The phytate content and iron‐binding capacity of various field bean (Vicia faba) preparations and extracts

Seed coats, cotyledons and whole grains from a number of field bean (Vicia faba) varieties were analysed for phytate content. In the case of the white flowered varieties, phytate content and its associated iron‐binding capacity appeared to be restricted to the cotyledons while seed coat extracts prepared from coloured flowered varieties had almost twice the iron‐binding capacity of similarly prepared cotyledon extracts. Further studies of these testa extracts revealed that this iron‐binding capacity was eliminated in the presence of either excess protein or polyvinyl pyrrolidone and it was concluded that the active constituents in the seed coats of coloured flowered varieties were the condensed tannins. The solubility and precipitation characteristics at different pH values of field bean phytate were also determined and although the points of minimum solubility broadly coincided with that of field bean protein, phytate solubility increased more rapidly thereafter with increasing pH. These differences in solubility facilitated the preparation of a range of protein isolates with phytate contents ranging from 1.08% at pH 6 to 6.13% at pH 3.