3.4.3. FRAP Assay

The FRAP assay, a fast and sensitive way for measuring the antioxidant capacity in samples via the reduction of ferric iron (Fe3<sup>+</sup>) to ferrous iron (Fe2<sup>+</sup>) by the antioxidants present in the samples, is a significant indication of the antioxidant activity.

In our analysis, the reducing power for the richest polyphenolic HI extract achieved using water/acetone (1:1) at pH 3 and stirring time 3 min was 350.52 mg TE/g involucre extract. FRAP data for related matrices were 12.0 mg GAE/g hazelnut shell [44] and 400.97 mg TE/g walnut septum extract [15].

Our findings are in agreement with previous studies, which show a positive correlation between phenolic compounds and the antioxidant activity [45,46].
