Anthocyanin intelligent preservative film and preparation method thereof

Abstract

This invention discloses an anthocyanin-infused smart food preservation film, made from the following raw materials in parts by weight: 1.5 parts starch, 0.8-1 parts polyvinyl alcohol, 1.0-1.3 parts glycerol, 0.6-1 parts anthocyanin slow-release granules, 0.15-0.2 parts rosemary extract, and 0.15-0.2 parts nanocrystalline cellulose. It exhibits clear pH change indication, high stability, good preservation effect, and excellent mechanical properties.

Description

Technical Field

[0001] This invention relates to the field of food preservation film technology, and in particular to anthocyanin-infused smart food preservation film and its preparation method. Background Technology

[0002] Food is highly susceptible to spoilage due to external conditions such as light, air, and mechanical stress. In recent years, cases of abdominal pain, diarrhea, and other illnesses caused by consuming food containing bacteria or toxic chemicals have become increasingly common. Packaging, as the final step in the food production process, plays a crucial role in food quality protection, storage, and sales. With consumers paying increasing attention to food safety and fierce market competition, there is a growing demand for food packaging technology. Retailers and consumers are most concerned about food freshness, which is a vital indicator of food quality and safety. Consumers generally evaluate food quality based on the expiration date on the packaging, but for fresh foods, the expiration date is not a reliable indicator. Currently, methods for testing food freshness are complex, requiring professional operation, expensive equipment, and time-consuming processes. They also often involve destructive treatment of the food, making them unsuitable for rapid on-site testing. Therefore, developing a smart packaging product that indicates food freshness is particularly important.

[0003] Anthocyanins, as a type of natural gas-sensitive material, can react with putrefactive gases to produce obvious color changes and are widely found in fruits, flowers, and vegetables, thus making them suitable for use in freshness-indicating packaging materials. Currently, there is extensive research on the application of anthocyanins in intelligent visual food preservation indicator films, but certain problems exist: some biodegradable raw materials are used, therefore the strength of the preservation film needs improvement; furthermore, the chemical properties of anthocyanins are unstable, and changes in environmental factors such as temperature, pH, oxygen, and light can lead to their degradation during the preparation process, thereby affecting the indication effect and stability of the preservation film. Summary of the Invention

[0004] In view of this, the purpose of this invention is to address the shortcomings of the prior art by providing an anthocyanin-infused smart preservation film that clearly indicates pH changes, exhibits high stability, good preservation effect, and excellent mechanical properties.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] An anthocyanin-infused smart food preservation film is made from the following raw materials in parts by weight: 1.5 parts starch, 0.8-1 parts polyvinyl alcohol, 1.0-1.3 parts glycerol, 0.6-1 parts anthocyanin slow-release granules, 0.15-0.2 parts rosemary extract, and 0.15-0.2 parts nanocrystalline cellulose.

[0007] Furthermore, the nanocrystalline cellulose is prepared by the following steps:

[0008] (1) Disperse microcrystalline cellulose in 10-15 times its weight of 60-65wt% p-toluenesulfonic acid solution, stir thoroughly at 65-70℃ for 3h, then add deionized water and centrifuge, remove the supernatant and continue centrifuging until the pH of the suspension is 7.0, concentrate and freeze dry to obtain solid powder.

[0009] (2) The solid powder was dispersed in 10-15 times its weight of 20-25 wt% ethylenediamine solution and stirred for 10 h. After the reaction was completed, the solution was dialyzed with methanol until the pH was constant. The resulting precipitate was freeze-dried to obtain nanocrystalline cellulose.

[0010] Furthermore, the anthocyanin sustained-release granules are prepared by the following steps:

[0011] (1) Prepare corn starch into starch milk with a mass fraction of 35-40%, adjust the pH to 9.0 with alkaline solution, then add 5% of the total amount of starch milk mixed acid, shake the reaction at 35-40℃, and maintain the pH of the system constant. After 2 hours, adjust the pH of the system to 6.5-7.0, filter, wash, dry and pulverize to obtain cross-linked starch;

[0012] (2) Prepare a suspension of cross-linked starch with water at a mass fraction of 30-35%, adjust the pH to 8.5, stir for 20-30 min, add octenyl succinic anhydride solution dropwise, and maintain the pH constant with alkaline solution. React for 3-4 h, adjust the pH to neutral with acid solution, filter, wash and dry to obtain modified cross-linked starch. The amount of octenyl succinic anhydride added is 2-3% of the total amount of cross-linked starch, and the octenyl succinic anhydride solution is an ethanol solution of octenyl succinic anhydride with a mass fraction of 25-30%.

