Mesoporous coating-based food freshness indicator strip and preparation method thereof

Abstract

The invention relates to a food freshness indicator strip based on a mesoporous coating and a preparation method of the food freshness indicator strip, and belongs to the technical field of food packaging. The PS-PLA copolymer is synthesized by adopting a two-step method of living free radical polymerization and ring-opening polymerization, the PS-PLA copolymer is used as a base material, and a regular mesoporous structure is prepared by selectively removing a PLA phase through alkaline solution etching. And adsorbing a bromocresol green indicator, and loading the bromocresol green indicator into the regular mesoporous structure to prepare the food freshness indicator strip. Volatile basic nitrogen released by the meat can change color of bromocresol green, so that indication of the freshness of the meat is realized.

Description

Technical Field

[0001] The invention relates to the technical field of food packaging, and in particular to a method for preparing a freshness indicator strip for perishable seafood and meat products by coating and selectively etching a block copolymer PS-PLA to prepare a mesoporous structure and adsorbing bromocresol green in the mesoporous material. Background Art

[0002] Food quality and safety are issues of widespread concern worldwide, especially during the storage and transportation of perishable foods such as seafood and meat. These foods are highly sensitive to environmental conditions and can easily go bad, which not only causes economic losses but may also cause serious food safety issues. Traditional food packaging methods mainly rely on sealed packaging and cold chain transportation to extend the shelf life of food. However, these methods have certain limitations and it is difficult to monitor the freshness and quality changes of food in real time.

[0003] Although Xinjiang is located inland, its aquaculture industry has developed rapidly in recent years due to its unique geographical and climatic conditions. Xinjiang has abundant and clean water resources and is far away from industrial pollution sources, making the aquaculture environment relatively superior. In particular, Xinjiang's cold-water fish, such as salmon and trout, are popular because of their delicious meat and rich nutrition. However, since these aquatic products have high requirements for storage conditions, it is crucial to ensure that they maintain optimal freshness during transportation and sales.

[0004] The regional advantages of Xinjiang aquatic products give local aquatic products unique market competitiveness, but at the same time, they also put forward higher requirements for their packaging and preservation. Effective food freshness monitoring technology can significantly improve the market value of Xinjiang aquatic products and ensure that they maintain high quality during long-distance transportation and sales.

[0005] At present, food freshness monitoring technologies mainly include chemical indicators, gas sensors, time temperature indicators (TTI) and smart packaging. Although these technologies can provide an indication of food status to a certain extent, they still have some shortcomings in practical applications:

[0006] Chemical indicators: Chemical indicators are a common type of freshness indicator technology that indicates the status of food by chemically reacting with specific ingredients in the food or packaging environment, thereby changing color or other physical properties. For example, some indicators can react to spoilage products such as ammonia or carbon dioxide. However, chemical indicators usually only target a single ingredient and are sensitive to environmental conditions, which may lead to misjudgment or failure.

[0007] Gas sensors: Gas sensors are used to detect changes in gas composition inside food packaging, such as oxygen, carbon dioxide or volatile organic compounds (VOCs). These sensors can provide more accurate detection results, but usually require complex sensing systems and external power supplies, increasing packaging costs and system complexity.

[0008] Time Temperature Indicator (TTI): TTI indicates the potential spoilage risk of food based on the time and temperature accumulation of food storage. Although TTI can help determine whether food has experienced inappropriate temperature conditions, it cannot directly reflect the actual quality changes inside the food.

[0009] Smart packaging: Smart packaging combines the above technologies and integrates monitoring, feedback and warning functions to achieve comprehensive monitoring of food status. However, the technical threshold of smart packaging is high, the cost is high and it is not easy to recycle, which limits its promotion in the low-cost market.

[0010] Block copolymers are a class of polymer materials with a multiphase structure, consisting of two or more polymer segments with different chemical properties. Due to the incompatibility between different blocks, block copolymers can spontaneously form various microphase-separated structures, such as spherical, columnar, lamellar or mesoporous structures. Based on these characteristics, block copolymers have been widely used in the field of functional materials, such as nanocomposites, membrane materials, drug delivery systems, etc.

