Antioxidant and acetylcholinesterase-inhibitory properties of long-term stored medicinal plants

Abstract

Background: Medicinal plants are possible sources for future novel antioxidant compounds in food and pharmaceutical formulations. Recent attention on medicinal plants emanates from their long historical utilisation in folk medicine as well as their prophylactic properties. However, there is a dearth of scientific data on the efficacy and stability of the bioactive chemical constituents in medicinal plants after prolonged storage. This is a frequent problem in African Traditional Medicine.Methods: The phytochemical, antioxidant and acetylcholinesterase-inhibitory properties of 21 medicinal plants were evaluated after long-term storage of 12 or 16 years using standardin vitromethods in comparison to freshly harvested materials.Results: The total phenolic content ofArtemisia afra,Clausena anisata,Cussonia spicata,Leonotis intermediaandSpirostachys africanawere significantly higher in stored compared to fresh materials. The flavonoid content were also significantly higher in storedA. afra,C. anisata,C. spicata,L. intermedia,Olea europeaandTetradenia ripariamaterials. With the exception ofEkebergia capensisandL. intermedia, there were no significant differences between the antioxidant activities of stored and fresh plant materials as measured in theβ-carotene-linoleic acid model system. Similarly, the EC₅₀values based on the 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging assay were generally lower for stored than fresh material. Percentage inhibition of acetylcholinesterase was generally similar for both stored and fresh plant material. Stored plant material ofTetradenia ripariaandTrichilia dregeanaexhibited significantly higher AChE inhibition than the fresh material.Conclusions: The current study presents evidence that medicinal plants can retain their biological activity after prolonged storage under dark conditions at room temperature. The high antioxidant activities of stable bioactive compounds in these medicinal plants offer interesting prospects for the identification of novel principles for application in food and pharmaceutical formulations.