A method for improving stability of anthocyanins by covalent binding with a dialdehyde polysaccharide
By covalently binding with dialdehyde polysaccharides, a dialdehyde polysaccharide-anthocyanin covalent complex was prepared, which solved the problem of poor anthocyanin stability and achieved improved stability and antioxidant activity under high temperature and neutral conditions, while maintaining the color and pH sensitivity of anthocyanins.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- YANGZHOU UNIV
- Filing Date
- 2024-01-29
- Publication Date
- 2026-05-19
AI Technical Summary
In existing technologies, anthocyanins have poor stability and are easily affected by external factors. Furthermore, existing methods for improving stability may alter the color of anthocyanins or involve complex synthesis and high costs.
The preparation of dialdehyde polysaccharide-anthocyanin covalent compounds by covalently binding with dialdehyde polysaccharides includes reacting anthocyanins and dialdehyde polysaccharides under specific conditions to form covalent compounds.
It improves the stability of anthocyanins, especially their storage stability under neutral pH and high temperature conditions, while maintaining the color and pH sensitivity of anthocyanins and exhibiting higher antioxidant activity. The synthesis process is simple and low-cost.
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Figure CN117964788B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to a method for improving the stability of anthocyanins by covalently binding with dialdehyde polysaccharides, belonging to the field of food chemistry. Background Technology
[0002] Anthocyanins are a class of water-soluble natural pigments widely found in the petals and fruits of plants, exhibiting a variety of colors including blue, purple, and red. Due to their wide availability, safety, non-toxicity, pH sensitivity, and diverse biological activities (such as antioxidant, anti-inflammatory, anti-obesity, anti-diabetic, anti-hypertensive, anti-cardiovascular disease, anti-cancer, and neuroprotective functions), natural anthocyanins have broad application prospects in the food industry. On the one hand, natural anthocyanins are pH sensitive, undergoing structural transformations and color changes in different acidic and alkaline environments, and can be added to food packaging materials to indicate the freshness of food; food packaging films with added natural anthocyanins are an important type of intelligent food packaging material. On the other hand, natural anthocyanins can be used as colorants, antioxidants, preservatives, and functional additives in food processing; adding natural anthocyanins to food not only gives it vibrant colors but also provides health benefits. However, natural anthocyanins have poor stability and are easily affected by external factors such as light, temperature, metal ions, and pH, causing structural changes that limit their application in the food industry. Therefore, improving the stability of anthocyanins is one of the urgent problems to be solved in the food industry.
[0003] Currently, various techniques (such as cochromic interactions, metal ion complexation, acylation modification, and polymer encapsulation) have been used to improve the stability of anthocyanins. Among these, cochromic interactions, metal ion complexation, and polymer encapsulation all rely on the non-covalent interactions between anthocyanins and exogenous additives (cochromates, metal ions, polymers) to enhance anthocyanin stability. However, these techniques all affect the original color of the anthocyanins, and the strength and stability of these non-covalent interactions are not high, and they can be destroyed under certain conditions. Furthermore, acylation modification improves anthocyanin stability through chemical or enzymatic catalysis, but it also suffers from complex synthesis processes and high costs. Therefore, there is an urgent need to research new methods to improve anthocyanin stability. Summary of the Invention
[0004] The purpose of this invention is to address the problems existing in the prior art, and to overcome the shortcomings of anthocyanin stabilization processes such as anthocyanin color change, low product stability, complex processes, and high costs, by providing a method to improve anthocyanin stability through covalent binding with dialdehyde polysaccharides.
[0005] To achieve the above-mentioned objectives, the present invention employs the following technical solution: a method for improving the stability of anthocyanins by covalently binding with dialdehyde polysaccharides, characterized by comprising the following steps:
[0006] (1) Plant tissue containing anthocyanins was soaked in an acidified ethanol aqueous solution, and then crushed, extracted and filtered to obtain crude anthocyanin extract.
