Extraction method of aromatic plant essential oil

Abstract

The invention discloses a method for extracting aromatic plant essential oil, which is suitable for labiatae isodon plants, and comprises the following steps: crushing a whole fresh plant, adding a buffer solution according to a material-liquid ratio of 1: (6-10) to prepare a suspension, carrying out enzymolysis at 40-50 DEG C for 1-8 hours by using a compound enzyme (cellulase: hemicellulase: pectinase = 2: 1: 1), carrying out low-temperature centrifugal solid-liquid separation dehydration, and carrying out vacuum drying to obtain the aromatic plant essential oil. Performing solvent-free microwave extraction at normal pressure of 100-1000W for 10-60 minutes, condensing, layering and drying to obtain essential oil; the method solves the problem of polysaccharide emulsification after enzymolysis, combines the advantages of enzymolysis wall breaking and microwave low consumption and fragrance retention, has the essential oil yield of 2-5%, has stable aroma components, and is simple in process and easy to industrialize.

Description

Technical Field

[0001] This invention belongs to the field of essential oil extraction, specifically relating to a method for extracting essential oils from aromatic plants. Background Technology

[0002] Aromatic plants of the Lamiaceae family, such as those in the genus *Plectranthus* spp., are important raw materials for the development of fragrances, cosmetics, food flavorings, insect repellents, and functional daily chemicals due to their rich volatile oil content. Taking *Plectranthus amboinicus* as an example, the composition and relative content of volatile compounds vary significantly among its different organs (roots, stems, and leaves): leaves and stems are often dominated by monoterpenes (such as limonene and α-piperine), while roots may be rich in camphene and other sesquiterpenes or components with woody, crisp aromas. These volatile oil molecules generally have low molecular weight, low boiling points, and are sensitive to heat and oxygen, making the choice of processing methods extremely influential on the final aroma spectrum and yield.

[0003] Currently, commonly used industrial and laboratory methods for essential oil extraction mainly include steam distillation (or water distillation), organic solvent extraction, supercritical CO2 extraction, and pressing. Among these, steam distillation is widely used due to its mature equipment and simple operation, but it has several significant drawbacks: First, the distillation process typically requires heating the system to near or at 100°C and maintaining this temperature for several hours. This can lead to side reactions such as oxidation, dehydrogenation, rearrangement, or polymerization of heat-sensitive monoterpenes and sesquiterpenes, resulting in the loss of top notes or highly volatile aroma components and changes in the aroma spectrum. Second, the mechanical and thermal integrity of plant cell walls during distillation restricts the complete release of intracellular essential oils, especially when the cell walls or mesoglea contain high levels of pectin and hemicellulose. These water-soluble polysaccharides dissolve under enzymatic hydrolysis or high-temperature aqueous phase conditions and form a stable emulsion system (oil / water emulsion) with the oil phase, resulting in slow stratification after condensation, reduced recovery rate, and the need for additional demulsification treatment. Third, prolonged high-temperature treatment not only consumes energy but also alters the sensory characteristics of the essential oils, affecting product consistency and commercial value.

[0004] To improve the release efficiency of volatile oils, reduce heat loss, and preserve the original aroma spectrum as much as possible, enzymatic hydrolysis-assisted extraction technology has been introduced as a pretreatment method. By specifically hydrolyzing cell wall polysaccharides such as cellulose, pectin, and hemicellulose, cellulase, pectinase, and hemicellulase can significantly increase cell wall permeability, promoting the rupture of essential oil glands and the release of volatile oils. However, the positive and negative effects of enzymatic hydrolysis need to be carefully weighed: on the one hand, enzymatic hydrolysis can promote essential oil release, shorten subsequent extraction time, and reduce the required heating intensity; on the other hand, the large amount of soluble polysaccharides produced by enzymatic hydrolysis (such as pectin fragments and hemicellulose hydrolysates) enters the aqueous phase, significantly reducing interfacial tension and forming a stable emulsion, making subsequent oil-water separation difficult, thus reducing the actual yield of essential oil and increasing the complexity of post-processing.

