Hull extracts from pigmented rice exert antioxidant effects associated with total flavonoid contents and induce apoptosis in human cancer cells

Residues from pigmented rice are attractive sources of active materials for human health. Methanol extracts from Ilpum (light-brown), Heugjinju (black), Jeogjinju (red), and WD-3 (purple) rice varieties were prepared and examined for antioxidant and anti-cancer activities. Bran and hull extracts from pigmented rice showed significantly (p<0.05) higher phenolic and flavonoidic compound contents, DPPH radical scavenging activities, and reducing powers than Ilpum extracts. Hull extracts showed greater cytotoxicity in human breast, melanoma, and oral cancer cells than bran extracts, where Heugjinju hull extract was the most potent. Hull extract-mediated cytotoxicity was due to apoptosis, based on the appearance of cellular shrinkage, DNA fragmentation, and nuclear condensation. The caspase-dependent and mitochondrial-mediated pathways were associated with hull extract-induced apoptosis in MCF-7 cells. Rice residues can be used as sources of phenolic antioxidants and as anti-cancer agents for human health.