Natural eutectic solvent, preparation method and application in extraction of aronia melanocarpa cyanidin

Abstract

The application provides a natural eutectic solvent, a preparation method and application in extraction of blackcurrant anthocyanins, and relates to the field of green extraction of natural products. The solvent is prepared by taking L-proline as a hydrogen bond acceptor and lactic acid as a hydrogen bond donor. The application also provides application of the natural eutectic solvent in extraction of blackcurrant anthocyanins. The specific method comprises the following steps: thawing, beating, vacuum freeze-drying, crushing and sieving blackcurrant fruit in sequence to obtain blackcurrant fruit powder; mixing the obtained fruit powder with the natural eutectic solvent, uniformly mixing, then performing ultrasonic-assisted extraction, centrifuging after the extraction is completed, taking supernatant to obtain an anthocyanin extract, and obtaining an anthocyanin extract after concentration. The prepared natural eutectic solvent has the characteristics of high extraction efficiency and high anthocyanin retention rate, can significantly improve the stability to light, heat and metal ions, and can effectively solve the problems of low extraction rate and easy degradation of anthocyanins in the traditional method.

Description

Technical Field

[0001] This invention relates to the field of green extraction of natural products, specifically to a natural eutectic solvent, its preparation method, and its application in the extraction of anthocyanins from black chokeberry. Background Technology

[0002] Anthocyanins from black chokeberry are the main bioactive components of black chokeberry, possessing various effects such as antioxidation, anti-inflammation, blood sugar reduction, and cardiovascular protection. However, the anthocyanin molecule contains a highly conjugated pyran ring and multiple phenolic hydroxyl groups. These phenolic hydroxyl groups give the anthocyanin molecule strong polarity and reactivity. In aqueous solutions and conventional extraction environments, anthocyanin molecules are prone to hydrolysis, ring-opening, and oxidative degradation, tending towards structural damage and content loss. This makes anthocyanins extremely unstable in conventional systems. Consequently, in practical applications, anthocyanins are difficult to maintain uniform stability during processing and storage, thus affecting their efficacy and bioavailability. While anthocyanins exhibit good biological activity when absorbed and utilized by the body, their structural instability and easy degradation prevent them from exerting their full active form, resulting in low bioavailability and significantly limiting their widespread application in food, medicine, and health products. Therefore, developing a technical system that combines efficient extraction with stabilization protection to improve the extraction rate, stability, and bioavailability of anthocyanins from black chokeberry has become a research hotspot.

[0003] The efficient extraction of natural eutectic solvents (NADES) relies on the strong hydrogen bond network and molecular interactions formed between hydrogen bond acceptors and donors. Unlike traditional organic solvents that rely on like dissolves like for extraction, NADES is formed by the association of natural metabolic components (amino acids, organic acids, sugars, etc.) through hydrogen bonds. Its structure is tunable and its polarity controllable, allowing it to form multiple molecular forces with target components, thus significantly enhancing its solubility and extraction capabilities. When NADES comes into contact with plant materials, it can synergistically disrupt the plant cell wall structure through hydrogen bonds, van der Waals forces, and hydrophobic interactions, promoting the rapid dissolution of intracellular active ingredients and significantly reducing mass transfer resistance from an energy perspective, thereby improving extraction efficiency. This enhancement manifests microscopically as the formation of stable supramolecular complexes between NADES and cell wall components and target components, effectively resisting the damage to active ingredients caused by external factors such as light, heat, and metal ions. Under harsh conditions such as high temperature, light, and oxidation, the internal hydrogen bond network and multiple interactions of NADES can maintain the structural integrity of active ingredients, preventing degradation and structural damage, thus significantly improving stability. In biological applications, NADES is prepared from natural, edible components, exhibits high biocompatibility, does not produce cytotoxicity or irritation, and is metabolically friendly, demonstrating excellent biosafety. Currently, NADES shows great potential in areas such as natural product extraction, active ingredient stabilization, food processing, and pharmaceutical preparation.

