Phytic acid

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Phytic acid
IUPAC name
(1R,2S,3r,4R,5S,6s)-cyclohexane-1,2,3,4,5,6-hexayl hexakis[dihydrogen (phosphate)]
3D model (JSmol)
ECHA InfoCard 100.001.369
E number E391 (antioxidants, ...)
Molar mass 660.03 g·mol−1
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Phytic acid (known as inositol hexakisphosphate (IP6), inositol polyphosphate, or phytate when in salt form) is the phosphate ester of inositol. It contains six phosphate groups. At physiological pH, these phosphates are partially ionized. The resulting anion is a colorless species that has significant nutritional role as the principal storage form of phosphorus in many plant tissues, especially bran and seeds.[1] It can be found in cereals and grains.

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

Significance in agriculture[edit]

Phosphorus and inositol in phytate form are not, in general, bioavailable to nonruminant animals because these animals lack the digestive enzyme phytase required to hydrolyze (break) the inositol-phosphate linkages. Ruminants are readily able to digest phytate because of the phytase produced by rumen microorganisms.[2]

In most commercial agriculture, nonruminant livestock, such as swine, fowl, and fish,[3] are fed mainly grains, such as maize, legumes, and soybeans.[citation needed] 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.[2] Excess phosphorus excretion can lead to environmental problems, such as eutrophication.[4]

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.[5] However, germination problems have reportedly hindered the use of these cultivars thus far. This may be due to phytic acid's critical role in both phosphorus and metal ion storage.[citation needed]

The use of sprouted grains will reduce the quantity of phytic acids in feed, with no significant reduction of nutritional value.[6]

Phytate variants also have the potential to be used in soil remediation, to immobilize uranium, nickel and other inorganic contaminants.[7]

Biological and physiological roles[edit]

Although indigestible for many animals, 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.[8]

In animal cells, myoinositol polyphosphates are ubiquitous, and phytic acid (myoinositol hexakisphosphate) is the most abundant, with its concentration ranging from 10 to 100 µM in mammalian cells, depending on cell type and developmental stage.[9][10]

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.[11][12] The best evidence from these studies suggests an intracellular role for phytic acid as a cofactor in DNA repair by nonhomologous end-joining.[11] Other studies using yeast mutants have also suggested intracellular phytic acid may be involved in mRNA export from the nucleus to the cytosol.[13][14]

Inositol hexaphosphate facilitates the formation of the six-helix bundle and assembly of the immature HIV-1 Gag lattice. IP6 makes ionic contacts with two rings of lysine residues at the centre of the Gag hexamer. Proteolytic cleavage then unmasks an alternative binding site, where IP6 interaction promotes the assembly of the mature capsid lattice. These studies identify IP6 as a naturally occurring small molecule that promotes both assembly and maturation of HIV-1.[15]

Food science[edit]

Phytic acid was discovered in 1903,[16] Phytic acid, mostly as phytate in the form of phytin, is found within the hulls of seeds, including nuts, grains and pulses.[1] 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, sprouting and lactic acid fermentation such as in sourdough and pickling.[17] No detectable phytate (less than 0.02 % of wet weight) was observed in vegetables such as scallion and cabbage leaves or in fruits such as apples, oranges, bananas, or pears.[18]

Phytic acid has a strong binding affinity to "minerals," such as calcium, iron, and zinc.[19][vague] 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.[20] When iron and zinc bind to phytic acid they form insoluble precipitates 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[21][22] and vegetarians.[23]

As a food additive, phytic acid is used as the preservative E391.[citation needed]

Food sources of phytic acid (g/100g) [24] [18] [25][26][27][28][29][30]
Food [% minimum dry] [% maximum dry]
Pumpkin seed 4.3 4.3
Linseed 2.15 2.78
Sesame seeds flour 5.36 5.36
Chia seeds 0.96 1.16
Almonds 1.35 3.22
Brazil nuts 1.97 6.34
Coconut 0.36 0.36
Hazelnut 0.65 0.65
Peanut 0.95 1.76
Walnut 0.98 0.98
Maize (Corn) 0.75 2.22
Oat 0.42 1.16
Oat Meal 0.89 2.40
Brown rice 0.84 0.99
Polished rice 0.14 0.60
Wheat 0.39 1.35
Wheat flour 0.25 1.37
Wheat germ 0.08 1.14
Whole wheat bread 0.43 1.05
Beans, pinto 2.38 2.38
Buckwheat 1.00 1.00
Chickpeas 0.56 0.56
Lentils 0.44 0.50
Soybeans 1.00 2.22
Tofu 1.46 2.90
Soy beverage 1.24 1.24
Soy protein concentrate 1.24 2.17
New potato 0.18 0.34
Spinach 0.22 NR
Avocado fruit 0.51 0.51
Food sources of phytic acid (fresh weight)[26]
Food [% minimum fresh weight] [% maximum fresh weight]
Taro 0.143 0.195
Cassava 0.114 0.152

Chestnuts contain 47 mg of phytic acid for 100g.[31]

Oak acorn of Quercus ilex contains 127 mg of phytic acid for 100g.[32]

Effect on human health[edit]

Some authors such as Norbdo and Gunnar (1972)[33] describe phytic acid as "cariostatic", or tending to inhibit the formation of caries (cavities). However, older literature contains more nuanced and sophisticated views on this substance. In a 1939 paper[34], Douglas Harrison and Edward Mellanby described how phytic acid can be mildly cariostatic in a diet where the Calcium to Phosphorus ratio is unbalanced. However, phytic acid typically leads to the development of rickets and caries because it binds to calcium (among other minerals) and can therefore cause deficiencies in calcium uptake. The rachitogenic action can be reduced through mineral supplementation, food preparation methods that destroy phytic acid, and/or the use of phytases (enzymes that convert the phosphorus in phytic acid into a usable inorganic form).

Because phytic acid can affect the absorption of iron, Hurrell et al argue that "dephytinization should be considered as a major strategy to improve iron nutrition during the weaning period".[35] Phytic acid's chelating properties have given the acid a reputation as an anti-nutrient with deleterious aspects; some authors argue that this stigmatization ignores its beneficial properties and modern uses.[36][37]

Many modern authors argue that phytic acid can be beneficial to human health because it is an antioxidant[38][39]. In-vitro experiments suggest that phytic acid may have cancer-fighting properties[40]. A pilot study of Inositol Hexaphosphate plus Inositol found that one patient exhibited a reduced tumor growth rate (no figures were provided); however, the researchers noted that controlled randomized clinical trials would be necessary to confirm those observations.[38] The same researchers, Ivana Vucenik and AbulKalam Shamsuddin, also argue that Inositol hexaphosphate is an "essential nutrient" and 'has many characteristics of a vitamin, contrary to the established and, unfortunately, still existing dogma among nutritionist about its “anti-nutrient” role'.[41]

See also[edit]


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