Phytic acid (1, 2, 3, 4, 5, 6-hexakis dihydrogen phosphate myoinositol) is a common storage form of phosphorus in seeds and is also considered as an antinutritional factor. The complexing of phytic acid with nutritionally essential elements and the possibility of interference with proteolytic digestion have been suggested as responsible for antinutritional activity. The phosphorus in phytic acid is not nutritionally available to the monogastric animals. Phytic acid also interferes with calcium and iron absorption. Hence, estimation of phytic acid in food grains becomes essential especially in cereals.
The phytate is extracted with trichloroacetic acid and precipitated as ferric salt. The iron content of the precipitate is determined colorimetrically and the phytate phosphorus content calculated from this value assuming a constant 4 Fe: 6 P molecular ratio in the precipitate.
» 3% Trichloroacetic Acid
» 3% Sodium Sulphate in 3% TCA
» FeCl3 Solution (Dissolve 583mg FeCl3 in 100mL of 3% TCA).
» 1.5 M Potassium thiocynate (KSCN)
(Dissolve 29.15g in 200mL water)
» Standard Fe(NO3)3 solution
Weigh accurately 433mg Fe(NO3)3 and dissolve in 100mL distilled water in a volumetric flask. Dilute 2.5mL of this stock standard and make up to 250mL in a volumetric flask. Pipette out 2.5,5,10,15 and 20mL of this working standard into a series of 100mL volumetric flasks and proceed from step 16.
Find out the mg iron present in the test from the standard curve, and calculate the phytate P as per the equation.
1. Wheeler, E L and Ferrel, R E (1971) Cereal Chem 48 312.
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