A method for improving the extraction rate of plant essential oil

Abstract

The application discloses a method for improving the extraction rate of plant essential oil, comprising the following steps: repeatedly freezing and thawing and low-temperature ultrafine grinding of plant raw materials rich in essential oil to obtain ultrafine powder with microporous structure; vacuumizing and pressurizing the ultrafine powder to remove adsorbed gas in the pores, injecting water-alcohol-ester-eutectic solvent quaternary extraction solvent, and driving the solvent to instantaneously infiltrate into the deep pores inside the particles by using the negative pressure rebound force; applying a "positive pressure-negative pressure" asymmetric alternating pulse to make the residual cell wall fragments and oil glands undergo high-frequency fatigue deformation and interlayer peeling under the stress of the back-and-forth pressure difference, coupling the negative pressure cavitation effect to strengthen the mass transfer of endogenous essential oil to the liquid phase body; and finally, through pressure reduction flash evaporation, three-stage gradient condensation and refining, the plant essential oil is obtained. Through the "negative pressure forced mass transfer into cells-alternating stress fatigue wall breaking" synergistic mechanism, the extraction rate of essential oil is significantly improved compared with the traditional steam distillation method, the P / C ratio reaches the standard of special grade products, and the method is suitable for the production of high-value plant essential oil.

Description

Technical Field

[0001] This invention relates to the field of essential oil extraction technology, and more specifically to a method for improving the extraction rate of plant essential oils. Background Technology

[0002] Plant essential oils are complex mixtures of various volatile secondary metabolites, including terpenes, phenols, esters, and aldehydes, and are widely used in food flavoring, daily fragrances, pharmaceuticals, and aromatherapy. With the increasing emphasis on green and efficient extraction, traditional steam distillation, while simple to operate, suffers from low extraction rates due to its high-temperature, long-duration processing, which easily triggers hydrolysis, cyclization, and oxidative degradation of heat-sensitive components (such as terpene esters and phenolic acids). Furthermore, the limited solubility in the aqueous phase results in generally low extraction rates. Summary of the Invention

[0003] In view of this, the present invention proposes a method to improve the extraction rate of plant essential oils in order to solve the above problems.

[0004] The technical solution of this invention is implemented as follows:

[0005] A method for improving the extraction rate of plant essential oils includes the following steps:

[0006] S1. Plant raw materials rich in essential oils are subjected to repeated freeze-thaw pretreatment, and then ultra-fine pulverization to obtain ultra-fine powder with microporous structure;

[0007] S2. Place the ultrafine powder into a sealed reactor, evacuate the sealed reactor and maintain pressure to remove the gas adsorbed in the pores of the ultrafine powder.

[0008] S3. Inject the extraction solvent into the sealed reactor after vacuuming and pressure preservation. Use the negative pressure rebound force to drive the extraction solvent to penetrate into the pores inside the ultrafine powder particles, thus completing the solvent impregnation.

[0009] S4. After solvent impregnation, periodically switching "positive pressure-negative pressure" alternating pulses are applied to the sealed container, causing the mechanically broken residual cell wall fragments and oil glands to undergo high-frequency fatigue deformation and interlayer peeling under the back-and-forth pressure difference. At the same time, the coupling negative pressure cavitation effect enhances the mass transfer of endogenous essential oil to the liquid phase, resulting in an extraction mixture.

[0010] S5. The extracted mixture is subjected to desolvation by flash evaporation under reduced pressure. The mixed steam generated by flash evaporation is liquefied by three-stage condensation. The condensates obtained by condensation are combined, allowed to stand and separate into layers, and the upper layer is collected to obtain crude essential oil. The crude essential oil is then decolorized and dehydrated to obtain plant essential oil.

[0011] Furthermore, in step S1, repeated freeze-thaw pretreatment is performed as follows: freeze at a freezing temperature of -20 to -5℃ for 4-12 hours, then thaw at a thawing temperature of 15-30℃ for 3-7 hours, and repeat the freeze-thaw cycle 2-4 times.

[0012] Furthermore, in step S1, the particle size D90 of the ultrafine powder is ≤45μm, preferably ≤30μm, and liquid nitrogen or dry ice is used to assist in low-temperature pulverization during the ultrafine pulverization process, with the pulverization temperature controlled between -10 and 10℃.

[0013] Furthermore, in step S2, the absolute vacuum degree of the vacuum is 20-60 kPa, the pressure holding time is 6-12 min, and ultrasonic vibration is applied as an auxiliary process during the pressure holding process to promote the removal of adsorbed gas in the pores of the ultrafine powder. The ultrasonic power is 300-600 W and the frequency is 30-40 kHz. The ultrasonic is carried out in an intermittent emission mode, with 5 seconds of emission and 5 seconds of pause. The ultrasonic is stopped during the last 1 / 3 of the pressure holding time to allow the escaped gas to be fully extracted.

[0014] Furthermore, in step S3, the amount of extraction solvent injected is 3-5 times the mass of the ultrafine powder. The extraction solvent is composed of an aqueous phase component, short-chain alcohol, ester co-solvent, and eutectic solvent in a mass ratio of (5-8.5):(1-3):(1-3):(0.2-1.0).

[0015] Furthermore, the aqueous phase component is a phosphate buffer solution with a concentration of 0.5-2.0% and a pH of 4.5-6.5. The short-chain alcohol is selected from one or more of ethanol, propylene glycol, and 1,3-butanediol. The ester co-solvent is selected from one or more of ethyl acetate, butyl acetate, and ethyl lactate. The eutectic solvent is prepared by mixing hydrogen bond acceptors and hydrogen bond donors in a molar ratio of 1:(1~4). The hydrogen bond acceptor is selected from one of betaine and choline chloride. The hydrogen bond donor is selected from one or more of lactic acid, glycerol, and glucose.

[0016] Furthermore, in step S4, the positive pressure in the "positive pressure-negative pressure" alternating pulse is 0.5-1.5MPa, the negative pressure is 5-15kPa, the pulse frequency is 1-3Hz, the ratio of the positive pressure holding time to the negative pressure holding time is (2-5):1, and the total processing time of the "positive pressure-negative pressure" alternating pulse is 20-30min.

[0017] Furthermore, in step S4, in the "positive pressure-negative pressure" alternating pulse, inert gas is introduced into the reactor during the positive pressure stage, and the pressure is reduced by evacuating the gas through a vacuum pump during the negative pressure stage. The pressure relief time when switching from the positive pressure stage to the negative pressure stage is ≤0.3s, preferably ≤0.1s, forming a cycle sequence of "positive pressure holding - instantaneous pressure relief explosion - negative pressure cavitation" in the reactor.

[0018] Furthermore, in step S4, while applying alternating pulses, the temperature inside the reactor is controlled by a programmed temperature increase, gradually increasing from room temperature to 60℃~80℃ at a rate of 2~5℃ / min, and the extraction solvent is kept in a liquid phase state during the temperature increase.

