Method for extracting anthocyanin from forest plants

Abstract

The invention discloses a method for extracting anthocyanin from forest plants, which comprises the following steps: (1) obtaining an extraction reagent which is an aqueous solution of a deep-eutectic solvent citric acid-beta-cyclodextrin or a deep-eutectic solvent lactic acid-beta-cyclodextrin; (2) cleaning fresh leaves or petals of forest plants, drying to constant weight, crushing by using a crusher, taking raw material powder with the particle size of 120-150 meshes, sealing and keeping in a dark place for later use; and (3) carrying out ultrasonic extraction on the raw material powder obtained in the step (2) by using the extraction reagent obtained in the step (1), and then separating material residues to obtain an anthocyanin extracting solution. The method disclosed by the invention is simple in process steps, stable and controllable in process, green and environment-friendly, and improves the extraction efficiency and stability of the anthocyanin.

Description

Technical Field

[0001] The invention relates to the field of natural plant dye extraction, and in particular to a method for extracting anthocyanin from forest-derived plants. Background Art

[0002] Anthocyanidin is a water-soluble natural pigment widely found in plants. It is not only brightly colored and used in the preparation of dyes and indicators, but also has high antioxidant activity. Therefore, the development and utilization of anthocyanin resources in plants has received increasing attention. However, anthocyanidins are easily affected by high temperature, ultraviolet rays and oxygen during extraction, processing and storage. In this process, various mechanisms affect anthocyanins, including glycosylation, isomerization, dehydrogenation, hydrolysis and decarboxylation, which lead to color loss and degradation. How to extract anthocyanins quickly and efficiently and improve the stability of anthocyanins has become a problem that needs to be solved.

[0003] Common anthocyanin extraction methods include solvent extraction, microbial fermentation extraction, ultrasound-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, using ultrasound-assisted ethanol to extract anthocyanins from mulberry fruit powder, and by optimizing process parameters, effectively improving the yield of anthocyanins. However, ethanol, as a traditional extraction solvent, still has the problem of low extraction efficiency, and the stability of anthocyanins extracted using ethanol is generally poor. Patent CN 118146184 A discloses a method for extracting anthocyanins from fresh leaves of Zijuan tea trees, using Zijuan tea as raw material, and extracting anthocyanins from freeze-dried tea powder through ultrasound-assisted enzymatic hydrolysis. Compared with traditional solvents, the mixed enzyme solution can extract products with higher yield and purity, but its process cost is high and it cannot improve the stability and antioxidant capacity of anthocyanins.

[0004] A low eutectic solvent refers to a two-component or three-component low eutectic mixture composed of a certain stoichiometric ratio of hydrogen bond acceptors (such as quaternary ammonium salts) and hydrogen bond donors (such as compounds such as amides, carboxylic acids and polyols). It has the characteristics of easy synthesis, low price and strong dissolving ability. In recent years, it has been often used as an extraction solvent in various studies. Patent CN118320457 A discloses a process for recovering phenolic compounds and anthocyanins from berries by ultrasonic-assisted extraction using deep eutectic solvents. Lactic acid is used as a hydrogen bond acceptor and maltose is used as a hydrogen bond donor to prepare a low eutectic solvent. The berries are subjected to ultrasonic-assisted extraction to recover anthocyanins, which significantly improves the extraction rate of anthocyanins in berries. However, it has not been proven that this extraction method can improve the stability of anthocyanins. Patent CN 110590730 B discloses a method for extracting anthocyanins from perilla leaves using a ternary low eutectic solvent. Ethylene glycol is used as a hydrogen bond donor, lactic acid is used as an auxiliary ligand, and they are mixed with choline chloride, a hydrogen bond acceptor, to prepare a ternary low eutectic solvent. The use of this solvent to extract anthocyanins from perilla leaves can effectively reduce the loss of solvent and significantly increase the content of anthocyanins. However, the preparation process of this solvent is relatively complicated, and it has not been proven that it has the ability to improve the stability of anthocyanins.

