Intelligent indicating film for freshness of aquatic products and preparation method of intelligent indicating film

Abstract

The invention discloses an intelligent indicating film for freshness of aquatic products and a preparation method thereof.The indicating film comprises a base film and a color developing agent, the base film is synthesized from soybean protein isolate and locust bean gum, the color developing agent is purple sweet potato anthocyanin and alizarin, the interior of the indicating film is of a porous structure, and the indicating film is spongy; the preparation method comprises the following steps: preparing a base film solution, then adding purple sweet potato anthocyanin and alizarin, uniformly mixing, then adjusting the pH value to 6.0 + / -0.1 to obtain a film-forming solution, pouring the film-forming solution into a mold, and freeze-drying to obtain the indicating film. The purple sweet potato anthocyanin and the alizarin are combined for use, the color developing sensitivity and stability of the indicating film are improved, the film has a porous structure by combining freeze drying, the color developing sensitivity and stability of the indicating film are further improved, and the indicating film has application potential in the field of intelligent food packaging.

Description

Technical Field

[0001] The invention relates to the technical field of food intelligent indicator films, and in particular to an intelligent indicator film for freshness of aquatic products and a preparation method thereof. Background Art

[0002] With the improvement of people's living standards and the enhancement of food safety awareness, consumers have higher and higher requirements for food freshness. As a high-protein, low-fat high-quality food, the freshness of aquatic products directly affects the quality and safety of food. However, aquatic products are very easy to deteriorate during storage and transportation. How to effectively monitor the freshness of aquatic products has become an urgent problem to be solved.

[0003] Traditional methods for testing the freshness of aquatic products mainly include sensory evaluation, chemical analysis, and microbial testing. Although these methods can provide relatively accurate test results, they are complex to operate, time-consuming, require professional equipment and personnel, and are not suitable for widespread use in daily life. Therefore, it is of great practical significance to develop an intelligent indicator membrane that is simple to operate, low-cost, and can monitor the freshness of aquatic products in real time.

[0004] In recent years, smart packaging technology has been increasingly used in the food industry. As an important component of smart packaging, smart indicator films can indicate the freshness of food through intuitive methods such as color changes. Existing smart indicator films mostly use synthetic pigments or chemical reagents as color developers. These materials may pose safety hazards during use, and their color development sensitivity and stability are low, making it difficult to meet actual application needs. Summary of the invention

[0005] Purpose of the invention: The first purpose of the present invention is to provide a safe, stable and highly sensitive intelligent indicator film for freshness of aquatic products; the second purpose of the present invention is to provide a method for preparing the intelligent indicator film for freshness of aquatic products.

[0006] Technical solution: The intelligent indicator film for freshness of aquatic products described in the present invention comprises a base film and a color developer. The base film is synthesized from soy protein isolate and locust bean gum, the color developer is purple sweet potato anthocyanin and alizarin, and the interior of the indicator film is a porous structure and has a sponge-like shape.

[0007] The purple sweet potato anthocyanins and alizarin are mixed to achieve a wider pH range through synergistic effects. The non-covalent interactions between molecules enhance stability and complementary spectral characteristics, achieving a more stable and sensitive color development effect. More importantly, the porous structure increases the specific surface area of ​​the membrane, making the membrane more sensitive.

[0008] Preferably, the mass ratio of the soy protein isolate, locust bean gum, purple sweet potato anthocyanin and alizarin is 10:5:4:0.0125-0.075.

[0009] The method for preparing the intelligent indicator film for freshness of aquatic products of the present invention comprises the following steps:

[0010] (1) dissolving soy protein isolate and locust bean gum respectively to obtain a soy protein isolate solution and a locust bean gum solution, and then mixing them to obtain a soy protein isolate-locust bean gum composite membrane solution;

[0011] (2) adding glycerol to the composite membrane solution obtained in step (1), and stirring at 40 to 60° C. for 20 to 40 minutes;

[0012] (3) adding purple sweet potato anthocyanins and alizarin to the membrane solution treated in step (2), mixing evenly, and then adjusting the pH to 6.0±0.1 to obtain a membrane-forming solution;

[0013] (4) After the film-forming solution is mixed evenly, it is poured into a mold and freeze-dried to obtain the indicator film.

