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Abstract

Objective

This study explored the advantages of deep eutectic solvents (DES) in extracting plant volatile components. We focused on evaluating the efficacy of DES in extracting essential oils (EOs) from Cinnamomum cassia (CC), Thymus mongolicus (TM), Illicium verum (IV), and Curcuma longa (CL). This was compared to the traditional steam distillation method.

Methods

DES was prepared with a 1:3 ratio of 1,3-butanediol to choline chloride. Its extraction efficiency was compared to steam distillation, and EOs were analyzed using GC-MS. The antioxidant properties of the extracts were assessed using the DPPH assay, and antimicrobial activities were tested against Escherichia coli and Staphylococcus aureus.

Results

DES extraction enhanced the extraction rate and content of specific compounds in IVEOs and increased the abundance of compounds in CCEOs and TMEOs. The TMEOs extracted with DES exhibited the most potent antioxidant capacity, whereas the CCEOs extracted with DES demonstrated the strongest antibacterial activity. The EOs obtained through DES extraction displayed higher quality and biological activity than those obtained through steam distillation.

Conclusion

DES is effective for extracting EOs from aromatic plants and may result in oils with enhanced biological activities. Further optimization of the DES formulation could enhance extraction efficiency and improve oil quality.

Keywords

deep eutectic solvents aromatic plant antibacterial antioxidant botany volatile oil

Introduction

China boasts a diverse flora of spice plants, with an estimated 500 species. A total of 254 common spice plants are categorized into 68 families and 159 genera. Prominent among 27 species of Lamiaceae Martinov, 22 species of Lauraceae Juss., and 17 species of Asteraceae Bercht. & J. Presl, 16 species of Magnoliaceae Juss., 15 species of Rutaceae Juss., 15 species of Apiaceae Lindl., 12 species of Zingiberaceae, 9 species of Liliaceae Juss., 9 species of Pinaceae Spreng. Ex F. Rudolphi, 9 species of Fabaceae Lindl., 8 species of Rosaceae Juss., and 7 species of Poaceae Barnhart, among others.¹

Cinnamomum cassia (CC) and Thymus mongolicus (TM) are highly valued for their culinary and medicinal uses. Cinnamomum cassia (CC), in its various forms, is renowned for its bark and leaves, which are rich in secondary metabolites, such as cinnamaldehyde and cinnamic acid, and exhibit antibacterial, antifungal, antioxidant, and anticancer properties.^2,3 Thymus mongolicus (TM), a fragrant herb native to China, is traditionally used to treat colds, coughs, and to promote perspiration. Its essential oils are known for their antibacterial and immune-boosting properties.^4-6 Illicium verum (IV), primarily grown in southern China, is economically significant for its use in food and beverages, with its fruit and trans-anethole compound showing therapeutic benefits against cancer, bacteria, and inflammation.^7-9 Curcuma longa (CL), or turmeric, has a long history of use in India and China, known for its anti-inflammatory and analgesic effects, and modern research further supports its therapeutic use in treating various diseases, particularly through its active compound, curcumin.^10-12 The bioactive constituents of these plants highlight their potential in both the food and pharmaceutical industries.

In line with the current focus on green analytical chemistry, novel alternative solvents, such as hydrophilic solvents, ionic liquids, and Deep Eutectic Solvents (DES), have emerged within the domain of analytical chemistry. These alternatives substitute conventional organic solvents in various sample pre-treatment procedures.¹³ DES represents a novel category of compounds formed by combining different hydrogen bond donors (HBD) and acceptors (HBA). The fine-tuning of their physical characteristics is achieved through the careful selection of constituent components and ratios of HBD to HBA. Typically, these eutectic blends are distinguished by their simple synthesis process, minimal vaporization under elevated temperatures, high specificity, as well as tunable solubility and polarity.¹⁴ As an alternative solvent, DES is anticipated not only to yield better extraction results but also to generate extracts of superior quality. Compounds extracted using DES are expected to exhibit significantly enhanced biological activity and greater bioactivity compared with essential oils (EOs) derived from aromatic plants via traditional steam distillation methods.^15,16

DES has emerged as a promising, natural, and environmentally friendly alternative for the extraction and isolation of natural products, demonstrating particular efficacy in recovering compounds such as flavonoids and phenols. Despite the documented advantages of DES in these contexts, their application in the extraction of volatile plant constituents remains underexplored. This study aimed to assess and compare the extraction yields, antioxidant properties, and antimicrobial activities of four aromatic plants using both steam distillation and DES extraction methods. The potential advantages of DES extraction over traditional steam distillation were highlighted through a comparative analysis, particularly in its ability to extract bioactive compounds from selected aromatic plants.