[0005] β-cyclodextrin is a cyclic compound composed of 7 glucoses connected in 1,4 groups. Due to its structural characteristics, it can produce inclusion complexes on anthocyanins, thereby effectively reducing the effects of environmental factors such as temperature and light on anthocyanins and improving the stability of anthocyanins. By preparing a low eutectic solvent, the solid β-cyclodextrin powder can be converted into a liquid solvent, which has the ability to dissolve and extract anthocyanins, which is conducive to inclusion complexes. The application of the low eutectic solvent prepared from β-cyclodextrin in the extraction of anthocyanins from forest plants can not only improve the extraction rate of anthocyanins, but also improve the stability of anthocyanins and enhance their antioxidant capacity. However, the application of this solvent in the extraction of anthocyanins from forest plants has not yet been seen. Summary of the invention

[0006] The present invention aims to solve the deficiencies of the prior art and provides a method for extracting anthocyanins from forest plants. The method has simple process steps, a stable and controllable process, is green and environmentally friendly, and improves the extraction efficiency and stability of anthocyanins.

[0007] To achieve this object, the present invention adopts the following technical solutions:

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

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

[0010] (2) Wash the fresh leaves or petals of the forest plant, dry them to constant weight, grind them with a grinder, take the raw material powder with a particle size between 120 mesh and 150 mesh, seal and store in a dark place for later use;

[0011] (3) Using the extraction reagent obtained in step (1) to perform ultrasonic extraction on the raw material powder obtained in step (2), and then separating the residue to obtain anthocyanin extract.

[0012] Preferably, in step (1), an aqueous solution of a low eutectic solvent citric acid-β-cyclodextrin is obtained by the following method: β-cyclodextrin and citric acid are mixed, water is added, and the mixture is heated and stirred until the solution becomes uniform and transparent, thereby obtaining an aqueous solution of the low eutectic solvent.

[0013] Preferably, in step (1), the low eutectic solvent lactic acid-β-cyclodextrin is obtained by the following method: β-cyclodextrin and lactic acid are mixed, heated and stirred until the solution is uniform and transparent, to obtain the low eutectic solvent lactic acid-β-cyclodextrin.

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

[0015] Preferably, in step (2), the leaves of the forest-derived plant are selected from one of the following: red leaves of Photinia fraseri, red leaves of Cinnamomum camphora, leaves of Loropetalum chinensis or leaves of Prunus purpurea, with Loropetalum chinensis leaves being further preferred; the petals of the forest-derived plant are selected from one of the following: petals of Camellia japonica, petals of Azalea and petals of Hibiscus sylvestris, with Azalea petals being further preferred.

[0016] Preferably, in step (2), the ultrasonic extraction conditions are: solid-liquid ratio of 1 g: 20-30 mL, extraction at 40-70° C., ultrasonic frequency of 40-45 kHz, extraction time of 30-90 min. More preferably, the extraction temperature is 60° C., ultrasonic frequency is 40 kHz, extraction time is 60 min, and solid-liquid ratio is 1:25 (g / mL).

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

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

[0019] (1) The present invention uses low-cost and easily available natural forest source plants as extraction raw materials, with low production cost and high added value, which is conducive to efficient utilization of resources and environmental protection, while improving the economic value of the product.

[0020] (2) The present invention controls the particle size of the raw material powder to be between 120 mesh and 150 mesh, so that there will be no problem of insufficient extraction due to excessively large raw material particles, nor will the raw material particles agglomerate into a mass due to being too small, resulting in incomplete contact between the raw material and the extraction reagent. Screening out raw material powder with a particle size between 120 and 150 mesh can effectively improve the extraction efficiency of anthocyanins.

