PH response indicating membrane as well as preparation method and application thereof

Abstract

The invention discloses a pH response indicating film as well as a preparation method and application thereof. The preparation method comprises the following steps: dissolving anthocyanin / curcumin mixed pigment powder in an ethanol solution; the preparation method comprises the following steps: dissolving mixed powder of carrageenan and gelatin in deionized water at 90 DEG C, adding glycerol, fully stirring, adding an anthocyanin / curcumin mixed pigment solution after the temperature is reduced to 60 DEG C, uniformly stirring and mixing, then adjusting the pH value to 6.0 + / -0.1, defoaming, and carrying out tape casting and standing on the liquid to form a film, so as to obtain an indication film outer layer; the preparation method comprises the following steps: dissolving chitosan powder in deionized water, adding linseed oil, then carrying out ultrasonic cell disruption, adjusting the pH value of an emulsion to 6.0 + / -0.1, and degassing to prepare a crude membrane emulsion; and pouring the crude membrane emulsion onto the outer layer of the indicating membrane, uniformly spreading, drying, and balancing in a drying box with the temperature of 25 DEG C and the relative humidity of 50% for 6 hours to obtain the pH response indicating membrane. The indication film prepared by the invention not only has good physicochemical properties, but also can sensitively and stably monitor the change of the freshness of food according to the change of the pH value of perishable meat.

Description

Technical Field

[0001] The invention relates to the technical field of food detection, and in particular to a pH response indicator film and a preparation method and application thereof. Background Art

[0002] In recent years, smart food packaging has attracted much attention due to its advanced features that can track food safety in real time. At present, there have been research reports at home and abroad on using purple sweet potato and blueberry anthocyanins and red cabbage and other plant pigments as natural indicators for smart food packaging. Among them, anthocyanins, as an edible natural pigment with a wide source (can be extracted from blueberries, mulberries, purple sweet potatoes, grape seeds, etc.), excellent water solubility, and strong pH sensitivity, can be used as indicators for smart food packaging, thereby better monitoring the safety of packaged food and providing information on the response of food to environmental conditions or determining shelf life.

[0003] The existing indicator films for intelligent food packaging have a narrow color change range, and the color-developing components in the indicator films have poor stability, and are prone to oxidation failure. Summary of the invention

[0004] In view of the above problems, the purpose of the present invention is to provide a pH-responsive indicator film and a preparation method and application thereof. The prepared pH-responsive indicator film can not only stably display color according to the pH change of food, but also has a wide color change range and also has good physical and chemical properties.

[0005] To achieve the above objectives, the present invention is implemented through the following technical solutions:

[0006] The present invention provides a method for preparing a pH-responsive indicator film, comprising the following steps:

[0007] S1, dissolving anthocyanin / curcumin mixed pigment powder in an ethanol solution to obtain an anthocyanin / curcumin mixed pigment solution;

[0008] S2, dissolving the mixed powder of carrageenan and gelatin in 90°C deionized water to obtain a mixed solution I, adding glycerol to the mixed solution I and stirring thoroughly, adding anthocyanin / curcumin mixed pigment solution after the temperature drops to 60°C, stirring and mixing to obtain a mixed solution II, then adjusting the pH to 6.0±0.1, and casting the liquid to form a film after defoaming to obtain an outer layer of the indicator film;

[0009] S3, dissolving chitosan powder in deionized water, adding linseed oil, and then subjecting the mixture to ultrasonic cell disruption, adjusting the pH value of the emulsion to 6.0±0.1 and degassing to obtain a crude membrane emulsion;

[0010] S4. Pour the crude film emulsion onto the outer layer of the indicator film and spread it evenly, then dry it in a 50°C forced air drying oven for 8 hours, and then balance it in a drying oven at 25°C and 50% relative humidity for 6 hours to obtain a pH responsive indicator film.

[0011] As a possible implementation manner, further, the anthocyanin / curcumin mixed pigment powder in step S1 is prepared by mixing anthocyanin powder and curcumin powder in a mass ratio of 1:1; and the concentration of the anthocyanin / curcumin mixed pigment solution is 0.04 g / mL.