[0005] Further research revealed that during enzymatic hydrolysis of aromatic plants, cellulase, pectinase, and hemicellulase, while disrupting cell wall structure and promoting the release of volatile oils, also release large quantities of pectin fragments, hemicellulose oligomers, and their derived polysaccharides that are originally insoluble in water or only exist in the cell wall network into the aqueous phase.

[0006] The aforementioned polysaccharides typically exhibit distinct hydrophilic-hydrophobic structural characteristics, which can significantly reduce the interfacial tension between oil and water and form an adsorption layer with steric hindrance on the surface of oil droplets. This stabilizes the dispersion of oil droplets, allowing essential oils to be uniformly dispersed in the aqueous phase in the form of fine oil droplets, forming a stable oil / water emulsion system that is difficult to separate naturally.

[0007] This type of emulsion system is difficult to demulsify quickly under conventional condensation conditions, which not only leads to slow separation of essential oils and difficulty in recovery, but also causes some essential oils to remain in the aqueous phase for a long time, resulting in a decrease in actual yield. It usually requires additional steps such as heating, chemical demulsifiers or high-intensity centrifugation, which significantly increases the complexity and cost of the process.

[0008] In recent years, solvent-free microwave extraction (SFME) has gained attention as a novel green extraction technology for essential oil extraction from aromatic plants. The basic principle of SFME is to rapidly stimulate free and bound water within the plant using microwaves. Local heating causes the endogenous water to evaporate, carrying volatile components out through distillation. The entire process is carried out under atmospheric pressure or a slight vacuum, without the need for external water or organic solvents. Compared to traditional steam distillation, SFME achieves shorter extraction times, lower energy consumption, and less thermal damage. It also reduces the problem of polysaccharide dissolution caused by dilution from external water, thus significantly improving essential oil yield and aroma retention in some cases. Existing literature reports that SFME can achieve yields and physicochemical properties equal to or better than traditional distillation methods in plants such as camphor leaves, wild chrysanthemum, and Sichuan pepper.

[0009] Nevertheless, the challenges of using SFME alone cannot be ignored: for some plants with thick cell walls or oil glands bound by fibrosis, relying solely on the endogenous water vapor pressure generated by microwave heating may not be enough to completely release all intracellular volatile oils; in addition, improper pretreatment (such as directly performing SFME on freshly harvested, high-moisture material) may lead to overheating, excessively high local pressure, or unstable emulsification due to excessive free water content. In summary, existing technologies still have significant shortcomings in addressing the issue of "how to simultaneously achieve high yield, low heat loss, and avoid demulsification caused by oil-water emulsification."

[0010] Therefore, there is an urgent need in this field for an extraction route that balances efficient cell wall disruption, avoids stable emulsification caused by polysaccharides after enzymatic hydrolysis, and fully utilizes the low heat loss advantage of SFME. This route should promote the release of volatile oils through gentle yet efficient enzymatic hydrolysis, and eliminate or significantly reduce the content of soluble polysaccharides after enzymatic hydrolysis through appropriate solid-liquid separation / dehydration strategies. This would allow for rapid essential oil distillation and condensation recovery using SFME without adding water or organic solvents to the system, enabling industrially scalable, energy-efficient, aroma-preserving essential oil production methods that do not require additional chemical demulsification.

[0011] The information disclosed in this background section is intended only to enhance the understanding of the overall background of the invention and should not be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art. Summary of the Invention

[0012] To address the shortcomings of existing technologies, this invention provides a method for extracting essential oils from aromatic plants. The method involves enzymatic hydrolysis to disrupt cell wall structures, promoting essential oil release. Subsequently, solid-liquid separation removes the polysaccharide-rich liquid, preventing emulsification issues during subsequent SFME (sulfurized water vapor extraction). Finally, SFME is used to efficiently extract the essential oil from the wet residue. Although the enzymatic hydrolysate is discarded, the improvement of the material structure through enzymatic hydrolysis remains a key step in increasing the overall yield. This process achieves an optimal balance in terms of simplicity, yield, and avoidance of emulsification.