[0019] Furthermore, in step S5, the flash evaporation time is 5-20 minutes, and the three-stage condensation and liquefaction are carried out according to the following method: the first-stage condensation uses a shell-and-tube condenser with circulating cooling water as the cooling medium and an inlet water temperature of 4-10℃, and the first-stage condensate is collected; the second-stage condensation uses a plate condenser with an ethylene glycol aqueous solution as the cooling medium and a temperature of -15 to -5℃, and the second-stage condensate is collected; the third-stage condensation uses a cold trap with a temperature of -20 to -10℃, and the third-stage condensate is collected.

[0020] Furthermore, the method of this application is applicable to the extraction of essential oils from flowers, leaves, herbs, fruit peels, rhizomes, and seeds.

[0021] Compared with the prior art, the beneficial effects of the present invention are:

[0022] 1. This invention utilizes a multi-stage synergistic "cell wall disruption-release-dissolution-recovery" chain through a two-stage physical pre-disruption process involving repeated freeze-thaw cycles and ultrafine pulverization, forced mass transfer via vacuum degassing and negative pressure rebound wetting, interlayer fatigue stripping via asymmetric alternating pulses, and broad-spectrum solubilization with a quaternary solvent of water, alcohol, ester, and eutectic solvent. This significantly improves the essential oil release rate. Extraction results from six major categories of plant materials—flowers (rose), leaves (mint), herbs (lemongrass), peels (lemon), rhizomes (turmeric), and seeds (star anise)—show that the extraction rate of this invention is 2-6 times higher than that of traditional steam distillation. In particular, the improvement is approximately 6 times for difficult-to-extract materials with dense tissues and starch or waxy barriers (such as fresh turmeric), indicating that this invention successfully overcomes the mass transfer limitations of traditional extraction methods for hard / high-starch plant tissues.

[0023] 2. This invention employs a mild extraction condition with programmed temperature rise, combined with inert gas protection and three-stage gradient condensation, which effectively inhibits the degradation, isomerization, and hydrolysis side reactions of heat-sensitive characteristic components such as terpenoids, aldehydes, and esters. The resulting plant essential oils meet the premium standard, significantly improving the extraction quality of essential oils.

[0024] 3. The method of this invention is not a customized solution for a specific raw material, but rather a universal "cell wall breaking-mass transfer" platform technology. Through extraction verification on six major categories of plant raw materials—flowers (rose), leaves (mint), herbs (lemongrass), fruit peels (lemon), rhizomes (turmeric), and seeds (star anise)—the extraction rate was increased by 2-6 times. This fully demonstrates that the method has good adaptability to various tissue structures (delicate petals, dense cuticle, lignified / silicified stems and leaves, deeply embedded oil glands, high-starch rhizomes, and stone cell seed coats) and various essential oil chemical types (terpenoids, ketones, aldehydes, and phenylpropanoids). It shows significant advantages, especially for high-starch, high-lignin, and high-wax raw materials that are difficult to process with traditional steam distillation, providing a universal technical solution for the industrial-scale, efficient extraction of different types of aromatic plants.

[0025] 4. This invention uses a water-alcohol-ester-eutectic solvent as the extraction solvent, avoiding the use of traditional organic solvents such as n-hexane and petroleum ether; the extraction temperature is low, the total processing time is short, and the energy consumption is significantly reduced compared to traditional steam distillation. Furthermore, operations such as ultrafine grinding, vacuum degassing, and alternating pressure fields are all suitable for industrial scale-up, the equipment has a high degree of automation, good batch-to-batch reproducibility, and is suitable for large-scale industrial production of high-value-added plant essential oils. Detailed Implementation

[0026] To better understand the technical content of this invention, specific embodiments are provided below to further illustrate the invention.

[0027] Unless otherwise specified, the experimental methods used in the embodiments of this invention are all conventional methods.

[0028] Unless otherwise specified, all materials and reagents used in the embodiments of this invention are commercially available.

[0029] Example 1

[0030] A method for improving the extraction rate of plant essential oils includes the following steps:

[0031] S1. Fresh Damask roses were subjected to repeated freeze-thaw pretreatment according to the following method: frozen at -10℃ for 6 hours, then thawed at 25℃ for 4 hours, and the freeze-thaw cycle was repeated 3 times; then ultra-fine pulverization was carried out, with the particle size D90≤30μm, and liquid nitrogen was used for low-temperature pulverization during the ultra-fine pulverization process, and the pulverization temperature was controlled at -5~0℃, to obtain rose ultra-fine powder with microporous structure.

[0032] S2. Place the rose ultrafine powder into a sealed reactor, evacuate the reactor and maintain pressure. The absolute vacuum degree is 30 kPa, and the pressure holding time is 9 min. During the pressure holding process, ultrasonic vibration is applied to promote the removal of adsorbed gas in the pores of the ultrafine powder. The ultrasonic power is 400 W and the frequency is 35 kHz. The ultrasonic is used in an intermittent emission mode, with 5 s emission and 5 s pause. The ultrasonic is continuously and intermittently turned on during the first 2 / 3 of the pressure holding time, and the ultrasonic is stopped during the last 1 / 3 of the pressure holding time to allow the escaped gas to be fully extracted and the adsorbed gas in the pores of the ultrafine powder to be removed.

[0033] S3. Inject the extraction solvent into the sealed reactor after vacuuming and pressure maintenance. The amount of extraction solvent injected is four times the mass of the rose ultrafine powder. The extraction solvent consists of an aqueous phase component, a short-chain alcohol, an ester co-solvent, and a co-crystal solvent in a mass ratio of 7.5:2.0:1.5:0.6. The extraction solvent is driven by negative pressure rebound force to penetrate the pores inside the ultrafine powder particles, completing the solvent impregnation. The aqueous phase component is a 1.0% phosphate buffer solution with a pH of 5.5. The short-chain alcohol is selected from anhydrous ethanol, the ester co-solvent is selected from ethyl acetate, and the co-crystal solvent is prepared by mixing hydrogen bond acceptors and hydrogen bond donors in a molar ratio of 1:2. The hydrogen bond acceptor is selected from betaine, and the hydrogen bond donor is selected from lactic acid. The co-crystal solvent is prepared by mixing the hydrogen bond acceptor and hydrogen bond donor, heating and stirring at 70°C for 2 hours to form a transparent and homogeneous liquid, and then adding deionized water to achieve a concentration of 30%, thus obtaining the co-crystal solvent.

[0034] S4. After solvent impregnation, periodically alternating "positive pressure-negative pressure" pulses are applied to the sealed container. During the positive pressure phase, inert gas is introduced into the reactor, and during the negative pressure phase, the pressure is reduced by evacuation using a vacuum pump. The pressure relief time from the positive pressure phase to the negative pressure phase is ≤0.1s, forming a cyclic sequence of "positive pressure holding - instantaneous pressure relief and explosion - negative pressure cavitation" within the reactor. Simultaneously with the application of the alternating pulses, the temperature inside the reactor is controlled by a programmed temperature increase, gradually rising from room temperature to 65℃ at a rate of 2℃ / ... During the heating process, the extraction solvent is kept in a liquid phase. In the "positive pressure-negative pressure" alternating pulse, the positive pressure is 0.8 MPa, the negative pressure is 12 kPa, the pulse frequency is 2 Hz, the ratio of positive pressure holding time to negative pressure holding time is 3:1, and the total processing time of the "positive pressure-negative pressure" alternating pulse is 25 min. This causes the mechanically broken residual cell wall fragments and oil glands to undergo high-frequency fatigue deformation and interlayer peeling under the reciprocating pressure difference. At the same time, the coupling negative pressure cavitation effect enhances the mass transfer of endogenous essential oil to the liquid phase, resulting in an extraction mixture.