[0013] (3) Mix the modified cross-linked starch with a citric acid-sodium citrate buffer solution at pH 5.4 at a weight ratio of 1:5. Heat the mixture to 50°C and add 3% of the total amount of modified cross-linked starch with a complex enzyme. React for 12 hours. Add 4 wt% sodium hydroxide solution to terminate the reaction. After filtration, wash and dry to obtain modified cross-linked porous starch.

[0014] (4) The modified cross-linked porous starch is mixed with an alcoholic solution of anthocyanin extract with a mass fraction of 2-3% and stirred for 2 hours. After centrifugation, it is freeze-dried and pulverized to obtain anthocyanin sustained-release particles. The weight ratio of the porous starch to the anthocyanin extract is 10:1-2.

[0015] Furthermore, the mixed acid in step (1) is a mixture of citric acid and acetic anhydride in a weight ratio of 1:20.

[0016] Furthermore, the complex enzyme in step (3) is a mixture of α-amylase and saccharifying enzyme in a weight ratio of 1:4.

[0017] Furthermore, the anthocyanin extract is prepared by the following steps:

[0018] After tearing fresh purple cabbage into pieces, wash it with distilled water and air dry it naturally. Then, put it into a Soxhlet extractor and use 50-60% ethanol solution as the extractant. Control the liquid-to-solid ratio at 35-40 mL / g and extract at 90℃ until the purple cabbage leaves are colorless to obtain anthocyanin alcohol solution. Finally, concentrate the anthocyanin alcohol solution by rotary evaporation at 50℃ in the dark to remove ethanol, and freeze-dry to obtain anthocyanin extract.

[0019] A method for preparing an anthocyanin-infused smart food preservation film includes the following steps:

[0020] (1) Weigh out the starch according to the amount, add an appropriate amount of water and stir, and add half of the glycerol. Stir and gelatinize at 100℃ for 30 minutes.

[0021] (2) Weigh out the polyvinyl alcohol according to the specified amount, add an appropriate amount of water and stir, then add the remaining glycerol and heat and stir at 100°C until dissolved;

[0022] (3) Mix the above polyvinyl alcohol solution and gelatinized starch, then add anthocyanin sustained-release granules, rosemary extract and nanocrystalline cellulose, stir evenly, remove bubbles and cast into a film.

[0023] The beneficial effects of this invention are:

[0024] 1. This application prepares an anthocyanin-infused smart preservation film, which contains anthocyanins that are highly sensitive to pH. Therefore, the freshness of the packaged food can be intuitively judged by the color change of the film. Moreover, the preservation film has excellent mechanical properties, good preservation effect, and strong stability.

[0025] 2. Adding a small amount of nanocrystalline cellulose to plastic wrap enhances its mechanical strength and flexibility due to its high flexibility and large specific surface area. In this application, the nanocrystalline cellulose is first acid-hydrolyzed with p-toluenesulfonic acid. Since p-toluenesulfonic acid is non-oxidizing, it reduces the generation of acid radicals after acid hydrolysis, thus increasing its stability. Then, it undergoes further treatment with ethylenediamine. The amino groups enter the cellulose and form hydrogen bonds or react with some groups, making the cellulose structure looser and exposing more active groups, thereby increasing its adhesion strength to the film-forming material.

[0026] 3. To increase the stability of anthocyanins, this application uses modified cross-linked porous starch for loading, which plays a role in slow release and stabilization, thereby reducing the degradation of anthocyanins during the preparation process. The modified cross-linked porous starch used is prepared by modifying and enzymatically hydrolyzing cross-linked starch. First, cross-linked starch is prepared by cross-linking corn starch with mixed acids, which improves the structural stability of the starch and reduces the structural breakage caused by subsequent enzymatic hydrolysis. Then, it is modified with octenyl succinic anhydride to further increase the interaction forces between the molecular chains of the cross-linked porous starch and increase structural stability. Finally, the cross-linked starch is enzymatically hydrolyzed with α-amylase and saccharifying enzyme to form a hollow structure in the starch granules, thereby increasing its adsorption performance for anthocyanins.

