Solvents for Ultrasonic Extraction from Plants
- Ultrasonic extraction features many advantages such as high yields, fast extraction rates, environmental-friendliness and low energy consumption.
- One of the strongest benefits is the use of water as extraction medium. However, sonication can be used with manifold solvent systems to deliver superior results for the targeted extract.
- The optimal solvent for ultrasonic extraction of vegetal bioactives is chosen in regards to the raw material.
Ultrasonic Extraction
Ultrasound is well known to disrupt cell structures and to improve mass transfer, thus increasing the extractability of biocompounds (e.g. phenolics, carotenoids).
Since the mechanical effects of sonication enhance the extraction process due to improved mass transfer greatly, the use of organic solvents is often superfluous. This means that for ultrasonic extraction, water is often a sufficient extraction medium which has many benefits such as being inexpensive, non-hazardous, easily available and environmental-friendly.
However, for specific bioactive compounds best results may be achieved by ultrasonic extraction in combination with a volatile solvent.
To choose the right solvent, the raw material (e.g. fresh or dried, macerated/grinded or powdered plant material) and the targeted substances (e.g. lipophilic, hydrophilic) must be considered.
The following table lists several solvents, which have been successfully tested for the ultrasonic extraction from plant material.
| Solvent | Plant | Kind of tissue |
|---|---|---|
| Acetic acid / urea / cetyltrim-ethylammonium bromide | rice | bran |
| Aqueous ethanol | distiller’s grain | grain |
| Aqueous isopropanol | soybean, rapeseed | seeds |
| Ethanol | Saccharina japonica | – |
| Glacial actic acid | sorghum | – |
| Phenol | tomato / potato / aloe vera / soybean | pollen / tuber / leaf / seed |
| Phenol/ammonium acetate | barley / banana | root / leaf |
| Phenol/ammonium acetate | avocado / tomato / orange / banana / pear / grape / apple / strawberry | fruits |
| Phenol/methanol-ammonium acetate | coniferous / banana / apple / potato | seed / fruits |
| Sodium dodecyl sulphate/acetone | coniferous / potato | seed / tuber |
| Sodium dodecyl sulphate/TCA/acetone | apple / banana | tissue |
| TCA | beans | anther |
| TCA/acetone | citrus / soybean / aloe vera | leafs |
| TCA/acetone | soybean / coniferous | seeds |
| TCA/acetone | tomato | pollen grain |
| TCA/acetone/phenol | olive / bamboo / grape / lemon | leafs |
| TCA/acetone/phenol | apple / orange / tomato | fruits |
| Thiourea/urea | soybean | seed |
| Thiourea/urea | apple / banana | tissues |
| Tris-HCL buffer | tomato | pollen grain |
Ultrasonic extraction from cells: the microscopic transverse section (TS) of apical stem of mint (Mentha piperita) shows the mechanism of actions during ultrasonic extraction from cells (magnification 2000x) [resource: Vilkhu et al. 2011]
Ultrasonicators for Extraction
From lab and bench-top ultrasonic devices up to full-industrial ultrasonic extraction systems – Hielscher Ultrasonics is you long-time experienced partner, when it comes to powerful and reliable ultrasonic devices for successful extraction processes.
Our ultrasonic systems are widely used in biochemical laboratories and pharmaceutical production plants. The ultrasonic sonotrodes and reactors are autoclavable and fulfil the standards of pharmaceutical production.
Hielscher’s ultrasonic extractors are available for any process scale – from lab to production.
Hielscher Ultrasonics’ industrial ultrasonic processors can deliver very high amplitudes in order to disrupt cell matrices and to release targeted substances. Amplitudes of up to 200µm can be easily continuously run in 24/7 operation. The power and robustness of Hielscher’s ultrasonic equipment ensure high yields, fast extraction rates and more complete extraction – excelling conventional extraction processes.
Our ultrasonic processors can be combined with conventional extraction methods such as Soxhlet extraction or supercritical CO2 extraction. Retrofitting into existing production lines can be easily accomplished.
Literature / References
- Dent M., Dragović-Uzelac V., Elez Garofulić I., Bosiljkov T., Ježek D., Brnčić M. (2015): Comparison of Conventional and Ultrasound Assisted Extraction Techniques on Mass Fraction of Phenolic Compounds from sage (Salvia officinalis L.). Chem. Biochem. Eng. Q. 29(3), 2015. 475–484.
- Petigny L., Périno-Issartier S., Wajsman J., Chemat F. (2013): Batch and Continuous Ultrasound Assisted Extraction of Boldo Leaves (Peumus boldus Mol.). International Journal of Molecular Science 14, 2013. 5750-5764.
- Dogan Kubra, P.K. Akman, F. Tornuk(2019): Improvement of Bioavailability of Sage and Mint by Ultrasonic Extraction. International Journal of Life Sciences and Biotechnology, 2019. 2(2): p.122- 135.
Facts Worth Knowing
Ultrasonic Extraction by Cavitation
Intense ultrasound waves generate acoustic cavitation in liquids. The cavitational shear forces breaks cell wall and membranes so that the intracellular material is released. Ultrasonic extraction achieves greater penetration of the solvent into a vegetal tissue and improves the mass transfer. Thereby, ultrasonic extraction intensifies the extraction process significantly resulting in higher yields, faster extraction rates and a more complete extraction.
Solvent Systems
For the extraction of bioactive compounds from vegetal material various solvent systems are available. For the extraction of hydrophilic compounds, mostly polar solvents such as methanol, ethanol or ethyl-acetate are chosen, whilst for the extraction of lipophilic compounds (e.g. lipids), solvent systems such as dichloromethane or dichloromethane/methanol (v/v 1:1) are preferred. Hexane is often used as solvent for chlorophyll extraction.
Organic Solvents
An organic solvent is a type of volatile organic compound (VOC). VOCs are organic chemicals which vaporise at room temperature.
Organic compounds used as solvents include:
- aromatic compounds, e.g. benzene and toluene
- alcohols, e.g. methanol
- esters and ethers
- ketones, e.g. acetone
- amines
- nitrated and halogenated hydrocarbons
Many organic solvents are classified as toxic or carcinogenic. In case of incorrect handling, they can be hazardous to humans and can contaminate air, water, and soil.
Bioactive Compounds
Bioactive compounds are defined as substances, which have impact on living organisms, tissues, or cells. Biologically active substances include antibiotics, enzymes, and vitamins. Bioactive substances such as carotenoids and polyphenols can be extracted e.g. from fruits, leafs and vegetables, whilst phytosterols are found in vegetal oils.
Plant-derived bioactive compounds include flavonoids, caffeine, carotenoids, choline, dithiolthiones, phytosterols, polysaccharides, phytoestrogens, glucosinolates, polyphenols, and anthocyanins. Many bioactive substances are valued for acting as antioxidants and are therefore considered as health beneficial.
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