[0013] To achieve the above objectives, the present invention adopts the following technical solution: a method for extracting aromatic plant essential oils, comprising the following steps:

[0014] 1) Pretreatment: The whole plant (including roots, stems and leaves) of the collected fresh aromatic plants is crushed and added to the buffer solution at a material-to-liquid ratio of 1:6-10 (w:v) to form a plant suspension;

[0015] 2) Enzymatic hydrolysis: Place the plant suspension in a water bath at 40–50℃ and hydrolyze it with a compound enzyme for 1–8 hours. Adjust the pH to 4–6 to obtain a mixture.

[0016] 3) Solid-liquid separation and dehydration: The enzymatically hydrolyzed mixture was centrifuged at low temperature at 3,000–8,000 rpm for 5–15 min; after centrifugation at 5,000 rpm for 10 min, the moisture content of the wet residue was 58%–65% (determined by drying at 105 ℃).

[0017] 4) Solvent-free microwave extraction (SFME): The dehydrated wet residue is transferred to a microwave extraction device and microwave distillation extraction is performed under normal pressure with a microwave power of 100–1000W for 10–60 minutes.

[0018] 5) Obtaining the finished product: The volatile oil vapor generated by microwave irradiation is discharged, condensed, and the upper essential oil is collected by layering and then dehydrated and dried to obtain the final essential oil.

[0019] The fundamental reason for the formation of a stable emulsion in the system after enzymatic hydrolysis, as described above, is not simply the presence of water, but rather the enrichment of soluble polysaccharides in the aqueous phase and their interfacial activity. Therefore, this invention introduces solid-liquid separation or dehydration treatment after the enzymatic hydrolysis step. By removing the aqueous phase rich in pectin and hemicellulose hydrolysis products, the concentration of polysaccharides capable of participating in oil-water interfacial stability in the system is significantly reduced.

[0020] After the above treatment, the moisture in the residual material mainly exists in the form of bound water or a small amount of free water. Its interfacial activity is significantly lower than that of the untreated system after enzymatic hydrolysis, making it difficult to form a stable adsorption layer on the surface of the essential oil, thus fundamentally weakening the conditions for emulsification. As a result, in subsequent extraction or condensation processes, the essential oil is more likely to precipitate as a continuous oil phase, avoiding the formation of a stable emulsion.

[0021] Preferably, the complex enzyme in step 2) includes cellulase, hemicellulase and pectinase.

[0022] Preferably, the composite enzyme has a mass ratio of cellulase:hemicellulase:pectinase = 2:1:1.

[0023] Preferably, the enzymatic hydrolysis time is 4–8 hours, and the amount of compound enzyme used is 0.5%–3% of the raw material mass.

[0024] Preferably, in step 4), the microwave power is 200–600W and the time is 10–30min.

[0025] Preferably, in step 4), the microwave power is 400–500W and the time is 20–30min.

[0026] Preferably, the buffer solution is one of citrate-sodium citrate, acetic acid-sodium acetate, or phosphate buffer.

[0027] Furthermore, the concentration of the buffer solution is 10–100 mM. When the buffer solution is citrate-sodium citrate, the concentration is prepared at 0.05–0.1 M with pH=5. When the buffer solution is phosphate, NaH2PO4 / Na2HPO4 is selected and the concentration is prepared at 0.05 M with pH=6. When the buffer solution is acetic acid-sodium acetate, the concentration is prepared at 0.05–0.1 M with pH=4.5–5.5.

[0028] Preferably, in step 5), the drying agent is one of anhydrous sodium sulfate or anhydrous magnesium sulfate.

[0029] Preferably, the essential oil yield is 2%–5%.

[0030] Preferably, the aromatic plant is a plant belonging to the Lamiaceae family and the genus Lespedeza.

[0031] Furthermore, the plant is Plectranthus, Mentha haplocalyx, or Variegated Hedyotis diffusa.

