CN115449171B - Preparation method of high-strength high-toughness starch-based pH response type intelligent indication film - Google Patents

Abstract

The invention discloses a preparation method of a high-strength high-toughness starch-based pH response intelligent indication film. The visual intelligent indicating film prepared from the purple cabbage pigment has sensitive response to pH value change in the environment, can accurately feed back the freshness information of meat foods, is expected to be applied to real-time monitoring of the freshness of the meat foods, has improved mechanical properties compared with a starch-based film with single components, has degradability, is nontoxic and harmless, and has wide application prospect.

Description

Preparation method of high-strength and high-toughness starch-based pH-responsive intelligent indicator film

Technical Field

The present invention relates to the technical field of intelligent packaging and food quality detection, and in particular to a method for preparing a high-strength and high-toughness starch-based pH-responsive intelligent indicator film.

Background technique

In the National Food Safety Standard for Fresh (Frozen) Livestock and Poultry Products (GB 2707-2016), freshness has become an important indicator for judging the quality of meat products. However, in order to extend the shelf life, large supermarkets usually store meat products in sealed packages, making it difficult to directly judge their freshness through sensory perception. Some packaged meat products may even deteriorate before the shelf life due to storage and transportation. Therefore, rapid non-destructive testing of the freshness of meat products in sealed packages has important practical value.

Meat products are rich in protein. Under the decomposition of bacteria, nitrogen-containing amino acids undergo decarboxylation or deamination reactions to produce ammonia/amines, namely volatile basic total nitrogen (TVB-N). The existing TVB-N test method is mainly carried out according to the chemical titration method (GB/T5009.44-2003), which requires professional technicians to operate. The process is complicated and time-consuming, and cannot meet the needs of real-time detection. The freshness indicator film has the advantages of small size, degradability, high strength and visualization. It can react with ammonia/amines in meat products, causing the color of the indicator film to change, thereby indicating the freshness of the food.

However, the existing intelligent indicator films have the following problems:

(1) When natural anthocyanins are combined with other substances, they may have problems such as poor stability, easy degradation by light, and easy oxidation by oxygen, which limits their promotion and application.

(2) The mechanical properties, degradability and stability of the smart indicator film are poor, and its comprehensive performance needs to be further improved.

(3) Currently, the chemically synthesized freshness indicators commonly used, such as bromocresol green, methyl red, and bromocresol purple, are toxic and pose safety risks.

Summary of the invention

The main purpose of the present invention is to provide a method for preparing a high-strength and high-toughness starch-based pH-responsive smart indicator film, so as to solve the problems of low strength, easy moldiness, and complicated preparation steps of the starch-based smart indicator film in the prior art, and at the same time solve the environmental protection and safety problems of commonly used chemically synthesized freshness indicators such as bromocresol green, methyl red, and bromocresol purple.

The technical solution adopted by the present invention to solve the technical problem is:

A method for preparing a high-strength and high-toughness starch-based pH-responsive intelligent indicator film specifically comprises the following steps:

(1) Starch and polyvinyl alcohol are placed in a heating container, glycerol is added, and distilled water is poured in and mixed uniformly to prepare a starch-polyvinyl alcohol solution; the glycerol is 20% of the sum of the mass of the starch and the polyvinyl alcohol. After constant volume, the mass fraction of the starch-polyvinyl alcohol in the starch-polyvinyl alcohol solution is 10%.

Starch is a natural polyhydroxy polymer material with abundant resources, low price, good biocompatibility and biodegradability. The reason for choosing polyvinyl alcohol and starch to make the film is that PVA, as a synthetic water-soluble polymer material, has a single C-C main chain and a polyhydroxy strong hydrogen bond molecular structure, and has good toughness, biocompatibility and mechanical properties. The role of glycerol is to enhance the gas barrier properties of the starch-based film and improve its transparency. When its addition amount is 20% of the total mass of starch-polyvinyl alcohol, the transparency is the highest. The starch used is soluble starch, the PVA specification is 1788, and the solubility is 88%.

