Preparation method of amino acid sensitized anthocyanin indicator and preparation method of smart label

Abstract

The present invention discloses a method for preparing an amino acid-sensitized anthocyanin indicator and a method for preparing a smart label, and relates to the field of smart labels. The method for preparing an amino acid-sensitized anthocyanin indicator comprises modifying the obtained anthocyanin solution with L-tryptophan; the method for preparing a smart label comprises adding an amino acid-sensitized anthocyanin indicator to an auxiliary agent mixed solution, adjusting the pH of the obtained mixed system, homogenizing, dispersing and emulsifying, and then ultrasonically treating to obtain a smart label preparation solution, preparing the obtained smart label preparation solution into a film, and obtaining an amino acid-assisted sensitized anthocyanin smart label. The method provided by the present invention effectively enhances the sensitivity of anthocyanin indicators and smart labels, and has good application prospects.

Description

Technical Field

[0001] The present invention relates to the field of smart labels, and more specifically, to a method for preparing an amino acid-sensitized anthocyanin indicator and a method for preparing a smart label. Background Art

[0002] During the storage and transportation of food, spoilage microorganisms grow and metabolize, producing volatile ammonia substances, which cause the pH value in the package to change. As a result, smart labels that monitor food quality changes through pH-sensitive indicators have emerged.

[0003] At present, most pH-sensitive indicators are synthetic indicators, such as bromocresol purple and bromothymol blue. However, synthetic indicators are toxic and harmful, and there are food safety issues. Anthocyanin is a pure natural pigment that has the characteristic of showing different colors depending on the external pH value. Therefore, the use of anthocyanin as a pH-sensitive indicator to prepare smart labels has market application potential.

[0004] However, there are currently various problems with the application of anthocyanins in this field. For example, "A pH-intelligent response fish packaging film: Konjac glucomannan / carboxymethyl cellulose / blackcurrant anthocyanin antibacterial composite film" (PY A et al., International Journal of Biological Macromolecules, 2022, 386-396.) discloses a technical solution for preparing an antibacterial composite film using konjac glucomannan, carboxymethyl cellulose and blackcurrant anthocyanin. The addition of blackcurrant anthocyanin enhances the antibacterial and antioxidant properties of the film, but its indicator is not sensitive to pH response. At the key point of pH 5-8, the color change is not visible to the naked eye, and the change in fish quality cannot be fed back in real time; "Biodegradable intelligent film for food preservation and real-time visual detection of food freshness" (Y Zhao et al., Food Hydrocolloids, 2022, 129, 107665.) discloses a technical solution for manufacturing a pH-sensitive smart packaging film using carboxymethyl cellulose as a matrix, anthocyanin as an indicator, and graphene as an enhancer. The smart packaging film prepared in this document is sensitive to pH response, but the preparation process is complicated, the raw material cost is high, and the product sensitivity is still limited. Summary of the invention

[0005] In order to solve the above problems, the present invention provides a method for modifying anthocyanin by using L-tryptophan to enhance the color intensity of anthocyanin and thus enhance the sensitivity of smart labels. The specific scheme is as follows:

[0006] A method for preparing an amino acid-sensitized anthocyanin indicator comprises the following steps:

[0007] S1, preparing anthocyanin solution;

[0008] S2. Take L-tryptophan to modify the obtained anthocyanin solution to obtain an amino acid-sensitized anthocyanin indicator.

[0009] Preferably, the preparation of anthocyanin solution in step S1 comprises: taking anthocyanin-containing raw material powder, adding an extractant formed by mixing citric acid aqueous solution and ethanol aqueous solution, stirring, separating the solid and liquid, and taking the supernatant to obtain the anthocyanin solution.

[0010] Preferably, the anthocyanin-containing raw material powder includes purple cabbage anthocyanin powder.

[0011] Preferably, the mass fraction of citric acid in the citric acid aqueous solution is 1%; the volume fraction of ethanol in the ethanol aqueous solution is 75%; and the volume ratio of the citric acid aqueous solution to the ethanol aqueous solution in the extractant is 1:1.

[0012] Preferably, the solid-liquid ratio of the anthocyanin-containing raw material powder to the extractant is 1:20 g / mL.

[0013] Preferably, the stirring treatment has a treatment temperature of 60° C., a stirring method including magnetic stirring, a rotation speed of 800 to 1200 rpm, and a stirring time of 2 to 4 hours.

[0014] Preferably, the solid-liquid separation comprises cooling to room temperature and then centrifuging at 8000 rpm for 10 min.

[0015] Preferably, before performing step S2, the anthocyanin concentration in the anthocyanin solution is detected and the anthocyanin concentration is adjusted to 140-150 mg / mL.

[0016] Preferably, in step S2, the obtained anthocyanin solution is modified by taking L-tryptophan, including: adjusting the pH of the obtained anthocyanin solution, adding L-tryptophan solution to mix, stirring evenly, and standing in the dark after ultrasonic treatment to obtain an amino acid sensitized anthocyanin indicator (L-PCA).

[0017] Preferably, the pH of the obtained anthocyanin solution is adjusted to 3.3; Tris-HCl buffer is used to adjust the pH.

[0018] Preferably, the solvent of the L-tryptophan solution is water, wherein the concentration of L-tryptophan is 15-20 mg / mL.

[0019] Preferably, the volume ratio of the anthocyanin solution to the L-tryptophan solution is 1:1.

