The polyphenols content in the RE was determined using
Folin–Ciocalteu reagent (Erkan et al., 2008). A volume of 1 ml of
RE solution, prepared in ethanol at a concentration of 0.1 mg/ml,
was mixed with 7.5 ml Folin–Ciocalteu reagent diluted 10 times.
The mixture is left 5min at room temperature before mixing
with 7.5 ml of 60 mg/ml of aqueous sodium bicarbonate solution
Na2CO3. The prepared mixture is placed at room temperature and
darkness for 2 h.
The absorbance of the sample was measured at 725nm using
spectrophotometer (Varian, Inc., CA, USA). The concentration was
determined using gallic acid as reference and the result is expressed
in gallic acid equivalents per gram extract (GAE/g).