The ABTS•+-solution obtained was diluted with 1 mM PBS buffer (pH 7.4) to an absorbance at 734 nm of 1.00 (± 0.02). Trolox dissolved in 1 mM PBS buffer was used as a reference. Ten microliters of the standard or sample were mixed with 1 mL of ABTS•+; as a control, 10 μL of PBS buffer were mixed with 1 mL of ABTS•+. After 60 min, absorbance at 734 nm was recorded in triplicate against PBS as a blank. The degree of quenching of the ABTS•+ radical was calculated as follows