[0011] Among them, polystyrene-polylactic acid (PS-PLA) block copolymers are ideal for developing functional packaging materials due to their good biocompatibility and easy processing. PS-PLA can be selectively etched to remove the PLA segment to form a film with a regular mesoporous structure. This mesoporous structure not only increases the specific surface area of ​​the material, but also provides abundant active sites that can be used to adsorb or capture target molecules.

[0012] In recent years, food freshness indication technology based on mesoporous materials has gradually attracted widespread attention. Mesoporous materials have become an ideal platform for the development of efficient sensing materials due to their high specific surface area, controllable pore size and excellent adsorption properties. By adsorbing pH indicators or other sensitive molecules in mesoporous materials, it is possible to detect gases or other indicators produced during food spoilage.

[0013] The present invention is based on this principle, by coating PS-PLA block copolymer on packaging film, selectively etching to form a mesoporous structure, and adsorbing bromocresol green as a pH indicator, to achieve real-time monitoring of food freshness. This method is not only simple in preparation process and low in cost, but also can provide fast and intuitive food quality indication, suitable for large-scale industrial applications, especially for the packaging of perishable seafood and meat products. Summary of the invention

[0014] The present invention relates to a food freshness indicator strip based on a mesoporous coating and a preparation method thereof, and belongs to the technical field of food packaging. The present invention adopts a two-step method of active free radical polymerization and ring-opening polymerization to synthesize a PS-PLA copolymer, and uses it as a substrate to selectively remove the PLA phase through alkaline solution etching to prepare a regular mesoporous structure. Then, by adsorbing a bromocresol green indicator and loading it into the regular mesoporous structure, a food freshness indicator strip is prepared. The volatile basic nitrogen released by meat can cause bromocresol green to change color, thereby realizing the indication of meat freshness.

[0015] The purpose of the present invention can be achieved through the following technical solutions:

[0016] A food freshness indicator strip based on a mesoporous coating comprises the following raw materials in parts by weight: 1-3 parts by weight of PS-PLA, 90-110 parts by weight of thinner, 100-300 parts by weight of etching solution, and 20-60 parts by weight of bromocresol green solution.

[0017] As a preferred technical solution of the present invention, the synthesis route of the PS-PLA is as follows:

[0018] As a preferred technical solution of the present invention, the preparation method of PS-PLA comprises the following steps:

[0019] S1. Dissolve neopentyl glycol in dichloromethane, and add sodium bicarbonate as a binding acid to the solution, add bromoisobutyryl bromide dropwise using a constant pressure funnel in an ice bath, stir at 15-25° C. for 20-28 hours, and remove excess solvent by reduced pressure distillation to obtain a crude product; purify the crude product using a silica gel column to obtain a light yellow liquid product, i.e., a double-end initiator Br-OH; the eluent is petroleum ether:ethyl acetate (v / v=15 / 1), and the product is a light yellow liquid; the mass ratio of the neopentyl glycol, bromoisobutyryl bromide, sodium bicarbonate and dichloromethane is 1:1.2-1.8:1.6-2.0:8-12;

[0020] S2, adding double-end initiator Br-OH, CuBr and styrene to a reaction bottle, adding solvent anhydrous toluene, ultrasonically treating and dissolving for 20-30 minutes, adding pentamethyldiethylenetriamine under nitrogen protection, and freeze-drying, placing the reaction system in an oil bath at 80-120°C, reacting for 3-5 hours, quenching the polymerization with liquid nitrogen, removing copper salt through a neutral alumina column or a silica gel column, and precipitating in methanol to obtain a polymer, filtering the polymer and vacuum drying to obtain the product PS-OH; the mass ratio of Br-OH, CuBr, styrene, pentamethyldiethylenetriamine and anhydrous toluene is 1:0.1-0.2:1-2:0.1-0.2:8-10;

