Comparative Study of Mineral Composition of Selected Staple Green Leafy Vegetables in Nigeria

Six varieties of green leafy vegetables, namely, Amaranthus hybridus, Corchorus olitorius, O. gratissimum, Talinum triangulare, Telfaria occidentalis and Vernonia amygdalina were estimated in their raw, steamed and boiled forms for their mineral compositions. The effect of two different cooking methods (steaming i.e. water blanching and boiling) on fresh leafy vegetables were also evaluated. The mineral contents of fresh leaves of the vegetables were determined using Energy Dispersive X-ray Fluorescence techniques (EDXRF). The results from EDXRF analysis of mineral contents of the six leafy vegetables revealed that fresh, steamed and boiled C. olitorius had the highest quantity of K (133.5, 131.5 and 91.2 mg/100 g) and Zn (28.9, 28.4 and 21.4 mg/100 g) respectively. The fresh, steamed and boiled T. occidentalis had the highest quantity of Ca (124.2, 122.2 and 80.3 mg/100 g), Na (102.2, 100.6 and 71.1 mg/100 g) and Mg (324.5, 319.2 and 225.5 mg/100 g) respectively, while the fresh, steamed and boiled A. hybridus had the highest quantity of Fe (48.6, 47.7 and 29.1 mg/100 g) respectively. The results of percentage loss of mineral composition revealed that almost 40 % of minerals in boiled vegetables was lost, while the amount lost in steamed vegetables was < 2 %. The results obtained from evaluation of sodium/potassium (Na/K) ratio showed that all fresh and steamed leafy vegetables have the same values but the boiled leafy vegetables gave different values. The results have shown that vegetables could serve a better source of some important minerals that can contribute qualitatively to the nutritional need of humans. Based on the results from the processing of vegetables, we suggest that the daily nutritional needs can better be acquired by consuming the steamed processed vegetables rather than consuming the boiled processed vegetables, which would also probably reduce high blood pressure diseases.