Method for extracting total flavonoids from shaddock peel

Abstract

The invention provides a method for extracting general flavone from shaddock peel, and relates to the technical field of flavone extraction. The method for extracting the general flavone from the shaddock peel comprises the following steps: S1, cleaning the shaddock peel, chopping, drying, crushing, and sieving with a 40-mesh sieve to obtain shaddock peel powder; s2, mixing the shaddock peel powder with petroleum ether, degreasing, filtering, and washing with distilled water until no petroleum ether is left; s3, mixing the degreased shaddock peel powder with a choline chloride-citric acid solution, extracting for a certain time, centrifuging, and concentrating and drying an extracting solution to obtain shaddock peel flavone; in the choline chloride-citric acid solution, the molar ratio of choline chloride to citric acid is 1: (0.75-1.5); the water content in the choline chloride-citric acid solution is 20%-50%. The method provided by the invention is simple in steps, easy to operate and low in energy consumption, does not need additional equipment investment, remarkably reduces the extraction cost of the total flavonoids in the shaddock peel, and is suitable for large-scale production.

Description

Technical Field

[0001] The invention relates to the technical field of flavonoid extraction, in particular to a method for extracting total flavonoids from pomelo peel. Background Art

[0002] Grapefruit (Citrus grandis) is a fruit of the Rutaceae family, belonging to the genus Citrus. It is a fruit that can be used as both medicine and food, and is mainly produced in the southern region. Grapefruit is rich in flavonoids, polyphenols, pectin, dietary fiber, polysaccharides, organic acids, vitamins, trace minerals and other beneficial ingredients for the human body. It has the effects of regulating qi and eliminating phlegm, strengthening the stomach and digestion, preventing arteriosclerosis, lowering blood lipids, and anti-oxidation.

[0003] At present, the processing of grapefruit mainly includes juice processing, grapefruit tea processing, grapefruit vinegar processing, grapefruit beverage processing, grapefruit essential oil processing, and extraction of pectin, cellulose, flavonoids, limonin and other substances. In the processing of these products, the pulp is mainly used, and the grapefruit peel is mostly discarded as waste. The weight of grapefruit peel accounts for 30% to 50% of the entire fruit, so the large amount of grapefruit peel discarded will not only cause environmental problems, but also cause a waste of resources.

[0004] Flavonoids are a type of biologically active substance that exists in nature and is yellow or light yellow. Its main types include flavonoids, flavonols, and flavanones. In the natural environment, flavonoids exist in two forms: aglycones and glycosides. A very small part exists in the form of free aglycones, and most of them exist in the form of glycosides combined with other substances. The most common glycosides are glycosides. Grapefruit is also rich in flavonoids, specifically including naringin, hesperidin, isohesperidin, etc., of which naringin accounts for more than 80%. Therefore, extracting flavonoids from grapefruit peel as raw material is one of the important directions for realizing the resource utilization of grapefruit peel.

[0005] The Chinese invention patent with publication number CN106822315A discloses a method for extracting flavonoids from grapefruit peel, which includes the following preparation steps: 1) drying and crushing the grapefruit peel; 2) treating the crushed grapefruit peel with a high-speed shear emulsifier; 3) ultrasonic extraction; 4) passing the crude flavonoid extract through a macroporous adsorption resin column chromatography and collecting the eluent; 5) passing the eluent through a hollow fiber membrane with different molecular weights; 6) concentrating and drying. Extracting flavonoids from grapefruit peel by this method can realize turning waste into treasure, making full use of resources, and the prepared flavonoids have high purity and high extraction rate. Although this method has the advantages of high purity and high extraction rate in extracting flavonoids, the entire extraction process requires the use of high-speed shear emulsifiers, ultrasonic extraction equipment, macroporous adsorption resin columns and hollow fiber membranes, resulting in high equipment investment costs and complex operations. Secondly, the ultrasonic extraction and concentration and drying processes require a lot of energy consumption, which increases the extraction cost.

