A water-resistant food freshness indicator colorimetric array and preparation method thereof

Abstract

A water-resistant food freshness indicator colorimetric array and its preparation method include the following steps: first, dissolving polyvinyl alcohol and zein in a mixed solvent of acetic acid and water, respectively; then, evenly mixing the polyvinyl alcohol solution and the zein solution in a certain proportion; then, adding curcumin-alizarin mixed pigments in different mass ratios; and mixing to obtain a final spinning solution. A nanofiber indicator membrane is prepared using electrospinning technology. The present invention proposes using two natural pigments, curcumin and alizarin, and loading the indicators onto the electrospun nanofiber membrane using electrospinning technology. This results in a meat product freshness indicator colorimetric array with a lower detection line, more diverse color variations, and excellent stability. The array can display significant color changes according to volatile gases generated during meat product storage.

Description

Technical Field

[0001] The invention belongs to food intelligent packaging technology, and in particular relates to a water-resistant food freshness indicating colorimetric array and a preparation method thereof. Background Art

[0002] Fresh pork is susceptible to physical, chemical, and biological influences during transportation, distribution, and storage, leading to spoilage. This quality deterioration severely impacts the nutritional value and sensory experience of fresh meat products, threatening consumers' health while also resulting in resource waste and economic losses. In real life, consumers often judge freshness based on sensory perceptions such as color, taste, and texture. However, these sensory characteristics are highly subjective and subject to significant individual variation. Traditional meat freshness testing and analysis methods are complex, time-consuming, and labor-intensive. Therefore, it is imperative to develop a quick and easy method for monitoring meat freshness in real time, suitable for use in both home and supermarket settings.

[0003] Freshness-indicating colorimetric labels offer a simple, efficient, and cost-effective solution for visualizing food freshness parameters. Their fundamental principle is that an indicator reacts with metabolic products during shelf life and spoilage, allowing for the detection of meat product freshness without damaging the packaging. Colorimetric labels typically consist of two components: a solid matrix and a chemical / biological dye loaded onto the matrix. The color change of the chemically responsive dye is correlated with the freshness or spoilage of the food.

[0004] Polyvinyl alcohol (PVA), a naturally biodegradable polymer, is widely used in packaging materials due to its excellent film-forming and mechanical properties. However, due to its polyhydroxy structure, it is prone to solid matrix swelling or partial dissolution in high humidity environments, disrupting the structural integrity of the film and affecting the interpretation of results.

[0005] During the spoilage process of meat products, volatile amine gases are produced by the breakdown of proteins. Therefore, monitoring these gases can be used to analyze changes in food freshness. Curcumin is a common natural pigment whose structure undergoes structural changes under different acidic and alkaline conditions, resulting in different color changes. However, single pigments suffer from a narrow pH response range and insignificant color change during application. Therefore, it is necessary to enhance the color richness and indication intensity of pH indicator labels to greatly improve their practicality. Summary of the Invention

[0006] The object of the present invention is to provide a water-resistant food freshness indicating colorimetric array and a preparation method thereof.

[0007] To achieve the above-mentioned and other related objectives, the present invention provides a technical solution: a method for preparing a water-resistant food freshness indicator colorimetric array, comprising the following steps:

[0008] Step 1, preparation of zein-polyvinyl alcohol mixed solution

[0009] Dissolving zein and polyvinyl alcohol in a mixed solvent of acetic acid and water respectively to obtain a zein solution and a polyvinyl alcohol solution; and uniformly mixing the zein solution and the polyvinyl alcohol solution to obtain a zein-polyvinyl alcohol mixed solution;

[0010] Step 2: Preparation of spinning solution

[0011] Mixing curcumin and alizarin in different mass ratios to obtain a plurality of mixed pigments; mixing the plurality of mixed pigments with the zein-polyvinyl alcohol mixed solution prepared in step 1, respectively, and stirring to obtain a plurality of spinning solutions;

[0012] Step 3: Preparation of nanofiber membrane

[0013] A variety of spinning solutions are used to prepare composite nanofiber membranes using an electrospinning machine. The composite nanofiber membranes on the drum receiver are removed and dried to complete the preparation of the nanofiber membranes. The food freshness indicator colorimetric array can be obtained by combining them according to the pigment ratio.

