A method for extracting anthocyanins from a forest-derived plant

Abstract

The application discloses a method for extracting anthocyanins from forest plants, which comprises the following steps: (1) obtaining an extraction reagent, wherein the extraction reagent is a eutectic solvent citric acid-beta-cyclodextrin aqueous solution or a eutectic solvent lactic acid-beta-cyclodextrin; (2) washing fresh leaves or petals of the forest plants, drying to a constant weight, crushing by using a pulverizer, taking raw material powder with a particle size of 120-150 meshes, and sealing and storing in the dark for standby; and (3) performing ultrasonic extraction on the raw material powder obtained in the step (2) by using the extraction reagent obtained in the step (1), then separating the residue, and obtaining an anthocyanin extraction solution. The method has simple process steps, a stable and controllable process, is green and environment-friendly, and improves the extraction efficiency and stability of the anthocyanins.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of natural plant dye extraction, in particular to a method for extracting anthocyanins from forest plants. BACKGROUND

[0002] Anthocyanidin is a water-soluble natural pigment widely present in plants. It is not only bright in color and used for the preparation of dyes and indicators, but also has high antioxidant activity. Therefore, the development and utilization of anthocyanin resources in plants have been increasingly valued by people. However, anthocyanins are easily affected by high temperature, ultraviolet light and oxygen during extraction, processing and storage. Various mechanisms affect anthocyanins during this process, including glycosylation, isomerization, dehydrogenation, hydrolysis and decarboxylation, which lead to color loss and degradation. How to quickly and efficiently extract anthocyanins and improve the stability of anthocyanins has become a problem to be solved.

[0003] Common methods for extracting anthocyanins include solvent extraction, microbial fermentation extraction, ultrasonic-assisted extraction, microwave-assisted extraction and supercritical fluid extraction. Patent CN 118580212 A discloses a method for improving the yield of anthocyanins in mulberry pomace. The method uses ultrasonic-assisted ethanol extraction to extract anthocyanins from mulberry powder, and effectively improves the yield of anthocyanins by optimizing process parameters. However, ethanol as a traditional extraction solvent still has the problem of low extraction efficiency, and the stability of anthocyanins extracted by ethanol is usually poor. Patent CN 118146184 A discloses a method for extracting anthocyanins from fresh leaves of purple tea tree. The method uses purple tea as raw material, and extracts anthocyanins from freeze-dried tea powder by ultrasonic-assisted enzymatic extraction. Compared with traditional solvents, the mixed enzyme solution can extract products with higher yield and purity, but the process cost is high, and it cannot improve the stability and antioxidant capacity of anthocyanins.

[0004] Deep eutectic solvent refers to a two-component or three-component deep eutectic mixture composed of a certain stoichiometric ratio of hydrogen bond acceptor (such as quaternary ammonium salt) and hydrogen bond donor (such as amide, carboxylic acid and polyhydric alcohol and other compounds), which has the characteristics of easy synthesis, low price and strong solubility, and has been used as an extraction solvent in various studies in recent years. Patent CN118320457 A discloses a process for recovering phenolic compounds and anthocyanins from berries by ultrasonic-assisted extraction using deep eutectic solvent, lactic acid as hydrogen bond acceptor, maltose as hydrogen bond donor to prepare deep eutectic solvent, and ultrasonic-assisted extraction of berries to recover anthocyanins, which significantly improves the extraction rate of anthocyanins in berries, but it is not confirmed that this extraction method can improve the stability of anthocyanins. Patent CN 110590730 B discloses a method for extracting perilla leaf anthocyanins using ternary deep eutectic solvent, ethylene glycol as hydrogen bond donor, lactic acid as auxiliary ligand, and hydrogen bond acceptor choline chloride to prepare a ternary deep eutectic solvent, which can effectively reduce the loss of solvent and significantly increase the content of anthocyanins, but the preparation process of the solvent is complex and its ability to improve the stability of anthocyanins has not been confirmed.

