Elemental distribution in selected edible trifolium species (clover) and the impact of soil quality on the chemical characteristics of trifolium dubium

Abstract

Trifolium (clover) species are edible herbs that are rich in proteins, phytocompounds and essential macro and micro-nutrients. These herbaceous plants can therefore contribute significantly to the nutritional needs of people and can play a significant role in traditional medicine. With malnutrition becoming a growing problem amongst poverty-stricken communities in African countries where food is unaffordable, the use of Trifolium, a common perennial herb, can provide much needed nutrition and can ameliorate food insecurity. The bioactive phytocompounds in Trifolium species promote its use in traditional medicine as this is an affordable and, debatably, better form of treatment. South Africa has a rich diversity of Trifolium species, however there is little to no information regarding the nutritional value of these herbs and the uptake of toxic heavy metals which can cause adverse health effects if ingested. The main aim of this study was to evaluate the elemental distribution and nutritional value of five edible Trifolium species, namely Trifolium africanum, Trifolium burchellianum, Trifolium repens, Trifolium dubium and Trifolium pratense in KwaZulu-Natal, South Africa. The results obtained were used to assess the potential of these herbs to alleviate malnutrition in KwaZulu-Natal. The chemical composition of the five edible herbs was determined by analysing for proteins, lipids, dry ash and carbohydrates. T. dubium proved to accumulate the highest concentrations of toxic heavy metals (Cd and Pb), therefore the elemental distribution of essential and toxic metals in T. dubium were assessed for impact of soil quality on uptake by the plant by obtaining samples from ten different geographic locations in KwaZulu-Natal. Trifolium species investigated in this study were rich in essential nutrients with concentrations of elements varying significantly (p<0.05) and were found in decreasing order of Ca > Mg > Fe > Mn > Zn > Se > Cu > Cr > Pb > Ni > Co > Cd > As. The species had vi adequate levels of lipids (4.2 to 8.6%), proteins (35.1 to 45.4%) and carbohydrates (26.7 to 47.0%). The results obtained suggested that T. pratense was the most suitable species for human consumption due to it having undetectable levels of toxic metals (As, Cd and Pb) and being rich in macro and micro-nutrients, especially Fe (7.84 mg/10 g, dry mass) and Se (0.36 mg/10 g, dry mass). The elemental uptake in T. dubium varied significantly with geographic location (p<0.05) and were found to be in descending order of Ca > Mg > Fe > Zn > Mn > Se > Ni > Cr > Cu > Co > Pb > Cd > As, where the availability and accumulation of heavy metals from soil were controlled by the plant to meet physiological needs. Soil quality parameters such as pH ranged from 6.15 to 6.68, soil organic matter ranged from 0.9 to 2.6% and cation exchange capacity ranged from 4.25 to 9.05 meq/100g. In general, this study indicated that Trifolium species investigated contain adequate concentrations of essential elements and low to undetectable levels of toxic elements which make it a safe and valuable source of nutrition. Therefore, these plant species can contribute positively to the diet of poverty-stricken communities and can aid in improving food insecurity in KwaZulu-Natal.