(2) Gelatinize in a water bath, then add CNC, continue heating and stirring until the solution becomes translucent, and stop heating; preferably, gelatinize in a water bath at 95° C. for 1 h.

CNC can be used as a reinforcing agent to enhance the strength of composite materials, which can effectively improve the performance of starch film and reduce water absorption. A digital display constant temperature water bath is used for heating, and a heat collecting magnetic stirrer is used for stirring.

(3) After cooling to room temperature, purple cabbage pigment is added to the mixed solution, and ultrasonic dispersion is performed using a 100W ultrasonic cleaning machine.

The main component of purple cabbage pigment is anthocyanin. Compared with other sources, it contains a higher proportion of acylated anthocyanin and is more stable than other sources. It is also a non-toxic and harmless natural pigment, and it will show different colors as the pH value changes. Use an ultrasonic cleaner for shaking.

(4) Pour 25 mL of mixed solution B into a plastic culture dish to form a film, dry it in a constant temperature drying oven, then remove the film and store it for later use.

In the above-mentioned method for preparing a high-strength and high-toughness starch-based pH-responsive intelligent indicator film, the plastic culture dish is square with a side length of 13 cm.

The above-mentioned method for preparing a high-strength and high-toughness starch-based pH-responsive intelligent indicator film, the starch is soluble starch, the PVA specification is 1788 type, and the solubility is 88%.

In the above-mentioned method for preparing a high-strength and high-toughness starch-based pH-responsive intelligent indicator film, in step (1), the ratio of starch to polyvinyl alcohol is 4:6, and polyvinyl alcohol is beneficial to enhancing the mechanical properties of the indicator film; glycerol is used as a plasticizer and has a good plasticizing effect, so that the material has better comprehensive properties.

In the above-mentioned method for preparing a high-strength and high-toughness starch-based pH-responsive intelligent indicator film, in step (2), the content of cellulose nanocrystals is 6% of the sum of the mass of starch and polyvinyl alcohol, which is beneficial to improving the physical properties of the indicator film and accelerating its degradation rate.

In the above-mentioned method for preparing a high-strength and high-toughness starch-based pH-responsive intelligent indicator film, in step (3), the content of purple cabbage pigment is 5% of the sum of the mass of starch and polyvinyl alcohol.

In the above-mentioned method for preparing a high-strength and high-toughness starch-based pH-responsive intelligent indicator film, in step (4), the oven temperature is 50° C. and the drying time is 24 hours.

A high-strength and high-toughness starch-based pH-responsive intelligent indicator film prepared by any of the preparation methods described above.

The high-strength and high-toughness starch-based pH-responsive intelligent indicator film prepared by the preparation method described in any of the above items has a dark pink color when the pH value is 3; a light red color when the pH value is 5; a blue-purple color when the pH value is 7; a green color when the pH value is 9-11; and a light yellow color when the pH value is 13.

The high-strength and high-toughness starch-based pH-responsive intelligent indicator film prepared by any of the above preparation methods will not be moldy or spotty within 100 days in an environment with a relative humidity of 50%.

The high-strength and high-toughness starch-based pH-responsive intelligent indicator film prepared by the preparation method described in any of the above items has a tensile strength of 142-156 MPa and an elongation at break of 7.57-10.27% when the purple cabbage pigment content is 3-7% of the sum of the mass of starch and polyvinyl alcohol; and a tensile strength of 112-148 MPa and an elongation at break of 10.25-16.75% when the cellulose nanocrystal CNC content is 4-6% of the sum of the mass of starch and polyvinyl alcohol.

The high-strength and high-toughness starch-based pH-responsive intelligent indicator film is used to indicate the freshness of meat products. When the color of the indicator film changes to purple, it indicates that the meat begins to deteriorate.