[0005] β-cyclodextrin is a cyclic compound composed of 7 glucose connected by 1,4, which can produce inclusion with anthocyanins due to its structural characteristics, thereby effectively reducing the influence of environmental factors such as temperature and light on anthocyanins and improving the stability of anthocyanins. By preparing deep eutectic solvent, solid β-cyclodextrin powder can be converted into liquid solvent, which has the ability to dissolve and extract anthocyanins, which is conducive to inclusion. The application of deep eutectic solvent prepared from β-cyclodextrin in the extraction of forest plant anthocyanins can not only improve the extraction rate of anthocyanins, but also improve the stability and antioxidant capacity of anthocyanins. However, the application of such solvent in the extraction of forest plant anthocyanins has not been reported. SUMMARY

[0006] The present application aims to solve the problems of the prior art and provides a method for extracting anthocyanins from forest plants, which has the advantages of simple process steps, stable and controllable process, green and environmental protection, and improved extraction efficiency and stability of anthocyanins.

[0007] To achieve this purpose, the following technical solutions are adopted in the present application:

[0008] A method for extracting anthocyanins from forest plants, comprising the following steps:

[0009] (1) obtaining an extraction reagent, the extraction reagent being an aqueous solution of a deep eutectic solvent citric acid-β-cyclodextrin or being a deep eutectic solvent lactic acid-β-cyclodextrin, in the aqueous solution of the citric acid-β-cyclodextrin, the mass ratio of water to citric acid-β-cyclodextrin is 1:4, and the molar ratio of citric acid to β-cyclodextrin is 10:1; in the lactic acid-β-cyclodextrin, the mass ratio of lactic acid to β-cyclodextrin is 4:1;

[0010] (2) washing fresh leaves or petals of a forest source plant, drying to a constant weight, crushing with a pulverizer, taking raw material powder with a particle size of 120-150 meshes, and sealing and storing in the dark for standby use;

[0011] (3) ultrasonic extraction of the raw material powder obtained in step (2) with the extraction reagent obtained in step (1), then separating the residue to obtain an anthocyanin extract.

[0012] Preferably, in step (1), the aqueous solution of the deep eutectic solvent citric acid-β-cyclodextrin is obtained by mixing β-cyclodextrin and citric acid, then adding water, and heating and stirring until the solution is uniform and transparent to obtain the aqueous solution of the deep eutectic solvent.

[0013] Preferably, in step (1), the deep eutectic solvent lactic acid-β-cyclodextrin is obtained by mixing β-cyclodextrin and lactic acid, and heating and stirring until the solution is uniform and transparent to obtain the deep eutectic solvent lactic acid-β-cyclodextrin.

[0014] Preferably, in step (1), the extraction reagent is an aqueous solution of the deep eutectic solvent citric acid-β-cyclodextrin.

[0015] Preferably, in step (2), the leaves of the forest source plant are selected from one of the following: red leaves of Photinia frasiri, red leaves of Cinnamomum camphora, leaves of Lagerstroemia speciosa, or leaves of Prunus cerasifera, and are further preferably leaves of Lagerstroemia speciosa; the petals of the forest source plant are selected from one of the following: petals of Camellia japonica, petals of Rhododendron simsii, and petals of Hibiscus syriacus, and are further preferably petals of Rhododendron simsii.

[0016] Preferably, in step (2), the ultrasonic extraction conditions are as follows: the solid-liquid ratio is 1g:20-30mL, and the extraction is carried out at 40-70℃ and an ultrasonic frequency of 40-45kHz for 30-90min. Further preferably, the extraction temperature is 60℃, the ultrasonic frequency is 40kHz, the extraction time is 60min, and the solid-liquid ratio is 1:25 (g / mL).

[0017] Preferably, in step (2), the raw material powder and the extraction reagent are thoroughly mixed before ultrasonic extraction, and are allowed to stand for 5-10min before ultrasonic extraction.

