relative humidity of 5-15%, and drying for 24-48 hours.

[0019] Preferably, the anthocyanin in step S2 is black rice anthocyanin, the sodium alginate / anthocyanin film-forming solution is sodium alginate / black rice anthocyanin film-forming solution, and the sodium alginate / anthocyanin / anemarrhena polysaccharide film-forming solution is sodium alginate / black rice anthocyanin / anemarrhena polysaccharide film-forming solution.

[0020] Another object of the present invention is achieved by the following technical solutions: a freshness intelligent indicator film, which is prepared by the above-mentioned preparation method of the freshness intelligent indicator film; and an application of the freshness intelligent indicator film in pork freshness indication.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] (1) Improve the performance of smart indicator films and simulate food spoilage effects

[0023] This study uses ammonia volatilized from meat as a characteristic gas in simulating food spoilage, and further explores the positive effects of Anemarrhena asphodeloides polysaccharides on the humidity stability, structural properties, color stability, and pH and NH3 sensitivity of a sodium alginate / anthocyanidin smart indicator film. Furthermore, by observing the color changes of the sodium alginate / anthocyanidin / Anemarrhena asphodeloides polysaccharide smart indicator film, the film's performance during food spoilage is accurately simulated, providing strong support for visual monitoring of food freshness.

[0024] (2) Enhanced stability and sensitive indication of food characteristics

[0025] By adding Anemarrhena polysaccharide, the present invention effectively enhances the water stability, color stability, and thermal stability of the smart indicator film, thereby significantly extending the product's service life. Furthermore, by adding an anthocyanin solution to the film-forming product and cleverly utilizing its color-changing properties with pH, the smart indicator film can sensitively indicate the shelf characteristics of food. pH-responsive color smart indicator films have been successfully used to indicate the freshness of pork, providing real-time information to consumers about product quality and safety, and providing a reliable basis for food quality monitoring.

[0026] (3) High safety, environmental protection and efficient utilization of by-products

[0027] The sodium alginate, black rice anthocyanins, and Rhizoma Anemarrhenae polysaccharides used in the present invention are all degradable packaging materials with extremely high safety and environmental protection, perfectly aligning with the trend of green packaging and sustainable development. In particular, the black rice anthocyanins, derived from black rice byproducts, significantly improve the comprehensive utilization rate of black rice byproducts and the degree of high-value processing, achieving efficient resource utilization and significant economic and environmental benefits.

[0028] (4) Significantly improve the service life of the smart indicator film

[0029] The present invention utilizes the numerous hydroxyl groups on the long-chain linear molecules of Anemarrhena polysaccharide to interact with the hydroxyl groups in the anthocyanin molecules through hydrogen bonds. This hydrogen bond interaction can fix the anthocyanin molecules in the entangled network structure formed by Anemarrhena polysaccharide, thereby enhancing the stability of the anthocyanin molecules. In addition, it limits the free movement of anthocyanin molecules to a certain extent, reduces the chance of direct contact with water molecules, oxygen molecules, etc. in the external environment, reduces the possibility of chemical reactions in anthocyanins, and thus improves the stability of anthocyanins. At the same time, the acidic groups of Anemarrhena polysaccharide dissociate in aqueous solution, releasing negative charges. Anthocyanins contain multiple phenolic hydroxyl groups and can carry positive charges under specific pH conditions. Therefore, ionic interactions are likely to occur between the two, further enhancing the stability of anthocyanins. This innovative method effectively solves the problem of poor indication effect of smart indicator films, significantly improves the service life of smart indicator films, and provides a higher quality and more lasting solution for the field of smart packaging. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 : The intelligent indicator film prepared by the present invention;

[0031] Figure 2 : Color stability diagram of the smart indicator film prepared in Example 1 under natural light and light-proof environments at different temperatures;

[0032] Figure 3 : Water vapor permeability curve of the smart indicator film prepared in Example 1 after storage for 5 days;

[0033] Figure 4 : A graph showing the water vapor adsorption capacity of the smart indicator film prepared in Example 1 during storage for 5 days;

[0034] Figure 5 : Thermal stability diagram of the smart indicator film prepared in Example 1 at 25°C-600°C;

[0035] Figure 6 : Test graphs of elongation at break, tensile strength and thickness of the smart indicator film prepared in Example 1;

[0036] Figure 7 :The intelligent indicator film prepared in Example 1 is at 4000-400cm -1 Infrared spectrum performance test chart;