[0007] (2) The crude anthocyanin extract obtained in step (1) is concentrated by rotary evaporation under reduced pressure, purified by macroporous resin, and dried under vacuum to obtain anthocyanins.
[0008] (3) Dissolve the polysaccharide in water to obtain a polysaccharide solution, add potassium periodate to the polysaccharide solution and react under the set conditions. The reaction product is dialyzed and freeze-dried to obtain dialdehyde polysaccharide.
[0009] (4) Dissolve the dialdehyde polysaccharide obtained in step (3) in water to obtain a dialdehyde polysaccharide solution, and dissolve the anthocyanin obtained in step (2) in water to obtain an anthocyanin solution. Then mix the dialdehyde polysaccharide solution and the anthocyanin solution to obtain a dialdehyde polysaccharide-anthocyanin mixed solution.
[0010] (5) Add hydrochloric acid to the dialdehyde polysaccharide-anthocyanin mixed solution obtained in step (4) and react under the set reaction conditions. The reaction product is dialyzed and freeze-dried to obtain the dialdehyde polysaccharide-anthocyanin covalent compound.
[0011] In step (1), the plant tissue soaking involves placing 100-200g of plant tissue in 1L of 60%-80% ethanol aqueous solution, wherein 0.1%-0.5% hydrochloric acid is added to the ethanol aqueous solution; the crushing involves crushing the plant tissue using a juicer; the extraction conditions are an extraction temperature of 2-8℃ and an extraction time of 8-24h; and the filtration is performed using 4-8 layers of gauze.
[0012] In step (2), the conditions for rotary evaporation concentration are: vacuum degree ≤ 98 kPa, temperature 30-50℃, and rotary evaporation speed 10-300 rpm; the conditions for macroporous resin purification are: loading 10-20 mL of anthocyanin rotary evaporation concentrate onto an AB-8 macroporous resin column, eluting sequentially with pure water, 20%, 40%, 60%, and 80% ethanol aqueous solution, and collecting the elution fraction of 20-80% ethanol aqueous solution; the conditions for vacuum drying are: vacuum degree < 133 Pa, drying temperature 30-50℃, and drying time 24-72 h.
[0013] In step (3), the polysaccharide solution is prepared by dissolving 1-3g of polysaccharide in 100mL of water; the amount of potassium periodate added is 0.5-1.5g; the set reaction conditions are a reaction temperature of 30-50℃, a reaction solution pH of 3.0-5.0, and a reaction time of 3-6h; the dialysis conditions are the use of a dialysis bag with a molecular weight cutoff of 3000-12000Da, dialysis with pure water for 24-72h, and water change every 4-8h; the freeze-drying conditions are a drying temperature of -45 to -50℃ and a drying time of 24-48h.
[0014] In step (4), the dialdehyde polysaccharide solution is prepared by dissolving 0.05-0.5g of dialdehyde polysaccharide in 5mL of water; the anthocyanin solution is prepared by dissolving 0.05-0.5g of anthocyanin in 5mL of water; and the dialdehyde polysaccharide-anthocyanin mixed solution is prepared by mixing the dialdehyde polysaccharide solution and the anthocyanin solution at 20-40℃ for 30-60min.
[0015] In step (5), the amount of hydrochloric acid added is 0.01-0.1 g; the reaction conditions are a reaction temperature of 20-40°C and a reaction time of 24-48 h; the dialysis conditions are the use of a dialysis bag with a molecular weight cutoff of 3000-12000 Da, dialysis with pure water for 24-72 h, and water change every 4-8 h; the freeze-drying conditions are a drying temperature of -45--50°C and a drying time of 24-48 h.
[0016] The dialdehyde polysaccharide-anthocyanin covalently bound compound prepared by the method described above.
