The biological source of curcumin is the rhizome of Curcuma longa, belonging to the family Zingiberaceae. The plant is extensively cultivated in the temperate regions of India, China, Pakistan and Malaysia.
The active ingredient curcumin is known for its active properties which are used for medical, pharmacological, biological, food, and cosmetic purposes. While Curcuma longa is the most prominent variety, other varieties such as C.alismatifolia, C.amarissima, C.cesia, and C.prakasha are also known to have curcumin.
Curcumin is also known as diferuloylmethane. The other secondary components in the plant source include curcuminoids, diarylheptanoid curcuminoids, bisdemethoxycurcumin, and demethoxycurcumin.
Structure of Curcumin
Extraction of Curcumin
Both traditional and modern techniques are used for the isolation of curcumin. However, due to the drawbacks of traditional methods, modern techniques are becoming more popular these days. Still, the conventional methods of isolation of curcumin are prevalent.
The conventional methods include soxhlet extraction, maceration, steam distillation, and liquid-liquid extraction.
Modern techniques include ultrasound-assisted extraction (UAE), microwave-assisted extraction, supercritical fluid extraction, ionic liquid-based extraction, supercritical carbon dioxide-aided extraction, pressurized liquid extraction, and ultrasonic extraction.
Since many of these extraction methods require a large volume of solvent, ionic liquids have been popularly used. Ionic liquids are considered eco-friendly, produce higher efficacy in the extraction process, and have higher stability at different temperature ranges. It is suitable to be used for various extraction techniques as well.
Conventional Methods of Extraction of Curcumin
The objectives of extraction methods are to
- Recover active compounds from the plant materials
- Increase the selectivity of the extraction method
- Improve the efficiency of the extraction
- Provide a stable and reproducible method
Based on these, these three conventional methods are used for curcumin isolation.
- The first method is Soxhlet extraction using alcohol. The alcoholic extract of powdered turmeric is concentrated and dried.
- The second method is hexane extraction followed by acetone extraction. Later the acetone extract is concentrated and dried to get curcumin.
- In the third method, the extract is taken in hot ethanol and the filtrate is concentrated. This concentrate is passed through kerosene to get a solid mass. This solid mass is treated with petroleum ether to separate from ethanol and the resultant product is re-crystallized curcumin. Curcumin will appear as orange-colored needles.
Although these methods are simple, they are non-selective and require higher temperatures. This temperature often causes the degradation of heat-sensitive compounds, thus the need for modern extraction techniques.
Modern Extraction Methods of Curcumin
The novel methods of curcumin isolation are as follows.
Ultrasound-assisted Extraction (UAE)
The UAE method uses ultrasonic waves that exert a force on the plant material. This force is converted into heat that acts as activation energy to promote diffusion of the active compounds into the solvent. The solvent used here is ethanol and the temperature is set at 35 °C. It takes about 1 hr for the process to complete at 250W ultrasonic power and a frequency of 22kHz.
Microwave-assisted Extraction (MAE)
Here, microwave energy is used to induce the transfer of compounds into the solvent. It uses less energy, time and solvent when compared to other methods but produces a higher yield.
Enzyme-assisted Extraction (EAE)
Enzymes such as α-amylase, amyloglucosidase, and glucoamylase are used here to break the plant cell walls and extract curcumin. This is a more cost-effective and eco-friendly approach. However, factors such as temperature, time, pH and enzyme concentration, pH, temperature and time are crucial for the success of this extraction method.
For example, 3% α-amylase at a pH value of 5 for 5 hrs of incubation, and 2% of glucoamylase at a pH of 4.5 with 5 hr of incubation and a later 8 h extraction with acetone for isolation of curcumin.
Pressurized Liquid Extraction (PLE)
The PLE method uses high temperature and pressure to increase the solubility and transfer of the active ingredients. The method is called subcritical water extraction (SWE) when the solvent used is water. Sometimes, co-solvents such as salts or other buffers are used to increase the efficiency.
Supercritical Fluid Extraction (SFE)
This type of extraction uses supercritical fluids such as carbon dioxide for the extraction. This is the most commonly used non-conventional extraction method. This method is more suitable for thermally unstable compounds.
For the isolation of curcumin, the addition of co-solvents such as ethanol and methanol is used. Sometimes, a combination of SFE followed by PLE is also used to get maximum curcumin from the plant materials.
Ionic Liquids-based Extraction
Ionic fluids are solvents that have good thermal stability, low volatility, and tunable viscosity. They can preserve the biological activities of the compounds. These are often used with other solvents and used for other extraction methods such as UAE, EAE and MAE. Depending on the extraction method used, the ionic liquid will be different. These liquids promote quick dissolution of curcumin and are highly sustainable options.
Isolation of Curcumin
The extracted crude curcumin is later subjected to various processes to isolate the curcumin. Depending on various factors, different methods such as column chromatography, preparative supercritical fluid chromatography, semi-preparative high-performance liquid chromatography, high-speed counter-current chromatography, and crystallization are used.
Column chromatography is used for the initial separation stage. The semi-preparative high performance chromatography or SPHPLC is highly expensive but efficient and popular.
References
- Shah, Biren N, Avinash Seth. (2010). Textbook of Pharmacognosy and Phytochemistry. Elsevier.
- Jiang, T., Ghosh, R., & Charcosset, C. (2021). Extraction, purification and applications of curcumin from plant materials-A comprehensive review. Trends in Food Science & Technology, 112, 419-430. https://doi.org/10.1016/j.tifs.2021.04.015
- https://pubs.acs.org/doi/10.1021/acsomega.3c04205#
