Trolox Equivalent Antioxidant Capacity (TEAC) Assay

The ABTS^·+ was generated from ABTS solution (7 mM) with potassium persulfate (2.45 mM) for 15 h. The radical cation absorbed at 734 nm and was stable for 2 days. ABTS^·+ was diluted in ethanol to 0.7 ± 0.02 absorbance units at 734 nm. Addition of antioxidants to the pre-formed radical cation reduces it to ABTS thus decreasing the absorbance. Twenty microliter of antioxidant solution (between 20 and 210 μ M) was added to 230 μL of adjusted ABTS^·+ solution. The decrease of absorbance of the ABTS^·+ solution was monitored at 734 nm during 6 min using a microplate reader (model Versamax, Molecular Devices). The decrease of absorbance was determined measuring the area under the curve. (R)-Trolox was used as a reference antioxidant. The TEAC value was expressed as the concentration (μM) at which the compound decreases the same absorbance as 1 μM (R)-Trolox.