Phytochemical and elemental studies of two indigenous medicinal plants of South Africa, Bridelia micrantha and Sideroxylon inerme.

Abstract

Bridelia micrantha (Euphorbaceae) and Sideroxylon inerme (Sapoacaea) are two indigenous medicinal plants found in KwaZulu-Natal and are both known as ‘uMhlalamagwababa’ in isiZulu. These two plants species have similar physical properties, they both contain black, berry-like edible fruits and they both produce milk sap. This similarity has led to them being confused for one species so they are both used by traditional healers to treat a variety of the same illnesses. Different parts of B. micrantha and S. inerme are used traditionally to treat a variety of ailments; the bark is used to treat burns, wounds, venereal diseases, tapeworm and toothache. They are also used as anti-diarrhoeal and anti-bacterial agents. The main aim of this study was to isolate, characterise and identify the phytocompounds in the leaves, stem bark, roots and fruits of the two plant species, B. micrantha and S. inerme, to evaluate if they can be used interchangeably in traditional medicine. The isolated compounds were also assessed for their antioxidant activity to determine the plants potential as natural antioxidants. The impact of soil quality parameters on elemental uptake of the wild fruits of B. micrantha from eight different geographic locations in KZN as well as the nutritional value of the edible fruits was also determined to evaluate the plants potential as a nutraceutical. The phytochemical investigation of S. inerme revealed the presence of three pentacyclic triterpenes (friedelin, stigmasterol and a mixture of α and β –amyrin), one carotenoid (lutein) and one megastigmane (apocynol B). Two flavonoids (quercetin and quercetin-3-O-glucoside) and two triterpenes (oleanolic acid and acacic acid lactone) were isolated from B. micrantha. The free radical scavenging activity of the extracts and selected phytocompounds was determined by the DPPH (2,2-diphenyl-1-picrylhydrazyl) assay. The antioxidant activity for both plants was good but that of B. micrantha was better than that of S. inerme. The concentrations of elements in the fruits were found to be in decreasing order of Mg > Ca > Mn > Zn ≈ Fe > Cu > Co > Ni > Cr > Pb > As ≈ Cd. It was also found that 100 g of the fruit contained about 90.1% moisture, 3.2% ash, 4.1% proteins, 0.9% oil and 1.7% carbohydrates. This study shows that the fruits of B. micrantha are a good source of essential elements and have low levels of the toxic metals investigated. The classes of compounds isolated from B. micrantha and S. inerme validate the ethnomedicinal use of these plant species in traditional medicine however, since the isolated compounds from each species were different it can be concluded that they cannot be used interchangeably for their medicinal benefit. The results obtained from this study provide baseline information on the plants’ potential as a source of medicine and also revealed the nutritional benefits of consuming the edible wild fruits of B. micrantha.