[0012] As a possible implementation manner, further, the ethanol in step S1 is 47.5% ethanol.

[0013] As a possible implementation manner, further, in step S2, the mass ratio of carrageenan to gelatin is 4:6 to 6:4, the concentration of the mixed solution I is 0.016 to 0.017 g / mL; the amount of glycerol added is 1% of the mass of the mixed solution I; and the concentration of the anthocyanin / curcumin mixed pigment powder in the mixed solution II is 0.4 to 0.6 mg / mL.

[0014] As a possible implementation mode, further, in step S3, chitosan powder is dissolved in deionized water at 60° C.; the amount of chitosan powder added is 1-2% of the mass of deionized water; the amount of linseed oil added is 1% of the mass of deionized water; and the mixture is subjected to cell disruption under ultrasonic conditions of 480 W and 20 kHz for 5 minutes.

[0015] As a possible implementation manner, further, in step S4, 20 mL of the crude membrane emulsion is poured onto the outer layer of the indicator membrane and spread evenly.

[0016] As a preferred embodiment, preferably, the mass ratio of carrageenan to gelatin powder in step S2 is 1.11:1; and the concentration of anthocyanin / curcumin mixed pigment powder in the mixed solution II is 53.99 mg / 100 mL.

[0017] As a preferred implementation, preferably, the amount of chitosan powder added in step S3 is 1.70% of the mass of deionized water.

[0018] The pH-responsive indicator film prepared by the above preparation method can be applied to monitoring the freshness of food, and specifically, can be applied to monitoring the freshness of perishable meat (eg, fish).

[0019] The outer layer of the indicator film in the present invention is mainly composed of carrageenan, gelatin, and anthocyanin / curcumin mixed pigment. By mixing anthocyanin and curcumin, the instability of anthocyanin and the limitation of the color change range of curcumin can be effectively compensated, so that the indicator film has a wider color change range; the reasonable compounding of carrageenan and gelatin can form a structurally stable polysaccharide-protein system, and at the same time, it plays a role in protecting and embedding the easily oxidized anthocyanin / curcumin mixed pigment. Anthocyanin / curcumin mixed pigment not only has an antioxidant effect, but also can intuitively respond to the pH value changes of food by virtue of its own pH sensitivity. Different pH values ​​of food will make the mixed color pigment present different colors, thereby sensitively indicating the freshness of food.

[0020] The inner layer of the indicator film in the present invention is mainly composed of chitosan and linseed oil. Chitosan itself has good film-forming properties, biocompatibility and biodegradability, and also has the antioxidant activity of polysaccharides. However, chitosan is a hydrophilic colloid, which is easily permeable to water and air. Therefore, after adding linseed oil, a lipid nanoemulsion can be formed under certain conditions. The addition of hydrophobic oils and fats can greatly improve the water vapor and oxygen barrier properties of the film, and greatly slow down the oxidative corruption of food.

[0021] In addition, the linseed oil in the present invention is a kind of grease, containing α-linolenic acid, phytosterols, vitamin E, polyphenols and other active substances, with high nutritional value, and has multiple functions such as anti-oxidation, anti-cancer, anti-inflammatory, and hypotensive, but it is easily oxidized because it contains unsaturated bonds. The compounding of chitosan and linseed oil under certain conditions can not only protect the easily oxidized oil from being oxidized, but also improve the physical, chemical and biological properties of the film.

[0022] The beneficial effects of the present invention are as follows:

[0023] The pH-responsive double-layer intelligent indicator film prepared by the present invention not only has good physical and chemical properties (such as elongation at break (EAB), tensile strength (TS), water vapor permeability (WVP) and hydroxyl radical scavenging rate), but is also edible and can sensitively and stably monitor the freshness changes of perishable meats such as fish according to the pH value changes. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0025] Figure 1 This is a physical picture of the pH response indicator film prepared in Example 1.

[0026] Figure 2 This is a scanning electron microscope image of the pH response indicator film prepared in Example 1.