[0035] S5. The extracted mixture is subjected to reduced pressure flash evaporation for 10 min. The mixed vapor generated by flash evaporation is liquefied through a three-stage condensation process as follows: the first stage condensation uses a shell-and-tube condenser with circulating cooling water as the cooling medium and an inlet water temperature of 6°C, and the first-stage condensate is collected; the second stage condensation uses a plate condenser with an ethylene glycol aqueous solution as the cooling medium and a temperature of -10°C, and the second-stage condensate is collected; the third stage condensation uses a cold trap at a temperature of -15°C, and the third-stage condensate is collected. The condensates obtained from the condensation and liquefaction processes are combined, allowed to stand for 60 min to separate into layers, and the upper layer is collected to obtain crude essential oil. Anhydrous sodium sulfate (5% by mass) is added to the crude essential oil and stirred for dehydration for 45 min. After filtration, the oil is decolorized by passing it through an activated carbon decolorization column at a flow rate of 1 BV / h. The activated carbon particle size is 40 mesh, and the column diameter-to-height ratio is 1:8. The effluent is collected to obtain the plant essential oil.

[0036] Example 2

[0037] A method for improving the extraction rate of plant essential oils includes the following steps:

[0038] S1. Fresh peppermint leaves were subjected to repeated freeze-thaw pretreatment. The freeze-thaw pretreatment was carried out in the following manner: freeze at -15℃ for 8 hours, then thaw at 20℃ for 5 hours, and repeat the freeze-thaw cycle 3 times; then ultrafine pulverization was performed, with the particle size D90≤30μm. Liquid nitrogen was used to assist in the ultrafine pulverization process, and the pulverization temperature was controlled between -5 and 0℃ to obtain peppermint ultrafine powder with a microporous structure.

[0039] S2. Place the peppermint ultrafine powder into a sealed reactor, evacuate the reactor and maintain pressure. The absolute vacuum degree is 35 kPa, and the pressure holding time is 12 min. During the pressure holding process, ultrasonic vibration is applied to promote the removal of adsorbed gas in the pores of the ultrafine powder. The ultrasonic power is 500 W and the frequency is 35 kHz. The ultrasonic transmission mode is intermittent, with a transmission time of 5 s and a pause time of 5 s. The ultrasonic transmission is continuously and intermittently turned on during the first 2 / 3 of the pressure holding time, and the ultrasonic transmission is stopped during the last 1 / 3 of the pressure holding time to allow the escaping gas to be fully extracted and the adsorbed gas in the pores of the ultrafine powder to be removed.

[0040] S3. Inject the extraction solvent into the sealed reactor after vacuuming and pressure maintenance. The amount of extraction solvent injected is 3.5 times the mass of the peppermint ultrafine powder. The extraction solvent consists of an aqueous phase component, a short-chain alcohol, an ester co-solvent, and a co-crystal solvent in a mass ratio of 7.0:2.5:1.2:0.8. The extraction solvent is driven by negative pressure rebound force to penetrate the pores inside the ultrafine powder particles, completing the solvent impregnation. The aqueous phase component is a 0.8% phosphate buffer solution with a pH of 5.8. The short-chain alcohol is selected from anhydrous ethanol, the ester co-solvent is selected from ethyl acetate, and the co-crystal solvent is prepared by mixing hydrogen bond acceptors and hydrogen bond donors in a molar ratio of 1:2. The hydrogen bond acceptor is selected from choline chloride, and the hydrogen bond donor is selected from glycerol. The co-crystal solvent is prepared by mixing the hydrogen bond acceptor and hydrogen bond donor, heating and stirring at 75°C for 2 hours to form a transparent and homogeneous liquid, and then adding deionized water to achieve a concentration of 30%, thus obtaining the co-crystal solvent.

[0041] S4. After solvent impregnation, periodically alternating "positive pressure-negative pressure" pulses are applied to the sealed container. During the positive pressure phase, inert gas is introduced into the reactor, and during the negative pressure phase, the pressure is reduced by evacuating the gas using a vacuum pump. The pressure relief time between the positive and negative pressure phases is ≤0.1s, forming a cyclic sequence of "positive pressure holding - instantaneous pressure relief and explosion - negative pressure cavitation" within the reactor. Simultaneously with the application of the alternating pulses, the temperature inside the reactor is controlled by a programmed temperature increase, gradually rising from room temperature to 60℃ at a rate of 3℃. / min, the extraction solvent is kept in liquid phase during the heating process; in the "positive pressure-negative pressure" alternating pulse, the positive pressure is 1.0MPa, the negative pressure is 8kPa, the pulse frequency is 2Hz, the ratio of positive pressure holding time to negative pressure holding time is 3:1, and the total processing time of the "positive pressure-negative pressure" alternating pulse is 25min. This causes the mechanically broken residual cell wall fragments and oil glands to undergo high-frequency fatigue deformation and interlayer peeling under the reciprocating pressure difference. At the same time, the coupling negative pressure cavitation effect enhances the mass transfer of endogenous essential oil to the liquid phase bulk, resulting in an extraction mixture.

[0042] S5. The extracted mixture is subjected to reduced pressure flash evaporation for 12 min. The mixed vapor generated by flash evaporation is liquefied through a three-stage condensation process as follows: the first stage condensation uses a shell-and-tube condenser with circulating cooling water as the cooling medium and an inlet water temperature of 6°C, and the first-stage condensate is collected; the second stage condensation uses a plate condenser with an ethylene glycol aqueous solution as the cooling medium and a temperature of -8°C, and the second-stage condensate is collected; the third stage condensation uses a cold trap at a temperature of -15°C, and the third-stage condensate is collected. The condensates obtained from the condensation and liquefaction processes are combined, allowed to stand and separate into layers, and the upper layer is collected to obtain crude essential oil. 5% (by weight) of anhydrous sodium sulfate is added to the crude essential oil and stirred for dehydration for 40 min. After filtration, the oil is decolorized by passing it through an activated carbon decolorization column at a flow rate of 1 BV / h. The activated carbon particle size is 40 mesh, and the column diameter-to-height ratio is 1:8. The effluent is collected to obtain the plant essential oil.

[0043] Example 3

[0044] A method for improving the extraction rate of plant essential oils includes the following steps:

[0045] S1. Fresh lemongrass leaves are subjected to repeated freeze-thaw pretreatment. The freeze-thaw pretreatment is carried out in the following manner: freeze at -20℃ for 12 hours, then thaw at 25℃ for 5 hours, and repeat the freeze-thaw cycle 3 times; then, the leaves are ultra-finely pulverized, with the particle size D90≤30μm. Liquid nitrogen is used to assist in the ultra-fine pulverization process, and the pulverization temperature is controlled between -5℃ and 0℃ to obtain lemongrass ultra-fine powder with a microporous structure.