[0020] Preferably, the ultrasonic treatment has an ultrasonic power of 400 W, and the ultrasonic treatment procedure is to turn off the ultrasonic treatment for 2 seconds after each ultrasonic treatment for 2 seconds, and the total time is 10 minutes; the light-proof standing time is 3 to 8 hours, until L-tryptophan is completely combined with anthocyanins.

[0021] Furthermore, the present invention also provides a method for preparing a smart label based on the above-mentioned amino acid-sensitized anthocyanin indicator, comprising the following steps:

[0022] S1, preparing anthocyanin solution;

[0023] S2, taking L-tryptophan to modify the obtained anthocyanin solution to obtain an amino acid-sensitized anthocyanin indicator;

[0024] S3, taking the auxiliary agent mixture, adding an amino acid sensitizing anthocyanin indicator to the auxiliary agent mixture, adjusting the pH of the obtained mixed system, homogenizing, dispersing and emulsifying, and then ultrasonically treating to obtain a smart label preparation solution;

[0025] S4. Form the obtained smart label preparation liquid into a film to obtain an amino acid-assisted sensitized anthocyanin smart label.

[0026] Preferably, the preparation of anthocyanin solution in step S1 comprises: taking anthocyanin-containing raw material powder, adding an extractant formed by mixing citric acid aqueous solution and ethanol aqueous solution, stirring, separating the solid and liquid, and taking the supernatant to obtain the anthocyanin solution.

[0027] Preferably, the anthocyanin-containing raw material powder includes purple cabbage anthocyanin powder.

[0028] Preferably, the mass fraction of citric acid in the citric acid aqueous solution is 1%; the volume fraction of ethanol in the ethanol aqueous solution is 75%; and the volume ratio of the citric acid aqueous solution to the ethanol aqueous solution in the extractant is 1:1.

[0029] Preferably, the solid-liquid ratio of the anthocyanin-containing raw material powder to the extractant is 1:20 g / mL.

[0030] Preferably, the stirring treatment has a treatment temperature of 60° C., a stirring method including magnetic stirring, a rotation speed of 800 to 1200 rpm, and a stirring time of 2 to 4 hours.

[0031] Preferably, the solid-liquid separation comprises cooling to room temperature and then centrifuging at 8000 rpm for 10 min.

[0032] Preferably, before performing step S2, the anthocyanin concentration in the anthocyanin solution is detected and the anthocyanin concentration is adjusted to 140-150 mg / mL.

[0033] Preferably, in step S2, the obtained anthocyanin solution is modified by taking L-tryptophan, including: adjusting the pH of the obtained anthocyanin solution, adding L-tryptophan solution to mix, stirring evenly, and standing in the dark after ultrasonic treatment to obtain an amino acid sensitized anthocyanin indicator (L-PCA).

[0034] Preferably, the pH of the obtained anthocyanin solution is adjusted to 3.3; Tris-HCl buffer is used to adjust the pH.

[0035] Preferably, the solvent of the L-tryptophan solution is water, wherein the concentration of L-tryptophan is 15-20 mg / mL.

[0036] Preferably, the volume ratio of the anthocyanin solution to the L-tryptophan solution is 1:1.

[0037] Preferably, the ultrasonic treatment has an ultrasonic power of 400 W, and the ultrasonic treatment procedure is to turn off the ultrasonic treatment for 2 seconds after each ultrasonic treatment for 2 seconds, and the total time is 10 minutes; the light-proof standing time is 3 to 8 hours, until L-tryptophan is completely combined with anthocyanins.

[0038] Preferably, the auxiliary agent mixture in step S3 includes gelatin, soybean oil, glycerol and Tween-80.

[0039] Preferably, the preparation step of the auxiliary agent mixture includes: uniformly dispersing 5% gelatin by mass into distilled water, adding soybean oil with a final concentration of 5% by mass, 3% by volume glycerol, and 0.1% by mass Tween-80, and stirring in a constant temperature water bath to obtain the auxiliary agent mixture.

[0040] Preferably, the constant temperature water bath is stirred at a temperature of 60° C., a rotation speed of 500 to 800 rpm, and a stirring time of 2 to 3 hours.

[0041] Preferably, the volume fraction of the amino acid sensitized anthocyanin indicator added in step S3 is 3% to 5% of the obtained mixed system.

[0042] Preferably, in step S3, the pH of the obtained mixed system is adjusted to a pH of 6 to 8; NaOH buffer is used to adjust the pH.

[0043] Preferably, in step S3, the homogenization dispersion has a rotation speed of 10000 rpm to 12000 rpm and a homogenization time of 3 min.

[0044] Preferably, in the ultrasonic treatment in step S3, the ultrasonic power is 10W to 1000W, and the ultrasonic treatment procedure is to turn off for 2s after every 2s of ultrasonic treatment, and the total time is 10min.

[0045] Preferably, the film is prepared in step S4 by using a casting method.

[0046] Preferably, the casting comprises casting the smart label preparation liquid on the glass surface, and peeling it off after drying and balancing.

[0047] Preferably, the drying is performed by ventilation drying at room temperature for 24 to 48 hours; and the balancing is performed by placing the culture dish in an environment with a relative humidity of 45% to 55% and a temperature of 20° C. to 25° C. for balancing for 24 to 48 hours.