Methods and Materials

Materials

The agar powder was obtained from Biosharp Technology Co., Ltd (Beijing, China). LB broth medium was sourced from Shanghai Bioway (Shanghai, China). DPPH was provided by Beijing Riotaibio Technology Co., Ltd (Beijing, China), and absolute ethyl alcohol was purchased from Tianjin Sun Technology Co., Ltd (Tianjin, China). Deionized water was prepared in the laboratory. The specific information on four traditional Chinese spice plants is shown in Table 1.

Table 1.

The Name, Voucher Specimen Number of Four Traditional Chinese Spice Plants.

Herbal drug name Scientific name (abbreviated)	Name in traditional Chinese medicine	Extraction site	Voucher number	Storage location
Cinnamomum cassia	Rougui, Yugui, Jungui, Mugui	Bark	Institute of Natural Medicine & Green Chemistry School of Chemical Engineering and Light Industry. Guangdong University of Technology^a	2022-101C
Thymus mongolicus	Bailixiang	Complete plant		2023-102T
Illicium verum	Bajiao, Bajiaohuixiang, Maijiao, Dahuixiang	Fruit		2023-103I
Curcuma longa.	Jianghuang, Yujin, Baodingxiang, Haoding, Huangsi, Huangjiang	Tuber		2024-101C

Plant materials were identified by Professor Liu Nian, Zhongkai University of Agricultural Engineering.

Extraction of Plant Essential Oils (EOs)

The EOs extraction rate is: mass of EOs (g) / mass of herbal powder (g) * 100%.

Steam Distillation Extraction of Volatile Oils from Spice Plant

The four spice plants selected for extraction, namely CC, IV, TM, and CL, were initially processed by finely grinding them in a high-speed multi-purpose grinder. The resulting powder was then sifted through a sieve with a 50-mesh sieve to ensure the desired fineness. Subsequently, 200 g of the powdered spices were accurately weighed and soaked in 2 L of distilled water for approximately 2 h. The resulting suspension was then transferred to a high-efficiency volatile oil extraction apparatus, with a condenser tube connected to facilitate the extraction of EOs. Following a 2-h extraction period, heating was discontinued, allowing the mixture to stand for a designated period. The valve at the bottom of the collection tube was then opened to drain off excess water, and the collected EOs were separated. Once stratification was complete, any residual water was removed using anhydrous sodium sulfate, and the extraction rate of EOs was calculated. The obtained EOs were transferred to special black test tubes and refrigerated at 4 °C to ensure their stability for subsequent analysis. The yield of EOs was determined by weighing and calculating.

Extraction of EOs from Spice Plants with DES

Choline chloride and 1,3-butanediol were weighed in a 1:3 molar ratio, mixed thoroughly, and continuously stirred in a water bath held at a constant temperature of 80 °C until a uniformly clear mixture was obtained. Subsequently, the mixture was left at room temperature for one day. Herbal powder, quantified at 200 g, was finely ground until it could pass through a 50-mesh sieve and mixed with the prepared Deep Eutectic Solvent (DES) at a liquid-to-solid ratio of 1:5. This mixture was introduced into a high-efficiency essential oil distiller, with the DES volume set at 1 L. The mixture was heated to boiling, with the temperature adjusted to maintain a gentle boil for 2 h. The essential oils (EOs) were subsequently collected, dried with anhydrous sodium sulfate, stored at 4 °C, and readied for further analysis. The yield of EOs was measured and determined.

