Preparation method and application of intelligent label for monitoring freshness of fruits and vegetables

Abstract

The invention relates to the technical field of food freshness monitoring, in particular to a preparation method and application of an intelligent label for monitoring freshness of fruits and vegetables. The preparation method of the intelligent label for monitoring the freshness of the fruits and vegetables comprises the following steps: S1, adding gellan gum into deionized water, and stirring and hydrating in a water bath to obtain a gellan gum solution; s2, adding the crataegus pinnatifida fruit extract into an ethanol solution to obtain a prepared solution, adding glycerol and the prepared solution into a gellan gum solution, and uniformly stirring to obtain a film forming solution; and S3, pouring the film forming liquid into a container, drying, balancing in a dryer for at least 48 hours to obtain a film, and cutting the film into a preset size to obtain the intelligent label for monitoring the freshness of fruits and vegetables. The intelligent label can perform color response in a solution with the pH value of 2-12, presents different colors, is shorter in response color change time under different pH values, and has better storage stability under normal-temperature and low-temperature conditions.

Description

Technical Field

[0001] The present invention relates to the technical field of food freshness monitoring, and in particular to a preparation method and application of a smart label for monitoring the freshness of fruits and vegetables. Background Art

[0002] With the improvement of people's living standards and the occasional occurrence of foodborne diseases, consumers' awareness of food safety has also increased. People pay more attention to the freshness of food when choosing food. However, consumers currently judge the freshness of food mainly by observing the surface of the food with the naked eye. This judgment method is not completely accurate and sometimes causes food waste. The traditional method of testing the freshness of food requires destroying the food to extract a part of the test sample. The entire testing and analysis process is complicated and time-consuming.

[0003] Therefore, in recent years, the use of smart labels to detect the freshness of food has gradually gained attention. Smart labels can directly reflect the real-time quality of packaged food through color changes, helping consumers to make quick judgments. The indicator materials used to prepare smart labels include synthetic pigments and natural pigments. Compared with synthetic pigments, natural pigments such as anthocyanins and alizarin are safer and have abundant sources. Among them, anthocyanins are widely used, such as blueberries and purple cabbage. However, there are no reports on the use of red ginseng fruit extracts to prepare smart labels for freshness applications. Summary of the invention

[0004] The main purpose of the present invention is to provide a preparation method and application of a smart label that can be used to monitor the freshness of fruits and vegetables, aiming to improve the technical problem that the indicator materials of existing smart labels mostly use blueberries or purple cabbages, and red ginseng fruit extracts are not used to prepare smart labels.

[0005] To achieve the above object, the present invention proposes a method for preparing a smart label that can be used to monitor the freshness of fruits and vegetables, comprising the following steps:

[0006] S1. Add gellan gum to deionized water and stir in a water bath to obtain a gellan gum solution;

[0007] S2. The red ginseng fruit extract is added to an ethanol solution to obtain a prepared solution, glycerol and the prepared solution are added to the gellan gum solution, and stirred to obtain a film-forming solution;

[0008] Wherein, the concentration of the red ginseng fruit extract in the prepared solution is 0.8-1.2% w / v;

[0009] S3. Pour the film-forming liquid into a container, dry it, and balance it in a dryer for at least 48 hours to obtain a film, and cut the film into a preset size to obtain the smart label that can be used to monitor the freshness of fruits and vegetables.

[0010] Preferably, in step S2, the method for extracting the red ginseng fruit extract comprises the following steps:

[0011] S21. After the red ginseng fruit is successively subjected to wall breaking, freeze drying and sieving, a red ginseng fruit dry powder is obtained;

[0012] S22. Place the red ginseng fruit dry powder in an ethanol-water solution for ultrasonic extraction, and obtain the red ginseng fruit extract after centrifugal filtration.

[0013] Preferably, in step S1, the concentration of the gellan gum solution is 0.8-1.2% w / v.

[0014] Preferably, in step S1, the water bath temperature is 58-62°C.

[0015] Preferably, in step S2, the concentration of glycerol is 0.3-0.7% w / v.

