Calcium-phytate complex

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. 

In a separate experiment with zinc supplied at 9 ppm in all diets, the effect of increasing dietary calcium in calcium or magnesium precipitated tofu or egg white diets on weight gain and tibia zinc accumulation was tested. From Table IV it can be noted that the performance of tofu-fed rats relative to zinc carbonate-fed rats was quite similar at 0.4% total dietary calcium, but was reduced as dietary calcium was increased to 0.7% and to 1.2%. These results suggest that a poorly available calcium-zinc-phytate complex not present in the soy curd can form in the gastrointestinal tract when sufficient calcium is added to the diet. 

Phytates found in cereals, legumes, nuts and oil seeds form complexes with minerals, the mineral-phytate complexes in decreasing order of stability being zinc > copper > nickel > cobalt > manganese > calcium. Thus, zinc is affected most. An increase in pH results in phytic acid becoming more ionized and initiates binding to cations. 

The ability of zinc ions to block copper absorption, possibly by formation of- intestinal metallothionein that strongly binds copper, has led to its use in pharmacological doses in the management of Wilson s disease/ Similarly molybdate ion can form insoluble copper-molybdate complexes in the intestine that limit copper absorption. The detrimental effects of organic phosphate (phytic acid) in limiting zinc absorption are aggravated by excess dietary calcium, probably by formation of a highly insoluble Ca-Zn-phytate complex. The subject of these and other interactions has been reviewed, ... 

The behavior of minerals is often influenced by the presence of other food constituents. The recent interest in the beneficial effect of dietary fiber has led to studies of the role fiber plays in the absorption of minerals. It has been shown (Toma and Curtis 1986) that mineral absorption is decreased by fiber. A study of the behavior of iron, zinc, and calcium showed that interactions occur with phytate, which is present in fiber. Phytates can form insoluble complexes with iron and zinc and may interfere with the... 

The complexity of food effects on zinc absorption is illustrated by the studies of Sandstrom et al.(25,37,38) in which phytate, protein, calcium, zinc and other factors appear to have variable effects on zinc absorption. Although It appears certain that food interferes with zinc absorption, the effects of individual food substances are unknown and difficult to predict. Regardless of individual effects, zinc administration with food will complicate efforts to measure the effects of other variables on intestinal absorption. 

As pointed out earlier in this review, increasing the level of dietary calcium decreases the zinc bioavailability from phytate-containing foods. Presumably the mechanism is through the formation of chemical complexes containing zinc, phytate and calcium which are insoluble at intestinal pH and nonabsorbable (24). Recently, our laboratories used slope ratio techniques to compare the bioavailability of zinc contained in calcium sulfate-and in magnesium chloride-precipitated soybean curd (Tofu) to that of zinc added as the carbonate to egg white diets by slope ratio techniques (25). Total dietary calcium level in all diets was adjusted to 0.7% with calcium carbonate. The results (not shown) indicated that the relative availability of zinc from both tofu preparations was 51% as measured by weight gain and 36-39% for bone zinc. These results are similar to those reported for full fat soy flour (16) in Table I. 

Plant foods contain relatively large amounts of inositol phosphates, including the hexaphosphate, phytic acid. Phytate chelates minerals, such as calcium, zinc, and magnesium, forming insoluble complexes that are not absorbed. However, both intestinal phosphatases and endogenous phosphatases (phytase) in many foods dephosphorylate a significant proportion of dietary phytate. The inositol released can be absorbed and utilized for phosphatidylinositol synthesis. 

J). Bread components other than phytate were examined for their ability to bind metals. Fiber, protein and starch of wheat formed stable complexes with zinc and calcium, and later iron was found to share this behavior. The metals combined with protein or wheat starch, however, were released during digestion with peptidases and amylases (2,1)5). By contrast dietary fiber, being resistant to digestive secretions, retained bound metal intact. Removal of phytate, which had in the past been held to be the main source of metal complexation by bread, did not decrease but tended to enhance the binding of the metal (J2.). Further doubt about the role of... 

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). 

Calcium absorption is reduced by high pH complex-ing agents such as oxalate, phytate, free fatty acids, and phosphate and shortened transit times. These factors are probably of clinical importance only when associated with vitamin D deficiency, marginal calcium intake, or malabsorption disorders. Absorption is also reduced by increased intake of protein, fat, and plant fiber increasing age stress chronic alcoholism immobilization (e.g., prolonged hospitalization) and drugs such as tetracycline, thyroid extract, diuretics, and aluminum-containing antacids. 

The results of dietary zinc analysis need to be considered in terms of the availability of the zinc in the food for intestinal absorption. The zinc content of whole meals and the total daily zinc intake are not sufficient information on their own, without knowledge of factors which inhibit or promote intestinal absorption (O Dell, 1984). Free ionic zinc probably does not exist in the intestinal tract, zinc being bound to molecular species such as protein, amino acids, phytic acid, citrate and others. The bioavailability of the metal is determined by the nature of these zinc binding ligands. When the zinc complex is insolubie as in Zn-phytate, the uptake from diet is poor, whereas zinc-protein or zinc-amino acid complexes are more easily dissociated and are a good source of available zinc. Other dietary components affect zinc absorption such as the amount of iron, calcium and phosphate. 

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. 

Gosselin, R.E. Coughlan, E.R. The stability of complexes between calcium and orthophosphate, polymeric phosphate and phytate. Arch. Biochem. Biophys. 1953, 45, 301-305. 

Early studies of the isolated ingredient may be helpful to identify biomarkers and to help in the design of more complex products. In addition to identifying any toxic or untoward reactions, preclinical studies may help identify appropriate levels of use. New ingredients should be evaluated in the matrix expected to be used in the final product in order to determine absorption, utilization, and activity when other ingredients are present. For example, soy formulas contain phytate, which can bind zinc, iron, and other divalent cations and make them unavailable. To allow for this, soy formulas are fortified with zinc, iron, and calcium. They also provide relatively large amounts of iron to allow for decreased absorption. 

Partial hydolysis of phytate to myo-inositoltetrakis- and -triphosphate is desirable from a nutritional physiological point of view. In comparison with phytate, these less phosphory-lated myo-inositols do not form such stable complexes with cations. Consequently, the absorption of zinc, iron, calcium and magnesium ions is not... 

Diets based on unleavened wheat bread contain a relatively large amount of phytic acid (inositol hexaphosphate), which can bind calcium, iron and zinc to form insoluble complexes that are not absorbed. Phytases in yeast catalyse dephosphorylation of phytate to products that do not chelate the minerals. 

Calcium forms stable insoluble salt with oxalic acid (see Section 10.2.3.2). In plant cells with higher concentrations of oxalic add, caldum oxalate can be actually present in the form of crystals. Some plants have been shown to bind metals in mixed complexes. For example, chromium can be bound in an oxalate-malate complex, and nickel and zinc can form a dtrate malate complex. Citric add has been proven to be a low molecular weight zinc ligand in human milk, and in casein micelles it binds calcium. It is also used as a food additive (acidulant, synergist to antioxidants and sequestrant), so great attention has been paid to the formation of its complexes with metal ions. The addition to cereal products leads to increased solubihty of naturally present iron, due to its release from phytic acid salts (phytates). 

Calcium is absorbed in the upper small intestine, a process which is promoted by vitamin D. Optimal absorption occurs at acid pHs. High dietary concentrations of phosphate, phytate or oxalate decrease absorption because of complex formation. 

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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