A kind of extraction method of D-limonene

Abstract

The present application adopts an ultrasound-assisted combined salting-out method, and by screening a specific salting-out reagent, not only can the extraction efficiency be improved, but also the content of D-limonene can be greatly increased, and the subsequent purification operation can be reduced; the ultrasonic extraction of the present invention can be carried out at room temperature without heating, and the time required for the ultrasonic extraction step is short, which is more conducive to industrial production.

Description

Technical Field

[0001] The invention relates to the field of D-limonene extraction methods. Background Art

[0002] Limonene, also known as limonene, belongs to the monoterpene compound. It is a basic chemical raw material widely used in medicine, washing, sterilization, insecticide, etc.

[0003] At present, the preparation method of limonene is mainly to extract it from natural plants with relatively high limonene content, such as citrus, by physical and / or chemical methods. Common extraction methods include cold pressing, steam distillation, organic solvent extraction, etc.

[0004] 1. Cold pressing method

[0005] The cold pressing method, also known as the pressing method, uses the pressure of mechanical equipment to destroy the oil cells on the surface of citrus peel under low temperature conditions to release citrus essential oils, collect the mixed liquid by water flushing, and filter and centrifuge the mixed liquid to obtain the crude essential oil. Since it is operated at room temperature, this method retains the natural quality of citrus essential oils, and the aroma is similar to the smell of citrus peels themselves. However, the purity of citrus essential oil products obtained by the cold pressing method is not high, the equipment requirements are high, and the extraction rate is very low, usually less than 60%, and the oil yield is low.

[0006] Masayoshi et al. (Biotechnology and Biochemistry, 2004, 68(8): 1690) used the cold-pressing method to obtain cold-pressed essential oil from mature ponkan peel and analyzed the main components of the cold-pressed essential oil. The results showed that monoterpenes were dominant (89.6% (w / w)), among which d-limonene had the highest content (80.3%).

[0007] 2. Steam distillation

[0008] Steam distillation is a method of separating target substances by using the difference in boiling points between the target substance and water. The d-limonene obtained by this method has a high purity, but due to the high temperature and long time of the azeotropic process, it will cause the loss and oxidation of d-limonene, and the aroma will also change significantly. Ding Jie (Hunan Agricultural Science, 2017, 56(17): 3326) et al. optimized the optimal steam distillation process conditions for citrus peel volatile oil through orthogonal experiments and analyzed the d-limonene content of citrus peel essential oil from five production areas, including 87.29% in Hanzhong orange, 95.80% in Hunan mandarin orange, 95.44% in Yichang orange, 75.66% in Sichuan sweet orange, and 90.18% in Yunnan mandarin orange. Gamarra (Brazilian Journal of Chemical Engineering, 2006, 23(01):147) et al. used lime as the raw material and adopted 110℃ steam distillation method (1.0 bar / 25℃) for 10 h to obtain lime volatile oil. The d-limonene content was 49.66 ml / Kg after gas chromatography analysis. It was also found that the aldehyde content in the volatile oil exceeded 3% due to oxidation reaction during the 10 h distillation process.

[0009] 3. Organic solvent extraction method

[0010] Organic solvent extraction is a selective separation method for substances, which mainly uses the principle that similar substances dissolve in each other. The temperature during the extraction process is not high, and it is not easy to cause d-limonene to decompose due to heat, but there is a problem of organic reagent residue. Yang Xiaofeng (Analytical Laboratory, 2007, 26 (1): 85) et al. used petroleum ether as an organic solvent to study the volatile components of fresh Ou orange pulp and fresh peel. The analysis found that d-limonene accounted for 86.39% in Ou orange peel extract and 4.31% in Ou orange pulp extract.

[0011] 4. Ultrasound-assisted extraction

[0012] Ultrasonic assisted extraction is an emerging technology that uses the physical effects of ultrasonic radiation, such as cavitation and disturbance effects, crushing and stirring, mechanical vibration, etc., to maximize the contact between the substance and the solvent substance, promote the dissolution of the target compound in the solvent, and achieve the purpose of separation. The d-limonene extracted by this method has good quality, high extraction rate, short time and high repeatability, but further research is needed for large-scale application in production.

