Mineral profile and the effect of processing of some leafy vegetables indigenous to Cameroon

Leafy vegetables form part of the diet of most people of tropical Africa. Thecontribution of these leafy vegetables to their mineral needs has not been wellelaborated. The aim of this study was to determine the effects of different processingmethods on the mineral composition and anti-nutritional components of some tropicalleafy vegetables. Twenty-one species of different vegetables locally grown andconsumed in the northern region of Cameroon were collected and analyzed for theiriron, copper, manganese, zinc, magnesium, calcium, sodium and potassium content.The levels of anti-nutrients like phytates, oxalates, tannins and saponins that are likelyto affect the bioavailability of these minerals were also determined. The effects ofprocessing methods on the mineral composition and anti-nutritional components ofthese leafy vegetables were also determined. Amongst these species, Moringaoleifera, Hibiscus canabinum, Solanum nigrum, Cucurbita maxima and Vernoniacalvoana that are used for soup, and found in relative abundance in the region weresubjected to two cooking methods (boiling plus squeeze-washing and a combinationof boiling in alkaline salt (kanwa) plus squeeze-washing). The levels of iron, zinc,manganese, copper, magnesium, calcium, sodium and potassium varied in thedifferent vegetables. In all vegetables studied, magnesium was the most abundantmineral. The iron levels ranged from 14.99±2.00mg/100g dry weight (DW) in M.oleifera to 167.42 ± 18.63mg/100g DW in H. sabdariffa. Boiling and squeezewashingled to significant losses of minerals with sodium being the most affected. Onthe contrary, higher values of iron, calcium and sodium were found in samples thatwere boiled in alkaline salt and squeeze-washed. The levels of antinutrients were alsoreduced as a consequence of processing. Percentage losses during boiling with orwithout alkaline salt were between 25.4 and 55.5% for phytates, 11.1 and 80% foroxalates, 16.4 and 68.5% for saponins and 25 and 26.44% for tannins. Boiling,therefore, with or without alkaline salt is an effective means of reducing the levels ofthese antinutrients in vegetables to tolerable levels.Key words: Leafy-vegetables, Processing methods, Mineral, Antinutrients, Saponins,Tannins, Oxalates, Kanwa