Kiwi fruit freshness indication array and preparation method and application thereof

Abstract

The invention provides a kiwi fruit freshness indicating array and a preparation method and application thereof. The kiwi fruit freshness indicating array is composed of six indicating labels D1-D6, wherein the indicating label D1 comprises a purple sweet potato anthocyanin indicator; the indication label D2 comprises a curcumin indicator; the indication label D3 comprises an alizarin indicator; the indication label D4 comprises purple sweet potato anthocyanin and an alizarin indicator; the indication label D5 comprises purple sweet potato anthocyanin and curcumin indicators; the indication label D6 comprises alizarin and a curcumin indicator. The indication array comprises six indicators, can simultaneously indicate the freshness state of kiwi fruits, and has the advantages of comprehensive information, accurate measurement result, visual and clear result, easy implementation of the preparation method, low cost, and simple operation in use.

Description

Technical Field The present application relates to the field of fruit preservation. Specifically, the present application provides a kiwifruit freshness indicator array and a preparation method and application thereof. Background Art Kiwi fruit is generally oval in shape and has edible flesh. The flesh of freshly picked kiwi fruit is hard and sour, but after being stored for a period of time, the flesh becomes soft and sweet. Kiwi fruit is rich in vitamin C, which can meet the needs of the human body and is loved by people. At the same time, it is planted in large quantities because of its fast economic benefits. Kiwifruit is difficult to store and easy to be damaged. During storage and transportation in warehouses, the commercial quality and shelf life of kiwifruit are affected due to inadequate cold chain, transportation conditions and preservation measures, resulting in serious economic losses. Therefore, strengthening the research on non-destructive testing methods for the freshness of fruits and vegetables and the comprehensive evaluation system of storage environment conditions has important social and economic benefits. Kiwifruit is often stored at room temperature and low temperature in the form of packaging. Packaging directly affects the quality and hygiene safety of food. Smart food packaging technology is a new packaging technology that has emerged in the food industry at home and abroad. By monitoring the changes in the environment inside the package and the changes in the characteristics of the packaging, information such as the quality and safety of the packaging during storage and transportation can be obtained. Compared with traditional packaging, smart packaging can provide producers, sellers and consumers with food quality and safety information. This technology is of great significance to food safety and nutritional value. Kiwifruit has high nutritional value and is prone to microbial decay during storage. Kiwifruit spoilage is mainly due to a series of chemical reactions caused by metabolism dominated by respiration and microbial growth, which produces a large amount of CO2 and quality deterioration phenomena such as decay and odor. Therefore, CO2 can be used to develop indicator labels to indicate the freshness of fruits and vegetables. There are many freshness detection technologies for fruits and vegetables, but many indicator labels use synthetic pigments, which are greatly limited in their application in fruits and vegetables and are not suitable for kiwifruit preservation. Therefore, it is necessary to develop a kiwifruit-specific freshness detection technology, which has great development prospects. At present, research work on combining sensory quality, physical and chemical properties, and intelligent identification systems for the freshness of fruits and vegetables has made progress. A method for preparing a carbon dioxide indicator label material for food packaging (application publication number: CN109666094A) uses an active polymerization method to prepare a polymer indicator label material with carbon dioxide responsiveness in one step. The transparency of the indicator label material changes with the emission of carbon dioxide, and the freshness of food can be identified by the human eye. The invention is complex to operate and has high material costs. A chitosan-based composite responsive membrane with carbon dioxide responsive behavior and its preparation method and application] (Application Publication No.: CN 112029158 A) Using bromothymol blue / methyl red as a color developer and N-succinylated chitosan / hydroxypropyl chitosan as a film-forming substrate, a bromothymol blue / methyl red composite pH-sensitive smart label is prepared for accurate real-time monitoring and detection of the freshness of fruits and vegetables to ensure food quality. The color developers of this invention are bromothymol blue and methyl red, which are harmful to the human body if in contact with the skin or swallowed, and there are safety hazards. A method for preparing a visual freshness label based on anthocyanins from black wolfberry [Application Publication No.: CN113279287A], the detection instrument includes a reaction chamber, an ultraviolet light emission source and an ultraviolet detector, and a focusing system and a quartz tube are provided inside the reaction chamber, and the quartz tube is connected to the external environment. It adopts a semiconductor laser generator as a light source for generating deep ultraviolet laser. The label prepared by the invention is safe and environmentally friendly. The method mainly focuses on the extraction of anthocyanins from black wolfberry, the indicator reagent is single, the range is narrow, and it cannot provide