[0016] Preferably, in step S22, the concentration of the ethanol-water solution is 68-72% v / v, the ultrasonic temperature is 38-42° C., and the ultrasonic time is 48-52 min.

[0017] Preferably, in step S22, the centrifugal speed is 7500-8500 r / min.

[0018] Preferably, in step S3, the drying temperature is 48-52°C.

[0019] Preferably, in step S3, the preset size is 1.5×1.5 cm to 1.8×1.8 cm.

[0020] In addition, the present invention also proposes an application of a smart label for monitoring the freshness of fruits and vegetables prepared by the preparation method of the smart label for monitoring the freshness of fruits and vegetables as described above, which can quickly detect changes in the pH value of fruits and vegetables by soaking or contacting the fruits and vegetables to determine whether they have deteriorated.

[0021] Compared with the prior art, the preparation method and application of the smart label for monitoring the freshness of fruits and vegetables of the present invention have the following beneficial effects: using gellan gum as a film-forming substrate, red ginseng fruit extract as an indicator material, and glycerin as a plasticizer to prepare a smart label for monitoring the freshness of fruits and vegetables. When the smart label is used for monitoring the freshness of fruits and vegetables (such as lychee), as the freshness of fruits and vegetables decreases, the smart label will show different color changes, and the corresponding ΔE values ​​are all greater than 5, which can be observed by the naked eye. By optimizing various parameters, the prepared red ginseng fruit extract can respond to color in a solution with a pH value of 2-12, showing different colors. In addition, compared with conventional smart labels containing blueberry anthocyanins / purple cabbage anthocyanins, the smart label of this scheme takes a shorter time to respond to color change at different pH values, and has good storage stability at both normal and low temperature conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying any creative work.

[0023] Figure 1 This is a diagram showing the color change of the red ginseng fruit extract prepared in Example 1 under different pH conditions.

[0024] The realization of the purpose, functional features and advantages of this application will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0025] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0026] In addition, the technical solutions between the various embodiments can be combined with each other, but it must be based on the fact that ordinary technicians in the field can implement it. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0027] A method for preparing a smart label that can be used to monitor the freshness of fruits and vegetables comprises the following steps:

[0028] S1. Add gellan gum powder to deionized water and place in a water bath at 58-62°C with magnetic stirring to obtain a gellan gum solution;

[0029] S2. The red ginseng fruit extract is added to an ethanol solution to obtain a prepared solution, glycerol, the prepared solution is added to the gellan gum solution, and the mixture is stirred to obtain a film-forming solution;

[0030] Wherein, the concentration of the gellan gum solution is 0.8-1.2%, the concentration of the glycerol is 0.3-0.7%, and the concentration of the red ginseng fruit extract in the prepared solution is 0.8-1.2%;

[0031] S3. The film-forming liquid is poured into a 90 mm disposable culture dish by solution casting, dried in an oven at 48-52° C., and then balanced in a dryer for at least 48 hours to obtain a film, and the film is cut into a preset size (such as 1.5×1.5 cm to 1.8×1.8 cm) to obtain the smart label that can be used to monitor the freshness of fruits and vegetables.

[0032] Gellan gum is a microbial anionic polysaccharide with good film-forming properties. The film is colorless, transparent, biodegradable, and environmentally friendly. However, the film made from gellan gum alone is brittle and has poor water resistance, which limits its application in the field of food packaging. This solution changes the original structure of the polysaccharide substance by adding a plasticizer, glycerol, to form a new molecular force, thereby improving the film performance. After the addition of glycerol, new hydrogen bonds are formed between the gellan gum molecules, changing the original intermolecular forces, enhancing the film ductility, and improving the disadvantage of the brittleness of the gellan gum film.

[0033] In particular, the indicator material used to prepare the smart label in the present scheme is the red ginseng fruit extract. The red ginseng fruit extract of the present invention contains anthocyanins, which can show different color changes under different pH conditions, and can give gellan gum the colorimetric properties required for realizing smart packaging. The characteristic gas generated during food storage can cause the pH in the environment to change, thereby changing the color of the smart label. Gellan gum can enhance the stability of anthocyanins in the red ginseng fruit extract through hydrogen bond interactions, and is a good film-forming material for fixing anthocyanins.

