The reported extraction methods of Fennel Oil include steam distillation (HD), microwave-assisted extraction (MAE), simultaneous distillation extraction (SDE) and supercritical CO2 fluid extraction (SFE-CO2).
1. Steam distillation (HD)
HD is the most commonly used method for separating volatile oil from plant samples. There have been many reports on the extraction of cumin oil by this method. This method is easy to operate and requires less equipment. However, it consumes a lot of energy, and due to the large water consumption, the volatile oil has different degrees of dissolution loss. In addition, due to the long heating time, the thermally unstable components in the volatile oil are prone to chemical reactions, so the aroma of the obtained volatile oil is not good.
2. Microwave Assisted Extraction (MAE)
Using absolute ethanol as the extractant, the volatile oil of fennel was extracted by MAE method. In fact, what is obtained by this method is the extract of cumin oil, not the volatile oil in the true sense. In order to obtain the volatile oil, the extract must be steam-distilled to separate the volatile oil from other non-volatile fat-soluble components in the extract. This method needs to deal with a large amount of organic solvent, and there is the problem of organic solvent residue, so it is rarely used at present.
3. Simultaneous Distillation Extraction (SDE)
SDE is a common method for extracting Fennel Oil, which is an extraction method that performs two steps of steam distillation and organic solvent extraction simultaneously. The SDE method realizes the extraction of volatile oil at one time through multiple and large-area contact between the water vapor phase and the organic solvent phase, and avoids the adsorption loss on the wall of the vessel and the operation of transferring a small amount of volatile oil when the steam distillation method is used to extract the volatile oil difficulty. It not only achieves high-efficiency extraction of volatile oil, but also reduces the possibility of a large amount of organic solvent remaining in the volatile oil, which is a great improvement on the extraction of volatile oil by steam distillation. This method is considered to have a high recovery rate for various compounds, and it is currently the most widely used sample preparation method for the analysis of plant aroma components. In domestic and foreign research, this method has been widely used in the extraction of aroma substances, and extensive research has also been done in the extraction of volatile oils from plants.
4. Supercritical CO2 Fluid Extraction (SFE-CO2)
SFE-CO2 uses higher than the critical temperature and critical pressure to avoid the decomposition of heat-sensitive components in the steam distillation process, and the possible loss of components caused by hydrolysis and water solubilization. This method has no solvent residue, will not cause environmental pollution, and the extracted product has good aroma quality. Compared with organic solvent extraction, it has the advantages of high selectivity and adjustable solvency. Specific operation: Put an appropriate amount of fennel powder in the extraction tank, and then open the supply valve of the CO2 tank. After the CO2 is compressed to the ideal pressure by the compressor, it is heated to make the system in a supercritical state, and flows through the extraction tank from bottom to top. The volatile oils are extracted along with other lipophilic components. The obtained extract is decompressed and then flows through two separators in sequence to obtain macromolecular substances such as resin and pigment in the primary separator, and to obtain cumin oil in the secondary separator. CO2 is vented in gaseous form or compressed and then recycled.