[0021] (3) The low eutectic solvent prepared by the low eutectic principle of the present invention is an environmentally friendly, renewable new green solvent. The viscosity of the solvent can be changed by adjusting the water content, thereby improving the solvent's dissolution capacity and extraction efficiency for anthocyanins. The low 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 the raw material for preparing the low eutectic solvent. During the extraction process, the benzene ring in the anthocyanin structure is included in the cavity of β-cyclodextrin to form a relatively stable inclusion complex, thereby improving the stability and antioxidant activity of anthocyanins. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0023] Figure 1 This is the preparation process of anthocyanin samples.

[0024] Figure 2 is the anthocyanin content of different raw material extracts.

[0025] Figure 3 The scavenging ability of the extracts obtained in Examples 1-4 and Vc [positive control] on DPPH free radicals.

[0026] Figure 4 The scavenging ability of the extracts obtained in Examples 1-4 and Vc [positive control] on ABTS free radicals.

[0027] Figure 5 It is the total reducing capacity of the extracts obtained in Examples 1-4.

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

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

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

[0031] Fig. 9 The reducing agent stability of the extracts obtained in Examples 1-4. DETAILED DESCRIPTION

[0032] The present invention is further explained below in conjunction with specific examples. The present invention is implemented according to the technical solution of the invention, and detailed implementation methods and operating steps are given, but the protection scope of the present invention is not limited to the following examples. The experimental methods in the following examples without specifying specific conditions are usually carried out under conventional conditions.

[0033] Examples 1-4

[0034] See also Figure 1 , a method for extracting anthocyanins from forest source 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 in a molar ratio of 1:10 are mixed, and then 20% mass fraction of deionized water is added, and the mixture is stirred and heated at 80°C for 2 hours until the solution is uniform and transparent to obtain cyclodextrin-citric acid (CD-CA) solution, and the mixture is cooled and stored in a constant temperature box at 25°C; β-cyclodextrin and lactic acid in a mass ratio of 1:4 are mixed, and the mixture is stirred and heated at 80°C for 2 hours until the solution is uniform and transparent to obtain cyclodextrin-lactic acid (CD-LA).

[0036] Step 2. Preparation of raw powder: Wash fresh plant leaves (red leaves of camphor tree, red leaves of photinia, red-flowered loblolly leaves and purple-leaf plum leaves) and petals (camellia petals, azalea petals and hibiscus petals), dry them at a constant temperature of 50°C for 5 to 8 hours until constant weight is achieved, pulverize them, first sieve through a 120-mesh sieve to obtain the finer powder, then sieve through a 150-mesh sieve to obtain the coarser powder that is not sieved, control the particle size of the powder between 120 mesh and 150 mesh, and store them in a sealed container away from light.

[0037] Step 3. Ultrasonic-assisted extraction: Weigh 0.4 g of each raw material powder into a beaker, add 1% hydrochloric acid ethanol, 50% ethanol, CD-CA and CD-LA solutions respectively according to a solid-liquid ratio of 1:25 (g / mL), mix the raw material powder and the extraction reagent thoroughly and let it stand for 5-10 minutes, then extract for 60 minutes at an extraction temperature of 60°C and an ultrasonic frequency of 40 kHz.

[0038] Step 4. Separation of residue: Filter the 1% hydrochloric acid ethanol and 50% ethanol extracts to separate the residues to obtain anthocyanin extracts; centrifuge the CD-CA and CD-LA extracts at 10,000 rpm for 10 minutes while they are hot, and take the clear liquid to obtain anthocyanin extracts.

[0039] Step 5. Determination of anthocyanin content: Take 1 mL of sample, dilute to 10 mL 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), stand in dark for 10 min, centrifuge at 8000 rpm for 5 min, take the supernatant, and measure its absorbance at 520 nm and 700 nm, respectively. Calculate anthocyanin content according to the following formula:

[0040]

[0041] Where: A 520 and A 700 are the absorbance of the sample at 520nm and 700nm respectively; M is the molecular weight of cyanidin-3-O-glucoside, and its value is 449.2; ε is the extinction coefficient of cyanidin-3-O-glucoside, and its value is 26900; DF is the dilution factor; l is the optical path length; 1000 is the factor for converting g to mg; m is the mass of raw material required for each liter of extract (g).

