Total flavonoid content of RBO was determined according to the
method reported by Jia, Tang, and Wu (1998), slightly modified.
Briefly, RBO was dissolved in DMSO (1.0 mg/mL DMSO) and an
appropriate dilution of RBO (250 mL) was diluted with distilled
water 1.25 mL and 75 mL of 0.05 mg/mL NaNO2 solution were
added. The mixture was allowed to stand at room temperature for
6 min before 150 mL of 0.1 mg/mL AlCl3 were added. This mixture
was allowed to stand for a further 5 min before 0.5 mL of 1 mol/L
NaOH was added. The solution was shaken vigorously before
absorbance at 510 nm was measured with a UVevis spectrophotometer
(UVeVIS 1700, Shimadzu, Japan). The results were
expressed as mg catechin equivalents per g of the oil (mg CE/g oil).