[0006] Therefore, how to develop an environmentally friendly, efficient and low-cost method for extracting total flavonoids from grapefruit peel to make full use of waste grapefruit peel resources, reduce environmental pollution during flavonoid extraction and reduce extraction costs is of great significance to the resource utilization of grapefruit peel and has broad application prospects. Summary of the invention

[0007] To solve the above problems, the present invention provides a method for extracting total flavonoids from pomelo peel. The method first performs appropriate pretreatment on the pomelo peel raw material, and then uses a specific low eutectic solvent to achieve environmentally friendly, efficient and low-cost extraction of total flavonoids in pomelo peel, which has broad application prospects.

[0008] The method for extracting total flavonoids from pomelo peel of the present invention comprises the following steps:

[0009] S1. Clean the grapefruit peel, chop it into pieces, dry it, crush it, and sieve it to obtain grapefruit peel powder;

[0010] S2, mixing the grapefruit peel powder with petroleum ether, defatting the mixture, filtering the mixture, and washing the mixture with distilled water until no petroleum ether remains;

[0011] S3, mixing the defatted grapefruit peel powder with the choline chloride-citric acid solution and extracting for a certain period of time, and then centrifuging, concentrating the extract, and drying to obtain grapefruit peel flavonoids.

[0012] Further, the drying temperature is 40°C to 80°C, and the drying time is 1 to 5 hours. Preferably, the drying temperature is 50°C to 70°C, and the drying time is 2 to 4 hours. More preferably, the drying temperature is 60°C, and the drying time is 3 hours.

[0013] Furthermore, the solid-liquid ratio of the grapefruit peel powder to petroleum ether is 1g:(1-10)mL, the degreasing temperature is room temperature, and the degreasing time is 0.5-5h. Preferably, the solid-liquid ratio of the grapefruit peel powder to petroleum ether is 1g:(2-6)mL, and the degreasing time is 1-3h. More preferably, the solid-liquid ratio of the grapefruit peel powder to petroleum ether is 1g:4mL, and the degreasing time is 2h.

[0014] Further, in the choline chloride-citric acid solution, the molar ratio of choline chloride to citric acid is 1:(0.75-1.5). Preferably, in the choline chloride-citric acid solution, the molar ratio of choline chloride to citric acid is 1:(0.75-1.25). More preferably, in the choline chloride-citric acid solution, the molar ratio of choline chloride to citric acid is 1:1.

[0015] Further, the water content of the choline chloride-citric acid solution is 20% to 50%. Preferably, the water content of the choline chloride-citric acid solution is 30% to 40%. More preferably, the water content of the choline chloride-citric acid solution is 37%.

[0016] Further, the solid-liquid ratio of the defatted grapefruit peel powder to the choline chloride-citric acid solution is 1g:(5-40)mL. Preferably, the solid-liquid ratio of the defatted grapefruit peel powder to the choline chloride-citric acid solution is 1g:(15-35)mL. More preferably, the solid-liquid ratio of the defatted grapefruit peel powder to the choline chloride-citric acid solution is 1g:30mL.

[0017] Further, the extraction temperature of the choline chloride-citric acid solution is 20°C to 70°C, and the extraction time is 15 to 45 minutes. Preferably, the extraction temperature of the choline chloride-citric acid solution is 30°C to 60°C, and the extraction time is 20 to 40 minutes. More preferably, the extraction temperature of the choline chloride-citric acid solution is 50°C, and the extraction time is 30 minutes.

[0018] Compared with the prior art, the beneficial technical effects of the present invention are:

[0019] The invention can significantly improve the extraction efficiency of flavonoid compounds by optimizing the drying temperature and time, the degreasing conditions, and the composition and extraction conditions of the extraction solution.

[0020] The present invention uses choline chloride-citric acid solution as an extraction solvent, avoids the use of traditional organic solvents, reduces environmental pollution, can appropriately lower the extraction temperature and significantly shorten the extraction time, reduces energy consumption during the extraction process, and complies with the principle of green chemistry.

[0021] The invention can obtain high-purity flavonoid compounds by precisely controlling the extraction conditions, and is suitable for application in the fields of food, medicine and the like.

[0022] The total flavonoids extraction method provided by the invention has simple steps, is easy to operate, has low energy consumption, does not require additional equipment investment, significantly reduces the total flavonoids extraction cost, and is suitable for large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The present invention will be further described below in conjunction with the accompanying drawings.

