Supercritical CO2 dynamic gradient extraction method for active ingredients of almonds

Abstract

The invention belongs to the technical field of natural product extraction, and discloses a supercritical CO2 dynamic gradient extraction method of an almond active component, which comprises the following steps: (1) raw material pretreatment; performing enzymolysis pretreatment; performing pulsed electric field treatment; drying and crushing; (2) dynamic extraction: the pretreated material is loaded into an extraction kettle for stage extraction, and stage II: the pressure is linearly increased to 35-40 MPa at the speed of 4-5 MPa / min, the temperature is increased to 52-58 DEG C, a composite entrainer (the addition amount is 4-8% w / w) containing ethyl lactate and fructo-oligosaccharide (the mass ratio is 3: 1-5: 1) is injected, and the temperature is maintained for 60-100 minutes; and (3) multi-stage separation: sequentially carrying out first-stage separation, second-stage separation and third-stage separation on the dynamically extracted material. Compared with a traditional supercritical method, the method has the advantages that the yield of flavonoids is increased by 55%, the recovery rate of terpenes is increased by 42%, mutual interference of components is avoided, and the extraction efficiency is remarkably improved; dynamic pressure regulation is adopted in the extraction process, so that the CO2 consumption is reduced by 28%, the system energy consumption is reduced by 35%, and energy is saved.

Description

Technical Field

[0001] The present invention belongs to the technical field of natural product extraction, and relates to a supercritical fluid extraction method, in particular to a supercritical CO2 dynamic gradient extraction method for active ingredients of almond flowers based on dynamic gradient coupling. Background Art

[0002] Almond, scientifically known as Prunus dulcis, belongs to the Rosaceae family and Prunus genus. Its flowers are white or light pink, and the flowering period is concentrated in spring. Almond flowers are considered in traditional Chinese medicine theory to have a sweet taste, a neutral nature, and to belong to the lung and kidney meridians, with the effects of tonifying the spleen and benefiting the lungs, nourishing blood and dispelling wind, calming the mind and relieving uneasiness, etc. Its active ingredients may include flavonoids, volatile oils, and polyphenols, but the specific components still need further research. Compared with the extensive application of almond fruits (almond kernels), the application research of almond flowers is less. Existing research shows that almond flowers can be used to assist in the treatment of symptoms such as spleen deficiency diarrhea, lung deficiency cough, pale complexion due to blood deficiency, and palpitations and insomnia, and are often combined with medicinal materials such as Chinese yam and astragalus membranaceus.

[0003] Through research and analysis, almond flowers and their extracts can be used in the fields of traditional medicine, food and health products, and cosmetics and skin care products. Especially in the field of cosmetics and skin care products, almond fruit extracts have been used in anti-aging and moisturizing products due to their rich vitamin E and antioxidant components. If almond flowers contain similar components (such as flavonoids), they can be extended to skin care products for soothing the skin or anti-inflammatory formulations.

[0004] Existing literature mostly focuses on the research of almond fruits, and there is insufficient research on the component analysis, pharmacological mechanism, and safety of almond flowers. High-efficiency methods such as supercritical CO2 extraction are widely used in fruits, but the extraction process of active ingredients in almond flowers needs to be optimized specifically. When using traditional supercritical CO2 to extract almond flowers, the static extraction parameters result in low extraction efficiency of polar components (such as polyphenols), and it is necessary to rely on a high proportion of entrainer (ethanol > 30%), which causes a burden on subsequent purification.