[0013] Sun hao (Flavour and Fragrance Journal, 2014, 29(5):305) et al. used grapefruit peel as the material, and extracted grapefruit peel volatiles with ultrasound-assisted n-hexane. The sensory analysis showed that the grapefruit volatile extract had a similar odor characteristic to natural grapefruit. GC-MS analysis showed that the d-limonene content in the grapefruit volatile extract was 464436±15467 μg / ml. Hu Junwu (Food Industry, 2012(1): 42) et al. used fresh ponkan peel as the experimental material, and the extraction solvent was n-hexane. They used ultrasound-microwave synergistic extraction method, and GC-MS analysis showed that the relative content of d-limonene in ponkan essential oil was 77.2%.

[0014] 5. Supercritical CO2 extraction

[0015] Supercritical CO2 extraction uses the special solubility of CO2 under supercritical conditions to extract the target component, which is especially suitable for the extraction of heat-sensitive substances. This method has low extraction temperature, short extraction time, high yield of d-limonene, and is green and safe. However, the equipment is expensive and requires high technical skills from the operator of the equipment.

[0016] Valle et al. (Journal of Supercritical Fluids, 2019, 144: 108) studied the effect of pressure drop in a 3.6-meter-high extraction vessel on CO2 extraction of citrus peel oil, and proposed that a reduction in extraction pressure may have a negative impact on supercritical CO2 extraction of citrus peel essential oil in industrial-scale extraction vessels. B. Mirra et al. used dried navel orange peel as experimental material to study the effect of pressure and temperature on the percentage of d-limonene in orange peel essential oil, and found that the optimal conditions for supercritical CO2 extraction of d-limonene were 12.5 MPa and 308K, at which time d-limonene accounted for more than 99.5% of the volatile oil.

[0017] 6. Molecular distillation

[0018] Molecular distillation is a physical technology for liquid-liquid separation that uses the difference in the mean free path of molecular motion between substances to achieve separation within a certain space. It ensures that the d-limonene separated from citrus essential oil is not contaminated, and at the same time avoids the polymerization, oxidation and isomerization reactions of d-limonene at high temperatures, thus ensuring the natural quality to the greatest extent. Wang Wenyuan (Food Research and Development, 2010, 3(10): 59) et al. used orange peel oil as the material to study the effects of vacuum degree, distillation temperature, feed rate, and film scraping speed of molecular distillation on the yield and purity of limonene. Under the optimal process conditions, the yield of d-limonene was 86.54% and the purity was as high as 99%. Wang Fang (Journal of the Chinese Cereals and Oils Association, 2018, 33(7): 65) et al. used molecular distillation to enrich d-limonene from grapefruit peel essential oil. The experiment showed that after molecular distillation of grapefruit peel essential oil, d-limonene was significantly enriched in the light fraction, with the absolute content enriched from 66.33 g / L to 324.27 g / L, and the concentration ratio reached 4.9, with a significant enrichment effect.

[0019] 7. Microwave-assisted water extraction

[0020] Microwave-assisted water extraction technology is a newly developed extraction method in recent years. Microwave-assisted water extraction technology mainly utilizes the thermal effect of microwaves to heat the solid matter containing limonene and water to boiling in a short time, so that limonene is separated from the solid and enters the water phase. The extraction temperature of this method is high, and because limonene has poor solubility in the water phase, it uses a large amount of water and consumes a lot of energy. Also, because of the strong thermal effect of microwaves, it is impossible to use mixed solvent extraction, resulting in a step-by-step operation, which complicates the operation process. For example, CN200510032262 provides a method for extracting orange oil and pectin using microwave-assisted water extraction technology, and the extraction rate of this method reaches about 95%. However, the water consumption of this method is high, and the process steps are cumbersome.

[0021] The prior art discloses a large number of D-limonene extraction methods, but the above methods have low extraction rates, low purity, or complex extraction processes and are not suitable for industrial production. Therefore, it is of great significance to provide a simple, efficient, and industrially applicable D-limonene extraction method. Summary of the invention

[0022] Although there are reports in the prior art of using ultrasound-assisted methods or water vapor-salting-out methods to extract D-limonene, the purity of the obtained crude D-limonene is low, and further purification by molecular distillation and other methods is required. The present application uses ultrasound-assisted combined with salting-out methods, by screening specific salting-out reagents, which can not only improve the extraction efficiency, but also greatly increase the content of D-limonene, reduce subsequent purification operations, and is more conducive to industrial production.

[0023] The purpose of the present invention is to provide a simple, efficient and industrially applicable D-limonene extraction method.

