Impact of Lubumbashi's solar irradiation and ambient air on the quality and pharmacological value of root barks from four of the most used medicinal plants

Abstract

BackgroundThe quality of medicinal plant products is highly dependent on drying conditions, which can lead to contaminated drugs, and/or with considerable phytochemical and pharmacological variations. In Lubumbashi (a very sunny city with polluted air), the used medicinal plants are exposed to the sun and ambient air for drying or on the sales premises, but the real impact of solar energy and ambient air on the quality and pharmacological value of exposed medicinal plant samples has never been studied. ObjectiveThis study seeks to determine the impact of solar irradiation and ambient air in Lubumbashi on the quality, and biological activities of samples from the most used medicinal plants in Lubumbashi/DR Congo. MethodsThe root barks of single-plant samples from Terminalia mollis M.A.Lawson, Securidaca longepedunculata Fresen, Oldfieldia dactylophylla (Welw. ex Oliv.) J.Léonard. and Phyllanthus muellerianus (Kuntze) Exell. were dried in the sun, oven, and shade respectively. Mineral and microbial contamination were assessed. In addition, phytochemical and pharmacological analyses were also done. ResultsSamples exposure to ambient air led to mineral contamination, with the appearance of highly toxic elements such as As, and a significant increase in others such as Al, Co, Cr, Cu, Ni, and Pb. Microbial contamination exceeded admissible limits in some samples and varied according to drying conditions and species, of which S. longepedunculata was the most contaminated. The levels of total phenols, flavonoids, and terpenoids varied significantly according to drying conditions and species. For example, in T. mollis, total phenols increased from 457.6 ± 2.33 to 536.4 ± 1.56 mg GAEq/g in fresh samples exposed to the sun for 10 days, total flavonoids increased from 455.2 ± 16.49 to 617.1 ± 14.29 mg QEq/g when dry samples were exposed to the sun for 10 days; total terpenoids decreased significantly compared to the shade-dried sample. Biological activity also varied according to species and experimental conditions. For example, an increase in activity against S. aureus (from 11.00 ± 1.00 to 17.33 ± 0.58 mm) was observed in the fresh sample of P. muellerianus exposed to sunlight for 10 days, while increases in hemozoin synthesis inhibitory (from 44.6 ± 3.9 to 52.7 ± 2.4 %) and antiradical activity (from 23.7 ± 0.7 to 29.5 ± 0.1 %) were observed in the fresh S. longepedunculata sample exposed to the sun for 5 days. ConclusionExposure of the studied medicinal plant samples to ambient air in the environmental conditions of Lubumbashi would result in worrying mineral contamination and drying of these samples in the sun in the above-mentioned region, in the oven, or the shade would result in variations, some of which are negative, in certain secondary metabolites and biological activities.