Method for improving water resistance and color sensitivity of food freshness indicating film and application

Abstract

The invention relates to a method for improving water resistance and color sensitivity of a food freshness indicating film and application, the method comprises the following steps: 1) adding gelatin and glycerol into distilled water, and stirring and mixing to obtain a gelatin solution; (2) adding purple cabbage anthocyanin and reducing sugar into the gelatin solution obtained in the step (1), adjusting the pH value to 5-7 by using acid or alkali, and magnetically stirring for 30 minutes to obtain a film forming solution; and (3) drying the film-forming liquid prepared in the step (2) to form a film, and then carrying out Maillard reaction to obtain the Maillard reaction modified food freshness indicating film. The indicating film prepared through the method has good water resistance and mechanical performance, is suitable for aquatic products and other high-humidity environments, is sensitive to the pH value and can well distinguish the putrefaction degree of the aquatic products, the preparation method is simple, rapid and good in repeatability, and the raw materials gelatin, purple cabbage anthocyanin and xylose of the indicating film are all edible substances, safe, non-toxic and free of pollution. The method has the advantages of sustainable development, good biocompatibility and environmental friendliness.

Description

Technical Field

[0001] The invention belongs to the technical field of food freshness monitoring, and particularly relates to a method for improving the water resistance and color sensitivity of a food freshness indicator film and its application. Background Art

[0002] In daily life, consumers can only determine the freshness of food based on the packaging date and expiration date, and cannot accurately assess changes in food quality during storage and transportation. Food freshness indicator labeling technology can more clearly and intuitively monitor food freshness in real time. Aquatic products are delicious and rich in high-quality protein, but their high moisture content and loose muscle tissue make them susceptible to spoilage during storage and transportation. This spoilage produces volatile gases, which cause changes in the pH value of the packaging environment. Anthocyanin-loaded food freshness indicator colorimetric films can change color according to changes in ambient gases, providing a new means for food quality control and promoting the sustainable development of the food industry.

[0003] In smart packaging research, biodegradable and renewable materials such as polysaccharides, proteins, lipids, and their complexes are primarily used. These materials are safe and environmentally friendly, reducing the environmental, public health, and economic burdens of traditional packaging materials. Gelatin and red cabbage anthocyanins are common materials in the food industry and hold great promise for their application in food packaging. Red cabbage anthocyanins are natural pigments belonging to the anthocyanin family, with a basic structure similar to cyanidin. As a natural indicator, they exhibit distinct colors depending on pH, appearing purple-red in acidic environments and yellow-green in alkaline environments. Gelatin, primarily derived from animal skins and bones, is a type of protein derived from the partial hydrolysis of collagen. Its molecular structure contains numerous hydroxyl groups, as well as numerous carboxyl and amino groups, making it highly hydrophilic. As a biodegradable material, it is widely used in the development of food coatings and composite films, exhibiting excellent film-forming properties and biocompatibility. Through hydrogen bonding and electrostatic interactions, red cabbage anthocyanins can be effectively immobilized within a gelatin matrix, enabling the preparation of colorimetric films that indicate food freshness. However, studies have shown that a single gelatin film has high water solubility and is easily affected by environmental factors, and has certain defects in practical applications. Patent 202310781695.0 discloses an indicator film based on blueberry anthocyanins and a preparation method thereof. By compounding a variety of biomacromolecules, the mechanical properties of the gelatin-based indicator film are enhanced; Patent 202111172154.5 discloses a colorimetric food freshness intelligent indicator label and a preparation method thereof, which utilizes alkyl ketene dimers to construct a hydrophobic structure, thereby improving water resistance while retaining a certain color rendering property. However, the preparation method of the existing technical solution is too complicated and difficult to operate, and it is necessary to use alkyl ketene dimers as base materials, which is not only costly, but also easy to cause environmental pollution, and the overall effect is not high. Summary of the Invention

[0004] In view of the problems existing in the prior art, the present invention aims to provide a method and application for improving the water resistance and color sensitivity of a food freshness indicator film.

[0005] The present invention is specifically implemented through the following technical solutions: A first aspect of the present invention provides a method for improving the water resistance and color sensitivity of a food freshness indicator film, the method comprising the following steps: 1) Add gelatin and glycerin to distilled water and stir to obtain a gelatin solution. 2) adding red cabbage anthocyanidins and reducing sugar to the gelatin solution of step 1), adjusting the pH to 5-7 with acid or base, and magnetically stirring for 30 minutes to prepare a membrane-forming solution; 3) Drying the film-forming liquid prepared in step 2) to form a film and then subjecting it to a Maillard reaction to obtain a Maillard reaction-modified food freshness indicator film.

