Preparation method of litchi peel anthocyanin

Abstract

The invention belongs to the field of food natural pigments, and relates to a preparation method of litchi pericarp anthocyanin. Lychee peel is freeze-dried and crushed into lychee peel freeze-dried powder; adding a ternary or binary natural eutecticevaporate solvent, stirring and extracting, and carrying out suction filtration to collect a red clear extracting solution; and filtering and centrifuging to remove solid residues and macromolecular impurities, adsorbing and enriching by using a pretreated moderate-polarity macroporous adsorption resin column, eluting to remove anthocyanin, collecting eluent, and concentrating under reduced pressure until no alcohol smell exists, thereby obtaining the litchi pericarp anthocyanin. The preparation method has the advantages of low toxicity, low volatility and environmental friendliness, anthocyanin can be rapidly and efficiently extracted from the litchi pericarp, green extraction of total anthocyanin in the litchi pericarp is achieved, the stability of the extracted anthocyanin is improved, the resource utilization rate and the product added value of the litchi pericarp can be increased, and the method is suitable for industrial production. Meanwhile, the waste liquid treatment cost can be remarkably reduced, and the influence on the environment is reduced.

Description

Technical Field

[0001] The invention belongs to the field of natural food pigments and relates to a method for preparing litchi peel anthocyanins. Background Art

[0002] Anthocyanins are a class of flavonoid compounds widely found in dark fruits, vegetables and grains, and are also natural edible water-soluble pigments. As a natural pigment, anthocyanins are highly safe and water-soluble, and are an important substitute for azo synthetic pigments. They can be widely used in food processing such as beverages, cakes and candies. At the same time, anthocyanins also have specific biological activities and pharmacological effects, such as anti-oxidation, anti-inflammatory, anti-aging, and hypolipidemic effects, and are potential functional active ingredients.

[0003] Litchi peel tissue accounts for about 15% of the weight of a single fresh lychee fruit, and contains high levels of anthocyanins and other polyphenols, which can chelate metal ions to form metal complexes, directly remove superoxide anions, and have good antioxidant activity. Litchi peel extract also has a variety of pharmacological effects such as anti-cancer, anti-aging, and prevention of cardiovascular diseases. In the process of industrial production, lychee peel is often discarded as a by-product, and its potential value has not been fully developed and utilized.

[0004] The research on the extraction of anthocyanins from litchi peel at home and abroad mainly focuses on the method of using organic solvent extraction. However, organic solvents are volatile, toxic, harmful to the environment, and the cost of waste liquid treatment is high, so traditional organic solvents have great limitations in the extraction process.

[0005] Compared with traditional organic reagents, natural deep eutectic solvents (NADES) significantly reduce volatility and toxicity, are easy to prepare and store, and are both sustainable and biodegradable. In addition, NADES has shown unique potential for insoluble drugs and unstable compounds, where unstable compounds can remain stable, effectively preventing degradation and failure during preparation and storage. There is currently no research on the use of NADES to extract anthocyanins from litchi peel. Summary of the invention

[0006] The object of the present invention is to provide a method for preparing litchi peel anthocyanins, which can realize the green extraction of total anthocyanins in litchi peel, not only quickly and efficiently extract anthocyanins from litchi peel, but also improve the stability of the extracted anthocyanins.

[0007] The method for preparing litchi peel anthocyanins of the present invention comprises the following steps: A. freeze-drying the litchi peel and processing it into powder using a high-speed grinder to obtain the litchi peel freeze-dried powder; B. Prepare a ternary or binary natural deep eutectic solvent, wherein the molar ratio of hydrogen bond acceptor to hydrogen bond donor in the ternary system is 1:1:1, and the molar ratio of hydrogen bond acceptor to hydrogen bond donor in the binary system is 2:1, 1:2 or 1:3, and the water content is 88-98% (W / V), heat and stir until a uniform, transparent, colorless solution is formed, slowly cool to room temperature, and set aside; C. Add the natural deep eutectic solvent obtained in step B to the lychee peel freeze-dried powder obtained in step A, with a solid-liquid ratio of 1:15 to 1:30 g / mL, stir and extract at 25° C. for 5-20 min, and collect the red clear extract by suction; D. filtering and centrifuging the extract obtained in step C to remove solid residues and macromolecular impurities, and then enriching the extract by adsorption on a pretreated medium-polarity macroporous adsorption resin column, using an 85% ethanol solution containing 0.1% HCl as an eluent to elute anthocyanins from the macroporous resin, and collecting the eluent; E. The eluate obtained in step D is concentrated under reduced pressure at 42° C. and the elution is determined multiple times by olfactory method until there is no alcohol smell, thereby obtaining the litchi peel anthocyanin.

