2.7.2. Scavenging activity of hydroxyl radicals (OH) assay
The ability of the TFs to scavenge OH was determined by the
method described by Kaur, Arora, and Singh (2008) using BHT as
the positive control. RSA was calculated using the equation
described above for DPPH and ABTS.
2.7.3. Scavenging activity of the superoxide anion (O
2 ) assay
Up to 0.5 ml of different concentrations of TFs was added to
4.5 ml of 50 mM Tris–HCl buffer (pH 8.2). The mixture was incubated
at 25 C for 20 min, and then 10 ll of 45 mM pyrogallol
(25 C) was added. The absorbance of the reaction mixture was
measured at 325 nm every 30 s until the reaction time reached
6 min. The same concentration of TFs without pyrogallol was used
as the blank. RSA was estimated as the % inhibition and was calculated
using the following formula: RSA (%) = [1 (A1 A2)/
A0] 100 (where A0 is the absorbance of the Tris–HCl buffer with
pyrogallol, A1 is the absorbance of the added TFs, and A2 is the
absorbance of the TFs blank).
2.7.4. Ferric-reducing antioxidant power (FRAP) assay
The reducing power of the TFs was determined according to the
method described by Chen et al. (2010). Slopes of the trend lines in
the reducing power assay (SRP) were calculated. Higher SRP values
indicate stronger reducing power.