Are long-term stored medicinal plants as active as the freshly harvested materials?

摘要

Medicinal plant materials are usually stored for a period of time by plant gatherers, traders or traditional healers before usage. Questions that frequently arise are: Do such plant materials retain their biological efficacy; Are they safe for consumption after a long period of storage In the present study, the iridoid and phenolic contents as well as the antioxidant and mutagenic properties of five South African medicinal plants stored for 16 years were compared to those of freshly harvested materials. The iridoid content of the freshly harvested materials of Ocotea bullata, Protorhus longifolia and Ziziphus mucronata were significantly higher when compared to the stored materials. Stored Acokanthera oppositifolia material had a significant higher iridoid content compared to the freshly harvested material. The total phenolic and flavonoid contents recorded in all freshly collected materials (except Artemisia afra) were significantly higher than the stored ones. With the exception of A. oppositifolia and P. longifolia, a significantly higher radical scavenging activity was observed in the stored compared to fresh materials. There was no significant difference in the antioxidant activity based on the β-carotene-linoleic acid model between the stored and fresh materials. Extract obtained from freshly harvested A. oppositifolia showed a mutagenic effect at 5 mg/ml against Salmonella typhimurium TA 1535 strain whereas no such effect was recorded in the stored material. There was no mutagenic effect detected in both the stored and fresh materials of other plant species. The results suggest that stored plant materials can still be biologically potent and possibly safe to use after prolonged storage. However, it would be prudent to study each plant individually, particularly those that may contain poisonous compounds.