[0008] According to a further feature of the method for preparing anthocyanins from litchi peel of the present invention, the litchi is selected from one of the following litchi varieties: Jizui litchi, Guiwei litchi, Huaizhi litchi and Nuomici litchi.

[0009] According to a further feature of the method for preparing litchi peel anthocyanins of the present invention, the ternary natural low eutectic solvent is a ternary system in which the molar ratio of choline chloride: citric acid: glucose is 1:1:1 or a ternary system in which the molar ratio of malic acid: glucose: glycerol is 1:1:1.

[0010] According to a further feature of the method for preparing litchi peel anthocyanins of the present invention, the binary natural deep eutectic solvent is selected from one of the following: a binary system in which the molar ratio of choline chloride: malic acid is 2:1, 1:2 or 1:3; a binary system in which the molar ratio of lactic acid: glycerol is 2:1, 1:2 or 1:3; a binary system in which the ratio of citric acid: glucose is 2:1, 1:2 or 1:3; a binary system in which the molar ratio of choline chloride: citric acid is 2:1, 1:2 or 1:3; a binary system in which the molar ratio of lactic acid: glucose is 2:1, 1:2 or 1:3.

[0011] The present invention uses a natural low eutectic solvent system to replace traditional organic solvents (such as ethanol) to extract the lychee peel freeze-dried powder, which has the advantages of low toxicity, low volatility, and environmental friendliness. It can quickly and efficiently extract anthocyanins from the lychee peel, realize the green extraction of total anthocyanins in the lychee peel, and improve the stability of the extracted anthocyanins, which is helpful to improve the resource utilization rate and product added value of the lychee peel. At the same time, it can significantly reduce the cost of waste liquid treatment, reduce the impact on the environment, and achieve the goal of sustainable development. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 This is the HPLC chromatogram (detection wavelength is 520nm) of total anthocyanin content in the pericarp of different varieties of litchi.

[0012] Figure 2 Showing the differences in total anthocyanin content of different varieties of litchi peel extracted by acidified ethanol.

[0013] Figure 3 is the extraction rate of anthocyanins from litchi peel in different systems.

[0014] Figure 4 The effect of water content on the extraction rate of anthocyanins from litchi peel.

[0015] Figure 5 The effect of the molar ratio of hydrogen bond donors to hydrogen bond acceptors on the extraction rate of anthocyanins from litchi peel.

[0016] Figure 6 The effect of stirring time on the extraction rate of anthocyanins.

[0017] Figure 7 The effect of solid-liquid ratio on the extraction rate of anthocyanins from litchi peel.

[0018] Figure 8 This is the HPLC chromatogram of C3G standard (detection wavelength is 520 nm).

[0019] Fig. 9 This is the HPLC chromatogram of the crude anthocyanin extract from litchi peel (detection wavelength is 520 nm).

[0020] Fig.10 This is a MS scan. DETAILED DESCRIPTION

[0021] The present invention is further described and explained below in conjunction with the drawings and the attached tables of the specification, but the embodiments do not limit the present invention in any form. Unless otherwise specified, the test methods used in the present invention are all conventional methods; the materials and reagents used are all reagents and materials that can be obtained from commercial channels.

[0022] Experimental reagents: The standard of cyanidin-3-glucoside (purity ≥ 97%) was extracted by the inventor's laboratory. The extraction method was based on the literature "Preparation and structural identification of anthocyanins from black soybean hulls by medium pressure liquid chromatography" (Li Xusheng, Jiang Xinwei, Shan Xiaoyu, Ran Guojing, Sun Jianxia, ​​Bai Weibin. Preparation and structural identification of anthocyanins from black soybean hulls by medium pressure liquid chromatography [J]. Food and Fermentation Industries, 2018, 44 (06): 51-57.).