[0014] The preferred technical solution is: in step 1, when zein is dissolved in a mixed solvent consisting of acetic acid and water, the temperature is 45-55°C and the time is 4-6 hours; when polyvinyl alcohol is dissolved in a mixed solvent consisting of acetic acid and water, the dissolution temperature is 85-95°C and the time is 2-4 hours.

[0015] The preferred technical solution is: in step 1, the mass percentage concentration of the zein solution is 8-12%; the mass percentage concentration of the polyvinyl alcohol solution is 8-12%.

[0016] The preferred technical solution is: in the mixed solvent consisting of acetic acid and water, the volume ratio of acetic acid to water is 3-5:1.

[0017] The preferred technical solution is: the volume ratio of the zein solution to the polyvinyl alcohol solution is 6-10:3.

[0018] The preferred technical solution is: the mass of the mixed pigment is 3 mg, and the mass ratios of curcumin and alizarin are 5-0:0-5 respectively.

[0019] The preferred technical solution is: in step 3, the distance between the propulsion pump and the drum receiver is 10-12 cm, the power supply voltage between the propulsion pump and the drum receiver is 14-16 kV, and the flow rate of the propulsion pump is 0.8-1.0 mL / h.

[0020] The preferred technical solution is: in step 3, the spinning environment temperature is adjusted to 25-35° C. and the environment humidity is adjusted to 25%-30% RH.

[0021] The preferred technical solution is: in step 3, the drying temperature is 22-28° C., and the array is assembled according to a mass ratio of curcumin:alizarin of 5-0:0-5.

[0022] To achieve the above-mentioned and other related purposes, the present invention provides a technical solution: a water-resistant food freshness indicator colorimetric array, which is prepared using the above-mentioned preparation method of the water-resistant food freshness indicator colorimetric array.

[0023] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art:

[0024] 1. The present invention adopts a method of mixing matrix materials and screens to determine the ratio of zein solution and polyvinyl alcohol solution to prepare a low water-soluble indicator label. The label can maintain structural integrity in a high-humidity environment, and the ingredients of the prepared freshness indicator label are safe and can be used for food freshness detection. The composite nanofiber membrane prepared by mixing polyvinyl alcohol solution, zein solution and natural pigment has a fiber membrane with increased rigidity compared with a single-component membrane.

[0025] 2. Electrospinning nanofiber membranes have the advantages of high surface area, dense structure, and small porosity, making them suitable for loading responsive substances. Using electrospinning technology, curcumin and alizarin in varying proportions were successfully loaded onto polyvinyl alcohol-zein nanofiber membranes to create a colorimetric array, enabling visual monitoring of food freshness. The resulting colorimetric array exhibited high sensitivity, low detection limits, and diverse color changes for a variety of volatile amines, overcoming the limitations of single natural pigments, which typically have a narrow pH response range and lack significant color change.

[0026] 3. Traditional meat product freshness detection methods are cumbersome and time-consuming. The water-resistant food freshness indicator colorimetric array in the present invention can intuitively visualize the freshness of the product, and its color change value is highly correlated with the spoilage index. It can effectively help consumers quickly understand the freshness of meat products and better help people ensure and determine the safety of meat products in all aspects of circulation, storage and sales. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1This is a graph showing the water solubility determination of the indicator labels of Examples 1.1-1.4 in Example 1.

[0028] Figure 2 This is a color difference curve of the indicator labels of Examples 2.1-2.6 in Example 2 in response to ammonia water.

[0029] Figure 3 This is a graph showing the color difference change in response of the indicator labels of Examples 2.1-2.6 in Example 2 to dimethylamine.

[0030] Figure 4 This is a graph showing the color difference change in response of the indicator labels of Examples 2.1-2.6 in Example 2 to trimethylamine.