[0027] Figure 3 This is a scanning electron microscope image of the inner surface of the pH-responsive indicator membrane prepared in Example 1.

[0028] Figure 4 Schematic diagram of the changes in moisture content of fish meat during storage at 25°C.

[0029] Figure 5 Schematic diagram of the changes in fat content of fish meat during storage at 25°C.

[0030] Figure 6 Schematic diagram of the changes in TVB-N value of fish meat during storage at 25°C.

[0031] Figure 7 Schematic diagram of the changes in TBARS content in fish meat during storage at 25°C.

[0032] Figure 8 Schematic diagram of the changes in moisture content of fish meat during storage at 37°C.

[0033] Fig. 9 Schematic diagram of the changes in fat content of fish meat during storage at 37°C.

[0034] Fig.10 Schematic diagram of the changes in TVB-N value of fish meat during storage at 37°C.

[0035] Fig.11 Schematic diagram of the changes in TBARS content in fish meat during storage at 37°C.

[0036] Fig.12 The color change of the pH-responsive indicator film prepared in Example 1 at different pH values. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0038] The present invention provides a method for preparing a pH-responsive indicator film, comprising the following steps:

[0039] S1, dissolving anthocyanin / curcumin mixed pigment powder (anthocyanin / curcumin mixed pigment powder is prepared by mixing anthocyanin powder and curcumin powder in a mass ratio of 1:1) in 47.5% ethanol solution to obtain a 0.04 g / mL anthocyanin / curcumin mixed pigment solution;

[0040] S2, dissolving a mixed powder of carrageenan and gelatin (the mass ratio of carrageenan to gelatin is 4:6-6:4) in 90°C deionized water to obtain a mixed solution I of 0.016-0.017 g / mL, adding glycerol to the mixed solution I and stirring it thoroughly (the amount of glycerol added is 1% of the mass of the mixed solution I), adding anthocyanin / curcumin mixed pigment solution and stirring and mixing after the temperature drops to 60°C to obtain a mixed solution II (the concentration of anthocyanin / curcumin mixed pigment powder in the mixed solution II is 0.4-0.6 mg / mL), then adjusting the pH to 6.0±0.1, and after defoaming, casting the liquid and standing it to form a film to obtain an outer layer of the indicator film;

[0041] S3, dissolving chitosan powder in deionized water at 60° C. (the amount of chitosan powder added is 1-2% of the mass of deionized water), adding linseed oil (the amount of linseed oil added is 1% of the mass of deionized water), and then subjecting the mixture to cell disruption under ultrasonic conditions of 480 W and 20 kHz for 5 min, adjusting the pH value of the emulsion to 6.0±0.1 and degassing to obtain a crude membrane emulsion;

[0042] S4. Pour 20 mL of the crude film emulsion onto the outer layer of the indicator film and spread it evenly, then dry it in a 50°C forced air drying oven for 8 hours, and then balance it in a drying oven at 25°C and 50% relative humidity for 6 hours to obtain a pH-responsive indicator film.

[0043] Example 1

[0044] The preparation method of the pH response indicator film in this embodiment comprises the following specific steps:

[0045] S1. Dissolve anthocyanin / curcumin mixed pigment powder (the anthocyanin / curcumin mixed pigment powder is prepared by mixing 0.8 g anthocyanin powder and 0.8 g curcumin powder) in 40 mL of 47.5% ethanol, and store the mixed pigment solution in a dark room at 4° C. until use;

[0046] S2, dissolving 5g of mixed powder of carrageenan and gelatin (the mass ratio of carrageenan to gelatin powder is 1.11:1) in 300mL of deionized water at 90°C to obtain mixed solution I, adding 1% of glycerol by mass of mixed solution I, stirring thoroughly until the temperature drops to 60°C, adding anthocyanin / curcumin mixed pigment solution in proportion, stirring and mixing, to obtain mixed solution II, wherein the concentration of anthocyanin / curcumin mixed pigment powder in mixed solution II is 53.99mg / 100mL; then adjusting the pH to 6.0±0.1, defoaming, pouring the liquid into a glass culture dish with a diameter of 10cm to form a film, and placing it at room temperature of 25°C for 0.5h to obtain an outer layer of the indicator film;

