Elemental composition and nutritional value of the edible fruits of coastal red milkwood (Mimusops caffra) and Transvaal red milkwood (Mimusops zeyheri) and the impact of soil quality.

Abstract

Mimusops caffra and Mimusops zeyheri, both of the plant family Sapotaceae are indigenous plant species that grow widely in most parts of South Africa and the edible fruits of these species are picked and eaten raw in rural communities across South Africa. This is done to help overcome the challenge of dietary diversity especially in these resource-limited communities where diets are based on starch staples that lack fruit and vegetables. Despite the dependence on these fruit for food and nutrition security, information on their nutritional value is lacking. The aim of this research was therefore to analytically investigate the elemental distribution of essential and toxic elements in the two edible fruits and corresponding growth soil using Inductively Coupled Plasma- Mass Spectrometry (ICP-MS). The nutritional value of the fruits was assessed to evaluate the plants potential as a source of nutrients and the impact of soil quality on elemental uptake was evaluated to determine the plants potential to accumulate toxic metals. The elemental analysis showed concentration of the elements in M. caffra fruit to be (in descending order): K > Na> Ca > Mg > Si > Al > Fe > Zn > Mn > Ni > Cr > Cu > Pb > Mo > Sb > As > Se > V > Cd > Co whilst for M. zeyheri fruit it was (in descending order): K > Na> Ca > Mg > Fe > Al > Zn > Mn > Cu > Cr > Sr > Pb > As > Li > Ni ≈ Co > Rb > U > Bi > Ga > Be > Tl > Mo > Ba > Ag > Cd. The concentration of most essential elements in both fruits was found to be within acceptable limits. M. caffra fruits were found to be rich in Fe, Si and Cr and M. zeyheri fruits were found to be rich in Cr and Mn. Analysis of soil and plant showed that M. caffra and M. zeyheri do not tend to accumulate toxic elements and would therefore be safe for human consumption. Statistical analyses showed that contamination in soil by the various heavy metals came from various sources however soil contamination did not affect the concentration of heavy metals in the fruits thereby indicating the plants ability to take up metals to meet metabolic needs and exclude metals, if at elevated levels, for survival.