[0027] 4. In addition, a small amount of rosemary extract is added. Rosemary contains a variety of antioxidants such as flavonoids, terpenoids, and organic acids. It can prevent and delay rancidity or extend the shelf life in animal and vegetable oils, oily foods and meat products. Adding it to the plastic wrap in this application increases the preservation effect of the plastic wrap. Attached Figure Description

[0028] Figure 1 A graph showing the color change of plastic wrap at different pH levels;

[0029] Figure 2 This is a graph showing the preservation performance of plastic wrap. Detailed Implementation

[0030] The present invention will be further described below with reference to the accompanying drawings and embodiments. Example 1

[0031] An anthocyanin-infused smart food preservation film is made from the following raw materials in parts by weight: 1.5 parts starch, 0.8 parts polyvinyl alcohol, 1.0 part glycerol, 0.6 parts anthocyanin slow-release granules, 0.15 parts rosemary extract, and 0.15 parts nanocrystalline cellulose.

[0032] The rosemary extract is rosemary powder (Henan Kezhao Food Technology Co., Ltd.).

[0033] Nanocrystalline cellulose is prepared by the following steps:

[0034] (1) Disperse microcrystalline cellulose in 10 times its weight of 65wt% p-toluenesulfonic acid solution, stir thoroughly at 65℃ for 3h, then add deionized water and centrifuge, remove the supernatant and continue centrifuging until the pH of the suspension is 7.0, concentrate using a rotary evaporator and freeze dry to obtain solid powder.

[0035] (2) The solid powder was dispersed in 10 times its weight of 25wt% ethylenediamine solution and stirred for 10h. After the reaction was completed, the solution was dialyzed with methanol until the pH was constant. The resulting precipitate was freeze-dried to obtain nanocrystalline cellulose.

[0036] Anthocyanin sustained-release granules are prepared by the following steps:

[0037] (1) Prepare corn starch into starch milk with a mass fraction of 35%, adjust the pH to 9.0 with alkaline solution, then add 5% of the total amount of mixed acid of starch milk, shake the reaction at 35°C, and maintain the pH of the system constant. After 2 hours, adjust the pH of the system to 6.5, filter, wash, dry and pulverize to obtain cross-linked starch. The mixed acid in step (1) is a mixture of citric acid and acetic anhydride in a weight ratio of 1:20.

[0038] (2) The cross-linked starch was prepared into a suspension with a mass fraction of 30% by adding water, the pH was adjusted to 8.5, stirred for 20 min, octenyl succinic anhydride solution was added dropwise, and the pH was kept constant with alkaline solution. The reaction was carried out for 3 h, the pH was adjusted to neutral with acid solution, filtered, washed and dried to obtain modified cross-linked starch. The amount of octenyl succinic anhydride added was 2% of the total amount of cross-linked starch, and the octenyl succinic anhydride solution was an ethanol solution of octenyl succinic anhydride with a mass fraction of 30%.

[0039] (3) The modified cross-linked starch and the citric acid-sodium citrate buffer solution at pH 5.4 are mixed evenly at a weight ratio of 1:5. The temperature is raised to 50°C and 3% of the total amount of modified cross-linked starch complex enzyme is added. The reaction is carried out for 12 hours. The pH is adjusted to neutral by adding 4wt% sodium hydroxide solution to terminate the reaction. After filtration, washing and drying, the modified cross-linked porous starch is obtained. The complex enzyme in step (3) is a mixture of α-amylase and saccharifying enzyme at a weight ratio of 1:4.

[0040] (4) The modified cross-linked porous starch was mixed with an ethanol solution of anthocyanin extract with a mass fraction of 2% and stirred for 2 hours. After centrifugation, it was freeze-dried and pulverized to obtain anthocyanin sustained-release particles. The weight ratio of the porous starch to the anthocyanin extract was 10:1.

[0041] Anthocyanin extract is prepared by the following steps:

[0042] After tearing fresh purple cabbage leaves apart, wash them with distilled water and air dry them naturally. Then, place them in the extraction tube of a Soxhlet extractor. Before adding the purple cabbage leaves, place some cotton at the bottom. Pour 50% ethanol solution as the extraction solvent into the extraction flask, controlling the liquid-to-solid ratio at 40 mL / g. Extract at 90°C until the purple cabbage leaves are colorless to obtain anthocyanin alcohol solution. Finally, concentrate the anthocyanin alcohol solution by rotary evaporation at 50°C in the dark to remove the ethanol, and freeze-dry to obtain the anthocyanin extract.