[0037] Figure 8 : XRD performance test diagram of the smart indicator film prepared in Example 1;

[0038] Figure 9 : Scanning electron microscope test image of the smart indicator film prepared in Example 1;

[0039] Figure 10: Atomic force microscope test image of the smart indicator film prepared in Example 1;

[0040] Figure 11 : pH sensitivity test of the smart indicator film prepared in Example 1 (A: apparent color; B: difference spectrum);

[0041] Figure 12 : NH3 sensitivity test of the smart indicator film prepared in Example 1 (A: apparent color; B: difference spectrum)

[0042] Figure 13 : RGB diagram of sensitivity test of the smart indicator film prepared in Example 1 (A: pH sensitivity; B: NH3 sensitivity);

[0043] Figure 14 : Monitoring effect of the intelligent indicator film prepared in Example 1 on pork freshness (A: Changes in pH and TVB-N of pork within 5 days; B: Monitoring of pork freshness by the indicator film within 5 days) DETAILED DESCRIPTION

[0044] To facilitate understanding of the present invention, the present invention will be described more comprehensively and in detail below with reference to the following embodiments, but the protection scope of the present invention is not limited to the following specific embodiments.

[0045] Unless otherwise defined, all technical terms used hereinafter have the same meanings as those generally understood by those skilled in the art. The technical terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention.

[0046] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0047] Example 1

[0048] Step S1: dissolving sodium alginate in distilled water and mixing thoroughly to obtain a film-forming solution with a sodium alginate concentration of 1.5 g / 100 mL;

[0049] Step S2: dissolving black rice anthocyanidin in the sodium alginate film-forming solution prepared in step S1, wherein the mass concentration of black rice anthocyanidin is 0.026 g / 100 mL, and fully mixing to obtain a sodium alginate / black rice anthocyanidin film-forming solution;

[0050] Step S3: dissolving Anemarrhena polysaccharide in distilled water to obtain a uniform Anemarrhena polysaccharide suspension after full dissolution, wherein the mass concentration of Anemarrhena polysaccharide is 0.01125 g / 100 mL; fully mixing the Anemarrhena polysaccharide suspension with the sodium alginate / black rice anthocyanin film-forming solution prepared in step S2 to obtain a sodium alginate / black rice anthocyanin / Anemarrhena polysaccharide film-forming solution.

[0051] Step S4: The sodium alginate / black rice anthocyanidin / anemarrhena polysaccharide film-forming solution obtained in step S3 was placed in an ultrasonic cleaner for 25 min to remove bubbles; 30 mL of the film-forming solution was poured onto the membrane embryo and dried at a temperature of 25° C. and a relative humidity of 5% for 24 h to obtain a sodium alginate / black rice anthocyanidin / anemarrhena polysaccharide intelligent indicator membrane. Figure 1 shown.

[0052] Example 2

[0053] Step S1: dissolving sodium alginate in distilled water and mixing thoroughly to obtain a film-forming solution with a sodium alginate concentration of 2.0 g / 100 mL;

[0054] Step S2: dissolving black rice anthocyanidin in the sodium alginate film-forming solution prepared in step S1, wherein the mass concentration of black rice anthocyanidin is 0.036 g / 100 mL, and mixing thoroughly to obtain a sodium alginate / black rice anthocyanidin film-forming solution;

[0055] Step S3: Dissolve Anemarrhena polysaccharide in distilled water to obtain a uniform Anemarrhena polysaccharide suspension after full dissolution, wherein the mass concentration of Anemarrhena polysaccharide is 0.015 g / 100 mL. The Anemarrhena polysaccharide suspension is fully mixed with the sodium alginate / black rice anthocyanin film-forming solution prepared in step S2 to obtain a sodium alginate / black rice anthocyanin / Anemarrhena polysaccharide film-forming solution;

[0056] Step S4: The sodium alginate / black rice anthocyanin / Anemarrhena polysaccharide film-forming solution obtained in step S3 is placed in an ultrasonic cleaner for 30 minutes to remove bubbles; 35 mL of the film-forming solution is poured onto the membrane embryo, and dried at a temperature of 30° C. and a relative humidity of 10% for 36 hours to obtain a sodium alginate / black rice anthocyanin / Anemarrhena polysaccharide intelligent indicator membrane.