[0047] S3, dissolving chitosan powder (the amount of chitosan powder added is 1.70% of the mass of deionized water) in deionized water at 60° C., adding linseed oil (the amount of linseed oil added is 1% of the mass of deionized water), and then disrupting the mixture at 480 W and 20 kHz for 5 min, adjusting the pH value of the emulsion to 6.0±0.1 and degassing to prepare a crude film emulsion;

[0048] S4. Take 20 mL of the crude film emulsion obtained in step S3, pour it onto the outer layer of the indicator film obtained in step S2 and spread it evenly, then dry it in a 50° C. forced air drying oven for 8 h, and then balance it in a drying oven at 25° C. and 50% relative humidity for 6 h to obtain a pH responsive indicator film (the actual picture of the obtained pH responsive indicator film is shown in FIG. Figure 1 As shown; scanning electron microscope image as Figures 2-3 shown).

[0049] Performance Testing

[0050] 1) The physicochemical properties of the pH-responsive indicator membrane prepared in Example 1 were tested.

[0051] Among them, the physical and chemical properties include: elongation at break (EAB), tensile strength (TS), water vapor transmission coefficient (WVP) and hydroxyl radical scavenging rate. The specific test methods are as follows:

[0052] a) Mechanical properties (elongation at break and tensile strength)

[0053] Fix the film sample on the texture analyzer, record the maximum tensile force F (N) when the film breaks, and the difference ΔL (m) between the breaking and the initial state. Make three sets of parallel measurements and take the average value of the results.

[0054]

[0055] Where EAB: elongation at break, %; ΔL: difference before and after film break, mm; L 0 : Initial value of membrane length, mm.

[0056]

[0057] Where TS is the tensile strength, MPa; F is the tensile force when the membrane is broken, N; D is the membrane thickness, mm; N is the membrane thickness, mm.

[0058] b) Hydroxyl radical scavenging rate

[0059] Add 0.2 mL of membrane solution to a test tube and dissolve it to 12 mL. Use 12 mL of distilled water as a blank. Then add FeSO 4 , H 2 O 2 Add 1 mL of each, mix well and then add 1 mL of salicylic acid. Shake and equilibrate in a water bath for 30 minutes. Finally, measure the absorbance at 510 nm and adjust to zero with salicylic acid solution.

[0060]

[0061] A i : film sample absorbance; A 0 : Blank sample absorbance.

[0062] c) Water vapor transmission coefficient (WVP)

[0063] Weigh 3g of anhydrous calcium chloride in a small glass jar, select an undamaged film, measure its thickness with a vernier caliper, and then fix the film to cover the mouth of the cup. After recording the initial weight, place the sample in a desiccator with a relative humidity of 100%, and weigh and record it every 2 hours.

[0064]

[0065] Wherein Δm: weight difference before and after 2h interval, g; d: film thickness, cm; S: area of ​​bottle mouth, cm; t: interval time, h; ΔP: water vapor pressure difference, KPa.

[0066] After testing, the physical and chemical properties of the pH-responsive indicator membrane prepared in Example 1 are as follows:

[0067] The EAB was 57.43±3.51%, the TS was 24.07±1.25MPa, the hydroxyl radical scavenging rate was 46.61±0.21%, and the WVP was 4.03±0.08g·cm / (cm 2 ·KPa·h).

[0068] 2) The color development effect of the pH-responsive indicator film prepared in Example 1 was tested at different pH values. The test results are as follows: Fig.12 shown.

[0069] As can be seen from the figure, the pH-responsive indicator film prepared by the scheme of the present invention can present different colors as the pH value changes, and the pH-responsive indicator film has a wide color development range.