[0024] Figure 1 The present invention is a process flow chart for extracting total flavonoids from pomelo peel. DETAILED DESCRIPTION

[0025] The present invention provides a method for extracting total flavonoids from pomelo peel, comprising the following steps:

[0026] S1. Clean the grapefruit peel, chop it into pieces, dry it, crush it, and sieve it to obtain grapefruit peel powder;

[0027] S2, mixing the grapefruit peel powder with petroleum ether, defatting the mixture, filtering the mixture, and washing the mixture with distilled water until no petroleum ether remains;

[0028] S3, mixing the defatted grapefruit peel powder with the choline chloride-citric acid solution and extracting for a certain period of time, and then centrifuging, concentrating the extract, and drying to obtain grapefruit peel flavonoids.

[0029] In one embodiment, the drying temperature is 40° C. to 80° C., and the drying time is 1 to 5 hours.

[0030] In one embodiment, the drying temperature is 50° C. to 70° C., and the drying time is 2 to 4 hours.

[0031] In one embodiment, the drying temperature is 60° C. and the drying time is 3 hours.

[0032] Studies have shown that the mass fraction of grapefruit peel in the whole grapefruit is as high as 43% to 48%. Grapefruit peel is not only rich in essential nutrients such as vitamins and minerals, but also contains a variety of non-nutritional active ingredients that are beneficial to health, such as flavonoids, and the content of these ingredients in grapefruit peel is much higher than that in grapefruit fruit. The flavonoids in grapefruit peel account for about 1% to 6%, mainly including naringin, hesperidin and neohesperidin, most of which are naringin. However, due to the high water content of grapefruit peel, the flavonoid content in the grapefruit peel raw material is relatively low, and the grapefruit peel is thick and hard, containing a large amount of cellulose and pectin, which will affect the release and extraction of flavonoids. Therefore, the present invention dries the grapefruit peel to improve the extraction efficiency of flavonoids. In addition, drying the grapefruit peel can also prevent the raw material from being corrupted, facilitate storage and transportation, and can centrally process and preserve a large amount of raw materials during the grapefruit listing process, reducing the pressure of subsequent extraction. This process not only improves the utilization rate of the raw materials, but also ensures the continuity and efficiency of the extraction process. Through drying treatment, the shelf life of grapefruit peel can be extended, reducing the waste caused by raw material deterioration, and also providing a more stable source of raw materials for the subsequent extraction of flavonoids.

[0033] The present invention does not strictly limit the drying process of grapefruit peel, and any conventional drying method can be applied to the total flavonoids extraction process of the present invention. Whether it is hot air drying, vacuum drying, freeze drying or microwave drying, it can be effectively used for the drying treatment of grapefruit peel to ensure the efficient extraction of flavonoid compounds. By flexibly selecting a suitable drying process, the extraction process can be optimized according to specific production conditions and requirements, and the extraction efficiency and product quality can be improved. However, in the specific embodiment of the present application, the grapefruit peel is dried by drying.

[0034] In one embodiment, the solid-liquid ratio of the grapefruit peel powder to petroleum ether is 1 g: (1-10) mL, the degreasing temperature is room temperature, and the degreasing time is 0.5-5 h.

[0035] In one embodiment, the solid-liquid ratio of the grapefruit peel powder to petroleum ether is 1 g: (2-6) mL, and the degreasing time is 1-3 h.

[0036] In one embodiment, the solid-liquid ratio of the grapefruit peel powder to petroleum ether is 1 g:4 mL, and the degreasing time is 2 h.

[0037] The purpose of the present invention is to remove fat and grease in the pomelo peel by mixing the pomelo peel powder with petroleum ether, which interfere with the extraction of flavonoids. Through the degreasing treatment, these interfering substances can be removed, the extraction efficiency can be improved, and the impurities in the extract can be reduced, thereby improving the purity of the flavonoids. In addition, the presence of fat and grease may affect the solubility of the flavonoids in the extraction solution. Through the degreasing treatment, the solubility of the flavonoids can be improved, and the extraction efficiency can be further improved.

[0038] In one embodiment, in the choline chloride-citric acid solution, the molar ratio of choline chloride to citric acid is 1:(0.75-1.5).