[0017] This invention employs an advanced and scientific method to synthesize dialdehyde polysaccharide-anthocyanin covalent compounds through a covalent reaction between dialdehyde polysaccharides and anthocyanins. The resulting dialdehyde polysaccharide-anthocyanin covalent compounds possess the same color as natural anthocyanins, and the synthesis process does not alter the color of the natural anthocyanins. Furthermore, the resulting dialdehyde polysaccharide-anthocyanin covalent compounds exhibit the same pH sensitivity (i.e., color development characteristics under different pH conditions) as natural anthocyanins, demonstrating excellent application potential in the field of intelligent food packaging. Compared to polysaccharides, the resulting dialdehyde polysaccharide-anthocyanin covalent compounds exhibit higher antioxidant activity, showing potential application potential in the field of functional foods. Compared to natural anthocyanins, the resulting dialdehyde polysaccharide-anthocyanin covalent compounds demonstrate higher storage stability under neutral pH and high temperature conditions. This method offers advantages such as simple synthesis process and low cost. Attached Figure Description
[0018] Figure 1 This is a UV-Vis spectrum; where:
[0019] A is the ultraviolet-visible spectrum of Example 1 of the present invention and Comparative Examples 1, 2 and 3;
[0020] B is the ultraviolet-visible spectrum of Example 2 of the present invention and Comparative Examples 4, 5 and 6;
[0021] Figure 2 This is an infrared spectrum; where:
[0022] A is the infrared spectrum of Embodiment 1 of the present invention and Comparative Examples 1, 2 and 3.
[0023] B is the infrared spectrum of Embodiment 2 of the present invention and Comparative Examples 4, 5 and 6;
[0024] Figure 3 This is an X-ray diffraction pattern; where:
[0025] A is the X-ray diffraction pattern of Embodiment 1 of the present invention and Comparative Examples 1, 2 and 3.
[0026] B is the X-ray diffraction pattern of Embodiment 2 of the present invention and Comparative Examples 4, 5 and 6;
[0027] Figure 4 This is a hydrogen nuclear magnetic resonance spectrum; where:
[0028] A is the proton nuclear magnetic resonance spectrum of Example 1 of the present invention and Comparative Examples 1, 2 and 3.
[0029] B is the 1H NMR spectrum of Example 2 of the present invention and Comparative Examples 4, 5 and 6;
[0030] Figure 5 Here are scanning electron microscope (SEM) images; where:
[0031] A is a scanning electron microscope image of Embodiment 1 of the present invention and Comparative Examples 1, 2 and 3;
[0032] B is a scanning electron microscope image of Embodiment 2 of the present invention and Comparative Examples 4, 5 and 6;
[0033] Figure 6 The results are the colorimetric diagram and the visible light absorption spectrum; where:
[0034] A shows the colorimetric diagrams and visible light absorption spectra of Comparative Example 1 of this invention in different buffer solutions (pH 3-12);
[0035] B shows the colorimetric diagrams and visible light absorption spectra of Example 1 of the present invention in different buffer solutions (pH 3-12);
[0036] C represents the colorimetric diagrams and visible light absorption spectra of Comparative Example 4 of this invention in different buffer solutions (pH 3-12);
[0037] D represents the colorimetric diagrams and visible light absorption spectra of Example 2 of the present invention in different buffer solutions (pH 3-12);
[0038] Figure 7 This is a graph showing antioxidant activity; where:
[0039] A is a graph showing the antioxidant activity of Example 1 of the present invention compared with Comparative Examples 1, 2 and 3.
