Water-resistant food freshness indication colorimetric array and preparation method thereof

Abstract

The invention relates to a water-resistant food freshness indication colorimetric array and a preparation method thereof, and the preparation method comprises the following steps: firstly, respectively dissolving polyvinyl alcohol and zein in a mixed solvent of acetic acid and water, and then uniformly mixing a polyvinyl alcohol solution and a zein solution according to a certain proportion; and adding curcumin-alizarin mixed pigments with different mass ratios, and uniformly mixing to obtain the final spinning solution. Preparing a nanofiber indicating film by utilizing an electrostatic spinning technology; according to the invention, two natural pigments, namely curcumin and alizarin, are utilized, and an indicator is loaded on an electrospinning nanofiber membrane by virtue of an electrospinning technology, so that the meat product freshness indication colorimetric array with lower detection line, more diversified color changes and excellent stability is obtained; and the color of the meat product can be obviously changed according to volatile gas generated by change of freshness in the storage process of the meat product.

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 easily affected by physical, chemical and biological factors during transportation, sales and storage, resulting in spoilage. This quality deterioration will seriously affect the nutritional value and edible sensory perception of fresh meat products, which not only threatens the health of consumers, but also causes waste of resources and economic losses. In real life, consumers mostly judge the freshness of meat by its color, taste, texture and other sensory performances. However, this sensory trait is highly subjective and has large individual differences. Traditional meat product freshness detection and analysis methods are complicated, time-consuming and labor-intensive. Therefore, it is necessary to develop a quick and easy detection method that can monitor the freshness of meat products in real time and can be used in home and supermarket scenarios.

[0003] Freshness indicator colorimetric labels are a simple, efficient and low-cost solution for visualizing food freshness parameters. The basic principle is that the indicator reacts with metabolites during the shelf life and spoilage of food, and the purpose of detecting the freshness of meat products can be achieved through the visible color change of the indicator without destroying the packaging. Colorimetric labels usually consist of two parts, a solid matrix and a chemical / biological dye loaded on the solid matrix. The color change of the chemical response dye is correlated with the freshness and spoilage of the food.

[0004] As a natural biodegradable polymer material, polyvinyl alcohol is widely used in packaging materials due to its good film-forming properties and mechanical properties. However, due to its polyhydroxy structure, in a high humidity environment, the solid matrix is ​​prone to swelling or partial dissolution, destroying the structural integrity of the film and affecting the interpretation of the results.

[0005] During the spoilage process of meat products, volatile amine gases are produced by decomposing proteins. Therefore, the freshness changes of food can be analyzed by monitoring volatile amine gases. Curcumin is a common natural pigment. Under different acid and alkaline conditions, its structure will change, thus showing different color changes. However, during the application of a single pigment, there are defects such as a narrow pH response range and insignificant color change. Therefore, it is necessary to enhance the color richness and indication intensity of the pH indicator label to greatly improve its 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 purpose and other related purposes, the technical solution provided by the present invention is: a method for preparing a water-resistant food freshness indicating 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 composed 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 indicating colorimetric array is then obtained by combining the pigments in proportion.

[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 combined according to a mass ratio of curcumin: alizarin of 5-0:0-5.

[0022] To achieve the above purpose and other related purposes, the technical solution provided by the present invention is: a water-resistant food freshness indicating colorimetric array, wherein the food freshness indicating array is prepared by using the preparation method of the water-resistant food freshness indicating 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 determines the ratio of zein solution and polyvinyl alcohol solution by screening to prepare a low water-soluble indicator label, which can maintain structural integrity in a high humidity environment, and the prepared freshness indicator label has safe ingredients 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 rigidity increased compared with a single component membrane.