[0057] Example 3

[0058] Step S1: dissolving sodium alginate in distilled water and mixing thoroughly to obtain a film-forming solution with a sodium alginate concentration of 2.5 g / 100 mL;

[0059] Step S2: dissolving black rice anthocyanidin in the sodium alginate film-forming solution prepared in step S1, wherein the mass concentration of black rice anthocyanidin is 0.046 g / 100 mL, and mixing thoroughly to obtain a sodium alginate / black rice anthocyanidin film-forming solution;

[0060] Step S3: Dissolve Anemarrhena polysaccharide in distilled water to obtain a uniform Anemarrhena polysaccharide suspension after full dissolution, wherein the mass concentration of Anemarrhena polysaccharide is 0.01875 g / 100 mL. The Anemarrhena polysaccharide suspension is fully mixed with the sodium alginate / black rice anthocyanin film-forming solution prepared in step S2 to obtain a sodium alginate / black rice anthocyanin / Anemarrhena polysaccharide film-forming solution;

[0061] Step S4: The sodium alginate / black rice anthocyanin / Anemarrhena polysaccharide film-forming solution obtained in step S3 was placed in an ultrasonic cleaner for 35 minutes to remove bubbles; 40 mL of the film-forming solution was poured onto the membrane embryo, and dried at a temperature of 35° C. and a relative humidity of 15% for 48 hours to obtain a sodium alginate / black rice anthocyanin / Anemarrhena polysaccharide intelligent indicator membrane.

[0062] Comparative Example 1

[0063] Step S1: dissolving sodium alginate in distilled water and mixing thoroughly to obtain a film-forming solution with a sodium alginate concentration of 2.5 g / 100 mL;

[0064] Step S2: dissolving black rice anthocyanidin in the sodium alginate film-forming solution prepared in step S1, wherein the mass concentration of black rice anthocyanidin is 0.046 g / 100 mL, and mixing thoroughly to obtain a sodium alginate / black rice anthocyanidin film-forming solution;

[0065] Step S3: The sodium alginate / black rice anthocyanin film-forming solution obtained in step S2 was placed in an ultrasonic cleaner for 35 minutes to remove bubbles; 40 mL of the film-forming solution was poured onto the membrane embryo, and dried at a temperature of 35° C. and a relative humidity of 15% for 48 hours to obtain a sodium alginate / black rice anthocyanin intelligent indicator membrane.

[0066] Color stability performance test of smart indicator film:

[0067] (1) Determine the color stability of the smart indicator film under different storage conditions.

[0068] The sodium alginate / black rice anthocyanin / Anemarrhena asphodeloides polysaccharide smart indicator film prepared in Example 1 and the sodium alginate / black rice anthocyanin smart indicator film prepared in Comparative Example 1 were placed in 25°C-natural light, 25°C-dark, 4°C-natural light, and 4°C-dark environments, respectively. The absorbance of the smart indicator film at 500 nm (the maximum absorption wavelength of black rice anthocyanin) was measured using an ultraviolet spectrometer every other day.

[0069] (2) Analysis of color stability of smart indicator films under different storage conditions

[0070] like Figure 2 As shown in the figure, the absorbance values of the two indicator films at 500nm wavelength under the conditions of 4℃ and 25℃ in the dark are shown in the figure. 500) did not change significantly (P>0.05), indicating that the color stability of the indicator film is better when protected from light. This phenomenon may be due to the photodegradation of anthocyanin molecules within the film under light, which breaks the conjugated double bonds in their molecular structure and triggers the color change. Furthermore, the study found that Anemarrhena polysaccharide did not significantly enhance the color stability of the sodium alginate / black rice anthocyanin indicator film.

[0071] Water stability test of smart indicator film:

[0072] (1) Water vapor permeability test of smart indicator film:

[0073] The sodium alginate / black rice anthocyanin / anemarrhena polysaccharide smart indicator film (4 cm × 4 cm) prepared in Example 1 and the sodium alginate / black rice anthocyanin smart indicator film (4 cm × 4 cm) prepared in Comparative Example 1 were respectively covered on the mouth of a glass bottle with a depth of 4 cm and a diameter of 1.5 cm. The bottle was filled with dry silica gel particles. Subsequently, the two glass bottles were placed in a desiccator (containing a saturated potassium sulfate solution) and the weight of the glass bottles was accurately weighed every day. The water vapor permeability was calculated as follows:

[0074]

[0075] Note: W is the added weight of the glass bottle (g), x is the initial thickness of the smart indicator film (m), t is the storage time (s), A is the penetration area of the smart indicator film (m 2 ), ΔP is the saturated vapor pressure of water at 25°C (Pa).

