Extraction is selective dissolution: a solvent is brought into contact with milled plant material and pulls out the constituents it has affinity for. The governing principle is “like dissolves like” — polar solvents extract polar compounds, non-polar solvents extract lipophilic ones, and mixtures span the middle. Choosing the solvent is, in effect, choosing the chemistry of your extract.
Polarity decides the profile
Botanical actives sit across a polarity spectrum. Sugars, many glycosides, tannins and some alkaloid salts are polar and water-loving. Aglycones, many flavonoids and moderately polar polyphenols favour ethanol or hydro-ethanolic blends. Essential oils, resins, carotenoids and lipophilic actives such as curcuminoids or boswellic acids need a less polar or non-polar solvent. Move the solvent along the polarity scale and the marker profile moves with it.
The main routes compared
| Solvent system | Polarity | Typically extracts | Yield character | Residual-solvent question |
|---|---|---|---|---|
| Water (aqueous / decoction) | Very polar | Polysaccharides, polar glycosides, tannins, water-soluble actives | Often high mass yield, lower selectivity | None — but microbial and endotoxin control matters |
| Hydro-ethanolic (e.g. 30–70% ethanol) | Tunable polar–mid | Broad polyphenols, flavonoids, many standardised actives | Balanced yield and selectivity; the common workhorse | Ethanol — Class 3, low-toxicity, generous ICH limit |
| Ethanol (high %) | Mid-polar | Aglycones, resins, less polar polyphenols | Lower mass yield, higher selectivity | Ethanol — Class 3 |
| Hydrocarbon / chlorinated (e.g. hexane, where permitted) | Non-polar | Oils, waxes, carotenoids, lipophilic actives | Selective for lipophilics; low polar carry-over | Class 2 solvents — tighter limits, must be quantified |
| Supercritical CO₂ | Tunable (non-polar to mid with co-solvent) | Volatiles, lipophilic actives, clean oleoresins | Selective, solvent-free product | None — CO₂ leaves no residue (co-solvent if used) |
Yield, selectivity and cost trade-offs
There is a constant tension between yield and selectivity. Water often gives a high mass yield but a diffuse profile — lots of material, less of it the target active. A more selective solvent or supercritical CO₂ yields less total mass but a cleaner, more concentrated marker profile. The downstream consequence: a high-yield, low-selectivity extract usually needs a higher dose or further purification to hit a specific marker claim, while a selective process front-loads cost but delivers a tighter, more standardisable product.
Process choices layer on top of solvent choice. Temperature and time affect both yield and the survival of heat-sensitive constituents; multiple extraction passes raise recovery; and the final drying or concentration step (covered in our format article) shapes what you actually receive.
What to ask a supplier
- 1Which solvent system was used, and at what ratio or condition (e.g. ethanol percentage, CO₂ with/without co-solvent)?
- 2How does that solvent map to the marker you are standardising — is the target active actually well-extracted by it?
- 3What is the residual-solvent result, against which ICH Q3C class limit, by what method?
- 4Is the extraction solvent stated on the specification and label as part of the product identity?
- 5If switching suppliers, does the new material use the same solvent system — or will the profile shift even at the same marker percentage?
Apply this to your sourcing
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