Effect of Phytate and Other Myo-inositol Phosphate Esters on α-Amylase Digestion of Starch

The effects of phytate and other myo-inositol phosphate esters (containing one or more phosphate groups) on α-amylase digestion of soluble potato starch were evaluated by an in vitro procedure. Human salivary or Bacillus subtilisα-amylase was treated with either 2 mM or 5 mM phytate, myo-inositol-2-monophosphate (l–2-MP), or phytate hydrolyzed to various degrees, and then incubated at 37°C with the starch at pH 4.15 or 6.90. Starch digestion varied with degree of phosphorylation of inositol, inositol phosphate ester concentration, pH and enzyme source. At pH 4.15, phytate (2 mM) and I-2-MP (2 mM) reduced starch digestion by salivary α-amylase to 8.5 and 78.3%, respectively, of the control.