[0039] In one embodiment, in the choline chloride-citric acid solution, the molar ratio of choline chloride to citric acid is 1:(0.75-1.25).

[0040] In one embodiment, in the choline chloride-citric acid solution, the molar ratio of choline chloride to citric acid is 1:1.

[0041] In one embodiment, the water content of the choline chloride-citric acid solution is 20% to 50%.

[0042] In one embodiment, the water content of the choline chloride-citric acid solution is 30% to 40%.

[0043] In one embodiment, the water content of the choline chloride-citric acid solution is 37%.

[0044] Deep eutectic solvent (DES) is a stable, homogeneous and transparent liquid formed by mixing hydrogen bond donor (HBD) and acceptor (HBA) in appropriate stoichiometric ratio. The hydrogen bonds formed between HBA and HBD can induce charge delocalization, resulting in a lower melting point of the complex than the components that constitute the solvent. As a new type of green extraction solvent, DES has significant advantages such as low toxicity, low volatility, good biocompatibility, and easy degradation, and can gradually replace traditional organic solvents.

[0045] Changing the HBD and HBA of the low eutectic solvent and their concentrations will significantly affect its performance. Specifically, different combinations of HBD and HBA will cause changes in the melting point, viscosity, solubility and stability of DES. Unsuitable combinations of HBD and HBA will significantly reduce the performance of DES, fail to significantly reduce the melting point of the mixture, and cause excessive viscosity, affecting fluidity and application performance. In addition, they may also lead to a decrease in solubility, fail to effectively dissolve the target substance, and affect the chemical and thermal stability of DES, making it easy to decompose or fail under different conditions, and unable to meet the extraction requirements of total flavonoids.

[0046] In addition, in the actual research process, it was found that changing the combination and ratio of HBD and HBA has a very significant effect on the extraction effect of total flavonoids. Although the extraction rate and product purity of some combinations can eventually reach the same level, the optimal extraction conditions will be affected to varying degrees. The final study showed that when using choline chloride-citric acid solution, not only can the total flavonoid extraction rate be maintained at a high level, but the optimal extraction temperature and extraction time are also reduced to varying degrees, while other HBD and HBA combinations do not have this effect.

[0047] Therefore, the present invention strictly limits the composition of DES to choline chloride-citric acid, and strictly limits the molar ratio and solution concentration of the two.

[0048] In one embodiment, the solid-liquid ratio of the defatted grapefruit peel powder to the choline chloride-citric acid solution is 1 g: (5-40) mL.

[0049] In one embodiment, the solid-liquid ratio of the defatted grapefruit peel powder to the choline chloride-citric acid solution is 1 g: (15-35) mL.

[0050] In one embodiment, the solid-liquid ratio of the defatted grapefruit peel powder to the choline chloride-citric acid solution is 1 g:30 mL.

[0051] In one embodiment, the extraction temperature of the choline chloride-citric acid solution is 20° C. to 70° C., and the extraction time is 15 to 45 minutes.

[0052] In one embodiment, the extraction temperature of the choline chloride-citric acid solution is 30° C. to 60° C., and the extraction time is 20 to 40 minutes.

[0053] In one embodiment, the extraction temperature of the choline chloride-citric acid solution is 50° C., and the extraction time is 30 min.

[0054] The present invention optimizes the extraction process by limiting the solid-liquid ratio of the defatted grapefruit peel powder to the choline chloride-citric acid solution, as well as the extraction temperature and extraction time, thereby ensuring the extraction efficiency and the quality of the extract. The appropriate solid-liquid ratio can ensure that the grapefruit peel powder is fully in contact with the extraction solution, thereby improving the extraction efficiency of the flavonoids. The extraction temperature will affect the dissolution capacity and extraction efficiency of the solvent, and the appropriate temperature can improve the solubility of the flavonoids while avoiding the destruction of the active ingredients by high temperature. The length of the extraction time will affect the extraction efficiency and energy consumption, and the appropriate extraction time can ensure that the flavonoids are fully dissolved while avoiding the increase in energy consumption and possible component degradation caused by too long a time. By optimizing these parameters, the activity and purity of the flavonoids can be retained to the greatest extent while ensuring the extraction efficiency, thereby ensuring the quality of the extract.

