Nutrient density and antioxidant capacity together with cyanide safety of cassava roots and leaves and ugali flour from smallholder households in Kamonyi District of Rwanda

Abstract Background Cassava is a staple food for smallholder households in Rwanda, but root-based diets are low in protein and micronutrients, and inadequately processed cassava can contain hazardous levels of cyanide. This study compared the nutrient composition, cyanide content, and antioxidant capacity of cassava roots, leaves, and ugali flour from smallholder households and estimated their contribution to the nutrient requirements of adult women. Methods In a cross-sectional study (May–August 2026), fresh roots, leaves, and ugali flour (36 samples each) were collected from three sampling units in each of the 12 sectors of Kamonyi District. Samples were analysed for proximate composition (AOAC methods), iron, zinc, calcium, and potassium (atomic absorption spectrophotometry), β-carotene (HPLC), vitamin C (2,6-dichlorophenolindophenol titration), hydrogen cyanide (alkaline titration), total phenolics, phytate, and antioxidant capacity (DPPH assay). Products were compared using Welch’s analysis of variance with Games–Howell post hoc tests. Results All parameters differed significantly among the three products (p < 0.001). On a dry-weight basis, leaves contained about 12 times more protein (24.7 ± 1.3 vs 2.1 ± 0.3 g/100 g) and 15 times more iron (18.6 ± 1.4 vs 1.2 ± 0.2 mg/100 g) than roots, with much higher zinc, calcium, β-carotene, vitamin C, and phenolics, and the strongest antioxidant activity. Fresh roots contained 47.3 ± 5.8 mg hydrogen cyanide/kg fresh weight, close to the Codex maximum of 50 mg/kg for sweet cassava, whereas ugali flour contained 6.2 ± 1.1 mg/kg, within the 10 mg/kg limit for cassava flour; the flour, however, contained over 90% less vitamin C than fresh roots. On a fresh-weight basis, 100 g of raw leaves could supply about 23% of the iron, 10% of the vitamin A, and 57% of the vitamin C requirements of adult women, compared with 12% or less from fresh roots. Conclusions Cassava leaves are a nutrient-dense, under-used food for cassava-reliant households, and locally processed ugali flour met the cyanide limit but retained little vitamin C. Promoting safe preparation and greater consumption of leaves, and refining flour processing to conserve vitamins, could improve diet quality; intervention studies are needed to confirm effects on nutrient intake and status.