[0043] A method for preparing an anthocyanin-infused smart food preservation film includes the following steps:

[0044] (1) Weigh out the starch according to the amount, add water to prepare a suspension with a mass fraction of 3%, stir and add half of the glycerol, and stir to gelatinize at 100℃ for 30 min;

[0045] (2) Weigh out the polyvinyl alcohol according to the specified amount, add water to prepare a mixture with a mass fraction of 2%, stir and add the remaining glycerol, heat and stir at 100°C until dissolved;

[0046] (3) Mix the above polyvinyl alcohol solution and gelatinized starch, then add anthocyanin slow-release granules, rosemary extract and nanocrystalline cellulose, stir evenly with a magnetic stirrer, remove bubbles with ultrasound, and cast into a film. Example 2

[0047] An anthocyanin-infused smart food preservation film is made from the following raw materials in parts by weight: 1.5 parts starch, 0.85 parts polyvinyl alcohol, 1.1 parts glycerol, 0.7 parts anthocyanin slow-release granules, 0.16 parts rosemary extract, and 0.16 parts nanocrystalline cellulose.

[0048] Nanocrystalline cellulose is prepared by the following steps:

[0049] (1) Disperse microcrystalline cellulose in 12 times its weight of 65wt% p-toluenesulfonic acid solution, stir thoroughly at 65℃ for 3h, then add deionized water and centrifuge, remove the supernatant and continue centrifuging until the pH of the suspension is 7.0, concentrate using a rotary evaporator and freeze dry to obtain solid powder.

[0050] (2) The solid powder was dispersed in 12 times its weight of 22wt% ethylenediamine solution and stirred for 10h. After the reaction was completed, the solution was dialyzed with methanol until the pH was constant. The resulting precipitate was freeze-dried to obtain nanocrystalline cellulose.

[0051] Anthocyanin sustained-release granules are prepared by the following steps:

[0052] (1) Prepare corn starch into starch milk with a mass fraction of 35%, adjust the pH to 9.0 with alkaline solution, then add 5% of the total amount of mixed acid of starch milk, shake the reaction at 35°C, and maintain the pH of the system constant. After 2 hours, adjust the pH of the system to 6.5, filter, wash, dry and pulverize to obtain cross-linked starch. The mixed acid in step (1) is a mixture of citric acid and acetic anhydride in a weight ratio of 1:20.

[0053] (2) Prepare a 30% mass fraction suspension of cross-linked starch with water, adjust the pH to 8.5, stir for 25 min, slowly add octenyl succinic anhydride solution, and maintain the pH constant with alkaline solution. React for 3.5 h, adjust the pH to neutral with acid solution, filter, wash and dry to obtain modified cross-linked starch. The amount of octenyl succinic anhydride added is 2.5% of the total amount of cross-linked starch, and the octenyl succinic anhydride solution is an ethanol solution of octenyl succinic anhydride with a mass fraction of 28%.

[0054] (3) The modified cross-linked starch and the citric acid-sodium citrate buffer solution at pH 5.4 are mixed evenly at a weight ratio of 1:5. The temperature is raised to 50°C and 3% of the total amount of modified cross-linked starch complex enzyme is added. The reaction is carried out for 12 hours. The reaction is terminated by adding 4wt% sodium hydroxide solution. After filtration, washing and drying, the modified cross-linked porous starch is obtained. The complex enzyme in step (3) is a mixture of α-amylase and saccharifying enzyme at a weight ratio of 1:4.

[0055] (4) The modified cross-linked porous starch was mixed with an alcoholic solution of anthocyanin extract with a mass fraction of 2.5% and stirred for 2 hours. After centrifugation, it was freeze-dried and pulverized to obtain anthocyanin sustained-release particles. The weight ratio of the porous starch to the anthocyanin extract was 10:1.5.