[0024] In one embodiment, the present invention provides a method for extracting D-limonene from citrus peel by ultrasonic-assisted solvent extraction combined with salting-out technology, the method comprising the following steps:

[0025] (1) Add citrus peels to an extraction kettle, add water, an organic solvent and an inorganic salt additive, and heat and stir until uniformly mixed;

[0026] (2) ultrasonic-assisted solvent extraction at 10°C to 70°C;

[0027] (3) Add activated carbon for decolorization, separate the decolorized product into solid and liquid to obtain filtrate and filter residue.

[0028] (4) separating the filtrate into a first organic phase and a first aqueous phase;

[0029] (5) Extracting the first aqueous phase with an organic solvent 2-3 times, taking the corresponding organic phase to obtain a second organic phase, and the remaining aqueous phase is the second aqueous phase;

[0030] (6) The first organic phase and the second organic phase are combined, and the organic solvent is removed by distillation to obtain D-limonene.

[0031] In one embodiment, before the citrus peels are added to the extraction kettle in step (1), the peels are also cleaned and crushed. Preferably, the peels are crushed to a particle size of 5-50 mesh.

[0032] In one embodiment, the inorganic salt additive in step (1) is selected from: one or more of ammonium chloride, sodium chloride, potassium chloride, ammonium sulfate, and calcium sulfate; preferably, the inorganic salt additive is ammonium sulfate; preferably, the mass ratio of the peel to the inorganic salt is 100:(1-10).

[0033] In one embodiment, the organic solvent in step (1) is selected from one or more of tetrahydrofuran, petroleum ether, butanone, ethyl acetate, methyl acetate, propyl acetate, and butyl acetate; preferably petroleum ether or ethyl acetate; the mass ratio of the organic solvent to the peel is 1-8:1, preferably 3-5:1.

[0034] In one embodiment, the mass ratio of water to peel in step (1) is 5-15:1, preferably 6-9:1.

[0035] In one embodiment, the frequency of the ultrasonic wave in the ultrasonic-assisted solvent extraction of step (2) is 20KHz-60KHz, etc., and the duration is 5 to 60 minutes; preferably, the frequency of the ultrasonic wave is 40KHz-50KHz, etc., and the duration is 5 to 15 minutes.

[0036] In one embodiment, the ultrasonic-assisted solvent extraction is performed at 20° C. to 40° C.; preferably, the ultrasonic-assisted solvent extraction is performed at room temperature.

[0037] In one embodiment, the method further comprises returning the filter residue from step (3) to the extraction kettle to repeat the secondary extraction.

[0038] In one embodiment, the solid separation method in step (3) is filtration separation or centrifugal separation.

[0039] In one embodiment, the organic solvent of step (5) is selected from ethers, ketones, esters and / or combinations thereof; preferably, the organic solvent of step (5) is selected from one or more of tetrahydrofuran, petroleum ether, butanone, ethyl acetate, methyl acetate, propyl acetate and butyl acetate.

[0040] In one embodiment, the method further comprises returning the organic solvent in step (6) to the extraction kettle for reuse.

[0041] In one embodiment, the method further comprises returning the first aqueous phase in step (4) to the extraction kettle for reuse.

[0042] The present invention uses ultrasonic mixed solvent extraction technology to quickly and efficiently separate limonene from citrus peels, and this method has a high extraction rate, a simple and economical process, and is suitable for large-scale industrial and industrial applications.

[0043] The present application adopts an ultrasound-assisted combined salting-out method and screens a specific salting-out reagent, which can not only improve the extraction efficiency, but also significantly increase the content of D-limonene, reduce subsequent purification operations, and be more conducive to industrial production.

[0044] Inorganic salts are added during the ultrasonic extraction step to change the osmotic pressure of cells in the citrus peel, making the cells easier to dehydrate, thereby facilitating the extraction of D-limonene substances in the peel and improving the extraction efficiency. At the same time, some impurities can undergo salt precipitation, thereby improving the purity of the product.

[0045] In order to improve the extraction rate, the prior art usually requires long-term extraction at a higher temperature in the extraction step of the peel. However, when the extraction temperature is high, it will cause the loss of d-limonene and oxidation and deterioration; when the extraction time is too long, a large amount of other impurities will also be extracted, which will bring great difficulties to the subsequent separation and extraction, and reduce the purity of the product.

[0046] The ultrasonic extraction of the present invention can be carried out at room temperature without heating, which can reduce energy consumption and thus reduce production costs. The ultrasonic extraction step of the present invention takes a short time, which can save production time. At the same time, since the extraction is carried out at a lower temperature and without the need for long time, the final product has high purity.

