The total flavonoid content (TFC) of the bitter melon
extracts was determined as described by Wu and Ng [11].
Briefly, 0.5 mL of diluted sample was mixed with 2 mL
of deionised water followed by the addition of 150 µL of
5% (w/v) sodium nitrite solution. After 6 min, 150 µL of
10% (w/v) aluminum chloride was added and the mixture
was incubated for another 6 min. Then, 2 mL of 4% (w/v)
sodium hydroxide was added and the solution was immediately made up to 5 mL with deionised water, mixed
thoroughly and placed in the dark at room temperature
for 15 min. The absorption of the solution was measured
at 510 nm against a reagent blank. Rutin was used as a
standard and the TFC was expressed as mg of Rutin
Equivalents (RE) per g of bitter melon powder on a dry basis (mg RE/g).