[0006] Furthermore, the gelatin solution in step 1) is a solution containing 3-5% gelatin; the mass ratio of gelatin to glycerol is 6-10:1.

[0007] Furthermore, the stirring and mixing in step 1) is carried out at a temperature of 60° C. and the stirring time is 30 min.

[0008] Furthermore, in step 2), the amount of anthocyanin added from purple cabbage is such that its final concentration in the film-forming solution is 0.2%, and the reducing sugar is xylose, and its amount of anthocyanin added in the film-forming solution is such that its final concentration in the film-forming solution is 0.5-2%.

[0009] Furthermore, in step 2), the pH value is adjusted using 1 M NaOH or 1 M HCl.

[0010] Furthermore, step 3) the Maillard reaction is specifically as follows: 20 mL of the film-forming liquid is poured into a square plastic Petri dish (10 cm × 10 cm), dried at 25°C and a relative humidity of 40% for 48 hours to form a film, the film is placed in an oven for heating reaction, and after the reaction is completed, it is placed in an environment of 25°C and a relative humidity of 50% for equilibrium for 24 hours, and the film is removed to obtain a Maillard reaction-modified food freshness indicator film.

[0011] Furthermore, the temperature of the heating reaction in the oven is 50-60° C., and the reaction time is 0.5-2 h.

[0012] The second aspect of the present invention provides a food freshness indicator film prepared by the above method.

[0013] A third aspect of the present invention provides the use of a food freshness indicator film in detecting the freshness of aquatic products.

[0014] The indicator film prepared by the method of the present invention has good water resistance and mechanical properties, is suitable for high-humidity environments such as aquatic products, is sensitive to pH values, and can well distinguish the degree of corruption of aquatic products. The preparation method is simple, rapid, and reproducible. The raw materials of the indicator film, gelatin, purple cabbage anthocyanin, and xylose, are all edible substances, safe and non-toxic, and have the advantages of sustainable development, good biocompatibility, and environmental friendliness. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 The following are scanning electron microscope images of the indicator films prepared in the examples and comparative examples of the present invention; Figure 2 The infrared spectra and X-ray diffraction patterns of the indicator films prepared in the examples and comparative examples of the present invention are shown; Figure 3 The pH color response diagram of the indicator film prepared in the examples and comparative examples of the present invention; Figure 4 Graphs showing ammonia sensitivity of indicator films prepared in Examples and Comparative Examples of the present invention; Figure 5 The color response sensitivity diagram of the indicator film prepared in the examples and comparative examples of the present invention; Figure 6 The color difference diagram of the storage stability of the indicator films prepared in the examples of the present invention and the comparative examples; Figure 7 The complete packaging, label color, and TVB-N value of whiteleg shrimp during storage. DETAILED DESCRIPTION

[0016] The present invention is further described below in conjunction with specific embodiments to facilitate a better understanding of the present technical solution.

[0017] Example 1

[0018] A food freshness indicator film comprises a matrix gelatin, a color indicator purple cabbage anthocyanin, and xylose. The preparation method comprises the following steps: 1. Prepare the membrane-forming solution: Mix 4 g of gelatin and 0.5 g of glycerol in 100 mL of distilled water and stir at 60°C for 30 min to create a 4% gelatin solution (w / v). Add 0.2% red cabbage anthocyanidins and 1% xylose to the gelatin solution to prepare the membrane-forming solution. Adjust the solution pH to 6.0 with 1 M NaOH or 1 M HCl and stir using a magnetic stirrer for 30 min. 2. Pour 20 mL of the film-forming solution into a square plastic Petri dish (10 cm × 10 cm) and dry at 25°C and 40% relative humidity for 48 hours to form a film. Heat the film in an oven at 50°C for 1 hour. After the reaction, equilibrate it at 25°C and 50% relative humidity for 24 hours. Remove the film to obtain the Maillard reaction-modified freshness indicator film GS.