[0018] Compared with the prior art, the present application has the following advantages:

[0019] (1) The present application uses natural forest source plants as extraction raw materials, which are low in cost and easy to obtain, low in production cost, high in added value, conducive to efficient use of resources and environmental protection, and improve the economic value of the product.

[0020] (2) The present application controls the crushing particle size of the raw material powder between 120-150 meshes, so that the problem of insufficient extraction caused by too large particle size of the raw material does not exist, and the raw material does not gather into a group because the particle size of the raw material is too small, so that the raw material and the extraction reagent do not contact completely. Screening the raw material powder with a particle size of 120-150 meshes can effectively improve the extraction efficiency of anthocyanins.

[0021] (3) The eutectic solvent prepared by the low eutectic principle is an environmentally friendly, renewable and new green solvent, which can also change the viscosity of the solvent by adjusting the water content, thereby improving the solubility and extraction efficiency of the solvent for anthocyanins; the eutectic solvent with organic acid as a hydrogen bond donor can provide an acidic environment for anthocyanins to maintain their stability, which can effectively reduce the degradation of anthocyanins; β-cyclodextrin is used as a raw material for preparing the eutectic solvent, and in the extraction process, the benzene ring in the structure of anthocyanins is included by the cavity of β-cyclodextrin to form a relatively stable inclusion compound, thereby improving the stability and antioxidant activity of anthocyanins. BRIEF DESCRIPTION OF DRAWINGS

[0022] The present application will be further described below in combination with the drawings and examples.

[0023] Figure 1 The preparation process of the anthocyanin sample.

[0024] Figure 2 The anthocyanin content of the extraction liquid of different raw materials.

[0025] Figure 3 The DPPH free radical scavenging capacity of the extraction liquid obtained in Examples 1-4 and Vc [positive control].

[0026] Figure 4 The ABTS free radical scavenging capacity of the extraction liquid obtained in Examples 1-4 and Vc [positive control].

[0027] Figure 5 The total reducing capacity of the extraction liquid obtained in Examples 1-4.

[0028] Figure 6 The temperature stability of the extraction liquid obtained in Examples 1-4.

[0029] Figure 7 The light stability of the extraction liquid obtained in Examples 1-4.

[0030] Figure 8 The oxidant stability of the extraction liquid obtained in Examples 1-4.

[0031] Figure 9 Reducing agent stability of the extract obtained in Examples 1-4. DETAILED DESCRIPTION

[0032] The application will be further described in the following with specific examples. The application is implemented according to the technical scheme of the application, and detailed implementation and operation steps are given, but the protection scope of the application is not limited to the following examples. The experimental methods not specified in the following examples are usually carried out according to the conventional conditions.

[0033] Examples 1-4

[0034] Reference Figure 1 A method for extracting cyanidin from forest plants, the specific steps are as follows:

[0035] Step 1. Preparation of extraction solvent: 37% concentrated hydrochloric acid is added to ethanol to prepare 1% hydrochloric acid ethanol (v / v); distilled water is added to ethanol to prepare 50% ethanol (v / v); cyclodextrin and citric acid with a molar ratio of 1:10 are mixed, then 20% mass fraction of deionized water is added, and stirring and heating at 80°C for 2h until the solution is uniform and transparent, obtaining cyclodextrin-citric acid (CD-CA) solution, which is stored in a 25°C constant temperature box after cooling; β-cyclodextrin and lactic acid with a mass ratio of 1:4 are mixed, and stirring and heating at 80°C for 2h until the solution is uniform and transparent, obtaining cyclodextrin-lactic acid (CD-LA).

[0036] Step 2. Preparation of raw material powder: fresh plant leaves (Cinnamomum camphora red leaves, Buxus sinica red leaves, Luvunga hybrida leaves and Prunus cerasifera leaves) and petals (Camellia japonica petals, Rhododendron simsii petals and Hibiscus syriacus petals) are washed and dried at 50°C for 5-8 hours to constant weight, then crushed and passed through a 120 mesh sieve to obtain finer powder, and then passed through a 150 mesh sieve to obtain coarser powder, the particle size of the powder is controlled between 120 mesh and 150 mesh, and the powder is sealed and stored away from light.

