2.4.1. DPPH Radical Scavenging Activity (DPPH Assay)

The DPPH free radical scavenging activity of samples was determined in 96-well microliter plates according to Ma et al. with some modifications [25,26]. The sample (20 μL) and DPPH reagent (0.26 mM, 100 μL) were mixed and kept in the dark for 30 min at room temperature, and the absorbance at 517 nm was recorded. The absorbance of the DPPH solution plus methanol was recorded as A₀; the DPPH solution plus the sample was recorded as A₁, and methanol (solvent) plus the sample was recorded as A₂. The DPPH radical scavenging rate was calculated according to the equation: DPPH radical scavenging rate (%) = [A₀ − (A₁ − A₂)]/A₀ × 100%. The results are expressed as mM trolox equivalents (TE) per gram of sample (mM TE/g).