Assessing African medicinal plants for efficacy and safety: agricultural and storage practices

The paper reviews an important but little researched area of ethnopharmacology, namely, the effect of cultivation and post-harvest storage practices on levels of biological activity in traditionally used medicinal plants. Changes in COX-1 inhibition and antibacterial activity, for example, occur at the onset of senescence and, in some species, are influenced by plant age. Plants in cultivation were also shown to have reduced anthelmintic and antibacterial activity while hypoxoside production was affected by nitrogen and phosphorous. Irrigation treatments, however, increased anthelmintic activity and, therefore, could be applied to medicinal plants cultivated in low rainfall areas. Pesticides have also been implicated in the regulation of plant growth and secondary metabolite production in cultivated medicinal plants, but residue levels have, so far, not been monitored. Post harvest storage of medicinal plants has been poorly researched in southern Africa. Available data indicates that antibacterial and anti-inflammatory activity changes following storage and is both species and temperature dependent. Similar trends were noted for materials that had been rapidly aged. Fatty acids with antibacterial activity are stable in dry specimens and, as such, may account for the fact that activity is unaffected by storage in certain instances.