[0076] (2) Water vapor adsorption test of intelligent indicator membrane:

[0077] The water vapor adsorption capacity of the smart indicator film was measured at 25°C. A 2 cm x 2 cm piece of smart indicator film was taken from each of the sodium alginate / black rice anthocyanin / anemarrhena polysaccharide smart indicator film prepared in Example 1 and the sodium alginate / black rice anthocyanin smart indicator film prepared in Comparative Example 1 and accurately weighed. The film was then placed in a desiccator containing a saturated potassium sulfate solution and accurately weighed daily. The water vapor adsorption capacity was calculated as follows:

[0078] Water vapor adsorption capacity = W t -W0 (2)

[0079] Where W0 is the initial membrane weight (g), W t is the membrane weight (g) measured every day.

[0080] (3) Analysis of water stability results of intelligent indicator membrane:

[0081] like Figure 3 and Figure 4As shown in the figure, after 5 days, the water vapor permeability of the sodium alginate / black rice anthocyanin intelligent indicator film prepared in Comparative Example 1 was 6.69 (g / m×s×Pa)×10 -9 , the water vapor adsorption capacity is 0.086 g, while the water vapor permeability of the sodium alginate / black rice anthocyanin / anemarrhena polysaccharide intelligent indicator film prepared in Example 1 is 5.86 (g / m×s×Pa)×10 -9 , the water vapor adsorption capacity is 0.073g.

[0082] This phenomenon is related to the following mechanisms: (1) Anemarrhena polysaccharide increases the diffusion path of water molecules within the membrane. Its large specific surface area consumes part of the diffusion energy through physical adsorption, thereby inhibiting the osmotic migration of water molecules. (2) The hydroxyl groups in the Anemarrhena polysaccharide molecules form an intermolecular hydrogen bond network with the carboxyl groups of sodium alginate and the phenolic hydroxyl groups of anthocyanins. This strong interaction enhances the density of the membrane matrix and effectively blocks the water transmission channel. (3) The acidic groups of Anemarrhena polysaccharide dissociate into negative charges in aqueous solution. They easily interact with the multiple phenolic hydroxyl groups of anthocyanins to increase the stability of the smart indicator membrane.

[0083] Thermal stability test of smart indicator film:

[0084] (1) Thermal stability test of intelligent indicator film:

[0085] The sodium alginate / black rice anthocyanin / Anemarrhena polysaccharide smart indicator film (10 mg) prepared in Example 1 and the sodium alginate / black rice anthocyanin smart indicator film (10 mg) prepared in Comparative Example 1 were respectively placed in the platinum plate of a thermogravimetric analyzer. In a nitrogen atmosphere of 20.0 mL / min, the temperature was increased from 25°C to 600°C at a heating rate of 10°C / min, and the temperature, time, sample mass and other data were recorded in real time during the experiment.

[0086] (2) Analysis of thermal stability results of intelligent indicator film:

[0087] like Figure 5 As shown in the figure, the dry matter retention rate of the sodium alginate / black rice anthocyanin / Anemarrhena asphodeloides polysaccharide smart indicator film prepared in Example 1 is 37.46%, and the dry matter retention rate of the sodium alginate / black rice anthocyanin smart indicator film prepared in Comparative Example 1 is 33.80%, indicating that Anemarrhena asphodeloides polysaccharide can enhance the thermal stability of the smart indicator film.

[0088] Elongation at break, tensile strength and thickness testing of smart indicator films:

[0089] (1) Intelligent indicator film elongation at break, tensile strength and thickness test:

[0090] The sodium alginate / black rice anthocyanin / Anemarrhena polysaccharide smart indicator film prepared in Example 1 and the sodium alginate / black rice anthocyanin smart indicator film prepared in Comparative Example 1 were cut into 1 cm × 5 cm strips. Five different locations were selected for comparison. The thickness was measured using a digital percentage thickness gauge. Strength tests were performed using a YG005E single fiber strength tester, with a tensile speed of 2 mm / min and a clamping distance of 10 mm. The calculation formula is as follows:

[0091]

[0092] Where: ΔL and L0 are the stretched length and original length of the film, respectively, in mm; F is the maximum tensile strength, in N; x is the thickness of the film, in mm; and W is the width of the film, in mm.

[0093] On a circular film with a diameter of 8.5 cm, 12 measurement points were evenly selected and their thickness (mm) was measured using a thickness gauge, and the average value was taken.