[0046] S2. Place the lemongrass ultrafine powder into a sealed reactor, evacuate the reactor and maintain pressure. The absolute vacuum degree is 30 kPa, and the pressure holding time is 12 min. During the pressure holding process, ultrasonic vibration is applied to promote the removal of adsorbed gas in the pores of the ultrafine powder. The ultrasonic power is 500 W and the frequency is 35 kHz. The ultrasonic transmission mode is intermittent, with a transmission time of 5 s and a pause time of 5 s. The ultrasonic transmission is continuously and intermittently turned on during the first 2 / 3 of the pressure holding time, and the ultrasonic transmission is stopped during the last 1 / 3 of the pressure holding time to allow the escaping gas to be fully extracted and the adsorbed gas in the pores of the ultrafine powder to be removed.

[0047] S3. Inject the extraction solvent into the sealed reactor after vacuuming and pressure maintenance. The amount of extraction solvent injected is four times the mass of the lemongrass ultrafine powder. The extraction solvent consists of an aqueous phase component, a short-chain alcohol, an ester co-solvent, and a co-crystal solvent in a mass ratio of 6.5:2.5:1.5:1.0. The extraction solvent is driven by negative pressure rebound force to penetrate the pores inside the ultrafine powder particles, completing the solvent impregnation. The aqueous phase component is a 1.0% phosphate buffer solution with a pH of 5.0. The short-chain alcohol is selected from anhydrous ethanol, the ester co-solvent is selected from ethyl lactate, and the co-crystal solvent is prepared by mixing hydrogen bond acceptors and hydrogen bond donors in a molar ratio of 1:2. The hydrogen bond acceptor is selected from choline chloride, and the hydrogen bond donor is selected from lactic acid. The co-crystal solvent is prepared by mixing the hydrogen bond acceptor and hydrogen bond donor, heating and stirring at 70°C for 2 hours to form a transparent and homogeneous liquid, and then adding deionized water to achieve a concentration of 30%, thus obtaining the co-crystal solvent.

[0048] S4. After solvent impregnation, periodically alternating "positive pressure-negative pressure" pulses are applied to the sealed container. During the "positive pressure-negative pressure" pulses, nitrogen gas is introduced into the reactor during the positive pressure phase, and the pressure is reduced by evacuation using a vacuum pump during the negative pressure phase. The pressure relief time from the positive pressure phase to the negative pressure phase is ≤0.1s, forming a cyclic sequence of "positive pressure holding - instantaneous pressure relief and explosion - negative pressure cavitation" within the reactor. Simultaneously with the application of the alternating pulses, the temperature inside the reactor is controlled by a programmed temperature increase, gradually rising from room temperature to 60℃ at a rate of 2℃ / ... During the heating process, the extraction solvent is kept in a liquid phase. In the "positive pressure-negative pressure" alternating pulse, the positive pressure is 1.2 MPa, the negative pressure is 5 kPa, the pulse frequency is 2 Hz, the ratio of positive pressure holding time to negative pressure holding time is 3:1, and the total processing time of the "positive pressure-negative pressure" alternating pulse is 25 min. This causes the mechanically broken residual cell wall fragments and oil glands to undergo high-frequency fatigue deformation and interlayer peeling under the reciprocating pressure difference. At the same time, the coupling negative pressure cavitation effect enhances the mass transfer of endogenous essential oil to the liquid phase, resulting in an extraction mixture.

[0049] S5. The extracted mixture is subjected to reduced pressure flash evaporation for 10 min. The mixed steam generated by flash evaporation is liquefied through a three-stage condensation process as follows: the first stage condensation uses a shell-and-tube condenser with circulating cooling water as the cooling medium and an inlet water temperature of 6°C, and the first-stage condensate is collected; the second stage condensation uses a plate condenser with an ethylene glycol aqueous solution as the cooling medium and a temperature of -10°C, and the second-stage condensate is collected; the third stage condensation uses a cold trap at a temperature of -15°C, and the third-stage condensate is collected. The condensates obtained from the condensation and liquefaction processes are combined, allowed to stand for 60 min to separate into layers, and the upper layer is collected to obtain crude essential oil. Anhydrous sodium sulfate (5% by mass) is added to the crude essential oil and stirred for dehydration for 30 min. After filtration, the oil is decolorized by passing it through an activated carbon decolorization column at a flow rate of 1 BV / h. The activated carbon particle size is 40 mesh, and the column diameter to height ratio is 1:8. The effluent is collected to obtain the plant essential oil.

[0050] Example 4

[0051] A method for improving the extraction rate of plant essential oils includes the following steps:

[0052] S1. Fresh lemon peel (with 2mm of white peel retained) is subjected to repeated freeze-thaw pretreatment. The freeze-thaw pretreatment is carried out in the following manner: freeze at -18℃ for 8 hours, then thaw at 25℃ for 4 hours, and repeat the freeze-thaw cycle 3 times; then it is subjected to ultrafine grinding, with the particle size D90≤30μm. Liquid nitrogen is used to assist in low-temperature grinding during the ultrafine grinding process, and the grinding temperature is controlled at -10~-5℃ to obtain ultrafine powder with microporous structure.

[0053] S2. Place the ultrafine powder into a sealed reactor, evacuate the reactor and maintain pressure. The absolute vacuum degree is 25 kPa, and the pressure holding time is 9 min. During the pressure holding process, ultrasonic vibration is applied to promote the removal of adsorbed gas in the pores of the ultrafine powder. The ultrasonic power is 450 W and the frequency is 35 kHz. The ultrasonic wave is emitted in an intermittent mode, with a 5 s emission followed by a 5 s pause. The ultrasonic wave is continuously and intermittently activated during the first 2 / 3 of the pressure holding time, and is stopped during the last 1 / 3 of the pressure holding time to allow the escaping gas to be fully extracted and the adsorbed gas in the pores of the ultrafine powder to be removed.

[0054] S3. Inject the extraction solvent into the sealed reactor after vacuuming and pressure maintenance. The amount of extraction solvent injected is three times the mass of the lemon peel ultrafine powder. The extraction solvent consists of an aqueous phase component, a short-chain alcohol, an ester co-solvent, and a co-crystal solvent in a mass ratio of 6.0:2.0:2.0:1.0. The extraction solvent is driven by negative pressure rebound force to penetrate the pores inside the ultrafine powder particles, completing the solvent impregnation. The aqueous phase component is a 0.5% phosphate buffer solution with a pH of 6.0. The short-chain alcohol is selected from 1,3-butanediol, the ester co-solvent is selected from ethyl acetate, and the co-crystal solvent is prepared by mixing hydrogen bond acceptors and hydrogen bond donors in a molar ratio of 1:1. The hydrogen bond acceptor is selected from betaine, and the hydrogen bond donor is selected from glucose. The co-crystal solvent is prepared by mixing the hydrogen bond acceptor and hydrogen bond donor, heating and stirring at 70°C for 2 hours to form a transparent and homogeneous liquid, and then adding deionized water to achieve a concentration of 35%, thus obtaining the co-crystal solvent.