[0032] This invention overcomes the shortcomings of existing technologies at multiple levels by systematically combining compound enzymatic hydrolysis with solvent-free microwave extraction (SFME) and incorporating necessary solid-liquid separation / dehydration steps between the two, achieving the following significant technical effects:

[0033] First, this invention significantly improves the actual yield of essential oils and the utilization rate of raw materials. By using a complex enzyme (cellulase, hemicellulase, and pectinase) to perform short-term enzymatic hydrolysis of fresh whole plants under mild conditions, the cell wall backbone and middle lamella can be selectively disrupted, releasing more volatile oil components bound by the cell wall and increasing the total amount of volatile substances that can be carried out by microwaves and recovered by condensation. Compared to direct SFME without enzymatic hydrolysis, enzymatic pretreatment increases the amount of volatile oil that can be released. Compared to the traditional combination of enzymatic hydrolysis followed by direct water distillation, this invention removes most of the soluble polysaccharides through solid-liquid separation after enzymatic hydrolysis, avoiding the stable emulsification caused by these polysaccharides in subsequent heat treatment or the presence of an aqueous phase. This avoids the loss caused by the oil phase being dragged down for a long time, resulting in slow layering or the need for chemical demulsification. In summary, this method can achieve a higher recovery rate under the same batch of raw materials, and the actual yield can reach an industrially acceptable range, thereby improving the economic value of each unit of raw material.

[0034] Secondly, this invention has significant advantages in maintaining or improving the aroma chemical fingerprint. Because SFME utilizes the endogenous water of the raw material as a heat transfer and carrying medium, it avoids the need for large amounts of external water and prolonged high-temperature distillation. This significantly reduces the pyrolysis, oxidation, and structural rearrangement of heat-sensitive monoterpenes and sesquiterpenes (such as limonene, linalool, camphene, etc.) during extraction, thereby retaining more top notes and highly volatile aroma components, ensuring the sensory quality and component stability of the product. Enzymatic hydrolysis uses mild conditions of 40–50 °C with controllable time, completing cell wall disruption without triggering high-temperature side reactions, further protecting the structural integrity of the target aromatic molecules.

[0035] Third, by introducing a solid-liquid separation / dehydration step after enzymatic hydrolysis, this invention effectively solves the problem of stable oil / water emulsification caused by soluble polysaccharides during enzymatic hydrolysis. On the one hand, reducing the content of free water and dissolved polysaccharides in the material helps to reduce non-selective heating caused by the absorption of energy by a large amount of water phase during microwave heating, allowing microwave energy to act more effectively on the oil gland structure and bound water region, and enhancing the formation of local endogenous water vapor pressure.

[0036] On the other hand, under conditions of significantly reduced polysaccharide content, the volatile components generated during microwave heating can migrate and escape more smoothly with endogenous water vapor, avoiding re-emulsification or retention in the aqueous phase during migration, thereby improving the instantaneous release efficiency and overall recovery rate of volatile oils.

[0037] Fourth, this invention offers significant energy and environmental benefits. The short-duration, high-efficiency heating mechanism of SFME drastically shortens the extraction process time, reducing total heating energy consumption. Furthermore, it eliminates the need for external water or organic solvents, avoiding solvent recovery and wastewater treatment issues and enhancing the process's green attributes. Combined with short-duration enzymatic hydrolysis, a low-temperature biological treatment, this method offers significant advantages in energy consumption and emissions compared to long-duration steam distillation, facilitating compliance with energy conservation and emission reduction requirements in industrial production.

[0038] Fifth, this invention balances process simplicity with industrial scale-up feasibility. The method flow is "raw material crushing → buffer suspension → short-time compound enzymatic hydrolysis → solid-liquid separation / dehydration → atmospheric pressure SFME → condensation and layering → drying to obtain oil". The process steps are clearly defined and are all unit operations that can be achieved by existing industrial equipment (enzymatic hydrolysis tank, centrifuge / pressure filter equipment, atmospheric pressure microwave extraction device, condensation recovery system, etc.), which facilitates parameter amplification and continuous modification during pilot and scale-up processes, reducing the technical threshold from laboratory to industrial production.

[0039] Sixth, this invention improves product consistency and controllability, which is beneficial for downstream application expansion. By controlling enzymatic hydrolysis parameters (enzyme ratio, dosage, pH, temperature, and time), solid-liquid separation threshold, and microwave power and irradiation time of SFME, the relative content of key aroma components in essential oils can be fine-tuned while ensuring high yield, to adapt to different downstream sensory or functional needs (e.g., insect repellents, antibacterial additives, fragrance formulations, etc.). In addition, the whole-plant treatment strategy for different organs (roots / stems / leaves) helps to preserve complex aroma profiles and achieve differentiated product development.