The mechanism of purple cabbage pigment as an indicator is that during the spoilage process of meat, protein decomposition will produce a large amount of volatile organic amines such as trimethylamine, causing the pH value in the packaging space to rise. Anthocyanin is a non-toxic and harmless natural pigment, and it will show different colors as the pH value changes. Purple cabbage is a herbaceous plant composed of a variety of anthocyanins. The main component of anthocyanin pigments is pelargonium pigments. It contains flavonoids and can be used as a color developer for the freshness of meat.

The beneficial effects of the present invention are as follows: compared with anthocyanins from sources such as grape skin, purple cabbage pigment with a higher acylated anthocyanin content is more stable than grape skin anthocyanins; adding polyvinyl alcohol can improve the toughness of the indicator film; adding cellulose nanocrystals (CNC) can improve the strength and antibacterial property of the film, solve the problem that ordinary starch films are prone to mold, and at the same time can also increase the degradation rate of the film; at the same time, the preparation method of the present invention is simpler, has no special requirements on equipment, can greatly reduce the cost of the indicator film, and is convenient for large-scale promotion and use; purple cabbage pigment, starch, polyvinyl alcohol and cellulose nanocrystals are used in combination to improve the compatibility between different components of the film, thereby improving the flatness of the film.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a diagram showing the color change response results of a high-strength and high-toughness starch-based pH-responsive intelligent indicator membrane under different pH conditions of the present invention.

FIG2 is a surface scanning electron microscope image of a high-strength and high-toughness starch-based pH-responsive intelligent indicator film of the present invention.

FIG3 is a graph showing the biodegradability of a high-strength and high-toughness starch-based pH-responsive intelligent indicator film according to the present invention.

FIG. 4 is a graph showing the mechanical properties test results of high-strength and high-toughness starch-based pH-responsive intelligent indicator films prepared with different purple cabbage pigment addition ratios.

FIG5 is a graph showing the mechanical properties test results of high-strength and high-toughness starch-based pH-responsive intelligent indicator films made with different CNC addition ratios.

FIG6 is a graph showing the stability analysis results of a high-strength and high-toughness starch-based pH-responsive intelligent indicator film of the present invention.

Detailed ways

In the PSCA indicator film of the present invention, P: PVA; S: starch; C: cellulose nanocrystal; A: purple cabbage pigment.

Example 1

A method for preparing a high-strength and high-toughness starch-based pH-responsive intelligent indicator film:

(1) Starch and polyvinyl alcohol are placed in a heating container at a certain mass ratio, specifically, the ratio of starch to polyvinyl alcohol is 4:6, and then glycerol is added in an amount of 20% of the total mass of starch and polyvinyl alcohol, and distilled water is poured in to mix evenly, and the volume is fixed to prepare a 10% (g/g) starch-polyvinyl alcohol solution.

(2) Heat and stir in a 95°C water bath for 1 hour of gelatinization, then add a certain amount of CNC, specifically, the mass fraction of cellulose nanocrystals is 6% of the sum of the mass of starch and polyvinyl alcohol. Continue heating and stirring until the solution becomes translucent, stop heating, and obtain mixed solution A.

(3) After cooling to room temperature, a certain amount of purple cabbage pigment is added to the mixed solution, specifically, the mass fraction of purple cabbage pigment is 5% of the sum of the mass of starch and polyvinyl alcohol, and ultrasonic vibration dispersion is performed using an ultrasonic cleaning machine to obtain a mixed solution B.

(4) Pour 25 mL of mixed solution B into a plastic culture dish to form a film, dry it in a constant temperature drying oven, then remove the film and store it for later use. In this embodiment, the inventor uses an oven to dry the solvent, the oven temperature is set to 50° C., the drying time is 24 hours, and the ultrasonic time is 30 minutes. It should be noted that in order to standardize the size and shape of the indicator film, in this embodiment, the plastic culture dish is square with a side length of 13 cm.