[0021] S3. Completely dissolve PS-OH, lactide and stannous isooctanoate in toluene under an argon atmosphere, stir at 100-120°C for 3 hours, cool and add tetrahydrofuran to dilute the reaction solution, pour into methanol to precipitate to obtain white floccules, and obtain white solid PS-PLA by filtration and drying; the mass ratio of PS-OH, lactide, stannous isooctanoate, tetrahydrofuran and toluene is 1:0.5-1.2:0.01-0.1:2-4:8-12.

[0022] As a preferred technical solution of the present invention, the etching solution is a 1-3 mol / L NaOH aqueous solution.

[0023] As a preferred technical solution of the present invention, the concentration of the bromocresol green solution is 2-5wt%.

[0024] Furthermore, the method for preparing the food freshness indicator strip comprises the following steps:

[0025] (1) Coating and drying: dissolve the PS-PLA copolymer in thinner, print the PS-PLA solution on the packaging film material using a screen printer or a coating machine, and dry it at room temperature to form a uniform film;

[0026] (2) Selective etching: The dried PS-PLA film is immersed in an alkaline etching solution for 10-30 min to selectively remove the PLA phase and retain the PS matrix, thereby forming a film with a regular mesoporous structure;

[0027] (3) Adsorption of bromocresol green: applying a bromocresol green solution to the mesoporous coating to load the dye for 3-10 min; followed by washing and drying;

[0028] (4) Packaging integration: The prepared mesoporous film containing bromocresol green is integrated into food packaging materials and used as a freshness indicator.

[0029] Beneficial effects of the present invention:

[0030] (1) Bromocresol green is a pH indicator that can change color under different pH environments. When food begins to spoil, the acidic or alkaline gas produced will cause the color of bromocresol green to change, thereby intuitively displaying the freshness of the food. However, low concentrations of bromocresol green often cannot accurately indicate the freshness of meat. Therefore, the present invention proposes to use a highly efficient encapsulation carrier to encapsulate bromocresol green to improve its detection ability. The mesoporous structure provides a larger specific surface area, and more indicator molecules can be fixed in a unit volume, which increases the chance of the indicator contacting the environment, so that even small pH changes can be quickly sensed; the mesoporous structure ensures the uniform distribution of the indicator inside the material, avoids the phenomenon of local concentration being too high or too low, and ensures that each tiny area can respond to environmental changes, thereby improving the accuracy and sensitivity of the overall detection.

[0031] (2) The food freshness indicator strip based on the mesoporous structure of the present invention has a simple preparation process, low cost, and is easy to integrate into various food packaging, and is particularly suitable for perishable seafood and meat products. The color change of the indicator strip can intuitively and real-time reflect the freshness of the food, thereby improving food safety assurance. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to facilitate understanding by those skilled in the art, the present invention is further described below with reference to the accompanying drawings.

[0033] Figure 1 It is an indicator label printed on BOPP;

[0034] Figure 2 For instruction labels printed on BOPET;

[0035] Figure 3 This is a SEM image of the microporous structure of the indicator label on the BOPP packaging bag;

[0036] Figure 4 The SEM image of the microporous structure of the indicator label on BOPET;

[0037] Figure 5 Bromocresol green is loaded on the indicator label on the BOPP packaging bag;

[0038] Figure 6 Bromocresol green is loaded on the indicator label on the BOPET packaging bag;

[0039] Figure 7 After the indicator label on the BOPP packaging bag is kept above a 10% trimethylamine aqueous solution for 2 hours;

[0040] Figure 8 The indicator label on the BOPET packaging bag was stored above a 10% trimethylamine aqueous solution for 2 hours. DETAILED DESCRIPTION

[0041] In order to further explain the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the specific implementation methods, structures, features and effects of the present invention are described in detail below in conjunction with the accompanying drawings and preferred embodiments.

