A food freshness intelligent indicator film and preparation method thereof

Abstract

The present invention provides a smart food freshness indicator film and its preparation method. The smart indicator film comprises montmorillonite, amino acids, pullulan, and anthocyanins. The unique composition of the smart indicator film allows for a longer indication period, helping consumers obtain more objective and accurate information about product freshness.

Description

Technical Field

[0001] The invention relates to an indicator film, in particular to an intelligent food freshness indicator film and a preparation method thereof, and belongs to the fields of biomass materials and colloid chemistry. Background Art

[0002] During transportation, distribution, and storage, food loses its freshness and produces characteristic gases due to physical, chemical, and microbiological effects, as well as enzymatic reactions and cellular respiration. Smart food packaging, a new type of packaging technology with indicator functions, has emerged in the food industry both domestically and internationally in recent years. It primarily monitors changes in the packaging environment or food characteristics to provide information on food quality and safety during storage and transportation. As a form of smart food packaging, food freshness indicator film utilizes an indicator to react with characteristic gases, emitting signals (optical, chemical, electrical, etc.) to inform consumers of food freshness.

[0003] However, the current food freshness indicator film cannot fully serve the entire freshness cycle of food. After being used to indicate part of the freshness cycle of food, its color no longer changes, making it difficult for consumers to obtain objective and accurate food freshness information. Summary of the Invention

[0004] The present invention provides a food freshness intelligent indicator film. The special composition of the intelligent indicator film enables it to have a longer indication period, which helps consumers obtain more objective and accurate product freshness information.

[0005] The present invention also provides a method for preparing a food freshness intelligent indicator film, which is used to prepare the above-mentioned food freshness intelligent indicator film and can effectively improve the problem of short indication period in the prior art.

[0006] The invention provides a food freshness intelligent indicator film, comprising montmorillonite, amino acids, pullulan and anthocyanin.

[0007] The smart indicator film as described above, wherein the mass ratio of montmorillonite, amino acid, pullulan and anthocyanin is (5-20):(25-50):(15-30):(3-6).

[0008] The smart indicator film as described above, wherein the pH of the smart indicator film is 8-10.

[0009] The smart indicator film as described above, wherein the pH of the smart indicator film is 5-6.

[0010] The smart indicator film as described above is prepared by a method comprising the following steps: mixing a montmorillonite-amino acid-water dispersion with a pullulan-anthocyanidin-water dispersion to obtain a film-forming liquid, and subjecting the film-forming liquid to a film-forming treatment.

[0011] The present invention also provides a method for preparing any of the above-mentioned food freshness intelligent indicator films, comprising the following steps:

[0012] The montmorillonite-amino acid-water dispersion is mixed with the pullulan-anthocyanidin-water dispersion to obtain a film-forming liquid, and the film-forming liquid is subjected to a film-forming treatment.

[0013] According to the preparation method described above, a montmorillonite aqueous solution with a mass fraction of 1-3% and an amino acid aqueous solution with a concentration of 0.1-0.2 g / L are mixed in a volume ratio of 1:2 to obtain the montmorillonite-amino acid-water dispersion.

[0014] In the preparation method as described above, pullulan, anthocyanin and water are mixed in a mass ratio of 5:1:(40-250) to obtain the pullulan-anthocyanin-water dispersion.

[0015] In the preparation method as described above, the montmorillonite-amino acid-water dispersion and the pullulan-anthocyanidin-water dispersion are mixed in a ratio of 1:1 to obtain the film-forming solution.

[0016] In the preparation method as described above, the film forming process comprises: degassing the film forming solution at a vacuum degree of 0.09 MPa for 20 minutes and then casting the solution.

[0017] The intelligent indicator film provided by the present invention is composed of montmorillonite, amino acids, pullulan and anthocyanins, which gives it a preservation function and a long indication period. On the basis of effectively extending the shelf life of food, it also helps consumers obtain more objective and accurate product freshness information. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a comparative diagram showing the storage color change behavior of Example 1 of the present invention and Comparative Example 1. DETAILED DESCRIPTION

[0019] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are 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 making creative efforts shall fall within the scope of protection of the present invention.