[0042] Step 6. Screening of extraction samples: Anthocyanins from leaves of four plants and petals of three plants were extracted using two organic reagents and two low eutectic solvents under ultrasonic conditions. The results of the determination of anthocyanin content are shown in Figure 2. Figure 2 As shown. The results showed that among the three leaves, the anthocyanin content of the extract of Loropetalum chinensis was the highest, reaching 5.72 mg / g, which was significantly higher than the extracts of the other three leaves. Among the two petals, the anthocyanin content of the azalea extract was higher, reaching 3.85 mg / g, which was higher than that of the camellia petal and hibiscus petal extracts. Therefore, Loropetalum chinensis and azalea were selected as the extraction raw materials.

[0043] Among the two organic reagents, 1% hydrochloric acid ethanol had a better extraction effect on anthocyanins in the leaves of Loropetalum chinensis and the petals of Rhododendron chinense. The anthocyanin contents of the extracts were 3.85 mg / g and 3.04 mg / g, respectively, which were about 1.16 times and 1.31 times that of the 50% extract. Among the two low eutectic solvents, the anthocyanin content of the CD-CA extract of 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 extract and CD-LA extract of Rhododendron chinense was not significantly different, which were 3.81 mg / g and 3.85 mg / g, respectively. In order to reduce the differences in conditions in subsequent experiments, 1% hydrochloric acid ethanol and CD-CA were uniformly selected as extraction reagents. Therefore, the 1% hydrochloric acid ethanol extract of Loropetalum chinensis was used as [Example 1], the CD-CA extract of Loropetalum chinensis was used as [Example 2], the 1% hydrochloric acid ethanol extract of Azalea was used as [Example 3], and the CD-CA extract of Azalea was used as [Example 4], and subsequent antioxidant capacity and stability tests were performed.

[0044] Embodiment 5:

[0045] (1) Determination of the DPPH radical scavenging ability of the extract 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 is dissolved in anhydrous ethanol and fixed to 100 mL), shake and mix, and measure the absorbance at 520 nm after 30 minutes, using 1 mg / L Vc solution as a positive control. Calculate the DPPH radical scavenging rate according to the following formula:

[0046]

[0047] Where: A i is the absorbance value after the sample is mixed with DPPH solution, A j A is the absorbance value after the sample and solvent are mixed. C It is the absorbance value after DPPH solution is mixed with solvent.

[0048] (2) Determine the ABTS free radical scavenging ability of the extract obtained in Examples 1-4: Prepare a mixed solution of 7 mmol / L ABTS and 2.45 mmol / L potassium persulfate with deionized water, and store it in the dark at room temperature for 12 to 18 hours to obtain an ABTS free radical base liquid. Take 3.9 mL of ABTS free radical base liquid and add 5 mL of sample, let it stand for 6 minutes, and measure the absorbance at 734 nm. Use 1 mg / L Vc solution as a positive control and deionized water as a blank control. Calculate the ABTS free radical scavenging rate according to the following formula:

[0049]

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

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

[0052] (4) Determination of the temperature stability of Example 1: Take 5 ml of the sample extract and keep it in a constant temperature water bath at room temperature, 60°C, 70°C, 80°C, and 90°C in the dark for 60 min, take it out and cool it to room temperature, and determine the anthocyanin content of the sample. Take room temperature as the control group and calculate the anthocyanin preservation rate according to the following formula, which is also applicable to other stability experiments.

[0053]

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

[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 after 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 using the anthocyanin content of the initial sample as a control.

