A method for separating phytate and manganese from protein and dietary fiber involves treatment of an aqueous slurry of phytatecontaining material at a low pH with insoluble alumina. In a batch treatment process the pH of the solution is increased, leaving phytate units attached to the alumina while freeing the protein and dietary fiber. In a column treatment process, the column containing alumina is rinsed, after the low pH treatment, with dilute acid and water to recover the protein and/or dietary fiber. This method may be employed either during the manufacture of protein and fiber isolates from flour or flakes, or for removing phytate from commercially available protein and fiber commodities. The spent alumina may be readily regenerated and reused. A method of separating manganese from rice protein using this same technology is also disclosed.