The total flavonoid content was determined according to
Zhishen et al. (1999). In brief, about 0.1 g of the dried and ground
each sample was extracted with 75% methanol for overnight at
room temperature. The sample was mixed with a reagent containing
aluminum chloride and sodium nitrite, and a pink-colored
flavonoid-aluminum complex was formed in alkaline medium.
A solution corresponding to 30 l of sodium nitrite (10%), 60 l
of aluminum chloride hexahydrate (20%), 200 l of NaOH (1 M)
and 400 l of water was added to 100 l of each sample. The
absorbance readings at 510 nm were started 5 min after the addition
of the sample, and were performed every 20 s for 1 min. A
reagent blank containing methanol instead of sample was used.
The total flavonoid content was determined using a standard curve
of naringin.