[0056] Anthocyanin extract is prepared by the following steps:

[0057] After tearing fresh purple cabbage leaves apart, wash them with distilled water and air dry them naturally. Then, place them in the extraction tube of a Soxhlet extractor. Before adding the purple cabbage leaves, place some cotton at the bottom. Pour 55% ethanol solution as the extraction solvent into the extraction flask, controlling the liquid-to-solid ratio at 38 mL / g. Extract at 90°C until the purple cabbage leaves are colorless to obtain anthocyanin alcohol solution. Finally, concentrate the anthocyanin alcohol solution by rotary evaporation at 50°C in the dark to remove the ethanol, and freeze-dry to obtain the anthocyanin extract. Example 3

[0058] An anthocyanin-infused smart food preservation film is made from the following raw materials in parts by weight: 1.5 parts starch, 0.9 parts polyvinyl alcohol, 1.2 parts glycerol, 0.8 parts anthocyanin slow-release granules, 0.18 parts rosemary extract, and 0.18 parts nanocrystalline cellulose.

[0059] Nanocrystalline cellulose is prepared by the following steps:

[0060] (1) Disperse microcrystalline cellulose in 14 times its weight of 62wt% p-toluenesulfonic acid solution, stir thoroughly at 70°C for 3 hours, then add deionized water and centrifuge, remove the supernatant and continue centrifuging until the pH of the suspension is 7.0, concentrate using a rotary evaporator and freeze dry to obtain solid powder.

[0061] (2) The solid powder was dispersed in 15 times its weight of 22wt% ethylenediamine solution and stirred for 10h. After the reaction was completed, the solution was dialyzed with methanol until the pH was constant. The resulting precipitate was freeze-dried to obtain nanocrystalline cellulose.

[0062] Anthocyanin sustained-release granules are prepared by the following steps:

[0063] (1) Prepare corn starch into a starch milk with a mass fraction of 40%, adjust the pH to 9.0 with alkaline solution, then add 5% of the total amount of mixed acid of starch milk, shake the reaction at 40°C, and maintain the pH of the system constant. After 2 hours, adjust the pH of the system to 7.0, filter, wash, dry and pulverize to obtain cross-linked starch. The mixed acid in step (1) is a mixture of citric acid and acetic anhydride in a weight ratio of 1:20.

[0064] (2) Prepare a suspension of cross-linked starch with water at a mass fraction of 32%, adjust the pH to 8.5, stir for 25 min, slowly add octenyl succinic anhydride solution dropwise, and maintain the pH constant with alkaline solution. React for 3.5 h, adjust the pH to neutral with acid solution, filter, wash and dry to obtain modified cross-linked starch. The amount of octenyl succinic anhydride added is 2.5% of the total amount of cross-linked starch, and the octenyl succinic anhydride solution is an ethanol solution of octenyl succinic anhydride with a mass fraction of 26%.

[0065] (3) The modified cross-linked starch and the citric acid-sodium citrate buffer solution at pH 5.4 are mixed evenly at a weight ratio of 1:5. The temperature is raised to 50°C and 3% of the total amount of modified cross-linked starch complex enzyme is added. The reaction is carried out for 12 hours. The reaction is terminated by adding 4wt% sodium hydroxide solution. After filtration, washing and drying, the modified cross-linked porous starch is obtained. The complex enzyme in step (3) is a mixture of α-amylase and saccharifying enzyme at a weight ratio of 1:4.

[0066] (4) The modified cross-linked porous starch was mixed with an alcoholic solution of anthocyanin extract with a mass fraction of 2.5% and stirred for 2 hours. After centrifugation, it was freeze-dried and pulverized to obtain anthocyanin sustained-release particles. The weight ratio of the porous starch to the anthocyanin extract was 10:1.5.

[0067] Anthocyanin extract is prepared by the following steps:

[0068] After tearing fresh purple cabbage leaves apart, wash them with distilled water and air dry them naturally. Then, place them in the extraction tube of a Soxhlet extractor. Before adding the purple cabbage leaves, place some cotton at the bottom. Pour 58% ethanol solution as the extraction solvent into the extraction flask, controlling the liquid-to-solid ratio at 36 mL / g. Extract at 90°C until the purple cabbage leaves are colorless to obtain an anthocyanin alcohol solution. Finally, concentrate the anthocyanin alcohol solution by rotary evaporation at 50°C in the dark to remove the ethanol, and freeze-dry to obtain the anthocyanin extract. Example 4

[0069] An anthocyanin-infused smart food preservation film is made from the following raw materials in parts by weight: 1.5 parts starch, 1 part polyvinyl alcohol, 1.3 parts glycerol, 1 part anthocyanin slow-release granules, 0.2 parts rosemary extract, and 0.2 parts nanocrystalline cellulose.