[0042] In the following examples and comparative examples, the BOPP was purchased from Chaozhou Xinhuang Plastic Film Company; BOPET was purchased from Longgang Daguyue Trading Co., Ltd. with a brand name of DZA.

[0043] Example 1

[0044] A food freshness indicator strip based on a mesoporous coating comprises the following raw materials in parts by weight: 2 parts by weight of PS-PLA, 100 parts by weight of thinner, 200 parts by weight of etching solution, and 40 parts by weight of bromocresol green solution.

[0045] The synthetic route of the PS-PLA is as follows:

[0046]

[0047] The preparation method of the PS-PLA comprises the following steps:

[0048] S1. Dissolve neopentyl glycol in dichloromethane, and add sodium bicarbonate as a binding acid to the solution, add bromoisobutyryl bromide dropwise using a constant pressure funnel in an ice bath, stir at 20°C for 24 hours, and remove excess solvent by reduced pressure distillation to obtain a crude product; purify the crude product using a silica gel column to obtain a light yellow liquid product, i.e., a double-end initiator Br-OH; the eluent is petroleum ether:ethyl acetate (v / v=15 / 1), and the product is a light yellow liquid; the mass ratio of the neopentyl glycol, bromoisobutyryl bromide, sodium bicarbonate and dichloromethane is 1:1.5:1.8:10;

[0049] S2, adding double-end initiator Br-OH, CuBr and styrene to a reaction bottle, adding solvent anhydrous toluene, ultrasonically treating and dissolving for 25 minutes, adding pentamethyldiethylenetriamine under nitrogen protection, and freeze-drying, placing the reaction system in an oil bath at 100°C, reacting for 4 hours, quenching the polymerization with liquid nitrogen, and then removing copper salt through a neutral alumina column or a silica gel column, and precipitating in methanol to obtain a polymer, filtering the polymer and vacuum drying to obtain the product PS-OH; the mass ratio of Br-OH, CuBr, styrene, pentamethyldiethylenetriamine and anhydrous toluene is 1:0.1:1.5:0.1:9;

[0050] S3. Completely dissolve PS-OH, lactide and stannous isooctanoate in toluene under an argon atmosphere, stir at 110°C for 3 hours, cool and add tetrahydrofuran to dilute the reaction solution, pour into methanol to precipitate to obtain white floccules, and obtain white solid PS-PLA by filtration and drying; the mass ratio of PS-OH, lactide, stannous isooctanoate, tetrahydrofuran and toluene is 1:1:0.05:3:10.

[0051] The etching solution is a 2 mol / L NaOH aqueous solution.

[0052] The concentration of the bromocresol green solution is 3 wt %.

[0053] The method for preparing the food freshness indicator strip comprises the following steps:

[0054] (1) Coating and drying: The PS-PLA copolymer is dissolved in thinner, and the PS-PLA solution is printed on the BOPP packaging film material by screen printing or coating machine, and dried at room temperature to form a circular film with a diameter of 1 cm; the porous coating appears white (such as the attached Figure 1 shown);

[0055] (2) Selective etching: The dried PS-PLA film was immersed in an alkaline etching solution for 20 min to selectively remove the PLA phase and retain the PS matrix, thereby forming a film with a regular mesoporous structure. The mesoporous structure in the coating (such as the attached Figure 3 shown);

[0056] (3) Adsorption of bromocresol green: Apply bromocresol green solution to the mesoporous coating to load the dye for 5 min; then wash with water and dry;

[0057] (4) Packaging integration: The prepared mesoporous film containing bromocresol green is integrated into food packaging materials and used as a freshness indicator (e.g., attached Figure 5 shown).

[0058] Example 2

[0059] A food freshness indicator strip based on a mesoporous coating comprises the following raw materials in parts by weight: 2 parts by weight of PS-PLA, 100 parts by weight of thinner, 200 parts by weight of etching solution, and 40 parts by weight of bromocresol green solution.