[0055] The technical solution provided by the present invention is further described below in conjunction with embodiments.

[0056] Example 1

[0057] A method for extracting total flavonoids from grapefruit peel, comprising the following steps:

[0058] S1. Wash and chop the grapefruit peel, dry at 60° C. for 3 h, crush, and pass through a 40-mesh sieve to obtain grapefruit peel powder;

[0059] S2, mixing the grapefruit peel powder and petroleum ether in a ratio of 1 g:4 mL, defatting at room temperature for 2 h, filtering, and rinsing with distilled water until no petroleum ether remains;

[0060] S3, mixing the defatted grapefruit peel powder with choline chloride-citric acid solution at a solid-liquid ratio of 1 g:30 mL, extracting at 50° C. for 30 min and centrifuging, concentrating the extract at 60° C. using a rotary evaporator for 30 min, and freeze-drying to obtain grapefruit peel flavonoids;

[0061] In the choline chloride-citric acid solution, the molar ratio of choline chloride to citric acid is 1:1, and the water content in the choline chloride-citric acid solution is 37%.

[0062] Example 2

[0063] A method for extracting total flavonoids from grapefruit peel, comprising the following steps:

[0064] S1. Wash and chop the grapefruit peel, dry at 50° C. for 4 h, crush, and pass through a 40-mesh sieve to obtain grapefruit peel powder;

[0065] S2, mixing the grapefruit peel powder and petroleum ether in a solid-liquid ratio of 1 g: 6 mL, defatting at room temperature for 1 hour, filtering, and rinsing with distilled water until no petroleum ether remains;

[0066] S3, mixing the defatted grapefruit peel powder with choline chloride-citric acid solution at a solid-liquid ratio of 1 g:15 mL, extracting at 30° C. for 40 min and centrifuging, concentrating the extract at 60° C. for 30 min using a rotary evaporator, and freeze-drying to obtain grapefruit peel flavonoids;

[0067] In the choline chloride-citric acid solution, the molar ratio of choline chloride to citric acid is 1:0.75, and the water content in the choline chloride-citric acid solution is 40%.

[0068] Example 3

[0069] A method for extracting total flavonoids from grapefruit peel, comprising the following steps:

[0070] S1. Wash and chop the grapefruit peel, dry at 70° C. for 2 h, crush, and pass through a 40-mesh sieve to obtain grapefruit peel powder;

[0071] S2, mixing the grapefruit peel powder and petroleum ether in a solid-liquid ratio of 1 g: 2 mL, defatting at room temperature for 3 hours, filtering, and rinsing with distilled water until no petroleum ether remains;

[0072] S3, mixing the defatted grapefruit peel powder with choline chloride-citric acid solution at a solid-liquid ratio of 1 g:35 mL, extracting at 60° C. for 20 min and centrifuging, concentrating the extract at 60° C. for 30 min using a rotary evaporator, and freeze-drying to obtain grapefruit peel flavonoids;

[0073] In the choline chloride-citric acid solution, the molar ratio of choline chloride to citric acid is 1:1.25, and the water content in the choline chloride-citric acid solution is 30%.

[0074] Comparative Example 1

[0075] Same as Example 1, except that the molar ratio of choline chloride to citric acid is 1:0.5.

[0076] Comparative Example 2

[0077] Same as Example 1, except that the molar ratio of choline chloride to citric acid is 1:1.75.

[0078] Comparative Example 3

[0079] Same as Example 1, except that citric acid is replaced by an equal molar amount of lactic acid.

[0080] Comparative Example 4

[0081] Same as Example 1, except that citric acid is replaced by an equal molar amount of glycerol.

[0082] Comparative Example 5

[0083] Same as Example 1, except that citric acid is replaced by an equal molar amount of ethylene glycol.

[0084] Comparative Example 6

[0085] Same as Example 1, except that the water content in the choline chloride-citric acid solution is 60%.