[0023] Choline chloride, DL-lactic acid, D-(+)-glucose, and glycerol were purchased from Shanghai Aladdin Chemical Co., Ltd. with analytical purity; citric acid and DL-malic acid were purchased from Shanghai McLean Biochemical Technology Co., Ltd. with analytical purity; acetonitrile (chromatographic grade) was purchased from Merck KGaA, Germany; anhydrous ethanol was purchased from Tianjin Damao Chemical Reagent Factory; and formic acid (chromatographic grade) was purchased from Tianjin Komiou Chemical Reagent Co., Ltd.

[0024] Experimental instruments and equipment: SCIENTZ-12N vacuum freeze dryer, Ningbo Xinzhi Biotechnology Co., Ltd.; high-speed crusher, Beijing Beixin Keyuan Instrument Co., Ltd.; Ultimate3000 high-performance liquid chromatograph, Thermo Fisher Scientific, USA; LC-MS 8045 liquid chromatography-mass spectrometry system, Shimadzu Corporation, Japan; PB-30 acidity meter, Sartorius Scientific Instruments (Beijing) Co., Ltd.; LE104E / 02 electronic balance, Mettler-Toledo Instrument Co., Ltd.; MS-H280-Pro magnetic stirrer, SCILOGEX, USA; XHRE-2000A rotary evaporator, Shanghai Jiapeng Technology Co., Ltd.; HH-2 digital display constant temperature water bath, Changzhou Aohua Instrument Co., Ltd.

[0025] Example 1: Extraction and structural identification of anthocyanins from litchi peel 1. Experimental Methods 1. Litchi peel pretreatment Select lychees with bright skin color and no worm holes on the branches, wash and peel them, and store the lychee peels in bags at -80°C. The frozen lychee peel samples were freeze-dried in a vacuum freeze dryer, and then processed into powder using a high-speed pulverizer. The powder was then stored in a ziplock bag and stored in a -20°C refrigerator for subsequent use.

[0026] 2. NADES preparation According to the proportions in Table 1 and Table 2, the hydrogen bond acceptor and the hydrogen bond donor are mixed in a beaker and a certain proportion (mass volume ratio, W / V) of pure water is added. The mixture is heated in a water bath at 80°C and stirred with a magnetic stirrer until a uniform, transparent, colorless solution is formed. The mixture is then slowly cooled to room temperature for use.

[0027] Table 1: Ternary natural deep eutectic solvents

[0028] Table 2: Binary Natural Deep Eutectic Solvents

[0029] Abbreviations of NADES components: Choline chloride (Ch); Citric acid (Cit); Malic acid (Ma); Glucose (Glu); Glycerol (Gly); Lactic acid (La).

[0030] 3. Litchi peel anthocyanin extraction process The freeze-dried powder of litchi peel was extracted with a natural low eutectic solvent with a water content of 90% for 5-15 min by stirring, and the extract was collected by filtration using a Buchner funnel and then loaded onto the column. The pretreatment, adsorption and elution process of the medium-polar macroporous adsorption resin column are as follows: (1) Pretreatment steps: ① Activation and soaking: Use 2 column volumes of 95% ethanol to activate the resin column at a flow rate of 1 column volume per hour, and soak for 6 hours. Then, wash the resin column with deionized water until the outflowing liquid has no alcohol smell. ② Acid washing: Use 2 column volumes of 2% HCl solution for acid washing and soak for 3 hours. Then, rinse repeatedly with deionized water until the pH value of the outflowing liquid is neutral. ③ Alkaline washing: Use 2 column volumes of 2% NaOH solution for alkaline washing and soak for 3 hours. Then, wash with deionized water until the pH value of the outflowing liquid is neutral. ④ Balance: Finally, wash the resin column with 2 column volumes of 0.1% HCl solution until the pH value of the upper layer of the column is the same as the pH value of the outflowing liquid, ensuring that the resin column is in a stable acid-base equilibrium state.

