The objective of this study was to degrade the phytic acid content in composite wheat/cassava/ sorghum bread by activating intrinsic cereal phytases during the baking process. The aim was to reach a phytate:iron molar ratio <1 in order to achieve an enhanced iron absorption in humans. Means to activate the phytase included dough preparation at different pH values and temperature as well as pre-soaking of the sorghum flour prior tobefore baking. The phytic acid and mineral content was measured by high high-performance ion chromatography. In the composite bread without pH adjustment of the dough, the phytate content was 1.58 µmol/g. After adjustment of the dough pH to 4.3, the phytate content in the composite bread decreased to 0.86 µmol/g. Soaking of the sorghum flour at 22°C for 3 h at pH 4.3 prior tobefore baking, further decreased the phytate content to 0.58 µmol/g. Increasing the soaking temperature to 37°C and addition of 10% wheat flour resulted in a phytate content of 0.14 µmol/g in the composite bread, that is a reduction by 97% of the initial phytate content. The phytate:iron molar ratio was then 0.70 and the phytate:zinc molar ratio was 1.1 that is expected to have a positive effect on the absorption of both minerals in humans.
Key words: Phytic acid, wheat flour, cassava flour, sorghum flour, bread making, soaking, pH.