[0040] B is a graph showing the antioxidant activity of Example 2 of the present invention compared with Comparative Examples 4, 5 and 6;
[0041] Figure 8 This is a storage stability diagram; where:
[0042] A is a storage stability diagram of Comparative Example 1 of the present invention at different temperatures (20℃, 37℃ and 80℃) and different pH values (pH 3, pH 5 and pH 7);
[0043] B is a storage stability diagram of Example 1 of the present invention at different temperatures (20℃, 37℃ and 80℃) and different pH values (pH 3, pH 5 and pH 7);
[0044] C is a storage stability diagram of Comparative Example 4 at different temperatures (20℃, 37℃ and 80℃) and different pH values (pH 3, pH 5 and pH 7);
[0045] D is a storage stability diagram of Example 2 of the present invention at different temperatures (20℃, 37℃ and 80℃) and different pH values (pH 3, pH 5 and pH 7). Detailed Implementation
[0046] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments:
[0047] Example 1
[0048] A method for improving the stability of purple sweet potato anthocyanins by covalently binding with dialdehyde locust bean gum;
[0049] 100g of purple sweet potato tubers were washed, cut into pieces, and soaked in 1L of 80% ethanol aqueous solution (with 0.5% hydrochloric acid added). The tubers were then crushed using a juicer and extracted at 4℃ for 24h. The extract was filtered through four layers of gauze to obtain a crude extract of purple sweet potato anthocyanins. The crude extract was concentrated by rotary evaporation at 95kPa, 45℃, and 100rpm. 15mL of the concentrated purple sweet potato anthocyanin extract was loaded onto an AB-8 macroporous resin column and eluted sequentially with pure water, 20%, 40%, 60%, and 80% ethanol aqueous solutions. The eluent from the 20% ethanol aqueous solution was collected. The collected eluent was vacuum-dried at 105Pa and 50℃ for 72h to obtain purple sweet potato anthocyanins, which were named PSPA. 1g of locust bean gum was dissolved in 100mL of water, and 1g of potassium periodate was added. The solution was then dried at 35℃ and pH... The reaction was carried out under 3.5 conditions for 4 hours. The reaction product was placed in an 8000-12000 Da dialysis bag and dialyzed with pure water for 72 hours, with the water changed every 6 hours. After dialysis, the solution was freeze-dried at -45℃ for 48 hours to obtain dialdehyde locust bean gum, which was named LBGA. 0.1 g of dialdehyde locust bean gum and 0.1 g of purple sweet potato anthocyanin were dissolved in 5 mL of water. The dialdehyde locust bean gum aqueous solution and the purple sweet potato anthocyanin aqueous solution were thoroughly mixed at 25℃. After 30 minutes, a mixed solution of dialdehyde locust bean gum and purple sweet potato anthocyanin was obtained. 0.5 g of hydrochloric acid was added to the mixed solution, and the reaction was carried out at 25 °C for 24 h. The reaction product was placed in a 3500 Da dialysis bag and dialyzed with pure water for 24 h, with the water changed every 6 hours. After dialysis, the solution was freeze-dried at -45 °C for 48 h to obtain the covalently bound dialdehyde locust bean gum and purple sweet potato anthocyanin, which was named PSPA-g-LBGA.
[0050] Example 2
[0051] A method for improving the stability of anthocyanins in purple cabbage by covalently binding with dialdehyde guar gum;
[0052] In Example 1, purple sweet potato was replaced with purple cabbage and locust bean gum was replaced with guar gum, while the other preparation conditions remained unchanged. The purple cabbage anthocyanin obtained during the preparation process was named PCA; the dialdehyde guar gum was named GGA; and the dialdehyde guar gum-purple cabbage anthocyanin covalent compound was named PCA-g-GGA.
[0053] Comparative Example 1
[0054] Purple sweet potato anthocyanins;
[0055] The purple sweet potato anthocyanin (PSPA) obtained in Example 1.
[0056] Comparative Example 2
[0057] Sophora japonica gum;
[0058] The commercially available locust bean gum used in Example 1 is named LBG and has a purity of 99%.
[0059] Comparative Example 3
[0060] Dialdehyde Sophora japonica gum;
[0061] The dialdehyde locust bean gum (LBGA) obtained in Example 1.
[0062] Comparative Example 4
[0063] Purple cabbage anthocyanins;
[0064] The purple cabbage anthocyanin (PCA) obtained in Example 2.
