3.6. Determination of Antioxidant Activity of Phenolic Extracts

The radical scavenging activity of phenolic extracts against ABTS radical cations was determined according to Re et al. [43]. Briefly, 100 μL of phenolic extract was mixed with 3.9 mL of the ABTS⁺ solution, and after 4 min, the absorbance was recorded at 734 nm against a control. The ABTS results were expressed as mg Trolox equivalents (TE) per g of plant dry weight (mg TE/g).

The DPPH (2,2-diphenyl-1-picrylhydrazyl) scavenging activity of phenolic extracts was measured according to a previous report [44], with slight modifications. Briefly, 100 μL of phenolic extract was mixed with 2.85 mL of freshly prepared 0.1 mM DPPH in methanol, and the decrease in absorbance was measured at 516 nm after 5 min of reaction. The DPPH values were expressed as mg TE/g of plant dry weight.

FRAP activity of the phenolic extracts was evaluated based on the method of Benzie and Strain [45]; 100 μL of phenolic extract was mixed with 3 mL of FRAP solution at 37 °C. After 4 min exactly, the absorbance at 593 nm was reordered against a control, and the FRAP values were expressed as mg TE/g of plant dry weight.