[0034] In addition, unlike blueberries and purple cabbages, when red ginseng fruit extract is used as the indicator material for preparing smart labels, the response color change time under different pH conditions is relatively short, and it also has good storage stability under low temperature conditions.

[0035] The method for extracting the red ginseng fruit extract comprises the following steps:

[0036] S21. Remove the rotten and bad fruits from the red ginseng fruit, wash and dry them, put them into a wall-breaking machine for even wall-breaking, freeze-dry for 3 to 4 days and pass through an 80-mesh sieve to obtain red ginseng fruit dry powder;

[0037] S22. With a solid-liquid ratio of 1:10 to 1:20, the red ginseng fruit dry powder is placed in a 68-72% ethanol-water solution for ultrasonic extraction to obtain an extract, the extract is centrifuged at a speed of 7500-8500 r / min for 15 min and then filtered, the filtrate is concentrated by rotary evaporation, and the red ginseng fruit extract is obtained after freeze-drying. The temperature during ultrasonic extraction is 38-42°C, and the ultrasonic time is 48-52 min.

[0038] The extraction method of the red ginseng fruit extract of the present invention is relatively simple, easy to industrialize, has a high wall breaking rate for red ginseng fruit, and has a high extraction rate of effective components in red ginseng fruit dry powder after freeze drying and sieving. The red ginseng fruit dry powder obtained after freeze drying is evenly mixed with an ethanol-water solution and placed in an ultrasonic environment, and the red ginseng fruit powder suspended in the solution is further broken by the cavitation effect and mechanical effect of the ultrasonic wave, which is conducive to the dissolution of the red ginseng fruit content, and the red ginseng fruit extract is obtained by centrifugal filtration after standing, and has a high extraction rate, a high impurity removal rate, and a high purity.

[0039] The present invention also proposes an application of a smart label for monitoring the freshness of fruits and vegetables prepared by the preparation method of the smart label for monitoring the freshness of fruits and vegetables as described above, which can quickly detect changes in the pH value of fruits and vegetables by soaking or contacting the fruits and vegetables to determine whether they have deteriorated.

[0040] The technical solution of the present invention is further described in detail below in conjunction with specific embodiments. It should be understood that the following embodiments are only used to explain the present invention, and are not used to limit the present invention.

[0041] Example 1

[0042] A method for preparing a smart label that can be used to monitor the freshness of fruits and vegetables comprises the following steps:

[0043] S1. Adding gellan gum to deionized water, stirring and hydrating in a water bath at 60°C to obtain a gellan gum solution; wherein the concentration of the gellan gum solution is 1% w / v;

[0044] S2. Add glycerol and red ginseng fruit extract to the gellan gum solution and stir to obtain a film-forming solution; wherein the concentration of the glycerol is 0.5%, and the concentration of the red ginseng fruit extract in the prepared solution is 1%;

[0045] S3. Pour the film-forming liquid into a container, dry it at 50° C., and balance it in a dryer for 48 hours to obtain a film. Cut the film into a size of 1.5×1.5 cm to obtain the smart label that can be used to monitor the freshness of fruits and vegetables.

[0046] Wherein, the extraction method of the red ginseng fruit extract comprises the following steps:

[0047] S21. After the red ginseng fruit was broken, freeze-dried for 3d and sieved through an 80-mesh sieve, the red ginseng fruit powder was obtained;

[0048] S22. The red ginseng fruit dry powder is placed in an ethanol-water solution for ultrasonic extraction at a solid-liquid ratio of 1:13, and the red ginseng fruit extract is obtained after centrifugal filtration, wherein the concentration of the ethanol-water solution is 70% v / v, the ultrasonic temperature is 40°C, the ultrasonic time is 50 min; and the centrifugal speed is 8000 r / min.

[0049] The red ginseng fruit extract of Example 1 was prepared into a solution with 70% ethanol solution, placed in a solution with a pH value of 2-12 and photographed and recorded. The results are as follows: Figure 1 shown.