[0020] The invention provides a food freshness intelligent indicator film, comprising montmorillonite, amino acids, pullulan and anthocyanin.

[0021] Food that is in its shelf life will release different chemical signals as time goes by. The food freshness intelligent indicator film of the present invention can indicate the freshness of food based on the chemical signals released by the food, thereby providing consumers with the most objective freshness information of the food at the moment, and can especially be used to indicate the current freshness of fresh foods with a shorter freshness cycle. In detail, the anthocyanin in the indicator film of the present invention has the color-changing behavior of showing different colors under different environments. Therefore, as the shelf life of food continues to extend, the chemical signals released by food (including carbon dioxide, ammonia and water, etc.) are also constantly changing, and can then indicate the freshness of the food during storage through different colors. In actual applications, the indicator film is generally placed inside the outer packaging of the food and is in the same space as the food to be indicated, so that the indicator film can quickly receive the chemical signals released by the food and give objective and accurate indication information.

[0022] In addition to having the function of indicating freshness, the ortho-phenolic hydroxyl groups contained in anthocyanidins make them easily oxidized to form quinone structures, thereby exerting an antioxidant effect, thereby enabling the indicator film of the present invention to also have a freshness-preserving function.

[0023] It's worth noting that the unique composition of the food freshness intelligent indicator film of the present invention also enables it to indicate the food's freshness throughout its entire lifespan. For example, for food with a seven-day freshness cycle, the food will release different chemical signals (e.g., different gases, or varying concentrations of the same gas) over time. The food freshness intelligent indicator film of the present invention can sense these chemical signals and respond differently. Furthermore, after seven days, it will provide consumers with a different response than on the seventh day, clearly informing them of the food's current freshness stage. This avoids the problem of current indicator labels failing to change color after the fourth day, leading consumers to misjudge the food's freshness.

[0024] Based on this phenomenon, the inventors analyzed the indication principle of the indicator film of the present invention and believed that it may be: on the one hand, amino acids and montmorillonite exist in the indicator film based on pullulan. When the chemical signals released by food (including carbon dioxide, ammonia and water) enter the indicator film, the amino acids and montmorillonite will become physical obstacles to the transmission of the chemical signals, extending the transmission path of the chemical signals. The "tortuous path" effect of the chemical signal reduces its penetration efficiency in the indicator film; on the other hand, the presence of amino acids and montmorillonite also causes hydrogen bond interactions between pullulan molecules, changes the "hole free volume" in the pullulan matrix, and thus changes the probability function of the chemical signal directly "jumping in" and occupying the hole free volume, thereby affecting the penetration behavior of the chemical signal in the pullulan matrix and ultimately leading to a decrease in permeability. Based on the above two reasons, when the chemical signal released by the food enters the indicator membrane, the lower penetration rate of the chemical signal in the indicator membrane controls the amount of anthocyanins participating in the signal response, thereby enabling sufficient anthocyanins to remain in the indicator membrane to interact with the chemical signal to be released subsequently and produce a response. Therefore, the effective service life of the indicator membrane of the present invention is extended, and it can more objectively reflect the current freshness of the food within the freshness cycle of the food.

[0025] In the above composition, the present invention does not limit the specific compound types or sources of each component. For example, the amino acid can be any amino acid compound known in the art, illustratively, at least one of lysine, histidine, and arginine. Of course, when making specific selections, the cost of each specific amino acid compound can be used as a reference to control the cost of the indicator film of the present invention. For another example, the anthocyanin can be at least some of purple potato anthocyanin, grape skin anthocyanin, and perilla leaf anthocyanin. In other words, the present invention does not limit the specific source of the anthocyanin.

[0026] In order to enhance the response sensitivity of the indicator film to the chemical signals released by food and further extend the indication period of the indicator film, the mass ratio of montmorillonite, amino acid, pullulan and anthocyanin in the indicator film of the present invention is (5-20):(25-50):(15-30):(3-6).