[0048] Preferably, the film preparation in step S4 includes: injecting the obtained smart label preparation solution into a culture dish, ventilating and drying at room temperature for 24 to 48 hours, then balancing in an environment with a relative humidity of 45% to 55% and a temperature of 20°C to 25°C for 24 to 48 hours, and peeling off the obtained film.

[0049] Beneficial Effects

[0050] The beneficial effects of the present invention are:

[0051] 1. L-tryptophan can preferentially absorb ultraviolet rays and reduce the damage of light to anthocyanins. In addition, L-tryptophan can combine with anthocyanins to form a vertically stacked complex, produce a hydrophobic effect, and protect the anthocyanin parent nucleus cation from attack. Therefore, L-tryptophan can effectively enhance the color intensity of anthocyanins. The present invention adopts a co-color method to combine L-tryptophan with anthocyanins to prepare an indicator L-PCA with better sensitivity, which provides a basis for the preparation of smart labels.

[0052] 2. The present invention uses modified anthocyanin as an indicator, gelatin as a base material, introduces an oil phase, and obtains a smart label with good performance, safety, and biodegradability through dispersion, emulsification, and ultrasound-assisted means. It can sensitively monitor the freshness and corruption of fish meat and has good application prospects.

[0053] 3. The whole set of technology of the present invention is simple and easy to implement, the product process is simple, and it is suitable for mass production.

[0054] 4. The method provided by the present invention improves the indication effect of smart labels using anthocyanins as indicators, and is particularly suitable for monitoring quality changes during the cold storage and preservation process of fish, and has good market potential. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 Analyze the technical roadmap of the present invention;

[0056] Figure 2The Fourier transform infrared spectra of anthocyanidin, L-tryptophan, the product obtained in Example 1, the product obtained in Example 2 and the product obtained in Comparative Example 2 are shown;

[0057] Figure 3 The color response of the products obtained in Example 1, Example 2, Comparative Example 1 and Comparative Example 2 in a buffer solution of pH 2-12;

[0058] Figures 4 to 7 The UV-visible spectra of the products obtained in Example 1, Example 2, Comparative Example 1 and Comparative Example 2 are shown;

[0059] Figure 8 The color development pictures of the products obtained in Example 3, Comparative Example 3 and Comparative Example 4 in a buffer solution of pH 2-12;

[0060] Figures 9-11 The color parameters of the indicator label of the products obtained in Example 3, Comparative Example 6 and Comparative Example 4 under a buffer solution of pH 2-12 are shown respectively;

[0061] Figures 12-13 The color stability of the products obtained in Example 3, Comparative Example 3 and Comparative Example 4 under light and dark conditions for 14 days respectively;

[0062] Fig.14 The color development pictures of the products obtained in Example 3, Comparative Example 3 and Comparative Example 4 in a buffer solution of pH 2-12 after storage for 14 days;

[0063] Figures 15 to 17 The color parameters of the indicator label of the products obtained in Example 3, Comparative Example 3 and Comparative Example 4 under a buffer solution of pH 2-12 are shown respectively;

[0064] Fig.18 The color change pictures of the products obtained in Example 3, Comparative Example 5 and Comparative Example 6 in pH 2-12 buffer;

[0065] Figures 19 to 21 The color parameters of the products obtained in Example 3, Comparative Example 5 and Comparative Example 6 in pH 2-12 buffer respectively;

[0066] Fig. 22 The changes in volatile basic nitrogen content and pH of fish meat during storage of the products obtained in Example 3 and Comparative Example 4 for 8 days;

[0067] Fig.23 The color changes of the products of Example 3 and Comparative Example 4 during storage;

[0068] Figures 24 to 27 They are the color parameters of the products of Example 3 and Comparative Example 4 during storage. DETAILED DESCRIPTION

[0069] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0070] Description of reagents and equipment used in the embodiments of the present invention:

[0071] The purple cabbage anthocyanin powder in step S1 is purchased from Laibao Biotechnology Co., Ltd.; the centrifuge model in step S1 is CR 22N high-speed refrigerated centrifuge from Hitachi Koki Co., Ltd. of Japan; the machine model used for ultrasonic treatment in step S2 is SONICS large-capacity ultrasonic crusher VCX 1600 from Sonics & Materials of the United States; the machine model used for dispersion and emulsification in step S3 is T25 digital display homogenizer from Guangzhou Branch of IKA Group of Germany; the machine model used for ultrasonic treatment in step S3 is SONICS large-capacity ultrasonic crusher VCX 1600 from Sonics & Materials of the United States; the culture dish used for preparing the film in step S4 is 9×9 mm in size. The storage described in the embodiments and comparative examples of the present invention is to wrap the product with the fish meat to be tested and then store it at 4°C.

[0072] Unless otherwise specified, the following examples and comparative examples are parallel experiments, and the same processing steps and parameters are used where not specified.

[0073] The preparation method of the amino acid sensitized anthocyanin indicator provided by the present invention is illustrated by using Example 1, Example 2 and Comparative Example 1:

[0074] Example 1

[0075] A method for preparing an amino acid sensitized anthocyanin indicator, comprising the following steps:

[0076] S1. Take purple cabbage anthocyanin powder, add 1% citric acid by mass and 75% ethanol by volume as extractant, the volume ratio of the extractant is 1:1, the ratio of raw material to extractant is 1:20g / ml, stir magnetically at 60°C for 3h, the speed is 800rpm; after stirring, centrifuge at room temperature at 8000rpm for 10min to obtain the supernatant;

[0077] S2. Take L-tryptophan powder, add water and stir until dissolved to obtain 2.5 mg / ml L-tryptophan solution, and adjust the pH value of the anthocyanin solution (140-150 mg / ml) to 3.3. Then, mix the anthocyanin solution and the L-tryptophan solution in a volume ratio of 1:1, stir evenly, and then ultrasonically treat at 400 W for 10 minutes, and stand in the dark for 3 hours until completely combined to obtain a modified anthocyanin solution (L1-PCA), that is, an amino acid-sensitized anthocyanin indicator.