[0094] (2) Analysis of test results of elongation at break, tensile strength and thickness of intelligent indicator film:

[0095] like Figure 6 As shown in the figure, the tensile strength and elongation at break of the sodium alginate / black rice anthocyanin smart indicator film prepared in Comparative Example 1 are 40.20 MPa and 2.72%, respectively, showing weak mechanical properties. The tensile strength of the sodium alginate / black rice anthocyanin / Anemarrhena polysaccharide smart indicator film prepared in Example 1 was significantly improved to 71.69 MPa, and the elongation at break increased to 5.92% (P<0.05), indicating that the rigidity and flexibility of the membrane material were improved simultaneously. This performance optimization is attributed to the hydrogen bonds and ionic interactions formed between Anemarrhena polysaccharide and the sodium alginate / black rice anthocyanin matrix, which promote the orderly arrangement of molecular segments and the formation of a dense network structure, thereby enhancing the stress bearing capacity of the material. The thickness of Anemarrhena polysaccharide increased significantly after addition (P<0.05), which may be due to the hydrogen bonds and ionic interactions between Anemarrhena polysaccharide and the polymer film.

[0096] Infrared spectrum performance test of smart indicator film:

[0097] (1) Intelligent indicator film infrared spectrum test:

[0098] The interfacial interaction of the sodium alginate / black rice anthocyanin / anemarrhena polysaccharide intelligent indicator film prepared in Example 1 and the sodium alginate / black rice anthocyanin intelligent indicator film prepared in Comparative Example 1 was analyzed by FT-IR with a scanning range of 4000-400 cm -1 , resolution 4cm -1 .

[0099] (2) Analysis of infrared spectrum test results of intelligent indicator film

[0100] like Figure 7 As shown, all samples were detected at 3425 cm -1 There are broad absorption peaks at 2815cm, which is attributed to the stretching vibration of the molecular / inter-hydroxyl groups. -1 The absorption peak at 1590 cm corresponds to the stretching vibration of the C-H bond. -1 The asymmetric stretching vibration of C=O is shown in Figure 1. Comparison of the sodium alginate / black rice anthocyanin / anemarrhena polysaccharide smart indicator film prepared in Example 1 and the sodium alginate / black rice anthocyanin smart indicator film prepared in Comparative Example 1 shows that the wave numbers of the latter at OH, CH and C=O bonds are 3422, 2810 and 1588 cm -1 Down to 3417, 2808, 1587cm -1 This change indicates that new hydrogen bonds and ionic interactions have formed between the polysaccharide molecules and sodium alginate and anthocyanins through hydroxyl and carbonyl groups. This is attributed to the multiple hydrogen bond networks and ionic interactions between the Anemarrhena polysaccharide segments and the matrix molecules.

[0101] XRD performance test of smart indicator film:

[0102] (1) XRD performance test of intelligent indicator film:

[0103] The crystal structures of the sodium alginate / black rice anthocyanin / anemarrhena polysaccharide smart indicator film (1 cm × 4 cm) prepared in Example 1 and the sodium alginate / black rice anthocyanin smart indicator film (1 cm × 4 cm) prepared in Comparative Example 1 were analyzed using an X-ray diffractometer. The experiment used a Co tube radiation source (λ = 0.179 nm), a scanning range of 5-80°, and a scanning speed of 2° / min.

[0104] (2) Analysis of XRD results of intelligent indicator film

[0105] like Figure 8As shown, the sodium alginate / black rice anthocyanin smart indicator film prepared in Comparative Example 1 presents a significant diffraction peak at 29.77°, indicating that the system has formed a relatively complete crystal structure. Although the diffraction peak position of the sodium alginate / black rice anthocyanin / Anemarrhena polysaccharide smart indicator film prepared in Example 1 is slightly offset, the overall structure still maintains obvious crystalline characteristics, indicating that the addition of the Anemarrhena polysaccharide component does not destroy the crystal forming ability of the original system. The crystallinity shows that the crystallinity of the sodium alginate / black rice anthocyanin smart indicator film prepared in Comparative Example 1 is 33.19% ± 1.26%, while the crystallinity of the sodium alginate / black rice anthocyanin / Anemarrhena polysaccharide smart indicator film prepared in Example 1 is 54.07% ± 1.69%. Anemarrhena polysaccharide maintains a certain degree of crystalline characteristics through intermolecular hydrogen bonds and steric hindrance effects. This structural feature has an important influence on the stability, barrier properties and mechanical strength of the material. The crystal structure has high stability and strength, and can resist interference from external factors such as temperature, humidity, and mechanical force. This may help improve the sensitivity and hydrophobicity of the smart indicator film and the stability of anthocyanins in the smart indicator film.