[0025] 2. The nanofiber membrane prepared by electrospinning has the advantages of high surface area, dense structure and small porosity, which makes it possible to load responsive substances. Curcumin and alizarin in different proportions were successfully loaded onto polyvinyl alcohol-zein nanofiber membranes using electrospinning technology to prepare a colorimetric array to achieve visual monitoring of food freshness; the prepared colorimetric array showed high sensitivity, low detection limit and diverse color changes to a variety of volatile amine substances, overcoming the defects of a single natural pigment with a narrow pH response range and insignificant 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 corruption index, which can effectively help consumers quickly understand the freshness of meat products and better help people ensure and determine the safety of meat products in each link of circulation, storage and sale. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

[0030] Figure 4 This is a color difference change curve of the indicator labels of Examples 2.1-2.6 in Example 2 in response 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 The total chromaticity change diagram of the colorimetric array during different storage periods of pork and the total volatile basic nitrogen content diagram of pork in Example 3 are shown. DETAILED DESCRIPTION

[0033] The following is a description of the implementation of the present invention by means of specific embodiments. Those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in the 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 that can be implemented in the present invention, so 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 acetic acid and distilled water mixed solvent (volume ratio of 4:1), 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 acetic acid and distilled water mixed solvent (volume ratio of 4:1), heat and stir at 90°C until fully dissolved, and then cool to room temperature. The zein solution and the polyvinyl alcohol solution are mixed evenly 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 and the zein-polyvinyl alcohol mixed solution prepared in step (1), and stir evenly to obtain a final spinning solution;

[0040] (3) Preparation of nanofiber membrane

[0041] After the spinning solution is prepared, the bubbles in the liquid are removed by ultrasound for 5 minutes, and 4 mL of the solution is drawn by a syringe for electrospinning. A composite nanofiber membrane with uniform thickness is prepared using a Yunfan YFSP-T electrospinning machine. 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 the nanofiber membrane is placed in a 22-28 ° C oven to dry overnight to remove the non-volatile solvent to obtain 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 evenly 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 evenly mixed 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, dried at 105 ° C to constant weight, recorded as M1, and the dried sample was completely immersed in 20 mL of distilled water and placed at 25 ° C for 24 h. After the immersion was completed, the residue was taken out 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, wherein 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 label for food containing curcumin

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

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

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

[0056] (3) Preparation of nanofiber membrane

[0057] After the spinning solution is prepared, the bubbles in the liquid are removed by ultrasound for 5 minutes, and 4 mL of the solution is drawn by a syringe for electrospinning. A composite nanofiber membrane with uniform thickness is prepared using a Yunfan YFSP-T electrospinning machine. 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 the nanofiber membrane is placed in a 22-28 ° C oven to dry overnight to remove the non-volatile solvent to obtain 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 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 test of Examples 2.1-2.6 was performed: at room temperature, 10×10 mm fiber membrane samples were respectively placed tightly against the inside of a glass dish and inverted on a flat glass dish to form a closed reaction chamber. The initial chromaticity values ​​of the membrane were recorded using a colorimeter, which were recorded as L0, a0, and b0. Ammonia water, dimethylamine, and trimethylamine were selected as test substances, and different concentrations of test substances (1ppm, 5ppm, 10ppm, 20ppm, and 40ppm) were injected into the reaction chamber. After 20 minutes, the chromaticity values ​​after the reaction were recorded again, which were recorded as L1, a1, and b1. The fiber membrane reaction color difference value △E was calculated according to the following formula:

[0069]

[0070] like Figure 2-4 As shown, the indicator label prepared in 2.1 (CR), the indicator label prepared in 2.2 (C4A1), the indicator label prepared in 2.3 (C3A2), the indicator label prepared in 2.4 (C2A3), the indicator label prepared in 2.5 (C1A4) and the indicator label prepared in 2.6 (AL) were tested for amine sensitivity. It is not difficult to find that the higher the concentration of amine substances, the more obvious the color change of the film. In general, the color change of AL in the response experiment of amine gas is not obvious, while CR shows an active color reaction. If △E>5 is used as an indicator of color change, then in ammonia solution (a), the detection limit of CR, C4A1, C3A2, and C2A3 is as low as 1ppm, while the minimum detection limit of C1A4 and AL is 5ppm. In dimethylamine solution (b), CR, C4A1, C3A2, C2A3, and C1A4 show strong color changes at a concentration of 1ppm, while AL has no obvious color change. The lowest detection line of CR in trimethylamine solution is between 10ppm and 20ppm, while C4A1, C3A2, C2A3, C1A4, and AL have shown color changes at 10ppm. Compared with single pigments, the colorimetric array composed of mixed pigments shows higher sensitivity, more obvious 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 acetic acid and distilled water mixed solvent (volume ratio of 4:1), 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 acetic acid and distilled water mixed solvent (volume ratio of 4:1), heat and stir at 90°C until fully dissolved, and then cool to room temperature. The zein solution and the polyvinyl alcohol solution are mixed evenly in a volume ratio of 7:3 to obtain a zein-polyvinyl alcohol mixed solution;