[0005] In addition, the existing extraction methods cannot regulate the polarity of the CO2 fluid in real time to dynamically adapt to the dissolution thresholds of different components, resulting in serious co-extraction of target components (such as cross-dissolution of fat-soluble components and flavonoids). Using a single decompression mode in the separation stage results in a loss rate of volatile components > 15%, and it is impossible to achieve molecular weight fractionated enrichment of active ingredients. Summary of the Invention

[0006] In order to solve the above problems existing in the existing almond flower extraction technology, the present invention proposes a supercritical CO2 dynamic gradient extraction method for active ingredients of almond flowers that can highly selectively extract flavonoids, terpenoids, and amide active ingredients from almond flowers.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] The first aspect of the present invention is to provide a supercritical CO2 dynamic gradient extraction method for active ingredients of almond flowers, comprising the following steps:

[0009] (1) Raw material pretreatment:

[0010] The almond flower raw material is enzymatically hydrolyzed with 0.5-1.5% (w / w) cellulase at pH 4.5-5.0 and 45-50° C. for 1.5-3 hours;

[0011] The enzymatically hydrolyzed material is placed in a pulsed electric field treatment chamber, and a pulse with a field strength of 0.8-1.5 kV / cm and a frequency of 10-15 Hz is applied for a treatment time of 15-25 minutes;

[0012] The material after the pulse electric field treatment is vacuum dried at 40-45° C. and vacuum degree -0.08 MPa to a moisture content of ≤8%, and then crushed to 60-100 mesh to obtain the pretreated material for later use;

[0013] (2) Dynamic extraction:

[0014] Load the pretreated material into the extraction kettle and operate according to the following procedures:

[0015] Stage I: CO2 pressure fluctuates between 25 and 35 MPa at a frequency of 0.3 to 0.8 Hz, with a temperature of 42 to 48°C, lasting 50 to 70 minutes;

[0016] Stage II: linearly increase the pressure to 35-40 MPa at a rate of 4-5 MPa / min, raise the temperature to 52-58°C, and inject a composite entrainer containing ethyl lactate and oligofructose (mass ratio 3:1-5:1) (addition amount 4-8% w / w) for 60-100 minutes;

[0017] Stage III: Reduce the pressure to 20-25 MPa in a stepwise manner at 3 MPa / step, and raise the temperature to 60-65°C for 30-50 minutes;

[0018] (3) Multi-stage separation:

[0019] The materials after dynamic extraction are separated according to the following procedures:

[0020] Primary separation: impurities with molecular weight greater than 500 Da are removed through a 0.5-2 nm zirconia ceramic membrane at 8-10 MPa and 32-35°C;

[0021] Secondary separation: 5-6 MPa, 40-45°C on a quercetin molecularly imprinted magnetic adsorption column (adsorption time 20-40 min);

[0022] Tertiary separation: It is obtained by electrostatic sedimentation for 60 - 120 minutes at -15 to -25°C and an electric field strength of 50 - 100 V / cm.

[0023] Preferably, in step (i), when the pulsed electric field treatment is performed on the enzymatically hydrolyzed material, the electrode spacing is 8 - 10 cm and the pulse width is 20 μs.

[0024] Preferably, in step (ii), during the extraction in stage I, the CO2 flow rate is 20 - 30 kg / h and the recycling utilization rate ≥ 99.2%.

[0025] Preferably, in step (ii), the CO2 pressure fluctuation range in stage I is ±5 MPa and the frequency is 0.5 Hz.

[0026] Preferably, in step (ii), in the entrainer in stage II, the ethyl lactate accounts for 70 - 80% and the fructooligosaccharide accounts for 20 - 30%.

[0027] Preferably, in step (ii), the stepped pressure reduction in stage III is divided into 3 steps: 38 → 30 → 25 → 20 MPa, and each step is maintained for 8 - 12 minutes.

[0028] Preferably, in step (iii), the pore size of the zirconia ceramic membrane used for the primary separation is 0.8 nm and the operating pressure difference is 0.6 - 0.8 MPa.

[0029] Preferably, in step (iii), the eluent of the molecularly imprinted adsorption column used for the secondary separation is an ethanol - water (70:30 v / v) solution with pH 3.0 and the elution flow rate is 1 mL / min.

[0030] Preferably, in step (iii), the electrostatic sedimentator used for the tertiary separation has copper plates, the plate spacing is 5 cm, and the DC voltage is 75 V.