[0037] Step 3. Ultrasonic-assisted extraction: 0.4g of each raw material powder is weighed into a beaker, 1% hydrochloric acid ethanol, 50% ethanol, CD-CA and CD-LA solution are added according to the solid-liquid ratio of 1:25 (g / mL), the raw material powder and the extraction reagent are mixed thoroughly, and then placed for 5-10min, then extracted at 60°C and ultrasonic frequency of 40kHz for 60min.

[0038] Step 4. Separation of residue: the 1% hydrochloric acid ethanol and 50% ethanol extract are filtered to separate the residue, obtaining cyanidin extract; the CD-CA and CD-LA extract is centrifuged at 10000rmp for 10min while hot, and the supernatant is taken, obtaining cyanidin extract.

[0039] Step 5. Determination of anthocyanin content: Take 1 mL of sample and dilute to 10 mL each with pH=1 buffer (0.025 mol / L potassium chloride solution, adjusted to pH=1 with HCl) and pH=4.5 buffer (0.4 mol / L sodium acetate solution, adjusted to pH=4.5 with glacial acetic acid). Incubate in the dark for 10 min, centrifuge at 8000 rpm for 5 min, collect the supernatant, and measure its absorbance at 520 nm and 700 nm. Calculate the anthocyanin content using the following formula:

[0040]

[0041] In the formula: A 520 and A 700 ε represents the absorbance of the samples at 520 nm and 700 nm, respectively; M is the molecular weight of cyanidin-3-O-glucoside, with a value of 449.2; ε is the extinction coefficient of cyanidin-3-O-glucoside, with a value of 26900; DF is the dilution factor; l is the optical path length; 1000 is the factor for converting g to mg; m is the raw material mass (g) required per L of extract.

[0042] Step 6. Sample Screening: Anthocyanins were extracted from the leaves of four plant species and the petals of three plant species using two organic reagents and two eutectic solvents under ultrasonic conditions. The anthocyanin content determination results are as follows: Figure 2 As shown in the figure. The results indicated that among the three leaf types, the anthocyanin content of the Loropetalum chinense extract was the highest, reaching 5.72 mg / g, significantly higher than that of the extracts from the other three leaf types. Among the two petal types, the anthocyanin content of the rhododendron extract was even higher, reaching 3.85 mg / g, which was greater than that of the camellia and hibiscus petal extracts. Therefore, Loropetalum chinense and rhododendron were selected as the extraction raw materials.

[0043] Among the two organic reagents, 1% hydrochloric acid ethanol showed better extraction efficiency for anthocyanins from Loropetalum chinense leaves and Rhododendron simsii petals, with anthocyanin contents of 3.85 mg / g and 3.04 mg / g, respectively, approximately 1.16 times and 1.31 times that of the 50% extract. In the two eutectic solvents, the anthocyanin content of the CD-CA extract from Loropetalum chinense (5.72 mg / g) was significantly higher than that of the CD-LA extract (4.85 mg / g), while the anthocyanin content of the CD-CA and CD-LA extracts from Rhododendron simsii showed no significant difference, at 3.81 mg / g and 3.85 mg / g, respectively. To minimize variations in conditions during subsequent experiments, 1% hydrochloric acid ethanol and CD-CA were consistently chosen as extraction reagents. Therefore, the 1% hydrochloric acid-ethanol extract of Loropetalum chinense [Example 1], the CD-CA extract of Loropetalum chinense [Example 2], the 1% hydrochloric acid-ethanol extract of Rhododendron simsii [Example 3], and the CD-CA extract of Rhododendron simsii [Example 4] were used for subsequent antioxidant capacity and stability determination.