specific and accurate judgment. In summary, the existing instruments and equipment for accurately measuring the freshness of fruits and vegetables are expensive, have a narrow scope of application, and require certain professional technical support; the reported label coloring substances are mostly artificially synthesized pigments, such as bromothymol blue, methyl red and other organic substances, which are harmful to the human body when in contact with the skin or swallowed, and there are potential safety hazards. The present invention uses carboxymethyl cellulose and polyvinyl alcohol as a composite substrate to improve the film-forming performance of the indicator label, selects natural pigments as indicators to prepare the indicator array, and uses mixed pigment indicator labels to show diversified color responses and higher stability than single pigment indicator labels. The indicator array can be used for rapid detection of the freshness of fruits and vegetables such as kiwis, and to judge the suitability of the fruit and vegetable packaging environment, thereby achieving the purpose of predicting commercial quality and shelf life. Summary of the invention In view of the above situation, on the one hand, the present application provides a kiwifruit freshness indicator array, which is composed of 6 indicator tags D1 to D6. The indicator label D1 includes a purple sweet potato anthocyanin indicator; The indicator label D2 includes a curcumin indicator; The indicator label D3 includes an alizarin indicator; The indicator label D4 includes purple potato anthocyanin and alizarin indicator; Indicator label D5 includes purple sweet potato anthocyanins and curcumin indicators; Indicator label D6 includes alizarin and curcumin indicators. Furthermore, the indicator labels D1 to D6 are indicator films with carboxymethyl cellulose and polyvinyl alcohol as a matrix. Furthermore, the kiwifruit freshness indicator array is prepared according to the following method: (1) adding carboxymethyl cellulose, polyvinyl alcohol and glycerol into distilled water to obtain solution A; the concentrations of carboxymethyl cellulose and polyvinyl alcohol in solution A are both 30 to 50 g / L, and the concentration of glycerol is 10 to 30 g / L; (2) preparing 8-10 g / L purple potato anthocyanin ethanol solution, 2-3 g / L curcumin ethanol solution, and 2-3 g / L alizarin ethanol solution; mixing the purple potato anthocyanin ethanol solution, curcumin ethanol solution, and alizarin ethanol solution in equal volumes to obtain a purple potato anthocyanin and curcumin ethanol solution containing 4-5 g / L purple potato anthocyanin and 1-1.5 g / L curcumin, a purple potato anthocyanin and alizarin ethanol solution containing 4-5 g / L purple potato anthocyanin and 1-1.5 g / L alizarin, and a curcumin and alizarin ethanol solution containing 0.5-0.75 g / L curcumin and 1.5-2.25 g / L alizarin, and adding NaOH solution to adjust the pH value to 10±0.1 to obtain indicators A1-A6; (3) adding the indicators A1 to A6 obtained in step (2) to 6 portions of solution A respectively to obtain mixed solutions B1 to B6; (4) drying the mixed solutions B1 to B6 obtained in step (3) to obtain indicator films C1 to C6; (5) The indicator films C1-C6 obtained in step (4) are made into indicator labels D1-D6 to form a kiwifruit freshness indicator array. Further, step (1) is: after dissolving carboxymethyl cellulose and polyvinyl alcohol in distilled water respectively, the two solutions are mixed in a volume ratio of 1:1, and glycerol is added to form a uniform colloidal solution, and air bubbles are removed by vacuuming and ultrasonication to obtain solution A; the concentrations of carboxymethyl cellulose and polyvinyl alcohol in solution A are both 30-50 g / L, and the concentration of glycerol is 10-30 g / L; Furthermore, step (2) is to prepare 8 g / L purple sweet potato anthocyanin ethanol solution, 2 g / L curcumin ethanol solution, and 2 g / L alizarin ethanol solution; the purple sweet potato anthocyanin ethanol solution, the curcumin ethanol solution, and the alizarin ethanol solution are mixed in equal volumes in pairs to obtain a purple sweet potato anthocyanin and curcumin ethanol solution containing 4 g / L purple sweet potato anthocyanin and 1 g / L curcumin, a purple sweet potato anthocyanin and alizarin ethanol solution containing 4 g / L purple sweet potato anthocyanin and 1 g / L alizarin, and a curcumin and alizarin ethanol solution containing 1 g / L curcumin and 1 g / L alizarin, and add NaOH solution to adjust the pH value to 10±0.1 to obtain indicators A1~A6. Furthermore, in step (3), 60 to 80 mL of purple sweet potato anthocyanin ethanol solution is added to each liter of solution A, and 40 to 60 mL of curcumin ethanol solution, alizarin ethanol solution, purple sweet potato anthocyanin and curcumin ethanol solution, purple sweet potato anthocyanin and alizarin ethanol solution, or curcumin and alizarin ethanol solution is added to each liter of solution A. Furthermore, the concentration of the NaOH solution is 0.5%. Furthermore, in step (5), the indicator films 1 to 6 obtained in step (4) are cut into indicator labels of 1 to 3 cm×1 to 3 cm. Furthermore, in step (4), the mixture is dried at 35 to 45° C. for 15 to 20 hours. On the other hand, the present application provides the use of the above-mentioned kiwifruit freshness indicator array in detecting or indicating the freshness of kiwifruit. Furthermore, in the application, the indicator labels D1 to D6 in the kiwi fruit freshness indicator array are affixed to the inner surface of the kiwi fruit package, or the indicator labels D1 to D6 in the kiwi fruit freshness indicator array are affixed to the bottom plate, and the bottom plate with the indicator labels D1 to D6 is placed in the kiwi fruit package. Furthermore, the application includes visually or machine reading the colors of the indicator labels D1 to D6 in the kiwifruit freshness indicator array. The color of the indicator label can be read using various known devices and software, including but not limited to a colorimeter / color picker and its supporting software, or taking a photo with a mobile phone or camera and then analyzing it using corresponding software. The indicator array of the present invention comprises six indicators, can indicate the freshness state of kiwi fruit at the same time, obtains comprehensive information, and the measurement result is accurate and intuitive. The preparation method is easy to implement and low in cost, and the operation is simple when used. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 This is a schematic diagram of the structure of Example 7 of the present invention. Figure 2 This is a diagram showing the color changes of six indicator labels of kiwifruit stored at 25° C. in Example 9 of the present invention. Figure 3 This is a diagram showing the color changes of six indicator labels of kiwifruit stored at 4° C. in Example 9 of the present invention. DETAILED DESCRIPTION Example 1 A method for preparing a kiwifruit freshness indicator array This embodiment is carried out in the following steps in sequence: 1. Dissolve carboxymethyl cellulose and polyvinyl alcohol in distilled water respectively, mix the two solutions in a volume ratio of 1:1, add glycerol to form a uniform colloidal solution, and remove bubbles by vacuuming and ultrasonication to obtain solution A; The concentrations of carboxymethyl cellulose and polyvinyl alcohol in the prepared solution A are both ρ1=30-50 g / L, and the concentration of glycerol is ρ2=10-30 g / L; 2. Divide solution A into six parts, add corresponding indicators and additives to mixed solutions B1-B6 as shown in Table 1, stir evenly, remove bubbles, and then dry at T=40°C for t=15h to obtain indicator films C1-C6; the concentration of purple sweet potato anthocyanin indicator is 8g / L, the concentration of curcumin indicator is 2g / L, the concentration of alizarin indicator is 2g / L, the concentration of purple sweet potato anthocyanin / curcumin indicator is 5g / L, the concentration of purple sweet potato anthocyanin / alizarin indicator is 5g / L, and the concentration of curcumin / alizarin indicator is 2g / L; the indicator added to each liter of mixed solution B1 is V1=60mL, the additive added to B1 is V2=20mL, the indicator added to each liter of mixed solution B2-B6 is V3=40mL, and the additive added to B2-B6 is V4=10mL; 3. Cut the indicator films C1 to C6 into 1 cm*1 cm pieces and stick them on the inner surface of the PET packaging box cover to obtain a kiwi fruit freshness indicator array including the first to sixth indicator labels D1 to D6. In this embodiment, the indicators and additives added to the mixed solutions B1 to B6 are shown in the following table: Table 1. Indicators and additives added to mixed solutions B1 to B6 Solution No. Indicator Add reagents B1 Purple sweet potato anthocyanin solution NaOH solution B2 Curcumin solution NaOH solution B3 Alizarin solution NaOH solution B4 Purple sweet potato anthocyanin and alizarin mixed solution NaOH solution B5 Purple sweet potato anthocyanin and curcumin mixed solution NaOH solution B6 Alizarin and curcumin mixed solution NaOH solution The concentration of NaOH solution in Table 1 is ω=0.5%. In practical applications, the size of the indicator film in step three can be determined according to actual needs. Example 2-6 A method for preparing a kiwifruit freshness indicator array The preparation process of Examples 2-6 is substantially the same as that of Example 1, except that the specific parameters are different. The parameters involved are shown in the following table. Table 2. Parameters of Examples 2-6 For ease of operation, in each of Examples 1-6, the concentration of the NaOH solution added to the mixed solutions B1 to B6 in step 2 is the same. In fact, the concentration of the additive added to the mixed solutions B1 to B6 in the same embodiment does not have to be consistent, and the concentration of the NaOH solution only needs to be in the range of 0.5% to 1%. Example 7 A kiwifruit freshness indicator array and its application The six indicator labels included in Examples 1-6 are placed in a packaging box / bag and fixed to form a packaging box / bag as shown in FIG. Figure 1 The square kiwifruit freshness indicator array shown in the figure shows the change of the freshness of the kiwifruit by changing the color of the indicator film included in the indicator label. The user can also change the shape of the kiwifruit freshness indicator array according to actual needs. Example 8: Indication Effect on Acid Gas The kiwifruit freshness indicator array prepared in Example 1 was placed in a fresh-keeping box and fixed on the lid of the fresh-keeping box, and finally formed as shown in FIG. Figure 1 The square kiwifruit freshness indicator array shown in the figure. Take 0.32g of sodium carbonate and place it on one side of the fresh-keeping box. Take 17ml of prepared dilute sulfuric acid and pour it into the fresh-keeping box quickly, but try to avoid splashing the liquid on the box lid. Quickly cover the box lid. Let it stand for about one hour, and observe the color changes of the first to sixth indicator labels D1 to D6. Use a colorimeter to measure the data of the six indicator labels, measure three groups of data for each indicator label and take the average value, and obtain the data of the response color difference as shown in Table 3. Table 3. Color difference in acidic gas environment Instruction label D1 D1 D3 D4 D5 D6 Total color difference ΔE 27.76 37.99 48.58 15.25 8.472 54.43