[0031] The second aspect of the present invention is to provide an almond flower extract prepared by the above - mentioned extraction method, with the total flavonoid content ≥ 15 mg / g (calculated as kaempferol - 3 - glucoside); the retention rate of α - terpineol ≥ 98.5% (detected by GC - MS); the water solubility of the extract is increased by 40% (compared with the traditional ethanol extraction method).

[0032] The present invention adopts the above - mentioned technical solution, and compared with the prior art, has the following technical effects:

[0033] (1) The present invention combines pulsed pressure fluctuation with bio - enzyme - physical field synergistic cell wall breaking, and through the regulation of the frequency and amplitude of pressure fluctuation (instead of the traditional constant pressure), induces the dynamic adaptation of the polarity of CO2 fluid to the solubility curve of the target component, breaking through the mass transfer limitation of the cell wall;

[0034] (2) The present invention develops a composite bio-derived entrainer (ethyl lactate-fructooligosaccharide composite system), which breaks through the polarity limitation of traditional single entrainers, significantly improves the solubility of polar components, and realizes the synchronous solubilization of flavonoid glycosides and free polyphenols;

[0035] (3) The composite entrainer system developed by the present invention reduces the dosage by 60% compared with traditional ethanol. The biodegradability rate of the composite entrainer reaches 100%, and 98.7% of it can be recycled online. It is completely biodegradable, green and environmentally friendly;

[0036] (4) Compared with the traditional supercritical method, the present invention increases the yield of flavonoids by 55% and the recovery rate of terpenes by 42%. Moreover, it avoids component interference and significantly improves the extraction efficiency. During the extraction process, dynamic pressure regulation is adopted to reduce the CO2 consumption by 28% and the system energy consumption by 35%, saving energy. Detailed implementation manners

[0037] The present invention will be introduced in detail and specifically through specific embodiments below to better understand the present invention. However, the following embodiments do not limit the scope of the present invention.

[0038] Example 1

[0039] (I) Raw material pretreatment

[0040] Raw material selection: 1 kg of fresh almond flowers, produced in Xinjiang, processed within 24 hours after harvesting, with an initial moisture content of 14%, and chopped into 5-mm segments.

[0041] Enzymatic hydrolysis pretreatment: The almond flower raw material is treated with 0.8% (w / w) cellulase (Novozymes Cellic CTec3) at pH 4.8 (adjusted with citrate buffer), temperature 48°C, rotation speed 150 rpm, and enzymatically hydrolyzed for 2.5 hours;

[0042] Pulsed electric field treatment: The enzymatically hydrolyzed material is placed in a pulsed electric field treatment chamber, and pulses with an electric field strength of 1.0 kV / cm and a frequency of 12 Hz are applied, with a pulse width of 25 μs and a treatment time of 20 minutes (electrode spacing 10 cm);

[0043] The pulsed electric field treatment equipment uses a high-voltage pulse generator (Suzhou Feituo Instruments, Model FT-PEF).

[0044] Drying and pulverizing: The material after pulsed electric field treatment is vacuum-dried at 45°C and a vacuum degree of -0.08 MPa until the water content reaches 7.8%. It is pulverized using a universal pulverizer (Retsch GM200, Germany), and then passed through an 80-mesh sieve. The average particle size of the particles is 180 μm to obtain the pretreated material for standby;

[0045] (II) Dynamic extraction process

[0046] Extraction equipment: extraction kettle, volume: 50 L (NovaWerke AG, Switzerland, pressure resistance 45 MPa); CO2 circulation system: cryogenic pump (flow accuracy ±0.5 kg / h);

[0047] Stage I (terpene extraction): Pressure mode: The CO2 pressure fluctuates dynamically in a triangular wave, ranging from 25 → 30 → 25 MPa, frequency 0.4 Hz; Temperature: 46 ± 1 °C; CO2 flow rate: 22 kg / h; Duration: 65 minutes.