[0070] 3) Food preservation effect test

[0071] The test methods are as follows A) and B):

[0072] A) In the experimental group (EG), 40 g of yellowfin fish meat was placed in a plastic culture dish (8.5 cm×8.5 cm), sealed with the pH-responsive indicator film prepared in Example 1, and stored at 25°C for 0 h, 12 h, 24 h, 36 h, and 48 h to measure the changes in the physicochemical indices of the fish meat, and the changes in the physicochemical indices of the samples at each time point were recorded. The control group (CG) was sealed with a single layer of carrageenan outer film.

[0073] B) Experimental group (EG) 40 g of yellowfin fish meat was placed in a plastic culture dish (8.5 cm×8.5 cm), sealed with the pH response indicator film prepared in Example 1, and stored at 37°C for 0 h, 2 h, 4 h, 6 h, and 8 h to measure the changes in the physicochemical indexes of the fish meat, and the changes in the physicochemical indexes of the samples at each time point were recorded. CG was sealed with a single layer of carrageenan outer film.

[0074] Among them, the physical and chemical indicators of fish meat freshness include: determination of fish meat moisture content, determination of fish meat fat content, determination of TVB-N value, determination of TBARS value, and analysis of PUFA fatty acid composition. The specific test methods are as follows:

[0075] ① Determination of moisture content in fish meat

[0076] Put 5.0g of fish meat into the dried weighing bottle and record the initial weight m. 1 Then place it in a drying oven at 105℃ for 2 hours, take it out, weigh and record after the weighing bottle cools down, and continue drying until the weight difference is less than 2mg (dry for 30 minutes each time after the second time)

[0077]

[0078] Where: m 0 is the weight of the undried sample / g; m 1 is the initial mass of the sample and weighing bottle / g; m 2 The mass of the weighing bottle and sample is constant weight / g.

[0079] ②Determination of fish fat content

[0080] Put 5.0g of fish meat into the dried weighing bottle and record the initial weight m. 1 Chloroform-methanol solution was added at a liquid-to-solid ratio of 12:1 (mL / g) and extracted at 40°C for 3 h. The solvent was then evaporated in a vacuum rotary evaporator at 45°C and weighed (recorded as m 2 ).

[0081]

[0082] ③Determination of TVB-N value

[0083] Add 10g of fish meat to 100mL of distilled water, stir in a blender for 0.5h and filter. Then add 1mL of boric acid solution and 1 drop of mixed indicator to the inner chamber of the Conway diffusion dish. Quickly take 1mL of filtrate and saturated potassium carbonate solution to the outer chamber, immediately cover with a glass cover (apply vaseline on the edge of the diffusion dish), shake well, then balance in a 37℃ incubator for 2h, titrate with 0.01mol / L hydrochloric acid standard solution until it turns blue-purple, and replace the filtrate with distilled water for blank control.

[0084]

[0085] Where: V 1 is the amount of standard hydrochloric acid in the experimental group minus the blank control (mL); c is the concentration of the hydrochloric acid standard solution (mol / L); m is the sample mass (g); V is the volume of the added filtrate (mL); V 0 is the total filtrate volume (mL).

[0086] ④Determination of TBARS value

[0087] Add 5.0g fish meat to a mixture of 50mL 10% trichloroacetic acid and 50mL ultrapure water, shake well, place in a 27℃ incubator for 1h, filter, take 8mL of the filtrate, add 2mL of TBA solution (0.06mol / l), and place in a water bath at 80℃ for 2h. After cooling, compare the color at a wavelength of 532nm, and make a blank tube control at the same time.

[0088]

[0089] Where: c is the concentration of MDA obtained from the standard curve (μg / mL); V is the volume of the sample solution (mL); m is the mass of the sample represented by the sample solution (g)

[0090] ⑤PUFA fatty acid composition analysis

[0091] The samples were subjected to fatty acid methyl esterification. The fatty acids were determined using a 7890B gas chromatograph, a flame ionization detector and a SH-RtTM-2560 column (Column 100m, 0.25mmID, 0.20μmfilm thickness), a split ratio of 10:1, an injection volume of 1μL, a carrier gas of nitrogen, a flow rate of 20mL / min, an injection port temperature of 250℃, and a detector temperature of 260℃. The temperature program of the column box was as follows: the starting temperature was 140℃, maintained for 1min, and then increased to 240℃ at 4℃ / min and maintained for 19min. The qualitative analysis of fatty acids was compared with the retention time of 37 mixed fatty acid methyl ester standards, and the quantitative analysis was performed by area normalization. The content of PUFA fatty acids was expressed as the relative proportion (%) of a single fatty acid to the total fatty acids.