[0031] Figure 5 This is a schematic diagram of the combination of the food freshness indication colorimetric array in Example 3.

[0032] Figure 6 This is a graph showing the total chromaticity change of the colorimetric array during different storage periods of pork and a graph showing the total volatile basic nitrogen content of pork in Example 3. DETAILED DESCRIPTION

[0033] The following describes the implementation of the present invention through specific embodiments. People skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in these embodiments.

[0034] See also Figure 1-6 . It should be noted that the structures, proportions, sizes, etc. illustrated in the drawings of this specification are only used to match the contents disclosed in the specification for people familiar with this technology to understand and read, and are not used to limit the limiting conditions for the implementation of the present invention. Therefore, they have no technical substantive significance. Any structural modification, change in proportional relationship or adjustment of size. The following examples are provided for a better understanding of the present invention, but are not intended to limit the present invention. Unless otherwise specified, the experimental materials used in the following examples were purchased from conventional biochemical reagent stores.

[0035] Example 1: Changes in water solubility of food freshness indicator labels

[0036] 1.1. Food freshness indicator label with a volume ratio of zein solution to polyvinyl alcohol solution of 8:2

[0037] (1) Preparation of Zein-Polyvinyl Alcohol Mixed Solution:

[0038] Weigh 10.0g of zein powder, add 100mL of a mixed solvent of acetic acid and distilled water (4:1 by volume), and stir in a 50°C water bath until the particles are completely dissolved to obtain a zein solution. Weigh 10.0g of polyvinyl alcohol, add 100mL of a mixed solvent of acetic acid and distilled water (4:1 by volume), heat and stir at 90°C until thoroughly dissolved, and then cool to room temperature. The zein solution and polyvinyl alcohol solution are mixed in a volume ratio of 8:2 to obtain a zein-polyvinyl alcohol mixed solution.

[0039] (2) Preparation of spinning solution: Weigh 3 mg of curcumin, mix the curcumin with the zein-polyvinyl alcohol mixed solution prepared in step (1), and stir evenly to obtain the final spinning solution;

[0040] (3) Preparation of nanofiber membranes

[0041] After the spinning solution was prepared, air bubbles were removed by ultrasonication for 5 minutes. 4 mL of the solution was then withdrawn by syringe for electrospinning. A Yunfan YFSP-T electrospinning machine was used to produce a composite nanofiber membrane of uniform thickness. The distance between the propeller pump and the roller receiver was adjusted to 10-12 cm, and the power supply voltage between the propeller pump and the roller receiver was maintained at 14-16 kV. The propeller pump flow rate was adjusted to 0.8-1.0 mL / h. The spinning environment temperature was maintained at 25-35°C, and the humidity was maintained at 25%-30% RH. After spinning, the nanofiber membrane was removed from the receiver and dried in an oven at 22-28°C overnight to remove any unvolatile solvent, resulting in a zein-polyvinyl alcohol composite nanofiber membrane.

[0042] 1.2 Food freshness indicator label with a volume ratio of zein solution to polyvinyl alcohol solution of 7:3

[0043] The difference from 1.1 is the preparation of the zein-polyvinyl alcohol mixed solution in step (1): the prepared zein solution and polyvinyl alcohol solution are mixed uniformly in a volume ratio of 7:3; the rest is the same as 1.1.

[0044] 1.3 Food freshness indicator label with a volume ratio of zein solution to polyvinyl alcohol solution of 6:4

[0045] The difference from 1.1 is the preparation of the zein-polyvinyl alcohol mixed solution in step (1): the prepared zein solution and polyvinyl alcohol solution are mixed evenly in a volume ratio of 6:4; the rest is the same as 1.1.

[0046] 1.4 Food freshness indicator label with a volume ratio of zein solution to polyvinyl alcohol solution of 5:5

[0047] The difference from 1.1 is the preparation of the zein-polyvinyl alcohol mixed solution in step (1): the prepared zein solution and polyvinyl alcohol solution are mixed evenly in a volume ratio of 5:2; the rest is the same as 1.1.