[0041] The above experimental results show that the total color difference values ​​△E of the six indicator labels in the acidic gas environment are all greater than 12, that is, people can easily observe the color changes with the naked eye, indicating that the first to sixth indicator labels D1 to D6 can quickly change color in response to the CO2 gas content. Therefore, it is feasible to use the color changes of the first to sixth indicator labels D1 to D6 to monitor the acidic gas content in the sealed packaging of kiwi fruit in real time. Example 9 Actual indication effect on kiwi fruit Taking kiwifruit packaged in a sealed box as an example, when in use, the six indicator labels included in the kiwifruit freshness indicator array prepared in Example 1 are placed in the sealed box and fixed on the cover, such as Figure 1 As shown, six indicator labels are distributed into a square kiwi fruit freshness indicator array. Purchase fresh kiwifruit from the market, weigh 300g ± 10g, put it into a sealed box, cover it with a lid with a kiwifruit freshness indicator array, and store it in an incubator at 4℃ and 25℃. Measure the total color difference of the color changes of the six indicator labels and judge the freshness of the kiwifruit. The final test results are shown in Tables 4 and 5 below. During the experiment, the color changes of the six indicator labels are as follows: Figure 2 and Figure 3 shown. Table 4. Color changes of indicator labels at 25°C Table 5. Color changes of indicator labels at 4°C The above experimental results show that: from the 0th day to the 16th day at 25°C storage, and from the 0th day to the 40th day at 4°C storage, the total color difference of the six indicator labels tends to gradually increase during the process of kiwifruit from fresh to corrupt. Therefore, when kiwifruit is corrupt, the kiwifruit freshness indicator array can convey accurate information through color changes visible to the naked eye. These six indicator labels can simultaneously indicate the freshness status of kiwifruit, and CO2 corrupt volatile gases can be indicated by the label array of the present invention, so that comprehensive information on the freshness of fruits and vegetables is obtained, the measurement results are accurate, and the results are intuitive and clear, which is conducive to wide promotion and industrial application. It has been verified that the kiwifruit freshness indicator arrays prepared in Examples 2-6 also have similar experimental effects as in Example 1, which will not be described one by one here.