Example 2

A method for preparing a high-strength and high-toughness starch-based pH-responsive intelligent indicator film:

(1) Starch and polyvinyl alcohol are placed in a beaker at a certain mass ratio, specifically, the ratio of starch to polyvinyl alcohol is 2:6, and then glycerol is added at 15% of the total mass of starch and polyvinyl alcohol, and distilled water is poured into the mixture to mix evenly to prepare a starch-polyvinyl alcohol solution with a mass fraction of 7%.

(2) Heat and stir in a 95°C water bath for 1 hour of gelatinization, then add a certain amount of CNC, specifically, the mass fraction of cellulose nanocrystals is 4% of the sum of the mass of starch and polyvinyl alcohol. Continue heating and stirring until the solution becomes translucent, stop heating, and obtain mixed solution A.

(3) After cooling to room temperature, a certain amount of purple cabbage pigment is added to the mixed solution (the amount added is the mass ratio of starch to polyvinyl alcohol), specifically, the mass fraction of purple cabbage pigment is 3% of the sum of the mass of starch and polyvinyl alcohol. Ultrasonic vibration dispersion is performed using an ultrasonic cleaning machine to obtain a mixed solution B.

(4) Pour 25 mL of mixed solution B into a plastic culture dish to form a film, dry it in a constant temperature drying oven, then remove the film and store it for later use. In this embodiment, the inventor uses an oven to dry the solvent, the oven temperature is set to 50° C., the drying time is 24 hours, and the ultrasonic time is 30 minutes. It should be noted that in order to standardize the size and shape of the indicator film, in this embodiment, the plastic culture dish is square with a side length of 13 cm.

Example 3

A method for preparing a high-strength and high-toughness starch-based pH-responsive intelligent indicator film:

(1) Starch and polyvinyl alcohol are placed in a beaker in a certain mass ratio, specifically, the ratio of starch to polyvinyl alcohol is 3:6, and then glycerol is added which is 25% of the total mass of starch and polyvinyl alcohol, and distilled water is poured in and mixed evenly to prepare a starch-polyvinyl alcohol solution with a mass fraction of 13%.

(2) Heat and stir in a 95°C water bath for 1 hour of gelatinization, then add a certain amount of CNC, specifically, the mass fraction of cellulose nanocrystals is 5% of the sum of the mass of starch and polyvinyl alcohol. Continue heating and stirring until the solution becomes translucent, stop heating, and obtain mixed solution A.

(3) After cooling to room temperature, a certain amount of purple cabbage pigment is added to the mixed solution (the amount added is the mass ratio of starch to polyvinyl alcohol), specifically, the mass fraction of purple cabbage pigment is 7% of the sum of the mass of starch and polyvinyl alcohol. Ultrasonic vibration dispersion is performed using an ultrasonic cleaning machine to obtain a mixed solution B.

(4) Pour 25 mL of mixed solution B into a plastic culture dish to form a film, dry it in a constant temperature drying oven, then remove the film and store it for later use. In this embodiment, the inventor uses an oven to dry the solvent, the oven temperature is set to 50° C., the drying time is 24 hours, and the ultrasonic time is 30 minutes. It should be noted that in order to standardize the size and shape of the indicator film, in this embodiment, the plastic culture dish is square with a side length of 13 cm.

Example 4

(1) Analysis of pH responsiveness of PSCA indicator membrane

The PSCA indicator film prepared in Example 1 was cut into a size of 1 cm × 3 cm, and immersed in pH buffer solutions of pH 3, 5, 7, 9, 11, and 13 for 1 min, and photographed and recorded. The results are shown in Figure 1. As can be seen from Figure 1, the indicator film material presents different colors at different pH values, which shows that the indicator film material has good response characteristics to pH value. When the pH value is 3, the color of the indicator film material is dark pink; when the pH value is 5, the color of the indicator film material gradually turns light red; when the pH value is 7, the color of the indicator film material is blue-purple; when the pH value is 9-11, the color of the indicator film material gradually turns green; when the pH value is 13, the indicator film presents light yellow. When the indicator film turns purple or green, it means that the meat is spoiled. When the indicator film turns light yellow, the meat is no longer edible.

