The effect of minerals and mineral chelators on the formation of phytase-resistant and phytase-susceptible forms of phytic acid in solution and in a slurry of canola meal

Minerals can readily bind to phytic acid and thus have the potential to form mineral-phytate complexes that may be resistant to hydrolysis by phytase activity of animal, plant and microbial origin. In simple solution, at pH 7.0, mineral concentrations from 0.053 mM for Zn2+ up to 4.87 mM for Mg2+ caused a 50% inhibition of phytate-P hydrolysis by microbial phytase. The rank order of mineral potency as inhibitors of phytate hydrolysis was Zn2+ >> Fe2+ > Mn2+ > Fe3+ > Ca2+ > Mg2+ at neutral pH. Acidification of the media to pH 4.0 decreased the inhibitory potency of all of the divalent cations tested. The inhibitory potency of Fe3+ showed a moderate increase with declining pH. Inclusion of 25 mM ethylenediamine-tetraacetic acid (EDTA) completely blocked Ca2+ inhibition of phytate hydrolysis at pH 7. Inorganic P comprised 0.20-0.25 of the total P in a slurry of canola meal. Incubation with microbial phytase increased inorganic P up to 0.50 of total P levels, Supplementation with chelators such as EDTA, citrate and phthalate increased the efficacy of microbial phytase in hydrolyzing phytic acid. Incubation of canola meal with 100 mM phthalic acid plus microbial phytase resulted in complete hydrolysis of phytate-P. Competitive chelation by compounds such as EDTA, citric acid or phthalic acid has the potential to decrease enzyme-resistant forms of phytic acid and thereby improve the efficacy of microbial phytase in hydrolyzing phytic acid. (C) 1999 Elsevier Science B.V. All rights reserved.