Herbal extracts are products formed by taking plants as raw materials, according to the needs of the use of the extracted end products, through physical and chemical extraction and separation processes, directed to obtain and concentrate one or more active ingredients in plants without changing the structure of their active ingredients, which can be used in medicine, food, health care products, cosmetics, and other industries. At present, the commonly used methods for extracting plant extracts include solvent extraction, ultrasonic extraction, microwave extraction, enzyme extraction, and supercritical fluid extraction.
1. Solvent extraction method
Solvent extraction method is to extract the active ingredients from solid raw materials with solvents, the solvent used must be compatible with the solute extracted. The plant material is crushed, put into a suitable container, add several solvents, and extracted by maceration, percolation, decoction, reflux and continuous extraction. During solvent extraction, solvent concentration, solid-liquid ratio, extraction temperature and extraction time will directly affect the extraction rate of active ingredients.
2. Ultrasonic extraction method
Ultrasonic extraction is the use of ultrasound generated by strong vibration and cavitation chemical effect (cavitation effect refers to the existence of micro-gas nuclei in the liquid cavitation bubble vibration under the action of sound waves, when the sound pressure reaches a certain value of the growth and collapse of the kinetic process that occurs), to accelerate the release of substances within the plant cells to the solvent, diffusion and dissolution, while maintaining the structure of extracted substances and biological activity is unchanged. The principle of ultrasonic extraction is mainly a physical process, and it is a relatively new extraction method that has gradually gained importance in recent years. Compared with the conventional solvent extraction method, the ultrasonic extraction method can greatly shorten the extraction time, consume less solvent, and have high leaching rate with high extraction efficiency. In the ultrasonic extraction process, the choice and concentration of solvent, solid-liquid ratio, extraction temperature and extraction time will directly affect the extraction rate.
3. Microwave Assisted Extraction method
Microwave-assisted extraction is a new technology that uses microwave energy to improve extraction efficiency. Microwave-assisted extraction is a method of selectively extracting target components from materials using microwave heating properties. By adjusting the microwave parameters, the target components can be effectively heated, which is conducive to the extraction and separation of the target components. The principle of microwave-assisted extraction of plants is that the plant sample absorbs a large amount of energy in the microwave field, while the surrounding solvent absorbs less, resulting in the generation of thermal stress within the cell. The plant cells are broken due to the thermal stress generated within the cells so that the substances within the cells come into direct contact with the relatively cooler extraction solvent, thereby accelerating the transfer of the target product from the cells to the extraction solvent and thus enhancing the extraction process. In principle, microwave-assisted extraction also uses thermal energy such as immersion and filtration, but extracts plant extracts much faster than traditional methods, reducing extraction time and avoiding the destruction and degradation of valuable plant extracts.
Currently, microwave-assisted extraction has become a powerful tool for extracting active ingredients from natural plants due to its fast extraction speed and good extraction quality. However, microwave-assisted extraction is selective internal heating, which requires the treated material to have good water absorption, in other words, the product to be separated is located in a position where it is easy to absorb water, otherwise, it is difficult for the cells to absorb enough microwaves and break themselves, and it is difficult for the product to be released quickly. For liquid extraction system, the solvent is required to be polar, the non-polar solvent is not sensitive to microwave.
4. Enzyme Extraction
The cell wall of natural plants consists of cellulose, in which the active ingredients of the plant are often encased in the cell wall. Enzymatic extraction is a method that uses cellulases, pectinases, proteases, etc. (mainly cellulases) to destroy the cell wall of the plant, thereby facilitating the dissolution and separation of the active ingredients of the plant to a greater extent. In the enzymatic extraction process, the choice of enzyme, enzyme concentration, pH, enzymatic temperature and enzymatic time all affect the extraction rate of plant extracts.
5. Supercritical Fluid Extraction
Supercritical fluid extraction (SFE) is a relatively new extraction and separation technique, generally using CO2 as the extractant. The principle of supercritical fluid extraction (SFE) is to make use of the special solubility of supercritical fluids and the sensitivity of the solubility of substances in supercritical fluids to changes in pressure and temperature to separate the dissolved substances in supercritical fluids by raising the temperature and lowering the pressure (or both), so as to achieve the purpose of separation and purification.SFE has the functions of both distillation and extraction, and has the function that the active ingredients are not easy to be inactivated, SFE has both functions of distillation and extraction, with the advantages that the active ingredients are not easily deactivated, the product quality is high, and the extraction and separation process is completed simultaneously. It is regarded as a green high-tech separation technology, especially suitable for unstable conditions.