[0065] Comparative Example 5
[0066] Guar gum;
[0067] The commercially available guar gum used in Example 2 is named GG and has a purity of 95%.
[0068] Comparative Example 6
[0069] Dialdehyde guar gum;
[0070] The dialdehyde guar gum (GGA) obtained in Example 2.
[0071] 1. Ultraviolet-visible spectroscopy, infrared spectroscopy, X-ray diffraction, nuclear magnetic resonance spectroscopy, and microstructure tests were performed on Examples 1, 2, 1, 2, 3, 4, 5, and 6, and the results are as follows.
[0072] The sample was dissolved in pure water, and the UV-Vis spectrum of the sample solution (0.1 mg / mL) in the range of 200–800 nm was measured using a UV / Vis spectrophotometer. Figure 1 A neutralization Figure 1 As shown in Figure B, LBG and GG do not have obvious absorption peaks in the range of 200–800 nm; LBGA and GGA have a small peak at 240 nm, indicating that LBG and GG have been successfully oxidized; while PSPA, PCA, PSPA-g-LBGA and PCA-g-GGA have anthocyanin characteristic absorption peaks at 289, 326, 328, 538 and 540 nm, indicating that dialdehyde polysaccharides have been successfully covalently bound to anthocyanins.
[0073] The sample powder was compressed into a tablet with potassium bromide, and Fourier transform infrared spectroscopy was used to analyze the sample at 400–4000 cm⁻¹. -1 The infrared spectrum of the sample was measured within a certain range. For example... Figure 2 A neutralization Figure 2 As shown in B, LBGA and GGA are at 1733 and 1723 cm.-1 The characteristic absorption peak of dialdehyde polysaccharide is present at 1500 cm⁻¹; the characteristic absorption peak of dialdehyde polysaccharide in PSPA-g-LBGA and PCA-g-GGA disappears, and the peak disappears at 1500 cm⁻¹. -1 The presence of characteristic absorption peaks for anthocyanins on both sides indicates that the dialdehyde polysaccharide and anthocyanin have successfully covalently bound.
[0074] The X-ray diffraction pattern of the sample was determined using a polycrystalline X-ray diffractometer, scanning from 5° to 75° at a rate of 2° / min. Figure 3 A and Figure 3 As shown in B, PSPA-g-LBGA and PCA-g-GGA have structures similar to LBGA and GGA, exhibiting an amorphous state; although PSPA and PCA also exhibit an amorphous state, they have different amorphous peaks compared to PSPA-g-LBGA and PCA-g-GGA.
[0075] The sample was dissolved in heavy water, and the 1H NMR spectrum of the sample solution (5 mg / mL) was measured using an AVANCE-600 NMR spectrometer. Figure 4 As shown in A and B of 4, PSPA-g-LBGA and PCA-g-GGA exhibit proton signals of PSPA and PCA at 6–8 ppm, indicating that the dialdehyde polysaccharide is successfully covalently bound to the anthocyanin.
[0076] The microstructure of the sample is analyzed using scanning electron microscopy. For example... Figure 5 A neutralization Figure 5 As shown in Figure B, LBG and GG exhibit irregular granular forms; LBGA and GGA are a mixture of sheet-like and filamentous forms; PSPA and PCA are block-like; while PSPA-g-LBGA and PCA-g-GGA have morphologies different from dialdehyde polysaccharides and anthocyanins. This indicates that dialdehyde polysaccharides and anthocyanins are successfully covalently bound.
[0077] 2. The pH sensitivity of Examples 1, 2, Comparative Example 1 and Comparative Example 4 was tested, and the results are as follows.