[0048] The water solubility of Examples 1.1-1.4 was measured: the nanofiber membrane was cut into 25 mm × 25 mm squares and dried at 105°C to constant weight, recorded as M1. The dried sample was completely immersed in 20 mL of distilled water at 25°C for 24 h. After the immersion was complete, the residue was removed and dried again at 105°C to constant weight, recorded as M2. The water solubility of the nanofiber membrane was calculated according to the following formula:

[0049]

[0050] like Figure 1 As shown, the preferred volume ratios of zein solution to polyvinyl alcohol solution are 8:2, 7:3, 6:4, and 5:5. The zein-polyvinyl alcohol mixed solution with a volume ratio of 8:2 cannot be spun due to its low viscosity, and the optimal ratio is 7:3.

[0051] Example 2: Study on the sensitivity of food freshness indicator labels to volatile amines

[0052] 2.1 Freshness indicator labels for foods containing curcumin

[0053] (1) Preparation of Zein-Polyvinyl Alcohol Mixed Solution:

[0054] Weigh 10.0g of zein powder, add 100mL of a mixed solvent of acetic acid and distilled water (4:1 by volume), and stir in a 50°C water bath until the particles are completely dissolved to obtain a zein solution. Weigh 10.0g of polyvinyl alcohol, add 100mL of a mixed solvent of acetic acid and distilled water (4:1 by volume), heat and stir at 90°C until thoroughly dissolved, and then cool to room temperature. The zein solution and polyvinyl alcohol solution are mixed in a 7:3 by volume ratio to obtain a zein-polyvinyl alcohol mixed solution.

[0055] (2) Preparation of spinning solution: Weigh 3 mg of curcumin, mix the curcumin with the zein-polyvinyl alcohol mixed solution prepared in step (1), and stir evenly to obtain the final spinning solution;

[0056] (3) Preparation of nanofiber membranes

[0057] After the spinning solution was prepared, air bubbles were removed by ultrasonication for 5 minutes. 4 mL of the solution was then withdrawn by syringe for electrospinning. A Yunfan YFSP-T electrospinning machine was used to produce a composite nanofiber membrane of uniform thickness. The distance between the propeller pump and the roller receiver was adjusted to 10-12 cm, and the power supply voltage between the propeller pump and the roller receiver was maintained at 14-16 kV. The propeller pump flow rate was adjusted to 0.8-1.0 mL / h. The spinning environment temperature was maintained at 25-35°C, and the humidity was maintained at 25%-30% RH. After spinning, the nanofiber membrane was removed from the receiver and dried in an oven at 22-28°C overnight to remove any unvolatile solvent, resulting in a zein-polyvinyl alcohol composite nanofiber membrane.

[0058] 2.2 Food freshness indicator label with a mass ratio of curcumin to alizarin of 4:1

[0059] The difference from 2.1 is the preparation of the spinning solution in step (2): 2.4 mg of curcumin and 0.6 mg of alizarin are weighed separately, mixed to obtain a mixed pigment, the mixed pigment is mixed with the zein-polyvinyl alcohol mixed solution prepared in step (1), and stirred evenly to obtain the final spinning solution; the rest is the same as 2.1.

[0060] 2.3 Food freshness indicator label with a mass ratio of curcumin to alizarin of 3:2

[0061] The difference from 2.1 is the preparation of the spinning solution in step (2): 1.8 mg of curcumin and 1.2 mg of alizarin are weighed separately, mixed to obtain a mixed pigment, the mixed pigment is mixed with the zein-polyvinyl alcohol mixed solution prepared in step (1), and stirred evenly to obtain the final spinning solution; the rest is the same as 2.1.

[0062] 2.4 Food freshness indicator label with a mass ratio of curcumin to alizarin of 2:3

[0063] The difference from 2.1 is the preparation of the spinning solution in step (2): 1.2 mg of curcumin and 1.8 mg of alizarin are weighed separately, mixed to obtain a mixed pigment, the mixed pigment is mixed with the zein-polyvinyl alcohol mixed solution prepared in step (1), and stirred evenly to obtain the final spinning solution; the rest is the same as 2.1.