[0027] The inventors discovered that when the indicator film has different pH values, it exhibits different indication behaviors for different types of food. This may be because the interaction between amino acids and montmorillonite varies under different pH environments, resulting in different degrees of obstruction for different chemical signals, ultimately producing different indication behaviors.

[0028] Specifically, when the pH value of the indicator film is 8-10, the indicator film is more sensitive to the chemical signals released by fruit and vegetable products, and is therefore more suitable for use as a freshness indicator film for fruit and vegetable products.

[0029] When the pH value of the indicator film is 5-6, the indicator film is more sensitive to the chemical signals released by meat food, and is therefore more suitable for use as a freshness indicator film for meat food.

[0030] It is understood that the specific pH value of the indicator film can be achieved by adjusting the pH value of the film-forming solution during the preparation of the indicator film. The present invention does not limit the method of adjusting the pH value of the film-forming solution.

[0031] The present invention does not limit the preparation method of the indicator film. In a specific embodiment, the indicator film is prepared by a method comprising the following steps:

[0032] The montmorillonite-amino acid-water dispersion liquid is mixed with the pullulan-anthocyanidin-water dispersion liquid to obtain a film-forming liquid, and the film-forming liquid is subjected to a film-forming treatment.

[0033] The montmorillonite-amino acid-water dispersion is a mixture of montmorillonite, amino acid and water, and the pullulan-anthocyanidin-water dispersion is a mixture of pullulan, anthocyanidin and water.

[0034] During the preparation process, the mass ratio of montmorillonite, amino acids, pullulan, and anthocyanins in the indicator film can be controlled by controlling the individual raw materials in the montmorillonite-amino acid-water dispersion and the pullulan-anthocyanin-water dispersion. Of course, the pH of the film-forming solution can also be adjusted using various pH adjusters (such as sodium hydroxide and hydrochloric acid) to ultimately achieve an indicator film that meets the target pH.

[0035] In addition, the specific operations of the mixing process and the film forming process in the above preparation process can be consistent with the existing operations in the art, and the present invention does not impose too many restrictions.

[0036] A second aspect of the present invention provides a method for preparing the indicator film of the first aspect, comprising the following steps:

[0037] The montmorillonite-amino acid-water dispersion liquid is mixed with the pullulan-anthocyanidin-water dispersion liquid to obtain a film-forming liquid, and the film-forming liquid is subjected to a film-forming treatment.

[0038] The definitions of montmorillonite-amino acid-water dispersion and pullulan-anthocyanidin-water dispersion are the same as those described above and will not be repeated here.

[0039] Specifically, a montmorillonite aqueous solution and an amino acid aqueous solution are mixed to obtain a montmorillonite-amino acid-water dispersion, pullulan, anthocyanin and water are mixed to obtain a pullulan-anthocyanin-water dispersion, and then the montmorillonite-amino acid-water dispersion and the pullulan-anthocyanin-water dispersion are mixed to obtain a film-forming liquid. Finally, a pH regulator is added to adjust the film-forming liquid to the desired pH value, and the film-forming liquid is subjected to film-forming treatment to obtain a freshness intelligent indicator film.

[0040] In a specific embodiment, when preparing a montmorillonite-amino acid-water dispersion, when a montmorillonite aqueous solution with a mass fraction of 1-3% and an amino acid aqueous solution with a concentration of 0.1-0.2 g / mL are mixed in a volume ratio of 1:2, the "tortuous path" effect of the chemical signal in the indicator membrane can be enhanced, thereby further reducing the penetration efficiency of the chemical signal in the indicator membrane.

[0041] In addition, in order to enhance the preservation function of the indicator film, when preparing the pullulan-anthocyanidin-water dispersion, pullulan, anthocyanidin and water are mixed in a mass ratio of 5:1:(40-250) to obtain the pullulan-anthocyanidin-water dispersion.

