Phytic acid

Phytic acid (known as inositol hexakisphosphate (IP6), inositol polyphosphate, or phytate when in salt form), discovered in 1903, a saturated cyclic acid, is the principal storage form of phosphorus in many plant tissues, especially bran and seeds. It can be found in cereals and grains.

Phytate is not digestible to humans or nonruminant animals, so it is not a source of either inositol or phosphate if eaten directly. Moreover, phytic acid chelates and thus makes unabsorbable certain important minor minerals such as zinc and iron, and to a lesser extent, also macro minerals such as calcium and magnesium; phytin refers specifically to the calcium or magnesium salt form of phytic acid.

Catabolites of phytic acid are called lower inositol polyphosphates. Examples are inositol penta- (IP5), tetra- (IP4), and triphosphate (IP3).

Significance in agriculture
Phosphorus and inositol in phytate form are not, in general, bioavailable to nonruminant animals because these animals lack the digestive enzyme phytase required to remove phosphate from the inositol in the phytate molecule.

On the other hand, ruminants readily digest phytate because of the phytase produced by rumen microorganisms.

In most commercial agriculture, nonruminant livestock, such as swine, fowl, and fish, are fed mainly grains, such as maize, and legumes, such as soybeans. Because phytate from these grains and beans is unavailable for absorption, the unabsorbed phytate passes through the gastrointestinal tract, elevating the amount of phosphorus in the manure. Excess phosphorus excretion can lead to environmental problems, such as eutrophication.

The bioavailability of phytate phosphorus can be increased by supplementation of the diet with the enzyme phytase.

Also, viable low-phytic acid mutant lines have been developed in several crop species in which the seeds have drastically reduced levels of phytic acid and concomitant increases in inorganic phosphorus. However, reported germination problems have hindered the use of these cultivars thus far.

The use of sprouted grains will reduce the quantity of phytic acids in feed, with no significant reduction of nutritional value.

Phytates also have the potential to be used in soil remediation, to immobilize uranium, nickel and other inorganic contaminants.

Biological and physiological roles
Although undigestable for many animals (as explained above), phytic acid and its metabolites as they occur in seeds and grains have several important roles for the seedling plant.

Most notably, phytic acid functions as a phosphorus store, as an energy store, as a source of cations and as a source of myoinositol (a cell wall precursor). Phytic acid is the principal storage form of phosphorus in plant seeds.

In animal cells, myoinositol polyphosphates are ubiquitous, and phytic acid (myoinositol hexakisphosphate) is the most abundant, with its concentration ranging from 10 to 100 uM in mammalian cells, depending on cell type and developmental stage.

This compound is not obtained from the animal diet, but must be synthesized inside the cell from phosphate and inositol (which in turn is produced from glucose, usually in the kidneys). The interaction of intracellular phytic acid with specific intracellular proteins has been investigated in vitro, and these interactions have been found to result in the inhibition or potentiation of the physiological activities of those proteins. The best evidence from these studies suggests an intracellular role for phytic acid as a cofactor in DNA repair by nonhomologous end-joining. Other studies using yeast mutants have also suggested intracellular phytic acid may be involved in mRNA export from the nucleus to the cytosol. There are still major gaps in the understanding of this molecule, and the exact pathways of phytic acid and lower inositol phosphate metabolism are still unknown. As such, the exact physiological roles of intracellular phytic acid are still a matter of debate.

Food science
Phytic acid is found within the hulls of nuts, seeds, and grains. In-home food preparation techniques can break down the phytic acid in all of these foods. Simply cooking the food will reduce the phytic acid to some degree. More effective methods are soaking in an acid medium, lactic acid fermentation, and sprouting.

Phytic acid has a strong binding affinity to important minerals, such as calcium, iron, and zinc, although the binding of calcium with phytic acid is pH-dependent. The binding of phytic acid with iron is more complex, although there certainly is a strong binding affinity, molecules like phenols and tannins also influence the binding. When iron and zinc bind to phytic acid they form insoluble precipitate and are far less absorbable in the intestines. This process can therefore contribute to iron and zinc deficiencies in people whose diets rely on these foods for their mineral intake, such as those in developing countries and vegetarians. Contrary to that, one study correlated decreased osteoporosis risk with phytic acid consumption. It also acts as an acid, chelating the vitamin niacin, the deficiency of which is known as pellagra. In this regard, it is an antinutrient, despite its possible therapeutic effects (see below). For people with a particularly low intake of essential minerals, especially those in developing countries, this effect can be undesirable.

It has been hypothesized, but not tested, that probiotic lactobacilli and other species of endogenous digestive microflora may be a sufficient source of the enzyme phytase to improve mineral absorption. Phytase catalyzes the release of phosphate from phytate and hydrolyses the complexes formed by phytate and metal ions or other cations, rendering them more soluble, which improves and facilitates the absorption of zinc and magnesium.

Other commercial uses
Phytic acid has been marketed as a fake cancer "cure".

As a food additive, phytic acid is used as the preservative E391.