Substrate Occurrence

Phytases from A. niger, Aspergillus terreus, E. coli or Bacillus sp. seem to have a high specificity for phytic acid, whereas plant phytases and some fungal enzymes such as the one from Aspergillus fumigatus have a broader substrate specificity. Chemically, phytic acid refers to myo-inositol-1,2,3,4,5,6-hexakis dihydrogen phosphate, which contains approximately 30% phosphorus. Phytate and phy-tin refer to salts of phytic acid with individual or mixed

and calcium.

metals such as calcium, sodium, potassium, magnesium, iron, zinc, copper, etc. In reality, all three of these compounds are indistinguishably called phytate. Total contents of phytate are 0.5 1.9% in cereals, 0.4 2.1% in legumes, 2.0 5.2% in oil seeds, and 0.4 7.5% in protein products.[4] Distribution of phytate varies with seeds. It is located in the germ of corn, in crystalloid-type globoids inside the protein bodies within the cotyledons of dicotyledoneous seeds (beans, soy, nuts, peanuts), or in the globoids of aleurone grains (protein bodies) present in the aleurone or bran layer of monocotyledoneous seeds (wheat, rice).[4] Phytate rapidly accumulates in seed ripening and serves mainly as storage of phosphorus, inositol, and minerals for the germinating seed. It may be involved in the control of inorganic phosphate levels in both developing seeds and seedlings, and it may also have antifungic and antioxidant roles.[1,4] Because of these functions of phytate and its universal abundance in all plants, caution should be given in developing low-phytate crops. However, phytate is an antinutrient factor in animal diets. With a poor availability of phosphorus, phytate also chelates divalent metals such as zinc and iron. There are twelve replaceable protons present in the phytic acid molecule: Six are dissociated in the strong acid range, one in the weak acid range, two with pK6.8 to 7.6, and three with pK>10.[5] At the neutral pH of small intestine, phytic acid is strongly negatively charged and is able to complex or bind to positively charged molecules. These complexes are rather insoluble, rendering the chelated metals unavailable for absorption.

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