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TECHNICAL REPORTS
Waste Management

Polyvalent Cation Effects on myo-Inositol Hexakis Dihydrogenphosphate Enzymatic Dephosphorylation in Dairy Wastewater

USDA-ARS, Animal Manure and By-Products Laboratory, BARC-East, 10300 Baltimore Ave., Beltsville, MD 20705

^* Corresponding author (thdao{at}anri.barc.usda.gov)

Received for publication March 11, 2002. Information is needed on organic polyphosphates such as myo-inositol 1,2,3,5/4,6-hexakis dihydrogenphosphate or phytate (IP6) contribution to the sources and sinks of dissolved phosphorus (PO₄–P) in the soil–manure–water system. Effects of Na⁺, Ca²⁺, Al³⁺, and Fe³⁺ and cation to IP6-P mole ratios on the enzymatic dephosphorylation of IP6 were studied to determine controlling mechanisms of dephosphorylation and persistence in manure. Phytate- and PO₄–P were analyzed by high-performance liquid chromatography. Phytate dephosphorylation by Aspergillus ficuum (Reichardt) Henn. phytase EC 3.1.3.8 decreases by 50 ± 3.6 and 40 ± 4% at pH 4.5 and 6, respectively, as Ca²⁺ concentrations increase and cation to IP6-P mole ratios reach 6:6. Polyanionic IP6 has a high affinity for Al³⁺ and Fe³⁺ and reductions in dephosphorylation average 27 and 32% at a cation to IP6-P mole ratio of 1:6 for Al³⁺ and Fe³⁺, respectively, while reaching more than 99% at a mole ratio of 6:6. A phytase-hydrolyzable phosphorus (PHP) fraction is native to ruminant animal manure and is proportional to total solids (TS) concentration in 1 to 100 g L^-1 suspensions. Added phytase, in effect, increases water-extractable P content of manure and the risk of environmental P dispersion. As the bioavailability and ecological effect of IP6-P appear to be regulated not only by pH-controlled enzyme activity but also by the associated counterions, the differential protective effects of cations influence the accuracy of manure PHP fraction estimates and increase phytate resistance to enzymatic dephosphorylation that may lead to its persistence in manure.

Abbreviations: IP6, phytate • PHP, phytase-hydrolyzable phosphorus • TS, total solids

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