[0040] In summary, this invention, through a process combination of "enzymatic hydrolysis—solid-liquid separation / dehydration—solvent-free microwave extraction," not only avoids the emulsification side effects of enzymatic hydrolysis but also significantly improves the extraction efficiency of SFME and the yield of essential oils. It achieves efficient and stable extraction of aromatic plant essential oils without introducing additional demulsification steps. Furthermore, it demonstrates significant improvements in yield, aroma retention, process simplicity, environmental impact, and industrial scalability, possessing strong industrialization potential and practicality for patent protection. Attached Figure Description

[0041] Figure 1 Images showing the comparison of emulsification stability of SFME after condensation;

[0042] Figure 2 This is a GC-MS comparison diagram of key aroma components and oxidation byproducts in the essential oils of the examples and comparative examples;

[0043] Figure 3 This is a line graph showing the yield of essential oils. Detailed Implementation

[0044] The present invention will be further described below through specific embodiments. To make the inventive objectives, technical solutions, and beneficial technical effects of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments. It should be understood that the embodiments described in this specification are merely for explaining the present invention and are not intended to limit the present invention.

[0045] Unless otherwise stated, all instruments and reagents used in the examples are commercially available or synthesized using conventional methods and can be used directly without further processing, and all instruments used in the examples are commercially available.

[0046] Example 1: Plectranthus amboinicus

[0047] Take 10.0 kg of freshly harvested whole Plectranthus amboinicus plant and crush it to a particle size suitable for suspension (crushed material ≤ 5–10 mm). Add citric acid-sodium citrate buffer (prepared as 0.05 M, pH adjusted to 5.0) at a material-to-liquid ratio of 1:8 (w:v) to obtain approximately 80.0 L of plant suspension. Place the suspension in a 45 ℃ water bath and add a compound enzyme (cellulase, hemicellulase, pectinase, mass ratio 2:1:1). The total amount of enzyme used is 1.0% of the fresh material mass (i.e., a total of 100 g of enzyme powder). The enzymatic hydrolysis reaction is maintained for 1.5 h (temperature controlled within the range of 40–50 ℃, pH maintained at 4.5–5.5). After enzymatic hydrolysis, the hydrolysate was centrifuged at low temperature for solid-liquid separation (5,000 rpm, 10 min, low temperature). The supernatant was discarded, and the centrifuged sediment (3.2 kg wet residue, 61% water content, 28% free water, 33% bound water) was retained. The centrifuged wet residue was then transferred to an atmospheric pressure microwave extraction device for solvent-free microwave extraction (SFME): irradiation was performed at 450 W microwave power for 25 min (at atmospheric pressure). The generated vapor and volatile components were condensed and allowed to stand for 15–30 min to separate into layers. The upper oil phase was collected, dried with anhydrous sodium sulfate, and weighed. The yield was 3.5% of the fresh material mass.

[0048] Example 2: Plectranthus amboinicus

[0049] Take 10.0 kg of freshly harvested whole *Plectranthus amboinicus* plant, crush it, and add it to an acetate-sodium acetate buffer solution (prepared as 0.08 M, pH adjusted to 4.8) at a material-to-liquid ratio of 1:6 (w:v) to make a suspension of approximately 60.0 L. Add a complex enzyme (cellulase:hemicellulase:pectinase = 2:1:1) to a 47 ℃ water bath, with the total enzyme dosage set at 1.5% of the fresh material mass (i.e., 150 g). Extend the enzymatic hydrolysis time to 6.0 h (maintain pH 4.5–5.0 to ensure enzyme activity) to more fully break down the cell walls and middle lamella. After enzymatic hydrolysis, centrifuge at 6,000 rpm for 10 min at low temperature to separate the solid and liquid phases. Discard the supernatant to remove a large amount of dissolved pectin and hemicellulose hydrolysates, retaining the wet residue. The wet residue was directly fed into an atmospheric pressure microwave extraction device for SFME: microwave power 400 W, irradiation for 30 min, condensation and static separation for 20–30 min, collection of the upper essential oil, drying with anhydrous magnesium sulfate and weighing, yield was 4.0% of the fresh material weight.

