Calcium-phytate complex solubility

Discussion. Oberleas discusses in these proceedings some of the factors that influence the solubility of zinc in the presence of phytate. Rats can utilize the zinc of water insoluble zinc phytate or calcium-zinc phytate complexes in the absence of any added phytate (1, 1 ). Growth, but not femur zinc response was equivalent to when ZnSOij was the dietary zinc source. 

Binding of iron by dietary fiber is strongly inhibited by ascorbic acid, citrate, cysteine, EDTA or phytate in concentrations as lew as 100 >uMols/Liter (A3). The inhibitors have the common property of being able to form soluble complexes with iron. The decarbox-ylic amino acids and their amides inhibit binding moderately as do lysine and histidine. Other amino acids either do not interfere with binding of iron fiber or do so only weakly. Calcium (as acetate) and phosphate act as moderate inhibitors. The detergents sodium lauryl sulfonate or cetyltrimethylammonium bromide had no effect on iron binding by fiber (A2). 

In soils and sediments, complexation can increase organic phosphorus stabilization, especially with iron (III) and calcium ions and their minerals (Harrison, 1987 House and Denison, 2002). The interaction with iron (III) was reported to transform a large part of the labile and moderately labile organic phosphorus forms supplied with manure to paddy soils into more resistant organic phosphorus, possibly because inositol phosphates initially bound to calcium or magnesium were transformed into iron-bound compounds (Zhang et aL, 1994). In the presence of calcium, myo-inositol hexakisphosphate can form two soluble calcium complexes with one or two calcium ions (Ca - or Ca2-phytate), but when three calcium ions are involved (Cag-phytate), the complex precipitates at all pH values (Graf, 1983). This enhances the interaction of myo-... 

But calcium citrate, which is more soluble at a neutral pH, may still be the preferable form for those with compromised levels of stomach acid. Phytates and oxalic acid, found in spinach, rhubarb, collard greens, sweet potatoes and beans bind calcium, creating insoluble complexes that cannot be absorbed. Calcium can also decrease the absorption of several medications including quinolone antibiotics, tetracycline, and thyroid replacement medication. 

The possibility of an adaptative increase in the fraction of Mg absorbed as Mg intake is lowered is controversial. In fact, experimental studies indicate that fractional intestinal absorption of Mg is directly proportional to dietary Mg intake. Because only soluble Mg is absorbed, all the factors increasing Mg solubility increase its absorption while formation of insoluble complexes in the intestine may decrease Mg absorption. Most well-controlled studies indicate that high calcium intake does not affect intestinal Mg absorption in humans. In contrast, dietary phytate in excess impairs Mg... 

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