[0078] Example 2

[0079] A method for preparing an amino acid sensitized anthocyanin indicator, comprising the following steps:

[0080] S1. Take purple cabbage anthocyanin powder, add 1% citric acid by mass and 75% ethanol by volume as extractant, the volume ratio of the extractant is 1:1, the ratio of raw material to extractant is 1:20g / ml, stir magnetically at 60°C for 3h, the speed is 800rpm; after stirring, centrifuge at room temperature at 8000rpm for 10min to obtain the supernatant;

[0081] S2. Take L-tryptophan powder, add water and stir until dissolved to obtain 5 mg / ml L-tryptophan solution, and adjust the pH value of the anthocyanin solution (140-150 mg / ml) to 3.3. Then, mix the anthocyanin solution and the L-tryptophan solution in a volume ratio of 1:1, stir evenly, and then ultrasonically treat at 400 W for 10 minutes, and stand in the dark for 3 hours until completely combined to obtain a modified anthocyanin solution (L2-PCA), that is, an amino acid-sensitized anthocyanin indicator.

[0082] Comparative Example 1

[0083] A method for preparing anthocyanin indicator, comprising the following steps:

[0084] S1. Take purple cabbage anthocyanin powder, add 1% citric acid by mass and 75% ethanol by volume as extractant, the volume ratio of the extractant is 1:1, the ratio of raw material to extractant is 1:20g / ml, stir magnetically at 60°C for 3h, the speed is 800rpm; after stirring, place at room temperature and centrifuge at 8000rpm for 10min to obtain the supernatant (PCA);

[0085] S2. The pH value of the anthocyanin solution (140-150 mg / ml) was adjusted to 3.3, and then the anthocyanin solution was mixed with water in a volume ratio of 1:1, stirred evenly, and then ultrasonically treated at 400 W for 10 min, and allowed to stand in the dark for 3 h until completely combined to obtain anthocyanin solution (PCA), i.e., anthocyanin indicator.

[0086] Comparative Example 2

[0087] S1. Take purple cabbage anthocyanin powder, add 1% citric acid by mass and 75% ethanol by volume as extractant, the volume ratio of the extractant is 1:1, the ratio of raw material to extractant is 1:20g / ml, stir magnetically at 60°C for 3h, the speed is 800rpm; after stirring, centrifuge at room temperature at 8000rpm for 10min to obtain the supernatant;

[0088] S2. Take L-tryptophan powder, add water and stir until dissolved to obtain 5 mg / ml L-tryptophan solution, and adjust the pH value of the anthocyanin solution (140-150 mg / ml) to 3.3. Then, mix the anthocyanin solution and the L-tryptophan solution in a volume ratio of 1:1, stir evenly, and stand in the dark for 3 hours until completely combined to obtain a modified anthocyanin solution (L-PCA), i.e., anthocyanin indicator.

[0089] The method for preparing a smart label based on an amino acid-sensitized anthocyanin indicator provided by the present invention is illustrated by using Example 3, Comparative Example 3 and Comparative Example 4, Comparative Example 5 and Comparative Example 6:

[0090] Example 3

[0091] A method for preparing a smart label based on an amino acid-sensitized anthocyanin indicator, comprising the following steps:

[0092] S1. Take purple cabbage anthocyanin powder, add 1% citric acid by mass and 75% ethanol by volume as extractant, the volume ratio of the extractant is 1:1, the ratio of raw material to extractant is 1:20g / ml, stir magnetically at 60°C for 3h, the speed is 800rpm; after stirring, centrifuge at room temperature at 8000rpm for 10min to obtain the supernatant;

[0093] S2. Take L-tryptophan powder, add water and stir until dissolved to obtain 5 mg / ml L-tryptophan solution, and adjust the pH value of the anthocyanin solution (140-150 mg / ml) to 3.3. Then, mix the anthocyanin solution and the L-tryptophan solution in a volume ratio of 1:1, stir evenly, and then ultrasonically treat at 400 W for 10 min, and stand in the dark for 3 h until completely combined to obtain a modified anthocyanin solution (L2-PCA).

[0094] S3, evenly disperse 5% gelatin in distilled water, add 5% soybean oil, 3% glycerol, and 0.1% Tween-80, and stir in a water bath at 60°C for 2 h at a speed of 500 rpm;

[0095] S4, adding the 4% L2-PCA solution described in S2 to the mixed solution described in S3, adjusting the pH to 6-8 with NaOH buffer, dispersing and emulsifying the mixed solution, homogenizing at 10000 rpm for 3 min, and ultrasonically treating at 600 W for 10 min under an ultrasonic instrument to obtain a smart label preparation solution;

[0096] S5. Cast the smart label preparation solution obtained in S4 into a culture dish, dry it under ventilation at room temperature for 24 hours, and then balance it in an environment with a relative humidity of 50±5% and a temperature of 20°C to 25°C for 24 hours before peeling it off.