[0055] S4. After solvent impregnation, periodically alternating "positive pressure-negative pressure" pulses are applied to the sealed container. During the positive pressure phase, inert gas is introduced into the reactor, and during the negative pressure phase, the pressure is reduced by evacuation using a vacuum pump. The pressure relief time between the positive and negative pressure phases is ≤0.1s, forming a cyclic sequence of "positive pressure holding - instantaneous pressure relief and explosion - negative pressure cavitation" within the reactor. Simultaneously with the application of the alternating pulses, the temperature inside the reactor is controlled by a programmed temperature increase, gradually rising from room temperature to 60℃ at a rate of 3℃ / ... During the heating process, the extraction solvent is kept in a liquid phase. In the "positive pressure-negative pressure" alternating pulse, the positive pressure is 1.2 MPa, the negative pressure is 10 kPa, the pulse frequency is 2 Hz, the ratio of positive pressure holding time to negative pressure holding time is 3:1, and the total processing time of the "positive pressure-negative pressure" alternating pulse is 20 min. This causes the mechanically broken residual cell wall fragments and oil glands to undergo high-frequency fatigue deformation and interlayer peeling under the reciprocating pressure difference. At the same time, the coupling negative pressure cavitation effect enhances the mass transfer of endogenous essential oil to the liquid phase, resulting in an extraction mixture.

[0056] S5. The extracted mixture is subjected to reduced pressure flash evaporation for 8 minutes. The mixed vapor generated by flash evaporation is liquefied through a three-stage condensation process as follows: the first-stage condensation uses a shell-and-tube condenser with circulating cooling water as the cooling medium and an inlet water temperature of 6°C, and the first-stage condensate is collected; the second-stage condensation uses a plate condenser with an ethylene glycol aqueous solution as the cooling medium and a temperature of -10°C, and the second-stage condensate is collected; the third-stage condensation uses a cold trap at a temperature of -15°C, and the third-stage condensate is collected. The condensates obtained from the condensation and liquefaction processes are combined, allowed to stand for 45 minutes to separate into layers, and the upper layer is collected to obtain crude essential oil. Anhydrous sodium sulfate (3% by mass) is added to the crude essential oil and stirred for dehydration for 30 minutes. After filtration, the oil is decolorized by passing it through an activated carbon decolorization column at a flow rate of 1.5 BV / h. The activated carbon particle size is 40 mesh, and the column diameter-to-height ratio is 1:8. The effluent is collected to obtain the plant essential oil.

[0057] Example 5

[0058] A method for improving the extraction rate of plant essential oils includes the following steps:

[0059] S1. Fresh turmeric rhizomes are subjected to repeated freeze-thaw pretreatment. The repeated freeze-thaw pretreatment is carried out according to the following method: freeze at a freezing temperature of -20℃ for 12 hours, and then thaw at a thawing temperature of 28℃ for 6 hours, with 4 freeze-thaw cycles; then ultrafine grinding is performed, with the particle size D90≤30μm of the ultrafine powder. Liquid nitrogen is used to assist in low-temperature grinding during the ultrafine grinding process, and the grinding temperature is controlled at -5~0℃ to obtain ultrafine powder with microporous structure.

[0060] S2. Place the ultrafine powder into a sealed reactor, evacuate the reactor and maintain pressure. The absolute vacuum degree is 20 kPa, and the pressure holding time is 12 min. During the pressure holding process, ultrasonic vibration is applied to promote the removal of adsorbed gas in the pores of the ultrafine powder. The ultrasonic power is 600 W and the frequency is 40 kHz. The ultrasonic wave is emitted in an intermittent mode, with a 5 s emission followed by a 5 s pause. The ultrasonic wave is continuously and intermittently activated during the first 2 / 3 of the pressure holding time, and is stopped during the last 1 / 3 of the pressure holding time to allow the escaping gas to be fully extracted and the adsorbed gas in the pores of the ultrafine powder to be removed.

[0061] S3. Inject the extraction solvent into the sealed reactor after vacuuming and pressure maintenance. The amount of extraction solvent injected is 5 times the mass of the turmeric ultrafine powder. The extraction solvent consists of an aqueous phase component, a short-chain alcohol, an ester co-solvent, and a co-crystal solvent in a mass ratio of 5.0:3.0:1.5:0.5. The extraction solvent is driven by negative pressure rebound force to penetrate the pores inside the ultrafine powder particles, thus completing the solvent impregnation. The aqueous phase component is a 0.8% phosphate buffer solution with a pH of 5.5. The short-chain alcohol is selected from propylene glycol, the ester co-solvent is selected from butyl acetate, and the co-crystal solvent is prepared by mixing hydrogen bond acceptors and hydrogen bond donors in a molar ratio of 1:2. The hydrogen bond acceptor is selected from choline chloride, and the hydrogen bond donor is selected from a 1:1 combination of lactic acid and glycerol. The co-crystal solvent is prepared by mixing the hydrogen bond acceptor and hydrogen bond donor, heating and stirring at 70°C for 2 hours to form a transparent and homogeneous liquid, and then adding deionized water to make its concentration 40%, thus obtaining the co-crystal solvent.

[0062] S4. After solvent impregnation, periodically alternating "positive pressure-negative pressure" pulses are applied to the sealed container. During the positive pressure phase, inert gas is introduced into the reactor, and during the negative pressure phase, the pressure is reduced by evacuation using a vacuum pump. The pressure relief time between the positive and negative pressure phases is ≤0.1s, forming a cyclic sequence of "positive pressure holding - instantaneous pressure relief and explosion - negative pressure cavitation" within the reactor. Simultaneously with the application of the alternating pulses, the temperature inside the reactor is controlled by a programmed temperature increase, gradually rising from room temperature to 70℃ at a rate of 2℃ / ... During the heating process, the extraction solvent is kept in a liquid phase. In the "positive pressure-negative pressure" alternating pulse, the positive pressure is 1.5 MPa, the negative pressure is 8 kPa, the pulse frequency is 1.5 Hz, the ratio of positive pressure holding time to negative pressure holding time is 4:1, and the total processing time of the "positive pressure-negative pressure" alternating pulse is 30 min. This causes the mechanically broken residual cell wall fragments and oil glands to undergo high-frequency fatigue deformation and interlayer peeling under the reciprocating pressure difference. At the same time, the coupling negative pressure cavitation effect enhances the mass transfer of endogenous essential oil to the liquid phase, resulting in an extraction mixture.

