Microwave - assisted Extraction of Effective Components from Traditional Chinese Medicine
In the microwave-assisted extraction process, the thermal and non-thermal effects of microwaves work together. As for which effect predominates, it may be related to many factors, especially the type of extractant.
Generally speaking, when the extracting agent is a non-polar substance, since the extracting agent is transparent to the microwave, most of the microwave is absorbed by the material, and the intracellular material is rapidly heated and broken, which is beneficial to the microwave thermal effect.
On the contrary, if the extractant is a strong polar substance, because the extractant strongly absorbs the microwave, only part of the microwave energy can reach the material, and the extractant and the material are simultaneously heated. This is not conducive to the function of microwave breaking, and the non-thermal effect may dominate. status.
Compared with traditional extraction methods, microwave extraction has the following characteristics:
(1)High quality, can effectively protect functional ingredients, and is beneficial for extracting heat-labile substances;
(3)High selectivity to the extract, thereby improving product purity and improving product quality;
(5)Less solvent l can be 50% to 90% less than conventional methods, thereby reducing the amount of pollutants, improving environmental conditions and reducing investment;
(6)Low energy consumption and labor consumption;
(7)Microwave-assisted extraction can extract or separate the required components by using two kinds of upper extractants in the same device, thereby reducing the process cost;
(8)It is not necessary to perform pretreatment such as drying as in other methods, simplifying the process and reducing investment.
In the microwave extraction, the choice of extraction solvent has a great influence on the extraction results, which has been proved by many studies.
Solvents reported for microwave extraction are: methanol, ethanol, isopropanol, acetone, acetic acid, toluene, dichloromethane, tetrachloromethane, hexane, isooctane, 2,2,4-trimethylpentane An organic solvent such as an alkane, tetramethylammonium, petroleum ether or cyclohexane; and an inorganic reagent such as nitric acid, hydrochloric acid, hydrofluoric acid or phosphoric acid; and a mixed solvent of hexane-acetone, dichloromethane-methanol, and water toluene.
The following points should be considered when selecting an extractant:
(1)According to the principle of similar compatibility, the extractant is selected, that is, the extractant has strong solvency for the Japanese standard component. Therefore, the polar solvent is selected as the polar solvent, and the non-polar material is generally selected as the non-polar solvent. For example, a substance having a small polarity such as an essential oil is generally selected as a solvent having a small polarity such as bad hexane.
(2)A medium that is transparent or partially transparent to microwaves should be selected as an extractant, that is, a solvent having a small dielectric constant is selected. In this way, the microwave can freely pass through the solvent and directly reach the vascular bundles and gland cells of the plant, and the water in the material is partially in the vascular tube and the gland cells, so the intracellular temperature rises rapidly. The lyophilized network is transparent or translucent to microwaves, and the temperature is low. Therefore, the continuous high temperature causes the intracellular pressure to exceed the cell wall swelling ability, causing the cells to rupture, the cells in the cells to flow freely, and the transfer to the solvent to be dissolved.
(3)The selected extractant should interfere less with subsequent operations of the extracted components.
Water is a substance with a large dielectric constant, which can effectively absorb microwave energy and convert it into heat energy. Therefore, the amount of water in the plant material has a great influence on the extraction rate. In addition, the amount of water content also has a great influence on the extraction time. In this case, for the microwave extraction of moisture-free dry materials, a rewet method should be adopted to contain suitable moisture to change the dielectric properties of the materials. Material humidity has a large impact on extraction efficiency.
The time of microwave extraction is generally within 30s to 2Omin, and the optimum extraction time is different for different substances. However, the continuous microwave irradiation during the leather extraction process should not be too long, otherwise it will cause the solvent to boil, which not only causes great waste of the solvent, but also takes away the target product and reduces the yield.
Microwave heating is very fast, so microwave extraction is difficult to control at a fixed temperature. In practice, it should be controlled as much as possible below the boiling point of the solvent.
In general, the extraction rate increases with the extension of the extraction time. However, when the extraction time reaches a certain value, the extraction time is extended, and the extraction rate increases little and is negligible.
The tendency for the extraction rate to increase with increasing temperature is also only in the not too high temperature range. Therefore, during the extraction process; delayed extraction is necessary.
In the microwave-assisted extraction process, the microwave power generally selected is 200-1000W. The required microwave dose should be determined by extracting the target component most effectively. Excessive power not only increases energy consumption, but also causes unfavorable factors such as solvent boiling.
Factors such as pH and material size also have different effects on extraction efficiency and solvent recovery. The selection of optimal conditions should be different depending on the materials being processed.
Microwave-assisted extraction of plant essential oils
Microwave assisted extraction of polysaccharides
Microwave assisted extraction of flavon
Microwave assisted extraction of alkaloids
Microwave-assisted extraction of saponins
Microwave-assisted extraction of other traditional Chinese medicine ingredients