Clove (Syzygium aromaticum) is a valuable medicinal and aromatic plant widely used in food, pharmaceuticals, and cosmetics. Its clove essential oil, rich in eugenol and other bioactive compounds, offers antimicrobial, antioxidant, and therapeutic properties. Traditional extraction methods, such as steam distillation and solvent extraction, often lead to lower yields, thermal degradation, and residual solvents.
In contrast, supercritical CO2 extraction has emerged as an advanced, green, and efficient technology for essential oil production. It operates at relatively low temperatures, ensuring better retention of heat-sensitive components, while CO2 is non-toxic, recyclable, and leaves no harmful residues. To further improve extraction efficiency, the uniform design method was applied in this study to optimize operating parameters and establish the best extraction conditions for clove essential oil.
Materials and Methods
Raw Materials
Dried clove buds were sourced from a local supplier, cleaned, and ground into powder for extraction experiments. The moisture content was controlled within the range of 8–10% to ensure consistency.
Supercritical CO2 Extraction Equipment
A laboratory-scale supercritical CO2 extraction system equipped with an extraction vessel, separation vessel, high-pressure CO2 pump, and temperature–pressure control units was used.
Experimental Design
The uniform design method was employed to investigate the influence of four main factors on extraction yield:
- Extraction pressure (MPa)
- Extraction temperature (°C)
- Extraction time (h)
- CO2 flow rate (L/h)
Each factor was set at multiple levels, and uniform design tables were used to minimize the number of experiments while maximizing information. The essential oil yield was taken as the evaluation index.
Analytical Methods
The extracted oil was collected in the separation vessel, weighed, and analyzed by GC–MS to determine the composition, focusing on eugenol content as a quality indicator. Statistical analysis and regression modeling were applied to evaluate factor significance.
Results and Discussion
Effect of Extraction Parameters
- Pressure: Higher extraction pressure increased CO2 density and solubility, resulting in higher yields, but excessive pressure raised operational costs without proportional benefits.
- Temperature: Moderate temperature enhanced mass transfer, while excessively high temperature reduced oil quality due to thermal degradation.
- Time: Prolonged extraction improved yield initially, but reached a plateau after a certain period.
- Flow rate: Adequate CO2 flow ensured efficient solute transport, but excessively high flow reduced extraction efficiency.
Optimization by Uniform Design Method
Regression analysis revealed that extraction pressure and temperature were the most significant factors affecting yield. The optimized conditions determined by the uniform design method were:
- Pressure: 28 MPa
- Temperature: 45 °C
- Time: 2.5 h
- CO2 flow rate: 20 L/h
Under these conditions, the yield of clove essential oil reached 12.3%, with high retention of eugenol and other volatile components.
Comparison with Traditional Methods
Compared with steam distillation, supercritical CO2 extraction provided:
- 30–40% higher yield
- Better preservation of aroma and bioactive compounds
- No solvent residues
- Lower environmental impact
This confirms the advantages of CO2 extraction as a green and efficient alternative for essential oil production.
Conclusion
The uniform design method effectively optimized the supercritical CO2 extraction of clove essential oil, identifying the best balance between yield, quality, and energy efficiency. The optimized conditions significantly improved extraction performance compared with conventional methods, making this approach highly suitable for large-scale industrial applications in food, pharmaceutical, and cosmetic industries.
Future studies may focus on scaling up the process, economic evaluation, and exploring synergistic extraction with co-solvents to further enhance yield and selectivity.
FAQ
Q1: Why is supercritical CO2 extraction better than steam distillation for clove essential oil?
A1: Supercritical CO2 extraction operates at lower temperatures, preserves heat-sensitive compounds like eugenol, provides higher yield, and avoids solvent residues.
Q2: What role does the uniform design method play in extraction optimization?
A2: The uniform design method helps efficiently determine optimal operating parameters with fewer experiments, ensuring reliable results.
Q3: Can this method be scaled up for industrial production?
A3: Yes, the optimized supercritical CO2 extraction process is highly scalable and eco-friendly, making it suitable for industrial applications in pharmaceuticals, food, and cosmetics.
Q4: What is the typical yield of clove essential oil under optimized conditions?
A4: The optimized yield reached about 12.3%, significantly higher than yields obtained through traditional steam distillation.
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