In vitro availability of iron and zinc in white and coloured ragi (Eleusine coracana): role of tannin and phytate

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Abstract
White and brown ragi (Eleusine coracana) varieties were analysed for tannin, phytate phosphorus, total phosphorus, iron, ionisable iron, zinc and soluble zinc content. White ragi had no detectable tannin while in brown varieties it ranged from 351 to 2392 mg per 100 g. Germination brought about a progressive decrease in tannin and phytate phosphorus and an increase in ionisable ion and soluble zinc content of grain ragi. Both in raw and germinated grain, ionizable iron was significantly higher in white than in brown varieties. While ionisable iron was inversely correlated with the level of tannin and phytate phosphorus, soluble zinc was negatively correlated with phytate phosphorus. After extraction of tannin, ionisable iron of brown ragi rose by 85%. On the other hand, in white varieties, addition of tannin extracted from brown ragi, resulted in a 52–65% decrease in ionisable iron content. These studies indicated that poor iron availability in ragi as judged by its low ionisable iron content was due to the presence of tannin in the grain.