The classical techniques for the solvent extraction of materials from vegetable sources are based upon the correct choice of solvent coupled with the use of heat and/or agitation.
The extraction of organic compounds contained within the body of plants and seeds by a solvent are significantly improved by the use of power ultrasound.
The mechanical effects of ultrasound provide a greater penetration of solvent into cellular materials and improve mass transfer.
There is an additional benefit for the use of power ultrasound in extractive processes which results from the disruption of biological cell walls to facilitate the release of contents.
This has been shown in a study of the rate of ultrasonic extraction of sugar from sugar beet.
Combined with this effect is enhanced mass transfer, due to the effects of microstreaming which results in a more efficient method for sugar extraction.
Ultrasonically assisted extraction can also be applied to the production of medicinal compounds such as helicid, berberine hydrochloride and bergenin from Chinese plants (Fig. 2).
In some cases sonication increased the efficiency of extraction at lower temperatures producing a purer product in a shorter time.
Thus helicid, which is normally extracted by refluxing in ethanol, can be obtained in a 50% higher yield in half the extraction time at room temperature using ultrasound.
Once again efficient cell disruption and effective mass transfer are cited as the major factors leading to this enhancement.