[0047] The citrus plants of the present invention include plants of 6 genera in the Rutaceae family, namely Fortunella, Eremocitrus, Poncirus, Clymenia, Microcitrus and Citrus. Specifically, the citrus plants of the present invention may be navel oranges, tangerines, etc. produced in Gannan, Jiangxi, Fengjie, Guangyuan, Sichuan, etc., tangerines, citrus, etc. produced in Zhejiang, Fujian, etc. In addition, although the present invention will be described with respect to the extraction of limonene from citrus peels, it should be understood that the method of the present invention is also applicable to all plant tissues or parts containing limonene, such as pulp, etc.

[0048] The amount of water added is 5 to 15 times the mass of the peel, preferably 6 to 9 times the mass. If the amount of water is greater than 15 times the mass, the amount of water used will increase, and wastewater will increase. In addition, excessive water will cause the organic solvent ratio to decrease, thereby reducing the solubility of limonene, resulting in a decrease in extraction efficiency. If the amount of water is less than 5 times the mass, the solid content of the system will increase, the fluidity of the system is poor, and in the ultrasonic-assisted extraction process, the ultrasonic oscillation effect is reduced, and the extraction effect is reduced.

[0049] The amount of organic solvent added is 1 to 8 times the volume of the peel, preferably 3 to 5 times the volume. If the amount of organic solvent is greater than 8 times the volume, although the product solubility increases, the extraction efficiency is high, and the extraction speed is fast, the energy consumption is high when the solvent is distilled and recovered. Organic solvents higher than 10 times the weight will cause unnecessary energy consumption losses, and at the same time, reduce equipment capacity, which is not easy for actual production applications. If the amount of organic solvent is less than 1 times the volume, the solubility of the mixed solvent to limonene is reduced, and the extraction efficiency is reduced.

[0050] Herein, the organic solvent includes, but is not limited to: ethers, such as petroleum ether, tetrahydrofuran; ketones, such as butanone; esters, such as ethyl acetate, methyl acetate, propyl acetate, butyl acetate, and / or combinations thereof. Considering factors such as environmental protection and economy and taking into account yield, in one embodiment, the organic solvent of the present invention is preferably petroleum ether, ethyl acetate, methyl acetate, propyl acetate and / or butyl acetate.

[0051] Subsequently, the mixture of the peel, water and the organic solvent is subjected to ultrasonic-assisted solvent extraction at 20° C. to 40° C., preferably, the mixture of the peel, water and the organic solvent is subjected to ultrasonic-assisted solvent extraction at room temperature.

[0052] At present, ultrasonic technology is mainly used in cleaning. In various cleaning applications, a large number of ultrasonic cleaning equipment of different models have been produced. As the power of ultrasonic generators continues to increase, the application scope of the equipment is also constantly expanding.

[0053] Prior art discloses the extraction of D-limonene by applying ultrasonic wave, and the vibration frequency of ultrasonic wave is very high, and this high-frequency vibration makes the peel particles vibrate rapidly, and the components such as limonene are separated from the attachment matrix of peel rapidly during the high-frequency vibration process, and enter the mixed solvent, so as to achieve the effect of rapid extraction. The penetration of ultrasonic wave effect is very strong, and the limonene in the peel particles can be released efficiently, so as to achieve high extraction efficiency. However, the inventors have found that while ultrasonic wave-assisted extraction improves the extraction efficiency, other impurities in the peel can be extracted together, and then the purity of the final product is reduced, which brings more difficulties for subsequent separation and purification. Therefore, the inventors add inorganic salts in the extraction step, and while improving the extraction efficiency, some impurities are salted out and precipitated, thereby improving the purity of the product.

[0054] Moreover, conventional ultrasonic-assisted solvent extraction for limonene extraction requires extraction at a relatively high temperature for a relatively long time. In the method of the present invention, due to the vibration effect of ultrasound and the wall-breaking effect of inorganic salts, extraction becomes easier. Therefore, the extraction can be carried out at a relatively low temperature and in a relatively short time, so that energy consumption is low, the extraction speed is fast, and the operation is convenient, which greatly reduces the extraction cost.