[0106] Scanning electron microscope test of smart indicator film:

[0107] (1) Scanning electron microscope test of smart indicator film:

[0108] The sodium alginate / black rice anthocyanin / Anemarrhena asphodeloides polysaccharide smart indicator film prepared in Example 1 and the sodium alginate / black rice anthocyanin smart indicator film prepared in Comparative Example 1 were respectively placed under a scanning electron microscope to observe their surface appearance.

[0109] (2) Scanning electron microscope test analysis of intelligent indicator film:

[0110] like Figure 9 As shown, the surface of the sodium alginate / black rice anthocyanin smart indicator film prepared in Comparative Example 1 has densely distributed small particle agglomerates. The surface of the sodium alginate / black rice anthocyanin / Anemarrhena polysaccharide smart indicator film prepared in Example 1 has relatively flat structural characteristics, with significantly reduced particle agglomeration and a compact layered stacking morphology on the cross section.

[0111] Atomic force microscopy testing of smart indicator films:

[0112] (1) Atomic force microscopy test of smart indicator film:

[0113] The sodium alginate / black rice anthocyanin / Anemarrhena polysaccharide smart indicator film (2 cm × 2 cm) prepared in Example 1 and the sodium alginate / black rice anthocyanin smart indicator film (2 cm × 2 cm) prepared in Comparative Example 1 were used as samples. Their surface morphology was observed using an atomic force scanning probe microscope (AFSPM) with a scanning area of 2 μm and a scanning rate of 1 Hz. The surface roughness Sq was calculated as the root mean square average of the height deviations from the average plane, and Sa was calculated as the average of the absolute values of the height deviations from the average plane.

[0114] (2) Analysis of atomic force microscopy test results of smart indicator film:

[0115] like Figure 10 As shown, the surface of the sodium alginate / black rice anthocyanin smart indicator film prepared in Comparative Example 1 has densely distributed tiny aggregates, the particle height on the surface of the smart indicator film is 0-0.43 μm, and the surface roughness Sq and Sa are relatively high (44.78 and 35.88 nm); the surface height range of the sodium alginate / black rice anthocyanin / anemarrhena polysaccharide smart indicator film prepared in Example 1 is 0-0.12 μm, and the surface roughness Sq and Sa are significantly reduced (17.47 and 13.73 nm) (P < 0.05). This phenomenon is consistent with the regulatory effect of anemarrhena polysaccharide on the particle size distribution and micromorphology of the smart indicator film, which may be attributed to the filling effect of anemarrhena polysaccharide on the sodium alginate / black rice anthocyanin matrix and the interaction between molecules.

[0116] Sensitivity test of smart indicator film:

[0117] (1) pH sensitivity determination

[0118] A series of buffer solutions with a pH range of 1 to 12 were prepared using 0.2 mol / L disodium hydrogen phosphate and 0.1 mol / L citric acid solution. The sodium alginate / black rice anthocyanin / Anemarrhena polysaccharide intelligent indicator film sample (size 2cm×2cm) prepared in Example 1 and the sodium alginate / black rice anthocyanin intelligent indicator film sample (size 2cm×2cm) prepared in Comparative Example 1 were immersed in each pH buffer solution for 5 minutes, taken out and placed under natural light conditions for image acquisition. Through digital image processing technology, the collected images were color analyzed using the Python 3.10 programming language combined with the PyCharm Community Edition 2022.1 development environment. Specifically, it includes extracting the R (red), G (green), and B (blue) three-channel values of each pixel in the image, calculating the color difference from the initial state, and generating a difference map and quantitatively analyzing the color response sensitivity SRGB value by calculating the sum of the absolute differences of the average values of the R, G, and B channels in the full pixel area. The formula is as follows:

[0119]

[0120] Where: R a , G a and B a is the color component value in the initial membrane image; R b , G b and B b is the color component value of the film image immersed in the pH solution.