[0019] Example 2

[0020] A food freshness indicator film comprises a matrix gelatin, a color indicator purple cabbage anthocyanin, and xylose. The preparation method comprises the following steps: 1. Prepare the membrane-forming solution: Mix 4 g of gelatin and 0.5 g of glycerol in 100 mL of distilled water and stir at 60°C for 30 min to create a 4% gelatin solution (w / v). Add 0.2% red cabbage anthocyanidins and 1% xylose to the gelatin solution to prepare the membrane-forming solution. Adjust the solution pH to 6.0 with 1 M NaOH or 1 M HCl and stir using a magnetic stirrer for 30 min. 2. Pour 20 mL of the film-forming solution into a square plastic Petri dish (10 cm × 10 cm) and dry at 25°C and 40% relative humidity for 48 hours to form a film. Heat the film in an oven at 60°C for 1 hour. After the reaction, equilibrate it at 25°C and 50% relative humidity for 24 hours. Remove the film to obtain the Maillard reaction-modified freshness indicator membrane (GM).

[0021] Comparative Example 1 1. Prepare the membrane-forming solution: Mix 4 g of gelatin and 0.5 g of glycerol in 100 mL of distilled water and stir at 60°C for 30 min to create a 4% gelatin solution (w / v, the same below). Add 0.2% red cabbage anthocyanidins and 1% xylose to the gelatin solution to prepare the membrane-forming solution. Adjust the solution pH to 6.0 with 1 M NaOH or 1 M HCl and stir using a magnetic stirrer for 30 min. 2. Pour 20 mL of the film-forming solution into a square plastic Petri dish (10 cm × 10 cm). Dry the film at 25°C and 40% relative humidity for 48 hours. Then equilibrate the film at 25°C and 50% relative humidity for 24 hours. Remove the film. This will yield freshness-indicating film G0.

[0022] Comparative Example 2 1. Prepare the membrane-forming solution: Mix 4 g of gelatin and 0.5 g of glycerol in 100 mL of distilled water and stir at 60°C for 30 min to create a 4% gelatin solution (w / v, the same below). Add 0.2% red cabbage anthocyanidin to the gelatin solution to prepare the membrane-forming solution. Adjust the solution pH to 6.0 with 1 M NaOH or 1 M HCl and stir using a magnetic stirrer for 30 min. 2. Pour 20 mL of the film-forming solution into a square plastic Petri dish (10 cm × 10 cm) and dry at 25°C and 40% relative humidity for 48 hours to form a film. Heat the film in an oven at 60°C for 1 hour. After the reaction, equilibrate it at 25°C and 50% relative humidity for 24 hours. Remove the film to obtain the freshness-indicating film GH.

[0023] The microstructure results of the indicator films obtained in the above examples and comparative examples are as follows: Figure 1 As shown, the surface and cross-sectional micromorphologies of the indicator membranes were observed using scanning electron microscopy at 1000x and 4000x magnification, respectively. The results show that the surface microstructures of all membranes remained smooth and dense, demonstrating the excellent film-forming properties of gelatin and its good compatibility with xylose and red cabbage anthocyanins. The cross-sectional surfaces of the membranes were continuous and uniform, with no pores, indicating that the Maillard reaction resulted in tight cross-linking between gelatin and xylose molecules, forming an ordered and dense structure.

[0024] The infrared spectra, X-ray diffraction patterns, thermogravimetric analysis and derivative thermogravimetric analysis patterns of the indicator films prepared in the above examples and comparative examples are shown in FIG. Figure 2 As shown. ATR-FTIR was used to measure the infrared spectrum in the 600-4000 cm-1 band with a resolution of 4 cm -1 , scanned 32 times, the results showed that the characteristic absorption bands of each indicator film had no obvious shift changes and no new peaks appeared, and heating, sugaring and Maillard reaction had no significant effect on the chemical structure of the gelatin film; the crystal structure of the indicator film (3cm × 3 cm) was determined using an X-ray diffractometer, 2θ=5°-60°, rate 2° / min, the results showed that G0 showed an obvious main diffraction peak at 21.2°, while the diffraction peak positions of GH, GS and GM were consistent with G0, indicating that gelatin and xylose had good compatibility, and heating, sugaring and Maillard reaction had no obvious effect on the crystallinity of the film.