[0050] Example 2

[0051] A method for preparing a smart label that can be used to monitor the freshness of fruits and vegetables comprises the following steps:

[0052] S1. Adding gellan gum to deionized water, stirring and hydrating in a water bath at 58°C to obtain a gellan gum solution; wherein the concentration of the gellan gum solution is 0.8% w / v;

[0053] S2. The red ginseng fruit extract is added to an ethanol solution to obtain a prepared solution, glycerol and the prepared solution are added to the gellan gum solution, and stirred to obtain a film-forming solution;

[0054] Wherein, the concentration of glycerol is 0.3%, and the concentration of the red ginseng fruit extract in the prepared solution is 0.8%;

[0055] S3. Pour the film-forming liquid into a container, dry it at 48° C., and balance it in a dryer for 48 hours to obtain a film. Cut the film into a size of 1.5×1.5 cm to obtain the smart label that can be used to monitor the freshness of fruits and vegetables.

[0056] Wherein, the extraction method of the red ginseng fruit extract comprises the following steps:

[0057] S21. After the red ginseng fruit was broken, freeze-dried for 3d and sieved through an 80-mesh sieve, the red ginseng fruit powder was obtained;

[0058] S22. The red ginseng fruit dry powder is placed in an ethanol-water solution for ultrasonic extraction at a solid-liquid ratio of 1:15, and the red ginseng fruit extract is obtained after centrifugal filtration, wherein the concentration of the ethanol-water solution is 68% v / v, the ultrasonic temperature is 38°C, the ultrasonic time is 48 min; and the centrifugal speed is 7500 r / min.

[0059] Example 3

[0060] A method for preparing a smart label that can be used to monitor the freshness of fruits and vegetables comprises the following steps:

[0061] S1. Adding gellan gum to deionized water, stirring and hydrating in a water bath at 60°C to obtain a gellan gum solution; wherein the concentration of the gellan gum solution is 1.2% w / v;

[0062] S2. The red ginseng fruit extract is added to an ethanol solution to obtain a prepared solution, glycerol and the prepared solution are added to the gellan gum solution, and stirred to obtain a film-forming solution;

[0063] Wherein, the concentration of glycerol is 0.7%, and the concentration of the red ginseng fruit extract in the prepared solution is 1.2%;

[0064] S3. Pour the film-forming liquid into a container, dry it at 52° C., and balance it in a dryer for 48 hours to obtain a film. Cut the film into a size of 1.5×1.5 cm to obtain the smart label that can be used to monitor the freshness of fruits and vegetables.

[0065] Wherein, the extraction method of the red ginseng fruit extract comprises the following steps:

[0066] S21. After the red ginseng fruit was broken, freeze-dried for 3d and sieved through an 80-mesh sieve, the red ginseng fruit powder was obtained;

[0067] S22. The red ginseng fruit dry powder is placed in an ethanol-water solution for ultrasonic extraction at a solid-liquid ratio of 1:18, and the red ginseng fruit extract is obtained after centrifugal filtration, wherein the concentration of the ethanol-water solution is 72% v / v, the ultrasonic temperature is 42°C, the ultrasonic time is 52 min; and the centrifugal speed is 8500 r / min.

[0068] Comparative Example 1

[0069] The preparation steps and parameters of this comparative example are consistent with those of Example 1, with the only difference being that the prepared solution prepared from the red ginseng fruit extract in Example 1 is replaced by a blueberry anthocyanin solution (also prepared with a 70% ethanol solution) and added to the gellan gum solution.

[0070] Comparative Example 2

[0071] The preparation steps and parameters of this comparative example are consistent with those of Example 1, with the only difference being that the prepared solution prepared from the red ginseng fruit extract in Example 1 is replaced by a purple cabbage anthocyanin solution (also prepared with a 70% ethanol solution) and added to the gellan gum solution.