[0014] Preferably, in step (1), the preparation method of the soy protein solution is: adding soy protein isolate to water, and magnetically stirring at 40-70° C. for 1.5-2 h to obtain a soy protein isolate solution, wherein the concentration of the soy protein isolate is 5-25 g / L.

[0015] Preferably, in step (1), the locust bean gum solution is prepared by adding locust bean gum to water and magnetically stirring at 75 to 90° C. for 1 to 1.5 hours, wherein the concentration of the locust bean gum solution is 5 to 25 g / L.

[0016] In step (2), the purpose of adding glycerol is mainly to improve the mechanical properties of the film, increase its elongation at break and toughness, and enhance the water vapor permeability and elasticity of the film. The hydroxyl groups in the glycerol molecules can form hydrogen bonds with the peptide bonds in the soy protein isolate molecules or the polar groups on the side chains. The formation of these hydrogen bonds weakens the hydrogen bonding forces between the original protein molecules, causing the protein network structure to become looser and more flexible. The addition of glycerol molecules may also produce a certain steric hindrance effect, further hindering the close packing and interaction between protein molecules, thereby promoting the mobility of the molecular chains and the flexibility of the film. Preferably, the amount of glycerol added is 35% to 55% of the sum of the mass of the soy protein isolate and locust bean gum added.

[0017] Preferably, in step (3), the pH is adjusted using NaOH solution and citric acid solution.

[0018] In step (4), the freeze drying time is 24 to 48 hours. Freeze drying makes the membrane have a porous structure inside.

[0019] Preferably, in step (4), the mixing is carried out by ultrasonic treatment. Further preferably, the conditions of the ultrasonic treatment are: ultrasonic power of 750W, and time of 10 to 40 minutes. Ultrasonic treatment makes the membrane solution more evenly mixed, and improves the stability and sensitivity of the membrane.

[0020] Preferably, in step (3), the method for preparing purple sweet potato anthocyanins comprises the following steps:

[0021] (1) Clean fresh purple sweet potatoes, slice them, dry them in a hot air drying oven at 30-50° C. to constant weight, crush them, and pass them through a 60-mesh sieve to obtain powder;

[0022] (2) adding purple sweet potato powder to a 65% ethanol solution at a solid-liquid ratio of 1:40 (g / mL), and adding citric acid to make the pH of the system reach 3.0;

[0023] (3) adding cellulase and α-amylase, performing enzymolysis at 30-60° C. for 5-20 min, performing ultrasonication for 20-50 min, and performing centrifugation at 3000-6000 r / min for 10-25 min. The supernatant was subjected to rotary evaporation to obtain a concentrated extract of purple sweet potato anthocyanins, and then freeze-dried to obtain purple sweet potato anthocyanins.

[0024] Preferably, the mass ratio of the cellulase to the α-amylase is 1:1, and the total amount of the enzyme is 0.4 mg / 100 mL.

[0025] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: (1) By combining purple sweet potato anthocyanins with alizarin, the color sensitivity and stability of the indicator membrane are improved, and freeze-drying makes the membrane have a porous structure, which further improves the color sensitivity and stability of the indicator membrane; (2) The raw materials are safe and environmentally friendly, and there is no food safety hazard; (3) The preparation method is simple and easy, which is convenient for large-scale production and promotion and application, providing a new technical means for food safety monitoring and helping to improve the level of food safety management; (4) The preparation process adopts environmentally friendly materials and methods, which reduces production costs and reduces the impact on the environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The SEM analysis diagrams of Examples 1 to 2 and Comparative Examples 1 to 2 are shown;

[0027] Figure 2 The infrared spectra of Examples 1 and 2 and Comparative Examples 1 and 2 are shown in FIG.