[0063] S5. The extracted mixture is subjected to reduced pressure flash evaporation for 15 min. The mixed vapor generated by flash evaporation is liquefied through a three-stage condensation process as follows: the first stage condensation uses a shell-and-tube condenser with circulating cooling water as the cooling medium and an inlet water temperature of 8°C, and the first-stage condensate is collected; the second stage condensation uses a plate condenser with an ethylene glycol aqueous solution as the cooling medium and a temperature of -12°C, and the second-stage condensate is collected; the third stage condensation uses a cold trap at a temperature of -18°C, and the third-stage condensate is collected. The condensates obtained from the condensation and liquefaction processes are combined, allowed to stand for 90 min to separate into layers, and the upper layer is collected to obtain crude essential oil. 6% (by weight) of anhydrous sodium sulfate is added to the crude essential oil and stirred for dehydration for 45 min. After filtration, the oil is decolorized by passing it through an activated carbon decolorization column at a flow rate of 0.5 BV / h. The activated carbon particle size is 60 mesh, and the column diameter to height ratio is 1:10. The effluent is collected to obtain the plant essential oil.

[0064] Example 6

[0065] A method for improving the extraction rate of plant essential oils includes the following steps:

[0066] S1. The dried star anise fruit was subjected to repeated freeze-thaw pretreatment. The repeated freeze-thaw pretreatment was carried out according to the following method: freeze at a freezing temperature of -20℃ for 12 hours, and then thaw at a thawing temperature of 25℃ for 7 hours. The freeze-thaw cycle was repeated 3 times. Then, it was ultra-finely pulverized. The particle size of the ultra-fine powder was D90≤30μm. Liquid nitrogen was used to assist in the ultra-fine pulverization process for low-temperature pulverization. The pulverization temperature was controlled at -15~-10℃ to obtain ultra-fine powder with microporous structure.

[0067] S2. Place the ultrafine powder into a sealed reactor, evacuate the reactor and maintain pressure. The absolute vacuum degree is 25 kPa, and the pressure holding time is 9 min. During the pressure holding process, ultrasonic vibration is applied to promote the removal of adsorbed gas in the pores of the ultrafine powder. The ultrasonic power is 550 W and the frequency is 40 kHz. The ultrasonic wave is emitted in an intermittent mode, with a 5 s emission followed by a 5 s pause. The ultrasonic wave is continuously and intermittently activated during the first 2 / 3 of the pressure holding time, and is stopped during the last 1 / 3 of the pressure holding time to allow the escaping gas to be fully extracted and the adsorbed gas in the pores of the ultrafine powder to be removed.

[0068] S3. Inject the extraction solvent into the sealed reactor after vacuuming and pressure holding. The amount of extraction solvent injected is 3.5 times the mass of the star anise ultrafine powder. The extraction solvent consists of an aqueous phase component, short-chain alcohol, ester co-solvent, and eutectic solvent in a mass ratio of 6.5:2.0:2.5:0.8. The extraction solvent is driven by negative pressure rebound force to penetrate into the pores inside the ultrafine powder particles to complete the solvent impregnation.

[0069] The aqueous phase is a 0.5% phosphate buffer solution with a pH of 6.5. The short-chain alcohol is selected from anhydrous ethanol, the ester co-solvent is selected from ethyl acetate, and the co-crystal solvent is prepared by mixing a hydrogen bond acceptor and a hydrogen bond donor in a molar ratio of 1:2. The hydrogen bond acceptor is selected from choline chloride, and the hydrogen bond donor is selected from glycerol. The co-crystal solvent is prepared by mixing the hydrogen bond acceptor and the hydrogen bond donor, heating and stirring at 70°C for 2 hours to form a transparent and homogeneous liquid, and then adding deionized water to make its concentration 25% to obtain the co-crystal solvent.

[0070] S4. After solvent impregnation, periodically alternating "positive pressure-negative pressure" pulses are applied to the sealed container. During the positive pressure phase, inert gas is introduced into the reactor, and during the negative pressure phase, the pressure is reduced by evacuation using a vacuum pump. The pressure relief time from the positive pressure phase to the negative pressure phase is ≤0.1s, forming a cyclic sequence of "positive pressure holding - instantaneous pressure relief and explosion - negative pressure cavitation" within the reactor. Simultaneously with the application of the alternating pulses, the temperature inside the reactor is programmed and gradually increased from room temperature to 65℃ at a rate of 3℃ / ... During the heating process, the extraction solvent is kept in a liquid phase. In the "positive pressure-negative pressure" alternating pulse, the positive pressure is 1.3 MPa, the negative pressure is 10 kPa, the pulse frequency is 2 Hz, the ratio of positive pressure holding time to negative pressure holding time is 3:1, and the total processing time of the "positive pressure-negative pressure" alternating pulse is 20 min. This causes the mechanically broken residual cell wall fragments and oil glands to undergo high-frequency fatigue deformation and interlayer peeling under the reciprocating pressure difference. At the same time, the coupling negative pressure cavitation effect enhances the mass transfer of endogenous essential oil to the liquid phase, resulting in an extraction mixture.

[0071] S5. The extracted mixture is subjected to reduced pressure flash evaporation for 12 min. The mixed vapor generated by flash evaporation is liquefied through a three-stage condensation process as follows: the first stage condensation uses a shell-and-tube condenser with circulating cooling water as the cooling medium and an inlet water temperature of 6°C, and the first-stage condensate is collected; the second stage condensation uses a plate condenser with an ethylene glycol aqueous solution as the cooling medium and a temperature of -8°C, and the second-stage condensate is collected; the third stage condensation uses a cold trap at a temperature of -15°C, and the third-stage condensate is collected. The condensates obtained from the condensation and liquefaction processes are combined, allowed to stand for 60 min to separate into layers, and the upper layer is collected to obtain crude essential oil. 4% (by weight) of anhydrous sodium sulfate is added to the crude essential oil and stirred for dehydration for 30 min. After filtration, the oil is decolorized by passing it through an activated carbon decolorization column at a flow rate of 1 BV / h. The activated carbon particle size is 40 mesh, and the column diameter-to-height ratio is 1:8. The effluent is collected to obtain the plant essential oil.

[0072] Comparative Example 1

[0073] The difference between Comparative Example 1 and Example 1 is that the traditional steam distillation method was used for extraction, and the extraction was carried out according to the following process: Damask rose flowers, the same as in Example 1, were placed in a distillation vessel, and distilled water was added at a material-to-liquid ratio of 1:8 (unit: kg / L). Steam distillation was carried out for 3 hours, and circulating cooling water was circulated through the condenser. The cooling water inlet temperature was 10°C. The distillate was collected and allowed to stand for 60 minutes to separate into layers. The upper oil phase was taken and dehydrated with 5% anhydrous sodium sulfate for 45 minutes. After filtration, it was decolorized by passing it through an activated carbon decolorization column at a flow rate of 1 BV / h. The activated carbon particle size was 40 mesh, and the column diameter-to-height ratio was 1:8. The eluent was collected to obtain the plant essential oil.

[0074] Comparative Example 2

[0075] The difference between Comparative Example 1 and Example 1 is that the vacuum degassing process in step S2 is not performed, and step S3 is performed after step S1. The other steps are the same as in Example 1.

