Flavonoid was analyzed as previously described (Ju et al., 1997). Fruit peel was
extracted three times with methanol±HCl (0.1% HCl v/v). The extracts were
combined and centrifuged at 5000 _ g for 5 min. The supernatant was diluted
with distilled water (containing 0.1% of HCl), and washed three times with
hexane in a separatory funnel to remove lipids, carotenoid, and chlorophyll. The
final methanol-water phase containing phenolics was applied to a C18 column
(2 _ 20 cm, 55±105 mm, Waters Associates, 50 g). The column was washed with
distilled water to remove more polar phenolics (most of which are phenolic acids)
and anthocyanin. The column was then washed with methanol±HCl (0.1% HCl,
v/v) to elute the flavonoid (Oleszek et al., 1988). The elution of flavonoid was
monitored at 350 nm and flavonoid concentration was measured by the Folin-
Ciocalteau procedure (Singleton and Rossi, 1965) using quercetin as standard.
Anthocyanin was measured at 530 nm and calculated by the method of Siegelman
and Hendricks (1958).