[0060] The synthetic route of the PS-PLA is as follows:

[0061]

[0062] The preparation method of the PS-PLA comprises the following steps:

[0063] S1. Dissolve neopentyl glycol in dichloromethane, and add sodium bicarbonate as a binding acid to the solution, add bromoisobutyryl bromide dropwise using a constant pressure funnel in an ice bath, stir at 20°C for 24 hours, and remove excess solvent by reduced pressure distillation to obtain a crude product; purify the crude product using a silica gel column to obtain a light yellow liquid product, i.e., a double-end initiator Br-OH; the eluent is petroleum ether:ethyl acetate (v / v=15 / 1), and the product is a light yellow liquid; the mass ratio of the neopentyl glycol, bromoisobutyryl bromide, sodium bicarbonate and dichloromethane is 1:1.5:1.8:10;

[0064] S2, adding double-end initiator Br-OH, CuBr and styrene to a reaction bottle, adding solvent anhydrous toluene, ultrasonically treating and dissolving for 25 minutes, adding pentamethyldiethylenetriamine under nitrogen protection, and freeze-drying, placing the reaction system in an oil bath at 100°C, reacting for 4 hours, quenching the polymerization with liquid nitrogen, and then removing copper salt through a neutral alumina column or a silica gel column, and precipitating in methanol to obtain a polymer, filtering the polymer and vacuum drying to obtain the product PS-OH; the mass ratio of Br-OH, CuBr, styrene, pentamethyldiethylenetriamine and anhydrous toluene is 1:0.1:1.5:0.1:9;

[0065] S3. Completely dissolve PS-OH, lactide and stannous isooctanoate in toluene under an argon atmosphere, stir at 110°C for 3 hours, cool and add tetrahydrofuran to dilute the reaction solution, pour into methanol to precipitate to obtain white floccules, and obtain white solid PS-PLA by filtration and drying; the mass ratio of PS-OH, lactide, stannous isooctanoate, tetrahydrofuran and toluene is 1:1:0.05:3:10.

[0066] The etching solution is a 2 mol / L NaOH aqueous solution.

[0067] The concentration of the bromocresol green solution is 3 wt %.

[0068] The method for preparing the food freshness indicator strip comprises the following steps:

[0069] (1) Coating and drying: Dissolve the PS-PLA copolymer in thinner, print the PS-PLA solution on the BOPET packaging film using a screen printer or a coating machine, and dry it at room temperature to form a uniform 1 cm × 2 cm rectangular film; the porous coating appears white as shown in the attached Figure 2 shown);

[0070] (2) Selective etching: The dried PS-PLA film was immersed in an alkaline etching solution for 20 min to selectively remove the PLA phase and retain the PS matrix, thereby forming a film with a regular mesoporous structure. The mesoporous structure in the coating (such as the attached Figure 4 shown);

[0071] (3) Adsorption of bromocresol green: Apply bromocresol green solution to the mesoporous coating to load the dye for 5 min; then wash with water and dry;

[0072] (4) Packaging integration: The prepared mesoporous film containing bromocresol green is integrated into food packaging materials and used as a freshness indicator (e.g., attached Figure 6 shown).

[0073] Comparative Example 1

[0074] On the basis of Example 1, PS-PLA is not etched, and the rest is consistent with Example 1.

[0075] Comparative Example 2

[0076] On the basis of Example 2, PS-PLA is not etched, and the rest is consistent with Example 2.

[0077] Performance Test:

[0078] The samples prepared in the example and the comparative example were fixed on 10% trimethylamine aqueous solution and 20% trimethylamine aqueous solution respectively, and the containers were sealed and left at room temperature for 1 h, 2 h and 3 h, and the color change of the coating on the indicator strip was observed.

[0079]

[0080] From the test results, it can be seen that the present invention prepares a regular mesoporous structure, adsorbs the bromocresol green indicator, loads it into the regular mesoporous structure, and prepares a food freshness indicator strip, which significantly improves the accuracy and sensitivity of detection.

