Vitamin A and mineral content of some common vegetables consumed in Swaziland

Abstract

Common Swazi leafy vegetables that are consumed by a significant number of the Swazi population include Corchorius olitorus [ligusha], Momordica involucrata [inkhakha], Amaranthus spinosus [imbuya], Bidens pilosa [chuchuza] and Solanum nigrum [umsobo]. Although they are part of the Swazi diet, no studies have been published so far on their nutritional composition. The objective of the project was to determine the levels of vitamin A, iron, calcium and zinc in these vegetables. The samples were collected from various areas throughout Swaziland. Vitamin A values were determined using reversed phase high performance liquid chromatography [HPLC] after saponification with potassium hydroxide, extraction with petroleum ether and dissolution in propan-2-ol. Iron, calcium and zinc values were determined using flame atomic absorption spectrometry [AAS]. Findings indicate that these vegetables are a good source of vitamin A with mean values for Corchorius olitorus, Momordica involucrata, Amaranthus spinosus, Bidens pilosa and Solanum nigrum being 959, 1194, 216, 1114 and 27 micrograms vitamin A per 100 g [All-trans retinal] respectively. All the samples analysed were good sources of iron, with Amaranthus spinosus having the highest concentration [41 mg/100 g] followed by Corchorius olitorus with 29 mg/100 while Momordica involucrata, Bidens pilosa and Solanum nigrum had the lowest content of iron [19 mg/100g]. The majority of the vegetables are good sources of calcium. The highest concentration of calcium [2683 mg/100 g] was found in Amaranthus spinosus while Corchorius olitorus and Bidens pilosa generally gave low calcium content [50 - 70 mg/100 g]. The highest zinc content [11.6 mg/100 g] was obtained from Amaranthus spinosus and the lowest [6.2 mg/100 g] from Momordica involucrata. The results obtained for common foodstuffs Vigna unguiculata, Vigna subterranea, Cucurbitea moschata, Phaseolus vulgaris and Persea americana agree with those of West [1987]. In general, micronutrient levels obtained from the five Swazi leafy vegetables are significantly higher than those from commonly consumed foodstuffs such as Phaseolus vulgaris. It is recommended that these leafy vegetables be eaten as a cheaper alternative to the expensive exotic foodstuffs consumed as sources of vitamin A, iron, calcium and zinc.