[0070] Nanocrystalline cellulose is prepared by the following steps:

[0071] (1) Disperse microcrystalline cellulose in 15 times its weight of 60wt% p-toluenesulfonic acid solution, stir thoroughly at 70℃ for 3h, then add deionized water and centrifuge, remove the supernatant and continue centrifuging until the pH of the suspension is 7.0, concentrate using a rotary evaporator and freeze dry to obtain solid powder.

[0072] (2) The solid powder was dispersed in 15 times its weight of 20wt% ethylenediamine solution and stirred for 10h. After the reaction was completed, the solution was dialyzed with methanol until the pH was constant. The resulting precipitate was freeze-dried to obtain nanocrystalline cellulose.

[0073] Anthocyanin sustained-release granules are prepared by the following steps:

[0074] (1) Prepare corn starch into a starch milk with a mass fraction of 40%, adjust the pH to 9.0 with alkaline solution, then add 5% of the total amount of mixed acid of starch milk, shake the reaction at 40°C, and maintain the pH of the system constant. After 2 hours, adjust the pH of the system to 7.0, filter, wash, dry and pulverize to obtain cross-linked starch. The mixed acid in step (1) is a mixture of citric acid and acetic anhydride in a weight ratio of 1:20.

[0075] (2) The cross-linked starch was mixed with water to prepare a suspension with a mass fraction of 35%, the pH was adjusted to 8.5, stirred for 30 min, octenyl succinic anhydride solution was slowly added dropwise, and the pH was kept constant with alkaline solution. The reaction was carried out for 3 h, the pH was adjusted to neutral with acid solution, filtered, washed and dried to obtain modified cross-linked starch. The amount of octenyl succinic anhydride added was 3% of the total amount of cross-linked starch, and the octenyl succinic anhydride solution was an ethanol solution of octenyl succinic anhydride with a mass fraction of 25%.

[0076] (3) The modified cross-linked starch and the citric acid-sodium citrate buffer solution at pH 5.4 are mixed evenly at a weight ratio of 1:5. The temperature is raised to 50°C and 3% of the total amount of modified cross-linked starch complex enzyme is added. The reaction is carried out for 12 hours. The reaction is terminated by adding 4wt% sodium hydroxide solution. After filtration, washing and drying, the modified cross-linked porous starch is obtained. The complex enzyme in step (3) is a mixture of α-amylase and saccharifying enzyme at a weight ratio of 1:4.

[0077] (4) The modified cross-linked porous starch was mixed with an alcoholic solution of anthocyanin extract with a mass fraction of 3% and stirred for 2 hours. After centrifugation, it was freeze-dried and pulverized to obtain anthocyanin sustained-release particles. The weight ratio of the porous starch to the anthocyanin extract was 10:2.

[0078] Anthocyanin extract is prepared by the following steps:

[0079] After tearing fresh purple cabbage leaves apart, wash them with distilled water and air dry them naturally. Then, place them in the extraction tube of a Soxhlet extractor. Before adding the purple cabbage leaves, place some cotton at the bottom. Pour 60% ethanol solution as the extraction solvent into the extraction flask, controlling the liquid-to-solid ratio at 35 mL / g. Extract at 90°C until the purple cabbage leaves are colorless to obtain an anthocyanin alcohol solution. Finally, concentrate the anthocyanin alcohol solution by rotary evaporation at 50°C in the dark to remove the ethanol, and freeze-dry to obtain the anthocyanin extract.

[0080] Comparative Example 1

[0081] Comparative Example 1 is a comparative example of Example 4, except that nanocrystalline cellulose was not added.

[0082] Comparative Example 2

[0083] Comparative Example 1 is a comparative example of Example 4, except that rosemary extract was not added.

[0084] Comparative Example 3

[0085] The difference between Comparative Example 3 and Example 4 is that the anthocyanin extract in Example 3 is not loaded, specifically:

[0086] An anthocyanin-infused smart food preservation film is made from the following raw materials in parts by weight: 1.5 parts starch, 1 part polyvinyl alcohol, 1.3 parts glycerol, 0.16 parts anthocyanin extract, 0.2 parts rosemary extract, and 0.2 parts nanocrystalline cellulose.