[0031] (2) Adsorption process: After the pretreatment is completed, the liquid to be treated can be added for adsorption. During the adsorption process, the flow rate and adsorption time should be controlled according to the actual situation to ensure that the target substance in the liquid is effectively adsorbed.

[0032] (3) Elution process: ① Preliminary cleaning: After adsorption is completed, first use 2 column volumes of 0.1% HCl solution at a flow rate of 1 column volume per hour to clean the resin column to remove unadsorbed impurities and residues. ② Elution: Then, use 85% ethanol solution containing 0.1% HCl to elute the target substance from the resin column. The flow rate and elution time of the eluent should be adjusted according to actual conditions to ensure the recovery rate and purity of the target substance. ③ Collection and concentration: Collect the eluent and concentrate it under reduced pressure at 42°C until there is no alcohol smell.

[0033] 4. Determination of anthocyanin content and calculation of its extraction rate Take a small amount of cyanidin-3-O-glucoside (C3G) standard, use anhydrous ethanol solution to prepare the final concentration to 0.2 mg / mL, balance in the dark for 1 hour, dilute the 0.2 mg / mL C3G standard with anhydrous ethanol in sequence, and then perform HPLC detection after passing through a 0.22μm water filter membrane.

[0034] Liquid phase conditions: HPLC instrument (Ultimate 3000); the chromatographic column used was Venusil ASB-C18 (250 mm×4.6 mm, 5μm); the column temperature was set at 30°C, mobile phase A and mobile phase C were used, the single injection volume was 10.0μL, the flow rate was maintained at 1 mL / min, and the detection was performed at a wavelength of 520 nm. The gradient elution program was as follows: from 0 to 34 minutes, the proportion of mobile phase C was gradually increased from 6% to 30%; from 34 to 35 minutes, it was rapidly increased to 95%; from 35 to 40 minutes, the proportion of 95% remained unchanged; from 40 to 41 minutes, it was rapidly reduced to 6%; finally, from 41 to 45 minutes, the proportion was maintained at 6%.

[0035] Calculation of anthocyanin extraction rate: Anthocyanin extraction rate (mg / g) = 𝐶 × 𝑉 / 𝑀 × 100, where C represents the measured anthocyanin concentration, in mg / mL; V represents the volume of the extract, in mL; M is the mass of the weighed lychee peel freeze-dried powder, in g.

[0036] 5. Selection of litchi varieties The extraction method of anthocyanins in litchi peel is to extract with acidified ethanol: 1 g of freeze-dried powder of different varieties of litchi peel is added to 20 mL of 1.5 M HCl in 95% ethanol, and the extraction is carried out by using magnetic stirring. The extraction is carried out at room temperature and in the dark for 12 hours, and the extract is collected by filtration using a Buchner funnel. The remaining residue is extracted again according to the above extraction steps, and the extracts obtained by the two filtrations are combined. The extracts are rotary evaporated at 42°C until there is no ethanol smell, and the crude extracts of anthocyanins in litchi peel of 4 different varieties are obtained. The extracts of each litchi variety are filtered with a water system membrane filter with a pore size of 0.22μm, and the anthocyanin content is analyzed by HPLC to screen the litchi peel variety with the highest anthocyanin content. Each group of experiments is repeated three times.

[0037] 6. Screening of NADES system Different NADES systems were used as solvents to extract anthocyanins from litchi peel. The experimental conditions were fixed as follows: the molar ratio of hydrogen bond donor to hydrogen bond acceptor was 1:1, the water content was 90% (mass volume, W / V), the extraction was carried out at room temperature for 10 min, and the solid-liquid ratio was 1:15. The anthocyanin extraction rate was used as the screening index to screen the optimal NADES system, and each group of experiments was repeated three times.

[0038] 7. Factors affecting the extraction of anthocyanins using the NADES system Effect of water content of natural deep eutectic solvent on the extraction rate of anthocyanins from litchi peel: Based on the partial screening of NADES species with the highest extraction rate, the effect of water content of hydrogen bond donors and hydrogen bond acceptors of NADES on the extraction rate of anthocyanins from litchi peel was explored.

