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.
Vegetable glycerine is an ideal extraction solvent due to its non-toxic, non-irritating properties and its ability to preserve the stability and potency of sensitive bioactive compounds. Both, pure glycerine and glycerine-water mixtures, are useful solvents for the production of extracts for supplements and nutraceuticals, flavor extracts, food additives and cosmetics.
UIP2000hdT sonicator for botanical extraction in large batches or inline operation
The following table lists several solvents, which are well established extraction solvents and are used for the ultrasonic extraction from plant material.
| Ethanol | One of the most common solvents for botanical extraction. As a polar solvent, ethanol dissolves polar compounds such as alkaloids and flavonoids. |
| Water | The universal solvent, often used for extracting hydrophilic compounds like polysaccharides, proteins, and some glycosides. |
| Aqueous Ethanol | A mixture of ethanol and water, this solvent can extract a wide range of polar and moderately polar compounds, providing a balance between the solvent power of ethanol and the ability of water to extract hydrophilic compounds. Aqueous ethanol can be prepared at different ratios adjusting the dissolving capacity to target compounds. |
| Glycerine | A highly polar solvent that is useful for extracting polar compounds and can be a safer alternative to other polar solvents, often used in tinctures and extracts meant for internal consumption. Read more about extracting phytochemicals in glycerine using sonication! |
| Methanol | A highly polar solvent effective in extracting a wide range of plant compounds including phenolics, flavonoids, and some alkaloids. |
| Hexane | A non-polar solvent used primarily for extracting non-polar compounds such as lipids, waxes, and essential oils. |
| Acetone | A polar aprotic solvent, acetone is effective for extracting a wide range of botanical compounds, particularly those that are less polar than those extracted by water or methanol. |
| Isopropanol | A polar solvent similar to ethanol, commonly used for extracting essential oils, resins, and some alkaloids. |
| Chloroform | A non-polar solvent effective in extracting alkaloids, terpenoids, and some glycosides. It is less commonly used due to its toxicity. |
| Ethyl Acetate | A moderately polar solvent used for extracting a range of compounds including flavonoids, alkaloids, and phenolics. |
| Toluene | A non-polar solvent used for extracting non-polar compounds such as essential oils, terpenes, and waxes. |
| Butanol | A moderately polar solvent effective in extracting medium-polarity compounds including some glycosides and saponins. |
| Petroleum Ether | A non-polar solvent primarily used for extracting fats, oils, and other non-polar compounds from plant materials. |
Powerful ultrasound waves disrupt the cell matrix of biological structures and release the bioactive compounds. Mass transfer between the plant material and the solvent is intensified. Due to these mechanisms, ultrasonic extraction is highly efficient for botanical extraction.
UP400ST ultrasonic homogenizer for herbal extraction allows to use the solvent of your choice.
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 industrial sonicators 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 ultrasonicators 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.
What are Bioactive Compounds?
Bioactive compounds or phytochemicals 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.
How do I select the best Extraction Solvent?
The guidelines below help you to select a suitable solvent for ultrasonic botanical extraction. As sonication is compatible with any standard solvent, you can select the solvent most ideal for your plant raw material, the targeted phytochemicals and cost-efficiency.
- Selectivity: Select a solvent that specifically dissolves the desired compounds while leaving unwanted components behind. For instance, use ethanol for polar compounds like alkaloids and flavonoids.
- Solubility: Based on the principle “like dissolves like,” choose a solvent with a polarity similar to that of the solute. Polar solvents (e.g., water, ethanol) dissolve polar compounds, while non-polar solvents (e.g., hexane) dissolve non-polar compounds like lipids and oils.
- Cost: Consider the cost-effectiveness of the solvent. Some solvents might be more expensive but offer higher yields or better selectivity, balancing the overall extraction cost.
- Safety: Ensure the solvent is safe for use and handling. Factors include toxicity, flammability, and environmental impact. For example, water and ethanol are safer choices compared to chloroform or toluene.
Polarity and Solvent Selection
According to the law of similarity and intermiscibility, solvents with a polarity value near to the polarity of the solute are likely to perform better. Here are some examples:
- Polar Solvents: Water, Ethanol, Methanol – Used for extracting polar compounds such as alkaloids, flavonoids, glycosides, and proteins.
- Moderately Polar Solvents: Acetone, Ethyl Acetate, Isopropanol – Suitable for extracting a wide range of compounds, including phenolics and some alkaloids.
- Non-Polar Solvents: Hexane, Toluene, Petroleum Ether – Ideal for extracting non-polar compounds such as lipids, waxes, terpenes, and essential oils.
Examples of Solvent Use
- Ethanol: One of the most common solvents for botanical extraction. As a polar solvent, ethanol dissolves polar compounds such as alkaloids and flavonoids.
- Water: The universal solvent, often used for extracting hydrophilic compounds like polysaccharides, proteins, and some glycosides.
- Methanol: A highly polar solvent effective in extracting a wide range of plant compounds including phenolics, flavonoids, and some alkaloids.
- Hexane: A non-polar solvent used primarily for extracting non-polar compounds such as lipids, waxes, and essential oils.
- Acetone: A polar aprotic solvent, acetone is effective for extracting a wide range of botanical compounds, particularly those that are less polar than those extracted by water or methanol.
- Isopropanol: A polar solvent similar to ethanol, commonly used for extracting essential oils, resins, and some alkaloids.
- Chloroform: A non-polar solvent effective in extracting alkaloids, terpenoids, and some glycosides. It is less commonly used due to its toxicity.
- Ethyl Acetate: A moderately polar solvent used for extracting a range of compounds including flavonoids, alkaloids, and phenolics.
- Toluene: A non-polar solvent used for extracting non-polar compounds such as essential oils, terpenes, and waxes.
- Butanol: A moderately polar solvent effective in extracting medium-polarity compounds including some glycosides and saponins.
- Petroleum Ether: A non-polar solvent primarily used for extracting fats, oils, and other non-polar compounds from plant materials.
The following solvents were tested in research studies investigating ultrasonic extraction of specific plant materials and phytochemicals.
| 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 |
What are 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. Due to the powerful mechanism of ultrasonic extraction, the use of organic solvents can be avoided replacing them with milder, non-toxic solvents.