[0097] Comparative Example 3

[0098] A method for preparing a modified anthocyanin smart label, comprising the following steps:

[0099] S1. Take purple cabbage anthocyanin powder, add 1% citric acid by mass and 75% ethanol by volume as extractant, the volume ratio of the extractant is 1:1, the ratio of raw material to extractant is 1:20g / ml, stir magnetically at 60°C for 3h, the speed is 800rpm; after stirring, centrifuge at room temperature at 8000rpm for 10min to obtain the supernatant;

[0100] S2. Take L-tryptophan powder, add water and stir until dissolved to obtain 2.5 mg / ml L-tryptophan solution, and adjust the pH value of the anthocyanin solution (140-150 mg / ml) to 3.3. Then, mix the anthocyanin solution and the L-tryptophan solution in a volume ratio of 1:1, stir evenly, and then ultrasonically treat at 400 W for 10 minutes, and stand in the dark for 3 hours until completely combined to obtain a modified anthocyanin solution (L1-PCA).

[0101] S3, evenly disperse 5% gelatin in distilled water, add 5% soybean oil, 3% glycerol, and 0.1% Tween-80, and stir in a water bath at 60°C for 2 h at a speed of 500 rpm;

[0102] S4, adding the 4% L1-PCA solution described in S2 to the mixed solution described in S3, adjusting the pH to 6-8 with NaOH buffer, dispersing and emulsifying the mixed solution, homogenizing at 10000 rpm for 3 min, and ultrasonically treating at 600 W for 10 min under an ultrasonic instrument to obtain a smart label preparation solution;

[0103] S5. Cast the smart label preparation solution obtained in S4 into a culture dish, dry it under ventilation at room temperature for 24 hours, and then balance it in an environment with a relative humidity of 50±5% and a temperature of 20°C to 25°C for 24 hours before peeling it off.

[0104] Comparative Example 4

[0105] A method for preparing a modified anthocyanin smart label, comprising the following steps:

[0106] S1. Take purple cabbage anthocyanin powder, add 1% citric acid by mass and 75% ethanol by volume as extractant, the volume ratio of the extractant is 1:1, the ratio of raw material to extractant is 1:20g / ml, stir magnetically at 60°C for 3h, the speed is 800rpm; after stirring, centrifuge at room temperature at 8000rpm for 10min to obtain the supernatant;

[0107] S2. The pH value of the anthocyanin solution (140-150 mg / ml) was adjusted to 3.3, and then the anthocyanin solution was mixed with water in a volume ratio of 1:1, stirred evenly, and then ultrasonically treated at 400 W for 10 min, and allowed to stand in the dark for 3 h until completely combined to obtain anthocyanin solution (PCA).

[0108] S3, evenly disperse 5% gelatin in distilled water, add 5% soybean oil, 3% glycerol, and 0.1% Tween-80, and stir in a water bath at 60°C for 2 h at a speed of 500 rpm;

[0109] S4, adding the 4% PCA solution described in S2 to the mixed solution described in S3, adjusting the pH to 6-8 with NaOH buffer, dispersing and emulsifying the mixed solution, homogenizing at 10000 rpm for 3 min, and ultrasonically treating at 600 W for 10 min under an ultrasonic instrument to obtain a smart label preparation solution;

[0110] S5. Cast the smart label preparation solution obtained in S4 into a culture dish, dry it under ventilation at room temperature for 24 hours, and then balance it in an environment with a relative humidity of 50±5% and a temperature of 20°C to 25°C for 24 hours before peeling it off.

[0111] Comparative Example 5

[0112] A method for preparing a modified anthocyanin smart label, comprising the following steps:

[0113] S1. Take purple cabbage anthocyanin powder, add 1% citric acid by mass and 75% ethanol by volume as extractant, the volume ratio of the extractant is 1:1, the ratio of raw material to extractant is 1:20g / ml, stir magnetically at 60°C for 3h, the speed is 800rpm; after stirring, centrifuge at room temperature at 8000rpm for 10min to obtain the supernatant;

[0114] S2. Take L-tryptophan powder, add water and stir until dissolved to obtain 5 mg / ml L-tryptophan solution, and adjust the pH value of the anthocyanin solution (140-150 mg / ml) to 3.3. Then, mix the anthocyanin solution and the L-tryptophan solution in a volume ratio of 1:1, stir evenly, and then ultrasonically treat at 400 W for 10 min, and stand in the dark for 3 h until completely combined to obtain a modified anthocyanin solution (L2-PCA).

[0115] S3, evenly disperse 5% gelatin in distilled water, add 5% soybean oil, 3% glycerol, and 0.1% Tween-80, and stir in a water bath at 60°C for 2 h at a speed of 500 rpm;

[0116] S4, adding the 2% L2-PCA solution described in S2 to the mixed solution described in S3, adjusting the pH to 6-8 with NaOH buffer, dispersing and emulsifying the mixed solution, homogenizing at 10000 rpm for 3 min, and ultrasonically treating at 600 W for 10 min under an ultrasonic instrument to obtain a smart label preparation solution;

[0117] S5. Cast the smart label preparation solution obtained in S4 into a culture dish, dry it under ventilation at room temperature for 24 hours, and then balance it in an environment with a relative humidity of 50±5% and a temperature of 20°C to 25°C for 24 hours before peeling it off.

