Phytic Acid Hydrolysis and Soluble Zinc and Iron in Whole Wheat Bread As Affected by Calcium Containing Additives

The effects of nonfat dry milk, CaCO₃, CaCl₂ and MgCl₂ on phytate hydrolysis and on Zn and Fe availability was evaluated in whole wheat bread and in a model fermentation system. CaCO₃ and CaCl₂ both depressed phytate hydrolysis to an equivalent degree, but the milk had a greater effect than could be accounted for by its Ca content. MgCl₂ had a less pronounced effect than the Ca salts in both the bread and the model system. Increasing fermentation time in the model system increased phytate hydrolysis, but the effect was delayed when milk or CaCl₂ was added. Supplementing the bread dough with Ca equivalent to that typically contributed by Ca-containing additives caused 50% reductions in the available quantities of soluble (“free”) zinc and iron; the decreases observed with varying added amounts of Ca or milk exhibited a high degree of correlation with the observed increases in residual phytate P.