Phytate Removal from soybean proteins

The ability of Ca++, Ba++ and Zn++ ions to complex with and precipitate phytate ions was investigated as a possible approach for producing phytate-reduced soy-protein isolates. The treatments involved adding divalent cation reagents to mildly alkaline soyprotein extracts, or using mildly alkaline solutions of the cation reagent as protein extractant. Treatments used up to 5% (w/v) divalent cation reagent in dilute NaOH at pH 8–9 at room temperature with stirring for 1 hr. The proteins that remained soluble, or that were extracted following the above treatments, were further fractionated by dialysis against distilled water and then adjusted to the isoelectric pH of 4.5 with HCl. All treatments generally precipitated 15–90% of the total extracted proteins. The resulting phytate-reduced fractions had their total P reduced by ca. 30–74%, but their yields were reduced to only 11–85% of the total extract proteins. On the basis of these findings and on other adverse factors, e.g., toxicity, possible off-flavor and reduced functionality from residual precipitant ions, the divalent cation-fractionation method is not recommended for producing phytate-reduced soy-protein isolates for food use.