[0064] 2.5 Food freshness indicator label with a mass ratio of curcumin to alizarin of 1:4

[0065] The difference from 2.1 is the preparation of the spinning solution in step (2): 0.6 mg of curcumin and 2.4 mg of alizarin are weighed separately, mixed to obtain a mixed pigment, the mixed pigment is mixed with the zein-polyvinyl alcohol mixed solution prepared in step (1), and stirred evenly to obtain the final spinning solution; the rest is the same as 2.1.

[0066] 2.6 Freshness indicator labels for foods containing alizarin

[0067] The difference from 2.1 is the preparation of the spinning solution in step (2): weigh 3 mg of alizarin, mix the alizarin and the zein-polyvinyl alcohol mixed solution prepared in step (1), and stir evenly to obtain the final spinning solution; the rest is the same as 2.1.

[0068] The volatile amine response assay described in Examples 2.1-2.6 was performed: At room temperature, a 10×10 mm fiber membrane sample was placed snugly inside a glass dish and then inverted onto a flat glass dish to form a sealed reaction chamber. The initial colorimetric values ​​of the membrane were recorded using a colorimeter, denoted as L0, a0, and b0. Ammonia, dimethylamine, and trimethylamine were selected as test substances. Different concentrations of the test substances (1 ppm, 5 ppm, 10 ppm, 20 ppm, and 40 ppm) were injected into the reaction chamber. After 20 minutes, the post-reaction colorimetric values ​​were recorded again, denoted as L1, a1, and b1. The color difference ΔE of the fiber membrane reaction was calculated according to the following formula:

[0069]

[0070] like Figure 2-4 As shown, amine sensitivity tests were conducted on the indicator label prepared in 2.1 (CR), 2.2 (C4A1), 2.3 (C3A2), 2.4 (C2A3), 2.5 (C1A4), and 2.6 (AL). It is clear that the higher the amine concentration, the more pronounced the color change of the film. Overall, AL exhibited a less pronounced color change in response to amine gas, while CR exhibited a vibrant color reaction. If ΔE > 5 is used as the indicator for color change, then in aqueous ammonia solution (a), the detection limits of CR, C4A1, C3A2, and C2A3 were as low as 1 ppm, while those of C1A4 and AL were as low as 5 ppm. In dimethylamine solution (b), CR, C4A1, C3A2, C2A3, and C1A4 exhibited a strong color change at a concentration of 1 ppm, while AL showed no noticeable color change. The lowest detection limit for CR in trimethylamine solution is between 10ppm and 20ppm, while C4A1, C3A2, C2A3, C1A4, and AL already exhibit color changes at 10ppm. Compared to single pigments, colorimetric arrays composed of mixed pigments exhibit higher sensitivity, more pronounced color changes, and wider applicability.

[0071] Example 3: Application of Food Freshness Indicator Colorimetric Array in Pork Freshness Detection

[0072] 3.1 Preparation of food freshness indicator colorimetric array

[0073] (1) Preparation of Zein-Polyvinyl Alcohol Mixed Solution

[0074] Weigh 10.0g of zein powder, add 100mL of a mixed solvent of acetic acid and distilled water (4:1 by volume), and stir in a 50°C water bath until the particles are completely dissolved to obtain a zein solution. Weigh 10.0g of polyvinyl alcohol, add 100mL of a mixed solvent of acetic acid and distilled water (4:1 by volume), heat and stir at 90°C until thoroughly dissolved, and then cool to room temperature. The zein solution and polyvinyl alcohol solution are mixed in a 7:3 by volume ratio to obtain a zein-polyvinyl alcohol mixed solution.