[0092] Using A) test method, the test results are as follows:

[0093] At 25℃, the moisture and fat content of fish meat is Figures 4-5 As shown. The changes in moisture and fat content of EG are smaller than those of CG, especially the difference in moisture content change is more significant in the later storage period. Therefore, the presence of the indicator film can improve the water retention rate of fish meat. As the storage time increases, the fat in fish meat is oxidized. The fat content of EG fish meat is higher than that of CG, indicating that the coverage of the indicator film can inhibit the oxidation and decomposition of fat more than CG.

[0094] The TVB-N value of fish meat changes as follows Figure 6 As shown (among which, the volatile basic nitrogen (TVB-N) content is one of the indicators for identifying the corruption of protein-containing products. It is mainly composed of volatile nitrogen-containing compounds produced by the degradation of amines. With the extension of storage time, the TVB-N value of fish meat continues to rise. This is because the protein in the fish meat is degraded by microorganisms to produce alkaline substances such as ammonia and amines. According to GB2733-2015, when the TVB-N value of fresh fish meat is greater than 20mg / 100g, it is not edible). At 25°C, when CG was stored for 24h, the TVB-N value was 29.31mg / 100g, while the TVB-N value of EG was 19.03mg / 100g, which did not exceed the standard.

[0095] Changes in TBARS values ​​of fish meat Figure 7 As shown in the figure (TBARS value is a common indicator for measuring fatty acid oxidation. The larger the value, the more serious the fat oxidation and the worse the product quality. When it is higher than 2.2 mg MDA / kg in fish meat, the fish meat has a distinct rancid smell). After storage at 25°C for 48 hours, the TBARS value of CG fish meat reached 2.39 mg MDA / kg, indicating that the fish meat was completely corrupt, while the TBARS value of EG was smaller than that of CG and did not exceed 2.2 mg.

[0096] The changes in fatty acid composition of EG and CG fish meat during storage at 25°C are shown in Table 1 below.

[0097] Table 1. Changes in fatty acid composition of fish meat during storage at 25°C (%)

[0098]

[0099]

[0100]

[0101] As shown in Table 1 above, at 25°C, the SFA content of EG and CG increased slightly, while PUFA decreased continuously, and the change was obvious within the first 24 h. From the comparison between the two groups, the change of fatty acid content in EG was less than that in CG.

[0102] Using test method B), the test results are as follows:

[0103] At 37℃, the water and fat content of fish meat is Figures 8-9 The changes of moisture content and fat content in EG were smaller than those in CG, indicating that the coverage of indicator film can inhibit the volatilization of fish moisture and the oxidative decomposition of fat.

[0104] The TVB-N value of fish meat changes as follows Fig.10 As shown. At 37°C, after CG was stored for 6 hours, the TVB-N value reached 19.18 mg / 100 g, and the fish meat was in a sub-fresh state. After 8 hours, the TVB-N value reached 24.15 mg / 100 g, which was no longer edible. After EG was stored for 8 hours, the TVB-N value reached 18.38 mg / 100 g. The TVB-N values ​​of CG at both temperatures were higher than those of EG, indicating that the indicator film inhibited the spoilage of fish meat to a certain extent and slowed down the increase of TVB-N.

[0105] Changes in TBARS values ​​of fish meat Fig.11 The TBARS values ​​of EG are all smaller than those of CG, which indicates that the application of indicator film can slow down the oxidation of fat in fish meat and improve the freshness of fish meat to a certain extent.

