Rosemary (Rosmarinus officinalis L.) is widely recognized as an important natural antioxidant source. Rosemary antioxidants, particularly carnosic acid and carnosol, show strong oxidative stability and are extensively applied in food, cosmetics, and pharmaceutical products. However, carnosic acid is chemically unstable and easily oxidized during conventional extraction processes. As a result, traditional solvent extraction often leads to low recovery and poor product stability.
Supercritical CO2 extraction offers several advantages for Rosemary processing. First, it operates under oxygen-free conditions, which effectively protects carnosic acid from oxidative degradation. Second, supercritical CO2 exhibits tunable solvating power, allowing selective extraction of Rosemary antioxidant compounds. In addition, CO2 is non-toxic, inexpensive, and easy to remove from the final Rosemary extract. Therefore, supercritical CO2 extraction is particularly suitable for producing natural Rosemary antioxidants with high purity and safety.
This study aims to optimize the supercritical CO2 extraction process for Rosemary residues. Orthogonal experiments and single-factor analyses were conducted to evaluate the effects of key process parameters. Special attention was given to the use of water as a co-solvent to improve Rosemary extract properties and industrial applicability.
1. Materials and Methods
1.1 Materials and Equipment
Rosemary residues were obtained after steam distillation for Rosemary essential oil. Supercritical CO2 extraction was performed using a system equipped with one extraction vessel and three separation vessels. Carbon dioxide (CO2), distilled water, and standard laboratory equipment were used throughout the experiments.
2. Orthogonal Experimental Design and Analysis
2.1 Extraction Procedure
The Rosemary residues were dried at 60℃ until the moisture content reached approximately 5–7%. After drying, the material was ground to 60–80 mesh and loaded into the extraction vessel. Supercritical CO2 extraction was then conducted, and Rosemary extracts were collected from three separation vessels. The total extraction yield was calculated based on the mass of Rosemary raw material.
The orthogonal design included three factors at three levels: pressure (20, 30, and 40 MPa), temperature (40, 60, and 80℃), and extraction time (2.0, 2.5, and 3.0 h).
2.2 Orthogonal Analysis Results
The results showed that Rosemary extraction yield increased with increasing pressure. Temperature also promoted yield, but its effect was less significant than that of pressure. In contrast, extraction time had a limited influence on Rosemary yield.
Statistical analysis confirmed that pressure was the most significant factor affecting Rosemary extraction efficiency. Temperature had a moderate effect, while time was not statistically significant. Therefore, within equipment safety limits, higher pressure and moderate temperature were beneficial for Rosemary antioxidant extraction.
Based on these results, 40 MPa, 80℃, and 2.5 h were selected as the optimal extraction conditions for further studies.
3. Effect of Water as a Co-Solvent
3.1 Single-Factor Experimental Design
Although the optimized parameters yielded high Rosemary antioxidant content, the extract appeared as a viscous paste with strong odor. This physical form limited industrial handling and application. Therefore, water was introduced as a co-solvent to modify extract properties.
Water was added at levels of 0%, 10%, and 20% (w/w) to the Rosemary raw material prior to extraction. All other extraction conditions remained constant.
3.2 Results and Discussion
The addition of water significantly affected Rosemary extract properties. Without water, the Rosemary extract remained paste-like with a strong odor. With increasing water content, the extract gradually transformed into a powder with a milder Rosemary aroma. Meanwhile, total Rosemary extraction yield increased from 5.5% to 7.2%.
This improvement can be explained by polarity modification. Supercritical CO2 is a weakly polar solvent, similar to n-hexane. Therefore, it preferentially extracts non-polar compounds. By adding water, the overall polarity of the extraction system increased, enhancing the solubility of polar Rosemary antioxidants such as carnosic acid and carnosol, while reducing resinous components.
4. Analysis of Carnosic Acid and Carnosol
The contents of carnosic acid and carnosol in Rosemary extracts were determined using HPLC analysis. The results showed that both higher pressure and water addition increased the concentrations of these antioxidant compounds.
Under optimal conditions with 20% water, carnosic acid reached 32%, while carnosol reached 8.1%. Therefore, water-assisted supercritical CO2 extraction significantly enhanced the antioxidant quality of Rosemary extracts.
5. Conclusion
Rosemary antioxidants are primarily composed of carnosic acid and carnosol, which directly determine the antioxidant performance of the final product. In this study, supercritical CO2 extraction was successfully applied to Rosemary residues to recover high-value antioxidants. The optimal conditions were identified as 40 MPa, 80℃, 2.5 h, with 20% water as a co-solvent.Under these conditions, the Rosemary extract exhibited high yield, high antioxidant content, powder-like physical form, and mild aroma. Therefore, supercritical CO2 extraction with water as a co-solvent is an efficient and industrially viable technology for producing natural Rosemary antioxidants.
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