[0025] The pH color response of the indicator film prepared in the above examples and comparative examples is as follows: Figure 3 As shown in the figure, the indicator membrane was immersed in a pH 2-12 buffer solution for 1 min to evaluate the color response of the indicator membrane to the pH buffer solution. The results showed that under different pH conditions, the indicator membrane showed different color changes. With the increase of pH value, the color of the indicator membrane changed from pink to purple, then to blue, and finally to yellow or green, indicating that the Maillard reaction modified membranes GS and GM have a pH color response similar to that of G0 and GH. In order to simulate the release of volatile amines in the process of spoilage of aquatic products, the response characteristics of the indicator membrane to volatile ammonia were tested. Figure 4As shown in the figure, all indicator films underwent significant color changes (from purple to yellow-green) within 24 min, indicating that the indicator films were all sensitive to ammonia. Among them, GM had a color response sensitivity similar to that of G0 and GH, while GS had a color response sensitivity higher than that of G0 and GH ( Figure 5 In order to evaluate the stability of the gelatin-based freshness indicator film more scientifically and rationally, the color parameters of the gelatin-based freshness indicator film were measured using a colorimeter every day during storage, and the ΔE value was calculated. The results are shown in the figure below. Figure 6 As shown, the ΔE value of the color change of the indicator membrane during storage was less than 5, making it indistinguishable to the naked eye, indicating that the indicator membranes had good storage stability. Water solubility and swelling rate are key indicators of membrane water resistance. As shown in Table 1, G0 and GH both have 100% water solubility and extremely high swelling rates. After Maillard reaction modification, the water solubility and swelling rates of GS and GM were significantly reduced, indicating that the Maillard reaction significantly improved the water resistance of the indicator membranes (Table 1). These results demonstrate that a moderate Maillard reaction can significantly improve the water resistance of gelatin-based freshness indicator membranes without reducing the membrane's color response sensitivity.

[0026] Table 1: Physical properties of the membranes

[0027] The indicator film was made into an indicator label for monitoring the freshness of whiteleg shrimp and its indicator performance was explored. Figure 7 When the TVB-N value of white shrimp is less than 10 mg / 100 g, G0, GH, GS, and GM appear pink-purple. When the TVB-N value is between 10 mg / 100 g and 25 mg / 100 g, G0, GH, GS, and GM appear blue. When the TVB-N value is greater than 28 mg / 100 g, GS and GM appear yellow-green, indicating that the shrimp have become spoiled. G0 and GH only undergo a red-to-blue color change during the indicator process and therefore cannot effectively indicate the degree of fresh spoilage of white shrimp. The Maillard reaction-modified colorimetric film has a good indicator effect on shrimp spoilage, and the visible color change is consistent with the degree of spoilage measured by the above chemical indicators.

Claims

1. A method for improving the water resistance and color sensitivity of a food freshness indicator film, characterized in that: The method comprises the following steps: 1) Add gelatin and glycerin to distilled water and stir to obtain a gelatin solution. 2) adding red cabbage anthocyanidins and reducing sugar to the gelatin solution of step 1), adjusting the pH to 5-7 with acid or base, and magnetically stirring for 30 minutes to prepare a membrane-forming solution; 3) Drying the film-forming liquid prepared in step 2) to form a film and then subjecting it to a Maillard reaction to obtain a Maillard reaction-modified food freshness indicator film.

2. A method for improving the water resistance and color sensitivity of a food freshness indicator film according to claim 1, characterized in that: In step 1), the gelatin solution contains 3-5% gelatin; the mass ratio of gelatin to glycerol is 6-10:

1.

3. The method for improving the water resistance and color sensitivity of a food freshness indicator film according to claim 1, wherein: The stirring and mixing in step 1) is carried out at a temperature of 60° C. and the stirring time is 30 min.

4. The method for improving the water resistance and color sensitivity of a food freshness indicator film according to claim 1, wherein: In step 2), the amount of anthocyanin from purple cabbage added is such that its final concentration in the film-forming solution is 0.2%, and the reducing sugar is xylose, and its amount of xylose added is such that its final concentration in the film-forming solution is 0.5-2%.

5. The method for improving the water resistance and color sensitivity of a food freshness indicator film according to claim 1, wherein: In step 2), the pH value is adjusted using 1 M NaOH or 1 M HCl.

6. The method for improving the water resistance and color sensitivity of a food freshness indicator film according to claim 1, wherein: Step 3) The Maillard reaction is as follows: 20 mL of the film-forming solution is poured into a square plastic Petri dish (10 cm × 10 cm), and the film is dried at 25°C and 40% relative humidity for 48 hours. The film is then placed in an oven for heating and reaction. After the reaction is completed, the film is placed in an environment of 25°C and 50% relative humidity for equilibration for 24 hours. The film is then removed to obtain a Maillard reaction-modified food freshness indicator film.

7. A method for improving the water resistance and color sensitivity of a food freshness indicator film according to claim 6, characterized in that: The temperature of the heating reaction in the oven is 50-60° C., and the reaction time is 0.5-2 h.

8. A food freshness indicator film prepared by the method according to any one of claims 1 to 7.

9. Use of the food freshness indicator film according to claim 8 in detecting the freshness of aquatic products.

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