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Norwegian University of Life Sciences (2010)

Ecology, conservation and bioactivity of food and medicinal plants in East Africa

Stangeland, Torunn

Titre : Ecology, conservation and bioactivity of food and medicinal plants in East Africa

Auteur : Stangeland, Torunn

Université de soutenance : Norwegian University of Life Sciences, Ås

Grade : Doctoral thesis 2010

Résumé partiel
In East Africa 70-80 % of the population is subsistence farmers. The rural health system is often poorly equipped both with personnel and medicines, and many depend on the use of medicinal plants for their primary health care. Malaria is the single most serious cause of morbidity, mortality and poverty, partly because the parasite causing the disease, Plasmodium falciparum, has developed resistance towards the most common and affordable medicines, and the fact that a large part of the population is malnourished. In East Africa many plants are used in the treatment of malaria, but most of them are poorly investigated for effect and safety. Bark and roots of trees are often used for medicine, and some of the trees are locally threatened because of population increase and deforestation. Traditional medicine has received increased attention from governments in Tanzania and Uganda. In Tanzania laws and regulations on management of natural resources and traditional medicine, which are in line with the Convention on Biological Diversity, are now in place. However, important ecosystems for medicinal plants are heavily degraded. In Uganda laws and regulations for traditional medicine are now under debate in the government. Experiments on germination and seedling growth for two Ugandan medicinal trees, Mitragyna (Hallea) rubrostipulata and Sarcocephalus latifolius, was conducted in controlled environments. Both needed light to germinate, Mitragyna rubrostipulata had a temperature optimum at 25°C with 79 % germination, while germination for Sarcocephalus latifolius after 28 days was around 60 % for the temperatures 20-35°C. A germination field experiment failed, indicated that these species need assistance from nursery to be able to establish in degraded areas. The framework tree species method was chosen to conserve and gain more knowledge about local medicinal trees. In this method 25-40 different local woody species are raised in nursery and planted in a single event in a mixed stand. The intention is to encourage regeneration of degraded forest. We raised and planted 27 mainly indigenous woody species in three plots in April 2008, and monitored survival and growth for 13 months. Eleven species turned out to be excellent framework species, while eight others were acceptable. Some of the important medicinal trees we failed to cultivate, partly because they have become so rare that we did not find seeds. Total antioxidant activity (AOA) in 35 Ugandan fruits and vegetables were measured using the Ferro Reducing Ability of Plasma (FRAP) method. The results showed large variation in AOA from 72.5 ± 13.5 (Syzygium cuminii seeds) to 0.09 ± 0.05 (Curcubita maxima fruit) mmol/100 g fresh weight. Antioxidant activity per serving was calculated, and the food with heighest AOA per serving were pomegranat (Punica granatum), Canarium schweinfurthii, guava (Psidium guajava), mango (Mangifera indica) and tree tomato (Cyphomandra betacea) with values from 8.91 to 3.00 mmol/serving. AOA for Ugandan mango in this study was five times higher than values found in another study of mangoes bought in Norway. In Uganda the intake of antioxidants can be relative easily increased by adding more of the fruits that are abundant in the fruiting seasons and green leafy vegetables. Raw extracts from tree medicinal plants that are used to treat malaria in Uganda were tested for antioxidant (DPPH, FRAP, Total phenols) and anti-plasmodial activity. The water extract of Mitragyna rubrostipulata showed highest anti-plasmodial activity (IC50= 1.95 μg/ml), and high antioxidant activity as well. Thirteen other extracts showed high anti-plasmodial activity ranging from 2.12 to 3.63 μg/ml (chloroquine control : IC50= 8 μg/ml). There was high correlation between the different antioxidant assays.


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