Cassava cyanogens and free amino acids in raw and cooked leaves

Abstract

Cassava leaves ( Manihot esculenta Crantz) constitute the main daily source of protein as supplement to the major staple food, the processed cassava roots in remote rural areas of Africa. Konzo, an upper motoneurone disease with permanent spastic paralysis of both legs, has been reported among populations consuming this unbalanced diet. In commercial pounded cassava leaves residual cyanogens and the presence of inherent potentially toxic non-protein amino acids were analysed to check their safety. The initial total cyanogens before cooking ranged from 35.9±0.4 to 107.5±0.8 mg HCN (hydrogen cyanide) equivalent kg −1 dry weight. After cooking, the residual cyanogens were significantly reduced ( P<0.05) ranging from 0.30±0.04 to 1.9±0.2 mg HCN equivalent kg −1 dry weight, and were below the recommended FAO/WHO safe limit set at 10 mg HCN equivalent kg −1 dry weight. The total free amino acids and trigonelline (N-methyl-nicotinic acid) detected varied from 10.8 g kg −1 dry weight to 38.2 g kg −1 dry weight in the raw and from 7.4 g kg −1 dry weight to 25.6 g kg −1 dry weight in the cooked cassava leaves. The non-protein amino acids γ-amino butyric acid (GABA) and α-amino butyric acid (α-ABA) were detected. No known potentially toxic non-protein amino acid was found. In konzo-affected areas, cassava leaves with inadequate preparation and cooking can be a non-negligible source of dietary exposure to cyanogens apart from the cassava roots that are suggested to be involved in the aetiology of konzo.