[0078] The sample was dissolved in a buffer solution with a pH value of 3–12, and the colorimetric characteristics of the sample in different buffer solutions were measured. The visible spectrum of the solution was also measured at 450–700 nm. Figure 6 As shown, PSPA-g-LBGA and PCA-g-GGA have the same color as PSPA and PCA in a buffer solution at pH 7, indicating that the covalent binding of anthocyanins to polysaccharides does not change the original color of anthocyanins. In addition, PSPA-g-LBGA and PCA-g-GGA show the same color and visible spectrum changes as PSPA and PCA at different pH values, indicating that the covalent binding of anthocyanins to polysaccharides does not affect the pH sensitivity of anthocyanins.
[0079] 3. The antioxidant activities of Examples 1, 2, 1, 2, 3, 4, 5 and 6 were tested, and the results are as follows.
[0080] Using Trolox as a positive control, the free radical scavenging rate was determined by reacting 1 mL of sample aqueous solution (0.1 mg / mL) with 3 mL of 100 μmol / L DPPH methanol solution under dark conditions at 25 °C for 30 min. The results are expressed as μmol Trolox equivalents / g. Figure 7 As shown, LBG, LBGA, GG, and GGA exhibited very weak antioxidant activity; PSPA and PCA possessed the highest antioxidant activity; and compared to LBGA and GGA, PSPA-g-LBGA and PCA-g-GGA exhibited even higher antioxidant activity. This indicates that covalent binding with anthocyanins can effectively enhance the antioxidant activity of dialdehyde polysaccharides.
[0081] 4. The storage stability of Examples 1, 2, Comparative Example 1 and Comparative Example 4 was tested, and the results are as follows.
[0082] The samples were dissolved in buffer solutions with different pH values (pH 3, pH 5, and pH 7) and stored at 20°C for 21 days, 37°C for 21 days, and 80°C for 1 day, respectively. The color changes of the sample solutions were recorded. Figure 8 As shown, PSPA, PCA, PSPA-g-LBGA, and PCA-g-GGA were relatively stable under low temperature and acidic conditions, and the color of the sample solutions did not change significantly. However, when PSPA and PCA were stored in a neutral buffer solution (pH 7) at 80℃ for 2 hours, the samples turned yellow, indicating significant degradation of anthocyanins. In contrast, PSPA-g-LBGA and PCA-g-GGA solutions retained a light pink color under the same storage conditions. These results indicate that covalent binding with dialdehyde polysaccharides can improve the storage stability of anthocyanins in neutral and high-temperature environments.
[0083] In summary, this invention provides a method for improving the stability of anthocyanins by covalently binding with dialdehyde polysaccharides. Multiple instrumental analyses have confirmed the successful covalent binding of dialdehyde polysaccharides and anthocyanins. The resulting dialdehyde polysaccharide-anthocyanin covalent conjugate has the same color as natural anthocyanins, and the synthesis process did not alter the color of the natural anthocyanins. The resulting dialdehyde polysaccharide-anthocyanin covalent conjugate exhibits the same pH sensitivity (i.e., color development characteristics under different pH conditions) as natural anthocyanins, showing great application potential in the field of intelligent food packaging. Compared to polysaccharides, the resulting dialdehyde polysaccharide-anthocyanin covalent conjugate has higher antioxidant activity, showing application potential in the field of functional foods. Compared to natural anthocyanins, the resulting dialdehyde polysaccharide-anthocyanin covalent conjugate shows higher storage stability under neutral pH and high temperature conditions.
[0084] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.