[0050] Example 3:

[0051] Take 8.0 kg of fresh whole *Mentha haplocalyx* plants, crush them, and add citrate-sodium citrate buffer (prepared as 0.06 M, pH 5.0) at a material-to-liquid ratio of 1:7 (w:v) to prepare a suspension of approximately 56.0 L. Place the suspension in a 42 ℃ water bath, add a complex enzyme (cellulase:hemicellulase:pectinase = 2:1:1), with a total enzyme dosage of 0.8% of the fresh material mass (i.e., 64 g), and hydrolyze for 2.0 h, maintaining the pH at 4.8–5.2. After hydrolysis, perform low-temperature centrifugation (5,000 rpm, 8 min), discard the supernatant to remove dissolved polysaccharides and reduce the surface activity of the system, retain the centrifuged sediment and slightly squeeze it manually to reduce the free liquid phase (this step is still within the scope of centrifugation and supernatant discarding, without adding other treatment methods). The treated wet residue was placed in a microwave extraction device and irradiated for 20 min at a microwave power of 500 W (atmospheric pressure SFME). After condensation and standing for 10–20 min, the layers were separated. The upper essential oil was collected, dried with anhydrous sodium sulfate, and weighed. The yield was 2.0% of the fresh material weight.

[0052] Example 4:

[0053] Take 12.0 kg of freshly harvested whole plant of *Hedyotis diffusa* variegata, crush it, and add phosphate buffer (prepared with NaH2PO4 / Na2HPO4 at a ratio of 1:10 (w:v), adjust the pH to 6.0) to obtain a suspension of approximately 120.0 L. Place the suspension in a 40 ℃ water bath, add a compound enzyme (cellulase:hemicellulase:pectinase = 2:1:1), the total amount of enzyme used is 1.0% of the fresh material mass (i.e., 120 g), and enzymatically hydrolyze for 4.0 h (maintaining the pH within the range of 5.5–6.0 to be compatible with the selected buffer system and enzyme activity). After enzymatic hydrolysis, perform solid-liquid separation by low-temperature centrifugation (4,500 rpm, 12 min), discard the supernatant to remove most of the dissolved polysaccharides, and retain the wet residue. The wet residue was transferred to an atmospheric pressure microwave extraction device for SFME: microwave power 420 W, irradiation for 30 min, condensation and standing for 20-30 min for separation, the upper oil phase was collected and dried with anhydrous magnesium sulfate and weighed, the yield was 5.0% of the fresh material mass.

[0054] Comparative Example 1: Plectranthus amboinicus – Control without enzymatic hydrolysis and subsequent dehydration treatment

[0055] Take 10.0 kg of freshly harvested whole Plectranthus plant, crush it, and add citric acid-sodium citrate buffer (0.05 M, pH=5.0) at a material-to-liquid ratio of 1:8 (w:v) to prepare 80.0 L of plant suspension.

[0056] The suspension was placed in a 45 ℃ water bath, and a complex enzyme (cellulase, hemicellulase, and pectinase in a mass ratio of 2:1:1) was added. The total enzyme dosage was 1.0% of the fresh material mass, and the enzymatic hydrolysis time was 4.0 h. The pH was controlled within the range of 4.5–5.5 during the enzymatic hydrolysis process to obtain an enzymatically hydrolyzed mixture. Extraction was performed under normal pressure using a solvent-free microwave extraction method, with the microwave power set to 450 W and the irradiation time to 25 min. The vapor generated during the extraction process was condensed, and the condensate was collected and allowed to stand for at least 60 min.

[0057] Comparative Example 2: Plectranthus amboinicus – No enzymatic hydrolysis performed, only SFME extraction.

[0058] Take 10.0 kg of freshly harvested whole Plectranthus plant, crush it without adding any enzyme preparations, and simply add citric acid-sodium citrate buffer (0.05 M, pH=5.0) at a material-to-liquid ratio of 1:8 (w:v) to form a plant suspension.

[0059] The suspension was then directly transferred to an atmospheric pressure microwave extraction device for extraction using a solvent-free microwave extraction method. The microwave power was set to 450 W and the irradiation time was 25 min. After condensation, the condensate was collected and allowed to stand for separation.