[0086] Test Example 1

[0087] Accurately weigh 10 mg of rutin standard dried at 120°C and constant weight, place it in a 50 mL volumetric flask, dissolve and dilute with 60% ethanol to obtain a rutin standard solution with a concentration of 0.2 g / L. Accurately measure 0, 0.5, 1.0, 2.0, 3.0, 4.0, and 5.0 mL of the standard solution and place it in a 25 mL volumetric flask, add 60% ethanol solution to 10 mL respectively, then add 1 mL of 5% NaNO2 in turn, shake well, let it stand for 6 minutes, add 1 mL of 10% Al(NO3)3 solution, shake well, let it stand for 6 minutes, add 1 mL of 4% NaOH solution, then add 60% ethanol to dilute, shake well, let it stand for 15 minutes, and measure the absorbance value at 500 nm. Use the absorbance value as the ordinate and the rutin concentration (mg / mL) as the abscissa to make a standard curve, and the regression equation of the standard curve is: y=9.745x-0.0033, R 2 =0.9999.

[0088] Use a 5mL pipette to take 2mL of the extract before concentration of Examples 1 to 3 and Comparative Examples 1 to 6, and slowly drip it into a 10mL test tube. Add 5% NaNO2, 10% Al(NO3)3 and 4% NaOH solutions respectively according to the preparation process of rutin standard solution. Finally, make up to volume with 60% ethanol solution, shake until uniform, let it stand for 15 minutes, and measure the absorbance.

[0089] Then the flavonoid concentration in the extract was calculated according to the standard curve, and the flavonoid extraction rate was calculated according to formula (1).

[0090] Total flavonoid extraction rate (%) = (C × V) / m × 100% (1)

[0091] Wherein: C is the concentration of flavonoids in the extract, mg / mL; V is the volume of the extract, mL; m is the mass of grapefruit peel powder, mg.

[0092] SPSS Statistics 26 was used for statistical analysis. The results were expressed as x±s. Each experiment was repeated at least three times, and P<0.05 was considered statistically significant. The test results are shown in Table 1.

[0093] Table 1 Total flavonoid extraction rate

[0094]

[0095]

[0096] * indicates P<0.05 compared with Example 1, ** indicates P<0.01 compared with Example 1.

[0097] Example 4

[0098] A method for extracting total flavonoids from grapefruit peel, comprising the following steps:

[0099] S1. Wash and chop the grapefruit peel, dry at 40° C. for 5 h, crush, and pass through a 40-mesh sieve to obtain grapefruit peel powder;

[0100] S2, mixing the grapefruit peel powder and petroleum ether in a ratio of 1 g:4 mL, defatting at room temperature for 2 h, filtering, and rinsing with distilled water until no petroleum ether remains;

[0101] S3, mixing the defatted grapefruit peel powder with choline chloride-citric acid solution at a solid-liquid ratio of 1 g:30 mL, extracting at 50° C. for 30 min and centrifuging, concentrating the extract at 60° C. using a rotary evaporator for 30 min, and freeze-drying to obtain grapefruit peel flavonoids;

[0102] In the choline chloride-citric acid solution, the molar ratio of choline chloride to citric acid is 1:1, and the water content in the choline chloride-citric acid solution is 37%.

[0103] Example 5

[0104] A method for extracting total flavonoids from grapefruit peel, comprising the following steps:

[0105] S1. Clean and chop the grapefruit peel, dry at 80° C. for 1 h, crush, and pass through a 40-mesh sieve to obtain grapefruit peel powder;

[0106] S2, mixing the grapefruit peel powder and petroleum ether in a ratio of 1 g:4 mL, defatting at room temperature for 2 h, filtering, and rinsing with distilled water until no petroleum ether remains;

[0107] S3, mixing the defatted grapefruit peel powder with choline chloride-citric acid solution at a solid-liquid ratio of 1 g:30 mL, extracting at 50° C. for 30 min and centrifuging, concentrating the extract at 60° C. using a rotary evaporator for 30 min, and freeze-drying to obtain grapefruit peel flavonoids;

[0108] In the choline chloride-citric acid solution, the molar ratio of choline chloride to citric acid is 1:1, and the water content in the choline chloride-citric acid solution is 37%.