[0121] (2) Ammonia sensitivity determination

[0122] The sodium alginate / black rice anthocyanin / anemarrhena polysaccharide smart indicator film sample (size 2cm×2cm) prepared in Example 1 and the sodium alginate / black rice anthocyanin smart indicator film sample (size 2cm×2cm) prepared in Comparative Example 1 were fixed on the top inner wall of a 9.5cm×7.5cm×3.5cm sealed container, and ammonia solutions with volume fractions of 20%, 40%, 60%, 80% and 100% were placed in the container respectively. The color changes of the smart indicator film were recorded using digital photography equipment at 10, 20, 60, 90, 120 and 150 minutes respectively. The images at different time points were subjected to R, G, and B three-channel color analysis using image processing technology, the color difference values with the initial state were calculated, the difference maps were generated and quantitative analysis was performed S RGB Sensitivity index.

[0123] (3) Analysis of pH sensitivity test results

[0124] like Figure 11 and Figure 13 As shown in Group A data ( Figure 11The A group part is the color change on the surface of the smart indicator film, and the B group part is the color difference of the color before the smart indicator film is calculated by the machine). The color change of the indicator film within the pH range is then collected, and the color signals (R, G and B) therein are converted into digital signals by a computer. Finally, the difference map is output, wherein the higher the brightness of the blue-green area of the difference map of the smart indicator film in different pH solutions, the greater the difference in color signal and the more obvious the discoloration of the indicator film. The color change of the sodium alginate / black rice anthocyanin / anemarrhena polysaccharide smart indicator film prepared in Example 1 under different pH environments can be quantitatively analyzed by the brightness value of the blue-green area of the difference map. The higher the brightness value of this area, the greater the amplitude of the color signal change and the higher the response sensitivity of the smart indicator film. It was also found that the RGB primary color component values were negatively correlated with the film color depth, that is, the darker the color, the lower the relative intensity values of the red, green and blue channels. The sodium alginate / black rice anthocyanin / Anemarrhena polysaccharide smart indicator membrane prepared in Example 1 and the sodium alginate / black rice anthocyanin smart indicator membrane prepared in Comparative Example 1 both exhibited a color gradient from pink to light purple to dark purple to brown in a pH gradient solution. This color transduction behavior was significantly correlated with the dynamic changes in TVB-N content during meat spoilage, demonstrating that both smart indicator membranes possessed highly sensitive response characteristics. Furthermore, there was no significant difference in the color changes between the two smart indicator membranes, indicating that the addition of Anemarrhena polysaccharide in Example 1 did not negatively affect the pH sensitivity of the smart indicator membrane.

[0125] (4) Analysis of NH3 sensitivity measurement results

[0126] like Figure 12 and Figure 13 As shown in B Figure 12 Group A shows the color change of the surface of the smart indicator film, and Group B shows the color difference of the initial color of the smart indicator film calculated by the machine). As the ammonia exposure time increases, the sodium alginate / black rice anthocyanin / anemarrhena polysaccharide smart indicator film prepared in Example 1 shows a chromaticity evolution of dark blue → blue-purple → dark purple → brown-purple → yellow-brown in sequence. The brightness value of the difference image and S RGB The parameters all increased significantly. This chromaticity conversion mechanism is mainly attributed to the diffusion of volatile ammonia molecules into the membrane matrix, hydrolysis reaction with water molecules in the membrane to generate hydroxyl anions (OH-), and then forming an alkaline microenvironment inside the membrane. When the local pH exceeds 8.5, the pyran ring structure of the anthocyanin molecule undergoes a ring-opening reaction to generate a chalcone-type yellow substance with a conjugated double bond. In addition, there is no significant difference in the color changes of the two smart indicator films, which shows that in Example 1, the addition of Anemarrhena polysaccharide did not have a negative impact on the NH3 sensitivity of the smart indicator film.

[0127] Smart indicator film sensitivity test on pork:

[0128] (1) Determination of pork sensitivity using intelligent indicator membrane

[0129] 20±1g of fresh pork tenderloin was placed at the bottom of a sterile glass culture dish with a size of 9.5cm×7.5cm×3.5cm, and covered with a sealing lid. The sodium alginate / black rice anthocyanin / Anemarrhena polysaccharide smart indicator film sample prepared in Example 1 (with a size of 2cm×2cm) was fixed to the inner surface of the lid to ensure that the vertical distance between the meat sample and the film surface was about 90mm. The packaged samples were stored in a constant temperature and dark environment at 4°C for 5 days. A digital camera was used to record the color evolution of the smart indicator film every day for 5 consecutive days to evaluate its monitoring efficiency. At the same time, the pH value and TVB-N content of the meat samples during storage were measured according to the Chinese national standard GB5009.937-2016 to characterize the changes in their freshness.