[0028] Figure 3 The XRD diffraction spectra of Examples 1-2 and Comparative Examples 1-2 are shown;

[0029] Figure 4The DSC curves of Examples 1 and 2 and Comparative Examples 1 and 2 are shown in FIG.

[0030] Figure 5 The ammonia response physical diagram of Examples 1-2 and Comparative Examples 1-2;

[0031] Figure 6 It is the ammonia response sensitivity diagram of Examples 1-2 and Comparative Examples 1-2;

[0032] Figure 7 The color change over time of Examples 1-2 and Comparative Examples 1-2 for shrimp freshness monitoring at 25°C;

[0033] Figure 8 The color change over time of Examples 1-2 and Comparative Examples 1-2 for shrimp freshness monitoring at 4°C;

[0034] Fig. 9 It is a graph showing the change of TVB-N content of shrimp and the color difference of the indicator films of Examples 1 to 2 and Comparative Examples 1 to 2 over time at 25°C;

[0035] Fig.10 It is a graph showing the change of TVB-N content of shrimp and the color difference of the indicator films of Examples 1 to 2 and Comparative Examples 1 to 2 over time at 4°C;

[0036] Fig.11 It is a correlation diagram between ΔE and TVB-N of the indicator film during the storage of shrimps at 25°C in Examples 1-2 and Comparative Examples 1-2;

[0037] Fig.12 It is a correlation diagram between ΔE and TVB-N of the indicator film during the storage of shrimps at 4°C in Examples 1-2 and Comparative Examples 1-2;

[0038] Fig.13 This is a picture of the actual appearance of packaging with a visual window used for monitoring shrimp freshness. DETAILED DESCRIPTION

[0039] The technical solution of the present invention is further described below in conjunction with embodiments.

[0040] Example 1

[0041] The preparation method of the aquatic product freshness intelligent indicator film of the present invention comprises the following steps:

[0042] (1) Add 2 g of soy protein isolate to distilled water to make a volume of 100 mL, and stir magnetically at 60° C. for 2 h until completely dissolved; add 1 g of locust bean gum to distilled water to make a volume of 100 mL, and stir magnetically at 85° C. for 1.5 h until completely dissolved; mix the soy protein isolate solution and the locust bean gum solution in a volume ratio of 1:1 to obtain a soy protein isolate-locust bean gum composite membrane solution;

[0043] (2) Add 0.75 g of glycerol to 100 mL of the composite membrane solution and stir at 60 °C for 30 min;

[0044] (3) Add 0.4 g of purple sweet potato anthocyanin and 0.0025 g of alizarin to the membrane solution of step (2), stir evenly, and adjust the pH of the membrane solution to 6.0±0.1 with NaOH solution and sodium citrate solution;

[0045] (4) The film-forming solution was stirred evenly, and then poured into a square dish mold with a mass of 50 g, and freeze-dried for 48 hours to obtain the aquatic product freshness intelligent indicator film, which was named SP-LB-P.

[0046] The preparation method of purple sweet potato anthocyanins comprises the following steps:

[0047] (1) Clean fresh purple sweet potatoes, cut them into 3 mm slices using a slicer, dry them in a hot air drying oven at 45° C. to constant weight, crush them, and pass them through a 60-mesh sieve to obtain powder;

[0048] (2) adding purple sweet potato powder to a 65% ethanol solution at a solid-liquid ratio of 1:40 (g / mL), and adding citric acid to make the pH of the system reach 3.0;

[0049] (3) Add cellulase and α-amylase in a mass ratio of 1:1, with a total enzyme amount of 0.4 mg / 100 mL, perform enzymolysis at 50°C for 10 min, perform ultrasonication for 30 min, and centrifuge at 4 000 r / min for 15 min. Take the supernatant and perform rotary evaporation to obtain a concentrated extract of purple sweet potato anthocyanins, which is then freeze-dried to obtain purple sweet potato anthocyanins.

[0050] The alizarin is a commercially available natural pigment.