[0076] Comparative Example 3

[0077] The difference between Comparative Example 1 and Example 1 is that constant positive pressure is used instead of alternating pulses, and step S4 is maintained at a constant positive pressure of 0.8 MPa for 25 minutes. The other steps are the same as in Example 1.

[0078] Comparative Example 4

[0079] The difference between Comparative Example 1 and Example 1 is that the alternating pulse uses a symmetrical square wave, and the ratio of positive pressure holding time to negative pressure holding time is 1:1. Other steps are the same as in Example 1.

[0080] Comparative Example 5

[0081] The difference between Comparative Example 1 and Example 1 is that the extraction solvent does not contain a eutectic solvent and is composed of an aqueous phase component, a short-chain alcohol, and an ester co-solvent in a mass ratio of 7.5:2.0:1.5. The other steps are the same as in Example 1.

[0082] Extraction rate comparison

[0083] The extraction rate of rose essential oil obtained from Example 1 and Comparative Examples 1-7 was calculated using the following formula:

[0084] Extraction rate = (mass of rose essential oil / mass of rose petals) × 100%

[0085] The calculation results are recorded in Table 1.

[0086] Table 1

[0087] Example 1 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Extraction rate % 0.108 0.022 0.052 0.069 0.078 0.075

[0088] As shown in Table 1, the extraction method of this invention is 3.9 times more efficient than the traditional steam distillation method. Comparative Example 2, lacking vacuum degassing, showed a 51.9% lower extraction rate compared to Example 1, demonstrating the causal coupling of "vacuum degassing + negative pressure rebound wetting." Without the vacuum degassing step, the gas adsorbed within the pores of the ultrafine powder forms "gas resistance," allowing the solvent to only wet the particle surface and shallow pores, failing to reach the deep oil glands inside the particles, resulting in a large amount of essential oil remaining inside the particles and unable to be extracted. Comparative Example 3 showed a 36.1% lower extraction rate compared to Example 1, indicating that constant pressure can only squeeze out some of the essential oil already freed on the surface, but cannot cause "interlayer fatigue peeling" of the remaining cell wall fragments, preventing the release of deeply bound essential oil. It is evident that the "alternating fatigue" mechanism of this invention is irreplaceable in its cell-wall breaking effect compared to the traditional "constant pressure extrusion." Comparative Example 4 showed a 27.8% reduction in extraction rate compared to Example 1. This indicates that the symmetrical cycle (positive pressure time = negative pressure time) lacks the rhythmic difference of "stress accumulation - instantaneous release," resulting in a lack of impact unloading of cell wall fragments between expansion and contraction. The interlayer peeling efficiency is lower than that of the asymmetric design of this invention (positive pressure holding time is much longer than negative pressure holding time, and pressure release time ≤ 0.1 s). Comparative Example 5 showed a 30.1% reduction in extraction rate compared to Example 1. This indicates that the eutectic solvent specifically contributes to disrupting the cellulose-hemicellulose-lignin hydrogen bond network of the cell wall.

[0089] Comparison of phenylethanol / citronellol (P / C) ratios

[0090] Accurately weigh 0.1000 g (accurate to 0.0001 g) of the essential oils extracted in Example 1 and Comparative Example 1, respectively, and place them in 10 mL volumetric flasks. Dissolve them in n-hexane and dilute to the mark. Accurately transfer 1.0 mL of the above solution to a gas chromatography-mass spectrometry (GC-MS) injection bottle, add 50 μL of n-tetradecane internal standard solution with a concentration of 100 μg / mL, vortex mix for 30 s, and seal for analysis. GC-MS analysis was performed using an HP-5MS quartz capillary column (30m × 0.25mm × 0.25μm), with high-purity helium (purity ≥ 99.999%) as the carrier gas. The column flow rate was 1.0 mL / min in constant flow mode, the injection port temperature was 250℃, the split ratio was 50:1, and the injection volume was 1.0 μL. The column oven temperature program was as follows: 50℃ for 2 min, then increased to 240℃ at 4℃ / min and held for 5 min. The transfer line temperature was 280℃, the ion source (EI) temperature was 230℃, the quadrupole temperature was 150℃, the ionization energy was 70 eV, the mass scan range was m / z 35~450, and the solvent delay was 3.5 min. Qualitative analysis employed double confirmation through retention time comparison with phenylethanol and citronellol standards and NIST 11 mass spectrometry library search (match ≥90%). Quantitative analysis used the internal standard curve method. A series of mixed standard solutions (concentration range 10–200 μg / mL) were prepared using phenylethanol and citronellol standards, and a fixed amount of internal standard (n-tetradecane, 10 μg / mL) was added for injection analysis. A standard curve was plotted with the peak area ratio of the target component to the internal standard as the ordinate and the concentration ratio as the abscissa (linear correlation coefficient R² ≥ 0.995). The absolute contents (μg / g essential oil) of phenylethanol and citronellol were calculated based on the peak area ratio of the target component to the internal standard in the sample, substituted into the standard curve. The phenylethanol / citronellol ratio (P / C) was calculated using the following formula:

[0091] P / C=C 苯乙醇 / C 香茅醇

[0092] Where C 苯乙醇 and C 香茅醇 The values ​​represent the absolute contents of phenylethyl alcohol and citronellol in the essential oils, respectively. Three parallel samples were prepared for each sample, and the average value was taken. The relative standard deviation (RSD) of the P / C ratio for three parallel determinations of the same sample was ≤3%, and no interfering peaks were detected in the blank injection (n-hexane) to ensure the accuracy and reliability of the experimental data. The results are shown in Table 2.

[0093] Table 2

[0094] Phenylacetyl alcohol content % Citronellol content % P / C ratio ISO 9842 quality level Example 1 61.2±1.8 29.5±1.2 2.07 Special Grade Comparative Example 1 28.6±2.1 22.3±1.5 1.28 Level 2

[0095] Phenylacetyl alcohol (2-phenylethanol) is the most abundant characteristic component in Damask rose essential oil, giving it its sweet and rose-scented main aroma. However, phenylethanol is highly water-soluble, and during traditional steam distillation, a large amount of it dissolves in the distilled water and is discharged from the system with the distillate, resulting in irreversible loss. Simultaneously, the high temperature and long distillation time of traditional methods cause phenylethanol to readily undergo esterification with organic acids in the system, forming phenethyl acetate, further reducing the content of free phenylethanol. This dual loss mechanism leads to a significant reduction in the phenylethanol content of Comparative Example 1. Citronellol has much lower water solubility than phenylethanol and better thermal stability at 100°C, resulting in a relatively smaller loss during traditional distillation. Consequently, the P / C ratio of Comparative Example 1 (1.28) is significantly lower than that of Example 1 (2.07). The method of this invention effectively avoids the loss of water solubility and thermal esterification degradation of phenylethanol during steam distillation through the synergistic protection of low temperature (65℃), short time, and three-stage gradient condensation, thus maximizing the retention of heat-sensitive / water-soluble characteristic components. The P / C ratio, a core evaluation indicator of rose essential oil quality, demonstrates the significant differences in this invention's method in protecting heat-sensitive characteristic components and enhancing the aroma quality of essential oils.

