A 2009 study in the journal Molecules tested the efficacy of conventional extraction techniques and methods in deriving antioxidants from various medicinal plants, including four solvents: absolute ethanol, absolute methanol, aqueous ethanol (80:20), and aqueous methanol (80:20).  The four solvents were coupled with two techniques utilized by researchers, shaking and refluxing.
They extracted leaves and roots of Moringa oleifera (horseradish); bark of Azadirachta indica (neem), Terminalia arjuna (arjuna), Acacia nilotica (gum arabic), Eugenia jambolana (black plum); fruit from Ficus religiosa (Bodhi tree); and leaves of Aloe barbadensis (aloe vera). Ground, air-dried plant material was extracted for six hours at room temperature using either an orbital shaker or reflux with a water bath. Extracts were filtered and residues extracted twice. The researchers used a rotary evaporator with reduced pressure at 45°C to remove solvent from extracts. Various tests were then performed to analyze total phenolic content, total flavonoid content, reducing power, free radical scavenging activity, and antioxidant activity.
The study concluded that higher “phenolic contents and plant material antioxidant properties were obtained using aqueous organic solvents, as compared to the respective absolute organic solvents.” Yields were also higher with the aqueous solvents as well as reflux extraction. That said, shaking was more effective in producing an end product with phenolic content and antioxidant activity. The higher temperature of reflux extraction may have degraded these compounds.
“The results of the present investigation revealed that aqueous solvent (80% methanol, 80% ethanol) extracts of plant materials, prepared by both the shaker and reflux extraction techniques, exhibited better antioxidant activities and higher phenolic contents,” the study concluded. Care must be taken, however, that higher temperatures involved in certain extraction techniques do not reduce the amount of valuable phenols and flavonoids.
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- Sultana B, Anwar F, Ashraf M. Effect of extraction solvent/technique on the antioxidant activity of selected medicinal plant extracts. Molecules. 2009;1(6):2167-2180. https://doi.org/10.3390/molecules1406. [Impact Factor: 3.267; Times Cited: 729 (Semantic Scholar)]