[0106] The changes in fatty acid composition of EG and CG fish meat during storage at 37°C are shown in Table 2 below.

[0107] Table 2. Changes in fatty acid composition of fish meat during storage at 37°C (%)

[0108]

[0109]

[0110] As can be seen from Table 2 above, at 37°C, the SFA content of EG and CG increased slightly, PUFA decreased significantly, and MUFA showed no regular changes. In general, the fatty acid content of EG changed less than that of CG, which shows that the indicator film can effectively inhibit the changes in fatty acid composition during storage, especially has a significant protective effect on PUFA.

[0111] In summary, the pH-responsive indicator film prepared by the present invention not only has good texture properties, water vapor barrier properties and antioxidant activity, but can also sensitively and stably monitor the freshness changes of food according to the pH value changes of perishable meats such as fish.

[0112] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a pH-responsive indicator film, It is characterized in that The steps include: S1, dissolving anthocyanin / curcumin mixed pigment powder in an ethanol solution to obtain an anthocyanin / curcumin mixed pigment solution; S2, dissolving the mixed powder of carrageenan and gelatin in 90°C deionized water to obtain a mixed solution I, adding glycerol to the mixed solution I and stirring thoroughly, adding anthocyanin / curcumin mixed pigment solution after the temperature drops to 60°C, stirring and mixing to obtain a mixed solution II, then adjusting the pH to 6.0±0.1, and casting the liquid to form a film after defoaming to obtain an outer layer of the indicator film; S3, dissolving chitosan powder in deionized water, adding linseed oil, and then subjecting the mixture to ultrasonic cell disruption, adjusting the pH value of the emulsion to 6.0±0.1 and degassing to obtain a crude membrane emulsion; S4. Pour the crude film emulsion onto the outer layer of the indicator film and spread it evenly, then dry it in a 50°C forced air drying oven for 8 hours, and then balance it in a drying oven at 25°C and 50% relative humidity for 6 hours to obtain a pH responsive indicator film.

2. A method for preparing a pH-responsive indicator film according to claim 1, It is characterized in that The anthocyanin / curcumin mixed pigment powder in step S1 is prepared by mixing anthocyanin powder and curcumin powder in a mass ratio of 1:1; the concentration of the anthocyanin / curcumin mixed pigment solution is 0.04 g / mL.

3. The method for preparing a pH-responsive indicator film according to claim 1, It is characterized in that The ethanol in step S1 is 47.5% ethanol.

4. The method for preparing a pH-responsive indicator film according to claim 1, It is characterized in that The mass ratio of carrageenan to gelatin in step S2 is 4:6-6:4, the concentration of the mixed solution I is 0.016-0.017 g / mL; the amount of glycerol added is 1% of the mass of the mixed solution I; the concentration of anthocyanin / curcumin mixed pigment powder in the mixed solution II is 0.4-0.6 mg / mL.

5. The method for preparing a pH-responsive indicator film according to claim 1, It is characterized in that In step S3, chitosan powder is dissolved in deionized water at 60° C.; the chitosan powder is added in an amount of 1-2% of the mass of deionized water; the linseed oil is added in an amount of 1% of the mass of deionized water; and the mixture is subjected to cell disruption under ultrasonic conditions of 480W and 20kHz for 5 minutes.

6. The method for preparing a pH-responsive indicator film according to claim 1, It is characterized in that In step S4, 20 mL of the crude membrane emulsion is poured onto the outer layer of the indicator membrane and spread evenly.

7. The method for preparing a pH-responsive indicator film according to claim 4, It is characterized in that The mass ratio of carrageenan to gelatin powder in step S2 is 1.11:1; the concentration of anthocyanin / curcumin mixed pigment powder in the mixed solution II is 53.99 mg / 100 mL.

8. The method for preparing a pH-responsive indicator film according to claim 5, It is characterized in that The amount of chitosan powder added in step S3 is 1.70% of the mass of deionized water.

9. A pH-responsive indicator membrane, It is characterized in that Prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the pH-responsive indicator film according to claim 9 in monitoring the freshness of food.

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