[0096] Extraction rate of each raw material

[0097] The extraction rates of the plant essential oils obtained in Examples 1-6 were calculated using the following formula:

[0098] Extraction rate = (mass of plant essential oil / mass of plant raw material) × 100%

[0099] The calculation results are recorded in Table 3.

[0100] Table 3

[0101] Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Extraction rate of this invention % 0.107 0.326 0.432 1.105 1.327 10.608 Traditional steam distillation extraction rate % 0.023 0.109 0.136 0.483 0.229 4.450

[0102] The results of Examples 1-6 demonstrate the broad applicability of the method of the present invention to six major categories of plant raw materials: flowers, leaves, herbs, fruit peels, rhizomes, and seeds (the absolute extraction rates vary considerably among different raw materials, mainly depending on their oil content). Furthermore, the extraction rate is significantly higher than that of traditional steam distillation, especially for difficult-to-extract raw materials with denser tissues or starch or waxy barriers (such as turmeric). This indicates that the method of the present invention has excellent industrial versatility and application value. The method of the present invention can be used to efficiently extract essential oils from plant raw materials whose essential oils are stored in oil glands, secretory cavities, oleoresin droplets, or xylem vessels within the cell wall, and which have mass transfer barriers such as dense cuticles, waxy layers, lignin / silica skeletons, or starch gel coatings.

[0103] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for improving the extraction rate of plant essential oils, characterized in that, Includes the following steps: S1. Plant raw materials rich in essential oils are subjected to repeated freeze-thaw pretreatment, and then ultra-fine pulverization to obtain ultra-fine powder with microporous structure; S2. Place the ultrafine powder into a sealed reactor, evacuate and pressurize the sealed reactor to remove the gas adsorbed in the pores of the ultrafine powder. S3. Inject the extraction solvent into the sealed reactor after vacuuming and pressure preservation. Use the negative pressure rebound force to drive the extraction solvent to penetrate into the pores inside the ultrafine powder particles, thus completing the solvent impregnation. S4. After solvent impregnation, periodically switching "positive pressure-negative pressure" alternating pulses are applied to the sealed container, causing the mechanically broken residual cell wall fragments and oil glands to undergo high-frequency fatigue deformation and interlayer peeling under the reciprocating pressure difference. At the same time, the coupling negative pressure cavitation effect enhances the mass transfer of endogenous essential oils to the liquid phase, resulting in an extraction mixture. S5. The extracted mixture is subjected to desolvation by flash evaporation under reduced pressure. The mixed steam generated by flash evaporation is liquefied by three-stage condensation. The condensates obtained by condensation are combined, allowed to stand and separate into layers, and the upper layer is collected to obtain crude essential oil. The crude essential oil is then decolorized and dehydrated to obtain plant essential oil.

2. The method for improving the extraction rate of plant essential oils as described in claim 1, characterized in that, In step S1, repeated freeze-thaw pretreatment is performed as follows: freeze at a freezing temperature of -20 to -5℃ for 4-12 hours, then thaw at a thawing temperature of 15-30℃ for 3-7 hours, and repeat the freeze-thaw cycle 2-4 times.

3. The method for improving the extraction rate of plant essential oils as described in claim 1, characterized in that, In step S1, the particle size D90 of the ultrafine powder is ≤45μm, preferably ≤30μm, and liquid nitrogen or dry ice is used to assist in low-temperature pulverization during the ultrafine pulverization process, with the pulverization temperature controlled between -10 and 10℃.

4. The method for improving the extraction rate of plant essential oils as described in claim 1, characterized in that, In step S2, the absolute vacuum degree of vacuuming is 20-60 kPa, the pressure holding time is 6-12 min, and ultrasonic vibration is applied to promote the removal of adsorbed gas in the pores of the ultrafine powder during the pressure holding process. The ultrasonic power is 300-600 W and the frequency is 30-40 kHz. The ultrasonic wave is emitted in an intermittent mode, with a 5-second emission followed by a 5-second pause. Ultrasonic waves are stopped during the last 1 / 3 of the pressure holding time to allow the escaped gas to be fully extracted.

5. The method for improving the extraction rate of plant essential oils as described in claim 1, characterized in that, In step S3, the amount of extraction solvent injected is 3-5 times the mass of the ultrafine powder. The extraction solvent is composed of an aqueous phase component, short-chain alcohol, ester co-solvent, and eutectic solvent in a mass ratio of (5-8.5):(1-3):(1-3):(0.2-1.0).

6. The method for improving the extraction rate of plant essential oils as described in claim 5, characterized in that, The aqueous phase component is a phosphate buffer solution with a concentration of 0.5-2.0% and a pH of 4.5-6.

5. The short-chain alcohol is selected from one or more of ethanol, propylene glycol, and 1,3-butanediol. The ester cosolvent is selected from one or more of ethyl acetate, butyl acetate, and ethyl lactate. The co-crystal solvent is prepared by mixing hydrogen bond acceptors and hydrogen bond donors in a molar ratio of 1:(1-4). The hydrogen bond acceptor is selected from one of betaine and choline chloride. The hydrogen bond donor is selected from one or more of lactic acid, glycerol, and glucose.

7. The method for improving the extraction rate of plant essential oils as described in claim 1, characterized in that, In step S4, the positive pressure in the "positive pressure-negative pressure" alternating pulse is 0.5-1.5MPa, the negative pressure is 5-15kPa, the pulse frequency is 1-3Hz, the ratio of positive pressure holding time to negative pressure holding time is (2-5):1, and the total processing time of the "positive pressure-negative pressure" alternating pulse is 20-30min.

8. The method for improving the extraction rate of plant essential oils as described in claim 1, characterized in that, In step S4, during the "positive pressure-negative pressure" alternating pulse, inert gas is introduced into the reactor during the positive pressure stage, and the pressure is reduced by evacuating the gas through a vacuum pump during the negative pressure stage. The pressure relief time between the positive pressure stage and the negative pressure stage is ≤0.3 s, preferably ≤0.1 s, forming a cyclic sequence of "positive pressure holding - instantaneous pressure relief explosion - negative pressure cavitation" in the reactor.

9. The method for improving the extraction rate of plant essential oils as described in claim 1, characterized in that, In step S4, while applying alternating pulses, the temperature inside the reactor is controlled by a programmed temperature increase, gradually increasing from room temperature to 60℃~80℃ at a rate of 2~5℃ / min. The extraction solvent is kept in a liquid phase during the heating process.

10. The method for improving the extraction rate of plant essential oils as described in claim 1, characterized in that, In step S5, the flash evaporation time is 5-20 minutes, and the three-stage condensation and liquefaction are carried out according to the following method: the first-stage condensation uses a shell-and-tube condenser with circulating cooling water as the cooling medium and an inlet water temperature of 4-10℃, and the first-stage condensate is collected; the second-stage condensation uses a plate condenser with an ethylene glycol aqueous solution as the cooling medium and a temperature of -15 to -5℃, and the second-stage condensate is collected; the third-stage condensation uses a cold trap with a temperature of -20 to -10℃, and the third-stage condensate is collected.