[0044] Example 5:

[0045] (1) Determination of the DPPH free radical scavenging ability of the extracts obtained in Examples 1-4: Take 1 mL of sample, add 1 mL of deionized water to dilute, then add 2 mL of DPPH solution (0.0079 g of DPPH solid dissolved in anhydrous ethanol and brought to a final volume of 100 mL), shake to mix, and measure the absorbance at 520 nm after 30 min. Use 1 mg / L Vc solution as a positive control. Calculate the DPPH free radical scavenging rate according to the following formula:

[0046]

[0047] In the formula: A i A represents the absorbance value after the sample is mixed with the DPPH solution. j A represents the absorbance value after the sample is mixed with the solvent. C The absorbance value is the result of mixing the DPPH solution with the solvent.

[0048] (2) Determination of the ABTS radical scavenging ability of the extracts obtained in Examples 1-4: A mixed solution of 7 mmol / L ABTS and 2.45 mmol / L potassium persulfate was prepared with deionized water and stored at room temperature in the dark for 12-18 hours to obtain the ABTS radical base liquid. 3.9 mL of the ABTS radical base liquid was added to 5 mL of sample, and after standing for 6 minutes, the absorbance at 734 nm was measured. A 1 mg / L vitamin C solution was used as a positive control, and deionized water was used as a blank control. The ABTS radical scavenging rate was calculated according to the following formula:

[0049]

[0050] In the formula: A1 is the absorbance value of the sample mixed with DPPH solution, A2 is the absorbance value of the sample mixed with deionized water, and A0 is the absorbance value of the DPPH solution mixed with deionized water.

[0051] (3) Determination of the total reducing power of the extracts obtained in Examples 1-4: Take 1.5 mL of sample, dilute with 1.5 mL of deionized water, then add 3 mL each of potassium ferricyanide solution (1% by mass) and phosphate buffer (pH 6.6), mix well, place in a 50℃ water bath for 20 min, cool, add 3 mL of trichloroacetic acid solution (10% by mass), shake to mix, centrifuge at 8000 r / min for 10 min, take 2.5 mL of supernatant, add 0.5 mL of ferric chloride solution (0.1% by mass), mix well, dilute 10 times with deionized water, and measure the absorbance at 700 nm. The absorbance is directly proportional to the total reducing power. A 1 mg / L vitamin C solution was used as a positive control.

[0052] (4) Temperature stability of Example 1: Take 5 ml of sample extract and keep it in a constant temperature water bath for 60 min at room temperature, 60℃, 70℃, 80℃ and 90℃ in the dark. Take it out and cool it to room temperature. Measure the anthocyanin content of the sample. Use room temperature as the control group. Calculate the anthocyanin retention rate according to the following formula. This formula is also applicable to other stability experiments.

[0053]

[0054] In the formula: A1 is the anthocyanin content (mg / L) of the sample at different temperatures, and A0 is the anthocyanin content (mg / L) of the sample at room temperature.

[0055] (5) Determine the light stability of the extracts obtained in Examples 1-4: The samples were sealed and placed under natural light indoors, and the anthocyanin content was measured at 1 day, 2 days, 3 days, 4 days, 5 days, 6 days, 7 days, 10 days, 15 days, 20 days and 30 days. The preservation rate was calculated with the anthocyanin content of the initial sample as a control.

[0056] (6) Determination of oxidant stability in Example 1: Take 5 mL of sample and add 10 mL of hydrogen peroxide solution with concentrations of 0%, 0.01%, 0.02%, 0.05%, 0.1% and 0.2%, respectively. Let stand in the dark for 60 min and determine the anthocyanin content. The preservation rate is calculated with 0% concentration as the control group.

[0057] (7) Determine the reducing agent stability of the extracts obtained in Examples 1-4: Take 5 mL of sample and add 10 mL of sodium sulfite solution with concentrations of 0%, 0.1%, 0.2%, 0.05% and 0.1%, respectively. Let stand in the dark for 60 min and determine the anthocyanin content. The preservation rate is calculated with 0% concentration as the control group.