[0051] Example 2

[0052] On the basis of Example 1, in the preparation process of the membrane, the stirring in step (4) was changed to ultrasonic treatment, the ultrasonic power was 750 W, the time was 30 min, and the other conditions remained unchanged to obtain an indicator membrane, which was named SP-LB-UP.

[0053] Comparative Example 1

[0054] On the basis of Example 2, the freeze drying was changed to natural air drying for 24 hours and then hot air drying at 35° C. for 15 minutes, and the other conditions remained unchanged to obtain an indicator membrane, which was named SP-LB-UF.

[0055] Comparative Example 2

[0056] On the basis of comparative example 1, in the preparation process of the membrane, ultrasonic mixing was not performed in step (4), but stirring was used, and other conditions remained unchanged to obtain an indicator membrane, which was named SP-LB-F.

[0057] Structural characterization

[0058] 1. The microstructure, thermal stability and ammonia sensitivity of the indicator films of Examples 1 to 2 and Comparative Examples 1 to 2 were tested, and the results were as follows.

[0059] The surface results of the indicator films were analyzed by scanning electron microscopy.

[0060] Test results, such as Figure 1 As shown in the figure, it can be seen from the surface structures of SP-LB-F, SP-LB-UF, SP-LB-P and SP-LB-UP that ultrasonic treatment can improve the uniformity of the indicator membrane. The freeze-dried indicator membrane has more pores and a sponge-like morphology, which increases its specific surface area, and the pores of the ultrasonic porous indicator membrane are more uniform. Therefore, SP-LB-P and SP-LB-UP have higher ammonia response sensitivity.

[0061] Fourier transform infrared spectrometer in attenuated total reflectance mode was used in the range of 400–4000 cm -1 Infrared spectrum of the indicator film measured within the range.

[0062] Test results, such as Figure 2 As shown in Figure 2, the SP-LB-F, SP-LB-UF, SP-LB-P and SP-LB-UP indicator films have similar infrared spectra, indicating that ultrasound and different drying methods do not significantly change the functional groups in the indicator films. The SP-LB-F and SP-LB-UF indicator films have a peak at 1628 cm -1 The corresponding peaks of SP-LB-P and SP-LB-UP indicator films appeared at 1580 cm -1 This peak may be caused by the C=C bond of the aromatic ring in the mixed pigment or the C=O bond connected to the aromatic ring. The reason for the peak shift may be due to the intermolecular interaction and the change of moisture content caused by different drying methods.

[0063] The X-ray diffraction pattern of the indicator film was measured using a polycrystalline X-ray diffractometer, scanning from 5° to 50° at a speed of 5° / min.

[0064] Test results, such as Figure 3 As shown, ultrasonic treatment changed the crystal structure of SP-LB-F and SP-LB-P indicator films, resulting in the characteristic peaks moving from 20.12° to 20.40° and 20.51°, respectively. This indicates that ultrasonic treatment affects the interaction between molecules through mechanical vibration, making the crystal structure more compact or changing its orientation. In addition, different drying methods also significantly affect the crystal structure: air drying may lead to a looser crystal structure, while freeze drying makes the structure more compact.

[0065] The thermal stability of the indicator film was measured using a differential scanning calorimeter, and the DSC curve was recorded in a nitrogen atmosphere, a temperature range of 25-250°C, and a heating rate of 10°C / min.

[0066] Test results, such as Figure 4 As shown in the figure, DSC results show that the melting temperatures of the four indicator membranes are SP-LB-F (152.74°C), SP-LB-UF (165.74°C), SP-LB-P (159.35°C) and SP-LB-UP (166.55°C). Ultrasonic treatment significantly increases the melting temperature of the indicator membrane and enhances its thermal stability. Freeze drying also improves the thermal stability of the porous indicator membrane, and the effect is best when used in combination with ultrasonic treatment.

