2.7. Determination of total phenolic contents
Total phenolic contents were determined by using the Folin–
Ciocalteu method (Singleton & Rossi, 1965). Briefly, 100 L of
the diluted sample were added to 2.5 mL 1:10 diluted Folin–
Ciocalteu reagent, and 2 mL of saturated sodium carbonate
solution (75 g/L) were added after 4 min. After incubation at
room temperature for 120 min, the absorbance of the mixture
was measured at 760 nm using the respective solvent as blank.
Gallic acid was used as the standard for a calibration curve,
and the results were expressed as mg of gallic acid equivalents
(mg GAE/g) dry weight of flower.
2.8. Determination of total flavonoid contents
Total flavonoid content (TFC) was determined by using colorimetric
method described previously (Xiong et al., 2014) with
slight modifications. Briefly, 1 mL of the extract (diluted with
distilled water to a suitable concentration) was mixed with
0.15 mL of 5% NaNO2 solution. After 6 min, 0.15 mL of 10% Al
(NO3)3 solution was added and allowed to stand for another
5 min before 1.0 mL of 1 M NaOH was added. The mixture was
vortexed well for 10 s and was then recovered with water to
a final volume of 10 mL. The absorbance was measured immediately
at 510 nm using a spectrophotometer. The results
are expressed as milligrams of rutin equivalents (mg RE/g) per
gram of dry weight.