(2) Performance test of PSCA indicator membrane and comparison membrane

According to the preparation method of Example 1, other conditions remain unchanged, and polyvinyl alcohol and starch; polyvinyl alcohol, starch, purple cabbage pigment; polyvinyl alcohol, starch, cellulose nanocrystals; polyvinyl alcohol, starch, cellulose nanocrystals, purple cabbage pigment are added respectively; four kinds of membranes, PS, PSA, PSC, and PSCA, are prepared respectively, and the prepared sample membranes are cut as required.

1. SEM analysis of sample membrane

The surface microstructure of the cut sample film was observed and photographed using a scanning electron microscope. Specifically, after drying the 1cm×1cm sample film, the surface was sprayed with gold, the acceleration voltage was 2KV, and the magnification was 10K. The results are shown in Figure 2. The SEM image mainly reflects the interface morphology and microstructure of the composite system. Generally speaking, if the chemical compatibility between substances is high, the surface is relatively flat, otherwise it will present a relatively rough small granular substance. As can be seen from Figure 2, the surface of the PSCA indicator film is smoother, indicating that the addition of purple cabbage pigment has a certain effect on improving the compatibility between starch, polyvinyl alcohol and cellulose nanocrystals.

2. Determination and analysis of sample membrane biodegradability

The four sample films were cut into pieces of about 5 cm × 5 cm, dried in a constant temperature drying oven until constant weight, and then buried in the soil. They were taken out every 3 days, dust was removed, and they were dried and weighed. The weight loss rate W% was calculated according to formula (1), which represents the biodegradability of the material:

W%＝(W ₀ -W ₁ )/W ₀ × 100% (1)

Wherein, _W0 is the mass of the sample before degradation, in g; _W1 is the mass of the sample after degradation, in g.

The weight loss data of the four types of sample membranes on the 7th and 27th days are shown in Table 1, and the actual pictures of the PSCA indicator membrane on the 1st, 7th, 17th and 27th days are shown in Figure 3. As the number of days buried in the soil increases, the degradation degree of the indicator membrane increases, and on the 27th day, it is almost degraded by 2/3.

(3) Mechanical properties analysis of PSCA indicator membrane

1. Effect of purple cabbage pigment content on the mechanical properties of indicator membrane

According to the preparation method of Example 1, other conditions remain unchanged, and purple cabbage pigment with mass fractions of 0, 3%, 5%, 7%, and 9% is added respectively to prepare PSCA indicator films with different purple cabbage pigment contents. The tensile mechanical properties of the indicator film, namely tensile strength (TS) and elongation at break (EB), were measured using a computer tensile tester. The test sample size was 130 mm × 15 mm, the nominal distance was 90 mm, the tensile speed was 300 mm/min, and the test method was based on the national standard GB/T1040.3-2006. The test results are shown in Figure 4 and Table 2.

Tensile strength TS: From the results, we can see that when the purple cabbage pigment content is 0-7%, the tensile strength gradually increases with the increase of purple cabbage pigment addition. When the addition amount is higher than 7%, due to the precipitation of some small pigment molecules, micropores and other defects appear on the film surface, and the tensile strength drops rapidly. The significant change of TS is likely related to the crystallization formation of the film and the interaction between atoms.

Elongation at break EB: For elongation at break, when the amount of purple cabbage pigment added is not higher than 7%, EB increases with the increase of pigment addition. The number of EB increases significantly, probably because purple cabbage pigment reduces the intermolecular force with the film-forming matrix, and the number of mobile polymer chains also increases. When the amount of pigment added continues to increase, EB decreases slightly.