[0048] Stage II (enhanced flavonoid extraction): Pressure increase rate: 4 MPa / min, target pressure 36 MPa; Temperature: 56 °C; Entrainer: ethyl lactate: fructooligosaccharide = 4:1 (total addition amount 5.5% w / w); Mixing method: premixed with CO2 through a static mixer (Sulzer SMX); Duration: 85 minutes.

[0049] Stage III (alkaloid capture): Pressure reduction program: 36 → 28 → 22 MPa, maintaining for 10 minutes at each step; Temperature: 62 °C; CO2 flow rate: 15 kg / h.

[0050] (III) Multi-stage separation system

[0051] Primary membrane separation: Membrane module: zirconia ceramic membrane (Inopor Nano, pore size 0.6 nm); Operating parameters: pressure 9 ± 0.5 MPa, temperature 34 °C, transmembrane flow rate 8 L / (m 2 ·h);

[0052] Secondary molecularly imprinted adsorption: Adsorption column specifications: diameter 10 cm, bed height 50 cm (filled with Fe3O4@SiO2-MIP particles); Adsorption pressure: 5.5 MPa, adsorption temperature: 42 °C, adsorption time: 35 minutes, flow rate 1.2 BV / h (bed volume); Eluent: 70% ethanol + 0.1% formic acid, elution volume 3 BV.

[0053] Tertiary electrostatic precipitation: Temperature: -18 °C; Electric field parameters: DC voltage 70 V, plate spacing 6 cm (titanium-plated platinum electrodes); Sedimentation time: 100 minutes, thus obtained.

[0054] The extract of Example 1 was detected and analyzed, and the detection results are shown in Table 1 below:

[0055]

[0056]

[0057] Example 2

[0058] Different from the above Example 1, the proportion of the composite entrainer was changed to ethyl lactate: fructooligosaccharide = 2:1 (the total addition amount was still 5.5% w / w). Other steps were exactly the same as those in Example 1 (including dynamic pressure, temperature, separation parameters).

[0059] The extract of this Example 2 was detected and analyzed, and the difference analysis was carried out with the extract of Example 1. The results of the detection and analysis are shown in Table 2 below:

[0060] Parameter Example 1 (4:1) Example 2 (2:1) Analysis of variation impact Polarity of entrainer (logP) 1.32 (calculated value) 1.08 (calculated value) Polarity enhanced, but hydrogen bond interaction weakened Yield of flavonoids 14.9 mg / g 11.2 mg / g ↓25.5% (decrease in glycoside solubility due to insufficient fructooligosaccharide) Loss rate of terpenes 1.3％ 4.9％ ↑3.6 times (competitive dissolution by polar entrainer) Separation emulsification phenomenon None Slight emulsification (centrifugation required) Hydrophilic-lipophilic balance of entrainer disrupted

[0061] It can be analyzed from Table 2 above that the optimal proportion of the entrainer for the extraction method of the present invention is: the mass ratio of ethyl lactate to fructooligosaccharide needs to be strictly controlled between 3.5:1 and 4.5:1. Beyond this range, the extraction efficiency of the target components will be significantly reduced.

[0062] Comparative Example 1

[0063] The traditional supercritical method was used to extract almond flowers, which specifically included the following steps:

[0064] (I) Pretreatment: Only hot air drying (60°C, 6 hours) until the water content was 8%, and then crushed to 80 mesh (without enzymatic hydrolysis / electric field treatment);

[0065] Extraction parameters: Constant pressure of 30 MPa, temperature of 50°C; Entrainer: 10% ethanol (without fructooligosaccharide); Total extraction time of 180 minutes, without a staged extraction procedure;

[0066] (II) Separation system:

[0067] Single-stage decompression separation was adopted (the pressure was reduced to 5 MPa, and the temperature was 40°C), without a membrane separation and molecular imprinting purification procedure, to obtain the almond flower extract.