[0087] Performance testing

[0088] 1. The thickness, tensile strength, elongation at break (GB / T1040.3-2006), and transmittance of the films prepared in Examples 1-4 and Comparative Examples 1-3 were tested. The test results are shown in Table 1.

[0089] 2. Freshness Indication of the Membrane: The experiment simulated pH changes at different times during shrimp storage by preparing buffer solutions with pH values ​​ranging from 3.0 to 12.0 using HCl and NaOH solutions and a pH meter. The indicator membranes prepared in Example 4 were cut into squares of roughly the same size. The prepared pH solution was dropped onto the membranes, and the color change was observed. Another group had the preservation films prepared in Example 4 and Comparative Example 3 placed at room temperature for 7 days, and their color changes at different pH values ​​were measured again. For specific results, see [link to results]. Figure 1 .

[0090] 3. Test the preservation performance of the film.

[0091] Shrimp purchased from the supermarket were wiped with 75% ethanol. The shrimp meat was then cut into 3g pieces using a sterilized knife. The cut pieces were divided into three groups, and the shrimp meat in the two groups was wrapped with the plastic wrap prepared in Example 4 and Comparative Example 2, respectively. The blank control group was not wrapped with plastic wrap. The shrimp meat was refrigerated at 0–4°C. The pH of the shrimp meat was measured on days 0, 1, 3, 5, 7, and 9. The results are shown in [link to relevant documentation]. Figure 2 .

[0092] Table 1 Performance Test Data

[0093]

[0094] As can be seen from the test results in Table 1, the thickness of the plastic wrap prepared in this application is about 0.14-0.15 mm, the tensile strength is 52.52-56.18 MPa, the elongation at break is 68-73.6%, and it has high mechanical strength and good flexibility. As can be seen from the light transmittance data, the addition of nanocrystalline cellulose has little effect on the light transmittance of the plastic wrap. However, as can be seen from the data of Comparative Example 1, nanocrystalline cellulose can improve the mechanical strength of the plastic wrap.

[0095] Figure 1 The pH indication performance of plastic wrap was simulated, from Figure 1 As can be seen, the plastic wrap prepared in Example 4 of this application is red at pH 3, darkens at pH 5, turns bluish-purple at pH 6, and gradually turns light green as the alkalinity of the solution increases at pH 7-8. At pH 9.0, the green becomes even deeper, and at pH 12, the color turns yellow again. The plastic wrap exhibits a clear color gradient with changing pH, thus serving as an indicator.

[0096] The cling film prepared in Example 4 and Comparative Example 3 was placed at room temperature for 7 days, and the indicator performance was retested. It can be clearly seen that after 7 days, the cling film in Example 4 still has an indicator function, but the cling film in Comparative Example 3 does not show obvious color changes at different pH values ​​and no longer has an indicator function. This shows that the loading treatment of anthocyanins in this application does not affect the pH indicator function of anthocyanins, and can also improve the stability of anthocyanins.

[0097] Based on pH changes during shrimp storage, the spoilage of refrigerated shrimp can be divided into three stages: fresh meat with a pH of 7.2–7.4, slightly fresh meat with a pH of 7.4–7.8, and spoiled meat with a pH above 7.8. Figure 2It can be seen that the pH of the unwrapped control group increased relatively quickly, while the pH of the shrimp meat wrapped in plastic wrap in Example 4 and Comparative Example 2 increased relatively slowly. The unwrapped control group remained fresh for the first three days, then became secondary fresh meat from day 3 to day 7, and began to spoil on day 7. The group without rosemary began to become secondary fresh meat on day 5 and only completely spoiled on day 9. In contrast, the shrimp meat preserved with the plastic wrap prepared in Example 4 entered the secondary fresh meat state on day 7. Therefore, the plastic wrap prepared in this application has a good preservation effect, and rosemary can further enhance the preservation effect of the plastic wrap.

[0098] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Any other modifications or equivalent substitutions made by those skilled in the art to the technical solutions of the present invention, as long as they do not depart from the spirit and scope of the technical solutions of the present invention, should be covered within the scope of the claims of the present invention.

