2.5. Determination of total flavonoids
Total flavonoid contents of pineapples were determined by using
the aluminium chloride colorimetric method as described by Willet
(2002), with some modifications. Methanol extracts (0.5 mL), 10%
aluminium chloride (0.1 mL), 1 M potassium acetate (0.1 mL) and
distilled water (4.3 mL) were mixed after incubation at room
temperature for 30 min. The absorbance was measured at 415 nm
using a HITACHI, U-2000 spectrophotometer. Quercetin was used to
make the calibration curve. The estimation of total flavonoids in the
extracts was carried out in triplicate and the results were averaged.