[0004] Common natural eutectic solvent components include amino acids (such as proline), which provide multiple hydrogen bonding sites and enhance system stability, but have high viscosity when used alone; organic acids (such as lactic acid and citric acid), which can adjust the pH of the system and provide an acidic microenvironment, contributing to anthocyanin stability, but have potential effects on some components; and sugars and sugar alcohols, which can enhance co-coloring effects and biocompatibility, but have high viscosity and slow mass transfer rates. Each component possesses unique physicochemical properties and plays a different role in the NADES system. Based on the requirements for natural product extraction and active ingredient stabilization, an ideal NADES should possess the following characteristics: non-toxic, safe, edible, and biodegradable; it should not adversely react with the active ingredients during preparation and storage; it should have simple components, suitable viscosity, and high extraction efficiency; and it should possess both extraction and stabilization protection functions.

[0005] Current research indicates that the main applications of anthocyanins from black chokeberry are in food and health supplements. However, during processing, storage, and in vivo transport, they are easily degraded by light, temperature, metal ions, and pH fluctuations, leading to loss of active ingredients and low bioavailability. Therefore, there is an urgent need to develop a green solvent system that can simultaneously achieve stabilization during the extraction stage to improve the stability and bioavailability of anthocyanins during preparation, storage, and in vivo environments. Summary of the Invention

[0006] The purpose of this invention is to provide a natural eutectic solvent, its preparation method, and its application in the extraction of anthocyanins from *Sorbus nigra*. This eutectic solvent is a bifunctional CNADES prepared from L-proline and lactic acid. L-proline has a cyclic structure and multiple hydrogen bond sites, which can form π-π stacking and hydrogen bonding with anthocyanins, achieving efficient co-color stabilization. Lactic acid, as a natural organic acid, can construct a weakly acidic microenvironment, maintain the stable structure of anthocyanins, and provide hydrogen bond donor / acceptor sites. The combined NADES possesses both high-efficiency extraction capability and in-situ co-color protection function, enhancing extraction efficiency and stability through a synergistic hydrogen bond network. This bifunctional CNADES simultaneously achieves efficient anthocyanin extraction and in-situ co-color stabilization, significantly improving anthocyanin extraction rate, structural integrity, and environmental stability, thereby enhancing its bioavailability.

[0007] To achieve the above objectives, the present invention is implemented through the following technical solution: The present invention first provides a natural eutectic solvent, which is prepared by using L-proline as a hydrogen bond acceptor and lactic acid as a hydrogen bond donor.

[0008] This invention also provides a method for preparing a natural eutectic solvent, comprising: L-proline and lactic acid are mixed, and water is added and stirred to obtain a natural eutectic solvent.

[0009] Preferably, the molar ratio of L-proline to lactic acid is 1:1.

[0010] Preferably, the stirring temperature is 80°C and the stirring time is 30 minutes.

[0011] Preferably, the water content of the natural eutectic solvent is 30% (w / w).

[0012] The present invention also provides the application of the above-mentioned natural eutectic solvent in the extraction of anthocyanins from black chokeberry.

[0013] Preferably, the application, specifically the method includes: Step 1: Thaw, pulp, freeze-dry under vacuum, pulverize, and sieve the frozen black chokeberry fruit to obtain black chokeberry fruit powder. Step 2: Mix the fruit powder obtained in Step 1 with a natural eutectic solvent, and after mixing, perform ultrasonic-assisted extraction. After extraction, centrifuge and take the supernatant to obtain anthocyanin extract. After concentration, obtain anthocyanin extract.

[0014] Preferably, the material-to-liquid ratio in step two is 1:30 g / mL.

[0015] Preferably, the extraction temperature in step two is 35°C, the ultrasonic power is 140W, and the extraction time is 30min.