[0060] The results of comparing Examples 1-2 with Comparative Examples 1-2 are shown in the following table:

[0061] Table 1 Comparison of soluble polysaccharide content in the aqueous phase of the system after enzymatic hydrolysis

[0062] Process conditions Soluble polysaccharide content (mg / mL) Example 1 Enzymatic hydrolysis + low-temperature centrifugation dehydration 0.35 ± 0.08 Example 2 Enzymatic hydrolysis + low-temperature centrifugation dehydration 0.42 ± 0.10 Comparative Example 1 No dehydration after enzymatic hydrolysis, directly SFME 3.8 ± 0.6 Comparative Example 2 No enzymatic hydrolysis, direct SFME 0.20 ± 0.05

[0063] The above data shows that if solid-liquid separation is not performed after enzymatic hydrolysis, a large amount of pectin and hemicellulose hydrolysis products dissolve into the aqueous phase, with a concentration approximately 8–10 times that of the dehydration treatment system, which is the material basis for the formation of a stable emulsion.

[0064] Table 2 Comparison of apparent viscosity of aqueous phase after enzymatic hydrolysis (25 ℃)

[0065] Apparent viscosity (mPa·s) Example 1 1.9 ± 0.3 Example 2 2.3 ± 0.4 Comparative Example 1 18.6 ± 2.1

[0066] Note that the viscosity of water is approximately 1.0 mPa·s. When the viscosity is greater than 10 mPa·s, the Brownian motion of oil droplets weakens and the coalescence rate decreases significantly. The high-viscosity aqueous phase in Comparative Example 1 significantly inhibits the floating and coalescence of oil droplets.

[0067] Table 3. Results of oil-water interfacial tension measurement in the enzymatic hydrolysis system (25 °C)

[0068] Oil-water interfacial tension (mN / m) Example 1 28.4 ± 1.6 Example 2 26.9 ± 1.8 Comparative Example 1 9.7 ± 1.2 Comparative Example 2 31.2 ± 2.0

[0069] Note that pectin / hemicellulose hydrolysates possess natural interfacial activity, resulting in a significant reduction in interfacial tension (<10 mN / m) in Comparative Example 1, making them highly susceptible to forming stable emulsions. In the examples, after dehydration, the polysaccharide concentration decreased, and the interfacial tension recovered to levels close to those of a pure oil-water system.

[0070] Table 4 Comparison of emulsification stability of SFME after condensation

[0071] Condensate appearance Layering after 30 minutes of standing Emulsification determination Example 1 Clear, with a distinct oil-water interface Fully layered Unstable emulsification Example 2 Slightly turbid Basic layering slight Comparative Example 1 milky No layering Stabilized emulsification Comparative Example 2 Slightly turbid Layerable Unstable emulsification

[0072] Table 5 Comparison of essential oil yield and separation efficiency (Plectranthus amboinicus)

[0073] Essential oil yield (% fresh weight) Stratification time (min) Example 1 2.8 ± 0.4 10–15 Example 2 3.6 ± 0.5 15–20 Comparative Example 1 1.1 ± 0.3 >60 (still incomplete) Comparative Example 2 0.8 ± 0.2 20–30

[0074] The condensate of Comparative Example 1 was distinctly milky white or translucent emulsion with an unclear oil-water interface and slow stratification. Even with prolonged settling time, the upper oil phase was difficult to completely separate, requiring artificial heating, prolonged settling, or additional demulsification treatment for partial separation. In Comparative Example 2, due to the ineffective disruption of plant cell wall structures, essential oil release was insufficient, resulting in a smaller oil phase volume in the condensate. Although stratification was faster than in Comparative Example 1, the overall oil content was significantly lower. (See attached table for details.) Figure 1 ; and from the appendix Figure 2 It is evident that the response of key monoterpenes such as limonene in the comparative sample was significantly reduced, and a new peak (limonene oxide) appeared at m / z 156.09, indicating that the heat-sensitive components underwent oxidative degradation, leading to a decline in aroma quality.

[0075] The oil phase of Comparative Example 1 was finally dried with anhydrous sodium sulfate and weighed. The yield of essential oil was only 0.8%–1.4% of the fresh material mass, which was significantly lower than the yield level after introducing solid-liquid separation and dehydration steps in the example. The yield of essential oil of Comparative Example 2 after drying with anhydrous sodium sulfate was only 0.6%–1.0%, which was significantly lower than the combined process of "enzymatic hydrolysis + dehydration + SFME" in the example.