[0055] Ultrasonic wave assisted mixed solvent extraction can be carried out at 20°C to 40°C. In one embodiment, ultrasonic wave assisted solvent extraction can be carried out at room temperature. The ultrasonic wave extraction of the present invention can be carried out by a commercially available ultrasonic wave generator. The ultrasonic wave has a pulse frequency of 20KHz, 25KHz, 28KHz, 33KHz, 40KHz, 60KHz, etc., and the duration is 5 to 15 minutes. Those skilled in the art can select appropriate ultrasonic wave extraction conditions according to the size of the extract, etc.

[0056] The inorganic salt additive is selected from: one or more of ammonium chloride, sodium chloride, potassium chloride, ammonium sulfate, and calcium sulfate; preferably, the inorganic salt additive is ammonium sulfate; preferably, the mass ratio of the peel to the inorganic salt is 100:(1-10).

[0057] After ultrasonic-assisted solvent extraction, activated carbon is added for decolorization, stirred for about 30 minutes and cooled to 15° C. to 25° C. In one embodiment, the amount of activated carbon added is 0.2 to 2% of the initial peel weight, preferably 0.5 to 1%, more preferably 0.8 to 1.2%, and most preferably 1%.

[0058] The decolorized crude product is subjected to solid-liquid separation to obtain a filtrate and a filter residue. The solid-liquid separation method includes filtering and centrifugation. In one embodiment, the filtered filter residue can be returned to the initial reflux extraction kettle again to enter the next cycle, so that the extraction rate of limonene can be maximized. The filtrate obtained after filtration can be separated by standing in a phase separator to obtain a first organic phase and a first aqueous phase.

[0059] Extract the first aqueous phase with an organic solvent 2-3 times, take the corresponding organic phase to obtain a second organic phase, and the remaining aqueous phase is the second aqueous phase;

[0060] The first organic phase and the second organic phase are combined. The organic solvent is removed from the combined organic phase to obtain D-limonene. The organic solvent can be recycled for the aforementioned extraction step. DETAILED DESCRIPTION

[0061] The technical solution of the present invention will be described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0062] Embodiment 1:

[0063] Take 100 grams of fresh peel of navel orange in Gannan, Jiangxi, wash it, crush it to 30 mesh, add it to a round-bottom flask, add 600 grams of water and 400 grams of ethyl acetate, then add 3g of ammonium sulfate, and stir evenly at room temperature. Then turn on the ultrasonic equipment and perform ultrasonic-assisted solvent extraction for 10 minutes. After ultrasonic extraction, add 2 grams of activated carbon and stir for 20 minutes. When the solution is cooled to 10°C, the reaction mixture is filtered to obtain a filtrate and a solid residue. After standing, the filtrate is layered into a first organic phase and an aqueous phase. The aqueous phase is extracted twice with ethyl acetate again to obtain a second organic phase. The first organic phase and the second organic phase are combined, and the organic phase is distilled and desolventized to obtain 3.3 grams of light yellow oil. The content of D-limonene was 95.8% as determined by HPLC.

[0064] Example 2-5: Ammonium sulfate in Example 1 was replaced by ammonium chloride, sodium chloride, potassium chloride and calcium sulfate respectively, and the amount of inorganic salt added was 3 grams. Other conditions were the same as in Example 1.

[0065] Comparative Example 1: No inorganic salt additive was added, and other conditions were the same as those in Example 1.

[0066] The extraction results are as follows:

[0067]

[0068] It can be seen from Examples 1-5 and Comparative Example 1 that, in the ultrasonic-assisted organic solvent extraction stage, adding an inorganic salt additive can improve the extractant of D-limonene and increase the purity of the product. The most preferred additive is ammonium sulfate.

[0069] Embodiment 6:

[0070] Take 100 grams of fresh peel of navel orange in Gannan, Jiangxi, wash it, crush it to 25 mesh, add it to a round-bottom flask, add 600 grams of water and 500 grams of petroleum ether, then add 2g of ammonium sulfate, and stir evenly at room temperature. Then turn on the ultrasonic equipment and perform ultrasonic-assisted solvent extraction for 8 minutes. After ultrasonic extraction, add 2 grams of activated carbon and stir for 20 minutes. When the solution is cooled to 10°C, the reaction mixture is filtered to obtain a filtrate and a solid residue. After standing, the filtrate is layered into a first organic phase and an aqueous phase. The aqueous phase is extracted twice with ethyl acetate again to obtain a second organic phase. The first organic phase and the second organic phase are combined, and the organic phase is distilled and desolventized to obtain 3.2 grams of light yellow oil. The content of D-limonene was 94.3% as determined by HPLC.

