Binding of iron, calcium and zinc by fibre of sorghum and ragi

Iron, calcium and zinc binding by flour, bran and neutral detergent fibre (NDF) of sorghum and ragi were investigated in vitro. The percentages of added iron, calcium and zinc bound by sorghum NDF were 54%, 88%, and 67.5%, respectively, and bound by ragi NDF were 59.6%, 88.8%, and 65.6% respectively. Brans were dephytinized by treatment with hydrochloric acid and the effect of phytate hydrolysis of brans on the iron-, calcium- and zinc-binding capacity of brans was tested. Brans treated with hydrochloric acid bound more iron, calcium and zinc than native brans. NDFs of sorghum and ragi were treated with proteases to assess the contribution of fibre-bound protein to mineral-binding capacity. The contribution of fibre-bound protein was 9.6% in sorghum and 19% in ragi for zinc binding. There was no impact of fibre-bound protein on iron and calcium binding. Ascorbic acid, one of the most potent inhibitors of iron binding, could release the bound iron from iron-fibre suspensions of both sorghum and ragi.