[0016] Beneficial effects of the present invention This invention provides a natural eutectic solvent, its preparation method, and its application in the extraction of anthocyanins from *Sorbus nigra*. The natural eutectic solvent, CNADES, is prepared from L-proline and lactic acid. This invention also provides the application of the aforementioned natural eutectic solvent in the extraction of anthocyanins from *Sorbus nigra*. This invention achieves efficient anthocyanin extraction with ultrasound assistance, simultaneously completing efficient anthocyanin enrichment and in-situ color stabilization. CNADES can form multiple hydrogen bonds, π-π stacking, and hydrophobic interactions with anthocyanin molecules, constructing a weakly acidic stable microenvironment, effectively locking the flavonoid cation structure of anthocyanins, achieving in-situ color stabilization and anti-degradation protection, and significantly reducing degradation losses of anthocyanins during extraction, storage, and application. The CNADES used in this invention has higher extraction efficiency and structure retention rate for anthocyanins, significantly improving the effective utilization rate of anthocyanins. The obtained anthocyanin extract can effectively resist damage from adverse factors such as light, high temperature, metal ions, and oxidation, and significantly extend the storage period. At the same time, the extract has excellent antibacterial properties, effectively solving the technical problems of low purity, poor stability, and easy degradation that exist in traditional extraction methods. Attached Figure Description

[0017] Figure 1 Characterization data of CNADES prepared in this invention.

[0018] Figure 2 The extraction rate curve of anthocyanins from black chokeberry corresponding to the process parameters for synthesizing CNADES from proline and lactic acid prepared in this invention.

[0019] Figure 3 Comparison image and scanning electron microscope image of anthocyanins extracted from black chokeberry by CNADES prepared in Example 1 of this invention with those extracted by traditional methods.

[0020] Figure 4 The storage stability of anthocyanins extracted from *Sorbus nigra* by CNADES prepared in Example 1 of this invention under conditions of 4°C, 25°C, and above 40°C, as well as stability curves under conditions of reducing agent, oxidant, and metal ions, are shown.

[0021] Figure 5 A comparison of the antioxidant properties of anthocyanins extracted from black chokeberry by CNADES prepared in Example 1 of this invention with those extracted by conventional solvents.

[0022] Figure 6 The antibacterial effects of CNADES-extracted anthocyanins from black chokeberry and anthocyanins obtained by conventional water extraction on Escherichia coli and Staphylococcus aureus are shown in the figure in Example 1 of this invention.

[0023] Figure 7 The mechanism of CNADES prepared in Example 1 of this invention for assisting anthocyanin coloration is shown in the diagram. Detailed Implementation

[0024] The present invention first provides a natural eutectic solvent, which is prepared by using L-proline as a hydrogen bond acceptor and lactic acid as a hydrogen bond donor.

[0025] This invention also provides a method for preparing a natural eutectic solvent, comprising: L-proline and lactic acid are mixed, and water is added and stirred. The stirring temperature is preferably 80°C, and the stirring time is preferably 30 min. The mixture is stirred until clear and transparent to prepare a natural eutectic solvent (Copigment-NADES, CNADES). The molar ratio of L-proline to lactic acid is preferably 1:1; the water content of the natural eutectic solvent is preferably 30% (w / w).

[0026] The present invention also provides the application of the above-mentioned natural eutectic solvent in the extraction of anthocyanins from black chokeberry.

[0027] According to the present invention, the application method specifically includes: Step 1: Thaw, pulp, freeze-dry under vacuum, and pulverize the frozen black chokeberry fruit through a 60-mesh sieve to obtain black chokeberry fruit powder; Step 2: Add the fruit powder prepared in Step 1 to the above-mentioned natural eutectic solvent CNADES and mix evenly to form a liquid system; the liquid-to-solid ratio is preferably 1:30 (g / mL); perform ultrasonic-assisted extraction on the liquid system; the extraction temperature is preferably 35℃; the ultrasonic power is preferably 140W; the extraction time is preferably 30min; after extraction, centrifuge and take the supernatant to obtain anthocyanin extract, which is then concentrated to obtain anthocyanin extract.

[0028] The technical solution of the present invention will be fully described below with reference to the accompanying drawings and specific embodiments. All raw materials involved in the embodiments are commercially available.