GC-MS Analysis Method of EOs

In this experiment, EOs from three spice plants were analyzed using gas chromatography-mass spectrometry (GC-MS) under analytical conditions tailored for each type: Cinnamomum cassia EOs (CCEOs), Thymus mongolicus EOs (TMEOs), Illicium verum EOs (IVEOs), and Curcuma longa EOs (CLEOs). The GC-MS instrument used was the GCMS-qp2010 PLUS (Shimadzu, Japan), equipped with a flame thermionic detector (FTD). The chromatographic conditions were as follows: a Rxi-5ms silica capillary column (30 m × 0.25 mm × 0.25 μm) was used with helium as the carrier gas at a flow rate of 1.0 mL/min and a split ratio of 5:1. The oven temperature was ramped to 280 °C at a rate of 10 °C/min and held for 2 min.¹⁷

Assay of Resistance to Oxidation

The DPPH method was initially employed to assess the antioxidant activity of various substances. Subsequently, numerous researchers devised methodologies to evaluate the antioxidant activity and capacity of plant extracts using the DPPH assay. In essence, this method hinges on the reduction of DPPH radicals by antioxidants present in plant extracts, which typically shifts to a yellowish hue, indicating the conversion of the radicals into their reduced form, diphenyl picrate hydrazine. This color change can be quantified using a spectrophotometer within the wavelength range of 515-520 nm. In this experiment, color change was measured using a microplate reader.

Initially, 2, 4, 6, 8, and 10 μL volumes of essential oils (EOs) were measured and mixed with 1 mL of anhydrous ethanol. Subsequently, 150 μL of varied concentrations of the sample solution were introduced into a 96-well plate. The DPPH solvent was prepared by accurately weighing 3.35 mg of DPPH powder, which was then dissolved in 50 mL of anhydrous ethanol. The solution was thoroughly mixed using a vortex shaker for approximately 5 min to accelerate the process. Following this, 150 μL of the 0.1 mmol/L DPPH solution was sequentially added to the 96-well plate. In the control group, 150 μL of essential oil diluent was mixed with 150 μL of anhydrous ethanol. The plate was then sealed with tin foil and left at room temperature, shielded from light, for 30 min. Subsequently, the absorbance (OD517) of each well was measured at 517 nm using a microplate reader. The DPPH clearance values are presented as mean ± standard deviation, where OD signifies optical density.¹⁸

DPPH clearance = [\frac{1 - (OD sample - OD control)}{OD reference}] \times 100 % .

Assay of Antimicrobial Activity

An aliquot of 100 μL from an overnight culture of Escherichia coli (E. coli, ATCC25922) was uniformly spread onto a Petri dish containing Luria-Bertani (LB) agar medium using an inoculating loop. After the dish was air-dried in a super-clean environment, a sterilized filter paper disc was aseptically positioned on the agar surface with sterilized forceps. It is essential to ensure that the filter paper is gently pressed down to establish contact with the agar surface, maintaining a minimum distance of 2 cm between the centers of adjacent filter papers. This procedure was conducted in triplicate for each experimental condition. To the center of each filter paper, 3 μL of EOs were applied, with deionized water serving as a negative control. The Petri dishes were sealed, inverted, and incubated at 37 °C for 24 h. The antibacterial activity was quantified by measuring the diameter of the zones of inhibition. The diameter of each inhibition zone was measured with a vernier caliper, and the average value was taken after six measurements of each inhibition zone. The same methodology was applied to Staphylococcus aureus (S. aureus, ATCC6538).

\begin{aligned} Antibacterial rate = & (\frac{1 - concentration of experimental group}{concentration of control group}) \\ \times 100 % \end{aligned}

Statistical Analysis

Data obtained from the experiments were analyzed using statistical software (GraphPad Prism 8). The data are presented as mean ± standard deviation (SD) of at least three independent experiments.