Claims
1. A method for improving the stability of anthocyanins by covalently binding with dialdehyde polysaccharides, characterized in that, Includes the following steps: (1) Plant tissue containing anthocyanins was soaked in an acidified ethanol aqueous solution, and then crushed, extracted and filtered to obtain crude anthocyanin extract. (2) The crude anthocyanin extract obtained in step (1) is concentrated by rotary evaporation under reduced pressure, purified by macroporous resin, and dried under vacuum to obtain anthocyanins. (3) Dissolve the polysaccharide in water to obtain a polysaccharide solution, add potassium periodate to the polysaccharide solution and react under the set reaction conditions. The reaction product is dialyzed and freeze-dried to obtain dialdehyde polysaccharide. (4) Dissolve the dialdehyde polysaccharide obtained in step (3) in water to obtain a dialdehyde polysaccharide solution, and dissolve the anthocyanin obtained in step (2) in water to obtain an anthocyanin solution. Then mix the dialdehyde polysaccharide solution and the anthocyanin solution to obtain a dialdehyde polysaccharide-anthocyanin mixed solution. (5) Add hydrochloric acid to the dialdehyde polysaccharide-anthocyanin mixed solution obtained in step (4) and react under the set reaction conditions. The reaction product is dialyzed and freeze-dried to obtain the dialdehyde polysaccharide-anthocyanin covalent compound.
2. The method for improving anthocyanin stability by covalently binding with dialdehyde polysaccharides according to claim 1, characterized in that: In step (1), the plant tissue soaking involves placing 100-200g of plant tissue in 1L of 60%-80% ethanol aqueous solution, wherein 0.1%-0.5% hydrochloric acid is added to the ethanol aqueous solution; the crushing involves crushing the plant tissue using a juicer; the extraction conditions are an extraction temperature of 2-8℃ and an extraction time of 8-24h; and the filtration is performed using 4-8 layers of gauze.
3. The method for improving anthocyanin stability by covalently binding with dialdehyde polysaccharides according to claim 1, characterized in that: In step (2), the conditions for vacuum rotary evaporation concentration are: vacuum degree ≤ 98 kPa, temperature 30-50℃, and rotary evaporation speed 10-300 rpm; the conditions for macroporous resin purification are: loading 10-20 mL of anthocyanin rotary evaporation concentrate onto an AB-8 type macroporous resin chromatographic column, and eluting sequentially with pure water, 20%, 40%, 60%, and 80% ethanol aqueous solution, and collecting the elution fraction of 20-80% ethanol aqueous solution; the conditions for vacuum drying are: vacuum degree < 133 Pa, drying temperature 30-50℃, and drying time 24-72 h.
4. The method for improving anthocyanin stability by covalently binding with dialdehyde polysaccharides according to claim 1, characterized in that: In step (3), the polysaccharide solution is prepared by dissolving 1-3g of polysaccharide in 100mL of water; the amount of potassium periodate added is 0.5-1.5g; the set reaction conditions are a reaction temperature of 30-50℃, a reaction solution pH of 3.0-5.0, and a reaction time of 3-6h; the dialysis conditions are the use of a dialysis bag with a molecular weight cutoff of 3000-12000Da, dialysis with pure water for 24-72h, and water change every 4-8h; the freeze-drying conditions are a drying temperature of -45 to -50℃ and a drying time of 24-48h.
5. The method for improving anthocyanin stability by covalently binding with dialdehyde polysaccharides according to claim 1, characterized in that: In step (4), the dialdehyde polysaccharide solution is prepared by dissolving 0.05-0.5g of dialdehyde polysaccharide in 5mL of water; the anthocyanin solution is prepared by dissolving 0.05-0.5g of anthocyanin in 5mL of water; and the dialdehyde polysaccharide-anthocyanin mixed solution is prepared by mixing the dialdehyde polysaccharide solution and the anthocyanin solution at 20-40℃ for 30-60min.
6. The method for improving anthocyanin stability by covalently binding with dialdehyde polysaccharides according to claim 1, characterized in that: In step (5), the amount of hydrochloric acid added is 0.01-0.1 g; the reaction conditions are a reaction temperature of 20-40°C and a reaction time of 24-48 h; the dialysis conditions are the use of a dialysis bag with a molecular weight cutoff of 3000-12000 Da, dialysis with pure water for 24-72 h, and water change every 4-8 h; the freeze-drying conditions are a drying temperature of -45--50°C and a drying time of 24-48 h.
7. The dialdehyde polysaccharide-anthocyanin covalent compound prepared by any one of claims 1-6.