[0042] Furthermore, when preparing the membrane-forming liquid, mixing montmorillonite-amino acid-water dispersion and pullulan-anthocyanin-water dispersion in a ratio of 1:1 can enhance the hydrogen bond interaction between pullulan molecules, further slowing down the penetration behavior of chemical signals in the pullulan matrix and causing a decrease in permeability, thereby extending the effective service life of the indicator membrane.

[0043] The present invention does not limit the film forming treatment method. In a specific embodiment, the film forming liquid is degassed at a vacuum degree of 0.09 MPa for 20 minutes and then cast, which has the characteristics of simple and easy operation and good film forming effect.

[0044] The present invention does not impose any restrictions on the specific operation of the mixing process in the above preparation process, which can be consistent with existing operations in the art. In addition, the present invention does not impose any restrictions on the vacuum equipment used when vacuum degassing the film-forming liquid.

[0045] Example 1

[0046] In the food freshness intelligent indicator film of this embodiment, the mass ratio of montmorillonite, lysine, pullulan, and anthocyanin is 5:25:15:3.

[0047] The preparation method of the intelligent indicator film comprises the following steps:

[0048] (1) 50 ml of an amino acid aqueous solution with a concentration of 0.1 g / mL was added to 100 ml of a 1% montmorillonite aqueous solution, magnetically stirred for 3 h, and then ultrasonically dispersed for 30 min to prepare a montmorillonite-amino acid-water dispersion;

[0049] (2) Weigh 1 g of pullulan and 0.2 g of purple sweet potato anthocyanidin, mix the pullulan, purple sweet potato anthocyanidin and water in a mass ratio of 5:1:250 to prepare a pullulan-anthocyanidin-water dispersion;

[0050] (3) 50 g of montmorillonite-amino acid-water dispersion was mixed with 50 g of pullulan-anthocyanidin-water dispersion, the pH of the mixture was adjusted to 8, and magnetic stirring was performed for 2 h to form a uniform film-forming liquid. The film-forming liquid was degassed at a vacuum degree of 0.09 MPa for 20 min, and the film was formed by flow casting to obtain the smart indicator film.

[0051] Example 2

[0052] The preparation method of the smart indicator film of this embodiment is basically the same as that of Example 1, except that the pH of the mixed solution is adjusted to 10. In the food freshness smart indicator film of this embodiment, the mass ratio of montmorillonite, lysine, pullulan, and anthocyanin is 5:25:15:3.

[0053] Example 3

[0054] The preparation method of this example's intelligent indicator film is essentially the same as that of Example 1, except that the mass fraction of the montmorillonite aqueous solution is 2%, and the concentration of the amino acid aqueous solution is 0.2 g / mL. In this example's food freshness intelligent indicator film, the mass ratio of montmorillonite, lysine, pullulan, and anthocyanin is 10:50:15:3.

[0055] Example 4

[0056] The preparation method of the smart indicator film of this embodiment is substantially the same as that of Example 1, except that the mass fraction of the montmorillonite aqueous solution is 3%, the concentration of the amino acid aqueous solution is 0.2 g / mL, and the pH of the mixed solution is adjusted to 10. In the food freshness smart indicator film of this embodiment, the mass ratio of montmorillonite, lysine, pullulan, and anthocyanin is 15:50:15:3.

[0057] Example 5

[0058] The preparation method of the smart indicator film of this embodiment is basically the same as that of Example 1, except that the mass fraction of the montmorillonite aqueous solution is 3%. In the food freshness smart indicator film of this embodiment, the mass ratio of montmorillonite, lysine, pullulan, and anthocyanin is 15:25:15:3.

[0059] Example 6

[0060] The preparation method of the smart indicator film of this embodiment is substantially the same as that of Example 1, except that the mass fraction of the montmorillonite aqueous solution is 3%, and the pH of the mixed solution is adjusted to 10. In the food freshness smart indicator film of this embodiment, the mass ratio of montmorillonite, lysine, pullulan, and anthocyanin is 15:25:15:3.

