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 ๐C for 10 min, the absorption at 570 nm was determined. A lower level of absorbance indicated a stronger superoxide inhibition.