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

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

[0058] The experimental results are as follows:

[0059] Antioxidant capacity and total reducing capacity determination: The extracts prepared in Examples 1 to 4 were subjected to antioxidant activity studies. The results are as follows: Figure 3 and Figure 4 As shown. The results of the DPPH method and the ABTS method are both expressed in terms of antioxidant rate (%). Combining the results of the above two methods, it can be seen that the antioxidant activity of the anthocyanin extracts determined by the DPPH method is in the following order from large to small: Azalea CD-CA extract > Loropetalum chinense CD-CA extract > Azalea 1% hydrochloric acid ethanol extract > Loropetalum chinense 1% hydrochloric acid ethanol extract, among which the Azalea CD-CA extract has the highest antioxidant activity among these extracts, and the Loropetalum chinense 1% hydrochloric acid ethanol extract has the lowest antioxidant activity; the antioxidant activity of the anthocyanin extracts determined by the ABTS method is in the following order from large to small: Loropetalum chinense CD-CA extract > Azalea CD-CA extract > Loropetalum chinense 1% hydrochloric acid ethanol extract > Azalea 1% hydrochloric acid ethanol extract, among which the Loropetalum chinense CD-CA extract has the highest antioxidant activity among these extracts, and the Loropetalum chinense 1% hydrochloric acid ethanol extract has the lowest antioxidant activity. Combining the results obtained by the above two methods, the sample solution extracted with a low eutectic solvent has a better antioxidant effect.

[0060] The total reducing capacity of Examples 1 to 4 was evaluated by an iron ion reduction experiment, and the results are as follows: Figure 5 As shown, there was no significant difference in the total reducing capacity of the four samples. The results showed that in this experiment, the extraction solvent had no significant effect on the total reducing capacity of anthocyanins.

[0061] Temperature stability: The temperature stability of the extracts prepared in Examples 1 to 4 was studied. Figure 6 As shown. When heated at a temperature above 60°C for 60 minutes, anthocyanins in the four samples were degraded to a certain extent. Compared with 1% hydrochloric acid ethanol, the CD-CA extraction of Loropetalum chinensis and Azalea sample solutions at high temperatures above 70°C was more retained, and the CD-CA extract of Loropetalum chinensis had the highest temperature stability. The above results show that the use of low eutectic solvents to extract anthocyanins can improve the temperature stability of anthocyanins to a certain extent.

[0062] Light stability: The light stability of the extracts prepared in Examples 1 to 4 was studied. Figure 7As shown. After the four samples were placed under natural light indoors for 30 days, the preservation rate of anthocyanins showed a downward trend. The anthocyanin retention rates of the four anthocyanin extracts stored under natural light for 30 days were as follows: Loropetalum chinense CD-CA extract > Azalea CD-CA extract > Azalea 1% hydrochloric acid ethanol extract > Loropetalum chinense 1% hydrochloric acid ethanol extract. Among them, the anthocyanin degradation rate of the 1% hydrochloric acid ethanol extract of Loropetalum chinense was the fastest, and the preservation rate dropped to 6.62% after 30 days. The CD-CA extract of Loropetalum chinense was relatively stable, and the anthocyanin preservation rate was 81.89% after 30 days. Similarly, after 30 days, the anthocyanin retention rate of the CD-CA extract of Azalea was significantly greater than that of the 1% hydrochloric acid ethanol extract. The above results show that the light stability of anthocyanins is poor when anthocyanins are extracted using 1% hydrochloric acid ethanol, while the light stability of anthocyanins can be significantly improved when anthocyanins are extracted using a low eutectic solvent.

[0063] Oxidant stability: The extracts prepared in Examples 1 to 4 were subjected to an oxidant stability study. The results are as follows: Figure 8 As shown. Under different concentrations of oxidants, the four samples all underwent a certain degree of degradation, and as the concentration of the oxidant increased, the degradation of anthocyanins became more obvious, and the retention rates of anthocyanins in the four samples showed certain differences under the action of the oxidants. Among them, when the concentration of the oxidant was less than 0.2%, the retention rates of the CD-CA extract of Loropetalum chinensis and the CD-CA extract of Azalea were significantly higher than those of the 1% hydrochloric acid ethanol extract of Loropetalum chinensis and the 1% hydrochloric acid ethanol extract of Azalea. When the concentration of the oxidant was 0.2%, anthocyanins in the four samples were greatly degraded, and the differences between the samples were not significant. Therefore, it is speculated that the use of low eutectic solvents for extraction can reduce the degradation of anthocyanins to a certain extent.