[0061] Example 7

[0062] The preparation method of the smart indicator film of this embodiment is substantially the same as that of Example 1, except that the mass fraction of the montmorillonite aqueous solution is 0.5%, and the pH of the mixed solution is adjusted to 10. In the food freshness smart indicator film of this embodiment, the mass ratio of montmorillonite, lysine, pullulan, and anthocyanin is 5:50:30:6.

[0063] Example 8

[0064] The preparation method of the smart indicator film of this embodiment is substantially the same as that of Example 1, except that the mass fraction of the montmorillonite aqueous solution is 4%, and the pH of the mixed solution is adjusted to 10. In the food freshness smart indicator film of this embodiment, the mass ratio of montmorillonite, lysine, pullulan, and anthocyanin is 20:25:15:3.

[0065] Example 9

[0066] The preparation method of the smart indicator film of this embodiment is basically the same as that of Example 1, except that the concentration of the amino acid aqueous solution is 0.3 g / mL. In the food freshness smart indicator film of this embodiment, the mass ratio of montmorillonite, lysine, pullulan, and anthocyanin is 15:25:15:3.

[0067] Example 10

[0068] The preparation method of the smart indicator film of this embodiment is substantially the same as that of Example 1, except that the volume of the amino acid aqueous solution and the montmorillonite aqueous solution in step (1) are both 50 ml. In the food freshness smart indicator film of this embodiment, the mass ratio of montmorillonite, lysine, pullulan, and anthocyanin is 10:25:30:6.

[0069] Example 11

[0070] The preparation method of the smart indicator film of this embodiment is substantially the same as that of Example 1, except that, in step (3), 50 ml of the montmorillonite-amino acid-water dispersion is mixed with 100 ml of the pullulan-anthocyanidin-water dispersion. In the food freshness smart indicator film of this embodiment, the mass ratio of montmorillonite, lysine, pullulan, and anthocyanidin is 5:25:30:6.

[0071] Comparative Example 1

[0072] The food freshness intelligent indicator film of this comparative example is composed of pullulan and anthocyanin, and the mass ratio of pullulan to anthocyanin is 1:5.

[0073] The preparation method of the intelligent indicator film comprises the following steps:

[0074] (1) Weigh 1 g of pullulan and 0.2 g of purple sweet potato anthocyanins and dissolve them in 50 mL of deionized water to prepare a pullulan-anthocyanin solution;

[0075] (2) Adjust the pH of the pullulan-anthocyanidin solution to 8, degas the film-forming solution under a vacuum degree of 0.09 MPa for 20 minutes, and then form the film by casting.

[0076] Comparative Example 2

[0077] The preparation method of the intelligent indicator film of this comparative example is basically the same as that of comparative example 1, except that the pH of the pullulan-anthocyanidin solution is adjusted to 10.

[0078] Test Example 1

[0079] The contact angle, water molecule permeability coefficient, and carbon dioxide coefficient of the indicator films obtained in Examples 1-11 and Comparative Examples 1-2 were measured. The water molecule permeability coefficient was measured using the water vapor permeability coefficient test method ASTM-E96 (1996), and the carbon dioxide permeability coefficient was measured using a carbon dioxide transmission rate tester (SYSTESTER, Jinan SYSTESTER Testing Technology Co., Ltd.). The measurement results are shown in Table 1.

[0080] Test Example 2

[0081] The color change behavior of the indicator films obtained in Example 1 and Comparative Example 1 was recorded under conditions of 25°C and 50% RH. The color of the smart films was measured using a colorimeter. The measurement results are shown in Table 2. L represents lightness and darkness; larger values ​​indicate lightness, and smaller values ​​indicate darkerness; A represents red and green; larger values ​​indicate redness, and smaller values ​​indicate greenness; and B represents yellow and blue; larger values ​​indicate yellowness, and smaller values ​​indicate blueness.

[0082] Figure 1 This is a comparative diagram showing the storage color change behavior of Example 1 of the present invention and Comparative Example 1. Figure 1 It can be seen that in the examples, the color change behavior of the membrane is slow and can last up to 16 days, while the membrane prepared in the comparative example begins to change color slowly on the 8th day.