Results

GC-MS Analyses of EOs

In Table S1, GC-MS analysis revealed a total of 58 components in the CCEOs extracted by both methods. The DES extraction preferentially isolates low boiling point compounds, which are known to evaporate early in the GC-MS analysis warming period, suggesting that DES may be more effective at capturing volatile compounds. The major constituents in the CCEOs extracted using DES were (-)-α-copaene (30.91%), trans-cinnamaldehyde (13.46%), (+)-δ-cadinene (13.32%), muurolene (10.63%), and 2,4-dimethyl-1,3-dioxane (7.13%). In contrast, steam distillation yielded a higher proportion of trans-cinnamaldehyde (34.31%) and (-)-α-copaene (25.61%), indicating a different extraction profile. This difference in chemical composition may influence the application-specific efficacy of the extracted oils. The DES extracts of TMEOs contained a greater diversity of constituents, including both low and high boiling point compounds, compared to those obtained through steam distillation. Among the 86 compounds identified, the top five constituents in the DES group were octadecyne (10.32%), 8,9-dehydro-9-formyl-cycloisolongifolene (8.53%), (+)-borneol (6.61%), methylpalmitate (5.98%), and thymol (2.07%). The steam distillation method primarily yielded (+)-borneol (35.72%), α-terpinol (20.30%), thymol (19.34%), 8,9-dehydro-9-formyl-cycloisolongifolene (2.88%), and bornyl acetate (2.67%). The abundance of different compounds in DES extracts may provide a broader spectrum of bioactivity compared to traditional methods. The GC-MS analysis of IVEOs indicated that trans-anisidine was the predominant component in DES extraction (93.70%), whereas the primary components obtained through steam distillation were 13,5-triethylbenzene (79.00%) and trans-anisidine (13.43%).

Regarding CLEOs, qualitative analysis by GC-MS demonstrated similar numbers of substances extracted by DES and steam distillation methods, with 20 and 17 substances, respectively. Only ar-tumerone or zingiberene were identical or chiral isomers. Thus, the selection of extraction methods can be tailored to specific requirements. In the case of CLEOs extracted from DES, the chemical composition yield was 98.66%, with α-curcumene (23.37%) as the principal component, followed by isolongifolene (14.42%), ar-tumerone (12.50%), α-selinene (9.24%), and β-cubebene (6.16%). Analysis of CLEOs extracted through steam distillation revealed a chemical composition yield of 98.81%, with the major components being ar-tumerone (25.52%), β-sesquiphellandrene (23.32%), and Zingiberene (19.68%). Tumerone (16.70%), (E)-2-penten-1-ol (4.05%), α-curcumene, and zingiberene were identified as the primary active ingredients extracted through DES and steam distillation methods, respectively, with over 5% zingiberene also present in the DES method. CLEOs act directly on bacterial cell membranes, disrupting their basic cellular structure and leading to bacterial death. Due to its safety and high efficacy, it holds significant potential for food antisepsis applications.¹⁸

GC-MS analysis has demonstrated that, despite similar overall extraction rates between DES and steam distillation, there are notable variances in the extraction rates of individual components. Therefore, the selection of the extraction method should be based on specific application requirements, and the appropriate extraction method can be selected based on the desired components.

Extraction Rate of EOs

The data presented in Table 2 and Figure 1 indicate that the extraction rates of CCEOs and TMEOs in the DES extraction group were significantly lower than those in the steam distillation group. Specifically, the extraction rate of TMEOs experienced the greatest decrease, with a reduction of only 0.41%, representing a 75.60% decline compared to the steam distillation group. Conversely, for IVEOs and CLEOs, the extraction yield in the DES extraction group surpassed that of the steam distillation group. Specifically, the extraction yields reached 7.62% and 2.90% for IVEOs and CLEOs, respectively, which were 12.60% and 16.21% higher than those achieved through steam distillation. The DES method may demonstrate lower performance than steam distillation extraction for substances like CC and TM, possibly due to variations in HBD and HBA. However, research by Liu et al¹⁹ has shown that a DES solvent prepared with choline chloride and 1,2-propylene glycol at a 1:3 molar ratio can achieve a cinnamon extraction yield of 3.645%, which is 29.52% higher than steam distillation extraction. These results underscore the versatility of DES as an extraction medium, highlighting its potential to improve the extraction of traditional spices. The variability in performance across different spice extracts suggests that the composition and ratios of the DES solvents can be optimized to enhance extraction efficiency, offering a promising avenue for future research in green extraction technologies.

Figure 1.

The extraction rate of four kinds of plants under DES extraction and steam distillation.

Table 2.

The Extraction Yield Difference Between the two Extraction Methods.

