Bound phenolic compounds were extracted using the method
of Nara et al. (2006) with some modification. Accurate weight of
rice flour (10 g) was shaken with 70% (v/v) methanol for 24 h at
ambient temperature. The supernatant was filtered through
a Whatman No. 42 filter paper. The rice residue was washed with
acetone and then dried, resulting the alcohol-insoluble solid (AIS).
Accurate weight of AIS (2.5 g) was shaken with 2 mol/L NaOH
(30 mL) at room temperature under nitrogen gas for 15 min. The
mixture was acidified to pHw2 with 6 mol/L HCl and then
extracted three times with 30 mL of hexane to remove lipid. The
solution was finally extracted three times with 30 mL ethyl
acetate. The organic fractions were pooled and evaporated to
dryness. The dry residue was analyzed in the same manner as
described in Section 2.5.