[0083] Test Example 3

[0084] Fresh shiitake mushrooms were subjected to a freshness test using the indicator film obtained in Example 1 and commercially available plastic wrap (the test method was based on the Technical Specification for Storage and Transportation of Agaricus bisporus and Flammulina velutipes, NY T 1934-2010). Fresh shiitake mushrooms without any film treatment were used as blank controls. The test results are shown in Table 3.

[0085] Table 1

[0086]

[0087]

[0088] As shown in Table 1, the contact angle of the indicator membrane increases with the addition of the montmorillonite-amino acid-water dispersion, indicating that the hydrophobicity of the indicator membrane improves, effectively slowing the entry of water into the membrane. Furthermore, the water and carbon dioxide permeability coefficients of the indicator membrane decrease with the addition of the montmorillonite-amino acid-water dispersion, indicating that the permeation rate of water and carbon dioxide molecules through the indicator membrane decreases. This, in turn, slows the contact rate between water and carbon dioxide and the anthocyanins in the indicator membrane, extending the indicator membrane's indication period.

[0089] Table 2

[0090]

[0091] As can be seen from Table 2, the brightness of all indicator films did not change significantly. The A value (red-green) of the film prepared in Example 1 continued to rise within 14 days of storage, reaching -10.06 on the 14th day, and its B value (yellow-blue) continued to rise, reaching 11.97 on the 14th day. However, the A value (red-green) of the film prepared in Comparative Example 1 slowed down its rising trend on the 10th day, reaching -13.95 on the 14th day, and its B value (yellow-blue) rose slowly, reaching 8.28 on the 14th day. This shows that the film of Example 1 has a longer-lasting indicator effect.

[0092] Table 3

[0093]

[0094]

[0095] As shown in Table 3, the indicator film of Example 1 has certain antioxidant activity due to the addition of anthocyanins, which can significantly inhibit the browning of edible fungi during storage and extend the shelf life of edible fungi.

[0096] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A food freshness intelligent indicator film, characterized in that: include: Montmorillonite, amino acids, pullulan, and anthocyanins; wherein the montmorillonite and amino acids are used to change the free volume of the cavities in the pullulan matrix; The mass ratio of the montmorillonite, amino acid, pullulan, and anthocyanin is (5-20): (25-50): (15-30): (3-6). The smart indicator film is prepared by a method comprising the following steps: mixing a montmorillonite-amino acid-water dispersion with a pullulan-anthocyanin-water dispersion to obtain a film-forming liquid, and performing a film-forming treatment on the film-forming liquid.

2. The smart indicator film according to claim 1, characterized in that: The pH value of the smart indicator film is 8-10.

3. The smart indicator film according to claim 1, characterized in that: The pH of the smart indicator membrane is 5-6.

4. A method for preparing the food freshness intelligent indicator film according to any one of claims 1 to 3, characterized in that: The following steps are involved: The montmorillonite-amino acid-water dispersion is mixed with the pullulan-anthocyanidin-water dispersion to obtain a film-forming liquid, and the film-forming liquid is subjected to a film-forming treatment.

5. The preparation method according to claim 4, characterized in that The montmorillonite-amino acid-water dispersion is obtained by mixing a montmorillonite aqueous solution with a mass fraction of 1-3% and an amino acid aqueous solution with a concentration of 0.1-0.2 g / mL in a volume ratio of 1:1-2.

6. The preparation method according to claim 5, characterized in that Pullulan, anthocyanin and water are mixed in a mass ratio of 5:1:(40-250) to obtain the pullulan-anthocyanin-water dispersion.

7. The preparation method according to claim 6, characterized in that The montmorillonite-amino acid-water dispersion and the pullulan-anthocyanidin-water dispersion are mixed in a ratio of 1:1 to obtain the film-forming solution.

8. The preparation method according to claim 4, characterized in that The film forming process includes: degassing the film forming liquid at a vacuum degree of 0.09 MPa for 20 minutes and then casting.

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