[0068] The performance comparison between Comparative Example 1 and Example 1 above is shown in Table 3 below:

[0069]

[0070]

[0071] It can be known from the comparative analysis in Table 3 above the necessity of the dynamic pressure fluctuation in the present application: Comparing Example 1 with Comparative Example 1, the diffusion rate of terpene components was increased by 2.3 times due to the pressure fluctuation (verified by the simulation of Fick's second law). The entrainer synergistic effect in the present application: The addition of fructooligosaccharide increased the solubility of flavonoid glycosides by 1.8 times). And the purity guarantee of the three-stage separation in the present application: The molecular imprinting adsorption increased the flavonoid purity from 78% (traditional method) to ≥91%, avoiding the consumption of organic solvents in silica gel column chromatography.

[0072] Comparative Example 2

[0073] Different from Example 1, in Comparative Example 2, a single entrainer was used, 10% ethanol was used, and other parameters were the same as those in Example 1.

[0074] Result: The extraction rate of flavonoid glycosides decreased by 52% (kaempferol-3-glucoside 6.2 mg / g); emulsification occurred during the separation stage, and the purity was only 72%.

[0075] Comparative Example 3

[0076] Different from Example 1, in Comparative Example 3, no dynamic pressure regulation was adopted, and the pressure was kept constant at 38 MPa, and other parameters were the same as those in Example 1.

[0077] Result: The over-extraction of terpenoids led to a decrease in flavonoid purity to 68%; the system energy consumption increased by 42%.

[0078] After testing, the technical effects of the above Example 1 and Comparative Examples 1 to 3 are compared as shown in Table 4 below.

[0079] Index Example 1 Comparative Example 1 Comparative Example 2 Comparative Example 3 Total flavonoid yield (mg / g) 14.7 7.8 6.2 9.8 Terpene retention rate (%) 99.2 80.2 88.5 91.4 Unit energy consumption (kW·h / kg) 18.1 31.6 24.6 26.1 Product purity (%) 96.5 78.2 72.0 82.7

[0080] From the comparative analysis in Table 4 above, it can be seen that the present invention combines pulsed pressure fluctuations with the synergistic cell wall breaking of bio-enzyme - physical fields to break through the mass transfer limitation of cell walls (see the comparison data in Example 1 and Comparative Example 3); the ethyl lactate - fructooligosaccharide entrainer system developed by the present invention significantly improves the solubility of polar components (see the difference in flavonoid yields between Comparative Example 1 and Comparative Example 2).

[0081] Example 3

[0082] (I) Raw material pretreatment:

[0083] Raw material selection: 3 kg of almond flowers, from Xinjiang, processed within 24 hours after harvesting, with an initial moisture content of 12%, and chopped into 5 mm segments.

[0084] Enzymatic pretreatment: The almond flower raw material was enzymatically hydrolyzed with 1.0% (w / w) cellulase (Novozymes CTec2) at pH 5.0 and 50 °C for 2 hours;

[0085] Pulsed electric field treatment: The enzymatically hydrolyzed material was placed in a pulsed electric field treatment chamber, and pulses with an electric field strength of 1.2 kV / cm and a frequency of 12 Hz were applied, with a pulse width of 25 μs and a treatment time of 25 minutes (electrode spacing 8 cm);

[0086] The pulsed electric field treatment equipment used a high-voltage pulse generator (Suzhou Feituo Instruments, Model FT-PEF).

[0087] Drying and pulverization: The material after pulsed electric field treatment was vacuum-dried at 45 °C and a vacuum degree of -0.08 MPa until the water content reached 7.2%. It was pulverized using a universal pulverizer (Retsch GM200 from Germany), then passed through an 80-mesh sieve, and the average particle size was 180 μm to obtain the pretreated material for standby.

[0088] (II) Dynamic extraction:

[0089] Extraction equipment: Extraction kettle, volume: 50 L (NovaWerke AG from Switzerland, pressure-resistant 45 MPa); CO2 circulation system: cryogenic pump (flow accuracy ±0.5 kg / h).