[0118] Comparative Example 6

[0119] A method for preparing a modified anthocyanin smart label, comprising the following steps:

[0120] S1. Take purple cabbage anthocyanin powder, add 1% citric acid by mass and 75% ethanol by volume as extractant, the volume ratio of the extractant is 1:1, the ratio of raw material to extractant is 1:20g / ml, stir magnetically at 60°C for 3h, the speed is 800rpm; after stirring, centrifuge at room temperature at 8000rpm for 10min to obtain the supernatant;

[0121] S2. Take L-tryptophan powder, add water and stir until dissolved to obtain 5 mg / ml L-tryptophan solution, and adjust the pH value of the anthocyanin solution (140-150 mg / ml) to 3.3. Then, mix the anthocyanin solution and the L-tryptophan solution in a volume ratio of 1:1, stir evenly, and then ultrasonically treat at 400 W for 10 min, and stand in the dark for 3 h until completely combined to obtain a modified anthocyanin solution (L2-PCA).

[0122] S3, evenly disperse 5% gelatin in distilled water, add 5% soybean oil, 3% glycerol, and 0.1% Tween-80, and stir in a water bath at 60°C for 2 h at a speed of 500 rpm;

[0123] S4, adding the 1% L2-PCA solution described in S2 to the mixed solution described in S3, adjusting the pH to 6-8 with NaOH buffer, dispersing and emulsifying the mixed solution, homogenizing at 10000 rpm for 3 min, and ultrasonically treating at 600 W for 10 min under an ultrasonic instrument to obtain a smart label preparation solution;

[0124] S5. Cast the smart label preparation solution obtained in S4 into a culture dish, dry it under ventilation at room temperature for 24 hours, and then balance it in an environment with a relative humidity of 50±5% and a temperature of 20°C to 25°C for 24 hours before peeling it off.

[0125] The differences and summary of the parameters of the above embodiments and comparative examples are shown in Table 1.

[0126] Table 1 Summary of main parameters of each embodiment and comparative example

[0127]

[0128]

[0129] The physicochemical properties, color development effect, stability, and fish storage monitoring of the anthocyanin indicators and anthocyanin smart labels obtained in the embodiments of the present invention and the comparative examples were systematically compared. The results are as follows: Figure 1 to Figure 27 As shown:

[0130] Figure 1 This is an analysis of the technical roadmap of the present invention. The main steps are the preparation of modified anthocyanins and the preparation of anthocyanin smart labels. All process steps are achieved by strict process parameter guarantee technology, which provides a guarantee for extending the validity period of the indicator label and monitoring the freshness and corruption of fish meat.

[0131] Figure 2 The following are Fourier infrared spectra of anthocyanidin, L-tryptophan, Example 1, Example 2 and Comparative Example 2. The =CH vibration at 744 cm-1 in Example 1 is a characteristic peak of L-tryptophan, indicating that L-tryptophan is bound to PCA through hydrogen bonding and hydrophobic interaction. However, there is no characteristic peak of L-tryptophan in Comparative Example 2 and Example 2. This indicates that ultrasound promotes better binding of L-tryptophan to PCA.

[0132] Figure 3The color response of the products obtained in Example 1, Example 2, Comparative Example 1 and Comparative Example 2 in a pH 2-12 buffer. Example 1, Example 2, Comparative Example 1 and Comparative Example 2 all have a color change from pink to blue-green to yellow in a pH 2-12 buffer. At pH 7-8, Comparative Example 1 and Comparative Example 2 change from pink to purple, while Example 1 and Example 2 change from pink to blue-green, indicating that the combination of L-tryptophan and PCA better distinguishes the color difference of pH 7-8. Ultrasonic assistance promotes the combination of L-tryptophan and PCA, providing a more intuitive and accurate indication for monitoring the freshness of fish meat.

[0133] Figures 4 to 7 The UV-visible spectra of the products obtained in Example 1, Example 2, Comparative Example 1 and Comparative Example 2 are shown in Figure 1. Under acidic, neutral and alkaline conditions, their maximum absorption peaks are all around 520 nm. Anthocyanins interact with co-colorants, often resulting in changes in absorption intensity and absorption shift. It can be observed that the maximum absorption peaks at 520 nm in Example 1 and Example 2 are lower than those in the PCA solution alone in Comparative Example 1, indicating that there is an interaction between L-tryptophan and PCA. Moreover, the degree of reduction in Example 1 is greater than that in Example 2, indicating that the hydrogen bonding between L-tryptophan and PCA in Example 1 is stronger.

[0134] The above results show that PCA and L-tryptophan bind to each other through hydrogen bonds and hydrophobic interactions. Intermolecular interaction is an important mechanism of co-pigmentation.

[0135] Figure 8 The pictures of the products obtained in Example 3, Comparative Example 3 and Comparative Example 4 in a buffer solution of pH 2-12 are shown. Comparative Example 3 and Comparative Example 4 gradually change from pink to pink purple (pH 2-8), with a trend of gradually becoming lighter, and turn green at pH 9-12. Example 3 has the same color change trend as Comparative Example 3 and Comparative Example 4 at pH 2-7, but when the pH value is 8, the label color deepens and tends to turn blue, and the key color turning point of pH 7-8 can be distinguished by the naked eye. At pH 9-12, the label color changes from blue to green. The above results show that the combination of L-tryptophan and anthocyanin enhances the sensitivity of the label.