[0067] Performance Testing

[0068] 1. Indicator film sensitivity test

[0069] The indicator film was fixed in the center of the round cover, and then inverted on top of a container filled with 250mL ammonia water (4mmol / L). The color change of the indicator film was recorded at regular intervals under the same conditions. The image characteristic signal of the indicator film was extracted using Photoshop, and the average value of R, G, and B of the center point and the surrounding 5 pixels was used as the characterization value of the sensor film. S was calculated according to the following formula: RGB value, using the total RGB change rate S of the indicator film RGB Characterize its sensitivity, the calculation formula is as follows:

[0070] △R=|R0-R|; △G=|G0-G|; △B=|B0-B|

[0071]

[0072] Among them, R0, G0, and B0 are the initial values ​​of the indicator film before reaction; R, G, and B are the values ​​after reaction.

[0073] Test results, such as Figure 5 , Figure 6As shown, the four indicator films all responded to ammonia gas, and the color changed from peach pink to gray purple or blue gray, among which the ultrasonically treated porous indicator film (Example 2) responded the fastest and had the highest sensitivity. The sensitivity of all indicator films first increased rapidly and then slowly increased, which may be caused by the change in the volatilization rate of ammonia gas.

[0074] 2. Indicator membrane detection of freshness test of aquatic products

[0075] Examples 1-2 and Comparative Examples 1-2 were used to monitor the freshness of shrimps, and the results were as follows.

[0076] Place the indicator film on Fig.13 Visualize the groove of the packaging box cover; then, place fresh prawns at the bottom of the packaging box and store at 4°C for 6 days and at 25°C for 24 hours, and record the color of the indicator film and the total volatile basic nitrogen (TVB-N) content of the prawns every 24 hours and every 6 hours, respectively. The determination of volatile basic nitrogen content is carried out according to the microdiffusion method in GB 5009.228-2016 "National Food Safety Standard Determination of Volatile Basic Nitrogen in Food".

[0077] TVB-N value is a commonly used indicator for evaluating the freshness of aquatic products. When the TVBN value is lower than 30mg / 100g, the prawns are fresh. After 24 hours of storage at 25℃, the TVB-N value of the prawns increased from the final 2.71mg / 100g to 55.21mg / 100g. At 12 hours, the TVB value of the prawns was 26.14mg / 100g, which was in a sub-fresh state. Figure 7 As shown in the figure, at this time, the four indicator films of SP-LB-F, SP-LB-UF, SP-LB-P and SP-LB-UP changed from the original flesh-pink color to purple-red; at 18h, the TVB value of the prawns was 46.31mg / 100g, and the shrimps were no longer edible. The four indicator films of SP-LB-F, SP-LB-UF, SP-LB-P and SP-LB-UP turned into obvious purple; Fig. 9 It can be seen that the ΔE values ​​are 27.57, 18.68, 33.82 and 50.08 respectively. Fig.11 , ΔE of SP-LB-UP indicator film to R of TVB-N 2 The maximum value reached 0.98112, indicating that at 25°C, the color difference of the SP-LB-UP indicator film has a good correlation with the TVB-N value of shrimp, and can be used to monitor the freshness of shrimp at room temperature. After being stored at 4°C for 6 days, the TVB-N value of shrimp increased from the initial 2.71 mg / 100g to 40.8567 mg / 100g. On the 5th day, the TVB-N value of shrimp was 32.42 mg / 100g, which was no longer edible. Figure 8As shown in the figure, at this time, the four indicator films SP-LB-F, SP-LB-UF, SP-LB-P and SP-LB-UP changed from the original flesh-pink color to dark red. Fig.10 It can be seen that the color difference values ​​are 20.88, 20.91, 35.13 and 33.81 respectively. Fig.12 , ΔE of SP-LB-P indicator film to R of TVB-N 2 The maximum is 0.80906, which shows that at 25℃, the color difference of SP-LB-P indicator film has a good correlation with the TVB-N value of shrimp, and can be used to monitor the freshness of shrimp under low temperature conditions.