[0064] Reducing agent stability: The extracts prepared in Examples 1 to 4 were subjected to a reducing agent stability study. The results are as follows: Figure 8 As shown. Under the conditions of different concentrations of reducing agents, the four samples all produced a certain degree of degradation. As the concentration of the reducing agent increased, the degradation of anthocyanins became more obvious, and the degradation rates of anthocyanins in the four samples showed certain differences under the action of the reducing agent. Among them, when the reducing agent concentration was less than 1.0%, the retention rates of the CD-CA extract of Loropetalum chinensis and the CD-CA extract of Azalea were significantly higher than those of the 1% hydrochloric acid ethanol extract of Loropetalum chinensis and the 1% hydrochloric acid ethanol extract of Azalea. When the oxidant concentration was 1.0%, anthocyanins in the four samples all underwent a large degree of degradation, and the differences between the samples were not significant. Therefore, it is speculated that the use of low eutectic solvents for extraction can reduce the degradation of anthocyanins to a certain extent.

[0065] The above description is only a preferred embodiment of the present invention, and therefore cannot be used to limit the scope of the present invention. That is, equivalent changes and modifications made according to the patent scope of the present invention 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 comprises the following steps: (1) obtaining an extraction reagent, wherein the extraction reagent is an aqueous solution of a low eutectic solvent citric acid-β-cyclodextrin or a low 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; and the mass ratio of lactic acid to β-cyclodextrin in the lactic acid-β-cyclodextrin is 4:1; (2) Wash the fresh leaves or petals of the forest plant, dry them to constant weight, grind them with a grinder, take the raw material powder with a particle size between 120 mesh and 150 mesh, seal and store in a dark place for later use; (3) Using the extraction reagent obtained in step (1) to perform ultrasonic extraction on the raw material powder obtained in step (2), and then separating the residue to obtain anthocyanin extract.

2. The method according to claim 1, characterized in that: In step (1), an aqueous solution of a low eutectic solvent citric acid-β-cyclodextrin is obtained by the following method: β-cyclodextrin and citric acid are mixed, water is added, and the mixture is heated and stirred until the solution is uniform and transparent, thereby obtaining an aqueous solution of a low eutectic solvent.

3. The method according to claim 1, characterized in that: In step (1), a low eutectic solvent of lactic acid-β-cyclodextrin is obtained by the following method: β-cyclodextrin and lactic acid are mixed, and heated and stirred until the solution is uniform and transparent, thereby obtaining a low eutectic solvent of lactic acid-β-cyclodextrin.

4. The method according to claim 1, characterized in that: In step (2), the leaves of the forest-derived plant are selected from one of the following: red leaves of Photinia fraseri, red leaves of Cinnamomum camphora, leaves of Loropetalum chinensis or leaves of Prunus purpurea; and the petals of the forest-derived plant are selected from one of the following: petals of Camellia japonica, petals of Azalea and petals of Hibiscus sylvestris.

5. The method according to claim 1, characterized in that: In step (2), the ultrasonic extraction conditions are: the solid-liquid ratio is 1 g: 20-30 mL, and the extraction is carried out at 40-70° C. and an ultrasonic frequency of 40-45 kHz for 30-90 min.

6. The method according to claim 5, characterized in that: In step (2), the ultrasonic extraction conditions are: extraction temperature is 60° C., ultrasonic frequency is 40 kHz, extraction time is 60 min, and solid-liquid ratio is 1 g:25 mL.

7. The method according to claim 1, characterized in that: In step (2), the raw material powder and the extraction reagent are fully mixed before ultrasonic extraction, and allowed to stand for 5-10 minutes, and then ultrasonic extraction is performed.

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