The total phenolic content of the extract was measured with the
Folin–Ciocalteau method as described by Taga, Miller, and Pratt
(1984), using gallic acid as a standard. A 0.1 ml of the extract solution (1.0 mg/ml DMSO) was sampled into 2 ml of 2% Na2
CO3 and
mixed for 3 min. After adding 0.1 ml of 50% Folin–Ciocalteau reagent, the final mixture was left for 30 min before reading the
absorbance at 750 nm (Hitachi U-2000, Tokyo, Japan). All measurements were conducted in triplicate and the data were expressed as
g gallic acid equivalent (GAE) per kg of the extract, based on the
calibration curve of gallic acid.