[0075] (2) Preparation of spinning solution

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

[0077] (3) Preparation of nanofiber membrane

[0078] After the spinning solution is prepared, the bubbles in the liquid are removed by ultrasound for 5 minutes, and 4 mL of the solution is drawn by a 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 the nanofiber membrane is 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 indicator 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 The indication 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 tenderloin was purchased from a local supermarket (Hefei, China) and immediately transported to the laboratory at 4°C. After removing fat and connective tissue, the pieces were cut and placed in packaging boxes. The packaging box was sealed with a lid attached with a colorimetric array. All samples were stored in a refrigerator at 4°C for 6 days, and the chromaticity values ​​of the indicator labels were measured every 24 hours. At the same time, in order to mitigate the potential effects of light and humidity, the color parameters of all indicator labels were adjusted by subtracting the color parameters 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 chromaticity change value X of the colorimetric array was the homogenization of the ΔE values ​​of the six indicator labels.

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

[0085] Use Kjeldahl nitrogen analyzer to determine the volatile basic nitrogen in meat. Transfer 5 ml of sample supernatant and 5 mL of MgO solution (10 g / L) to a Kjeldahl nitrogen tube. Transfer 5-6 drops of boric acid solution (10 ml, 20 g / L) containing an indicator to a receiving bottle. After 5 minutes of distillation, titrate the solution in the receiving bottle to the endpoint with 0.001 M HCl solution. Perform a blank test at the same time.

[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 15 mg / 100 g. Figure 6 The total volatile basic nitrogen value results showed that the sample was less than 10 mg / 100g 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 / 100g, 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 / 100g, 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 It can be seen that X was initially 3.00 and increased to 4.95 on the third day, and then increased sharply to 9.44 on the fourth day. At this time, it is considered that the naked eye can see obvious color changes. The change value of the colorimetric array is highly correlated with the spoilage value of pork. Compared with the colorimetric array, the single indicator label has a delayed or unclear color change in actual application, and the colorimetric array makes up for this defect through the processing and analysis of multiple indicator label information. The color change presented by the colorimetric array is highly consistent with the spoilage index of pork tenderloin, which can realize the tracking of the freshness of pork and has the application potential of monitoring the freshness of food.

[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 in that: The following steps are involved: Step 1, preparation of zein-polyvinyl alcohol mixed solution Dissolving zein and polyvinyl alcohol in a mixed solvent consisting of acetic acid and water respectively; obtaining a zein solution and a polyvinyl alcohol solution; The zein solution and the polyvinyl alcohol solution are mixed uniformly to obtain a zein-polyvinyl alcohol mixed solution; Step 2: Preparation of spinning solution Curcumin and alizarin are 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 evenly 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 indicating colorimetric array is then obtained by combining the pigments in proportion.

2. The method for preparing the water-resistant food freshness indicating colorimetric array according to claim 1, characterized in that: 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 indicating colorimetric array according to claim 1, characterized in that: 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 indicating colorimetric array according to claim 1, characterized in that: 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 indicating colorimetric array according to claim 1, characterized in that: 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 indicating colorimetric array according to claim 1, characterized in that: 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 indicating colorimetric array according to claim 1, characterized in that: 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.

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

9. The method for preparing the water-resistant food freshness indicating colorimetric array according to claim 1, characterized in that: 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.

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

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