[0076] As can be seen from the data in the table above, while the enzymatic hydrolysis step is beneficial for breaking down plant cell walls and releasing essential oils, it also leads to a large amount of polysaccharides such as pectin and hemicellulose dissolving into the aqueous phase. These polysaccharides significantly increase the viscosity of the system in the aqueous phase and form a stable adsorption layer at the oil-water interface through their hydrophilic-hydrophobic structure, greatly reducing the interfacial tension between oil and water. This results in the formation of a stable emulsion during the microwave distillation and condensation stage, severely hindering the precipitation of essential oils.

[0077] This invention introduces solid-liquid separation and dehydration treatment after enzymatic hydrolysis, effectively removing the polysaccharide-rich aqueous phase. This ensures that residual water in the system exists primarily as bound water or a small amount of free water, significantly reducing interfacial activity. The treated system exhibits a marked increase in oil-water interfacial tension and a significant decrease in viscosity. Essential oils can rapidly precipitate as a continuous oil phase during SFME, avoiding emulsification and thus significantly improving essential oil separation efficiency and yield.

[0078] Although the enzymatic hydrolysis step involves liquid disposal, its disruption of the cell wall provides a more readily released material basis for subsequent SFME, which is a necessary prerequisite for improving the overall yield. Experimental data show that the combination of enzymatic hydrolysis + dehydration + SFME is superior to other methods in terms of yield, emulsification avoidance, and process simplicity.

[0079] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for extracting aromatic plant essential oils, characterized in that, Includes the following steps: 1) Pretreatment: The whole plant (including roots, stems and leaves) of the collected fresh aromatic plants is crushed and then added to the buffer solution at a material-to-liquid ratio of 1:6-10 (w:v) to form a plant suspension; 2) Enzymatic hydrolysis: Place the plant suspension in a water bath at 40–50℃ and hydrolyze it with a compound enzyme for 1–8 hours. Adjust the pH to 4–6 to obtain a mixture. 3) Solid-liquid separation and dehydration: Centrifuge the enzymatically hydrolyzed mixture at low temperature at 3,000–8,000 rpm for 5–15 min; 4) Solvent-free microwave extraction (SFME): The dehydrated wet residue is transferred to a microwave extraction device and microwave distillation extraction is performed under normal pressure with a microwave power of 100–1000W for 10–60 minutes. 5) Obtaining the finished product: The volatile oil vapor generated by microwave irradiation is discharged, condensed, and the upper essential oil is collected by layering and then dehydrated and dried to obtain the final essential oil.

2. The method for extracting aromatic plant essential oils according to claim 1, characterized in that, The complex enzymes in step 2) include cellulase, hemicellulase and pectinase.

3. The method for extracting aromatic plant essential oils according to claim 2, characterized in that, The compound enzyme, by mass ratio, has cellulase:hemicellulase:pectinase = 2:1:

1.

4. The method for extracting aromatic plant essential oils according to claim 2, characterized in that, The enzymatic hydrolysis time is 4–8 hours, and the amount of compound enzyme used is 0.5%–3% of the raw material mass.

5. The method for extracting aromatic plant essential oils according to claim 1, characterized in that, In step 4), the microwave power is 200–600W and the time is 10–30min.

6. The method for extracting aromatic plant essential oils according to claim 5, characterized in that, In step 4), the microwave power is 400–500W and the time is 20–30min.

7. The method for extracting aromatic plant essential oils according to claim 1, characterized in that, The buffer solution is one of citrate-sodium citrate, acetic acid-sodium acetate, or phosphate buffer.

8. The method for extracting aromatic plant essential oils according to claim 1, characterized in that, In step 5), the drying agent is either anhydrous sodium sulfate or anhydrous magnesium sulfate.

9. The method for extracting aromatic plant essential oils according to claim 1, characterized in that, The essential oil yield is 2%–5%.

10. The method for extracting aromatic plant essential oils according to claim 1, characterized in that, The aromatic plant in question belongs to the Lamiaceae family and the genus *Corydalis*.

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