[0071] Embodiment 7:

[0072] Take 100 grams of fresh peel of navel orange in Gannan, Jiangxi, wash it, crush it to 30 mesh, add it to a round-bottom flask, add 700 grams of water and 600 grams of methyl acetate, then add 5 grams of ammonium sulfate, and stir evenly at room temperature. Then turn on the ultrasonic equipment and perform ultrasonic-assisted solvent extraction for 10 minutes. After ultrasonic extraction, add 2 grams of activated carbon and stir for 20 minutes. When the solution is cooled to 10 ° C, the reaction mixture is filtered to obtain a filtrate and a solid residue. After standing, the filtrate is layered into a first organic phase and an aqueous phase. The aqueous phase is extracted twice with ethyl acetate again to obtain a second organic phase. The first organic phase and the second organic phase are combined, and the organic phase is distilled and desolventized to obtain 3.4 grams of light yellow oil. According to HPLC, the content of D-limonene is 94.6%.

[0073] Embodiment 8:

[0074] Take 100 grams of fresh peel of navel orange in Gannan, Jiangxi, wash it, crush it to 30 mesh, add it to a round-bottom flask, add 500 grams of water and 700 grams of methyl acetate, then add 4 grams of ammonium sulfate, and stir evenly at room temperature. Then turn on the ultrasonic equipment and perform ultrasonic-assisted solvent extraction for 15 minutes. After ultrasonic extraction, add 2 grams of activated carbon and stir for 20 minutes. When the solution is cooled to 10 ° C, the reaction mixture is filtered to obtain a filtrate and a solid residue. After standing, the filtrate is layered into a first organic phase and an aqueous phase. The aqueous phase is extracted twice with ethyl acetate again to obtain a second organic phase. The first organic phase and the second organic phase are combined, and the organic phase is distilled and desolventized to obtain 3.3 grams of light yellow oil. According to HPLC, the content of D-limonene is 92.6%.

[0075] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for extracting D-limonene, characterized in that: The method comprises the following steps: (1) adding citrus peels into an extraction kettle, and adding water, an organic solvent and an inorganic salt additive, heating and stirring until uniform mixing; (2) performing ultrasonic-assisted solvent extraction at 10°C to 70°C; (3) adding activated carbon for decolorization, and performing solid-liquid separation on the decolorized product to obtain a filtrate and a filter residue, (4) separating the filtrate into a first organic phase and a first aqueous phase; (5) extracting the first aqueous phase with an organic solvent 2-3 times, taking the corresponding organic phase to obtain a second organic phase, and the remaining aqueous phase is the second aqueous phase; (6) combining the first organic phase and the second organic phase, and distilling off the organic solvent to obtain D-limonene; Wherein, the inorganic salt additive in step (1) is ammonium sulfate; the mass ratio of the peel to the inorganic salt is 100:(1-10); Wherein, the organic solvent in step (1) is selected from one or more of petroleum ether, butanone, ethyl acetate, methyl acetate, propyl acetate, and butyl acetate; the mass ratio of the organic solvent to the peel in step (1) is 1-8:1; and the mass ratio of water to the peel in step (1) is 5-15:

1.

2. The extraction method according to claim 1, characterized in that The organic solvent in step (1) is selected from petroleum ether and ethyl acetate; In step (1), the mass ratio of the organic solvent to the peel is 3-5:1; In step (1), the mass ratio of water to peel is 6-9:

1.

3. The extraction method according to claim 1, characterized in that The frequency of the ultrasonic wave in the ultrasonic-assisted solvent extraction of step (2) is 20 KHz-60 KHz, and the duration is 5 to 60 minutes.

4. The extraction method according to claim 3, characterized in that The frequency of the ultrasonic wave in the ultrasonic-assisted solvent extraction of step (2) is 40KHz-50KHz, and the duration is 5 to 15 minutes.

5. The extraction method according to claim 1, characterized in that The ultrasonic-assisted solvent extraction is performed at 20°C to 40°C.

6. The extraction method according to claim 5, characterized in that The ultrasonic-assisted solvent extraction was performed at room temperature.

7. The extraction method according to claim 1, characterized in that The solid separation method in step (3) is filtration separation or centrifugal separation.

8. The extraction method according to claim 1, characterized in that The method further comprises returning the filter residue from step (3) to the extraction kettle for repeated secondary extraction.

9. The extraction method according to claim 1, characterized in that The method further comprises returning the organic solvent in step (6) to the extraction kettle for reuse.

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