[0130] (2) Analysis of pork sensitivity using intelligent indicator membrane

[0131] like Figure 14 As shown in Figure 1, according to the GB2707-2016 standard, when the storage time reaches 48h, the TVB-N value of the meat sample increases from the initial 8.3mg / 100g to 16.7mg / 100g, breaking through the 15mg / 100g safety threshold, indicating that it has entered a sub-fresh state. At this time, the sodium alginate / black rice anthocyanin / anemarrhena polysaccharide intelligent indicator film sample prepared in Example 1 undergoes a significant color change (blue-purple → light yellow-brown), and its RGB sensitivity reaches 16.92% ± 0.45% (Table 1), which is highly consistent with the TVB-N value change trend. After storage for 4 days, the TVB-N value of the meat sample has exceeded the 25mg / 100g limit specified in the national standard. The color sensitivity of the sodium alginate / black rice anthocyanin / anemarrhena polysaccharide intelligent indicator film sample prepared in Example 1 further deepens to 39.47% (dark yellow-brown), successfully achieving visual monitoring of the corruption stage.

[0132] Table 1 Sensitivity values of sodium alginate / black rice anthocyanin / anemarrhena polysaccharide intelligent indicator film as freshness changes

[0133]

[0134] The sodium alginate / black rice anthocyanin / Anemarrhena polysaccharide smart indicator films prepared in Examples 2 and 3 showed similar performance to the sodium alginate / black rice anthocyanin / Anemarrhena polysaccharide smart indicator film prepared in Example 1 in the test.

Claims

1. A method for preparing a freshness intelligent indicator film, characterized in that: The following steps are involved: Step S1: dissolving sodium alginate in distilled water and mixing thoroughly to obtain a sodium alginate film-forming solution; Step S2: dissolving anthocyanidin in the sodium alginate film-forming solution prepared in step S1, and mixing thoroughly to obtain a sodium alginate / anthocyanidin film-forming solution; Step S3: dissolving the Anemarrhena polysaccharide in distilled water to obtain a Anemarrhena polysaccharide suspension after sufficient dissolution, and thoroughly mixing the Anemarrhena polysaccharide suspension with the sodium alginate / anthocyanidin film-forming solution prepared in step S2 to obtain a sodium alginate / anthocyanidin / Anemarrhena polysaccharide film-forming solution; Step S4: The obtained sodium alginate / anthocyanidin / Anemarrhena polysaccharide film-forming solution is placed in an ultrasonic cleaner to remove bubbles; The sodium alginate / anthocyanidin / anemarrhena polysaccharide film-forming solution is poured onto the film embryo, dried, and peeled off to obtain a freshness intelligent indicator film.

2. The method for preparing the freshness intelligent indicator film according to claim 1, characterized in that: In step S1, the mass concentration of sodium alginate in the sodium alginate film-forming solution is 1.5-2.5 g / 100 mL.

3. The method for preparing the freshness intelligent indicator film according to claim 1, wherein: In step S2, the mass concentration of anthocyanins in the sodium alginate / anthocyanin film-forming solution is 0.026-0.046 g / 100 mL.

4. The method for preparing the freshness intelligent indicator film according to claim 1, wherein In step S3, the mass concentration of Anemarrhena asphodeloides polysaccharide in the sodium alginate / anthocyanidin / Anemarrhena asphodeloides polysaccharide film-forming solution is 0.01125-0.01875 g / 100 mL.

5. The method for preparing the freshness intelligent indicator film according to claim 1, wherein: In step S4, the ultrasonic cleaning time is 25-35 minutes, the volume of the film-forming solution is 30-40 mL, and the drying conditions are a temperature of 25-35° C., a relative humidity of 5-15%, and a drying time of 24-48 hours.

6. The method for preparing the freshness intelligent indicator film according to any one of claims 1 to 5, characterized in that: The anthocyanin in step S2 is black rice anthocyanin, the sodium alginate / anthocyanin film-forming solution is sodium alginate / black rice anthocyanin film-forming solution, and the sodium alginate / anthocyanin / anemarrhena polysaccharide film-forming solution is sodium alginate / black rice anthocyanin / anemarrhena polysaccharide film-forming solution.

7. A freshness intelligent indicator film, characterized in that: The freshness intelligent indicator film is prepared by the preparation method of any one of claims 1 to 5.

8. Use of the freshness intelligent indicator film according to claim 7 in pork freshness indication.

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