[0039] Accurately weigh 1 g of lychee peel freeze-dried powder, with a molar ratio of hydrogen bond donor to hydrogen bond acceptor of 1:1 and a solid-liquid ratio of 1:15. Stir at room temperature for 10 min. The NADES water contents were 88%, 90%, 92%, 94%, 96%, 97%, 98%, 99%, and 100% (mass volume ratio, W / V), respectively. According to the extraction rate of anthocyanins from lychee peel as the screening index, the effects of different water contents on the extraction effect were analyzed, and the appropriate NADES water content was selected. Each group of experiments was repeated three times.

[0040] Effect of the molar ratio of natural deep eutectic solvent components on the extraction rate of anthocyanins from litchi peel: After partially screening out the NADES with the highest extraction rate, we explored how the change in the molar ratio of hydrogen bond donors to hydrogen bond acceptors in NADES affects the extraction rate of anthocyanins from litchi peel.

[0041] Accurately weigh 1 g of lychee peel freeze-dried powder, with a solid-liquid ratio of 1:15, and stir at room temperature for 10 min. The molar ratios of hydrogen bond acceptors and hydrogen bond donors in binary natural deep eutectic solvents are 3:1, 2:1, 1:1, 1:2, and 1:3, respectively, and the molar ratios of hydrogen bond acceptors and hydrogen bond donors in ternary natural deep eutectic solvents are (1:1:1, 2:1:1, 1:2:1, 3:2:1, and 5:2:1). Based on the extraction rate of anthocyanins from lychee peel as the screening index, the optimal ratio of hydrogen bond acceptors and hydrogen bond donors was determined, and each group of experiments was repeated three times.

[0042] Effect of stirring time on the extraction rate of anthocyanins from litchi peel: The effect of stirring time on the extraction rate of anthocyanins from litchi peel was investigated. 1 g of lychee peel freeze-dried powder was accurately weighed, with a solid-liquid ratio of 1:15. The stirring time was 0, 1, 3, 5, 10, 15, 20, and 25 min, respectively. The extraction rate of anthocyanins from litchi peel was used as the screening index. The effect of different stirring times on the extraction effect was analyzed, and the appropriate stirring extraction time was selected. Each group of experiments was repeated three times.

[0043] Effect of solid-liquid ratio on the extraction rate of anthocyanins from litchi peel: After partially screening out the time with the highest extraction rate, the effect of solid-liquid ratio on the extraction rate of anthocyanins from litchi peel was explored. Accurately weigh 1 g of lychee peel freeze-dried powder, and the solid-liquid ratios were 1:10, 1:15, 1:20, 1:25, and 1:30, respectively. According to the extraction rate of anthocyanins from litchi peel as the screening index, the effects of different solid-liquid ratios on the extraction effect were analyzed, and the appropriate solid-liquid ratio was selected. Each group of experiments was repeated three times.

[0044] 8. Identification of the structure of anthocyanins in litchi peel by liquid chromatography-mass spectrometry Liquid phase conditions: (30AD) UFLC; the chromatographic column used in the experiment was C18 (250 mm×4.6 mm, 5 μm), acetonitrile was used as mobile phase A, and 0.1% formic acid solution was used as mobile phase B. The gradient elution program was set as follows: in the initial stage (0-3 min), the proportion of mobile phase B was 6%; then (3-6 min), the proportion of phase B gradually increased from 6% to 13%; then (6-26 min), the proportion of phase B continued to increase linearly to 30%; within (26-28 min), the proportion of phase B increased rapidly to 95%; then (28-30 min), the proportion of phase B was maintained at 95%; then (30-32 min), the proportion of phase B was rapidly reduced to 6%; finally (32-38 min), the proportion of phase B was maintained at 6% until the end of elution. During the experiment, the flow rate was controlled at 0.7 mL / min, the column temperature was set at 30 °C, the injection volume was 10 μL each time, and detection was performed at a wavelength of 520 nm.

[0045] Mass spectrometry conditions: (8045) MS; nebulizer flow rate 2.5 L / min; dryer flow rate 10 L / min; heater flow rate 10 L / min; heating block temperature 400°C; interface voltage 4.0 KV; interface temperature 300°C; DL temperature 250°C; CID 230 kPa; scan range m / z 100~1000; temperature 300°C; drying gas pressure 40 psi; flow rate 0.2 mL / min; capillary voltage 3500 V.

