Storage of frequently used traditional South African medicinal plants.
The post-harvest physiology of nine frequently used indigenous southern African medicinal plants was investigated, in particular the effects of storage time and accelerated ageing on the biological activity and chemical constituents of these plants. Water, ethanol and hexane extracts of fresh plant material as well as material that had been stored in dry form in paper bags at room temperature for 90 days (short-term) were tested. Three bioassays, the COX-1 anti-inflammatory assay, nematode anthelmintic assay and minimum inhibitory concentration anti-bacterial assay, were used to determine biological activity. Thin layer chromatography of all the plant extracts were used to determine changes in chemical composition. The plants tested were Alepidea amatymbica Eckl. & Zeyh., Leonotis leonurus (L.) R. Br., Drimia robusta Bak., Vernonia colorata (Willd.) Drake, Scilla natalensis Planch., Eucomis autumnalis (Mill.) Chitt. subsp. autumnalis, Bowiea volubilis Harv. ex Hook. f., Helichrysum cymosum (L.) D. Don and Siphonochilus aethiopicus (Schweinf.) B. L. Burtt. Only those plants, which are known to exhibit a particular biological activity either traditionally or scientifically, were tested in the relevant bioassays. Of the plant extracts tested for anthelmintic activity only the water extracts showed activity and very little change in activity was observed after storage. Of the plant extracts tested for anti-inflammatory activity the ethanol extracts generally yielded highest activity. S. natalensis and B. volubilis both showed an increase in cyclooxygenase inhibition (anti-inflammatory) activity after storage whereas S. aethiopicus, H. cymosum, D. robusta and V. colorata showed a loss in activity after storage. The anti-inflammatory activity of E. autumnalis did not change. The water extracts of plants tested for antibacterial activity showed no activity, whereas the ethanol extracts generally showed an increase in activity. The TLC fingerprints indicated that there was chemical break-down during storage in certain species. These corresponded to the changes in biological activity. Alepidea amatymbica, Eucomis autumnalis, Helichrysum cymosum, Leonotis leonurus, Siphonochilus aethiopicus and Vernonia colorata were investigated further as to the effect of one year's storage (long-term storage) on their chemical composition and biological activity. Similar trends to that of the 90-day storage were observed. Activity gained in plants that were stored for 90 days was retained after a year of storage. Elevated temperature and humidity (55 C and 100% relative humidity) were used to accelerate the ageing process of Alepidea amatymbica, Leonotis leonurus and Vernonia colorata plant material. Again changes in the chemical composition and biological activity were observed, and the extent of these changes was greater than those in the stored material. The compounds responsible for the cyclooxygenase inhibition in the ethanolic extracts of Alepidea amatymbica leaf material appear to be stable and were not affected by the conditions of the accelerated ageing procedure (55 C and 100% humidity for seven days), but the root material lost activity, as did the leaf material of Leonotis leonurus. The leaf material of Vernonia colorata showed a slight (8%) increase in cyclooxygenase inhibition activity. The response of the plant material to accelerated ageing with respect to antibacterial activity varied with plant species. Alepidea amatymbica root material and Vernonia colorata leaf material appear to be stable whereas the other plant materials lost activity after prolonged (25 days) ageing.
- Masters Degrees (Botany) 
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