[0078] In summary, the two indicator films, SP-LB-P and SP-LB-UP, exhibited a more compact and uniform microstructure, with good thermal stability and ammonia sensitivity. The experimental results of the indicator film application showed that the two indicator films, SP-LB-P and SP-LB-UP, could effectively monitor the freshness of shrimp under refrigerated and room temperature conditions, and had application potential in the field of smart food packaging.

Claims

1. An intelligent indicator film for freshness of aquatic products, characterized in that: The invention comprises a base film and a color developer. The base film is synthesized from isolated soybean protein and locust bean gum. The color developer is purple sweet potato anthocyanin and alizarin. The interior of the indicator film is a porous structure and the shape is sponge-like.

2. The aquatic product freshness intelligent indicator film according to claim 1, characterized in that: The mass ratio of the soybean protein isolate, locust bean gum, purple sweet potato anthocyanin and alizarin is 10:5:4:0.0125-0.

075.

3. A method for preparing the intelligent indicator film for freshness of aquatic products according to claim 1, characterized in that: The following steps are involved: (1) dissolving soy protein isolate and locust bean gum respectively to obtain a soy protein isolate solution and a locust bean gum solution, and then mixing them to obtain a soy protein isolate-locust bean gum composite membrane solution; (2) adding glycerol to the composite membrane solution obtained in step (1), and stirring at 40 to 60° C. for 20 to 40 minutes; (3) adding purple sweet potato anthocyanins and alizarin to the membrane solution treated in step (2), mixing evenly, and then adjusting the pH to 6.0±0.1 to obtain a membrane-forming solution; (4) After the film-forming solution is mixed evenly, it is poured into a mold and freeze-dried to obtain the indicator film.

4. The method for preparing the intelligent indicator film for freshness of aquatic products according to claim 3, characterized in that: In step (4), the uniform mixing is performed by ultrasonic treatment.

5. The method for preparing the intelligent indicator film for freshness of aquatic products according to claim 3, characterized in that: In step (1), the preparation method of the soy protein solution is: adding soy protein isolate into water, and magnetically stirring at 40-70° C. for 1.5-2 h to obtain a soy protein isolate solution, wherein the concentration of the soy protein isolate is 5-25 g / L.

6. The method for preparing the intelligent indicator film for freshness of aquatic products according to claim 3, characterized in that: In step (1), the locust bean gum solution is prepared by adding locust bean gum to water and magnetically stirring at 75 to 90° C. for 1 to 1.5 hours, wherein the concentration of the locust bean gum solution is 5 to 25 g / L.

7. The method for preparing the intelligent indicator film for freshness of aquatic products according to claim 3, characterized in that: In step (2), the amount of glycerol added is 35% to 55% of the sum of the mass of the added soy protein isolate and locust bean gum.

8. The method for preparing the intelligent indicator film for freshness of aquatic products according to claim 3, characterized in that: In step (3), the pH is adjusted using NaOH solution and citric acid solution.

9. The method for preparing the intelligent indicator film for freshness of aquatic products according to claim 3, characterized in that: In step (3), the method for preparing purple sweet potato anthocyanins comprises the following steps: (1) Clean fresh purple sweet potatoes, slice them, dry them in a hot air drying oven at 30-50° C. to constant weight, crush them, and pass them through a 60-mesh sieve to obtain powder; (2) adding purple sweet potato powder to a 65% ethanol solution at a solid-liquid ratio of 1:40 (g / mL), and adding citric acid to make the pH of the system reach 3.0; (3) adding cellulase and α-amylase, performing enzymolysis at 30-60° C. for 5-20 min, performing ultrasonication for 20-50 min, and performing centrifugation at 3000-6000 r / min for 10-25 min. The supernatant was subjected to rotary evaporation to obtain a concentrated extract of purple sweet potato anthocyanins, and then freeze-dried to obtain purple sweet potato anthocyanins.

10. The method for preparing the intelligent indicator film for freshness of aquatic products according to claim 9, characterized in that: The mass ratio of the cellulase to the α-amylase is 1:1, and the total amount of the enzyme is 0.4 mg / 100 mL.

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