Sodium phytate is the salt form of Phytic acid which is found in plants. It's estimated 1- 5 percent of the weight of legumes, cereals, oil seeds and nuts is phytic acid. It forms iron chelate which suppresses iron-catalyzed oxidative reactions. Some researches show it may even serve as a potent antioxidant in the preservation of seeds.
We use sodium phytate as a chelator: it has a characteristic to bind to metal ions to removes traces of heavy metal ions that potentially may be present. It also enhances the effectiveness of preservatives.
Graf, Ernst, Katherine L. Empson, and Jone W. Eaton. "Phytic acid. A natural antioxidant." Journal of Biological Chemistry 262.24 (1987): 11647-11650.