Role of metal complexation on the solubility and enzymatic hydrolysis of phytate

Authors: SUN, MINGJING - University Of Delaware; He, Zhongqi; JAISI, DEB - University Of Delaware

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/23/2021
Publication Date: 8/13/2021
Citation: Sun, M., He, Z., Jaisi, D.P. 2021. Role of metal complexation on the solubility and enzymatic hydrolysis of phytate. PLoS ONE. 16(8). Article e0255787. https://doi.org/10.1371/journal.pone.0255787.
DOI: https://doi.org/10.1371/journal.pone.0255787

Interpretive Summary: Phytate is a dominant form of organic phosphorus (P) in the environment. As it can interact with metal ions and form complex, which limits its hydrolysis by enzymes, knowledge of the formation of metal phytate complexes and their fate is essential to develop a comprehensive understanding of the role phytate. In this work, we studied the stability and hydrolyzability of ten metal phytate complexes (Na, Ca, Mg, Cu, Zn, Al, Fe, Al/Fe, Mn, and Cd). The order of solubility among ten metal phytate complex tested is as follows: i) for metal species: Na, Ca, Mg > Cu, Zn, Mn, Cd > Al, Fe, ii) for different pHs: pH 5.0 > pH 7.5), and iii) for chelates: EDTA> citric acid. Inhibition of metal complex towards enzymatic hydrolysis Aspergillus Niger phytase was variable and was highest with Fe (III) and/or Al (III) phytate complex. Inclusion of additional complexing agent such as EDTA and dithionite decrease the inhibitory effect. The insights developed from the basic research on metal phytate chemistry are expected to be helpful in evaluating the effects of agricultural management practices on the fate of manure organic P, mainly in the form of phytate.

Technical Abstract: Phytate is a dominant form of organic phosphorus (P) in the environment. It can interact with metal ions and form complex, which limits its hydrolysis by enzymes. We studied the stability and hydrolyzability of ten metal phytate complexes (Na, Ca, Mg, Cu, Zn, Al, Fe, Al/Fe, Mn, and Cd). Metal phytate complexes were generally stable in common buffer solutions. Nearly all metal phytate complexes were stable at high pressure and temperature under autoclave except Ca phytate, which hydrolyzed about 32%. Similarly, all phytate complexes were found to be resistant towards acid hydrolysis except Al-phytate. Based on the degree of inhibition towards enzymatic hydrolysis, the metal complexes are grouped into three: almost no effect (Na, Ca, Mg, and Mn phytate), partial (Cu, Zn, and Cd phytate), and significant (Fe and Al phytate). The presence of EDTA did not significantly facilitate the enzymatic hydrolysis of Fe and Al phytate, as opposed to dithionite which enabled hydrolysis of 83% Fe and 36% Al/Fe complexes, respectively. These results suggest phytate-metal complexes are stable and most of them largely resist acid and enzymatic hydrolysis. The strong chelating agent such as EDTA is insufficient on releasing metal from the complex unless reduction of metals (such as Fe) occurs first. The insights gained from this research are expected to contribute to the current understanding of the fate of phytate in the presence of metals that are commonly present in soils.