[0075] (2) Preparation of spinning solution

[0076] Weigh curcumin and alizarin respectively, and mix them in a mass ratio of 5:0, 4:1, 3:2, 2:3, 1:4, and 0:5 to obtain 3 mg of a mixed pigment; mix the mixed pigment with the zein-polyvinyl alcohol mixed solution prepared in step (1), and stir evenly to obtain a final spinning solution. At the same time, prepare a blank spinning solution without pigment;

[0077] (3) Preparation of nanofiber membranes

[0078] After the spinning solution is prepared, the bubbles in the liquid are removed by ultrasonication for 5 minutes, and 4 mL of the solution is drawn into the syringe for electrospinning. A Yunfan YFSP-T electrospinning machine is used to prepare a composite nanofiber membrane with uniform thickness. The distance between the propulsion pump and the roller receiver is adjusted to 10-12 cm, and the power supply voltage between the propulsion pump and the roller receiver is 14-16 kV. The propulsion pump flow rate is adjusted to 0.8-1.0 mL / h, the spinning environment temperature is 25-35 ° C, and the ambient humidity is 25%-30% RH. After spinning is completed, the nanofiber membrane on the receiver is removed and placed in a 22-28 ° C oven to dry overnight to remove the non-volatile solvent to obtain a nanofiber indicator membrane;

[0079] (4) Combination of food freshness indication colorimetric array

[0080] The nanofiber indicator membrane prepared in step (3) was cut into 15 cm × 15 cm squares and named CR, C4A1, C3A2, C2A3, C1A4 and AL according to the mass ratio of curcumin to alizarin (curcumin: alizarin was 5:0, 4:1, 3:2, 2:3, 1:4, 0:5). The blank group without pigment was named PZ. Figure 5 , and the indicator labels are respectively attached to the inner surface of the packaging box cover.

[0081] 3.2 Application of Food Freshness Indicator Colorimetric Array in Pork Freshness Detection

[0082] (1) Pork freshness monitoring experiment

[0083] Fresh pork tenderloins were purchased from a local supermarket (Hefei, China) and immediately transported to the laboratory at 4°C. After removing fat and connective tissue, the pork tenderloins were cut into pieces and placed in packaging boxes. The boxes were sealed with lids attached to colorimetric arrays. All samples were stored in a refrigerator at 4°C for 6 days, and the colorimetric values ​​of the indicator labels were measured every 24 hours. To mitigate the potential effects of light and humidity, the color parameters of all indicator labels were adjusted by subtracting the color parameter of the PZ group located at the center point of the glassware. The adjusted color parameters were then used to calculate the ΔE values ​​throughout the storage period. Given the presence of multiple pigment combinations in the freshness indicators, the total color change value, X, of the colorimetric array was the average of the ΔE values ​​of the six indicator labels.

[0084] (2) Measurement of total volatile basic nitrogen value of pork

[0085] Volatile basic nitrogen in meat was determined using a Kjeldahl nitrogen analyzer. 5 mL of sample supernatant and 5 mL of 10 g / L MgO solution were transferred to a Kjeldahl nitrogen tube. 10 mL of 20 g / L boric acid solution containing 5-6 drops of indicator was transferred to a receiving flask. After 5 minutes of distillation, the solution in the receiving flask was titrated to the endpoint with 0.001 M HCl solution. A blank test was also performed.

[0086] According to the national standard GB 2707-2016 "Hygienic Standards for Fresh (Frozen) Meat of Livestock and Poultry", the total volatile basic nitrogen content in fresh meat should be less than or equal to 15mg / 100g. Figure 6 The total volatile basic nitrogen value results showed that the sample was less than 10 mg / 100 g on the first day, indicating freshness. Then, the total volatile basic nitrogen values ​​on the second and third days were between 10 and 15 mg / 100 g, at which time the freshness of the tenderloin became medium freshness. The initial stage of deterioration was on the fourth day, with a total volatile basic nitrogen value of 15.54 ± 0.39 mg / 100 g, and the pork began to enter the corruption stage. During the storage of pork, the indicator array gradually evolved from the initial light yellow to reddish brown or purple, while the mixed pigment label showed a series of transitional colors. Figure 4 As can be seen, X initially increased from 3.00 to 4.95 on the third day, and then sharply increased to 9.44 on the fourth day, at which point a noticeable color change is considered visible to the naked eye. The colorimetric array's change values ​​are highly correlated with the pork spoilage level. Compared to colorimetric arrays, single indicator tags often exhibit delayed or inconspicuous color changes in practical applications. The colorimetric array addresses this limitation by processing and analyzing information from multiple indicator tags. The color changes displayed by the colorimetric array are highly consistent with the spoilage indicators of pork tenderloin, enabling tracking of pork freshness and showing potential for food freshness monitoring.