[0090] Stage I (terpene extraction): Pressure fluctuation: 28 → 32 → 25 MPa (frequency 0.5 Hz, triangular waveform); temperature 45 °C, CO2 flow rate 25 kg / h, lasting for 60 minutes.

[0091] Stage II (enhanced flavonoid extraction): Linearly increase the pressure to 38 MPa (rate 5 MPa / min); temperature 55 °C, inject 6% composite entrainer (ethyl lactate: fructooligosaccharide = 4:1); maintain for 90 minutes.

[0092] Stage III (alkaloid capture): Stepwise pressure reduction: 38 → 30 → 25 → 20 MPa (each step for 10 minutes); temperature 62 °C, CO2 flow rate reduced to 18 kg / h.

[0093] (III) Separation and purification:

[0094] Primary separation: Pass through a 0.8 nm zirconia membrane (Inopor membrane module from Germany) at 9 MPa and 35 °C.

[0095] Secondary separation: Molecularly imprinted column (quercetin template, adsorption time 30 minutes) → eluent pH 3.0 ethanol-aqueous solution.

[0096] Tertiary separation: Electrostatic precipitation at -20 °C (copper plate spacing 5 cm, voltage 80 V) for 90 minutes to obtain the product.

[0097] After detection, using the extraction method of this example, the total flavonoid yield: 16.2 mg / g (HPLC, compared with the traditional method of 8.7 mg / g); the retention rate of α-terpineol: 99.1% (GC-MS, compared with the traditional method of 81.3%); the unit energy consumption: 17.6 kW·h / kg (compared with the traditional method of 29.4 kW·h / kg).

[0098] Comparative example 4

[0099] The difference from Example 3 is that pulsed electric field is missing and only enzymatic hydrolysis treatment is carried out, and other parameters are the same as those in Example 3.

[0100] Result: The yield of total flavonoids decreased to 11.8 mg / g (↓27%); The extraction time needed to be extended to 180 minutes to achieve the same extraction rate.

[0101] Comparative Example 5

[0102] Different from Example 3, a constant pressure was adopted, that is, a constant 30 MPa was adopted in Stage I (pressure fluctuation was cancelled), and other parameters were the same as those in Example 3.

[0103] Result: The extraction amount of terpenoids decreased by 32% (detected by GC); The CO2 consumption increased by 22%.

[0104] Comparative Example 6

[0105] Different from Example 3, a traditional entrainer was adopted, that is, 10% ethanol was used in Stage II, and other parameters were the same as those in Example 3.

[0106] Result: The flavonoid yield was 9.3 mg / g (only 57% of that in Example 3); Emulsification and stratification occurred in the separation stage, and additional centrifugation was required.

[0107] After testing, the technical effects of the above Example 3 and Comparative Examples 4 to 6 are compared as shown in Table 5 below.

[0108] Process parameters Example 3 Comparative Example 4 Comparative Example 5 Comparative Example 6 Pretreatment time 2 h enzymatic hydrolysis + 25 min electricity 2 h enzymatic hydrolysis Same as Example 3 Same as Example 3 Pressure mode in Stage I Dynamic fluctuation Same as Example 3 Constant 30 MPa Same as Example 3 Type of entrainer Ethyl lactate - fructooligosaccharide Same as Example 3 Same as Example 3 10% ethanol Total flavonoid yield (mg / g) 16.2 11.8 13.1 9.3 Unit energy consumption (kW·h / kg) 17.6 21.3 23.8 25.6

[0109] The specific embodiments of the present invention have been described in detail above, but they are only examples, and the present invention is not limited to the specific embodiments described above. For those skilled in the art, any equivalent modifications and substitutions to the present invention are also within the scope of the present invention. Therefore, all equivalent transformations and modifications made without departing from the spirit and scope of the present invention should be covered within the scope of the present invention.