Claims

1. An anthocyanin intelligent preservative film, characterized in that: It is made from the following raw materials in parts by weight: 1.5 parts starch, 0.8-1 parts polyvinyl alcohol, 1.0-1.3 parts glycerol, 0.6-1 parts anthocyanin sustained-release granules, 0.15-0.2 parts rosemary extract, and 0.15-0.2 parts nanocrystalline cellulose; The nanocrystalline cellulose is prepared by the following steps: (1) Disperse microcrystalline cellulose in 10-15 times its weight of 60-65wt% p-toluenesulfonic acid solution, stir thoroughly at 65-70℃ for 3h, then add deionized water and centrifuge, remove the supernatant and continue centrifuging until the pH of the suspension is 7.0, concentrate and freeze dry to obtain solid powder. (2) The solid powder was dispersed in 10-15 times its weight of 20-25 wt% ethylenediamine solution and stirred for 10 h. After the reaction was completed, the mixture was dialyzed with methanol until the pH was constant. The resulting precipitate was freeze-dried to obtain nanocrystalline cellulose. The anthocyanin sustained-release granules are prepared by the following steps: (1) Prepare corn starch into starch milk with a mass fraction of 35-40%, adjust the pH to 9.0 with alkaline solution, then add 5% of the total amount of starch milk mixed acid, shake the reaction at 35-40℃, and maintain the pH of the system constant. After 2 hours, adjust the pH of the system to 6.5-7.0, filter, wash, dry and pulverize to obtain cross-linked starch; (2) Prepare a suspension of cross-linked starch with water at a mass fraction of 30-35%, adjust the pH to 8.5, stir for 20-30 min, add octenyl succinic anhydride solution dropwise, and maintain the pH constant with alkaline solution. React for 3-4 h, adjust the pH to neutral with acid solution, filter, wash and dry to obtain modified cross-linked starch. The amount of octenyl succinic anhydride added is 2-3% of the total amount of cross-linked starch, and the octenyl succinic anhydride solution is an ethanol solution of octenyl succinic anhydride with a mass fraction of 25-30%. (3) Mix the modified cross-linked starch with a citric acid-sodium citrate buffer solution at pH 5.4 at a weight ratio of 1:

5. Heat the mixture to 50°C and add 3% of the total amount of modified cross-linked starch with a complex enzyme. React for 12 hours. Add 4 wt% sodium hydroxide solution to terminate the reaction. After filtration, wash and dry to obtain modified cross-linked porous starch. (4) The modified cross-linked porous starch is mixed with an alcoholic solution of anthocyanin extract with a mass fraction of 2-3% and stirred for 2 hours. After centrifugation, it is freeze-dried and pulverized to obtain anthocyanin sustained-release particles. The weight ratio of the porous starch to the anthocyanin extract is 10:1-2.

2. The anthocyanin intelligent preservative film according to claim 1, characterized in that: characterized in that: The mixed acid in step (1) of the preparation of the anthocyanin sustained-release granules is a mixture of citric acid and acetic anhydride in a weight ratio of 1:

20.

3. The anthocyanin intelligent preservative film according to claim 1, characterized in that: The complex enzyme in step (3) of the preparation of the anthocyanin sustained-release granules is a mixture of α-amylase and saccharifying enzyme in a weight ratio of 1:

4.

4. The anthocyanin intelligent preservative film according to claim 1, characterized in that: The anthocyanin extract is prepared by the following steps: After tearing fresh purple cabbage into pieces, wash it with distilled water and air dry it naturally. Then, put it into a Soxhlet extractor and use 50-60% ethanol solution as the extractant. Control the liquid-to-solid ratio at 35-40 mL / g and extract at 90℃ until the purple cabbage leaves are colorless to obtain anthocyanin alcohol solution. Finally, concentrate the anthocyanin alcohol solution by rotary evaporation at 50℃ in the dark to remove ethanol, and freeze-dry to obtain anthocyanin extract.

5. A method of preparing the anthocyanin smart preservative film according to claim 1, characterized by: Includes the following steps: (1) Weigh out the starch according to the amount, add an appropriate amount of water and stir, and add half of the glycerol. Stir and gelatinize at 100℃ for 30 minutes. (2) Weigh out the polyvinyl alcohol according to the specified amount, add an appropriate amount of water and stir, then add the remaining glycerol and heat and stir at 100°C until dissolved; (3) Mix the above polyvinyl alcohol solution and gelatinized starch, then add anthocyanin sustained-release granules, rosemary extract and nanocrystalline cellulose, stir evenly, remove bubbles and cast into a film.

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