Group	Extraction rate
Group	DES extraction	Steam distillation
CCEOs	2.16 ± 0.07%	2.57 ± 0.10%
TMEOs	0.41 ± 0.05%	1.68 ± 0.07%
IVEOs	7.62 ± 0.32%	6.66 ± 0.09%
CLEOs	2.90 ± 0.05%	2.43 ± 0.01%

DPPH Free Radical Scavenging Assay

Table 3 and Figure 2 present the comparative antioxidant capacities of the four spices extracted using the DES method, ranking them as follows: CCEOs > TMEOs > CLEOs > IVEOs. Table 4 and Figure 3 demonstrate the antioxidant capacity hierarchy under steam distillation, with TMEOs > CLEOs > CCEOs > IVEOs. DES extraction significantly boosted the antioxidant properties of CCEOs and IVEOs, which may be associated with the change in the extraction rates of trans-cinnamaldehyde²⁰ and trans-anisidine.²¹ This makes DES a preferred method for extracting antioxidants from these oils. However, a decrease in antioxidant capacity in TMEO and CLEO with DES may be attributed to reduced yields of relevant compounds.

Figure 2.

Comparison of free radical scavenging data of four spice plants under DES extraction.

Figure 3.

Comparison of free radical scavenging data of four spice plants under steam distillation.

Table 3.

Comparison of Free Radical Scavenging Data of Four Spice Plants Under DES Extraction.

Name	DPPH clearance (DES extraction) (%)					IC₅₀ (mmol/L)
Concentration (mmol/L)	0.200	0.400	0.600	0.800	1.000
CCEOs	61.10 ± 4.56	80.23 ± 1.18	82.11 ± 1.26	85.03 ± 0.38	82.95 ± 1.47	0.105
TMEOs	37.58 ± 4.07	56.42 ± 1.40	66.42 ± 5.15	68.28 ± 3.36	70.39 ± 3.86	0.324
IVEOs	16.03 ± 5.53	13.25 ± 2.51	15.03 ± 3.15	14.86 ± 2.19	17.34 ± 4.68	>1.000
CLEOs	39.30 ± 4.37	39.29 ± 1.03	35.48 ± 3.37	40.71 ± 4.21	44.61 ± 3.07	>1.000

Table 4.

Comparison of Free Radical Scavenging Data of Four Spice Plants Under Steam Distillation.

Name	DPPH clearance (Steam distillation) (%)					IC₅₀ (mmol/L)
Concentration (mmol/L)	0.200	0.400	0.600	0.800	1.000
CCEOs	9.03 ± 7.03	12.79 ± 6.31	13.79 ± 8.21	16.00 ± 6.67	19.10 ± 6.10	>1.000
TMEOs	64.67 ± 2.77	76.57 ± 1.36	90.82 ± 6.01	90.29 ± 7.40	91.26 ± 7.25	0.124
IVEOs	9.17 ± 7.04	10.38 ± 5.09	7.17 ± 4.54	11.82 ± 5.86	7.96 ± 5.48	>1.000
CLEOs	52.61 ± 4.29	66.12 ± 7.87	76.50 ± 2.74	71.58 ± 6.44	74.72 ± 5.32	0.153

Antibacterial Ability

The antibacterial activity of essential oils extracted using the DES method was compared against those extracted via steam distillation, with the results detailed in Table 5 and Figure 4. The DES-extracted CCEOs demonstrated superior antibacterial efficacy against both E. coli and S. aureus compared to the steam distillation method. This enhanced activity may result from the preservation of specific antibacterial compounds during the DES extraction process. In contrast, the antibacterial activity of TMEO was reduced when extracted using DES. This reduction can be attributed to changes in the composition of its primary constituents, such as α-terpinol²² and thymol.²³ The extraction efficiency of TMEOs using DES was notably lower, potentially leading to a decrease in its antibacterial potency. IVEOs extracted from DES also had no obvious antibacterial effect. Notably, DES-extracted IVEOs contained elevated levels of trans-fennel brain, a compound known for its anti-inflammatory and analgesic properties, but typically not for its bacteriostatic abilities.²⁴ It is plausible that the DES extraction procedure inefficiently extracts compounds relevant to antibacterial activity, resulting in its diminished antibacterial efficacy.²⁵ Among the four essential oils, CLEOs extracted by DES exhibited the most potent antibacterial activity against S. aureus (13.32 ± 0.75%), surpassing that of chloramphenicol. However, its antibacterial activity against E. coli was lower than that of steam distillation, which may result from the antibacterial properties of ar-tumerone, zingiberene, and β-sesquiphellandrene obtained through steam distillation, which likely contributed to the bactericidal effects against E. coli.²⁶

Figure 4.