[0109] Example 6

[0110] A method for extracting total flavonoids from grapefruit peel, comprising the following steps:

[0111] S1. Wash and chop the grapefruit peel, dry at 60° C. for 3 h, crush, and pass through a 40-mesh sieve to obtain grapefruit peel powder;

[0112] S2, mixing the grapefruit peel powder and petroleum ether in a solid-liquid ratio of 1 g:1 mL, defatting at room temperature for 5 h, filtering, and rinsing with distilled water until no petroleum ether remains;

[0113] S3, mixing the defatted grapefruit peel powder with choline chloride-citric acid solution at a solid-liquid ratio of 1 g:30 mL, extracting at 50° C. for 30 min and centrifuging, concentrating the extract at 60° C. using a rotary evaporator for 30 min, and freeze-drying to obtain grapefruit peel flavonoids;

[0114] In the choline chloride-citric acid solution, the molar ratio of choline chloride to citric acid is 1:1, and the water content in the choline chloride-citric acid solution is 37%.

[0115] Example 7

[0116] A method for extracting total flavonoids from grapefruit peel, comprising the following steps:

[0117] S1. Wash and chop the grapefruit peel, dry at 60° C. for 3 h, crush, and pass through a 40-mesh sieve to obtain grapefruit peel powder;

[0118] S2, mixing the grapefruit peel powder and petroleum ether in a solid-liquid ratio of 1 g:10 mL, defatting at room temperature for 0.5 h, filtering, and rinsing with distilled water until no petroleum ether remains;

[0119] S3, mixing the defatted grapefruit peel powder with choline chloride-citric acid solution at a solid-liquid ratio of 1 g:30 mL, extracting at 50° C. for 30 min and centrifuging, concentrating the extract at 60° C. using a rotary evaporator for 30 min, and freeze-drying to obtain grapefruit peel flavonoids;

[0120] In the choline chloride-citric acid solution, the molar ratio of choline chloride to citric acid is 1:1, and the water content in the choline chloride-citric acid solution is 37%.

[0121] Example 8

[0122] A method for extracting total flavonoids from grapefruit peel, comprising the following steps:

[0123] S1. Wash and chop the grapefruit peel, dry at 60° C. for 3 h, crush, and pass through a 40-mesh sieve to obtain grapefruit peel powder;

[0124] S2, mixing the grapefruit peel powder and petroleum ether in a ratio of 1 g:4 mL, defatting at room temperature for 2 h, filtering, and rinsing with distilled water until no petroleum ether remains;

[0125] S3, mixing the defatted grapefruit peel powder with choline chloride-citric acid solution at a solid-liquid ratio of 1 g:30 mL, extracting at 50° C. for 30 min and centrifuging, concentrating the extract at 60° C. using a rotary evaporator for 30 min, and freeze-drying to obtain grapefruit peel flavonoids;

[0126] In the choline chloride-citric acid solution, the molar ratio of choline chloride to citric acid is 1:0.75, and the water content in the choline chloride-citric acid solution is 20%.

[0127] Example 9

[0128] A method for extracting total flavonoids from grapefruit peel, comprising the following steps:

[0129] S1. Wash and chop the grapefruit peel, dry at 60° C. for 3 h, crush, and pass through a 40-mesh sieve to obtain grapefruit peel powder;

[0130] S2, mixing the grapefruit peel powder and petroleum ether in a ratio of 1 g:4 mL, defatting at room temperature for 2 h, filtering, and rinsing with distilled water until no petroleum ether remains;

[0131] S3, mixing the defatted grapefruit peel powder with choline chloride-citric acid solution at a solid-liquid ratio of 1 g:30 mL, extracting at 50° C. for 30 min and centrifuging, concentrating the extract at 60° C. using a rotary evaporator for 30 min, and freeze-drying to obtain grapefruit peel flavonoids;

[0132] In the choline chloride-citric acid solution, the molar ratio of choline chloride to citric acid is 1:1.5, and the water content in the choline chloride-citric acid solution is 50%.

[0133] Example 10

[0134] A method for extracting total flavonoids from grapefruit peel, comprising the following steps:

[0135] S1. Wash and chop the grapefruit peel, dry at 60° C. for 3 h, crush, and pass through a 40-mesh sieve to obtain grapefruit peel powder;

[0136] S2, mixing the grapefruit peel powder and petroleum ether in a ratio of 1 g:4 mL, defatting at room temperature for 2 h, filtering, and rinsing with distilled water until no petroleum ether remains;

[0137] S3, mixing the defatted grapefruit peel powder with choline chloride-citric acid solution at a solid-liquid ratio of 1 g:5 mL, extracting at 70° C. for 15 min and centrifuging, concentrating the extract at 60° C. for 30 min using a rotary evaporator, and freeze-drying to obtain grapefruit peel flavonoids;

[0138] In the choline chloride-citric acid solution, the molar ratio of choline chloride to citric acid is 1:1, and the water content in the choline chloride-citric acid solution is 37%.