[0046] 2. Experimental Results In order to select the lychee peel with the highest anthocyanin content from the four varieties of lychee, Huaizhi, Guiwei, Jizui and Nuomici, acidified ethanol was used to extract anthocyanin substances from the peel of the four varieties of lychee, and the total anthocyanin content was determined by HPLC. Figure 1 and Figure 2It can be seen that the total anthocyanin content of different varieties of litchi peel is significantly different, among which "Huaizhi" has the highest total anthocyanin content, and "Guiwei" has the lowest.

[0047] Figure 3 The results show that the effects of 90% NADES on anthocyanin extraction from litchi peel The results of the extraction rate of anthocyanins in litchi peel by ternary NADES (ChCitGly, ChCitGlu) and binary NADES (ChMa, LaGly, CitGlu, ChCit, LaGlu) showed no significant difference, and both were helpful to improve the extraction rate of anthocyanins; there was a significant difference in the extraction rate of anthocyanins in litchi peel by ChCitGlu and MaGluGly in the ternary NADES system; there was a significant difference in the extraction rate of anthocyanins in litchi peel by CitGlu, ChCit, LaGlu and MaGlu in the binary NADES system, and the extraction rate of anthocyanins in litchi peel by ChGly, ChLa and ChGlu was the lowest in the binary NADES system. The pH values ​​of the nine NADES systems, ChMa, LaGly, CitGlu, ChCit, LaGlu, LaGlu, MaGlu, MaGluGly, ChCitGly, and ChCitGlu, are all around 1.7, while the pH values ​​of the three NADES systems, ChGly, ChLa, and ChGlu, are all around 4.8.

[0048] Optimize the water content of NADES system: 88%, 90%, 92%, 94%, 96%, 97%, 98%, 99%, 100% (mass volume ratio, W / V) for the extraction of anthocyanins from the peel of "Huaizhi" litchi. Figure 4 As shown in the figure, water content is one of the important factors affecting the extraction efficiency of anthocyanins. At a certain level, the extraction efficiency of anthocyanins from litchi peel did not increase with the increase of water content in the NADES system. On the contrary, excessive water content in the NADES system reduced its extraction rate. The water content of the NADES system was optimal when it was between 88% and 98% (W / V), which may be due to the formation of hydrogen bonding interactions between NADES molecules and phenolic target compounds, thereby enhancing the extraction efficiency of anthocyanins.

[0049] The experimental conditions were a solid-liquid ratio of 1:15 (g / mL), a solvent water content of 90% (mass volume ratio, W / V), and an extraction time of 10 min. The changes in anthocyanin extraction rate at different molar ratios were explored. Figure 5As shown. There was no significant difference in anthocyanin extraction rate when the molar ratio was 2:1, 1:2, and 1:3, and the anthocyanin extraction rate was significantly higher than that of other molar ratios; there was no significant difference in anthocyanin extraction rate when the molar ratio was 3:1 and 1:1; there was a significant difference in anthocyanin extraction rate when the molar ratio was 2:1, 3:1, and 1:1.

[0050] like Figure 6 As shown in the figure, the extraction rate data of anthocyanins at different times showed that in the extraction period of 0-25 minutes, the extraction rate did not increase significantly with time, but remained relatively stable.

[0051] Five different solid / liquid ratios of 1:10, 1:15, 1:20, 1:25 and 1:30 g / mL were investigated. The experimental conditions were a 1:1 molar ratio of hydrogen bond donor to hydrogen bond acceptor, 90% water content in the solvent (mass volume ratio, W / V), and an extraction time of 10 min. Figure 7 It shows that under the conditions of solid-liquid ratios of 1:15, 1:20, 1:25 and 1:30 g / mL, the extraction rate of anthocyanins is better than that of 1:10 g / mL. This shows that increasing the amount of solvent helps the target compound to fully contact with the solvent, thereby achieving maximum extraction of the target compound. Under the conditions of solid-liquid ratios of 1:15, 1:20, 1:25 and 1:30 g / mL, there is no significant difference in the extraction rate of anthocyanins, and the extraction rate of anthocyanins is significantly improved.