[0136] Figures 9-11 In the graph, L value indicates the depth of black and white, a* indicates red and green, and b indicates yellow and blue. The L value of the indicator label decreases with the increase of pH, a* increases, b value decreases, red gradually fades, and blue becomes more obvious. Between pH 7-8, the a* value of Example 3 changes the most, and the red decreases the most; the ΔE value of Comparative Example 3 is 1.1 at pH 7 and 8, Comparative Example 4 is 0.89, and Example 3 is 1.79, among which Example 3 changes the most. This is consistent with the results observed with the naked eye, proving that Example 3 is more sensitive to pH changes.

[0137] The above results show that L-tryptophan exhibits a stronger color intensity by hydrogen bonding with PCA. The indicator label shows obvious different color changes in the pH range of 2-12, which can be distinguished by the naked eye, providing the possibility for monitoring the freshness and spoilage of fish meat.

[0138] Note: In the figure, the L value represents the depth of black and white, a* represents red and green, b represents yellow and blue, and the ΔE value represents the total color difference.

[0139] Figures 12-13 The color stability of the products obtained in Example 3, Comparative Example 3 and Comparative Example 4 under light and dark conditions for 14 days. The ΔE value changes of Example 3 under light and dark conditions are smaller than those of Comparative Example 3 and Comparative Example 4, and the ΔE value changes of Example 3 under dark conditions are 10.26-14.13, and the ΔE value changes under light conditions are 10.81-14.67, both less than 5, showing good stability. Compared with anthocyanins alone, the hydrogen bond interaction between L-tryptophan and PCA can extend the effective indication period of the smart label.

[0140] Fig.14 The color development pictures of the products obtained in Example 3, Comparative Example 3 and Comparative Example 4 after storage for 14 days in a buffer solution of pH 2-12 are shown in the figure; in the figure, Comparative Example 3 and Comparative Example 4 gradually change from pink-purple to purple-gray at pH 2-8, turn blue at pH 9, and gradually turn green at pH 12. While Example 3 is purple-gray at pH 7, and the color deepens to dark purple at pH 8, which can be distinguished by naked eyes, which is consistent with the results before storage. The results show that Example 3 after storage can also indicate the freshness of fish meat, and its sensitivity is higher than that of Comparative Example 3 and Comparative Example 4.

[0141] Figures 15 to 17 The color parameters of the products obtained in Example 3, Comparative Example 3 and Comparative Example 4 in a buffer solution of pH 2-12 are shown in the figure; in the figure, the L value, ΔE, a* value of Example 3, Comparative Example 3 and Comparative Example 4 decrease, the b value increases, the red color gradually fades, and the blue color becomes more obvious. At pH 2-12, the values ​​of Comparative Example 3 and Comparative Example 4 are 45.06-50.78 and 42.89-48.34 respectively, while the ΔE of Example 3 changes to 43.94-50.07, which is greater than 5. This shows that the color parameters of Example 3 change significantly in the pH range of 2-12, and can accurately indicate the change of pH after storage for 14 days.

[0142] The above results show that the combination of L-tryptophan and anthocyanin, the hydrogen bonds formed between molecules and the hydrophobic effect are very effective in protecting the color stability of anthocyanin and can extend the validity period of the indicator label.

[0143] Fig.18The following are pictures of the color changes of the products obtained in Example 3, Comparative Example 5 and Comparative Example 6 in pH 2-12 buffer. The colors of Example 3, Comparative Example 5 and Comparative Example 6 are all pink between pH 2 and pH 5, and the color intensity gradually decreases. When the pH reaches 6-8, the color gradually changes to blue, and when the pH reaches 9-12, the color gradually changes to yellow-green. Comparative Examples 4 and 5 are blue between pH 6 and pH 8, and there is only a difference in color intensity. The change is not clear enough and cannot be identified. However, Example 3 has a more obvious color difference (pink purple-purple-blue) between pH 6 and pH 8, which can be distinguished by the naked eye.

[0144] Figures 19 to 21 The color parameters of the products obtained in Example 3, Comparative Example 5 and Comparative Example 6 in pH 2-12 buffer. It was found that, except for b in the pH range of 5-8, a*, L and ΔE showed a close relationship with the pH value. The a* value of Example 3 changed the most compared with the b value of Comparative Example 5 and Comparative Example 6. The results show that the color parameter difference of Example 3 changed the most in the pH range of 2-12, which is consistent with the color results observed by the naked eye, suggesting that Example 3 is highly sensitive to changes in pH value.

[0145] The results of Example 3, Comparative Example 5 and Comparative Example 6 above show that the 4% mixed solution added in Example 3 can be used to prepare a pH sensitive label with good indication function. It shows obvious different color changes in the pH range of 2-12, which can be distinguished by the naked eye, providing the possibility of monitoring the freshness and spoilage of fish meat.