[0029] Example 1 Preparation of proline-lactic acid NADES: Weigh L-proline and lactic acid in a molar ratio of 1:1, add deionized water to adjust the moisture content to 30% (w / w), stir at 80℃ until clear, and prepare proline-lactic acid NADES.

[0030] The proline-lactic acid NADES obtained was used to extract anthocyanins from black chokeberry. The specific method is as follows: Step 1, Sample processing: Thaw frozen black chokeberry fruit at room temperature, pulp it, freeze-dry it under vacuum, and then pulverize it through a 60-mesh sieve to obtain black chokeberry fruit powder. Step 2: Weigh 0.1g of black chokeberry fruit powder, add the above NADES at a material-to-liquid ratio of 1:30 (g / mL), and mix thoroughly; place the material-liquid system in an ultrasonic extractor and extract ultrasonically at 35℃ and 140W for 30 minutes to obtain anthocyanin extract.

[0031] The anthocyanin extracts obtained above were evaluated for thermal stability, reducing agent stability, and metal ion stability. Simultaneously, their antioxidant and antibacterial activities were evaluated and compared with those obtained using conventional solvent extraction. The specific methods are as follows: The obtained anthocyanin extracts were stored at 25°C, 4°C, and -20°C for 7 days. Subsequently, the anthocyanin content in the extracts was analyzed every 2 days and compared with the group stored in conventional solvents.

[0032] Anthocyanin extracts were placed in a water bath at 40, 50, 60, 70, and 80°C in the dark for a period of time. Samples were taken every 1 hour, and the anthocyanin content was determined after cooling.

[0033] Add 2.0% (v / v) Na₂SO₃ solution with concentrations of 1%, 2%, 3%, 4%, 5%, and 6% to the anthocyanin extract, mix well, and then react at room temperature in the dark for 1 hour. The anthocyanin content was measured by taking samples again; solutions of various metal ions with a concentration of 0.1 mol / L were prepared, and the anthocyanin extract was diluted by 1-fold with the above metal ion salt solutions. After mixing evenly, the solution was stored at room temperature in the dark for 1 hour, and the anthocyanin content was measured by taking samples again and calculating the anthocyanin retention rate.

[0034] Anthocyanin content and extraction rate determination: Anthocyanin content was determined using the pH differential method. Two 1 mL aliquots of anthocyanin extract were taken. One aliquot was diluted to 10 mL with KCl-HCl buffer (pH 1.0), and the other aliquot was adjusted and diluted to 10 mL with HAC-NaAC buffer (pH 4.5). After mixing, the aliquots were equilibrated at room temperature in the dark for 30 min, centrifuged at 8000 rpm for 5 min, and the supernatant was measured at 510 nm and 700 nm. The anthocyanin extraction rate was calculated as cyanidin-3-glucoside equivalents (mg / g) using the following formula: (1) (2) In the formula, Mω is the relative molecular mass of cyanidin-3-glucoside, 449.2 g / mol; n is the dilution factor; V is the total volume of the extract, mL; ε is the extinction coefficient of cyanidin-3-glucoside, 26900; and m is the mass of black chokeberry powder, g. Ultraviolet absorbance; Based on the above calculations, the anthocyanin content of Example 1 is 28.7 mg / g.

[0035] Figure 1 Characterization data of the CNADES prepared in this invention, wherein... Figure 1 A shows the infrared spectra of proline, lactic acid, and CNADES. It can be seen that the amino group of proline and the carboxyl and hydroxyl groups of lactic acid work together through multiple hydrogen bonds to build a stable intermolecular network, which is the core chemical mechanism for the formation and structural stability of CNADES.

[0036] Figure 1 B shows the infrared spectra of CNADES at different scales. It can be seen that although the scales are different, the infrared spectra of the synthesized CNADES all have the same characteristics.

[0037] Figure 1 C represents the Raman spectra of proline, lactic acid, and CNADES. It can be seen that the interaction between the components is caused by hydrogen bonding, which is verified by infrared spectroscopy. Figure 1 D represents the XRD patterns of proline, lactic acid, and CNADES, showing the changes in crystal structure before and after CNADES formation. Figure 1The TGA of E-proline, lactic acid, and CNADES shows that they have good thermal stability below 150℃, providing a basis for temperature operation in subsequent extraction processes based on this CNADES.

