In black rice grains, the predominant flavonols were kaempferol and quercetin (0.10-3.68 mg/100 g) (Table 1). A previous
study showed that the kaempferol and quercetin contents in
French bean were 1.2 and 3.9 mg/100 g, respectively (17).
Recently, these compounds were found to act synergistically in
the inhibition of cell proliferation in human gut cancer lines (18).
Furthermore, the level of the vitamin A precursor, β-carotene,
was significantly higher in black rice than in red and white rice.
While Frei and Becker reported that black rice samples from the
Philippines had β-carotene values up to 0.013 mg/100 g (19), the
β-carotene contents in black varieties in the present study ranged
from 0.026 to 0.048 mg/100 g. The rice cultivars showed distinct
differences in the lutein content depending upon grain color. The
highest average content was found in black cultivars, with values
up to 0.643 mg/100 g. Lutein has no function as a vitamin A
precursor but is a principal component of the macular pigment in
the eyes.