[0139] Embodiment 11

[0140] A method for extracting total flavonoids from grapefruit peel, comprising the following steps:

[0141] S1. Wash and chop the grapefruit peel, dry at 60° C. for 3 h, crush, and pass through a 40-mesh sieve to obtain grapefruit peel powder;

[0142] S2, mixing the grapefruit peel powder and petroleum ether in a ratio of 1 g:4 mL, defatting at room temperature for 2 h, filtering, and rinsing with distilled water until no petroleum ether remains;

[0143] S3, mixing the defatted grapefruit peel powder with choline chloride-citric acid solution at a solid-liquid ratio of 1 g:40 mL, extracting at 20° C. for 45 min and then centrifuging, concentrating the extract at 60° C. for 30 min using a rotary evaporator, and freeze-drying to obtain grapefruit peel flavonoids;

[0144] In the choline chloride-citric acid solution, the molar ratio of choline chloride to citric acid is 1:1, and the water content in the choline chloride-citric acid solution is 37%.

[0145] The principles and implementation methods of the present invention are described in this article using specific examples. The description of the above embodiments is only used to help understand the method and core idea of ​​the present invention. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A method for extracting total flavonoids from grapefruit peel, characterized in that: The following steps are involved: S1. Clean the grapefruit peel, chop it into pieces, dry it, crush it, and sieve it to obtain grapefruit peel powder; S2, mixing the grapefruit peel powder with petroleum ether, defatting the mixture, filtering the mixture, and washing the mixture with distilled water until no petroleum ether remains; S3, mixing the defatted grapefruit peel powder with the choline chloride-citric acid solution and extracting for a certain period of time, then centrifuging, concentrating the extract, and drying to obtain grapefruit peel flavonoids; In the choline chloride-citric acid solution, the molar ratio of choline chloride to citric acid is 1:(0.75-1.5); the water content in the choline chloride-citric acid solution is 20wt%-50wt%.

2. A method for extracting total flavonoids from pomelo peel according to claim 1, characterized in that: The drying temperature is 40° C. to 80° C., and the drying time is 1 to 5 hours.

3. A method for extracting total flavonoids from pomelo peel according to claim 1, characterized in that: The material-liquid ratio of the grapefruit peel powder to petroleum ether is 1 g: (1-10) mL, the degreasing temperature is room temperature, and the degreasing time is 0.5-5 h.

4. A method for extracting total flavonoids from pomelo peel according to claim 1, characterized in that: In the choline chloride-citric acid solution, the molar ratio of choline chloride to citric acid is 1:(0.75-1.25).

5. A method for extracting total flavonoids from pomelo peel according to claim 4, characterized in that: In the choline chloride-citric acid solution, the molar ratio of choline chloride to citric acid is 1:

1.

6. A method for extracting total flavonoids from pomelo peel according to claim 1, characterized in that: The water content of the choline chloride-citric acid solution is 30 wt % to 40 wt %.

7. A method for extracting total flavonoids from pomelo peel according to claim 6, characterized in that: The water content of the choline chloride-citric acid solution is 37 wt %.

8. The method for extracting total flavonoids from pomelo peel according to claim 1, characterized in that: The material-liquid ratio of the defatted grapefruit peel powder to the choline chloride-citric acid solution is 1 g: (5-40) mL.

9. The method for extracting total flavonoids from pomelo peel according to claim 1, characterized in that: The extraction temperature of the choline chloride-citric acid solution is 20° C. to 70° C., and the extraction time is 15 to 45 minutes.

10. The method for extracting total flavonoids from pomelo peel according to claim 9, characterized in that: The extraction temperature of the choline chloride-citric acid solution is 30° C. to 60° C., and the extraction time is 20 to 40 minutes.

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