[0038] Figure 1 The DSC plots of F-proline, lactic acid, and CNADES show that the maximum decomposition rate is around 230℃, which, together with the TGA results, provides a basis for temperature operation in subsequent extraction processes.

[0039] Comparative Example 1 The preparation steps and parameters were exactly the same as in Example 1, except that the molar ratio of L-proline to lactic acid was 2:1, 1:2, 1:3, 1:4, and 1:5. The anthocyanin extraction rate was determined under different molar ratios, and the results are as follows: Figure 2 As shown in Figure A.

[0040] Comparative Example 2 The preparation steps and parameters were exactly the same as in Example 1, except that the material-to-liquid ratio in step two was 1:20, 1:40, 1:50, 1:60, 1:70, and 1:80 (g / mL). The anthocyanin extraction rate was measured under different material-to-liquid ratios, and the results are as follows: Figure 2 As shown in B.

[0041] Comparative Example 3 The preparation steps and parameters were exactly the same as in Example 1, except that the water content of the NADES system was 15%, 20%, 25%, 35%, 40%, and 45% (w / w). The anthocyanin extraction rate was measured under different water content conditions, and the results are as follows: Figure 2 As shown in C.

[0042] Comparative Example 4 The preparation steps and parameters were exactly the same as in Example 1, except that the extraction temperatures in step two were 15℃, 25℃, 45℃, 55℃, 65℃, and 75℃. The anthocyanin extraction rate was measured under different temperature conditions, and the results are as follows: Figure 2 As shown in F.

[0043] Comparative Example 5 The preparation steps and parameters were exactly the same as in Example 1, except that the ultrasonic power in step two was 80W, 100W, 120W, 160W, 180W, and 200W. The anthocyanin extraction rate was measured under different ultrasonic power conditions, and the results are as follows: Figure 2 As shown in D.

[0044] Comparative Example 6 The preparation steps and parameters were exactly the same as in Example 1, except that the extraction time in step two was 10 min, 20 min, 40 min, 50 min, 60 min, and 70 min. The anthocyanin extraction rate was measured under different extraction time conditions, and the results are as follows: Figure 2 As shown in E.

[0045] like Figure 3 The image shown is a comparison diagram and scanning electron microscope image of anthocyanins extracted from *Sorbus nigra* using CNADES prepared in Example 1 of the invention, and extracted using traditional methods. Figure 3 A represents the extraction amount in different solvents. Figure 3 B represents untreated black chokeberry powder. Figure 3 C is extracted by CNADES. Figure 3 D represents the product extracted with acidic ethanol. Figure 3 After extraction with water (E), it can be seen that CNADES, as the extraction solvent, yielded the highest anthocyanin extraction rate. Furthermore, CNADES showed the strongest etching effect on the black chokeberry powder.

[0046] Storage stability tests were conducted on the NADES co-coloring anthocyanin extract prepared in Example 1 and the anthocyanin solution co-coloring with conventional solvents. One 10 mL aliquot of the NADES co-coloring extract prepared in Example 1 and one 10 mL aliquot of the extract co-coloring with conventional solvents (malic acid, MA; citric acid, CA; lactic acid, LA; proline, Pro) were bottled and sealed. Storage stability tests were conducted for 7 days at 4°C, 25°C, 40°C and above, and under light-protected conditions. Anthocyanin content was measured every 2 days, and the anthocyanin retention rate was calculated. The results are shown below. Figure 4 As shown, Figure 4 A represents the retention rate of anthocyanins at 4℃. Figure 4 B represents the retention rate at 25°C. Figure 4 C represents the retention rate of anthocyanins at -20℃. Figure 4 D represents the retention rates of different solvents at 40℃, 50℃, 60℃, 70℃, and 80℃. Specifically, the retention rates of NADES at 40℃, 50℃, 60℃, 70℃, and 80℃ were 97.48%, 91.66%, 83.22%, 75.38%, and 64.26%, respectively; MA's were 90.47%, 85.39%, 75.38%, 63.69%, and 51.48%; CA's were 91.37%, 84.65%, 73.48%, 62.37%, and 50.39%; LA's were 93.58%, 87.47%, 77.45%, 66.48%, and 53.68%; and Pro's were 89.48%, 82.46%, 73.74%, 61.59%, and 48.19%. Figure 4 E represents the retention rate of anthocyanins under reducing agent conditions. Figure 4 F represents the retention rate of anthocyanins under metal ions.