Comparison of inhibition zone data of four spice plants under two extraction methods.

Table 5.

Comparison of Inhibition Zone Data of Four Spice Plants Under two Extraction Methods.

Group	Diameter of inhibition circle (mm)^a
Group	E. coli	S. aureus
DES CCEOs	10.20 ± 0.42^b	9.80 ± 0.86
Steam CCEOs	9.54 ± 0.46	9.80 ± 1.18
DES TMEOs	–^c	–
Steam TMEOs	6.91 ± 1.09	6.83 ± 1.17
DES IVEOs	–	–
Steam IVEOs	6.54 ± 0.47	–
DES CLEOs	8.84 ± 0.50	13.32 ± 0.75
Steam CLEOs	9.60 ± 0.74	–
ampicillin	\^d	22.12 ± 0.37
chloramphenicol	9.60 ± 0.74	\

Note: ^aThe diameter of the inhibition zone includes 6 mm of filter paper.

Data are mean ± SD of triplicate.

No effective antimicrobial activity against the bacteria tested.

The bacteriostatic test was not performed on the tested flora.

Discussion

This study aimed to assess the effectiveness of DES in extracting EOs from four traditional Chinese spice plants: CC, TM, IV, and CL. The DES extraction method was compared against the conventional steam distillation method in terms of extraction efficiency, antioxidant capacity, and antimicrobial activity. The results provide valuable insights into the potential of DES as an alternative green extraction technology.

Our results showed that DES extraction enhanced the extraction rate and content of specific compounds in IVEOs and increased the abundance of compounds in CCEOs and TMEOs. This suggests that DES can be tailored to target specific compounds in plant materials, which is a significant advantage over traditional extraction methods. The superior extraction efficiency observed with DES could be attributed to its unique solvent properties, such as its ability to form hydrogen bonds and its tunable polarity, which allows for better solubilization of target compounds.^14,15 In principle, DES extraction is anticipated to exceed traditional steam distillation extraction in terms of extraction efficiency and biological activity due to its unique solvent characteristics. However, the advantages of DES extraction were not as pronounced in the case of CLEOs. However, studies by Patil et al²⁷ and Abouheif et al²⁸ showed that DES extraction significantly improved the extraction rate, compound abundance, and biological activity of CLEOs. This could be attributed to the type and proportion of HBD and HBA in the chosen DES solvent. This study used a single DES solvent; future research should explore the appropriate DES solvent formulation for different fragrant plants and its influence on composition analysis and activity evaluation to fully exploit the DES extraction method's application potential.

In terms of antioxidant activity, DES extraction significantly enhanced the antioxidant properties of CCEOs compared to steam distillation. This increase in biological activity could be attributed to the more efficient extraction of α-pinene by DES, a compound known for its antioxidant properties.²⁹ However, it is notable that DES extraction did not uniformly surpass steam distillation for all plant materials, as evidenced by CLEOs. Previous research has indicated that ar-tumerone and β-sesquiphellandrene,³⁰ key constituents of CLEOs, exhibit significant antioxidant potential. Nonetheless, under DES extraction conditions, the yields of these compounds were observed to decrease, with α-curcumene (23.37%) emerging as the predominant component. The observed reduction in the antioxidant capacity of CLEOs extracted using DES is likely due to this change in compound distribution. The antioxidant activity of IVEOs was found to be independent of concentration levels for both steam distillation and DES extraction methods. However, in A. Padmashreede's study,³¹ the antioxidant capacity of steam distillation was also found to be independent of concentration reach. The reasons for this phenomenon may stem from the incompatibility of the extraction methods with the specific properties of IVEOs or varietal factors, necessitating further research to clarify the underlying mechanisms. The antimicrobial activity of the EOs also varied depending on the extraction method. This could also stem from the distinct ingredients yielded by various extraction techniques.