[0081] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technical personnel in this field can make some changes or modify the technical contents disclosed above into equivalent embodiments without departing from the scope of the technical solution of the present invention. However, any brief modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A food freshness indicator strip based on a mesoporous coating, characterized in that: The method comprises the following raw materials in parts by weight: 1-3 parts by weight of PS-PLA, 90-110 parts by weight of thinner, 100-300 parts by weight of etching solution, and 20-60 parts by weight of bromocresol green solution.

2. The food freshness indicator strip based on the mesoporous coating according to claim 1, characterized in that: The synthetic route of the PS-PLA is as follows:

3. The food freshness indicator strip based on the mesoporous coating according to claim 1, characterized in that: The preparation method of the PS-PLA comprises the following steps: S1. Dissolve neopentyl glycol in dichloromethane, add sodium bicarbonate as a binding acid to the solution, add bromoisobutyryl bromide dropwise using a constant pressure funnel in an ice bath, stir at 15-25° C. for 20-28 hours, and remove excess solvent by reduced pressure distillation to obtain a crude product; purify the crude product using a silica gel column to obtain a light yellow liquid product, i.e., a double-end initiator Br-OH; the mass ratio of the neopentyl glycol, bromoisobutyryl bromide, sodium bicarbonate, and dichloromethane is 1:1.2-1.8:1.6-2.0:8-12; S2, adding double-end initiator Br-OH, CuBr and styrene to a reaction bottle, adding solvent anhydrous toluene, ultrasonically treating and dissolving for 20-30 minutes, adding pentamethyldiethylenetriamine under nitrogen protection, and freeze-drying, placing the reaction system in an oil bath at 80-120°C, reacting for 3-5 hours, quenching the polymerization with liquid nitrogen, removing copper salt through a neutral alumina column or a silica gel column, and precipitating in methanol to obtain a polymer, filtering the polymer and vacuum drying to obtain the product PS-OH; the mass ratio of Br-OH, CuBr, styrene, pentamethyldiethylenetriamine and anhydrous toluene is 1:0.1-0.2:1-2:0.1-0.2:8-10; S3. Completely dissolve PS-OH, lactide and stannous isooctanoate in toluene under an argon atmosphere, stir at 100-120°C for 3 hours, cool and add tetrahydrofuran to dilute the reaction solution, pour into methanol to precipitate to obtain white floccules, and obtain white solid PS-PLA by filtration and drying; the mass ratio of PS-OH, lactide, stannous isooctanoate, tetrahydrofuran and toluene is 1:0.5-1.2:0.01-0.1:2-4:8-12.

4. The food freshness indicator strip based on the mesoporous coating according to claim 1, characterized in that: The molecular weight of the PS-PLA ranges from 10000 g / mol to 40000 g / mol.

5. The food freshness indicator strip based on mesoporous coating according to claim 1, characterized in that: The etching solution is a 1-3 mol / L NaOH aqueous solution.

6. The food freshness indicator strip based on the mesoporous coating according to claim 1, characterized in that: The concentration of the bromocresol green solution is 2-5 wt %.

7. A method for preparing a food freshness indicator strip based on a mesoporous coating according to any one of claims 1 to 6, characterized in that: The following steps are involved: (1) Coating and drying: Dissolve the PS-PLA copolymer in thinner, print the PS-PLA solution on the packaging film material using a screen printer or a coating machine, and dry it at room temperature to form a uniform film; (2) Selective etching: The dried PS-PLA film is immersed in an alkaline etching solution for 10-30 min to selectively remove the PLA phase and retain the PS matrix, thereby forming a film with a regular mesoporous structure; (3) Adsorption of bromocresol green: applying a bromocresol green solution to the mesoporous coating to load the dye for 3-10 min; followed by washing and drying; (4) Packaging integration: The prepared mesoporous film containing bromocresol green is integrated into food packaging materials and used as a freshness indicator.

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