[0047] The formula for calculating anthocyanin retention rate is as follows: (3) In the formula, A1 is the absorbance value of anthocyanins after treatment; A0 is the absorbance value of anthocyanins before treatment.

[0048] Antioxidant tests were performed on the anthocyanins extracted from black chokeberry fruit using CNADES prepared in Example 1. First, 3.9 mL of 0.1 mmol / L DPPH solution was added to 0.1 mL of anthocyanin extracts of different concentrations (20, 40, 80, 120, 160, 200 μg / mL), respectively. After mixing, the solutions were allowed to stand in the dark for 30 min, and the absorbance of the reaction solutions at 517 nm was measured. Water-extracted anthocyanins were used as a positive control.

[0049] (4) In the formula, A0 is the absorbance value of the control group and A1 is the absorbance value of the sample group.

[0050] First, ABTS stock solution was prepared by mixing 7.4 mM ABTS solution and 2.6 mM potassium persulfate solution at a 1:1 volume ratio and reacting in the dark for 12 h. The concentration of the ABTS stock solution was then adjusted with 200 mM phosphate buffer solution (pH 7.4) to achieve an absorbance of 0.700 ± 0.02 at 734 nm. Next, 0.05 mL of anthocyanin extracts of different concentrations were added to 4 mL of ABTS working solution, mixed thoroughly, and reacted in the dark at room temperature for 6 min. The absorbance was then measured at 734 nm, with water-extracted anthocyanins used as a positive control.

[0051] (5) In the formula, A0 is the absorbance value of the control group and A1 is the absorbance value of the sample group.

[0052] The results are as follows Figure 5 As shown, where Figure 5 A represents a comparison of DPPH free radical scavenging rates between CNADES and water extraction methods. Figure 5 B represents a comparison of the ABTS free radical scavenging rates of NADES and water extraction. It can be seen that, compared with the traditional water extraction method, the anthocyanins extracted from black chokeberry by the NADES method exhibit stronger antioxidant properties.

[0053] Figure 6 The anthocyanins extracted from black chokeberry by CNADES and those obtained by conventional water extraction prepared in Example 1 of this invention are effective against Escherichia coli (E. coli). Figure 6 A) and Staphylococcus aureus ( Figure 6B) shows the antibacterial effect. In the two graphs, 1 represents 2 mg / mL NADES anthocyanin extract; 2 represents sterile distilled water; and 3 represents water-extracted anthocyanin extract. It can be seen that both the black chokeberry anthocyanin extract (containing anthocyanins and NADES) and the water-extracted anthocyanin have certain antibacterial effects on the two test bacteria, and the antibacterial effect against Staphylococcus aureus is stronger than that against Escherichia coli.

[0054] To evaluate the color-enhancing effect and anti-degradation protection of anthocyanins by CNADES, this study assessed the stability of the color-enhancing effect under four degradation factors (pH degradation, thermal degradation, photodegradation, and oxidative degradation). A certain amount of anthocyanin aqueous solution (ACN) was mixed with CNADES to obtain a CNADES-anthocyanin mixed solution as the experimental group; the same mixed solution was prepared as the control group using lactic acid (LA), proline (Pro), malic acid (MA), and citric acid (CA).