A key advantage of DES is its environmental friendliness, as it is composed of renewable and biodegradable components.¹⁴ This makes DES an attractive alternative to traditional organic solvents, which can have negative environmental impacts. The ability of DES to enhance both the extraction efficiency and biological activity of EOs makes it a valuable tool for the extraction of high-quality plant materials with potential applications in the food, pharmaceutical, and cosmetic industries. Despite showing potential for enhancing the extraction efficiency and biological activity of EOs from four spice plants, the current study's results were not significantly improved, possibly due to the specific composition and ratio of the DES used. This highlights the need for future research to optimize DES formulations to better suit various plant materials and to explore the synergistic effects of DES with other extraction techniques to maximize efficiency. Additionally, the study's limitations include the lack of investigation into the recovery and reuse of DES, which is essential for the process's scalability and environmental sustainability. Future work should also expand the analysis to a broader range of plant materials and develop strategies for the efficient recovery and recycling of DES.^32,33

Conclusion

This study investigated the effect of a deep eutectic solvent (DES) formulated with a 1:3 ratio of 1,3-butanediol to choline chloride on the extraction of volatile oils from four traditional aromatic plants: CC, TM, IV, and CL. The results demonstrated that the DES extraction method effectively enhanced the extraction rate of IVEOs and increased the content of trans-anethole in CCEOs and TMEOs. Concerning biological activity, DES extraction significantly improved the antioxidant capacity of CCEOs and the antibacterial capacity of CLEOs. These findings are likely due to an increased abundance of specific compounds within the essential oils, thus confirming the DES extraction method's ability to yield high-quality essential oils with enhanced biological activity. This indicates that DES can be tailored to target specific compounds in plant materials, offering a significant advantage over traditional extraction methods. The superior extraction efficiency observed with DES can be attributed to its unique solvent properties, such as its ability to form hydrogen bonds and its tunable polarity, which facilitates better solubilization of target compounds.

The findings of this study highlight the potential of DES in obtaining high-quality essential oils. By optimizing the solvent ratio and selecting more appropriate extraction materials, it may be possible to enhance extraction efficiency, compound abundance, and biological activity. Therefore, to enhance the extraction rate of specific plant components, further research and optimization of the DES components and extraction conditions are necessary. The variety of compounds that can be extracted using DES and the criteria for selecting DES in the extraction process necessitate further investigation. DES presents a promising and environmentally friendly alternative to conventional steam distillation methods, with the potential to enhance both the extraction efficiency and biological activity of essential oils.

Supplemental Material

sj-docx-1-npx-10.1177_1934578X251330769 - Supplemental material for Comparison of Composition and Bioactivity Between DES and Steam Distillation Extraction of Four Traditional Chinese Spice Plants

Supplemental material, sj-docx-1-npx-10.1177_1934578X251330769 for Comparison of Composition and Bioactivity Between DES and Steam Distillation Extraction of Four Traditional Chinese Spice Plants by Yingjuan Jiang, Yanqing Ma, Juting Li, Lanyue Zhang, Geng Liu, Yan Zhao and Junlin Cen in Natural Product Communications

Footnotes

ORCID iD

Lanyue Zhang

Statement of Informed Consent

There are no human subjects in this article and informed consent is not applicable.

Ethical Considerations

Ethical Approval does not apply to this article.

Author Contributions/CRediT

All authors contributed to the study's conception and design. Material preparation, data collection, and analysis were performed by Yingjuan Jiang, Yanqing Ma, Juting Li, Geng Liu, Yan Zhao, Junlin Cen, and Weiguang Huang. The first draft of the manuscript was written by Yanqing Ma. Resources and writing – review & editing were performed by Lanyue Zhang. All authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.

Funding

The authors disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This study was financially supported by the Guangzhou Municipal Science and Technology Project (SL2022A03J00152), National Natural Science Foundation of China (No. 22408058), Guangdong Basic and Applied Basic Research Foundation (No. KTP20240675).

Conflicting Interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Supplemental Material

Supplemental material for this article is available online.

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