Facile decomposition of phytate in the solid-state: Kinetics and decomposition pathways

GRAPHICAL ABSTRACT

ABSTRACT

The thermal decomposition of myo-inositol hexakisphosphate (phytate) in the solid state and in aqueous solution was investigated using ³¹P NMR spectroscopy. The progression of phytate decomposition was consistent with facile thermal dephosphorylation resulting in a cascading mixture of lower order inositol phosphates with similar, but not identical, trajectories in the solid state and in aqueous solution. In both states, phytate decomposition was well described by a simple exponential decay function, consistent with first order kinetics. At 60°C the reaction proceeded more rapidly in the solid state (k = 2.03 × 10⁻⁴ min⁻¹; t_1/2 = 2.4 days) than in aqueous solution (pH 3.84; k = 0.387 × 10⁻⁴ min⁻¹; t_1/2 = 12.4 days). In the solid state at 80°C (k = 19.6 × 10⁻⁴ min⁻¹; t_1/2 = 5.9 h) and 95°C (k = 106 × 10⁻⁴ min⁻¹; t_1/2 = 65.4 min) phytate loss also closely followed an exponential decay function. We hypothesise the rapid thermal decomposition is due to an impurity present in the phytate source that acts as a catalyst for facile transfer of the phospho (H₂PO₃ / HPO₃- / PO₃²⁻) group from phosphate esters to a range of oxygen functionalities present (water, alcohol groups, phosphate group). These reactions have important implications for understanding the stability of phytate under environmental conditions.

KEYWORDS:

• inositol phosphate
• ³¹P NMR
• phytate
• thermal decomposition

Acknowledgments

We thank the late Dr Max Tate for providing a sample of myo-Inostiol hexakisphosphate and for his continued interest in this work, valuable discussions on earlier versions of this manuscript and vast knowledge of P chemistry.