[0072] The smart labels prepared in the above Examples 1-3 and Comparative Examples 1-2 were subjected to the following performance tests:

[0073] 1. The smart labels prepared in Examples 1-3 and Comparative Examples 1-2 were placed in solutions with pH values ​​of 2-12, and the time for each label to respond to color change was recorded. The results are shown in Table 1:

[0074] Table 1 The response color change time of the two smart tags under different pH conditions

[0075]

[0076]

[0077] From the observation results in Table 1 above, it can be seen that compared with the labels containing blueberry and purple cabbage anthocyanins, the smart label made from red ginseng fruit extract in this scheme takes a shorter time to respond to color change, and the time to respond to color change in some pH ranges is even shortened by more than 10 seconds.

[0078] In addition, acidic conditions have an enhancing effect on the color development of anthocyanins (red ginseng fruit extract). Compared with neutral and alkaline conditions, the time for determining the color change of the smart label in this section is generally longer; when pH>7, as the pH value increases, anthocyanins are relatively unstable and transform into quinone bases and chalcone structures. Compared with acidic conditions, the anthocyanins contained in the smart label change color faster due to the large pH changes in the environment.

[0079] 2. After cold chain transportation, Guiwei lychees are stored in a refrigerator at 7°C. The bad lychees are removed, and the fruits with uniform quality and size are selected and placed in a disposable transparent fresh-keeping PP box together with the smart label in Example 2. The label is glued to the inner surface of the box lid so that it does not come into direct contact with the lychees. The fresh-keeping box is stored for 4 days at an ambient temperature of 28±2°C and a relative humidity of 70-85%. The color change of the label is recorded using a colorimeter. The color difference values ​​of the smart label during storage and the corresponding color changes are shown in Table 2:

[0080] Table 2 Color difference values ​​of smart labels and corresponding color changes during litchi storage

[0081]

[0082]

[0083] From the test data in Table 2, it can be seen that during the storage period, when the smart label of this solution is used, the ΔE value at different days is greater than 5, indicating that the color change of the smart label is visible to the naked eye. The first and second days are fresh quality. Due to the respiration of litchi, the CO in the packaging environment 2 As the concentration increases, the pH decreases. At this time, the color of the label will become darker than the initial period, and the overall color will be dark pink. On the third day, the surface of some samples will rot and they are no longer recommended for consumption. At this time, the color of the label will be less pink than the initial label. On the fourth day, the pink color of the label has basically disappeared and the color will be light brown.

[0084] Compared with Comparative Example 1 and Comparative Example 2, the ΔE value of the smart label made from the red ginseng fruit extract of the present invention is larger, and the color distinction obtained by the naked eye is also larger. For example, on the third day, the ΔE of Comparative Example 1 and Comparative Example 2 is less than 5, indicating that it is difficult for the naked eye to perceive the color change at this time point, and the freshness is not enough to judge based on the label color alone. During the 4-day storage period of litchi, the effect of this solution is better than that of Comparative Example 1 and Comparative Example 2.

[0085] It should be noted here that on the 3rd and 4th days, the water vapor generated by the respiration during the storage of litchi may have accumulated and remained on the label, resulting in the measured brightness value (L*) being larger than that on the 1st and 2nd days, and ultimately causing the ΔE value to decrease relatively. On the 4th day, the red value (a*) of the label dropped to the minimum, and the calculated ΔE value increased compared to the 3rd day. In addition, due to the influence of the respiration water vapor, some pigments in the extract of the label were dissolved, making the overall color of the label lighter.

[0086] 3. The smart labels prepared in Examples 1-3 and Comparative Examples 1-2 were stored at 25°C and 4°C in the dark for 14 days, and the color difference was measured with a colorimeter every 2 days. The storage stability of the labels was evaluated based on the changes in the color difference over time. The changes in the color difference during storage are shown in Tables 3 and 4:

[0087] Table 3 Color difference values ​​of smart labels and corresponding color changes at 25°C

[0088]

[0089]

[0090] Table 4 Color difference values ​​of smart labels and corresponding color changes at 4°C

[0091]

[0092]

[0093] It can be seen from the test data in Tables 3 and 4 that in this scheme, the smart label made from the red ginseng fruit extract has no observable color change at 25°C or at low temperature of 4°C, the maximum ΔE at 25°C is <1.4, and the maximum ΔE at 4°C is even <0.8, and there is no color change when ΔE is below 5, that is, the color difference at all time points for 14 days under normal temperature or low temperature conditions is small, and ΔE does not exceed 1.4, indicating that the labels made by this scheme have good storage stability.

