with minor modifications.
Briefly, half milliliter of appropriately diluted sample was
mixed with 2.5 mL of Folin-Ciocalteu reagent (0.2 mol/L), and
2.0 mL of sodium carbonate (7.5 g/100 mL) was added 5 min
later. The mixture was kept at room temperature for 2 h after
fully shaken.