Mechanisms and pathways of phytate degradation: Evidence from oxygen isotope ratios of phosphate, HPLC, and phosphorus-31 NMR spectroscopy

Phytate, the salt of myo-inositol hexakisphosphate, and its partially dephos-phorylated products are commonly present in the environment, but their origins and bioavailability are not well understood. This research applied phosphate O isotope ratios (δ¹⁸O_p) in combination with nuclear magnetic resonance (NMR) and high-performance liquid chromatography (HPLC) methods to characterize the kinetics and pathways of phytate degradation by wheat phytase and the O isotopic composition during progressive degradation of phytate. Our results show that phytate degradation undertakes two pathways: D-inositol-1,2,3,5,6-pentakisphosphate, D-inositol-1,2,5,6-tet-rakisphosphate, D-inositol-1,2,6-trisphosphate, D-inositol-1,2-bisphosphate, D-inositol-1-phosphate; and D-inositol-1,2,4,5,6-pentakisphosphate, D-inositol-1,2,5,6-tetrakisphosphate, D-inositol-1,5,6-trisphosphate. The first pathway is similar to that previously known, while the other one is a new pathway. Isotope results show that the cleavage of the P-O bond during phytate degradation is accompanied by the introduction of one O atom solely from water to the released inorganic orthophosphate. Interestingly, isotopic compositions of all phosphate moieties in K phytate used in this study were found to be the same. This means that the original source of phytate can be tracked from its partially dephosphorylated products. Overall, these results provide improved insights into the mechanisms and pathways of phytate degradation and highlight the importance of an isotopic tool that can potentially be used for tracking phytate source and its degradation products in the environment.