[0055] To investigate the co-coloring effect of CNADES as a co-colorant on anthocyanins under alkaline conditions, the prepared solution was adjusted to the same pH value (pH=8) by adding an alkaline solution. The shift of the maximum absorption peak of anthocyanins was then measured using UV-Vis spectroscopy, and a portion of the sample was characterized by 1H-NMR. Figure 7 A and Figure 7 As shown in B, it can be seen that compared with the drawbacks of single components having limited effects and insufficient stability, CNADES has outstanding advantages in synergistic color enhancement and can significantly improve the pH tolerance of anthocyanins.

[0056] To investigate the co-coloring effect of CNADES as a co-colorant on anthocyanins under light conditions, the prepared solution was irradiated with natural light for 8 hours daily for five consecutive days. The shift of the maximum absorption peak of anthocyanins in the treated solution was measured using UV-Vis spectroscopy, and samples were taken for circular dichroism spectroscopy. Figure 7 C and Figure 7 As shown in D, it can be seen that compared with single components, CNADES can effectively inhibit the photo-oxidative degradation and structural deterioration of anthocyanins, and significantly improve the photostability of anthocyanins.

[0057] To investigate the co-coloring effect of CNADES as a co-coloring agent on anthocyanins under high-temperature conditions, the prepared solution was heated in a 60°C water bath in the dark for 1 hour. The resulting sample was then subjected to Raman spectroscopy to obtain its spectrum. An untreated sample was then subjected to thermogravimetric analysis using a simultaneous thermal analyzer. Figure 7 E and Figure 7 As shown in F, it can be seen that compared with single components, the colorant effect of CNADES can significantly improve the thermal decomposition initiation temperature and thermal stability of anthocyanins, and inhibit their thermally induced degradation process.

[0058] To investigate the role of CNADES as a co-coloring agent in the color enhancement of anthocyanins under oxidative conditions, a 1 mol / L FeCl3 solution was added to the prepared solution to simulate oxidation. The solution was then placed at 25°C in the dark. After 12 hours, samples were taken, and the retention rates of anthocyanins before and after oxidation were calculated according to formula (2). FT-IR was used to observe the peak shape changes before and after oxidation. Figure 7 G and Figure 7 As shown in H, it can be seen that when intersecting with a single component, CNADES can form a stable chelate network through synergistic action, effectively shielding the catalytic activity of metal ions, inhibiting their oxidative degradation of anthocyanins, and significantly improving the stability of anthocyanins under metal ion stress.

[0059] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific embodiments of the present invention are limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such deductions or substitutions should be considered within the scope of protection of the present invention.

Claims

1. A natural eutectic solvent, characterized in that, The solvent was prepared using L-proline as the hydrogen bond acceptor and lactic acid as the hydrogen bond donor.

2. The method for preparing a natural eutectic solvent according to claim 1, characterized in that, include: L-proline and lactic acid are mixed, and water is added and stirred to obtain a natural eutectic solvent.

3. The method for preparing a natural eutectic solvent according to claim 2, characterized in that, The molar ratio of L-proline to lactic acid is 1:

1.

4. The method for preparing a natural eutectic solvent according to claim 2, characterized in that, The stirring temperature is 80℃ and the stirring time is 30 minutes.

5. The method for preparing a natural eutectic solvent according to claim 2, characterized in that, The moisture content of the natural eutectic solvent is 30% (w / w).

6. The use of the natural eutectic solvent as described in claim 1 in the extraction of anthocyanins from black chokeberry.

7. The application according to claim 6, characterized in that, Specific methods include: Step 1: Thaw, pulp, freeze-dry under vacuum, pulverize, and sieve the frozen black chokeberry fruit to obtain black chokeberry fruit powder. Step 2: Mix the fruit powder obtained in Step 1 with a natural eutectic solvent, and after mixing, perform ultrasonic-assisted extraction. After extraction, centrifuge and take the supernatant to obtain anthocyanin extract. After concentration, obtain anthocyanin extract.

8. The application according to claim 7, characterized in that, In step two, the material-to-liquid ratio is 1:30 g / mL.

9. The application according to claim 7, characterized in that, The extraction temperature in step two is 35℃, the ultrasonic power is 140W, and the extraction time is 30min.

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