[0094] On the other hand, for Comparative Examples 1 and 2, at 25°C, the ΔE on the sixth day was greater than 5, indicating that the color of the label had changed visibly to the naked eye. The storage stability was further monitored, and the ΔE was greater than 15 on the 12th day, indicating that the color of the label had degraded and was not suitable for further use. At 4°C, the ΔE was also greater than 15 on the 14th day, and it should not be used. The smart label made using blueberry / purple cabbage as the indicator material had a relatively large ΔE value after being stored for a certain period of time at low temperature and room temperature, indicating that the storage stability of the label was not as good as that of the present solution.

[0095] The above embodiments are only preferred implementation modes of the present invention, and they do not limit the patent scope of the present invention. The embodiments mentioned in the present invention are not limited to the above ones, so the above embodiments cannot be regarded as limiting the protection scope of the present invention. All equivalent structural transformations made by using the contents of the present invention specification under the inventive concept of the present invention, or direct / indirect application in other related technical fields are included in the patent protection scope of the present invention.

Claims

1. A method for preparing a smart label that can be used to monitor the freshness of fruits and vegetables, characterized in that: The steps include: S1. Add gellan gum to deionized water and stir in a water bath to obtain a gellan gum solution; S2. The red ginseng fruit extract is added to an ethanol solution to obtain a prepared solution, glycerol and the prepared solution are added to the gellan gum solution, and stirred to obtain a film-forming solution; Wherein, the concentration of the red ginseng fruit extract in the prepared solution is 0.8-1.2%; S3. Pour the film-forming liquid into a container, dry it, and balance it in a dryer for at least 48 hours to obtain a film, and cut the film into a preset size to obtain the smart label that can be used to monitor the freshness of fruits and vegetables.

2. The method for preparing a smart label for monitoring the freshness of fruits and vegetables according to claim 1, characterized in that: In step S2, the method for extracting the red ginseng fruit extract comprises the following steps: S21. After the red ginseng fruit is successively subjected to wall breaking, freeze drying and sieving, a red ginseng fruit dry powder is obtained; S22. Place the red ginseng fruit dry powder in an ethanol-water solution for ultrasonic extraction, and obtain the red ginseng fruit extract after centrifugal filtration.

3. The method for preparing a smart label for monitoring the freshness of fruits and vegetables according to claim 1, characterized in that: In step S1, the concentration of the gellan gum solution is 0.8-1.2%.

4. The method for preparing a smart label for monitoring the freshness of fruits and vegetables according to claim 1, characterized in that: In step S1, the water bath temperature is 58-62°C.

5. The method for preparing a smart label for monitoring the freshness of fruits and vegetables according to claim 1, characterized in that: In step S2, the concentration of glycerol is 0.3-0.7%.

6. The method for preparing a smart label for monitoring the freshness of fruits and vegetables according to claim 2, characterized in that: In step S22, the concentration of the ethanol-water solution is 68-72%, the ultrasonic temperature is 38-42°C, and the ultrasonic time is 48-52 minutes.

7. The method for preparing a smart label for monitoring the freshness of fruits and vegetables according to claim 2, characterized in that: In step S22, the centrifugal speed is 7500-8500 r / min.

8. The method for preparing a smart label for monitoring the freshness of fruits and vegetables according to claim 1, characterized in that: In step S3, the drying temperature is 48-52°C.

9. The method for preparing a smart label for monitoring the freshness of fruits and vegetables according to claim 1, characterized in that: In step S3, the preset size is 1.5×1.5 cm to 1.8×1.8 cm.

10. An application of a smart label for monitoring the freshness of fruits and vegetables prepared by the method for preparing a smart label for monitoring the freshness of fruits and vegetables as claimed in any one of claims 1 to 9, characterized in that: By soaking or touching fruits and vegetables, the pH value of fruits and vegetables can be quickly detected to determine whether they have deteriorated.

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