[0146] Fig. 22 The volatile basic nitrogen content and pH change of the fish meat of the products obtained in Example 3 and Comparative Example 4 during storage for 8 days; in the figure, the initial volatile basic nitrogen content of the fish meat wrapped in Example 3 and Comparative Example 4 during storage is 7mg / 100g. According to the national standard, fresh fish with a TVB-N content lower than 12mg / 100g is fresh fish, 12-25mg / 100g is edible fresh fish, and greater than 25mg / 100g is inedible spoiled fish. When stored to the sixth day, the TVB-N content reached 25.9mg / 100g, and the comparative example 4 was 27.3mg / 100g. On the 8th day, the pH value of Example 3 was 35.8mg / 100g, and the pH value of Comparative Example 4 was 36.4mg / 100g. . Among them, the pH value of Example 3 changed to 6.48-7.005, and the pH value of Comparative Example 4 was 6.48-7.02. The TVBN and pH values ​​of Example 3 were lower than those of Comparative Example 4. The above results indicate that the combination of L-tryptophan and anthocyanins has a certain antibacterial effect and can extend the shelf life of fish.

[0147] Figures 23 to 25The color changes and parameters of Example 3 and Comparative Example 4 during storage. Comparative Example 4 and Example 3 have the same color changes during storage, but the color change of Example 3 is more obvious when observed with the naked eye. In addition, the a* values ​​of Example 3 and Comparative Example 4 have a good linear relationship with time, but the change of Example 3 is greater. It can also be seen from the ΔE value that the ΔE value of Comparative Example 4 ranges from 42.37 to 47.47, while the ΔE value of Example 3 ranges from 41.07 to 47.87. It is consistent with the color change observed with the naked eye. The results show that the color change of Example 3 is more sensitive and more suitable for monitoring the freshness and spoilage of fish meat.

[0148] Figures 26-27 The ΔE values ​​of Example 3 and Comparative Example 4 are closely linearly related to pH and TVBN. The correlations of the ΔE value of Comparative Example 4 with TVBN and pH are R 2 =0.97607, R 2 =0.77542, and in Example 3, R 2 =0.99284, R 2 =0.78625. The results show that Example 3 has a better correlation and is suitable for monitoring the freshness and spoilage of fish meat.

[0149] Based on the results of various embodiments and comparative examples, in order to achieve the purpose of improving the sensitivity of anthocyanin indicator labels, the present invention uses amino acids as sensitizing and modifying components, and together with other components, gives anthocyanin indicator labels better sensitivity, improves the indication effect of smart labels with anthocyanin as indicators, and as an auxiliary effect, extends the validity period of anthocyanin indicator labels. This set of technology can be used to monitor the freshness and corruption of fish meat, and has good market prospects.

[0150] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for preparing an amino acid sensitized anthocyanin indicator, characterized in that: The following steps are involved: S1, preparing anthocyanin solution; S2, taking L-tryptophan to modify the obtained anthocyanin solution to obtain an amino acid-sensitized anthocyanin indicator; Among them, step S2, taking L-tryptophan to modify the obtained anthocyanin solution, including: adjusting the pH of the obtained anthocyanin solution, adding L-tryptophan solution to mix, stirring evenly, ultrasonically treating and standing in the dark to obtain an amino acid sensitized anthocyanin indicator; adjusting the pH of the obtained anthocyanin solution to a pH of 3.3; using Tris-HCl buffer to adjust the pH.

2. The method for preparing an amino acid sensitized anthocyanin indicator according to claim 1, characterized in that: The solvent of the L-tryptophan solution is water, wherein the concentration of L-tryptophan is 15-20 mg / mL; the volume ratio of the anthocyanin solution to the L-tryptophan solution is 1:

1.

3. The method for preparing an amino acid sensitized anthocyanin indicator according to claim 1, characterized in that: The ultrasonic treatment has an ultrasonic power of 400 W, and the ultrasonic treatment procedure is to turn off the ultrasonic treatment for 2 seconds after each ultrasonic treatment for 2 seconds, and the total time is 10 minutes; the light-proof standing time is 3 to 8 hours, until L-tryptophan is completely combined with anthocyanin.

4. The method for preparing an amino acid sensitized anthocyanin indicator according to claim 1, characterized in that: The step S1 of preparing anthocyanin solution comprises: taking anthocyanin raw material powder, adding an extractant formed by mixing citric acid aqueous solution and ethanol aqueous solution, stirring, separating the solid and liquid, and taking the supernatant to obtain anthocyanin solution.

5. The method for preparing an amino acid sensitized anthocyanin indicator according to claim 1, characterized in that: Before performing step S2, the anthocyanin concentration in the anthocyanin solution is detected and adjusted to 140-150 mg / mL.

6. A method for preparing a smart label based on the amino acid-sensitized anthocyanin indicator according to any one of claims 1 to 5, characterized in that: The following steps are involved: S1, preparing anthocyanin solution; S2, taking L-tryptophan to modify the obtained anthocyanin solution to obtain an amino acid-sensitized anthocyanin indicator; S3, taking the auxiliary agent mixture, adding an amino acid sensitizing anthocyanin indicator to the auxiliary agent mixture, adjusting the pH of the obtained mixed system, homogenizing, dispersing and emulsifying, and then ultrasonically treating to obtain a smart label preparation solution; S4. Form the obtained smart label preparation liquid into a film to obtain an amino acid-assisted sensitized anthocyanin smart label.

7. The method for preparing a smart label according to claim 6, characterized in that: The auxiliary agent mixture in step S3 includes gelatin, soybean oil, glycerol and Tween-80.

8. The method for preparing a smart label according to claim 6 or 7, characterized in that: The preparation steps of the auxiliary agent mixture include: uniformly dispersing 5% gelatin in distilled water, adding 5% soybean oil, 3% glycerol and 0.1% Tween-80, and stirring in a constant temperature water bath to obtain the auxiliary agent mixture.

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