Superoxide radical generated from NADH–PMS system and quantified by measurement
of the reduction of NBT (Rao, 1989). Briefly, each sample (0.1 ml) was
incubated with 0.1 ml of PMS (0.1 mM), 0.1 ml of NBT (1 mM) and finally quantified
to 0.9 ml with 50 mM KH2PO4 buffer (pH 7.4). The reaction mixtures were initiated
by addition of 0.1 ml of NADH (2 mM). After incubation at 25 _C for 10 min, the
absorption at 570 nm was determined. A lower level of absorbance indicated a
stronger superoxide inhibition.