The contents of total phenolics in the aqueous extracts of in vivo
leaves and in vitro calli were determined spectrometrically according
to the Folin–Ciocalteu procedure using gallic acid as standard
(Singleton and Rossi, 1965). One mL of the extract was mixed with
1 mL of a Folin–Ciocalteu reagent (Sigma). After 3 min incubation,
1 mL of saturated sodium bicarbonate (3.5%) was added. The volume
was made up to 10 mL with distilled water. The reaction mixture was
kept in the dark for 90 min. Absorbance was read at 650 nm. The
amount of total phenolic content was calculated from the calibration
curve (y = 2.9671x + 0.0199, R2 = 0.9761) of gallic acid standard
solution.