Claims

1. A supercritical CO2 dynamic gradient extraction method for the active ingredients of almond flowers, characterized in that, It includes the following steps: (1) Raw material pretreatment: Use 0.5 - 1.5% (w / w) cellulase to enzymatically hydrolyze the almond flower raw material at pH 4.5 - 5.0 and 45 - 50°C for 1.5 - 3 hours; Place the enzymatically hydrolyzed material in a pulsed electric field treatment chamber, apply pulses with an electric field strength of 0.8 - 1.5 kV / cm and a frequency of 10 - 15 Hz, and the treatment time is 15 - 25 minutes; Vacuum dry the material after pulsed electric field treatment at 40 - 45°C and a vacuum degree of -0.08 MPa until the water content ≤ 8%, and crush it to 60 - 100 meshes to obtain the pretreated material for standby; (2) Dynamic extraction: Load the pretreated material into the extraction kettle and operate according to the following procedure: Stage I: The CO2 pressure fluctuates in the range of 25 - 35 MPa at a frequency of 0.3 - 0.8 Hz, the temperature is 42 - 48°C, and it lasts for 50 - 70 minutes; Stage II: Linearly increase the pressure to 35 - 40 MPa at a rate of 4 - 5 MPa / min, raise the temperature to 52 - 58°C, inject a composite entrainer containing ethyl lactate and fructooligosaccharide (mass ratio 3:1 - 5:1) (addition amount 4 - 8% w / w), and maintain for 60 - 100 minutes; Stage III: Stepwise reduce the pressure to 20 - 25 MPa at a rate of 3 MPa / step, raise the temperature to 60 - 65°C, and last for 30 - 50 minutes; (3) Multistage separation: Separate the material after dynamic extraction according to the following procedure: Primary separation: Remove impurities with a molecular weight > 500 Da through a 0.5 - 2 nm zirconia ceramic membrane at 8 - 10 MPa and 32 - 35°C; Secondary separation: Pass through a quercetin molecularly imprinted magnetic adsorption column at 5 - 6 MPa and 40 - 45°C (adsorption time 20 - 40 minutes); Tertiary separation: Electrostatic precipitation for 60 - 120 minutes at -15 - 25°C and an electric field strength of 50 - 100 V / cm to obtain the product.

2. The extraction method according to claim 1, wherein In step (1), when performing pulsed electric field treatment on the enzymatically hydrolyzed material, the electrode distance is 8 - 10 cm and the pulse width is 20 μs.

3. The extraction method according to claim 1, characterized in that, In step (2), during the extraction process in stage I, the CO2 flow rate is 20 - 30 kg / h and the recycling utilization rate ≥ 99.2%.

4. The extraction method according to claim 1, characterized in that, In step (2), the fluctuation range of the CO2 pressure in stage I is ±5 MPa and the frequency is 0.5 Hz.

5. The extraction method according to claim 1, wherein In step (2), in the entrainer in stage II, the proportion of ethyl lactate is 70 - 80% and the proportion of fructooligosaccharide is 20 - 30%.

6. The extraction method according to claim 1, characterized in that, In step (2), the stepwise pressure reduction in stage III is divided into 3 steps: 38 → 30 → 25 → 20 MPa, and each step is maintained for 8 - 12 minutes.

7. The extraction method according to claim 1, characterized in that, In step (3), the aperture of the zirconia ceramic membrane used in the primary separation is 0.8 nm, and the operating pressure difference is 0.6 - 0.8 MPa.

8. The extraction method according to claim 1, characterized in that In step (3), the eluent of the molecularly imprinted adsorption column used in the secondary separation is an ethanol - water (70:30 v / v) solution with a pH of 3.0, and the elution flow rate is 1 mL / min.

9. The extraction method according to claim 1, wherein In step (3), the electrostatic precipitator used in the tertiary separation is made of copper plates, the plate distance is 5 cm, and the DC voltage is 75 V.

10. An extract of almond flower prepared by the extraction method according to any one of claims 1 to 9, characterized in that: Total flavonoid content ≥ 15 mg / g; retention rate of α-terpineol ≥ 98.5%; water solubility of the extract increased by 40%.

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