[0087] The above description is only used to explain the preferred embodiments of the present invention and is not intended to limit the present invention in any form. Therefore, any modifications or changes made to the present invention under the same inventive spirit should still be included in the scope of protection intended by the present invention.

Claims

1. A method for preparing a water-resistant food freshness indicator colorimetric array, characterized by: The following steps are involved: Step 1, preparation of zein-polyvinyl alcohol mixed solution Zein and polyvinyl alcohol are dissolved in a mixed solvent consisting of acetic acid and water respectively; obtaining a zein solution and a polyvinyl alcohol solution; uniformly mixing the zein solution and the polyvinyl alcohol solution to obtain a zein-polyvinyl alcohol mixed solution; Step 2: Preparation of spinning solution Curcumin and alizarin were mixed in different mass ratios to obtain a variety of mixed pigments; The multiple mixed pigments are mixed with the zein-polyvinyl alcohol mixed solution prepared in step 1, respectively, and stirred to obtain multiple spinning solutions; Step 3: Preparation of nanofiber membrane A variety of spinning solutions are used to prepare composite nanofiber membranes using an electrospinning machine. The composite nanofiber membranes on the drum receiver are removed and dried to complete the preparation of the nanofiber membranes. The food freshness indicator colorimetric array can be obtained by combining them according to the pigment ratio.

2. The method for preparing the water-resistant food freshness indicator colorimetric array according to claim 1, wherein: In step 1, when zein is dissolved in a mixed solvent consisting of acetic acid and water, the temperature is 45-55°C and the time is 4-6 hours; when polyvinyl alcohol is dissolved in a mixed solvent consisting of acetic acid and water, the dissolution temperature is 85-95°C and the time is 2-4 hours.

3. The method for preparing the water-resistant food freshness indicator colorimetric array according to claim 1, wherein: In step 1, the mass percentage concentration of the zein solution is 8-12%; the mass percentage concentration of the polyvinyl alcohol solution is 8-12%.

4. The method for preparing the water-resistant food freshness indicator colorimetric array according to claim 1, wherein: In the mixed solvent consisting of acetic acid and water, the volume ratio of acetic acid to water is 3-5:

1.

5. The method for preparing the water-resistant food freshness indicator colorimetric array according to claim 1, wherein: The volume ratio of the zein solution to the polyvinyl alcohol solution is 6-10:

3.

6. The method for preparing the water-resistant food freshness indicator colorimetric array according to claim 1, wherein: The mass of the mixed pigment is 3 mg, and the mass ratios of curcumin and alizarin are 5-0:0-5, respectively.

7. The method for preparing the water-resistant food freshness indicator colorimetric array according to claim 1, wherein: In step 3, the distance between the propulsion pump and the roller receiver is 10-12 cm, the power supply voltage between the propulsion pump and the roller receiver is 14-16 kV, and the flow rate of the propulsion pump is 0.8-1.0 mL / h.

8. The method for preparing the water-resistant food freshness indicator colorimetric array according to claim 1, wherein: In step 3, the spinning environment temperature is adjusted to 25-35° C. and the ambient humidity is adjusted to 25%-30% RH.

9. The method for preparing the water-resistant food freshness indicator colorimetric array according to claim 1, wherein: In step 3, the drying temperature is 22-28° C., and the array is assembled according to a curcumin:alizarin mass ratio of 5-0:0-5.

10. A water-resistant food freshness indicator colorimetric array, characterized in that: The food freshness indicating colorimetric array is prepared by using the preparation method of the water-resistant food freshness indicating colorimetric array according to any one of claims 1 to 9.

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