2. Effect of CNC content on the mechanical properties of indicator membranes

According to the preparation method of Example 1, other conditions remain unchanged, and cellulose nanocrystal CNC with mass fractions of 0, 2%, 4%, 6%, and 8% are added respectively to prepare PSCA indicator films with different CNC contents. The tensile mechanical properties of the indicator film, namely tensile strength (TS) and elongation at break (EB), were measured using a computer tensile tester. The test sample size was 130 mm × 15 mm, the nominal distance was 90 mm, the tensile speed was 300 mm/min, and the test method was based on the national standard GB/T1040.3-2006. The test results are shown in Figure 5 and Table 3.

Tensile strength TS: As can be seen from the figure, when the CNC content is 0-6%, the tensile strength of the indicator film increases slowly with the increase of CNC content, and the tensile strength increases significantly when the CNC content is 6%. This is because the CNC surface has a large number of hydroxyl groups, which interact with starch molecules to form a rigid network structure, thereby improving the strength of the material. When the CNC addition amount is 6-8%, the tensile strength of the indicator film material decreases significantly with the increase of CNC content. This is generally because when the CNC dosage is too much, its distribution in the starch matrix is uneven, and it is easier to agglomerate, which significantly reduces the tensile strength of the indicator film material.

Elongation at break EB: As can be seen from the figure, when the CNC content is 0-6% of the sum of the mass of starch and polyvinyl alcohol, the elongation at break of the indicator film increases slowly with the increase of CNC content, and the elongation at break increases significantly when the CNC content is 6%. When the CNC addition amount is 6-8% of the sum of the mass of starch and polyvinyl alcohol, the elongation at break of the indicator film material decreases significantly with the increase of CNC content.

In summary, in this experiment, when the content of purple cabbage pigment is 5% of the sum of the mass of starch and polyvinyl alcohol, and when the content of CNC is 6%, the material exhibits high strength and high toughness mechanical properties.

(4) Determination and analysis of PSCA indicator membrane stability

In order to investigate the stability of the PSCA indicator film, the indicator film prepared in Example 1 was placed in a dryer at a relative humidity of 50%, and was taken out and photographed after the 50th and 100th days. The actual picture is shown in FIG6 , and no signs of mold, spots, etc. were found on the surface of the indicator film.

The present invention discloses a method for preparing a high-strength and high-toughness starch-based pH-responsive intelligent indicator film. The present invention uses starch/PVA as a matrix, glycerol as a plasticizer, CNC as a reinforcing agent, and purple cabbage pigment as an indicator, and adopts a cast film method to prepare the starch/PVA/CNC/purple cabbage pigment indicator film. This visual intelligent indicator film made with purple cabbage pigment is sensitive to changes in pH in the environment and can accurately feedback information on the freshness of meat products. This intelligent indicator film is expected to be used in real-time monitoring of the freshness of meat products. At the same time, compared with a single-material starch-based film, this intelligent indicator film has high-strength and high-toughness mechanical properties, is degradable, non-toxic and harmless, and has broad application prospects.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Table 1 Weight loss rate of sample films

Table 2 Effect of purple cabbage pigment content on the mechanical properties of indicator membrane

Purple cabbage pigment content (%) Tensile strength(Mpa) Elongation at break (%) 0 96 6.19 3 142 7.57 5 152 10.55 7 156 10.27 9 96 10.19

Table 3 Effect of cellulose nanocrystal CNC content on the mechanical properties of indicator membrane

CNC content (%) Tensile strength(Mpa) Elongation at break (%) 0 105 9.14 2 109 9.19 4 112 10.25 6 148 16.75 8 37 11.27

Claims (8)

1. A preparation method of a high-strength high-toughness starch-based pH response intelligent indication film is characterized by comprising the following steps: the method comprises the following steps:

(1) Placing starch and polyvinyl alcohol PVA in a heating container, adding glycerol, pouring distilled water, and uniformly mixing to prepare a starch-polyvinyl alcohol solution;

(2) Pasting in a water bath, then adding cellulose nanocrystalline CNC, continuing heating and stirring until the solution is semitransparent, and stopping heating to obtain a mixed solution A;

(3) After cooling to room temperature, adding purple cabbage pigment into the mixed solution A, and performing ultrasonic dispersion by using an ultrasonic cleaner to obtain a mixed solution B;

(4) Pouring the mixed solution B into a flat bottom container to form a film, drying in a constant temperature drying oven, uncovering the film, and preserving for later use;

In the step (1), starch and polyvinyl alcohol are placed in a heating container, glycerol accounting for 15-25% of the sum of the mass of the starch and the mass of the polyvinyl alcohol is added, distilled water is poured into the container to be uniformly mixed, the volume is fixed, and a starch-polyvinyl alcohol solution with the mass fraction of 7-13% is prepared, wherein the mass ratio of the starch to the polyvinyl alcohol is 2-4:6;

in the step (2), adding CNC accounting for 6% of the sum of the mass of the starch and the mass of the polyvinyl alcohol;

in the step (3), adding purple cabbage pigment accounting for 5% of the sum of the mass of starch and polyvinyl alcohol into the mixed solution A after cooling to room temperature, and performing ultrasonic dispersion by using an ultrasonic cleaner to obtain a mixed solution B;

when the pH value is 3, the color of the indicating film material is dark pink; when the pH value is 5, the color of the indicating film material gradually changes into light red; when the pH value is 7, the color of the indicating film material is blue-violet; when the pH value is 9-11, the color of the indicating film material gradually changes into green; at a pH of 13, the indicator film appears pale yellow, indicating that the meat is spoiled when the indicator film turns purple or green, and that the meat is no longer edible when the indicator film turns pale yellow.

2. The method for preparing the high-strength high-toughness starch-based pH response type intelligent indication film according to claim 1, which is characterized by comprising the following steps: in the step (1), the glycerol is 20% of the sum of the mass of the starch and the mass of the polyvinyl alcohol, and after the volume is fixed, the mass fraction of the starch-polyvinyl alcohol in the starch-polyvinyl alcohol solution is 10%.

3. The method for preparing the high-strength high-toughness starch-based pH response type intelligent indication film according to claim 1, which is characterized by comprising the following steps: in the step (2), gelatinizing for 1h in a water bath kettle at the temperature of 95 ℃, and then adding cellulose nanocrystalline with the mass sum of 6% of starch and polyvinyl alcohol.

4. The method for preparing the high-strength high-toughness starch-based pH response type intelligent indication film according to claim 1, which is characterized by comprising the following steps: in the step (1), the mass ratio of the starch to the polyvinyl alcohol is 4:6.

5. The method for preparing the high-strength high-toughness starch-based pH response type intelligent indication film according to claim 1, which is characterized by comprising the following steps: the starch is soluble starch, PVA specification is 1788 type, and solubility is 88%.

6. The method for preparing the high-strength high-toughness starch-based pH response type intelligent indication film according to claim 1, which is characterized by comprising the following steps: in step (4), the oven temperature was 50℃and the drying time was 24 hours.

7. The high strength high toughness starch-based pH responsive intelligent indicator film made according to the method of any one of claims 1-6, wherein the indicator film material is dark pink in color when the pH is 3; when the pH value is 5, the color of the indicating film material gradually changes into light red; when the pH value is 7, the color of the indicating film material is blue-violet; when the pH value is 9-11, the color of the indicating film material gradually changes into green; at a pH of 13, the indicator film appeared pale yellow.

8. The high strength, high toughness starch-based pH responsive intelligent indicator film of claim 7 for indicating freshness of meat products, wherein the color of the indicator film changes from red to purple, indicating that the meat begins to deteriorate.