[0058] The experimental results are as follows:

[0059] Antioxidant and total reducing power determination: The extracts prepared in Examples 1-4 were subjected to antioxidant activity studies, and the results are as follows. Figure 3 and Figure 4 As shown in the figure. Both the DPPH and ABTS results are expressed as antioxidant rates (%). Combining the results from both methods, the antioxidant activity of the anthocyanin extracts measured by the DPPH method, in descending order, is: Rhododendron CD-CA extract > Loropetalum chinense CD-CA extract > Rhododendron 1% hydrochloric acid-ethanol extract > Loropetalum chinense 1% hydrochloric acid-ethanol extract. Among these, the Rhododendron CD-CA extract has the highest antioxidant activity, while the Loropetalum chinense 1% hydrochloric acid-ethanol extract has the lowest. Similarly, the antioxidant activity of the anthocyanin extracts measured by the ABTS method, in descending order, is: Loropetalum chinense CD-CA extract > Rhododendron CD-CA extract > Loropetalum chinense 1% hydrochloric acid-ethanol extract > Rhododendron 1% hydrochloric acid-ethanol extract. Again, the Loropetalum chinense CD-CA extract has the highest antioxidant activity, while the Rhododendron chinense 1% hydrochloric acid-ethanol extract has the lowest. Based on the results obtained from the two methods, the sample solution extracted with eutectic solvent has a better antioxidant effect.

[0060] The overall reducing power of Examples 1-4 was evaluated through iron ion reduction experiments, and the results are as follows: Figure 5 As shown, there was no significant difference in the total reducing power of the four samples. The results indicate that the extraction solvent had no significant impact on the total reducing power of anthocyanins in this experiment.

[0061] Temperature stability: The temperature stability of the extracts prepared in Examples 1-4 was studied, and the results are as follows: Figure 6 As shown, heating at temperatures above 60℃ for 60 min resulted in some degree of anthocyanin degradation in all four samples. Compared to 1% hydrochloric acid-ethanol, the CD-CA-extracted solutions of Loropetalum chinense and Rhododendron exhibited higher retention rates at temperatures above 70℃, with the CD-CA extract of Loropetalum chinense showing the highest temperature stability. These results indicate that using a eutectic solvent to extract anthocyanins can improve their temperature stability to some extent.

[0062] Light stability: The extracts prepared in Examples 1-4 were subjected to light stability studies, and the results are as follows: Figure 7As shown in the figure, the anthocyanin retention rates of all four samples decreased after 30 days of storage under natural indoor light. The anthocyanin retention rates of the four anthocyanin extracts after 30 days of storage under natural light were, in descending order: Loropetalum chinense CD-CA extract > Rhododendron simsii CD-CA extract > Rhododendron simsii 1% hydrochloric acid-ethanol extract > Loropetalum chinense 1% hydrochloric acid-ethanol extract. Among them, the anthocyanin degradation rate of the Loropetalum chinense 1% hydrochloric acid-ethanol extract was the fastest, with a retention rate decreasing to 6.62% after 30 days. The Loropetalum chinense CD-CA extract was relatively the most stable, with an anthocyanin retention rate of 81.89% after 30 days. Similarly, after 30 days, the anthocyanin retention rate of the Rhododendron simsii CD-CA extract was significantly higher than that of the 1% hydrochloric acid-ethanol extract. The above results indicate that anthocyanin is poorly photosensitive when extracted with 1% hydrochloric acid and ethanol, while its photosensitive stability is significantly improved when extracted with a eutectic solvent.

[0063] Oxidizing agent stability: The extracts prepared in Examples 1-4 were subjected to oxidizing agent stability studies, and the results are as follows: Figure 8 As shown, under different concentrations of oxidant, all four samples underwent some degree of degradation. The degradation of anthocyanins became more pronounced with increasing oxidant concentration, and the retention rates of anthocyanins varied among the four samples under the influence of the oxidant. Specifically, when the oxidant concentration was less than 0.2%, the retention rates of CD-CA extracts from *Loropetalum chinense* and *Rhododendron simsii* were significantly higher than those from the 1% hydrochloric acid-ethanol extracts of both. When the oxidant concentration was 0.2%, anthocyanins in all four samples underwent significant degradation, with no significant differences between samples. Therefore, it is speculated that using a eutectic solvent for extraction can reduce anthocyanin degradation to some extent.

