2.5 Phytic acid content determination
Phytic acid of the polished rice samples was
determined according to Wei et al. (2012). The rice
flour (0.5 g) was placed into a 50-ml centrifuge tube
and extracted with 10 ml 0.2 mol/L HCl, and vibrated
in a rotary shaker for 2 h, then centrifuged at 10 000×g
for 10 min. The resulting supernatants (2.5 ml) were
transferred into an anther centrifuge tube, and 2 ml of
2 g/L FeCl3 was added, then mixed thoroughly. The
mixtures were boiled in a bath for 30 min, cooled at
room temperature, and then centrifuged at 10 000×g
for 15 min. The resulting supernatants were discarded,
while the precipitates were washed three times with
5 ml ultrapure water. After adding 3 ml of 1.5 mol/L
NaOH to the precipitates, the tubes were then centrifuged
at 10 000×g for 10 min. Supernatants was
discarded, and 3 ml of 0.5 mol/L HCl was added to
dissolve the precipitates. Finally, ultrapure water was
added to the solution up to a volume of 20 ml. The Fe
concentration in the solution was determined by ICPMS
(Agilent 7500a, USA). Phytic acid content was
measured by multiplying Fe content by the factor 4.2.