Claims

1. A kiwifruit freshness indicator array, characterized in that: The kiwifruit freshness indicator array is composed of 6 indicator labels D1 to D6. The indicator label D1 includes a purple sweet potato anthocyanin indicator; The indicator label D2 includes a curcumin indicator; The indicator label D3 includes an alizarin indicator; The indicator label D4 includes purple potato anthocyanin and alizarin indicator; Indicator label D5 includes purple sweet potato anthocyanins and curcumin indicators; Indicator label D6 includes alizarin and curcumin indicators. 2 . The kiwifruit freshness indicator array according to claim 1 , wherein the indicator labels D1 to D6 are indicator films with carboxymethyl cellulose and polyvinyl alcohol as a matrix.

3. The kiwifruit freshness indicator array according to claim 1, wherein the kiwifruit freshness indicator array is prepared according to the following method: (1) adding carboxymethyl cellulose, polyvinyl alcohol and glycerol into distilled water to obtain solution A; the concentrations of carboxymethyl cellulose and polyvinyl alcohol in solution A are both 30 to 50 g / L, and the concentration of glycerol is 10 to 30 g / L; (2) preparing 8-10 g / L purple potato anthocyanin ethanol solution, 2-3 g / L curcumin ethanol solution, and 2-3 g / L alizarin ethanol solution; mixing the purple potato anthocyanin ethanol solution, curcumin ethanol solution, and alizarin ethanol solution in equal volumes to obtain a purple potato anthocyanin and curcumin ethanol solution containing 4-5 g / L purple potato anthocyanin and 1-1.5 g / L curcumin, a purple potato anthocyanin and alizarin ethanol solution containing 4-5 g / L purple potato anthocyanin and 1-1.5 g / L alizarin, and a curcumin and alizarin ethanol solution containing 0.5-0.75 g / L curcumin and 1.5-2.25 g / L alizarin, and adding NaOH solution to adjust the pH value to 10±0.1 to obtain indicators A1-A6; (3) adding the indicators A1 to A6 obtained in step (2) to 6 portions of solution A respectively to obtain mixed solutions B1 to B6; (4) drying the mixed solutions B1 to B6 obtained in step (3) to obtain indicator films C1 to C6; (5) The indicator films C1-C6 obtained in step (4) are made into indicator labels D1-D6 to form a kiwifruit freshness indicator array.

4. The kiwifruit freshness indicator array according to claim 3, wherein step (1) comprises: dissolving carboxymethyl cellulose and polyvinyl alcohol in distilled water respectively, mixing the two solutions in a volume ratio of 1:1, adding glycerol to form a uniform colloidal solution, and removing bubbles by vacuumizing and ultrasonicating to obtain solution A; the concentrations of carboxymethyl cellulose and polyvinyl alcohol in solution A are both 30-50 g / L, and the concentration of glycerol is 10-30 g / L.

5. The kiwifruit freshness indicator array according to claim 3, wherein step (2) comprises: preparing 8 g / L purple sweet potato anthocyanin ethanol solution, 2 g / L curcumin ethanol solution, and 2 g / L alizarin ethanol solution; mixing the purple sweet potato anthocyanin ethanol solution, the curcumin ethanol solution, and the alizarin ethanol solution in equal volumes to obtain a purple sweet potato anthocyanin and curcumin ethanol solution containing 4 g / L purple sweet potato anthocyanin and 1 g / L curcumin, a purple sweet potato anthocyanin and alizarin ethanol solution containing 4 g / L purple sweet potato anthocyanin and 1 g / L alizarin, and a curcumin and alizarin ethanol solution containing 1 g / L curcumin and 1 g / L alizarin, and adding NaOH solution to adjust the pH value to 10±0.1 to obtain indicators A1 to A6.

6. The kiwifruit freshness indicator array according to claim 3, wherein in step (3), 60 to 80 mL of purple sweet potato anthocyanin ethanol solution is added to each liter of solution A, and 40 to 60 mL of curcumin ethanol solution, alizarin ethanol solution, purple sweet potato anthocyanin and curcumin ethanol solution, purple sweet potato anthocyanin and alizarin ethanol solution, or curcumin and alizarin ethanol solution is added to each liter of solution A. The kiwi fruit freshness indicator array according to claim 3 , wherein the concentration of the NaOH solution is 0.5%.

8. The kiwifruit freshness indicator array according to claim 3, wherein in step (5), the indicator films 1-6 obtained in step (4) are cut into indicator labels of 1-3 cm x 1-3 cm.

9. The kiwifruit freshness indicator array according to claim 3, wherein the step (4) is performed by drying at 35-45°C for 15-20 hours.

10. Use of the kiwifruit freshness indicator array according to any one of claims 1 to 9 in detecting or indicating the freshness of kiwifruit.

11. The application according to claim 10, wherein the indicator labels D1-D6 in the kiwi fruit freshness indicator array are affixed to the inner surface of a kiwi fruit package, or the indicator labels D1 to D6 in the kiwi fruit freshness indicator array are affixed to a bottom plate, and the bottom plate with the indicator labels D1 to D6 is placed in the kiwi fruit package.

12. The use according to claim 10 or 11, comprising visually or machine reading the colors of the indicator labels D1 to D6 in the kiwifruit freshness indicator array.

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