[0064] Reducing agent stability: The extracts prepared in Examples 1-4 were subjected to reducing agent stability studies, and the results are as follows: Figure 8 As shown, under different concentrations of reducing agent, all four samples underwent some degree of degradation. The degradation of anthocyanins became more pronounced with increasing reducing agent concentration, and the degradation rates of anthocyanins varied among the four samples under the influence of the reducing agent. Specifically, when the reducing agent concentration was less than 1.0%, the retention rates of the CD-CA extracts of *Loropetalum chinense* and *Rhododendron simsii* were significantly higher than those of the 1% hydrochloric acid-ethanol extracts of *Loropetalum chinense* and *Rhododendron simsii*. When the oxidant concentration was 1.0%, anthocyanins in all four samples underwent significant degradation, with no significant differences between samples. Therefore, it is speculated that using a eutectic solvent for extraction can reduce anthocyanin degradation to some extent.

[0065] The above description is merely a preferred embodiment of the present invention, and therefore should not be construed as limiting the scope of the present invention. All equivalent changes and modifications made in accordance with the scope of the patent and the contents of the specification should still fall within the scope of the present invention.

Claims

1. A method for extracting anthocyanins from forest plants, characterized in that: The method includes the following steps: (1) Obtain the extraction reagent, wherein the extraction reagent is an aqueous solution of eutectic solvent citric acid-β-cyclodextrin or an aqueous solution of eutectic solvent lactic acid-β-cyclodextrin, wherein the mass ratio of water to citric acid-β-cyclodextrin in the aqueous solution of citric acid-β-cyclodextrin is 1:4 and the molar ratio of citric acid to β-cyclodextrin is 10:1; wherein the mass ratio of lactic acid to β-cyclodextrin in the aqueous solution of lactic acid-β-cyclodextrin is 4:1; the aqueous solution of eutectic solvent citric acid-β-cyclodextrin is obtained by mixing β-cyclodextrin and citric acid, then adding water, heating and stirring until the solution is uniform and transparent, thereby obtaining an aqueous solution of eutectic solvent citric acid-β-cyclodextrin; the aqueous solution of eutectic solvent lactic acid-β-cyclodextrin is obtained by mixing β-cyclodextrin and lactic acid, heating and stirring until the solution is uniform and transparent, thereby obtaining an aqueous solution of eutectic solvent lactic acid-β-cyclodextrin; (2) Wash the fresh leaves or petals of the forest plants, dry them to constant weight, crush them with a pulverizer, take the raw material powder with a particle size between 120 mesh and 150 mesh, seal and store it in the dark for later use. (3) The raw material powder obtained in step (2) is subjected to ultrasonic extraction using the extraction reagent obtained in step (1), and then the residue is separated to obtain anthocyanin extract.

2. The method as described in claim 1, characterized in that: In step (2), the leaves of the forest source plants are selected from one of the following: red leaves of photinia, red leaves of camphor, leaves of red-flowered loropetalum or leaves of purple-leaf plum; the petals of the forest source plants are selected from one of the following: petals of camellia, petals of rhododendron and petals of hibiscus.

3. The method as described in claim 1, characterized in that: In step (2), the ultrasonic extraction conditions are: a material-to-liquid ratio of 1 g: 20-30 mL, and extraction at 40-70 ℃ and an ultrasonic frequency of 40-45 kHz for 30-90 min.

4. The method as described in claim 3, characterized in that: In step (2), the ultrasonic extraction conditions are: extraction temperature of 60℃, ultrasonic frequency of 40 kHz, extraction time of 60 min, and material-liquid ratio of 1g:25mL.

5. The method as described in claim 1, characterized in that: In step (2), the raw material powder and extraction reagent are thoroughly mixed before ultrasonic extraction and allowed to stand for 5-10 minutes before ultrasonic extraction.

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