[0052] Liquid chromatography analysis of crude extract of anthocyanins from litchi peel Fig. 9 As shown in the figure, two substances were detected at 520 nm. In the HPLC analysis, peaks P1 and P2 appeared at approximately 15.8 minutes and 16.5 minutes, respectively. By comparing the experimental data with the HPLC spectrum of the C3G standard ( Figure 8 ) and found a substance whose retention time matched that of the C3G standard at 15.6 minutes, and it was preliminarily inferred that the substance was C3G.

[0053] Depend on Fig.10It can be seen that the fragment ion m / z 287 is cyanidin, which is formed by the parent ion (m / z 449) losing a neutral fragment of glucose (m / z 162). Therefore, it is judged that the substance represented by the molecular ion of m / z 449 is cyanidin-3-O-glucoside (C3G). The molecular ion of m / z 595 was collided at a voltage of 18 V and the product ion scan was performed. From Table 3, it can be seen that the fragment ion m / z 287 is cyanidin and m / z 449 is C3G, which are formed by the parent ion (m / z 595) losing a neutral fragment of rutin (m / z 308) and a neutral fragment of rhamnose (m / z 146), respectively. Therefore, it is judged that the substance represented by the molecular ion of m / z 595 is C3R.

[0054] Table 3:

[0055] The results of HPLC-MS / MS identification of the anthocyanin structure in litchi peel showed that litchi peel mainly contains two anthocyanins: cyanidin-3-glucoside (C3G) and cyanidin-3-rutinoside (C3R).

Claims

1. A method for preparing litchi peel anthocyanins, characterized in that: The following steps are involved: A. freeze-drying the litchi peel and processing it into powder using a high-speed grinder to obtain the litchi peel freeze-dried powder; B. Prepare a ternary or binary natural deep eutectic solvent, wherein the molar ratio of hydrogen bond acceptor to hydrogen bond donor in the ternary system is 1:1:1, and the molar ratio of hydrogen bond acceptor to hydrogen bond donor in the binary system is 2:1, 1:2 or 1:3, and the water content is 88-98% (W / V), heat and stir until a uniform, transparent, colorless solution is formed, slowly cool to room temperature, and set aside; C. Add the natural deep eutectic solvent obtained in step B to the lychee peel freeze-dried powder obtained in step A, with a solid-liquid ratio of 1:15 to 1:30 g / mL, stir and extract at 25° C. for 5-20 min, and collect the red clear extract by suction; D. filtering and centrifuging the extract obtained in step C to remove solid residues and macromolecular impurities, and then enriching the extract by adsorption on a pretreated medium-polarity macroporous adsorption resin column, using an 85% ethanol solution containing 0.1% HCl as an eluent to elute anthocyanins from the macroporous resin, and collecting the eluent; E. The eluate obtained in step D is concentrated under reduced pressure at 42° C. and the elution is determined multiple times by olfactory method until there is no alcohol smell, thereby obtaining the litchi peel anthocyanin.

2. The method for preparing anthocyanins from litchi peel according to claim 1, characterized in that: The lychee is selected from one of the following lychee varieties: Jizui lychee, Guiwei lychee, Huaizhi lychee and Nuomici lychee.

3. The method for preparing anthocyanins from litchi peel according to claim 1, characterized in that: The ternary natural deep eutectic solvent is a ternary system in which the molar ratio of choline chloride: citric acid: glucose is 1:1:1 or a ternary system in which the molar ratio of malic acid: glucose: glycerol is 1:1:

1.

4. The method for preparing litchi peel anthocyanins according to claim 1, characterized in that: The binary natural deep eutectic solvent is selected from one of the following: a binary system in which the molar ratio of choline chloride to malic acid is 2:1, 1:2 or 1:3; a binary system in which the molar ratio of lactic acid to glycerol is 2:1, 1:2 or 1:3; A binary system in which the molar ratio of citric acid to glucose is 2:1, 1:2 or 1:3; a binary system in which the molar ratio of choline chloride to citric acid is 2:1, 1:2 or 1:3; A binary system in which the molar ratio of lactic acid:glucose is 2:1, 1:2 or 1:3.

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